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Frans_Jozef
Sunday, January 2nd, 2005, 10:58 AM
On the Ecological Connection Between Sabre-tooths and Hominids:
Faunal Dispersal Events in the Lower Pleistocene and a Review of the
Evidence for the First Human Arrival in Europe

Source:
http://www.igme.es/internet/museo/investigacion/paleontologia/invesce
no2/orce3.htm




Alfonso Arribas

Museo Geominero, Instituto Tecnológico Geominero de España. Ríos
Rosas, 23. 28003 Madrid, Spain.


Paul Palmqvist

Departamento de Geología y Ecología (Área de Paleontología),
Facultad de Ciencias, Universidad de Málaga. 29071 Málaga, Spain.


Abstract

The chronology of the first colonization of Europe by hominids has
been a rather controversial issue until this decade, with most
palaeoanthropologists claiming that there was no significant
habitation until middle Pleistocene times. However, recent findings
in Spain, Italy, Georgia and China, as well as the re-evaluation of
the evidence from Java and Israel, indicate an earlier arrival of
Homo in Eurasia, during the lower Pleistocene. The systematic
revision of European assemblages of large mammals has shown a faunal
break at the Plio-Pleistocene boundary, marked by the arrival of
African and Asian species, which allows the tracing of the
ecological and biogeographical scenario in which the first dispersal
of hominids out of Africa took place. African immigrants include
among others two carnivore species, the giant hyaena Pachycrocuta
brevirostris and the sabre-tooth Megantereon whitei. Sabre-tooth
cats were extinct in East Africa by 1.5 Ma, which coincides with the
emergence of the Acheulean Industrial Complex, but inhabited Eurasia
until 0.5 Ma. Given that M. whitei was a hypercarnivorous predator
that presumably left, on the carcasses of the ungulates hunted,
large amounts of flesh and bone nutrients within, its arrival in
Eurasia opened broad opportunities for scavenging by hominids and
helps to explain the success of the Oldowan tools until 0.5 Ma.


Keywords: DISPERSAL OF HOMO TO EUROPE, MEGANTEREON, PACHYCROCUTA,
LOWER PLEISTOCENE, OLDOWAN TOOLS.


Introduction

Until this decade most palaeoanthropologists believed that there was
no significant habitation in Europe before middle Pleistocene times
(Carbonell & Rodríguez, 1994; Roebroeks & Kolfschoten, 1994, 1995).
However, new findings suggest that the first arrival of hominids in
Java and Southern Asia took place during the late Pliocene, and
recent discoveries in Spain, Italy and Georgia are providing
increasing evidence of an early colonization of Europe in lower
Pleistocene times. Although these findings have forced several
researchers to change their understanding of the
palaeoanthropological and archaeological record (Carbonell et al.,
1995a; Dennell & Roebroeks, 1996), a very restrictive geographic
system of reference (i.e. Europe) still prevails in the analysis of
this matter, and the study is usually focussed only on the fossil
record of the genus Homo. In addition, the approach applied in the
analysis of the new evidence is rather limited, since the main aim
of the majority of prehistorians is to confirm the oldest proposed
ages for the earliest human settlements in Europe, and this issue
overshadows all others (i.e. the causes and the ecological scenario
of this dispersal). The palaeobiological information preserved in
the fossil record is not accessed by this restrictive approach,
which is strongly biased by our comprehension of what we think human
beings are, and even by the extrapolation in time of what we call
now Europe.


Has Europe, a political entity defined only by historical
attributes, any type of specific meaning 0.1, 0.5 or 1.0 Ma ago? The
answer is probably not, but what seems clear, and it is thus
attested to by the palaeontological record, is that during all of
the Quaternary Europe had no palaeobiological meaning dissociated
from Asia. Due to this reason, Eurasia is the geographic unit to
which the first human dispersal out of Africa should be referred. On
the other hand, we should be asking what is more relevant, that
humans spread from Africa or that they reached some places in
Eurasia? From our point of view the most important issue is to
establish the biogeographical scenario and the ecological causes
that allowed this dispersal, although this probably may only be
addressed by the comparative analysis of the palaeontological and
archaeological assemblages preserved in Eurasia. This study will be
possible if all the information recorded in both Europe and Asia,
although heterogeneous, is considered in an unitary way, as the
result of a single cause. Therefore, if we try to establish when the
genus Homo arrived to Eurasia, the fraction of the record which has
been recovered in Europe may be taken to be a first-hand source of
information. However, a coherent approach to this issue should take
into account not only those aspects related to the chronology or the
anatomical features of the Eurasian hominids, but also the climatic
and ecological context, the faunal assemblages present in each site,
and the role that the technological acquisitions may have played in
facilitating the first dispersal of Homo outside Africa. We must
emphasize here that the lithic artefacts are objects which must be
understood by palaeontologists as ethological structures in sensu
stricto when interpreting their presence in the geological record,
i.e. as ichnofossils or indirect evidence of the presence of the
organism which produced them (in this case, the object is due to a
specific biological activity, the cultural one).

The Palaeoanthropological and Archaeological Record in Eurasia

Only a few, scattered archaeological sites or hominid remains have
yet been found in early Pleistocene deposits from Europe, and until
very recently most European prehistorians believed that there were
no significant human settlements in Europe before 0.5 Ma
(Bilzingsleben, Boxgrove, Mauer, Schöningen), with most evidences
concentrating on <0.3 Ma (Arago, Tautavel, Petralona, La Sima de los
Huesos at Atapuerca, Swanscombe, Steinheim) (Arsuaga et al., 1993;
Carbonell & Rodríguez, 1994; Roebroeks & Kolfschoten, 1994, 1995).
Introducing a note of discord, some archaeological sites (but
without human remains) in Europe like Le Vallonet Cave and the
Soleilhac open air site, which are placed within the Jaramillo
Normal Subchron, have been known from several decades.


