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Thread: The Tabun Mandible

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    Post The Tabun Mandible

    THE TABUN C2 MANDIBLE: AN ASSESSMENT OF MANDIBULAR RAMUS AND RETROMOLAR SPACE MORPHOLOGY

    NATHAN E. HOLTON




    As the geographic link between Africa and the remainder of the Old World, Western Asia has played a crucial role in understanding the origin of modern humans and the role of Neandertals in the evolutionary history of Homo sapiens. Revised dates of Levantine material (Grün and Stringer, 1991; Grün et al. 1991; McDermott et al., 1993) have pushed back the antiquity of Western Asian hominids and reinforced the coexistence of Neandertals and anatomically modern humans. This allows for an opportunity to test questions regarding the biological relationships between Neandertals and modern humans that have been central to debates regarding modern human origins. The revised chronology of Western Asia has nullified theories of a continuous in situ evolutionary scheme (Jelinek, 1982; Trinkaus, 1984; Clark and Lindley, 1989a, 1989b), and has lent credence to theories arguing for a late migration of Neandertals from Europe into Western Asia (Vandermeersch 1979, 1981, 1989), although such theories are not without contention.

    Levantine hominids exhibit a high degree of morphological variation and a mosaic patterning of archaic and modern traits. Thus, sorting out this variation has been difficult but is important to understanding questions regarding modern human origins. This has raised questions of hybridization between Neandertals and modern humans in the Levant (Trinkaus, 1986; Bräuer, 1989) in contrast to the existence of discrete biological boundaries between the two forms (Stringer, 1989; Vandermeersch, 1989, 1992, 1997; Grün and Stringer, 1991; Bar-Yosef, 1989, 1992, 1994, Trinkaus, 1995; Rak, 1998).. This region is also crucial to understanding the movement of populations or at least genes from Europe to Northern Africa in accordance with ideas of circum-Mediterranean gene exchange (Simmons and Smith, 1991; Smith, et al., 1995).

    The site of Tabun at Mount Carmel located in northern Israel has proven to be important in an understanding of the Levantine archaeological and fossil record as well an overall understanding of modern human origins. This stems from the mosaic morphology exhibited by Tabun C2 (Figure 1) represented by a nearly complete mandible excavated from Mousterian deposits along with the cranial and post-cranial remains of the Tabun C1 Neandertal specimen which date to approximately 100 kya according to McDermott et al. (1993) and possibly as early as 170 kya based on the work of Mercier et al. (1995). Recently, the taxonomic and phylogenetic affinities of the Tabun C2 mandible have been the source of contention (Quam, 1995; Quam and Smith, 1998; Rak, 1998; Stefan and Trinkaus, 1998). Disagreement stems from the mosaic morphology of this specimen which exhibits indications of a full mental trigone while exhibiting a retromolar space as well as medial pterygoid tubercles (Rak et al., 1996) on the medial aspect of the mandibular ramus.

    This analysis focuses on two aspects of the unusual morphology of the Tabun C2 mandible to determine if this specimen is a representative of modern humans, Neandertals or the result of a combination of genes from both. First, an analysis of retromolar space morphology will be undertaken to determine if and what differences exist between the retromolar space of Neandertals and a sample of modern humans including early and recent specimens.

    This includes an analysis of the morphology of the modern human retromolar space relative to modern humans who lack this feature. The morphology of the Tabun C2 retromolar space is then compared to both samples to understand the nature of this feature. The second aspect examines the morphology of the mandibular ramus again comparing the morphology exhibited by Neandertals and modern humans to determine which group Tabun C2 aligns most closely with.

    Although providing an understanding of the affinities of the Tabun C2 mandible is the primary focus of this thesis, the results presented are pertinent to larger paleoanthropological issues. The Neandertal retromolar space, though considered apomorphic by some (Stringer, et al., 1984; Condemi, 1991) has also been removed from the list of possible Neandertal apomorphies resulting from the fact that this feature is not exclusive to Neandertals (Frayer, 1993; Franciscus and Trinkaus, 1995). To determine the nature of the retromolar space of Tabun C2, a sample of modern humans exhibiting retromolar spaces will be compared to a Neandertal sample to determine the differences between the two samples with respect to this feature with the hope of not only determining the affinities of Tabun C2’s retromolar space but also to discover if the Neandertal and modern human retromolar spaces are homologous structures or the result of different underlying developmental and evolutionary trajectories.

    Although there is a significant overlap in the occupation of Neandertals and modern humans in the Levant, there has been disagreement regarding the coexistence of these two groups. Bar-Yosef (1988, 1989) and Hublin (1998) have argued that Neandertal populations in the Western Asia resulted from the inhospitable European environment brought on by glacial advance. Supporters of this late-migration hypothesis contend that Neandertal and modern human populations, though occupying the same geographic region, did so at different times and therefore were never in contact with one another. Level C at Tabun has been a thorn in the side of researchers who advocate this disassociation of modern and archaic populations due to the early date of the Tabun C1 specimen. As a result, it has been argued that the Tabun C1 Neandertal is actually derived from level B (Bar-Yosef and Callander, 1999; Bar-Yosef, 2001) and is thus commensurate with the late-migration of Neandertals into the Western Asia. Though no definitive evidence has been provided that would undoubtedly substantiate the idea of a Tabun B1, the unusual combination of features exhibited by Tabun C2, which is unequivocally derived from Level C, could potentially damage the idea of a late migration if it can be shown that the morphology of this specimen is the result of a combination of genes from Neandertal and modern populations. Thus, even if it can be proven that Tabun C1 is actually derived from Level B, the presence of Neandertal genes as well as Neandertal culture would still be present in Level C. If a late migration did occur, it is possible that Neandertal genes made it to the Levant before Neandertal populations migrated to the region.

    Population interactions around the Mediterranean via a mechanism of circum- Mediterranean gene flow has been proposed by Simmons (1991), Simmons, et al. (1991) and Smith et al. (1995) finding evidence for the spread of genes in this region which would have served as a contact zone between Neandertal and modern African populations. Analyses of frontal bone morphology have reveled morphometric similarities between the Gibraltar Neandertal and the Jebel Irhoud specimens dated at between 130-190 Kya (Grun and Stringer, 1991). Furthermore, the work of Hutchinson (2000) has shown Neandertal affinities for the sub-adult Tangier maxilla. These analyses have provided substantial evidence for genetic relationships between Neandertals and modern humans in North Africa possibly resulting from migrations across the Straits of Gibraltar. Thus, as this region served as a contact zone for modern and archaic populations on the western edge of the Mediterranean, it would stand to reason that the Levant, a land bridge between Africa and the rest of the Old World, would certainly serve as a contact zone for more eastern populations. The Tabun C2 mandible, exhibiting both modern and archaic features provides the opportunity to further examine ideas of circum-Mediterranean gene flow on the eastern side of these genetic connections.

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    Post Re: The Tabun Mandible

    THE ARCHAEOLOGICAL RECORD

    The chronology of the Levant relies primarily on the archaeological sequence (Garrod and Bate, 1937; Jelinek, 1982; Bar-Yosef, 1992, 1993, 1994, 1998) and chronometric dates derived from Tabun cave which has served as a point of reference for relative dating of other Levantine sites.

    In their initial description of the excavation of Tabun, Garrod and Bate (1937) described several layers defined by changes in lithic assemblages (Figure 2). Among the lowest layers of the cave, Layers E and F were associated with the pre-Mousterian Upper Acheulean industry. Layer F was distinguished from E by the absence of scrapers while retaining the presence of hand axes. Layer E was divided into 4 sub-layers, Ea-Ed, the distinction being the relative frequency of hand axes recovered with the frequency increasing with the deeper subdivisions. The cultural sequence of Layer E was later given a new designation after Rust (1950) who used the term “Acheulo-Jabrudian” to refer to the presence of Acheulian bifaces and Jabrudian scrapers in the lithic assemblage from the lower levels of Yabrud Rockshelter I in Syria. Finding a distinction between the between the early blade industries at Tabun and Yabrud, Garrod used the term “Amudian” to refer to industries at sites such as Tabun and Zuttiyeh that exhibited a high frequency of backed elements as opposed to Yabrud with its preponderance of burins.

    New excavations by Jelinek (1982) led to the interpretation of a more refined stratigraphy at Tabun, recognizing fourteen levels on the basis of the site’s geology, therefore, archeological assemblages in this stratigraphic framework were correlated to natural layers rather than cultural. It was recognized by Garrod and Kirkbride (1961) that different facies were present at Tabun and like Rust (1950), Garrod believed that these entities were the lithic representation of different cultural traditions. Jelinek (1982, 1990) in contrast argued for cultural continuity within the within this sequence dubbing the term “Mugharan” to replace the Acheulo-Yabrudian for the lower levels of the site, represented by three alternating industrial facies within this inclusive cultural tradition. The “Yabrudian facies” is predominated by sidescrapers and is also characterized by the near absence of Levallois artifacts (Jelinek, 1982). The “Acheulian facies” is defined by an increase in bifaces while retaining a high frequency of scrapers, the “Amudian facies” occurs between the alternating phases of the Yabrudian and Acheulian. This entity is more similar in its assemblage to Acheulian than to the Yabrudian (Bar-Yosef, 1994) and provides evidence for the production of Levallois artifacts (Jelinek, 1982).

    Above the Acheulo-Yabrudian, Tabun’s stratigraphic sequence is characterized by a Mousterian industry. This transition corresponds to Garrod and Bate’s (1937) Layer D. Jelinek (1982) recognizes a transitional unit X, which sees an increase in Levallois elements providing evidence of an in situ transition to the Levantine Mousterian artifact assemblage present in unit IX. According to Jelinek, two trends characterize the transition, an increase in flakes and blades produced by Levallois core preparation and a decrease in retouched tools. This lithic industry occurs in three phases that correspond to Garrod and Bate’s layers D, C and B. The Levantine Mousterian industry differs from the Mousterian assemblages found in the Zagros and Taurus Mountains (Bar-Yosef, 1994) in that the Zagros and Taurus assemblages consist primarily of non-Levallois artifacts (Dibble, 1984) such as those represented at Shanidar Cave (Trinkaus, 1983). Assemblages in the Zagros and Taurus regions consist of a higher frequency of retouched artifacts, which may be the result of constraints on the availability of raw material (Bar-Yosef, 1994).

    The “Tabun D type”, corresponding to Jelinek’s (1982) unit IX, consists largely of triangular Levallois flakes, elongated points and racloirs (Garrod and Bate, 1937). This type is also represented at other Levantine sites such as Rosh Ein Mor and Jerf Ajla’ (Bar-Yosef, 1993). No fossil material is associated with this assemblage. Tabun Layer C is characterized by a lower frequency of points and a high frequency of radially prepared Levallois flakes. This artifact assemblage is also present at the sites of Skhul and Qafzeh. In contrast to the Tabun D assemblage, there is fossil material associated with Mousterian deposits at Tabun C. The early modern hominid remains from Skhul and Qafzeh were excavated from within the context of the Tabun C assemblage as well as the Tabun C2 mandible and the partial remains of the Tabun C1 Neandertal. The “Tabun B type” is found at Kebara and Amud with the fossil material from these sites associated with this assemblage (Meignen and Bar-Yosef, 1991).



    CHRONOMETRIC DATING

    Early Levantine chronology was based on relative dating through the use of stratigraphy, faunal correlations, lithic industries and paleoenvironmental data. These early chronologies led to interpretations of human evolution in the Levant quite different to more recent analyses employing dates derived from new dating techniques. Bate (Garrod and Bate, 1937) found, on the basis of relative frequencies of Dama and Gazelle, a correlation between Tabun C and the site of Skhūl suggesting a similar date. This information was tied further to interpretations about the Levantine paleoenvironment. According to Bate, the genus Dama was found in cooler, wetter environments and the decreasing frequency relative to Gazelle, adapted to warmer, drier environments, argued for decreasing precipitation and increasing temperatures from Layer E through Layer C. Faunal remains from Layer B implied a rapid return to a cooler, wetter environment. On the basis of this information, Zeuner (1946) dated Layer B to earlier part of the last glacial and layers C and D to the last interglacial.

    The progression of lithic assemblages at Tabun was argued by Jelinek (1982) to represent change in technology over time by a single population, thus representing cultural continuity in the Levant based on a continuous increase in the width and thickness of complete flakes. Shifts in artifact assemblages and the emphasis on particular tools, were believed to correspond with changes in climate and thus changes in available resources and their utilization. Using 14C dates to calibrate the sequence, Unit I was found to date to 50,000 kya (Weinstein, 1984) although given the limitations of radiocarbon dating, this date should be viewed as a minimum value. With this date as a baseline, the various units of Jelinek’s sequence were correlated with oxygen isotope ratios. Employing such paleoenvironmental data, Jelinek found that the Yarbrudian corresponded to a warmer climatic phase, as did Tabun C. Given the relatively high frequency of scraper in both of these assemblages, this was offered as evidence of the same cultural tradition using similar means to exploit resources available in similar climates.

    The continuity found in the Tabun archaeological sequence was taken as evidence of biological continuity in the Levant (Jelinek, 1982). Based on the correlation of artifact assemblages, the fossil material from Tabun was found to be equivalent in age with the Neandertal infant from Kebara. The fossil material from Skhūl, with its modern morphology was believed to be more recent than the Neandertal material as well as the Qafzeh hominids, believed to be later still. This position was contradictory to that of Vandermeersch (1979) who viewed the occurrence of Neandertals in the Levant as a result of migration from Western Europe, arriving second to modern humans represented at Qafzeh, the date for which he estimated at 75,000 ka. This interpretation is consistent with the presence of two forms of archaic rodents occurring at Qafzeh that are not found in the upper units of Tabun. A more modern form of rodent is found at Tabun that does not occur at Qafzeh (Tchernov, 1981).

