View Full Version : Temporal bone morphology, size and relationships among apes

Wednesday, December 1st, 2004, 07:46 PM
Here is a study of ape phylogeny, which also considers the differences between populations of chimpanzees, gorillas and orang-utans, to see if the methods used to study morphology are good at detecting the phylogenetic signals suggested by the genetic evidence which suggest a large difference between chimpanzee, gorilla and orang-utan populations as well as a relationship of chimpanzees with bonobos to humans and more distantly to gorillas.

The temporal bones are investigated to see if they support the genetic phylogeny, and three dimensional landmark data are used to improve the reliability of the results. The temporal bone provides numerous landmarks to use and reflects evolution of things like mastication and posture, and 22 were compared. Both western lowlands and mountain gorillas, bonobos, the central, eastern and western chimpanzees, and both Bornean and Sumatran orang-utans were included. Because of the phenetic and size differences to these larger apes, Hylobates wasnt included in the study.

The human temporal bone is found to be divergent from the others, but humans are still found to be most closely related to chimps with bonobos. However despite this relationship, the temporal shape in the shared ancestor is inferred to closer to that in gorillas than to chimpanzees, in other words the chimpanzee temporal isnt like that of human ancestors. Among the chimpanzees, the eastern chimpanzee retains more ancestral characters than other chimps and bonobos do and some evidence suggests they diverged from the central and western chimp samples before bonobos.

Although size is reflected in temporal morphology, the results suggest that neither the affinity between chimps, bonobos and humans or between gorillas and orangutans are because of size. Within the orang-utans in Sumatra and Borneo, and the western lowland and mountain gorillas, the differences are found here to be as important as those seperating bonobos are from chimpanzees, which mignt support different orang-utans and gorillas being classified as seperate species.

They say that "The congruence of our results with the consensus molecular tree, and the strong bootstrap support for the Pan–Homo clade, reaffirms the potential of skeletal evidence to recover hominoid relationships."