However, recent findings in Spain, Italy, Georgia and China, as well
as the re-evaluation of the evidence from Java and Israel, indicate
an earlier arrival of Homo in Eurasia, during lower Pleistocene
times. If we evaluate the palaeoanthropological and archaeological
record available and its most likely interpretation, we have then a
history which is constituted by complementary information from the
three geographical fringes into which Eurasia can be divided. As the
most significant examples, we can mention the following ones:


In East Eurasia:


1. Until very recently, the ages currently accepted for the
specimens of Homo erectus from Java ranged between 1.2 and 0.7 Ma
(Leinders et al., 1985). However, the radiometric ages of several
human remains (Mojokerto cranium, Sangiran 27 and 31) obtained using
the single-crystal Ar/Ar method (Swisher et al., 1994) indicate 1.6-
1.8 Ma for them, thus suggesting that the first occupation of this
area may have been latest Pliocene, which coincides with the arrival
to Java of several species of mammals originating in Asia (Satir
fauna, 1.7 Ma; Semah, 1997). The ages proposed by Swisher et al.
(1994) are somewhat controversial, since the provenance of the
Mojokerto child (the best documented specimen) and even the location
of the findspot is uncertain; on the other hand, the chemical
analysis of pumiceous materials adhering to this skull shows
similarities but not identity to the volcanic pumice dated
radiometrically, what opens the possibility that the calvaria may
have been transported and then filled with materials including
pieces of a tuff older than the specimen. In any case, the
disagreement between the results obtained in both geochemical
analyses does not justify rejecting this evidence, since the
chemical composition of any clastic deposit always shows small
differences due to the compositional gradient present in this type
of sediments; on the other hand, the human remains were obviously
transported, but this transport must have been shorter than some
hundred meters, given the good preservational state of several
anatomical regions of the skull. It is very significant that the
splacnocranium was not preserved, since this is the first part which
is separated with the movement, in contrast with the complete
preservation of the neurocranium, and more specifically the
integrity of the squamose regions. The temporal bone is the first
which separates from the other bones of the neurocranium in the
skull of juvenile humans, given the structural precarity of the
temporoparietal suture. In fact, this bone is always isolated from
other neurocranial fragments, and its separation may owe to a simple
gravitational transport of some tens of meters, or even following
the putrefaction of soft tissues in addition to a slight rolling
movement.


2. The finding of archaic hominid dental fragments, which are
associated with Giganthopithecus teeth and primitive Oldowan stone
tools in Longgupo Cave (Wushan, Sichuan Province, China) (Wanpo et
al., 1995), is another source of significant information about this
dispersal event. Palaeomagnetic, biostratigraphical and
geochronological (electron spin resonance) analyses indicate that
the hominid-bearing levels date to the latest Pliocene, within the
normal Olduvai event (1.96-1.78 Ma). Comparative study of hominid
teeth revealed affinities with H. habilis and H. ergaster, thus
suggesting that hominids entered in Asia before 2.0 Ma, coincident
with the diversification of the genus Homo in Africa, and that this
inmigrant species was other than H. erectus (Larick & Ciochon,
1996). However, it has been argued that these teeth resemble those
of Lufengpithecus, a fossil ape related to Pongo (Wolpoff, 1996).
Even if the teeth prove to be of this ape, the hypothesis of human
presence at this site would stand, because the lithic artefacts
(only two pieces) are significant evidence of human activity, and
this evidence should not be affirmed or denied only on the basis of
its age.


3. Additionally, several teeth of H. erectus claimed to be of early
Pleistocene times, with ages in excess of a million years, have been
reported from different sites in Northern China (Jianshi, Luonan,
Yuanmon), and a cranium from Gonqwangling, near the village of
Lantian, has been dated to 1.15 Ma (Zhisheng & Chuankun, 1989).


4. Two core flake assemblages of late Pliocene age have been
described from the Indian subcontinent, at Pabbi Hills and Riwat
(Pakistan). Palaeomagnetic analyses indicate an age close to 2.0 Ma
for the small number of quartzite pieces found at Riwat, and
probably also a similar age for the larger assemblage at Pabbi Hills
(Rendell et al., 1987; Dennell et al., 1988). However, there are
some reservations about their stratigraphical position (Hemingway &
Stapert, 1989).


In Central Eurasia:


1. A human mandible associated with pre-Acheulean lithic artefacts
in the Plio-Pleistocene site at Dmanisi (East Georgia, Caucasus).
The mandible has been determined as H. erectus (Gabunia & Vekua,
1995a, 1995b; Bräuer & Schultz, 1996), although it shows some
evolved features like the presence of a vertical chin. The site was
originally reported to be 1.8-1.6 Ma (Dzaparidze et al., 1989;
Gabunia & Vekua, 1995a) as suggested by the date of the basalts
below the deposit, which was estimated by the K/Ar method in 1.8+0.1
Ma. It is interesting to note that both the fossiliferous levels and
the volcanic tuff show normal polarity, and they have been thus
included within the Olduvai Subchron. The age of the deposit which
contains the human mandible has been discussed during recent years,
and it was subsequently estimated, rather arbitrarily, in older than
1.0 Ma, due to uncertainties related to several stratigraphical and
taphonomic aspects as the possibility of diachronic deposits, given
the presence of burrows. However, the faunal assemblage from this
site, which is clearly not reworked (Dzaparidze et al., 1989;
Gabunia & Vekua, 1995b), is of late Pliocene age, since it comprises
several species of rodents, perissodactyls and artiodactyls which
are exclusive of the end of the European Pliocene (biozone MN17),
what is coherent with the original date proposed for this site. The
determination of the mandible as H. erectus has probably forced some
palaeoanthropologists to place this specimen at around 1.0 Ma, thus
omitting the biostratigraphical information from the site, although
it is possible that this determination will be changed in the
future, because the fossil shows several anatomical features similar
to those of African hominids (H. ergaster) like the WT 15000
mandible, such as a mandibular body not particularly tall, with a
curved symphyseal surface having a weak mandibular trigone and
lacking a mental eminence, the molar size sequence (M1 > M2 > M3)
and the elongated shape of the third premolar (P3), which is similar
to that of Olduvai Bed IV specimen OH 22. As indicated above, the
presence of burrows has been argued as a way by which the human
mandible could have been infilled into older sediments; however, it
would be difficult to explain how this process could have affected
the mandible but not the other fossils, thousands of teeth and bones
of several species of large and small mammals, which represent a
biostratigraphically homogeneous assemblage with a composition
typical of the Plio-Pleistocene transition.


2. In Israel, the site at 'Ubeidiya provides additional evidence of
human presence during lower Pleistocene times, since important
assemblages of lithic artefacts and faunal remains have been dated
biostratigraphically at around 1.4-1.3 Ma (Tchernov, 1986). The
lithic assemblages comprise two sets: the oldest one is clearly pre-
Acheulean (i.e. absence of bifacial handaxes), and the youngest one
includes typical Acheulean tools. Several isolated human teeth were
also recovered, but their precise stratigraphical context is known
only for one of them. Bar-Yosef (1994) indicates that the presence
of two different techno-complexes is due to the occupation of this
region by two distinct human groups, one replacing the other in a
very short time span. Also in Israel, two core tools have been
recovered in the sites at Yiron and Erq-el-Ahmar; the first
assemblage has been dated radiometrically (K/Ar method) in 2.4 Ma,
and the second one was dated palaeomagnetically at 1.9-1.8 Ma,
although there are some reservations about both their age and
stratigraphic position, as well as on the artefacts themselves (Bar-
Yosef, 1994).