    The application of ESR and TL dating techniques has had a major impact on Levantine chronology and has brought about a shift in theories of human evolution in the Levant as newly acquired dates attest to the greater antiquity of Levantine archeological and fossil material. Furthermore, these dates have shown that a continuous, linear biological sequence of hominid evolution (Jelinek, 1982; Trinkaus, 1984; Clark and Lindley, 1989a, 1989b) is no longer tenable. This chronological revision is not without its problems as inconsistencies between TL and ESR as well as discrepancies with early (EU) and late (LU) uranium uptake models of ESR dating have produced incompatible dates.

    In that the Tabun sequence provides a baseline from which the temporal organization of other Levantine sites is derived, precise dating of this site is crucial to obtaining an accurate chronology of the Levant. Many researchers, employing various techniques have arrived at a variety of dates for Tabun. Grun et al. (1991, see also Grun and Stringer, 1991) used ESR to date 20 bovid teeth from Garrod’s excavation, measuring uranium concentrations in the enamel and dentine by means of neutron activation analysis. The dates of the hominid bearing Layer C were averaged to 102±17 kya and 119±11 kya for early and late uptake models respectively. According to these researchers, late uptake dates generally correlate to independent dating results while an early uptake model tends to provide dates closer to the lower range of ESR dates. Bar-Yosef and Pilbeam (1993) and Bar-Yosef (1998) argue that these dates are unreliable given the fact that the precise provenience of the teeth used to date the site is unknown.

    McDermott et al. (1993), used mass-spectrometic U-series dating techniques to provide a broader chronology of the Levant by dating dental remains from the early modern Homo sapiens sites of Skhul and Qafzeh as well as the site of Tabun. The sequence at Tabun dated from 160-168 ka for Layer Ea to 50 ka for Layer B, with Layer C providing dates ranging from 97 ka to 105 ka. Layer XIX at Qafzeh was dated between 103 and 105 ka while layer B at Skhul provided a much wider range with dates from 40 ka to 80 ka. The authors suggest that this may be due to a more complex stratigraphy than had been assumed as two or more faunal stages are represented in layer B. Furthermore, the hominid remains at this site may come from different assemblages (McCown and Keith, 1939). Comparing the 230Th/234U dates obtained from this study, McDermott et al. (1993) found that these dates correlate for more than 70% of the samples with previously published EU-ESR dates (i.e., Bar-Yosef and Vandermeersch, 1981; Stringer, et al., 1989; Aitken and Valladas, 1992). According to the temporal similarities of these sites, a model of human evolution suggesting a linear biological progression from a Neandertal form to an early modern form is nullified.

    TL dating techniques applied to burnt flints by Mercier et al. (1995) push the Tabun sequence even further back in time. Layer C has been dated to approximately 170 ka, almost 70,000 years earlier than the dates provided by McDermott et al. (1993). The lower levels of the cave (D-Ed) are dated as far back as 330 ka. When placed into a larger geographic framework, Tabun predates the early modern humans at Skhul and Qafzeh as well as other Levantine Neandertal sites by as much as 110-120,000 years (this range of Neandertal occupation in the Levant is narrower if Tabun C1 does in fact come from Layer B). This long chronology has more recently been supported by Schwarcz and Rink (1998) and Valladas et al. (1998) by dating lithic assemblages at Hayonim. Level E of this site, located in the Upper Galilee region corresponding to Tabun C and D industries (Meignen, 1998) has been dated by ESR to c. 164 ka (EU) and 171 ka (LU) (Schwarcz and Rink, 1998) and by TL to between 150-200 ka (Valladas et al., 1998).

    Dates for the Neandertal sites of Kebara and Amud provide evidence for a late occupation of Neandertals in the Levant. A well preserved skeleton uncovered near the top of layer XII at Kebara is thought to represent a burial during an occupation of the site corresponding to Layer X. Valladas et al. (1987), using TL techniques to date burnt flints, found the age of the site to range from 48±4 ka for layer VI to 60±4 ka for layer XII. These dates have been corroborated by Schwarcz et al. (1989) who provide ESR dates of around 60 ka (EU) to 64 ka (LU) for this layer.

    The Neandertal fossil material from the Mousterian deposits of Amud was recovered from formation B. The remains of numerous individuals have been recovered from this site including a nearly complete cranium (Suzuki and Takai, 1970) and more recently the remains of a Neandertal infant (Rak et al., 1994). Amud Cave was originally dated by 14C at around 19 ka, and u-series at 28 ka (Suzuki and Takai, 1970). ESR dates pushed back the age of the remains to 42±3 to 49±3 (EU) and 49±4 to 50±4 (LU) (Grün and Stringer, 1991). Recently published TL dates from Valladas et al. (1999) attests to the greater antiquity of the site with an age ranging from 50-70 ka.

    The early dates for the assemblages within the lower levels of Tabun suggest an even greater antiquity for the Zuttiyeh specimen relative to the other Levantine hominids. This partial cranium, it has been argued, lacks Neandertal apomorphic features and is ancestral to modern hominids at Skhul and Qafzeh (Vandermeersch, 1989). This assessment has been contested by Simmons et al. (1991) and will be discussed in more detail below. TL dates from the Mousterian levels from this site have provided an age of 106-157 ka for the layers above the specimen (Valladas et al., 1998). Flints associated with the specimen were not heated at a high enough temperature to allow of TL dating of the Acheuleo-Yabrudian material. 230Th/234U dates by Schwarcz et al. (1980) offer an age of around 150 ka although various dates for this assemblage at Tabun may push the Zuttiyeh specimen back even further.





    THE LEVANTINE FOSSIL RECORD



    The discovery of hominid remains from the sites of Tabun and Skhul in the 1930’s exhibiting a high degree of morphological variability led to the initial assertion by Keith and McCown (1937) that two distinct morphotypes were present in the sample, suggesting that these two variants were predecessors to Neandertals and modern humans. In their final analysis however, McCown and Keith (1939) concluded instead that, a single, highly variable population was represented in the Levant. In regard to mandibular morphology, McCown and Keith state, “In both Skhūl IV and V there are many points in which they resemble Tabūn II, just as this in turn is linked on to Tabūn I.” (McCown and Keith, 1939:228). In terms of general morphology, the number of characters found linking this sample were so overwhelming, it was felt that the only reasonable conclusion that one could arrive at was that of a single population, albeit a highly variable one. Workers such as Coon (1939) and Dobzhansky (1944) felt that the range of variation was the result of interbreeding between a Neandertal and a more modern form. For Dobzhansky, this type of situation was not unusual and provided a racial distinction between Neandertals and modern types rather than a specific one.

    This perception of Levantine hominid evolution was revised by Howell (1959) who, after reanalyzing stratigraphic and biological data, argued that there were indeed two populations represented by the Tabun Neandertals and the more modern looking Skhul hominids. Howell suggested an ancestral link between the Skhul sample and the more modern Western European Cro Magnons and proposed the term “proto-Cro-Magnon” in reference to the former. That two distinct populations existed in the Mousterian Levant has continued to be argued by many researchers (Stringer, 1989; Vandermeersch, 1989, 1992, 1997; Grün and Stringer, 1991; Bar-Yosef, 1989, 1992, 1994, Trinkaus, 1995; Rak, 1998).

    In a comparison of Near Eastern Neandertal and modern specimens to the Early Upper Paleolithic European Předmostí III and the European Neandertals represented by La Chapelle-aux-Saints, Vandermeersch (1992) found that of 13 cranial measurements, the Neandertal sample significantly differed from the early modern specimens. Vandermeersch noted that the Qafzeh specimens exhibit a modern supraorbital morphology and while the specimens from Skhul do exhibit a supraorbital torus, it is not as large as those found in Neandertals. Vandermeersch (1992) further argues that the temporal morphology of the Skhul/Qafzeh sample argues for the case of modernity with the mastoid processes separated from the petrous body as well as exhibiting a lack of a sagittal orientation. In terms of mandibular morphology, the presence of an incurvatio mandibulae and mental trigone further attest to the modern status of this sample.

    The placement of the Skhul/Qafzeh sample within the category “modern” has not reached a consensus. In a multivariate analysis of cranial morphometrics, Kidder et al.,(1992) found Skhul IV and V to fall outside the range of modern cranial variation. While Skhul maintains a rather modern appearance, it is relatively robust and exhibits distinct brow ridges. The analysis of Qafzeh 6 and 9 produced similar results with inability to attribute Qafzeh 6 to modern human status. Qafzeh 9 on the other hand was found to fall within the range of modern variation with a facial morphology more similar to recent specimens and a reduction in the size of the brow ridges. The authors suggest that the allocation of Qafzeh 9 to the status of modern human may be a result of the juvenile status of the individual. Corrucinni (1992) examined the amount of variation present in the Skhul sample and found it to be nearly as great as the amount of variation between Neandertals and more modern forms. Thus, he argues that the distinction of discrete biological populations is difficult to assert and therefore the Levantine fossil record represents a single, highly variable population.

    The presence of discrete populations has also been contended by Trinkaus (1995) stating that the archaic humans found in the Near East represent an evolutionary lineage distinct from early moderns in the area. The fate of the Levantine Neandertals he claims is that of extinction and while he suggests that some degree of gene flow may have existed between these populations it would have been negligible. Among other lines of support, differences in body proportions are used as evidence for the distinction (Trinkaus, 1981, 1995). Near Eastern Neandertals tend to exhibit cold-adapted body proportions, as do European Neandertals while the Skhul/Qafzeh sample retains proportions typical of equatorial populations such as modern Africans. Though a look at the variation in body proportions blurs the line between climatic adaptations. For instance, the crural index of Skhul V is closer to Neandertal specimens (Frayer et al., 1993) and the stature of Amud I is closer to the Skhul/Qafzeh sample exhibiting long bone lengths that fall closer to tropically-adapted specimens (Feldsmen et al., 1990).

    Other researchers have found it much more difficult to distinguish between populations in the Levant, thus suggesting an increased amount of variation within a single population. Most recently, Kramer et al., (2001) conducted a cladistic analysis of Levantine crania attributed to Neandertals and modern humans. On the basis of the twelve, variable non-metric traits no distinction was made between the two morphs, that is, neither of the populations formed a clade exclusive of the other.

    Arensburg and Belfer-Cohen (1998) found that Neaderthal autapomorphies are also found in the Skhul/Qafzeh sample while more modern features are exhibited by Neaderthals. The same conclusion was reached in an earlier analysis by Arensburg (1989), of the Kebara skeleton. A mosaic of Neandertal and modern features were described in this specimen such as Neandertal-like mandible, metacarpals, pelvis and cervical vertebrae as well as a more modern appearance in the morphology of vertebral column (in regard to length), hyoid and thorax. Rather than make an attempt at discerning the taxonomic affinity of this sample, to be cautious, the term “Mousterian Men” was suggested to encompass the total range of variation of Levantine Middle Paleolithic hominids. Regarding the Levantine sample as a single population Arensburg and Belfer-Cohen (1998) believe that given the wide range of variation present in the Skul/Qafzeh sample “the emergence of Neandertal features in the course of human evolution may well reflect a genetically inherent human variability…[as] is expressed in the wide range of morphological diversity observed among the early AMHS specimens from the Near East.” (1998; 320).

    Those who agree that the Levantine fossil material is composed of two separate species attempt to explain the co-existence of Neandertals and modern humans as the result of an influx of European populations resulting from environmental pressures in the form of glacial expansion (Bar-Yosef, 1988, 1989, 1992; Hublin, 1998). As the European environment became inhospitable, the Levant would have provided a more attractive location with warmer temperatures and more stable resources (Bar-Yosef, 1992). If Tabun C1 does in fact derive from Layer B as suggested by Bar-Yosef’s (2001) latest chronology of the Levant then it would represent the earliest Neandertal specimen in the Levant, therefore, all Levantine Neandertals could be bracketed within OIS 4, the cold episode suggested to have displaced northern populations (Bar-Yosef, 1988). Hublin (1998) suggests that such a migration could have occurred earlier, thus population displacement should not be restricted to OIS 4 but rather could have also occurred during the Riss glaciation. An earlier migration might then be the cause of the morphological difference exhibited between European and Levantine Neandertals.







    AN ASSESSMENT OF THE TABUN C2 MANDIBLE



    The Tabun C2 mandible (Figure 3) is derived from Layer C of Tabun Cave at Mount Carmel and was originally described by McCown and Keith (1939). Due to the massiveness of the specimen, it was described as a male and compared in detail to the Maüer mandible, as it was the only specimen that resembled Tabun C2 in terms of rugosity. Associated with this mandible were the remains of a partial female skeleton, Tabun C1, which, although differing in morphology from C2, was viewed

    by McCown and Keith to be one end in a broad spectrum of variation representing a single population at Mount Carmel.

    The context of Tabun C1 has been treated as somewhat of a mystery among anthropologists as the stratigraphic position of the specimen was unclear when excavated (see Bar-Yosef and Callander, 1999 for a detailed discussion). Garrod (Garrod and Bate, 1937) suggested, that while the specimen was excavated from Layer C, its position was so close to the surface of the level that it is possible that C1, in actuality represents a burial from Layer B. She states that while there is no sign of disturbance in site stratigraphy at the position of the remains, this could be the result of a blurred distinction between the two layers.

    A late migration hypothesis for Neandertals relies on a higher stratigraphic position of the Tabun woman (Bar-Yosef, 2001) although, the presence of Tabun C3, a femoral diaphysis with archaic characteristics from Layer C suggests that it is likely that C1 is also derived from this level. Trinkaus (1993) points out that the Tabun C4 and C5, a right radius and hamate are virtually identical to the right counterparts exhibited by Tabun C1, furthermore, these elements were noted by Garrod and Bate (1937) as having been derived from Level C. The presence of these two elements from Level C suggests that the C4 and C5 were separated from the from the C1 skeleton prior to the deposition of Level B (Quam and Smith, 1998). Furthermore, if Simmons et al., (1991) are correct about the taxonomic assignment of Zuttiyeh, this places an archaic lineage in the Near East at a much earlier date. The possibility of Tabun C2 deriving from Layer D has also been suggested (Trinkaus, 1984) but is unsubstantiated.