In Western Eurasia:


1. The finding of human remains and pre-Acheulean stone tools in the
karstic site at the Gran Dolina of Atapuerca (Burgos, Spain), in
stratigraphic levels which according to palaeomagnetic studies are
located below the Bruhnes-Matuyama reversal, and thus have an age of
>0.78 Ma (Carbonell et al., 1995b; Parés & Pérez-González, 1995),
suggests a continued human settlement in Europe at the end of the
lower Pleistocene. However, the age obtained using geochronological
techniques seems to be incompatible with the relative dating deduced
from the assemblage of mammals present in this site (TD-6 Level),
which includes several typical middle Pleistocene taxa originating
in Asia (Equus caballus, Sus scrofa, Ursus praearctos/U. deningeri,
Cervus elaphus, Dama cf. clactoniana, Capreolus sp.) but no species
exclusive of the early Galerian (i.e. the arctic ovibovini Soergelia
elisabethae and Ovibos sussenbornensis, the microtids Allophaiomys
bourgondiae and Allophaiomys nutienesis), which should be recorded
in an European assemblage with the age proposed for this site
(Azzaroli et al., 1988; Sala et al., 1992). On the other hand, some
genera of large mammals which have their first appearance datums
during the middle Galerian (Crocuta, Bos and Panthera) are
represented in TD-6; from a biostratigraphical point of view, this
assemblage should therefore be included within the middle Galerian,
in the base of the middle Pleistocene. This conclusion is
corroborated by the absence of Castillomys crusafonti from the
micropaleontological record of Atapuerca, even in stratigraphic
levels older than TD-6, since this species is always present in
those Spanish sites of lower Pleistocene age, being extint shorly
before the beginning of the middle Pleistocene (Sesé, 1994; Sesé &
Sevilla, 1996). Finally, the presence of Mimomys savini at TD-6 has
been claimed to indicate a lower Pleistocene or early middle
Pleistocene age for this site (Carbonell et al., 1995b); however,
this arvicolid presents a wide biostratigraphical distribution,
between the end of the lower Pleistocene and the lower third of the
middle Pleistocene (Sesé, 1994), being its biostratigraphic value
clearly insufficient to clarify the age of TD-6. On the other hand,
the Asian origin of the fauna preserved in TD-6 contrasts with the
phylogenetic link inferred for the hominids, which have been
nominated as Homo antecessor (Bermúdez de Castro et al., 1997), a
species supposedly originating in Africa, which it is proposed as
the ancestor in Europe of `archaic sapiens' (H. heidelbergensis) and
Neanderthals. The new species has been erected using a maxilla of a
juvenile individual, whose midfacial profile resembles that of
modern H. sapiens, although the adult specimens show several
anatomical features which are exclusive of the oldest East African
populations (H. ergaster), for example the particular root
morphology of the mandibular premolars (Bermúdez de Castro et al.,
1997).


2. The finding of a human calvarium in Ceprano (Italy) seems to
introduce more complexity into this analysis, since the skullcap
shows characteristics of H. erectus, but also some distinctive
features as the absence of a slight crest along the center of the
skull or its larger brain; the fossil was unearthed in a clay level
below sandy volcaniclastic gravels whose age was estimated by the
K/Ar method in 0.7 Ma (Ascenzi et al., 1996).


3. A human phalanx has been described (Palmqvist et al., 1996a) in
the lower Pleistocene karstic site at Cueva Victoria (Murcia,
Southeastern Spain). The specimen was discovered in a rich bone-
bearing breccia, associated with fossils of European Villafranchian
mammals, which also contained a molar of an African inmigrant in
Western Eurasia, the cercopithecoid Theropithecus oswaldi (Gibert et
al., 1995). Carbonell & Rodríguez (1994) have reported on a
manufactured piece of quartz in this locality, but it must be
discarded from this analysis, because the artefact was recovered
from an exokarstic deposit close to the entry of the cave, which has
no fossil content and can not be correlated lithostratigraphically
with the inner bone-breccia.


4. The discovery in several lower Pleistocene sites located below
the lower limit of the Jaramillo Normal Subchron (>1.07 Ma) within
the Orce-Venta Micena sector of the Guadix-Baza Basin (Granada,
Spain) of some controversial palaeoanthropological remains (Orce
skull from the Venta Micena site; see review in Palmqvist, 1997) and
an important assemblage of lithic artefacts of Developed Oldowan
type (Fuente Nueva-3 and Barranco León-5 sites; Turq et al., 1996),
contributes new evidence of human presence in this area during the
mid third of the lower Pleistocene. The tool assemblage of Fuente
Nueva-3 (more than one hundred pieces) is composed of limestone
cobbles and knapped flint (Martínez-Navarro et al., 1997), which are
associated in the deposits with several species of large mammals
originating in Africa (Martínez-Navarro & Palmqvist, 1995).


The Role of Technology in the Spread of Homo

One of the most important consequences of the adaptive shift
involved in the origin of Homo was habitat expansion (Wolpoff,
1996): Humans became a colonizing species as populations expanded
their ecological range into arid and highland-to-mountainous
habitats, and moved out of Africa to spread across the tropical and
subtropical regions of the Old World. By late Pliocene times the
revolutionary discovery by hominids of how to make stone tools took
place. This industry is the Oldowan, and the earliest artefacts are
dated between 2.6 and 2.5 Ma at Gona, Ethiopia (Semaw et al., 1997).
Oldowan assemblages comprise manuports, hammerstones, simple cores
and unmodified flakes, and their characteristics are crudeness and
opportunistic forms. The main cause of artefact shape variation
comes from the shape of the initial blank, and not from an
preexisting idea of the tool maker about its final form. In fact,
there are no tool types in the Oldowan Industry, since the artefacts
are crudely made without regular form, thus suggesting that they
were mainly the debris left behind from rook-smashing activities
whose main focus was to produce sharp flakes. This technology was
useful for scavenging activities, since the cores allowed to break
long bones for accessing their marrow content, and the juxtaposition
of gnawing marks and tool-produced scratches on bones suggests that
some of the flakes were used for dismemberment of carcasses after
the bones were gnawed by flesh-eating carnivores (Capaldo, 1997;
Selvaggio, 1998).


By the times of middle Bed II at Olduvai (1.4 Ma) a more complex,
better-made tool set was being manufactured, the Acheulean
Industrial Complex, which is first recorded at Konso, Ethiopia
(Asfaw et al., 1992). These lithic artefacts will span more than a
million years, and are ultimately found across all the inhabited
world (i.e. from South Africa to Indonesia). Unlike the Oldowan, the
forms of Acheulean tools appear to have been preconceived by their
makers. One tool type, the symmetric handaxe bifacially flaked, is
its defining characteristic. As stated before, important evidence on
the presence of this typology has been detected in the 'Ubeidiya
site (Israel), one of the gateways to Europe, with an age of 1.4-1.3
Ma. According to Wolpoff (1996), significant adaptive changes
associated with the spread of the Acheulean complex include more
effective habitat utilization and additional food resources
available through organized hunting, confrontational scavenging and
improved techniques for collecting and preparing gathered foodstuffs.

However, the archaeological record of the upper Pliocene and the
lower Pleistocene in Eurasia is composed (with the exception of the
upper lithic assemblage from 'Ubeidiya) exclusively by tool
assemblages belonging to the Oldowan techno-complex, during a time
interval which comprises from 1.8 Ma (China, Java and Georgia) to
0.78 Ma (Atapuerca, Spain), with the intermediate chronological
position (1.4-1.0 Ma) well characterized in the archaeological sites
from Orce (Spain). Given the fact that during these ages tool-making
technologies seem to be linked to human species, this line of
discussion (i.e. the technological one) allows us to presuppose that
the first human dispersal to Europe must have involved one species
that was only capable of making Oldowan tools, as recorded in the
European lower Pleistocene, and not those included in the Acheulean
Industrial Complex. By this reason, the most parsimonious hypothesis
is that the human populations that first colonized Eurasia, and more
specifically Western Europe, made it before the technological change
from the Oldowan to the Acheulean took place in Africa, that is,
prior to 1.4 Ma. The likely new reinterpretation of the Dmanisi
mandible as H. ergaster, as well as the anatomical affinities
between the adult hominids from Atapuerca TD-6 Level and H.
ergaster, both could corroborate this hypothesis as a second source
of evidence (i.e. the palaeoanthropological one).


African Species in the Lower Pleistocene of Europe

The well-known sea-level fluctuations and climatic shifts evidenced
by stable isotopes provide a basis for the study of major
vegetational changes in the Eurasian continent during the Plio-
Pleistocene. Three major sea-level drops stand out in this time
interval, due to the wide-ranging environmental changes that
accompanied them in the continental area (Azzaroli, 1995): the
Aquatraversan, the Aullan, and the Cassian erosional phases. The
older of these sea-level falls, the Aquatraversan or `Elefant-Equus
event', took place halfway through the Pliocene (2.6-2.4 Ma) and was
accompanied by a marked cooling of ocean waters, by massive
extinctions in marine fauna, and by wide-ranging changes in
vegetation and faunas on the continents (the transition from the
warm Reuverian to the cooler Pretiglian in Western Europe),
including the extinction of warm-forest faunal elements such as
zygodont mastodon and tapir, and the arrival from Asia of both
elephants and monodactyl equids. The second event, the Aullan (1.8-
1.6 Ma), corresponds with a relatively minor retreat of the sea-
level, and coincides with the arrival of several African inmigrants
to Europe, including the genus Homo (Martínez-Navarro & Palmqvist,
1995), and with the conventional Neogene-Quaternary boundary. This
event will be discussed at depth below. Finally, the Cassian sea-
level fall (1.2-0.9 Ma) also coincided with a new cooling of the
ocean waters, but it did not affect marine faunas to any great
extent; on the other hand, it deeply affected continental vegetation
and faunas, what has been called in Europe the `end-Villafranchian'
dispersal event, marking the transition to the new mammalian
assemblages of the middle Pleistocene (these faunal associations
have received the name of Galerian in Western Europe). These major
climatic changes were accompanied in East Africa by a shift from
mesic, closed environments to more xeric, open habitats, which was
reflected in the assemblages of large mammals by a significant
faunal turnover between 2.5 and 1.6 Ma (Behrensmeyer et al., 1997),
by an increase of the percentage of grazers, and by a corresponding
decline of both frugivores and species with arboreal locomotion
(Reed, 1997).


The systematic study of the macrovertebrate assemblages from Orce
and Dmanisi has shown a faunal break at the Plio-Pleistocene
boundary in at least the western and central fringes of Eurasia. It
has been recorded in part in the Villafranchian of Italy, within the
Olivola and Tasso faunal units, where the faunal replacement was
called `the Wolf event' (Azzaroli, 1983; Azzaroli et al., 1988).
This break is marked by the arrival in Europe of both African and
Asian species shortly before and during the beginning of the
Pleistocene (Martínez-Navarro, 1991; Martínez-Navarro & Palmqvist,
1995, 1996; Gibert et al., 1995). Immigrants originating in Asia are
basically ruminant species (four bovids and two cervids), while
African ones include a megaherbivorous species, the hippo, an equid
similar to modern grevy's zebra, a large cercopithecoid and several
carnivore species, as a giant hyaena, a sabre-tooth, and probably
also a wild dog.


However, two general considerations are necessary before starting a
discussion in depth on the palaeobiogeographical spread of these
taxa in Europe. The first deals with the chronology of most
palaeontological and archaeological sites in Europe and Asia, which
is rather vague except for a few cases in which
magnetostratigraphical data are available, thus relying heavily on
the biostratigraphical study of the faunal assemblages; this
situation contrasts with that of those hominid-bearing sites from
the main sedimentary basins of the Rift Valley in East Africa, where
the stratigraphical sequences include ash layers which have been
radiometrically dated. The second problem is concerned with the
reliability of taxonomic assignments, since the faunal lists from
different palaeontological sites are usually made by different teams
of palaeontologists working in Asia and Europe, and thus there
exists a high potential for inter-analyst discrepancies, which
precludes any reasonable analysis of faunal correspondence between
different sites. Both limitations hinder any possibility of testing
accurately how well the FADs (first appearance datums) and LADs
(last appearance datums) of particular taxa within Europe correspond
in time (for an application of this methodology to the analysis of
patterns of faunal turnover during the late Pliocene in the Turkana
Basin, see Behrensmeyer et al., 1997).