    Recent direct dates taken from the Tabun C1 mandible and femur using U-series dates have yielded extremely late dates for this specimen suggesting to Schwarcz et al. (1998) that this specimen is younger than the Level C deposits. Using an early uptake model the C1 mandible is dated at 34 kya with the femur dated at 19 kya. Rather than being one of the earliest archaic representatives in the Levant, Tabun C1 would be the one of the last if these dates are correct. Millard and Pike (1998) have argued that caution must be used when obtaining U-series dates from bone and the dates obtained by Schwarcz et al. (1998) should be viewed as provisional. Furthermore, such a late date is difficult to reconcile with the Tabun C4 and C5 specimens which are securely derived from Level C and most likely belong to the Tabun C1 skeleton.

    Quam (1996) has noted that until recently, any assessment of the taxonomic affinity of the Tabun C2 mandible was largely brief and superficial. As the importance of this specimen has since been recognized, recent studies have resulted in disagreement as to the assignment of this specimen and its morphology (Quam, 1996; Quam and Smith, 1998; Rak, 1998; Stefan and Trinkaus, 1998). The recognition of two morphological types coexisting in the Levant makes an understanding of this area particularly important in understanding biological relationships between Neandertals and more modern forms as well as in providing an overall understanding of modern human origins. Given the mosaic nature of the morphology of the Tabun C2 mandible, an accurate assessment will provide insight and help discern the biological relationship of Levantine inhabitants.

    In a metric and morphological analysis by Quam and Smith (1998) the Tabun C2 mandible aligned more closely with early modern Western Europeans. Among the features possessed by Tabun C2, the mandibular symphysis has a very modern morphology. While it has been asserted that a mental trigone is present (Rak, 1998), the lack of preservation of the symphyseal region makes a proper assessment of this area impossible. Although, features are present that indicate the possibility that this specimen may have possessed a trigone. Quam and Smith (1998) point to features defined by Weidenreich (1936) as being indicative of modern symphyseal morphology. The Tabun C2 specimen clearly possesses an incuvatio mandibulae, which indicates, at least, the presence of a mentum osseum. The presence of this feature is also indicated by the anterior projection of the basal symphysis. The left aspect of the symphysis displays a fossa mentalis and an anterior marginal tubercle, both indicators of a mental trigone.

    Rak (1998) finds that Neandertal and modern mandibular morphology can be distinguished on the basis of the intersection of the mandibular incisure with the condyle. Modern humans tend to be characterized by a lateral intersection while in Neandertals the intersection is located more centrally. Quam and Smith (1998) found that of the 70% of the Neandertal mandibles examined possessed this characteristic. The incisure position of the Tabun C2 mandible lateral and is therefore consistent with the morphology of modern humans.

    Other features point toward the more archaic nature of this specimen. The mandibular foramina exhibit a horizontal-oval (H-O) pattern, which tends to be characteristic of Neandertals. Although this feature is not a derived Neandertal trait, it has been shown to occur in 52.6% of European Neandertals (Frayer, 1992). A pooled sample of European and Near Eastern Neandethals yielded a frequency of 46.2% (Smith, 1978). The frequency among Early Upper Paleolithic specimens maintain a much lower frequency of 23.1%, while among recent and living populations, the occurrence is almost negligible (Smith, 1978). In contrast to the more modern mental symphysis, the mandibular foramina reflect the more archaic tendencies of this specimen.

    A distinct retromolar space is present on the Tabun C2 mandible, further attesting to mosaic pattern exhibited by this specimen. This morphology of this character, though, has been a point of contention. Franciscus and Trinkaus (1995) found that the presence of a retromolar space results from the combined effects of the reduced length of the dental arcade and a reduction in the breadth of the mandibular ramus. Rak (1998) argues that the presence of the retromolar space is a function of the depth of the pre-angular notch exhibited on the ramus. The anterior aspect of the

    ramus he argues, recedes beyond the posterior edge of the M3 giving the appearance of a retromolar space. If the breadth of the ramus is increased by filling in the angular notch (Figure 4), the retromolar space disappears. Interestingly enough, a pre-angular notch is also present on the Tabun C1 mandible and a clear retromolar space is present on Skhul V.

    The presence of the medial pterygoid tubercle, which provides the insertion for the medial pterygoid muscle, has been described by Rak et al., (1994) as diagnostic of Neandertals. The presence of this feature is noted on Tabun C1, Kebara 2 as well as various European Neandertals. Quam and Smith (1998) found this

    feature to be present on 7 out of 9 Neandertals. This feature is also present among subadult individuals. Rak et al., (1994) have described the presence of this feature on the Amud 7 mandible. The Tabun C2 mandible has distinct medial pterygoid tubercles.



    SUMMARY





    That the hominid fossil sample form the Levant exhibits a high degree of variation has been recognized since the early work of McCown and Keith (1939). The difficulty has been in accurately sorting out this variation and interpreting it in the context of different theories regarding the origins of modern humans. According to proponents of a late migration of Neandertals into the Levant (Bar-Yosef, 1988; Vandermeersch 1979, 1981, 1989), the Levantine inhabitants can be recognized as two distinct biological species, with Neandertals making no contribution to the evolution of modern humans.

    While Neandertal and modern types do exist in the Near Eastern Paleolithic, there is a significant amount of overlap in morphology further characterized by mosaic patterning of characters. This is readily apparent in the morphology of the Tabun C2 mandible. While studies have found that this specimen aligns with modern human morphology (Quam, 1996; Quam and Smith, 1998; Rak, 1998), the presence of archaic traits has also been emphasized (Quam, 1996; Quam and Smith, 1998; Stefen and Trinkaus, 1998). Given the location of the Levant as a bridge between Africa and Europe, it seems a distinct possibility that the Levantine morphological pattern is a result of the hybridization of two morphological groups.

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    Post Re: The Tabun Mandible

    To better understand the taxonomic affiliation of the Tabun C2 mandible in relation to Neandertals and modern humans, this analysis is divided into two parts. First, an analysis of the nature of the retromolar space will be undertaken. This feature has been the source of debate both in terms of its evolutionary development and phylogenetic implications. Though various analyses have sought to provide an explanation for the presence of the retromolar space in Neandertals (Rak, 1986; Trinkaus1987; Spencer and Deems, 1993; Franciscus and Trinkaus, 1995), a similar analysis for modern humans is lacking. Therefore, this analysis will provide a comparative study of the retromolar space for these two groups followed by a comparison of the retromolar space of Tabun C2. Second, the nature of the superior aspect of ramus morphology will be studied. Specifically this will take into account the size and shape of the coronoid process as well as the shape of the mandibular notch as a derived morphology of this region has been argued for Neandertals (Rak, 1998). Using both multivariate and univariate methods the size and shape of the mandibular ramus will also be examined.




    COMPARATIVE SAMPLES



    Measurements for the Tabun C2 mandible, the recent sample, a subset of the Neandertal and an early modern sample were taken on the original fossils and remains housed at the University of Tel Aviv in Tel Aviv, Israel. The Neandertal and modern sample were supplemented with measurements taken from fossil casts at Northern Illinois University. Published data was utilized for various measurements when available to increase sample sizes (Trinkaus, 1983; Franciscus and Trinkaus, 1995; Quam, 1998).

    For this study only adult specimens were selected. Adult status was determined by full eruption of the third molars. Furthermore, no distinctions were made between the sexes in any of the analyses. While variation does exist on the basis of sex and sex could be determined for the modern human sample with relative ease, such accuracy in determining the sex for Neandertal material is not as realistic. Although some do assign sex to fossils specimens (e.g., Wolpoff,1999), given the fragmentary nature of the remains under analysis and the lack of standards by which sex can be determined (as have been developed for modern humans) sex determination was not attempted. Clearly specimens such as Kebara 2 and Tabun C2 are males. On the basis of relative size and general robusticity, while one can assume that Tabun C1 is a female, other specimens are either lacking the diagnostic areas or are somewhere in between the range of Tabun C2 and Tabun C1. Furthermore, paleoanthropological studies are plagued by small sample sizes, thus subdivision of samples on the basis of sex would further decrease the size of the available samples to the point where statistical analyses could be considered meaningless. Therefore it is the opinion of the author that because of the uncertainty associated with assigning sex, males and females will be pooled.

    To determine the taxonomic and phylogenetic status of the Tabun C2 mandible, three comparative samples were examined, a Neandertal, modern human and Middle Pleistocene sample. The Tabun C2 mandible was directly compared only to the Neandertal and modern human sample with the Middle Pleistocene sample used for the retromolar space analysis described below.

    The Neandertal sample (Table 1) consists of both original specimens and casts with measurements for Kebara 2 and Amud 1 taken on the original fossils. Specimens were chosen on the basis of completeness of the mandibular ramus with primary concern on the preservation of the coronoid process and region surrounding the retromolar space. Unfortunately the coronoid process is lacking on many Neandertal mandibles, therefore the number of available specimens available for study was rather low. Sample sizes were larger for the analysis of the retromolar space as the features associated with this region were preserved at a higher frequency. Of the three Neandertal mandibles that share the closest geographic proximity to the Tabun C2 mandible only two, Tabun C1 and Amud 1, were complete enough for comparisons pertaining to the coronoid process and overall size and shape of the ramus. The majority of Neandertal specimens are derived from Europe and span several thousand years, thus the geographic and temporal range must certainly introduce a degree of bias in terms of variation when compared to a recent sample that is restricted in terms of geography and time.

    The modern human sample consists of both early modern fossil and recent human samples. The early modern human material is listed in Table 1 and the recent human sample is listed in Table 2. Like the Neandertal sample the early modern sample is also derived from the Near East, Europe and as well as from Africa. The modern human sample included measurements taken from both original fossil and skeletal material as well as casts. Previous studies concerning the Tabun C2 mandible have lacked the inclusion of African material, thus three African specimens are included in this analysis, one of which, KRM 41815 is missing most of the mandibular ramus although it was complete enough to be included in some of the univariate analyses. The South African specimen, Fish Hoek has also been included but more importantly, the Haua Fteah 1 mandible is also examined. The inclusion of this specimen is an interesting addition to the modern sample as it is derived from Mousterian deposits in Libya (Tobias, 1967). An comparative analysis including the Haua Fteah 1 mandible may provide insight into ideas concerning circum-Mediterranean gene flow (Simmons and Smith, 1991; Smith, et al., 1995).

    The recent sample comes from three sites located in Israel, Hayonim, Ain Mallah and Fallah. As with the Neandertal sample, recent specimens consisting of 16 males and 10 females were chosen on the basis of preservation of the ramus and completeness of the coronoid process in particular. This sample was also chosen because of the presence of retromolar spaces in some of the individuals (Table 2). In addition to retromolar spaces exhibited by Skhul 5 and Predmosti 3, this allows for the unique opportunity to study the morphology of the modern human retromolar space to determine if this feature is a homologous structure relative to Neandertals or if the retromolar space in these two groups are morphologically different with similarities exhibited purely on a phenetic basis.

    As can be seen from Table 2, the frequency of retromolar spaces is only 15% of a total modern human sample of n=34. Thus any analysis on the morphology of the retromolar space among modern humans should be viewed as preliminary. Certainly larger samples and the inclusion of a larger geographic area in necessary before a truly adequate analysis of this feature can be undertaken.




    MEASUREMENTS



    Measurements used in this analysis are listed below in Table 3 and are organized by general ramus features. Measurements were taken using spreading calipers, mandibulometer and for measurements that were difficult to take on the mandibles themselves, photographs taken by the author were used. When possible, measurements were taken on both the left and right side of the specimens and were then averaged for statistical analyses. Although there were a number of standard measurements employed, the measurements of various features required the addition of “non-traditional” measurements. These are listed and described below. Figures 5 and 6 are graphical representations of the measurements to accompany the descriptions given below.

    Length of the retromolar space- This is a measurement (A in Figure 5) of the distance between the distal aspect of the third molar at the occlusal surface to the anterior edge of the mandibular ramus.

    M3-Posterior edge of mandibular ramus- This is a measurement (B in Figure 5) of the length of the retromolar space as suggested by Rak (1998). This measurement consists of the distance between the distal edge of the third molar at the edge of the occlusal surface to the posterior edge of the mandibular ramus.

    Lateral prominence position- This is a measurement (C in Figure 5) of the lateral prominence to the posterior edge of the mandibular ramus. The most prominent aspect of the lateral prominence was used as the landmark for this measurement.

    Maximum breadth of coronoid process- This is a measurement (A in Figure 6) of the deepest point of the sigmoid notch to the anterior-most aspect of the coronoid process.

    Maximum breadth of ramus at the coronoid process- This is a measurement (B in Figure 6) of the maximum breadth of the mandibular ramus from the posterior edge of the condylar process to the anterior-most aspect of the coronoid process.

    Condyle-superior coronoid process- This a measurement (C in Figure 6)of the distance between the center of the condyle to the superior aspect of the coronoid process.

    Height at the coronoid process- This is a measurement (D in Figure 6) of the height of the mandibular ramus from the base of the mandible to the superior aspect of the coronoid process.

    Height of the coronoid process- This is a measurement (E in Figure 6) taken from the base of the coronoid process marked by the base of the sigmoid notch to the superior aspect of the coronoid process.



    QUALITATIVE OBSERVATIONS



    Lateral prominence position- In addition to a quantitative measurement for this feature, the position of the lateral prominence was also judged in relation to the dental arcade.

    Medial Pterygoid tubercle- The inside of the mandibular ramus was examined to determine the presence/absence of this feature (Figure 7).

    Mandibular Foramen Shape- Specimens were examined to determine if they exhibited a V-shaped or H-O shaped mandibular foramen.






    INDICIES





    Pre-angular notch index- The pre-angular notch index was measured from photographs of the specimens taken by the author and is determined by measuring the distance from the anterior-most aspect of the coronoid process to a perpendicular line drawn at the point of the base of the sigmoid notch. A second measurement is taken from the deepest point of the notch (D and E of Figure 5) to the same perpendicular line with the pre-angular notch index equal to the maximum length/minimum length. This value provides a measure of the depth of the notch relative to the anterior edge of the coronoid process.

    Mandibular Notch Position- This index, A/B in Figure 4, was used to determine the position of the deepest point of the mandibular notch.





    RETROMOLAR SPACE



    The presence of a retromolar space has commonly been cited as a feature unique to Neandertals (Coon, 1962; Howells, 1975; Trinkaus, 1987; Rak, 1986, 1998). As a clear separation between the distal edge of the M3 and the anterior margin of the ascending ramus of the mandible, the retromolar space is a feature that is nearly ubiquitous among Neandertals. This feature is noticeably absent from the Middle Pleistocene European precursors and occurs in much lower frequencies among early modern and recent Homo sapiens populations. Though often cited as an autapomorphic feature for Neandertals (Stinger et al., 1984; Condemi, 1991) the occasional presence of this feature in Upper Paleolithic hominids have led some individuals to disregard this characteristic as a phylogenetic marker distinguishing between archaic and modern populations (Frayer, 1993).

    With debate focusing on the usefulness of the retromolar space as a defining feature of Neandertals, the causal factors responsible for the presence of this trait have also been a source of contention with various researchers developing various ideas as to the development of this feature. Coon (1962) viewed the retromolar space as one aspect of a craniofacial complex marked by an increase in prognathism stemming from an adaptation to cold temperatures resulting in an expansion of the nasal apparatus. This anterior projection of the face also resulted in a anterior displacement of the mandible leaving a space behind the third molar.

    A biomechanical explanation for the presence of the Neandertal retromolar space was offered by Rak (1986). This view envisioned the development of the retromolar space as a consequence of a reorientation of the infraorbital plate in Neandertals. Differential loading patterns on the anterior and posterior dentition, evidenced by the excessive degree of wear exhibited on the anterior teeth, resulted in the production of rotational forces about an axis located between the anterior bite point and the cheek teeth. The infraorbital plate shifted to a parasagittal orientation to better accommodate the moments oriented about the sagittal plane . This reorganization of the Neandertal face resulted in an anterior repositioning of the dental arcade and this coupled with a reduction in the size of the cheek teeth resulted in the development of a distinctive gap on the distal aspect of the third molar.

    Trinkaus (1987), also examining the craniofacial complex in Neandertals offered a different explanation for the distinctive facial morphology and the retromolar space in terms of dental arcade length and the position of the zygomatic root. Viewing the dental arcade in a fixed position, Trinkaus (1987) notes the posterior movement of the zygomatic root from M1-M2 in Middle Pleistocene European hominids to M2-M3 in Neandertals. This shift relates to a posterior migration of the muscles associated with the masticatory apparatus resulting in an increase in the distance between the dental arcade and the posterior aspect of the mandible and masticatory muscles resulting in a decrease in the mechanical advantage of the anterior dentition. This analysis found a slight decrease in the length of the dental arcade in Neandertals relative to their Middle Pleistocene predecessors although this difference was not statistically significant.

    Yet another explanation was posited by Spencer and Deems (1993) who argued, contra Trinkaus (1987), for an anterior migration of the masticatory muscles in Neandertals as well as a decrease in the distance between the temporo-mandibular joint and the anterior dentition. This repositioning resulted in a system that was well designed to produce high levels of incisal force relative to Homo sapiens. These researchers interpret the decrease in dental arcade length in Neandertals as resulting from the anterior migration of the cheek teeth and a posterior displacement of the anterior dentition. It is through the anterior displacement of the posterior tooth row and the masticatory musculature that the high frequency of retromolar spaces in Neandertals is explained. According to Spencer and Deems (1993), the anterior migration of these features is not great enough to decrease the mechanical advantage of the masseter and temporalis.

    Franciscus and Trinkaus (1995) examined samples of Middle Pleistocene and Neandertal mandibles to examine morphological trends that led to the development of the retromolar space in Neandertals. This analysis considered three variables, mandibular length, dental arcade length and ramus breadth. Although these variables were considered by Trinkaus (1987), they were examined independently of one another, thus Franciscus and Trinkaus (1995), employing multiple regression, examined these three variables together to determine the effects they have on the development of the retromolar space. It was found, relative to the Middle Pleistocene sample, that a combination of a decrease in the length of the dental arcade coupled with a reduction in the breadth of the mandibular ramus were contributing factors to the development of the retromolar space. The shortening of the dental arcade is attributed to a reduction in the mesiodistal dimension of the molars in contrast to Spencer and Deems (1993) who maintained the position that molar diminution was not causal factor in dental arcade shortening.

    Several factors in this analysis were taken into consideration in determining the composition of the retromolar space in Neandertals and modern humans. The position of the lateral prominence was determined both quantitatively by measuring the distance of this feature to the posterior edge of the mandibular ramus, and qualitatively by noting its position relative to the dental arcade. This feature is found at the junction of the mandibular ramus and the lateral aspect of the corpus and has been shown to take on more of a distal positioning in Neandertals (Rosas, 2001). Furthermore, the data from Rosas (2001, Table 6) reveals a correlation between the position of the lateral prominence in Neandertals and size of the retromolar space when measured qualitatively in terms of a fully exposed M3 in contrast to a partially exposed M3. With this data, in conjunction with the reduction in the ramus breadth in Neandertals as being a contributing factor in the development of the retromolar space (Franciscus and Trinkaus, 1995), it appears that the position of the lateral prominence is a unique feature among Neandertals in terms of the overall morphology of the retromolar space. This is not to imply that the retromolar space in Neandertals is caused by the distal migration of the lateral prominence, it is only noted that there is a correlation and therefore, this feature serves as an important characteristic in marking a Neandertal-type retromolar space. Therefore, justification is found in using this feature to determine if differences do exist in the composition of the Neandertal and modern human retromolar space.

    Other features were also examined to determine differences in the composition of the retromolar space in Neandertals and modern humans. Following Franciscus and Trinkaus (1995), maximum mandibular length, dental arcade length and minimum ramus breadth were also examined. Because of the trends noted by these researchers when comparing Neandertals to a Middle Pleistocene sample, those same trends were examined in this analysis and then compared to modern humans with retromolar spaces to discover if those same trends existed in the development of this feature in the modern sample especially when compared to modern humans lacking a retromolar space.

    Although several hypotheses have been asserted concerning the development of the retromolar space in Neandertals, there is a paucity of research concerning the cause of the feature among modern humans. In fact, the assertion that the retromolar space cannot be considered an autapomorphic character for Neandertals (Frayer, 1993) suggests that overall morphology of this feature is the same for both taxonomic groups. Rak (1998) on the other hand has suggested that a difference does exist in the composition of the retromolar space in modern humans relative to Neandertals, thus preserving the autapomorphic status for this feature in Neandertals. The development of this feature among modern humans, he argues, is the result of an enlargement of the pre-angular notch, a recess on the anterior aspect of the mandibular ramus that occurs between the coronoid process and the lateral prominence which he states is a feature that is found much more frequently in modern human population. The size of the retromolar space in modern humans is closely tied to the size of the retromolar space. The Tabun C2 specimen exhibits a rather large pre-angular notch and therefore the presence of this feature explains the presence of the retromolar space in this individual.

    In addition to an examination of the differences between the Neandertal and modern retromolar space, the pre-angular notch was also examined to determine if this feature is in fact responsible for the modern retromolar space. This was achieved by using the pre-angular notch index described above and subjecting it to correlation analysis to determine if there is in fact a correlation between the size of the notch and the size as well as the presence/absence of the modern retromolar space.

    The retromolar space itself was measured by two methods. First, the size of the retromolar space was determined by measuring the distance between the third molar at the level of the occlusal surface to the anterior edge of the mandibular ramus. The second measure of the retromolar space follows Rak (1998) who suggests that this feature should be measured from the third molar to the posterior edge of the mandibular ramus to “neutralize” the influence of the pre-angular notch. Measuring the length of the retromolar space in this manner provides a distinction between the more anteriorly positioned molars in Neandertals as opposed to modern humans.






    MANDIBULAR RAMUS



    Relative to the amount of research conducted on determining the causal factors of the retromolar space, less focus has been placed on quantitative analyses of the size and shape of the mandibular ramus especially in terms of the superior aspect of the ramus. Werth (1928) noted a distinction in the shape of the superior ramus between the Maüer mandible and the morphology exhibited by modern humans. According to Werth’s description, the morphology of Maüer and of modern humans marked the extreme ends of a range of variation with Neandertals falling between the two morphotypes. Weidenreich (1936) argued that ramus morphology was not diagnostic based on the modern appearance of the superior ramus morphology of Homo erectus, as well as the archaic appearance of an Eskimo mandible that appeared similar to Neandertals. Rak (1998) describes a distinction between the shape of the coronoid process and the sigmoid notch noting that there is a marked asymmetry found among Neandertal mandibular rami with the coronoid process dominating in size over the condylar process. Modern humans on the other hand are marked by a symmetrical appearance of these two features.

    Other features, primarily non-metric, have been described as unique or occurring in a high frequency among Neandertals. Smith (1978) found that a high frequency of Neandertals exhibit a horizontal-oval (H-O) shaped mandibular foramen as opposed to the modern condition described as a V or U shaped foramen. This study found that among recent modern samples the frequency of the H-O condition was between 0-3.72%. Upper Paleolithic European hominids exhibited an H-O mandibular foramen with a frequency of around 23% and Neandertals, European and Near Eastern, exhibited this condition in 46% of the sample. Frayer (1992) found that among recent Mesolithic and Medieval Hungarians the frequency of H-O foramina ranged from 1.4-1.9%. Early Upper Paleolithic individuals exhibited a frequency of around 44% while the Late Upper Paleolithic had a frequency of 5.3%. Neandertals exhibited the highest frequency of this trait at 52.6%. The H-O shape of the mandibular foramen clearly cannot be considered apomorphic for Neandertals but is interesting to note the high frequency of this feature and it can certainly be considered much more common among Neandertals than in modern populations.

    The medial aspect of the mandibular ramus exhibits other interesting Neandertal features. Among these is the presence on the medial pterygoid tubercle resulting from hypertrophy of the superior fibers of the medial pterygoid muscle (Rak et al. 1994) producing a bony tubercle just superior to the gonial region. This feature is distinguished from modern humans who exhibit a consistent size in areas of attachment for the medial pterygoid while Neandertals exhibit a gradual increase in robusticity with the greatest size occurring at the medial pterygoid tubercle (Rak et al. 1996). These authors note the presence of this feature on the immature Amud 7 mandible indicating that this feature is not produced through a plastic response to the environment but rather is a heritable trait. This has been contested by Creed-Mills et al. (1996) who state that the tubercle exhibited by the Amud 7 mandible is not homologous to the medial pterygoid tubercle found among adult Neandertals but rather is the same condition exhibited by modern humans. The tubercle found on the Amud 7 mandible is argued to be the tuberculum pterygoideum inferius, a feature that occurs in the postnatal development of the mandible among modern humans and is found in the same position as the medial pterygoid tubercle and is offset at its superior boarder by the presence of the sulcus colli. Rak et al. (1996) show that while these features are present on the Amud 7 mandible they are in fact distinct from the medial pterygoid tubercle and thus maintain the heritable status of this feature.

    As most studies of the mandibular ramus have been either descriptive or have examined the frequency of non-metric traits, this analysis will provide an overall quantitative analysis of the size and shape of the mandibular ramus with respect to Neandertals and modern humans. This will include both univariate and multivariate methods with an emphasis placed on the size and shape of the coronoid process. The measurements utilized are listed in Table 3 and are graphically depicted in Figure 6.





    STATISTICAL ANALYSIS



    Aside from examining frequency data from qualitative features examined in this analysis, three types of statistical analyses were employed in this study. Univariate analyses were conducted on Minitab while SAS was used for bivariate and multivariate statistical analyses. Measurements were taken from both the left and right sides of specimens when available and the averages were used for statistical tests. Features of the retromolar space and mandibular ramus were subjected to t-tests assuming unequal variances. The features in included in the univariate portion part of the analysis were then compared to the Tabun C2 mandible via interval plots to determine where this specimen falls relative to the other samples. Ideally, the measurements taken from the Tabun C2 mandible would be compared to one specimen-one sample t-tests, but given the small sample sizes for various features, it was felt by the author that such comparisons could result in inaccurate interpretations.

    To determine the contribution of the pre-angular notch to the retromolar space among modern humans correlation analysis is employed. This consists of plotting the pre-angular notch index against two measures of retromolar space size, the distance between the M3 and the anterior aspect of the mandibular ramus and the distance between the M3 and the posterior aspect of the mandibular ramus. This analysis will include the sample of modern humans exhibiting retromolar spaces as well as the Tabun C2 mandible. One should expect a high correlation between these features in the size of the pre-angular notch is indeed responsible for the presence/absence of the retromolar space in modern humans.

    The third aspect of this study involves a multivariate analysis of overall size and shape of the mandibular ramus by employing principle component analysis on various measures of the ramus. Principle components will be taken from the covariance matrix of log size and shape and of log shape transformations of the raw data (Darroch and Mosimann, 1985). Log size and shape variable are simply log-transformations of the raw measurements. Log shape variables are an index of raw measurements and the geometric mean. Thus, the geometric mean for each individual is determined followed by the division of each individual’s measurements by that individual’s geometric mean. This has the effect of removing the size component from each measurement with the residual ideally containing only shape information. The log shape data will then be subjected to a cluster analysis using Euclidian distance and average linkage which takes the average of all the distances between each pair of specimens in different clusters to determine distance. Only specimens with all variables used in the principle component analysis are included in the multivariate portion of the study. Although this results in a decrease in sample sizes, the estimation of missing values is not conducted.