Due to the limitations and uncertainties cited above, the focus of
the following discussion will be centered on those species of large
mammals for which detailed systematic comparisons between Eurasian
and African assemblages have been carried out.


The genus Equus is first recorded in North America (Hagerman
Formation, Idaho) at 3.4 Ma by the species E. simplicidens. A
comparative multivariate study of both modern and extinct
populations of Equus in the Old and New World (Guerrero-Alba &
Palmqvist, in press) has shown two main evolutionary lines in the
history of horses. The first one is represented by the `simplicidens
type' equids, with species which have slender metapodials, well
adapted to open and dry plains, like African zebra E. grevyi, and
Asian hemiones E. kiang and E. hemionus. The second line includes
the `stenonis type' horses, equids which are characterized by more
robust metapodials, as E. przevalskii in Asia, and E. burchelli, E.
zebra, E. africanus and E. asinus in Africa. The first monodactyl
equids arrived to Eurasia at around 2.5 Ma, where they are
represented during the upper Pliocene by the species E. stenonis in
Russia (Livezovka), Italy (Olivola, Montopoli), France (Saint
Vallier, Chilhac) and Spain (Huélago, Rincón, La Puebla de
Valverde). Between 2.3 and 1.4 Ma equids of two species of
the `simplicidens type' are found in East Africa (Omo Shungura,
Olduvai, East Turkana), North Africa (Aïn Boucherit, Aïn Hanech) and
the Middle East ('Ubeidiya). The first of these species (E.
numidicus) had a larger body size, comparable with that of modern
grevy's zebra, while the second (E. tabeti) was of smaller size,
similar to that of extant hemionus. During the Plio-Pleistocene
transition E. numidicus arrived in Europe (where it has been called
E. altidens) and is found in Spain (Orce, Cúllar de Baza, Cueva
Victoria, Huéscar-1), Italy (Pirro Nord, Selvella), France
(Sainzelles) and Germany (Süssenborn). The replacement of E.
stenonis by E. altidens at the beginning of the Pleistocene
indicates a change from wet, woodland habitats to more open and dry
savannas.


The presence of the African cercopithecoid Theropithecus oswaldi in
the lower Pleistocene of Southeast Spain (Gibert et al., 1995)
constitutes an important faunal event, since it is the second
occasion in which fossils of this genus have been found out of
Africa. The palaeogeographical distribution of this large species,
whose weight has been estimated in 65 kg, was basically restricted
to Africa until it was discovered in the karstic site at Cueva
Victoria, although fossils of Theropithecus have been found at
Mirzapur, India (Delson, 1993).


The arrival in the Old World of the genus Canis from North America
took place approximately 3.0 Ma ago, as evidenced by the finding of
Canis etruscus-like forms in deposits of this age in China (Flynn et
al., 1981). The first record of this coyote-sized species in Europe
is in the Olivola faunal unit (Azzaroli, 1983; Azzaroli et al.,
1988; Torre et al., 1992) and defines the `Wolf event'. Canis
(Xenocyon) falconeri was a hypercarnivorous canid widely distributed
during the late Pliocene and early Pleistocene in the Old World
(Rook, 1994). This species had a large body size, comparable with
that of the living northern races of Canis lupus, and was
characterized by a relatively short neural cranium with a strong
sagittal crest and a narrow muzzle. The second metacarpal has a very
reduced articular facet for the first metacarpal, what indicates
that the latter bone was vestigial if not absent, a condition
similar to that of African Lycaon pictus, the only extant canid with
a tetradactyl forelimb. According to the revision made by Rook
(1994), C. falconeri is first recorded in China, within the upper
Pliocene locality at Fan Tsun (2.5 Ma). The arrival of this species
in East Africa is recorded at Olduvai Bed I (1.9 Ma), what
chronologically coincides with the earliest evidence of human
presence in Asia. C. falconeri spread in Africa between 1.5 and 1.4
Ma (Kromdraai A and Olduvai Bed II, respectively). The first record
of this species in Western Europe is in the Upper Valdarno, within
the Tasso faunal unit, which according to palaeomagnetic data in
Torre et al. (1996) is tentatively included in the upper part of the
Olduvai Subchron (1.8-1.7 Ma). In spite of the Asian origin of this
species, we can not rule out the possibility that it reached Europe
from Africa, since its first record in Europe is simultaneous with
that of other African inmigrant, Hippopotamus antiquus. However, the
arrival of both species also coincides with those of other Asian
immigrants, like Canis arnensis, Praeovibos, and Allophaiomys
pliocaenicus.


Pachycrocuta brevirostris was a large, short-faced hyaena relatively
common in lower Pleistocene European assemblages of large mammals.
It had a body and skull 10-20% larger than the modern spotted
hyaena, Crocuta crocuta, and was well adapted for destroying
carcasses and consuming bone (Palmqvist et al., 1996b; Arribas &
Palmqvist, 1998). This species differed from other hyaenids in
having a relative shortening of the distal limb segments, what
suggests a less cursorial life style, although such shortening could
provide greater power and more stability for dismembering and
carrying large pieces of carcasses obtained from aggressive
scavenging (Turner & Antón, 1996). P. brevirostris is recorded in
China from the end of the Pliocene (Nihowan) to middle Pleistocene
times (Choukoutien Locality I). This hyaenid was present in India
(Pinjor Formation) not before 2.5 Ma. Howell & Petter (1980) think
that the South African hyaenid Hyaena bellax from Kromdraai could be
a member of the genus Pachycrocuta, and suggest that it would be the
direct ancestor of P. brevirostris. This species is recorded in
South Africa at Kromdraai A (1.5 Ma), Sterkfontein (Members 4 and 5,
2.6-1.0 Ma) and Makapansgat (Member 3, 3.0 Ma) (Howell & Petter,
1980; Turner, 1990). If its presence at Laetoli (3.5-3.2 Ma, East
Africa) is confirmed (specimens tentatively identified as H. bellax
by Leakey & Hay, 1979), the age of the first appearance of this
species on the austral continent would be older. The arrival of this
hyaenid to Europe was a significant faunal event. P. brevirostris is
first recorded in upper Pliocene deposits at Olivola (1.8 Ma), and
its latest appearances are in early middle Pleistocene sites from
Central Europe, like Süssenborn (Turner & Antón, 1996). In the
Iberian Peninsula this species is found exclusively in early lower
Pleistocene sites, and its record during middle Pleistocene times is
not known. It is difficult at present to decide if P. brevirostris
originated in Asia or in Africa; however, what seems clear is the
presence of this hyaenid in Africa when it spread in Europe during
the beginning of the Eburonian event. The extinction in Europe of P.
brevirostris seems to have been linked to the decline and subsequent
disappearance of machairodonts at approximately 0.5 Ma (Turner,
1990, 1992), particularly Megantereon whitei (Martínez-Navarro &
Palmqvist, 1995), what implied the loss of an important source of
partly-consumed carcasses, and thus a change in the interactions
between flesh-eating and bone-consuming species of the carnivore
guild (Turner & Antón, 1996).