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    Post Re: The Tabun Mandible

    This chapter details the results of the morphometric analysis of the Tabun C2 mandible and is divided into three primary sections. The first details the results of the univariate analysis consisting of t-tests and correlation analysis of the retromolar space as well as a descriptive analysis of features relevant to the retromolar space. This part of the analysis examines four samples, Neandertals, Middle Pleistocene European and African hominids, modern humans with retromolar spaces and modern humans without retromolar spaces. This is followed by the result of the multivariate analysis of the mandibular ramus. Finally a descriptive analysis of the Tabun C2 mandible in terms of non-metric features with emphasis on the medial side of the mandibular ramus is discussed.



    RETROMOLAR SPACE ANALYSIS



    Four different samples are examined to determine if a difference in the morphology exists between the Neandertal retromolar space and its modern analogue. Frayer (1993) argues that the retromolar space in Neandertals cannot be considered autapomorphic for this group because of the presence of this feature in Upper Paleolithic modern samples. This statement implies that the two taxa should exhibit the same morphological pattern for the retromolar space.



    To determine if this is the case Neandertals are compared to a sample of Middle Pleistocene mandibles while a sample of modern humans lacking a retromolar space are compared to a sample of modern humans exhibiting this feature. Modern humans with retromolar spaces are also compared to the Neandertal sample to determine differences in morphology. Table 4 provides a list of sample comparisons and results of t-tests.



    Dental Arcade Length

    When compared to the Middle Pleistocene sample, Neandertals exhibited a statistically significant reduction in the length of the dental arcade at p<.05 with a Neandertal mean of 55.18mm and a mean of 62.82mm for the Middle Pleistocene specimens (Figure 8). Modern humans with retromolar spaces compared to modern humans lacking this feature could not be distinguished statistically. The averages for dental arcade length for the two modern samples were similar with mean for the retromolar space sample was 54.86mm and the sample without retromolar spaces slightly smaller with a mean was 52.46mm. When Neandertals were compared to the sample of modern humans exhibiting retromolar spaces, again there was no significant difference as the Neandertal mean was only slightly higher that that of the modern human sample mean.



    Dental Arcade Length/Maximum Length

    The same pattern as that found for comparisons of the length of the dental arcade is found for this index as well (Figure 9). Neandertals with a average of .50 and the Middle Pleistocene sample with an average of .53 were found to be statistically significant, but only at the p<.10 level. At the p<.05 level there was no distinction between the samples. The comparison of the modern human sample lacking retromolar spaces and the sample with retromolar spaces found no distinction between the samples with means of .50 and .48 respectively. Neandertals compared to modern humans were also found to be statistically insignificant indicating a similar proportion of the dental arcade relative to the entire length of the mandible.

    Lateral Prominence to Posterior Ramus

    The distance between the most prominent aspect of the lateral prominence and the posterior edge of the mandibular ramus was found to be statistically insignificant when comparing Neandertals with a mean of 55.55mm and the Middle Pleistocene sample (Figure 10) with a mean of 58.04mm. A comparison of this measure for modern humans lacking retromolar spaces versus modern humans with this feature was again statistically insignificant with mean values of 47.45mm and 49.00mm respectively. There was a statistically significant distinction when comparing Neandertals and modern humans with retromolar spaces at the p<.05 level. Neandertals exhibited a significantly larger value with a mean of 55.55mm compared to the modern human sample with a mean of 49.70mm.

    Maximum Mandibular Length

    The maximum length of the mandible (Figure 11) was found to differ statistically significant when comparing Neandertals (mean = 112.70mm) to the Middle Pleistocene sample (mean = 119.20mm) but only at the p<.10 level. There was no distinction between the samples at the p<.05 level. A comparison of modern humans without retromolar spaces exhibiting a mean of 105.76mm and modern humans with retromolar space with a mean value of 112.50mm was found statistically significant at the p<.05 level. Neandertals and modern humans with retromolar spaces exhibited mean values that were almost equal and a comparison of the two samples was therefore statistically insignificant.

    Minimum Ramus Breadth

    The minimum breadth of the mandibular ramus (Figure 12) was found to differ significantly (p <.05) between Neandertals to the Middle Pleistocene sample. Neandertals exhibited a mean value of 40.54mm compared to the greater average of 46.96mm for the Middle Pleistocene. When modern humans without retromolar spaces (mean = 36.22mm) were compared to modern humans with retromolar spaces (mean =35.93mm), the samples were statistically indistinguishable from one another. Differences Neandertals and modern humans were found to be significant at the p<.05 level.



    M3 to Posterior Ramus



    The mean distance between the distal edge of the third molar and the posterior edge of the mandibular ramus did not differ significantly between Neandertals and the Middle Pleistocene sample (Figure 13). The Neandertal mean of 49.78mm and the mean value of 48.32mm for the Middle Pleistocene proved to be statistically insignificant. Modern humans lacking retromolar spaces mean when compared to modern humans with retromolar spaces mean did differ statistically. The mean value of 39.12mm for individuals exhibiting retromolar spaces was significantly larger at the p<.05 level than the average of 35.89mm for the sample lacking retromolar spaces. A distinction was also made when comparing the Neandertal sample to modern humans with retromolar spaces at the p<.05 level.

    M3 to Posterior Ramus/Maximum Mandibular Length



    When the distance between M3 and the posterior edge of the mandibular ramus are compared relative to the maximum length of the mandible, a slightly different pattern emerges than that of the absolute measure of M3 to the posterior edge of the ramus (Figure 14). The Neandertals and Middle Pleistocene samples do exhibit a significant difference between their mean values of .44 and .40 respectively although this difference is made only at the p<.10 level. No distinction is made at the p<.05 level. The two modern human samples were not statistically different with a mean values of .34 for modern humans without retromolar spaces versus .35 for modern humans exhibiting a retromolar space. When Neandertals are compared to modern humans their mean values are statistically distinct at the p<.05 level.

    THE RETROMOLAR SPACE OF TABUN C2



    Due to small sample sizes, no statistical tests were performed to compare the Tabun C2 mandible to the sample of Neandertals or modern humans with retromolar spaces. A one sample-one specimen test can be performed but again, because of small sample sizes, it was felt by the author that the result would have ultimately been meaningless. Therefore, the measurements of Tabun C2 are compared to the mean values of the Neandertal sample and modern humans with retromolar spaces for measurements that were found to differ statistically and are plotted against these two samples via interval plots. This certainly is not the most sophisticated method for understanding the morphology of the retromolar area on the Tabun mandible but nonetheless does provide very useful information in determining the nature of its retromolar space. The measurements and values used to compare Tabun C2 are found listed in Table 5.



    Lateral Prominence to Posterior Ramus



    Neandertals were found to exhibit a significantly higher mean value for this measurement when compared to modern humans with retromolar spaces at the p<.05 level. Tabun C2 exhibits a value of 53.8mm for this measurement and plots closer to the mean value of 55.55mm for the Neandertal sample than it does to the modern human sample with a mean of 49.70mm (Figure 15). The Tabun C2 mandible falls well within the range of variation exhibited by the Neandertal sample with the lowest value at 48.7mm for Tabun C1 to 59.0mm for La Ferrasie. When compared to the modern humans sample, Tabun C2 falls toward the end of the range of variation with the highest value at 55.7mm.



    Minimum Ramus Breadth

    The minimum breadth of the ramus also differed significantly between the Neandertal and modern samples. Tabun C2 clearly plots to the Neandertal mean in terms of this measurement (Figure 16). For this comparison the Tabun C2 mandible with a value of 42.0mm falls outside of the range of variation for the modern humans sample whose highest value 40.4mm. Tabun does fall toward the high end of the range of variation for Neandertals exceeding the mean value of 40.5 for this sample.



    M3 to Posterior Ramus



    The distance between the third molar and the posterior edge of the mandibular ramus differed significantly between moderns with retromolar space and Neandertals. In the case of Tabun C2, a measurement of 48.5mm fell well within the range of variation of Neandertals (Figure 17) and was not to far from the Neandertal mean of 49.8mm. There was no overlap between the Neandertal sample and the modern sample for this measurement with the highest modern value at 34.4mm and the lowest Neandertal value at 42.6mm.



    M3 to Posterior Ramus/Maximum Mandibular Length

    Tabun C2 aligns more closely to Neandertals as well when the distance between the third molar and the posterior edge of the ramus are standardized against the maximum length of the mandible (Figure 18). There is no overlap of this value for Neandertals, who exhibit a range of .42-.46 and modern humans with retromolar spaces who range from .31-.37, although Tabun C2 exceeds the modern range of variation with a value of .41 just below the Neandertal mean of .44.



    Pre-Angular Notch

    As discussed in Chapter two, the pre-angular notch has been argued to be the causal factor in determining the presence/absence of the retromolar space in modern humans (Rak, 1998). Figure 19 is a scatterplot of pre-angular index scores on the y-axis plotted against the length of the retromolar space measured by the distance between the distal edge of the third molar and the anterior border of the anterior ramus on the x-axis.



    Pearsons correlation was conducted on three samples for this analysis. The first consisted only of modern humans with retromolar spaces including the Tabun C2 mandible. The second sample consisted of modern humans with retromolar spaces excluding the Predmosti 3 specimen. The third sample consisted of the entire modern human sample, with the exception of Predmosti 3 that preserved enough of the ramus to make a determination of pre-angular notch size. Measurements used to determine this index are discussed in the previous chapter. Individuals without retromolar spaces were scored as 0.0mm.

    Result of this analysis revealed that modern humans with retromolar spaces exhibit a correlation of 0.03 for the length of the retromolar space plotted against the pre-angular notch index. One individual from this sample, Predmosti 3, exhibited an pre-angular notch value of greater than one resulting from the absence of a notch on the side from which the length of the retromolar space could be measured. This resulted in the numerator of the index being a larger value than the denominator. Due to this extreme value, this specimen was removed for a second analysis of modern humans with retromolar spaces. The results of this second analysis found an increase in the correlation coefficient from 0.03 to 0.29. Finally the total sample available for correlation analysis minus the Predmosti 3 specimen produced a correlation coefficient of 0.19.

    In terms of the depth of the pre-angular notch there was a high degree of overlap between modern humans with retromolar spaces and modern humans without retromolar spaces. Modern humans lacking a retromolar space exhibited a range of pre-angular notch size from 0.86-0.97 while modern humans with retromolar spaces had a range of 0.86-0.96. Including the Predmosti 3 specimen, this range increases to 0.86-1.76. This high value for the Predmosti 3 specimen is perhaps insignificant in and of itself but in terms of the sample as a whole becomes very important in determining the role that the pre-angular notch plays in the presence/absence of the retromolar space in modern humans. This will be discussed further in the next chapter. The Tabun C2 specimen exhibited a relatively low value for the pre-angular notch index indicating the presence of a large pre-angular notch. It is also interesting to note at this time that the modern human specimen exhibiting the largest retromolar space (with the exception of Tabun C2) did not exhibit the lowest value for the pre-angular notch index, rather this specimen MH10-11 exhibited a pre-angular notch size of 0.96 and a retromolar space length of 4.4mm indicating that this individual has only a slight pre-angular notch and yet retains a large retromolar space.





    Qualitative Analysis of Lateral Prominence Position



    This analysis examines the position of the lateral prominence in terms of its absolute distance from the posterior edge of the mandibular ramus. It was determined that there is a marked distinction between modern humans with retromolar spaces and Neandertals. Comparisons between Neandertals and the Middle Pleistocene sample and modern humans with retromolar spaces versus modern humans lacking a retromolar space were statistically indistinguishable for this measurement. A second measure of this feature provides very interesting and useful information regarding the formation of the retromolar space in Neandertals and modern humans. This measure examines the position of the lateral prominence relative to the dental arcade. This becomes integral to understanding the underlying development of the retromolar space for two reasons, First, this feature marks the area where the ramus joins the mandibular corpus. Thus changes in the relative placement of the mandibular ramus through differential process of deposition/resorption affect the position of the lateral prominence during growth remodeling of the ramus (Rosas, 2001). Second, the position of this feature will be affected by changes in the length and position of the dental arcade and can aid in providing a distinction between different developmental processes that can result in the production of a retromolar space.

    The position of the retromolar space relative to the dental arcade was noted for all Middle Pleistocene, Neandertal and modern human specimens. For this analysis modern humans with retromolar spaces were separated from those lacking the feature. The frequency data obtained from this analysis is found in Table 6.

    The data presented in Table 6 marks a clear distinction between Neandertals and both samples of modern humans. Neandertals exhibit a frequency of 100% of the positioning of the lateral prominence under the third molar. Modern humans never exhibited this condition as the lateral prominence was always found under M2 or the M2/M3 septum. Among the Middle Pleistocene sample, there was variability between the third molar and the M2/M3 septum. The Tabun C2 mandible exhibited a lateral prominence in the Neandertal position. This data is consistent with that of Rosas (2001) who found that among Neandertals the lateral prominence was always positioned under the third molar with the exception of Krapina G, Hortus IV, Le Moustier and Vindija 250. Of these four specimens, the last three are described as exhibiting partially covered third molars. Thus, Neandertals without full retromolar spaces tend to have the lateral prominence positioned more anteriorly relative to the tooth row. This distinction does not appear to be a marked when comparing the modern human samples. Although there is a tendency for the lateral prominence to be anteriorly displaced relative to the dental arcade in individuals with retromolar spaces, this also occurred among 50% of individuals lacking a retromolar space.





    MANDIBULAR RAMUS ANALYSIS



    The multivariate analysis of the mandibular ramus was conducted on Neandertals, modern humans and the Tabun C2 mandible. In the previous analysis modern humans were divided into two groups on the basis of presence/absence of a retromolar space. For the purposes of analysis of the mandibular ramus the modern human samples are pooled. Specimens were used only when they preserved all of the areas measured for this sample, missing values were not estimated. These measurements are outlined in the previous chapter and the descriptive statistics for the samples used in this analysis are shown in Table 7.