The sabre-tooth genus Megantereon shares much in common with
Smilodon, and both genera form the tribe Smilodontini. The earliest
presence of Megantereon is recorded at 4.5 Ma in the Bone Valley
Formation (Florida), where it is represented by M. cultridens. This
species dispersed from North America between 3.5 and 3.0 Ma, and
expanded all over the Old World. Europe was also home to M.
cultridens until the lower Pleistocene, and in China it lingered
well into the middle Pleistocene at Choukutien Locality I (Turner
1987). In Africa M. cultridens gave rise to a new species, M.
whitei, which is characterized by a reduction in the size of both
the maxillary carnassial (P4) and the mandibular premolars, which is
reflected in a diastema between P3 and P4 (Martínez-Navarro &
Palmqvist, 1995). M. whitei replaced M. cultridens in Western and
Central Eurasia at the Plio-Pleistocene boundary, as recorded at
Orce, Apollonia (Mygdonia Basin, Greece) and Dmanisi. The arrival of
this carnivore species to Eurasia may have played a very significant
role in facilitating the dispersal of Pachycrocuta and Homo outside
Africa, since it was an ambush predator with great killing
capability in relation to its flesh requirements, and presumably
left large amounts of carrion for both hyaenas and hominids
(Palmqvist et al., 1996b; Martínez-Navarro & Palmqvist, 1996).


As we have seen in the above discussion, it seems clear that a flux
of African species to Eurasia, mainly to its western fringe, took
place during the end of the Pliocene and the beginning of the
Pleistocene. The fact that most African species are found in
Southern Spain is explained if we consider that the Iberian
Peninsula was faunally and climatically a part of Africa during the
Neogene, far more than it was a part of Europe, which many
palaeontologists consider to begin at the Pyrenees. This is the
third approach to the dispersal of hominids to Europe, which allows
inclusion of the genus Homo in a faunal set which expanded its
palaeogeographical range during these times.


The Role of Sabre-tooths in Facilitating the First Dispersal of Homo
to Europe

The marked seasonality which characterized temperate Europe for most
of the Pleistocene, with cooler and drier conditions than those of
tropical Africa, made the availability of large ungulate carcasses
for scavenging a key resource for hominids to survive during the
cool season (Turner, 1990, 1992). Between 1.5 and 0.5 Ma the
composition of the European carnivore guild was quite different from
that of East Africa, including two species of sabre-tooth cats
(Homotherium latidens and Megantereon whitei), which presumably
maximized the amount of flesh that remained on their kills, thus
opening broad opportunities of scavenging for both hyaenas and
hominids.


Sabre-tooth cats, which belong to the subfamily Machairodontinae,
share among others the following craneodental derived characters
(see for review and references Emerson & Radinsky, 1980; Marean,
1989; Van Valkenburgh & Ruff, 1987; Martin, 1989; Biknevicius et
al., 1996; Arribas & Palmqvist, 1998):

1. Elongate and flattened upper canines of two basic types:
Homotherium (tribe Homotherine) had scimitar-shaped canines
relatively short and broad, which were serrated bearing coarse
crenulations, while Megantereon (tribe Smilodontini) showed dirk-
shaped canines, extremely long, narrow, and without serrations.

2. Enlarged upper incisors, which are relatively longer, thicker,
more pointed and procumbent than in modern felids, and reduced,
incisor-shaped lower canines. The incisor row is long and strongly
curved, what suggests for sabre-tooths a functional emphasis on
these teeth for tearing and stripping flesh from carcasses, a task
that modern felids perform with the assistance of their stout and
conically shaped canines; the extremely large upper canines of the
sabre-tooths would probably be ineffective at the manipulation of
chunks of flesh.

3. Upper carnassials (P4) with a reduced or absent protocone
(lingual lobe), which is lowered away from the occlusal surface in
Megantereon, thus removing it from its role as a hammer for bone
crushing (a condition that is present among extant felids in the
hypercarnivorous cheetah), and is lost in Homotherium, in which
there is also an anteriorly added accesory cusp. This tooth forms in
sabre-tooths a long thin blade, which is extremely specialized for
slicing flesh, and allowed them to deflesh their prey rapidly.

4. A lowered glenoid fossa, a reduced height of the coronid process,
a laterally shifted angular process, and a shortened zygomatic arch.
All these features allow a wider gape than that of modern felids,
but suggest that the temporalis muscle was weaker. However, the
temporal fossae were shorter and narrower, which indicates that the
temporalis was oriented in sabre-tooths more vertically and
perpendicular to the tooth row than in modern felids. This increased
the bite force at the carnassial (M1), which was closer to the
mandibular condyle, although it remained significantly lower than in
felids.

5. An enlarged, lowered and ventrally extended mastoid process,
which is enormous relative to modern felids, thus indicating that
the cleido- and sterno-mastoid muscles must have been
correspondingly large. The occiput is in most sabre-tooths
relatively higher and narrower than in felids, and the
temporomandibular joint is located more ventrally. The mastoid
process is rotated further below the skull joint so that the
leverage of the neck muscle is increased, thus suggesting that a
head-depressing motion was involved in the penetration of the
canines.


The postcranial skeletons of scimitar-toothed and dirk-toothed
machairodonts are quite different (Martin, 1989). Homotherium was a
relatively long legged pursuit predator with the size of a modern
lion (150-220 kg, according to regressions of body mass against
postcranial measurements in modern carnivores; Anyonge, 1993), which
had a comparatively large brain with an enlargedment of the optic
centre, a condition similar to that of the cheetah (Rawn-
Schatzinger, 1992). The morphology of Homotherium is unique among
extant and past felids, showing relative limb proportions which
indicate increased cursoriality and less prey grappling capabilities
than other sabre-tooths. Given the strikingly elongated forelimbs
but rather short hindlimbs that characterize the species within this
genus, they probably had a sloping back. The brachial index in
Homotherium (radius length/humerus length) takes values close to or
above 100%, what implies that most species of this genus preferred
open habitats (Lewis, 1997). According to the results obtained by
Anyonge (1996) in a comparative multivariate analysis of the
locomotor behaviour of both extinct and modern species of large
carnivores, based on cross-sectional geometric properties and linear
dimensions of their femora and humeri, the North American species H.
serum was classified by the discriminant functions in the cursorial
category but with a probability of only 0.6; the next group of most
likely membership (0.4) was the ambush category. The mean brachial
index (103%) is intermediate to that in hyaenids and canids, whereas
the mean crural index (tibia length/femur length, 78%) compares with
that of the larger living felids; this species therefore had a
postural stance that was rather intermediate between cursors and
ambushers.