    Principle component analyses were carries out using log size-and-shape and log shape variables after Darroch and Mossiman (1985). Log size-and-shape variables are simply log transformations of the raw data while log shape variables are corrected against the geometric mean of individual specimens. The results of these analyses are shown in Tables 8 and 9 with graphical representations of the results shown in Figures 20 and 21.

    An analysis of the eigenvectors from the Log size-and-shape analysis offers interesting results. The first principle component distinguishes between specimens on the basis of size as all values in this eigenvector are positive. When the individual values were plotted against individual values for the geometric mean there was a correlation of r2=.92, p=0.000 further indicating the size properties of the first principle component. The scores along the axis of the second principle component were not correlated with size (r2=.18, p=0.372). The first eigenvector accounted for 58% of the variation while the 16% was accounted for by the second eigenvector with the two eigenvectors accounting for a total of 75% of the total variance.



    An examination of the principle components reveals that measurements pertaining to the coronoid process appear to play an important role in determining were the individual points are plotted. The height of the coronoid process clearly dominates over the other variables and is the most important variable in determining where points are plotted along the x-axis. The maximum breadth of the coronoid process, the height of the mandibular ramus and to a lesser extent, the maximum height of the ramus are also determining factors. Variables such as the minimum breadth of the ramus, maximum breadth, the distance between the condyle and the superior aspect of the coronoid as well as the maximum horizontal breadth of the ramus had very little impact on the position of individuals along the x-axis.

    The position of points along the y-axis were also highly affected by variables pertaining to the coronoid process. There was a marked distinction between the maximum breadth of the coronoid which dominated the positive values and the height of the coronoid which exhibited the lowest negative value. By themselves these variables tend to distinguish between long, narrow coronoid processes and shorter, broader coronoid. Other values such as the maximum height of the mandible and the height of the ramus at the coronoid process were also important variables in this portion of the analysis.

    A study of the scatterplot in Figure 20 reveals a clustering of Neandertal specimens but with significant overlap with the modern human sample. The specimens plotted on the x-axis do conform to the above results that the first principle component is a size component. This explains the near extreme position of the Tabun C2 mandible along this axis next to La Chancelade specimen, and the placement of the Tabun C1 mandible on the negative aspect of this axis well within the modern human cluster.



    Not only is there overlap with the first component but also with the second principle component. It is interesting to note that Regordou 1 plots at nearly the same point as the Ohalo 2 mandible while the Krapina 63 mandibular ramus falls immediately adjacent to the recent MH 37 specimen. The two African specimens included in this analysis, Fish Hoek and Haua Fteah were both found to plot on the edge of the modern human cluster.

    The log shape analysis also provided interesting results regarding differences between modern humans and Neandertals. As with the log size-and-shape analysis, the principle component values obtained for the individual specimens were plotted against the geometric means obtained from those individuals. The correlation coefficient for PC1 versus the geometric mean provided a result of r2=-0.545, p=0.003 indicating a significant correlation between the two variables. The same was true for PC2 with an r2=-0.403, p=0.034. This indicates that size information was retained when transforming the raw data to the values used in this portion of the study. Ideally this correlation would have been insignificant meaning that the variables would reflect only shape information, unfortunately this was not the case. Therefore, results from the log shape analysis still retain a size residual.

    The first principle component accounted for 48% of the variance and marked a distinction primarily between variables pertaining to the height of the coronoid process and the mandibular ramus versus measures of ramus breadth. The height of the ramus at the ramus at the coronoid process represented the most extreme negative value followed closely by the maximum height of the ramus.



    These were contrasted against the positive values for the maximum breadth of the ramus, condyle to superior coronoid and maximum horizontal breadth of the ramus. Measures of the height of the coronoid process itself as well as minimum ramus breadth and maximum breadth of the coronoid were negligible for PC1. This component therefore appears to distinguish between individuals on the basis of general ramus shape.

    The second principle component accounts for 22% of the variance and as stated above still retains a degree of size information. Of the values of the second eigenvector, maximum height of the mandible clearly dominates and contrasts significantly with the height and the maximum breadth of the coronoid process. Maximum ramus breadth was also an important variable in the plotting of individual specimens.

    The scatterplot of the log shape variables marks a clearer distinction between the Neandertal and modern human sample with Neandertals falling along the edge of the modern cluster. The only exception is the Tabun C1 mandible which plots well within the modern human cluster. The Tabun C2 mandible also plots with modern humans in this analysis falling closest to the Dolni Vestonice 3 mandible. The two African mandibles did not cluster together and neither mandible plotted near the Tabun C2 mandible.

    Figure 22 is a phenogram of all log shape principle components and Table 10 is the minimum spanning tree distance for all of the specimens used in the shape analysis.



    The Neandertal sample clusters together on the periphery of the tree with a single recent specimen, MH-37 included within this grouping. Both Regordou and Fish Hoek represent extreme outliers with Fish Hoek branching off at the first node and Regordou and the remainder of the tree forming the second branching point. As should be expected the results from the cluster analysis mirror the log shape analysis in that Tabun C2 plots with the modern human cluster, its closest neighbor being Dolni Vestonice 3. Tabun C1 also remains in the modern cluster plotting most closely to members of the recent sample and Haua Fteah plots closest to the European Predmosti 3 specimen. Due to the fact that the data used to produce the phenogram were the same as used in the scatterplot of the log shape analysis the explanation for the pattern exhibited is the same as that for the log shape analysis and therefore will not be discussed here.

    The measurements in this analysis were not necessarily attuned to deriving all possible information regarding understanding the shape of the mandibular notch. To remedy this, a univariate analysis was conducted on the maximum breadth of the coronoid process relative to the distance between the posterior edge of the mandibular condyle and the anterior most aspect of the coronoid process providing a general measure of the relative position of the deepest point of the mandibular notch. A clear distinction was found between Neandertals and modern humans. The Neandertal sample exhibited an average value of .56 as opposed to a value of .47 for the modern human sample and was significant at the p<.05 level indicating a more anterior position for the deepest point of the mandibular notch for modern humans. The Tabun C2 mandible exhibited a value of .48 and clearly plots with the modern sample for this feature (Figure 23).

    Qualitative Analysis

    This section details the results of an analysis of non-metric features of the mandibular ramus including characteristics of the lateral prominence, the shape of the mandibular foramen, the presence/absence of a medial pterygoid tubercle and the shape of the gonial region. These results are presented simply as descriptive and frequency data.

    The position of the lateral prominence was addressed above. It was determined that a distinct difference is present in the position of this feature relative to the dental arcade when comparing Neandertal and modern human samples. This conclusion was also reached by Rosas (2001). It was also determined that the Tabun C2 mandible exhibits the Neandertal condition. A second characteristic of the lateral prominence that appears to distinguish Neandertals and moderns is the prominence of this feature. It was noted that the lateral prominence in Neandertals is nearly flush with the mandibular corpus. This is especially true when examining specimens such as Kebara, Amud and Regordou 1. The lateral prominence exhibited by this individual is very slight and may result from the overall robusticity of the individual. The opposite is true of modern human mandibles which exhibit a pronounced lateral prominence.

    The medial aspect of the mandibular ramus was examined for the presence of two features, the medial pterygoid tubercle and the H-O mandibular foramen shape. The medial pterygoid tubercle has been argued to be a derived feature for Neandertals and appears very early in the ontogenetic development of the mandible (Rak et al., 1996). The presence of the H-O mandibular foramen, although not an apomorphic feature for Neandertals, certainly occurs at a higher frequency among Neandertal specimens than in modern human populations (Smith, 1978; Frayer, 1992).

    The Tabun C2 mandible falls within the Neandertal sample for both features. The medial pterygoid tubercle was found to be present in all Neandertal specimens used in this analysis. The opposite was true for the modern human sample as no individual was found to exhibit a medial pterygoid tubercle. The Tabun C2 mandible displays a well defined tubercle at the anterior aspect of the gonial region. If Rak et al., (1996) are correct about the autapomorphic nature of this feature one should not expect its presence on the Tabun C2 mandible without the presence of Neandertal genes.

    The shape of the mandibular foramen does not provide an absolute distinction between modern and archaic samples due to the presence of the H-O and V-shaped foramen occurring in both samples used in this analysis. Of the ten Neandertal mandibles examined for this feature 60% were found to exhibit the H-O condition while the remaining 40% lacked this feature. Modern humans on the other hand overwhelmingly lacked the H-O mandibular foramen with 93% of the sample exhibiting the V-shaped condition. Tabun C2 displays an H-O foramen which by itself does not necessarily group this specimen with the Neandertal sample but when taking into account the presence of the medial pterygoid tubercle as well as a truncated gonial region, does show that the overall morphology of the inside of the mandibular ramus is typical of Neandertals.




    SUMMARY

    This study first examines the nature of the retromolar space in Neandertals and modern humans to determine differences between these two samples with regard to this feature. This was accomplished by examining the trends toward a retromolar space from the Middle Pleistocene hominids to Neandertals and examining the difference between modern humans with retromolar spaces and modern humans lacking this feature. Although it is difficult to determine the reason why modern humans can exhibit a retromolar space with a small, geographically restricted sample and without the associated crania, it does appear that the retromolar space in modern humans results at least partially from an overall size increase of the mandible. In contrast, Neandertals appear to exhibit this feature due at least partially to a reduction in overall robusticity. This will be examined in further detail below. The Tabun C2 mandible was then compared to the Neandertals and modern humans with retromolar space samples and was found to exhibit a Neandertal-type retromolar space.

    Principle component analyses made a distinction between the mandibular rami of Neandertals and modern humans. It was determined that the size and to some extent, the shape of the coronoid process are important determinants in distinguishing between the two samples. This comparison resulted in the Tabun C2 mandible plotting with modern humans and thus exhibiting a mandibular ramus that preserves a very modern morphology. Furthermore, a distinction does exist between Neandertals and modern humans in terms of the position of the mandibular notch. Tabun C2 exhibits the modern condition with respect to this feature. This is also evident when examining the patterns produced by the cluster analysis. There is a distinction made between the Neandertal and modern human samples with Tabun C2 clustering with the modern sample.

    Various non-metric features including the size and position of the lateral prominence, the shape of the mandibular foramen and the presence/absence of the medial pterygoid tubercle displayed a tendency to group the Tabun C2 mandible with the Neandertal sample. Although this specimen exhibited the Neandertal condition in terms of lateral prominence position, it was the size of the prominence that was characteristic of modern humans.

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    Post Re: The Tabun Mandible

    The taxonomic position of the Tabun C2 mandible has been a recent source of contention (Quam, 1995; Quam and Smith, 1998; Rak, 1998; Stefan and Trinkaus, 1998). The mosaic morphology of this specimen as well as the geographic location from which it was discovered makes an accurate assessment critical to understanding the relationship between modern humans and Neandertals and provides insight regarding the existence of biological boundaries separating these two groups. This chapter examines in detail the results presented in this analysis and examines the nature of the retromolar space in Neandertals and modern humans to determine where the Tabun C2 mandible falls regarding these two samples. This is followed by an examination of the results provided from the analysis of mandibular ramus morphology.





    RETROMOLAR SPACE



    Several explanations have been proposed to explain the presence of the retromolar space in Neandertals (Coon, 1962; Rak, 1986; Trinkaus, 1987; Spencer and Deems, 1993; Franciscus and Trinkaus, 1995) and although these various researchers have arrived at different interpretations, they have all maintained one common position, they all view the development of the retromolar space as the result of processes affecting larger aspects of craniofacial morphology. Thus when stating that the retromolar space cannot be viewed as a Neandertal apomorphy (Frayer, 1993; Franciscus and Trinkaus, 1995) due to its presence in modern samples, this implies the same general morphology for both the modern and archaic type. The retromolar space is therefore viewed from a phenetic perspective and is removed from its larger developmental and functional context, when in reality the Neandertal retromolar space is just one aspect of a larger, related complex of features.

    This follows from the fact that aspects of the mandible grow in response to cranial. For example, the growth of the mandibular corpus and its spatial relationship to the ramus is determined in part by growth at the lingual tuberosity which is closely tied to growth at the maxillary tuberosity (Enlow, 1990). Therefore it follows that a unique cranio-facial morphology in Neandertals results in a uniquely derived mandibular morphology and a retromolar space that is unique to this evolutionary lineage.

    Kimble and Rak (1993) have stated that while apomorhic features distinguish between systems of phylogenetic ancestry and descent, not all organisms encompassed within a phylogenetic species must exhibit that feature, rather it must be shown that character distributions will distinguish relatively between non-overlapping groups in a sample. As an extension of this, it is suggested here, that while individual features may vary in a particular taxon, one is able to consider larger morphological complexes that encompass those variable individual features to be the source of phylogenetic distinction. Given that the “typical” Neandertal sample spans a large quantity of time as well as encompassing specimens from various geographical regions, it is unrealistic to expect all representatives of that sample to exhibit a particular apomorphic feature. It is more reasonable, on the other hand, to expect these specimens to exhibit the same larger evolutionary trends and functional complexes.

    If the retromolar space is examined in terms of its components and the general evolutionary trends as well as the overarching functional and developmental processes that result in the development of this feature, the Neandertal retromolar spaces maintains its apomorphic status when compared to the modern human analogue. It should be kept in mind however that phylogenetic distinctions should be viewed merely as advise on how to distinguish between samples strictly on a morphological basis and do not reflect the underlying biological nature of species (Mayr, 2000). Interestingly enough it is the morphological distinction of the retromolar space exhibited by these two morphological taxa that provides evidence of genic exchange between Neandertal and modern populations as will be shown below.