Dirk-toothed machairodonts (Megantereon, Smilodon) were relatively
short limbed ambush hunters, with a comparatively smaller brain,
showing olfactory lobes well developed. They had powerfully
developed forelimbs, what suggests that a killing bite in the throat
may have been coupled with the immobilization of the prey by the
front limbs. Comparative multivariate analyses of postcranial
measurements (Lewis, 1997) indicate for Megantereon an overall
morphology similar to that of extant jaguars, with tree catching and
long distance dragging capabilities; the low value for the brachial
index (slighty greater than 80% in eurasian M. cultridens; Lewis,
1997) suggests closed habitat preferences. Morphofunctional studies
of African M. whitei (Palmqvist et al., 1996b; Martínez-Navarro &
Palmqvist, 1996) indicate that this predator generated large amounts
of carrion, since it would exploit the carcasses of its prey to a
smalll degree. According to the results obtained by Anyonge (1996)
in the multivariate analysis of postcranial measurements in extant
and extinct carnivores cited above, the larger and related New World
species Smilodon fatalis (350 kg; Anyonge, 1993), a descendant of M.
hesperus, was placed in the ambush category with a probability of
0.51, and the next most likely category was ambulator (i.e. that of
ursids); femoral and humeral cross-sectional properties in Smilodon
approach those of modern bears. The metapodials of this species were
shorter than those of large modern felids and, in addition to
slighty smaller brachial and crural indices, the possession of a
relatively short tail argues for slower locomotory speeds in this
sabre-tooth cat (Anyonge, 1996).


All these craniodental and postcranial features indicate (1) that
sabre-tooth felids were able to hunt very large prey relative to
their own size, and (2) that they left on the carcasses of the
ungulates hunted large amounts of flesh and all within bone
nutrients, which were available to be subsequently scavenged by
hyaenas and hominids (Marean, 1989). Sabre-tooths became extinct in
East Africa by 1.5 Ma ago, what coincides with the emergence of the
Acheulean Industrial Complex, but inhabited Eurasia until 0.5 Ma
(Turner, 1990, 1992). Their persistence may then explain the success
of the Oldowan tools in Eurasia, where the Oldowan/Acheulean
transition took place much later than in Africa, at approximately
0.5-0.4 Ma (i.e. when sabre-tooths disappeared in this continent),
since the sharp flakes characteristic of Oldowan assemblages were
fully appropiate to scavenge on partially defleshed carcasses and
the cores were used in breaking bones for their marrow content. In
this context, the striding gait for the emergence of the genus Homo,
the elementary Oldowan stone tools and the expansive pattern of
scavenging, also served its initial dispersal from Africa (Larick &
Ciochon, 1996), which was facilitated by the availability of
ungulate carcasses supplied by sabre-tooth cats.


An opposite interpretation of the ecological opportunities opened by
sabre-tooths for the hominids has been argued by Turner (1990,
1992), who considers that the competition with the large and
efficient bone-cracking hyaenid P. brevirostris made it difficult
for hominids to develop an adaptive pattern of scavenging on the
carcasses left by sabre-tooth cats, and that a stable and productive
niche for the hominids in Europe was only possible after the
replacement during middle Pleistocene times (0.5 Ma) of sabre-tooths
and giant hyaenas by modern African carnivores like the lion, the
leopard and the spotted hyaena.


However, this argument is contradicted by the results obtained
recently in two independent comparative studies (Capaldo, 1997;
Selvaggio, 1998) of the incidence and distribution of tool marks and
tooth marks on bovid long bone specimens from the FLK 22 assemblage
at Olduvai Bed I ('Zinjanthropus' site, 1.8-1.76 Ma) and different
experimental control samples, which have shown a three stage
sequence (carnivore to hominid to carnivore involvement) of site
formation. In stage one flesh-eating carnivores (probably sabre-
tooths in most cases) partially defleshed long bones, as deduced
from the high frequency of tooth marks on midshaft fragments; in
stage two hominids processed intact long bones for their marrow
content, as inferred from percussion mark percentages, and the
presence of cut marks indicates that the bones still retained at
this stage variable amounts of flesh; finally, in stage three bone-
cracking carnivores consumed long bone epiphyses for grease, as
inferred from the under-representation of these elements in the
assemblage (the abundance of major long bone epiphyses is inversely
correlated with their structural density) and the high percentage of
tooth marks on near-epiphyses and surviving epiphyses. Therefore,
the results obtained clearly indicate that competition between
hominids and bone-cracking carnivores was low at FLK 22, and that
hominids had access before than hyaenids to those carcasses
partially defleshed by sabre-tooths; such situation was probably the
same in Europe during lower Pleistocene times.


Dispersal Routes to Europe

Most palaeoanthropologists consider that Homo spread out of Africa
by the Eastern Mediterranean or levantine land corridor
('Ubeidiyah), reaching Europe through the Straits of Dardanelles,
which were closed by low water levels during the glacial cycles.
However, it has been suggested that these hominids could have also
crossed the Mediterranean via the Gibraltar Strait or even through
Sicily (Alimen, 1975; Martínez-Navarro & Palmqvist, 1995, 1996);
this possibility would require crossing open waters, even at lowest
sea-levels.


The minimum width of the Strait of Gibraltar is nowadays 14.5 km,
but a sea-level fall of 200 m during the Aullan event (1.8-1.6 Ma)
would result in the narrowing of this passage up to 6.5 km
approximately and a drop of 300 m would nearly close it. No evidence
confirming the ability of Homo to cross stretches of open waters has
been yet found in Spain or Italy, although the presence of narrow
sea stretches does not seem to have represented and effective
geographical barrier for human dispersal during the Plio-
Pleistocene, as suggested by recent data on the colonization of
Flores by H. erectus (as well as by other species of continental
Southeast Asian fauna), dated at 0.9-0.8 Ma by zyrcon fission-tracks
(Morwood et al., 1998): even when the sea level was at its lowest,
these human populations would have to cross 19 km of water to get to
Flores from the closest island of Sumbawa.


There are two additional lines of reasoning that support the
possibility of a dispersal through Gibraltar (and perhaps even
through the passage between Tunicia and Sicily): (1) the levantine
corridor requires longer distance movements to reach Western Europe,
crossing large rivers and mountainous chains, with adaptations to
different vegetation zones and to broader ranges of temperature and
rainfall, and (2) a simultaneous colonization of Europe through
Gibraltar, perhaps Sicily, and the Eastern Mediterranean helps to
explain the presence in several north circummediterranean sites of
Spain (Orce), Italy (Pirro Nord), Greece (Apollonia) and Georgia
(Dmanisi) of certain African species of large mammals which have not
been found by the moment in Central Europe during lower Pleistocene
times, such as M. whitei, whose dispersal seems to have been limited
up to the 40ºN parallel (Martínez-Navarro & Palmqvist, 1996).


The Dispersal of Homo out of Africa: Alone or Lonely with Others?

Until now, three chronological hypotheses regarding the first
arrival of humans to Europe had been proposed: the Europe of 0.5 Ma
(the `Young Europe' of Carbonell et al., 1995a), which was accepted
until 1994; the Europe of 1.0 Ma (called the `Mature Europe'), which
has been followed since then by most palaeoanthropologists; and the
Europe of 1.5 Ma (the `Old Europe'), which is for us the most
reliable chronological scenario, although there are still
reservations about this possibility due to disputes on the human
affinities of some controversial fossil remains from Orce (see
Palmqvist, 1997), and also due to uncertainties on the age of
Dmanisi. In order to decide in favour of any of them, it is
neccesary to answer the following question: Did humans leave Africa
alone or simultaneously a set of large mammals? This question has
fortunately only two possible answers:

1. Humans left the austral continent alone. If this hypothesis were
correct, the dispersal of Homo out of Africa would not depend on any
extrinsic factor, but on intrinsic ones (i.e.
population 'saturation', technological advances in tool making, etc)
and supposed abilities or attitudes which need to be further
established and demonstrated. From this premise, if humans left
Africa alone they could do so at any given moment from the time of
their origin whenever the geographical and climatic barriers allowed
them to disperse. According with the available palaeoanthropological
record, the oldest presence of Homo in Asia would be then restricted
to 1.8-1.6 Ma (Java, Southern China), in the Caucasus to 1.6 Ma
(Dmanisi, Georgia), and in Western Europe to approximately 0.8 Ma
(Atapuerca, Spain). In this case it would make no sense to consider
in this discussion those aspects related with the technological
level adquired by the genus Homo or with faunal dispersal events
during the Plio-Pleistocene. The oldest archaeological and
palaeontological evidences recovered in Southeast Spain (Orce) would
not be relevant for this history, since the information supplied by
these sites points to a faunal turnover which is not detected in
Atapuerca (where the record comprises species originating more
recently in Asia, during the middle Galerian). In this case the
arrival of Homo to Europe would be independent of other
palaeobiological factors, and thus the dispersal would be
monospecific.

2. Humans left Africa accompanied by other animals. If this scenario
is correct, the fossil record should preserve species originating in
Africa within the Eurasian ecosystems of lower Pleistocene times,
and the faunal turnover should concentrate on a restricted
chronological interval. This hypothesis is widely corroborated by
the fossil record in Europe, as discussed before. If we consider the
partial faunal replacement of large mammals which took place in
Europe at the Plio-Pleistocene limit (`Wolf event': Asian
species, `Homo event': inmigrants from Africa), it is then possible
to explain the presence of both African carnivores and Asian
ruminants in the lower Pleistocene of the circummediterranean area,
and their coexistence with members of the genus Homo, who showed
anatomical affinities with H. ergaster and possesed the Oldowan
Industrial Complex.


The first evidence of this faunal dispersal is recorded at the Plio-
Pleistocene transition (1.8-1.6 Ma) in Western Europe, within the
Olivola and Tasso faunal units, and in Central Eurasia (Dmanisi),
where exists a complete record of this dispersal event, including
human remains and evidence of cultural activity. Southeast Spain
(Orce-Cueva Victoria, 1.4-1.1 Ma) has an exceptional record of these
faunal assemblages, as well as the technological evidence of the
first human populations. Finally, the most complete anatomical and
cultural evidence of the hominids who could have been the descendant
of those directly implied in the first colonization of Eurasia is
found at the Gran Dolina of Atapuerca (< 0.8 Ma).


Therefore, the recent findings in Atapuerca TD-6 Level do not
support the scenario of the mature hypothesis for a colonization of
Europe at around 1.0 Ma, given (1) the anatomical features of the
hominid remains (which could be better related to H. ergaster), (2)
the lack of fit between the age proposed for the site, its
geographical location and the Oldowan/Acheulean chronology, and (3)
the faunal incongruity (i.e. Asian origin of the middle Galerian
species preserved in the assemblage). On the contrary, the record
from Atapuerca fills in part the palaeoanthropological hiatus of the
old hypothesis, i.e. the colonization of Europe before 1.5 Ma ago.
It is then possible that the hominids from TD-6 represent one of the
latest European populations, descended from the ancestor lineage
defined by H. ergaster, which retained its initial Oldowan
technology and survived in Europe after the extinction that affected
other African species of large mammals. It is also possible that
this species, which has been called `Homo antecessor', could coexist
in Europe with other populations of hominids originating in Asia, as
H. erectus (Ceprano, Italy), which arrived to Western Europe within
the middle Pleistocene faunal set from Asia, but this would be
another history.


Acknowledgements

We gratefully acknowledge constructive remarks made by J. Damuth
(University of California at Santa Barbara), R. G. Klein (Stanford
University, California), R. Potts (Smithsonian Institution,
Washington D. C.) and R. A. Reyment (University of Uppsala). B.
Martínez-Navarro (Orce Research Project, Granada) greatly helped us
with the revision of the Villafranchian assemblages of large mammals
from Europe, and also made very insightful comments which improved
the article. This research was supported in part by a general grant
from the `Leakey Foundation' and by DGES project number PB97-1082
from the Spanish Ministry of Education and Culture.


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Referencia del artículo:


Arribas, A. y Palmqvist, P. 1999. On ecological Connection Between
Sabre-tooths and Hominids: Faunal Dispersal Events in the Lower
Pleistocene and a Review of the Evidence for the First Human Arrival
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