    The Neandertal Retromolar Space

    Neandertals were compared to Middle Pleistocene mandibles from Europe and North Africa to develop a better understanding of the development and evolutionary trajectory of the retromolar space. Though this analysis was not as sophisticated as that conducted by Franciscus and Trinkaus (1995), the same general conclusions were reached indicating a general trend for a decrease in the robusticity from the Middle Pleistocene sample to Neandertals. This trend was also discussed in terms of general robusticity by Trinkaus (1987).

    The length of the dental arcade as well as the minimum breadth of the mandibular ramus were found to be significantly smaller in the Neandertals sample when compared to the Middle Pleistocene at the p<.05 level (Table 4). The same was found to be true of the minimum breadth of the ramus with a significant reduction found in the Neandertal sample. The distance between the distal edge of the third molar and the posterior edge of the ramus were not significantly different indicating that the reduction in the breadth of the ramus may have to do with an increase in the rate of resorption on the anterior aspect relative to the deposition of bone on the posterior edge of the ramus. Thus the development of the retromolar space in Neandertals is partially the result of a decrease in the length of the dental arcade length in conjunction with a relative increase in the resorption of bone on the anterior edge of the ramus.

    The maximum length of the mandibular ramus, although decreased in the Neandertal sample, was significant only at the p<.10 level. This slight decrease is evident as well when examining the dental arcade length and the distance between M3 and the posterior edge of the mandibular ramus relative to the maximum length of the mandible. In both cases significance was found at the p<.10 level with Neandertals exhibiting a decrease in size when compared to the Middle Pleistocene for the first measure while exhibiting a larger value for the second measure. Both of these measurements further indicated the relative decrease in the size of the dental arcade while the overall size of the mandible itself remains relatively unchanged. Even though there is an indication of a decrease in the length of the mandible, this appears to occur anterior to the mandibular ramus as indicated by the greater distance between the M3 and posterior edge of the ramus in Neandertals.

    An important determinant in understanding the development of the Neandertal retromolar space is the position of the lateral prominence relative to the tooth row. Among the Neandertals examined for this analysis the lateral prominence was found below the M3 in 100% of the sample. The Middle Pleistocene sample only the Mauer mandible exhibited this condition while the remainder of the sample had the lateral prominence positioned under the M2/M3 septum. Rosas (2001) also found that the lateral prominence position in Neandertals was also posteriorly displaced relative to the tooth row except for specimens that lacked a full retromolar space. Those specimens that were defined as having only a partially exposed third molar, Hortus IV, Le Moustier and Vindija 250, exhibited a more anterior lateral prominence relative to the dental arcade with this feature positioned under the M2/M3 septum. The only specimen found to deviate from this pattern is Krapina G which lacks total exposure of the M3, with the inferior most distal edge covered by the ramus, while maintaining the typical Neandertal condition in terms of lateral prominence placement.











    The Modern Human Retromolar Space

    There is a paucity of research examining the nature of the modern human retromolar space. The fact that this feature is present in both modern human and Neandertal populations makes an understanding of the underlying morphology of this feature that much more important for the reasons discussed above. Though this analysis does provide insight on the modern human retromolar space, certain factors should be taken into account and this analysis should be viewed strictly as preliminary.

    There are various limitation to this section of the analysis that should be stated. First of all, the sample of modern humans with retromolar spaces with which this analysis is conducted is rather small and makes up only 18% of the entire modern human sample. Furthermore, this sample of modern humans with retromolar space is almost entirely confined to a single geographic area. It should also be noted that the crania of the individuals with retromolar spaces were not examined. Therefore while difference in mandibles with retromolar spaces are examined, it is difficult to determine the causes of the differences.

    Overall, very few differences were found to occur between modern humans with retromolar spaces compared to those lacking the feature. As shown in the previous chapter, there was high frequency of insignificant results between these two samples (Table 4) as only two of the seven comparisons were found to be statistically significant. Modern humans with retromolar spaces were found to be significantly larger in terms of maximum mandibular length than those lacking this feature. The same was true of the distance between the third molar and the posterior edge of the ramus with a significantly higher mean for the retromolar space sample. The dental arcade length, though slightly higher in the retromolar space sample was not significant. Furthermore, the minimum breadth of the mandibular ramus did not differ significantly between the two samples, rather the average values were nearly identical.

    The position of the lateral prominence, though important in distinguishing between Neandertals with and without retromolar spaces, does not appear to have the same effect for the modern human sample. Although there was a tendency for modern humans with retromolar spaces to exhibit the lateral prominence under the M2/M3 septum, the posterior condition for modern humans, 50% of individuals without retromolar spaces exhibited this condition as well. No modern individuals exhibited the lateral prominence positioned under the M3 making this condition exclusive to Neandertals.

    The pre-angular notch cannot be considered as the cause of the retromolar space in modern humans based on the sample examined in this analysis. An examination of this feature found that significant overlap in the depth of the notch when comparing the two modern human samples. Modern humans without retromolar space exhibit the same variation in the size of the pre-angular notch as do modern humans with retromolar spaces. It is clear that the size of the pre-angular notch can certainly affect the length of the retromolar space as is evident from the cluster at the center of the scatter plot in Figure 19. Among individuals with retromolar spaces there is a positive relationship between the length of the retromolar space and the depth of the notch. Though the evidence provided does not support the assertion by Rak (1998) that the pre-angular notch causes the modern human retromolar space. As discussed in the previous chapter, the modern human mandible exhibiting the largest retromolar space, MH10-11, did not have the deepest pre-angular notch as would be expected. Although the pre-angular notch can result in a larger retromolar space, the retromolar space must already be present for the reasons discussed above.

    Although the exact cause of the modern human retromolar space cannot be determined in the absence of the associated crania it is possible to discuss the differences between the two samples. On the basis the material presented here it would appear that modern humans exhibiting retromolar spaces have on average a longer mandible as indicated by the maximum mandibular length as well as the distance between the third molar and the posterior edge of the ramus. In spite of this difference, the average minimum ramus breadth was nearly identical for the two samples. Thus, it can be suggested that the retromolar space results from an overall elongation of the mandible while the breadth of the mandibular ramus remains the same. Therefore, it is the proportionately narrower ramus that may result in full exposure of the third molar. Given that the growth and development of the mandible is closely tied to the growth and development of the cranium it might be suggested that individuals with retromolar spaces exhibit a form of facial prognathism. This suggestion is purely conjecture at this point in time.





    Summary

    Differences are noted between the Neandertal and modern human retromolar spaces. Neandertals exhibit a chronological trend toward a reduction in robusticity while maintaining a high degree of facial prognathism as originally shown by Franciscus and Trinkaus (1995). The data presented here is in accordance with those findings. It is also noted that the position of the lateral prominence relative to the dental arcade covaries with the presence/absence of the Neandertal retromolar space. This was not the case with the modern human retromolar space as the relative position of the lateral prominence shifted between M2 and the M2/M3 septum regardless of the presence of a retromolar space. Furthermore, it appears that the retromolar space in the modern human sample was the result of a relatively narrower mandibular ramus resulting from an elongation of the mandible in individuals with retromolar spaces while the minimum ramus breadth remained constant when compared to individuals lacking the retromolar space. Therefore, distinctions can be made between the Neandertal and modern human retromolar space. These distinctions are likely the result of the different craniofacial complexes.















    Comparison of the Neandertal and Modern Retromolar Space

    with the Morphology of Tabun C2



    To understand the relationship between modern humans and Neandertals it is important to not only understand the gross morphology of features used to examine similarities and differences between the two taxa but also understand the underlying nature and development of those features. Although phenetically, the modern human and Neandertal retromolar space appear to be similar morphological features and therefore appear to be insignificant in distinguishing between the two groups, a detailed analysis of the morphology surrounding the development of the retromolar space can yield very different results.

    As discussed earlier, Frayer (1993) has stated that the retromolar space cannot be used to distinguish between modern and Neandertals populations given that this feature occurs can occur in modern humans. This assumes that the underlying nature of this feature is the same in both archaic and modern populations. Franciscus and Trinkaus (1995) have also stated that the retromolar space can not be considered as a Neandertal apomorphy due to the frequency of this feature in early modern samples. In contrast, Rak (1998) states the morphology of the retromolar space exhibited by Neandertals is unique when compared to the modern human version. This interpretation maintains the derived status of the Neandertal retromolar space and thus, this feature can be used to differentiate between the modern and Neandertal samples. Furthermore, it is based on these differences that Rak argues for a modern status for the retromolar space of the Tabun C2 mandible. The results presented in this analysis agree with Rak’s interpretation of a difference in the morphology of the retromolar space but arrives at different conclusions regarding the nature of those differences. The results presented in this analysis also find that the retromolar space of the Tabun C2 mandible is typical of Neandertals and not modern humans. Interestingly enough it is the dissimilarity of the retromolar spaces exhibited by moderns and Neandertals that provides evidence of genic exchange between modern and archaic populations.

    Rak’s (1998) argument that Tabun C2 is modern in its morphology rests on two points. First of all, the modern retromolar space is the result of an enlargement of the pre-angular notch which has the result of completely exposing the third molar and creating a space between the M3 and the anterior edge of the mandibular ramus. Because Tabun C2 exhibits a rather large pre-angular notch, it is attributed modern status. The second point of Rak’s argument pertains to the proper method for measuring the retromolar space itself. Rather than measuring the retromolar space itself, one can neutralize the effects of the pre-angular notch by measuring the distance between the M3 and the posterior edge of the mandibular ramus. Figure 4 of Rak (1998) compares the Tabun C2 mandible to La Ferrassie in terms of this second measure and finds the distal edge of the M3 of La Ferrassie at the same point as the middle of Tabun C2’s M2. The combination of the enlarge pre-angular notch and the posteriorly positioned M3 of Tabun C2 are therefore provided as evidence of the modernity of this specimen with respect to the retomolar space.

    Both aspects of this analysis prove to be incorrect when comparing the Tabun C2 mandible to both modern humans with retromolar space and a larger Neandertal sample. The pre-angular notch, as discussed above, was not found to be a causal factor in the presence/absence of the modern retromolar space.

    most certainly has an affect on the size of the retromolar space but the retromolar space must already be present for other reasons before this affect can occur. In terms of the distance between the M3 and the posterior edge of the mandibular ramus, it was determined that a distinction can be made between modern humans with retromolar spaces and Neandertals, but unlike Rak’s analysis, the Tabun C2 mandible plotted near the Neandertal mean. The same is true when quantitatively examining the relationship between the position of the M3 and the lateral prominence. The line graph in Figure 24 reveals that there is a difference in the spatial relationship between the distance of the M3 to the posterior edge of the ramus and the lateral prominence to the posterior edge of the ramus. The discrepancy between the two measurements is much less in the Neandertal sample when compared to both modern humans samples. Tabun C2 exhibits the same pattern as the Neandertal sample. The same is true when looking at these measurements relative to the maximum length of the mandible. Figure 25 again shows a greater disparity between the two measures for the modern humans samples. The Tabun C2 mandible clearly plots closer to modern humans in terms of M3-posterior ramus/maximum mandibular length but the relationship between the two indicies indicates Neandertal affinities for this specimen.



    MANDIBULAR RAMUS



    The mandibular ramus has provided valuable information regarding the taxonomic and phylogenetic position of Neandertals relative to modern humans and their Middle Pleistocene predecessors (e.g., Smith, 1978; Rak et al., 1994; Rak, 1998; Rosas, 2001). In contrast to the conclusion reached by Weidenreich (1936), Rak (1998) has argued that the superior region of the mandibular ramus is diagnostic in Neandertals as an asymmetry exists between the coronoid and condylar processes (Figure 26). Such asymmetry was noted with the early discovery of Neandertal remains such as Krapina J (Gorjanović-Kramberger,1906). It is based partially on this lack of symmetry in Neandertal remains that Rak (1998) argues for the modern status for the Tabun C2 mandible which exhibits symmetry between the two processes. An analysis of features of the mandibular ramus resulted in distinctions being made regarding the morphology of Neandertals versus modern humans in terms of both metric and non-metric features. A comparison of the Tabun C2 mandible to these two samples revealed that this specimen exhibits a mosaic of features that aligns the specimen with both Neandertal and modern populations.

    The multivariate analysis of the mandibular ramus produced interesting results. Neither test completely distinguished between the Neandertal and modern human sample at either the x or y axis. In the case of the size and shape analysis there was significant overlap between the two samples. The shape analysis provided a greater distinction between Neandertals and modern humans along the x-axis with Neandertals as outliers to the modern human cluster.





    The log shape data distinguish between specimens on the basis of general ramus shape with a contrast between variables pertaining to the height of the ramus versus those that measure breadth. Therefore, it was not simply differences in the coronoid process but rather overall differences in the shape of the ramus. Differences along the x-axis were better at distinguishing between the modern human and Neandertal sample as there was a larger spread of Neandertals along the y-axis. The modern human sample tends to exhibit a short, broad ramus with Fish Hoek representing the extreme end of the range of variation, while Neandertals have a long and relatively narrow ramus. These differences in ramus shape explain the positioning of Skhul V along the x-axis, which is second only to Amud 1 in its extreme positioning and exhibits a very long and narrow ramus. The cluster analysis found that Skhul V did not cluster closely with any other single specimen but rather shared a branching point with the cluster of Neandertal mandibles as well as with a group of recent specimens. The position of the Skhul V mandible relative to the rest of the modern human sample is consistent with the findings of Kidder et al. (1992) who found on the basis of cranio-metrics that this specimen falls outside the range of modern cranial variation. A cluster analysis conducted by Corruccini (1992) found the Skhul V cranium to cluster with the Steinheim and Ehringsdorf specimens.

    Only one specimen from the Neandertal sample plotted well within the modern human cluster, Tabun C1. This mandible exhibits typical Neandertal characteristics and its inclusion with modern humans was unexpected. Tabun C1does exhibit a short, broad ramus when compared to the remainder of the Neandertal sample although the major difference between the Tabun C1 mandible and the remainder of the Neandertal sample is that of size. Tabun C1 exhibited the lowest geometric mean of the Neandertal sample, although the Regordou mandible was only slightly behind. Figure 27 is a scatterplot of the first principle component of log shape versus the geometric mean for Neandertals and modern humans. There is a distinction between Neandertals and modern humans although the Tabun C1 mandible falls within the modern human cluster. Given the negative correlation between the shape principle component and the geometric mean, it most likely due to the small size of this specimen that has resulted in its inclusion with the modern human cluster.

    argued by Rak (1998), the size and shape of the coronoid process does provide a distinction between the two samples although it is not as powerful in marking differences than the overall shape of the ramus as there is a significant amount of overlap between Neandertals and modern humans in terms of the size and shape of this feature. This may be partially due to the inability of the measurements employed in this analysis to accurately reflect the shape of the coronoid process. It is evident from the univariate analysis of the position of the mandibular notch that this feature takes on a more posterior position in Neandertals than in modern humans (Figure 23). Therefore, the assertions made by Rak (1998) appear to be confirmed by the data presented when taking into account the results from both the univariate and multivariate analyses of the superior aspect of the ramus.

    The pattern exhibited by the log shape principle components is also reflected in the phenogram (Figure 22) produced by the cluster analysis performed on the log shape principle components. There is a distinction made between the Neandertal and modern human sample with Tabun C2 plotting within the modern group. It is rather interesting to note that when shape is removed, the robust Tabun C2 mandible is clustered most closely to the rather gracile Dolni Vestonice 3 specimen. It is also interesting that the Haua Fteah 1 mandible is neighbored by the Predmosti 3 specimen. Again, this relationship pertains the very short, blunt coronoid processes exhibited by these specimens.

    The modern status of Tabun C2’s mandibular ramus is also confirmed by both the multivariate and univariate tests. Certainly the specimen’s size is commensurate with the Neandertal sample and this is confirmed by its position on the x-axis of the log size-and-shape scatterplot. Based on the shape this specimen is grouped with modern humans due to a mandibular ramus shape that is more similar to the short, broad condition of the modern human sample as opposed to the linear Neandertal condition.

    The mandibular notch of Tabun C2 is modern not only in its appearance (Figure 26) but also when examined metrically. The position of the notch is anteriorly displaced relative to the Neandertal sample and is nearly equal to the modern human mean. There is a degree of overlap in the range of the position of the mandibular notch with the lowest Neandertal value equal to .51 while Tabun C2 exhibits a value of .49 and is therefore out of the Neandertal range of variation.





    SUMMARY



    The Tabun C2 mandible has been shown to exhibit a mosaic of Neandertal and modern features. Based on the findings presented here, this specimen cannot be placed exclusively into modern Homo sapiens as proposed by Rak (1998) or late-archaic humans as argued by Stefan and Tinkaus (1998). The Tabun C2 mandible exhibits a retromolar space morphology that is commensurate with the Neandertal-type retromolar space. The results presented here contradict the findings of Rak (1998) and show that the pre-angular notch cannot account for the presence of a retromolar space in this specimen. Furthermore, the distance between the third molar and the posterior edge of the mandibular ramus of Tabun C2 plots with the Neandertal sample. This is commensurate with the posterior position of the lateral prominence which is placed beneath the M3 rather as opposed to the more anterior positioning of this feature exhibited by modern humans. The relationship between the M3-posterior ramus and lateral prominence-posterior ramus also clearly places the Tabun C2 mandible with Neandertals.

    The mandibular ramus of Tabun C2 exhibits an overall shape that aligns it with the modern sample as put forward by Rak (1998). The Neandertal and modern human samples are best distinguished on the basis of overall ramus shape with Neandertals exhibiting a more linear ramus and modern human exhibiting a shorter, broader ramus. The position of the mandibular notch also distinguishes the two samples with modern humans exhibiting an anteriorly displaced notch relative to the Neandertal sample. Tabun C2 exhibits the modern condition for both shape and position of the mandibular notch. The ramus of Tabun C2 also exhibits a medial pterygoid tubercle which according to Rak, et al. (1994) is a Neandertal apomorphy which further supports the mosaic nature of this specimen. These findings are consistent with Quam and Smith (1998) who have emphasized both the archaic and modern aspects of Tabun C2 and have suggested the possibility that the morphology exhibited by this specimen is the result of interbreeding.

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    Post Re: The Tabun Mandible

    (This bit is interesting)

    The study of modern human origins has been dominated for the last two decades by opposing theories regarding the biological relationship between Neandertals and modern humans. At one extreme, based on data provided by the fossil record and mtDNA (Cann et al., 1987) is the notion that modern humans and Neandertals represent discrete biological entities with modern populations ultimately replacing archaic groups after an African diaspora (Stringer and Andrews, 1998 among others). Others (e.g., Wolpoff, 1989) have argued for a single species status for modern and archaic groups with intercontinental gene flow as a mechanism for the spread of modern features. Such an approach argues for continuity between archaic and modern groups throughout Africa, Europe and Asia.

    Within the context of this debate the Levant has played a unique role in the study of modern human origins as it is the only geographic link between Africa and the remainder of the Old World as it would have served as a corridor for the migration of modern populations leaving Africa. This region would have also had the unique position of serving as a major contact zone between early modern African and Neandertal populations. Since the discovery and description of modern and archaic forms at the sites of Tabun and Skhul (McCown and Keith, 1939), debate has stemmed from the high level of morphological variation, not only between the two forms but also within. Sorting out this variation has proven to be difficult and has led to different interpretations pertaining to the biological relationships between modern and archaic forms in western Asia. Central to this debate and the ability to adequately sort out this variation is whether or not modern humans and Neandertals coexisted in the Levant or occupied the area at different times that co-vary with environmental fluctuation in Europe as well as climatic changes occurring in Africa.

    Bar-Yosef (1988, 1989, 1992) and Hublin (1998) have argued that the Levant served as a refuge for Neandertals who would have migrated south in search of a more hospitable environment during periods of glacial expansion. Furthermore, Bar-Yosef (1994) has asserted that there is no evidence to support the notion that the occupation of Neandertals and modern humans populations in the Levant occurred at the same time rather than corresponding with climatic fluctuations. Rather he views the occupation of the Levant primarily as an area of migration occurring over a period of 150 kya and therefore lacking the presence of stable populations.

    The late migration of Neandertals rests primarily on two lines of reasoning. The first is the belief that the Tabun C1 mandible is actually derived from a higher stratigraphic position. Suspicion stems from the fact that Garrod (Garrod and Bate, 1937) suggested that while the specimen was excavated from Layer C, its position was so close to the surface of the level that there is a possibility that the Tabun C1 specimen may represent a burial from Layer B. Due to the uncertainty surrounding the position of this specimen Bar-Yosef (2001) places this mandible at the beginning of OIS 4. The second line that the late migration hypothesis relies on is that Tabun C1 is the earliest representative of Near Eastern Neandertals. Bar-Yosef (1992) suggests a date of no earlier than 80 kya for Tabun C1, Amud, Kebara and the material from Shanidar while the fossil remains from Skhul and Qafzeh predate the 80 ky mark. Certainly debate surrounding the true stratigraphic position of Tabun C1 will never be resolved as long as it is suggested that Neandertals were relatively late migrants into the Levant. Suffice it to say that, other than conjecture, no evidence has yet been brought forward that would undoubtedly place Tabun C1 at a higher stratigraphic level.

    Vandermeersch (1989) has argued for a late migration of Neandertal populations on the basis of the Zuttiyeh frontal which is argued to lack any Neandertal apomorphic characteristics and therefore represents the early presence of early modern human in the region. This specimen, a complete frontal bone and left zygomatic, is described as having a long frontal squama and less anterior projection at nasion. The width of the frontal is within the range of modern humans and the zygomatic faces more anteriorly. While Vandermeersch does not find any features that are specifically Cro-Magnon in morphology, it is argued that very little morphological change would be necessary to develop a morphology consistent with Early Upper Paleolithic Europeans. Thus, he suggests that this specimen places an ancestral form of H. sapiens in Levant at an early date. Due to the fact that the derived Neandertal morphology was present in Europe at this time in specimens such as Arago or Petralona, Zuttiyeh is not ancestral to Near Eastern Neandertals.

    A study of Near Eastern frontal bone morphology has challenged this argument. Simmons et al., (1991) conducted an analysis of Near Eastern frontal bone morphology to determine where the Zuttiyeh specimen falls in terms of Levantine neandertals and modern humans. The results of this analysis showed the total morphological pattern of Zuttiyeh to be more similar to the neandertal sample, suggesting to the authors that this specimen “is more likely to be an immediate ancestor of Levantine Neandertals than of the Skhūl/Qafzeh hominids” (1991; 265). This study suggests that the late migration hypothesis is incorrect as Neandertal ancestors were present in the pre-Mousterian Levant. Provided the various dates discussed above, the age of this specimen is consistent with OIS 6 (Bar-Yosef, 1992) or perhaps even stage 8 (McDermott et al. 1993). Therefore Hublin (1998) may be correct in his suggestion that a Neandertal migration may have occurred earlier than OIS 4 as suggested by Bar-Yosef (1988).

    Maintaining that Tabun C1 is derived from Level C, there is evidence that not only were Neandertals present in the Levant at an early date but there is also evidence for the mixture of genes between Neandertal and modern populations at this time. This places a biological connection between Neandertals and modern humans in the Levant at 100-120 kya, prior to the material from Skhul and Qafzeh. Given that Tabun C2 possibly represents the earliest evidence of modern humans in Levant due to the presence of modern features, it can be asserted that the earliest modern occupation of this region was in the form of genes, not population migrations.

    The Levant can therefore be viewed as a contact zone between modern human and Neandertal populations. Contra Bar-Yosef (1994) and Stefan and Trinkaus (1998) who argue that Level C was exclusively occupied by Neandertals, albeit for different reasons, the evidence presented in this analysis suggests a coexistence of at least modern and Neandertal genes at Level C at Tabun.

    Such ideas are consistent with previous comparisons of fossil material from North Africa with Levantine and European Middle Paleolithic hominids. A genetic connection between these populations over the last 200 kya has been supported by a morphometric and qualitative analysis of the crania from the site of Jebel Irhoud (Simmon and Smith, 1991; Smith et al., 1995). Contra Hublin (1992) who argues that no Neandertal apomorphic features are present in the Jebel Irhoud material, Smith et al. (1995) point to three aspects of similarity between European Neandertals and the Jebel Irhoud specimens, occipital bunning, frontal bone shape and supraorbital torus form. Cluster analysis results indicate that the crania from Jebel Irhoud exhibit a close phenetic similarity to the Neandertal from Gibraltar as well as to the Qafzeh 6 specimen. Further similarities were found between the Jebel Irhoud crania and the South African Florisbad crania and to the East African LH 18 cranium.

    Hutchinson (2000), in an analysis of the subadult Tangier maxilla found that this specimen exhibits closer affinities to immature Neandertals than to modern humans based on the lack of a canine fossa as well as other features that indicate that this individual exhibited subnasal prognathism.

    Thus, substantial evidence exists that links Neandertal populations to fossil remains from North Africa. Furthermore, biological connections between North Africa and the Near East are supported by the aforementioned analyses as well as by Hublin (1992). The Tabun C2 mandible is just one more piece of evidence of the complex population interactions along the eastern edge of the Mediterranean. Sufficient evidence has been put forth that indicates that the origin of modern morphology in Africa can no longer be viewed as a speciation event. Questions regarding the origin of modern humans can no longer be viewed in terms of continuity versus replacement. Rather it is becoming increasing clear that the appropriate questions to ask pertain not to whether Neandertal and modern populations were capable of interbreeding; instead, research should continue to be focused on determining how much gene flow took place.

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    Post Re: The Tabun Mandible

    The idea of the Mediterranean as a genetic highway in which moderns and Neanderthals met and exchanged genes is interesting. Modern humans apparently used the Pacific to settle the New World, hugging the coast as they went South. The problem is that Neanderthals didn't seem to need the sea. They didn't fish to any great extent as moderns did. They must have exploited it somehow and that would make this idea attractive.

    Culture is another indicator. In the West, we have 5 or so Neanderthal cultures all grinding along without much change in France. My opinion is that one of the, the Dentriculate, was a woman's culture and the men, who may have lived seperately, accounted for the other four. Perhaps Mousterian of Achulean Tradition came into being as a man entered the culture of women and became their "stud" for a time before being deposed. Anyway, the culture seems simple and enduring.

    In the East we have seemingly many sub-cultures of Mousterian. The interesting thing here is that the pre-Out Of Africa sapiens were using the very same culture as the Neanderthals. No art, sculpture, etc. Also, the Out Of Africa sapiens people don't seem to have been special in a cultural sense until they entered Europe. Where is the UP culture for Iraq or Saudi Arabia which is radically new? I know there are always guys talking about a proto-UP stone culture in Asia but it just never seems to be the real deal.

    Then, all of a sudden, in Eastern Euorpe UP stone cultures appear along with ivory sculptures. It seems most likely to me that there was a biologic and cultural fusion in Palestine or to the region immediately North of it. This biologic fusion is what we Europeans are. We are sapiens people with a touch of Neanderthal genes. This fusion shook our brains somehow and the result was modern conciousness as we know it. Blacks in Africa live as they always have, just like Neanderthals did. This was our mental state before fusion.

    Neanderthals come from a long line of perhaps 500,000 years in the making, in Europe. They had eons to adapt physically and meantally and did so. Yet, we credit ourselves with making a biologic jump into modernness upon leaving Africa. Why not before? Why, obviously, didn't Black Africans make this jump? The only reason and the reason it was so sudden is because hybridization was involved.

    The Tabun mandible looks Neanderthal to me. To me its real value is putting Neanderthals at the right place and right time to interact with sapiens. The problem nowadays is that no amount of morphological evidence is going to convince science of even a slight Neanderthal ancestry since the advent of modern genetic methods. I hope that as the search for genetic markers becomes increasingly sophisticated, we will find the evidence which must be there.

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