The Caveman’s Corner

So the whole weekly thing is pretty much out the window. I’ve been experiencing some technical difficulties for a while and I’ve had other matters to attend to/lacked motivation. But, you may unbate your breath, we have Meet an Ancestor entry number two: Propliopithecus chirobates.

A reconstruction of Propliopithecus

Woohoo, we finally got our super-obscure species that Google hasn’t heard of (Did you mean: propliopithecus chorobates). It is, however, a member of a quite famous and extremely important lineage.

Propliopithecus is the titular genus of the Propliopithecidea, a family of early anthropoids from the Oligocene epoch of the Fayum in Egypt. Living anthropoids consist of monkeys (New and Old World; the difference is important), apes, humans. Stem anthropoids were more-or-less ancestral to these three groups but don’t fit precisely in any of them. There are three major families of these in North Africa: The Parapithicidae, the Oligopithecidae, and the Propliopithecidae.

The Parapithicidae are very primitive and are seen to have split off before the New World monkeys or just afterwards. The Oligopithecidae are similarly primitive but shows some very odd specialized features that make their relations to any living anthropoid group dubious. The Propliopithecidae are the most securely established in their relations and are viewed with some measure of consensus as the unique ancestors of the modern Catarrhini (Old World monkeys, apes, and humans).

A schematic representation of the place of the Propliopithecidae

The biggest single reason many scientists feel this to be the case is details of the teeth of the Propliopithecidae which they share with living apes. Both possess bunodont molars with low crowns arranged in a distinctive, staggered pattern.

Bunodont upper molars of the chimpanzee. Propliopithecid molars look sort of like this.

The Propliopithecidae’s most famous member is species you may well have heard of called Aegyptopithecus zeuxis. It is the Lucy of Oligocene paleoanthropology and about made Elwyn Simons.

Simons with two A. zeuxis, male on the left, female on the right

P. chirobates was a cousin of this much more famous early primate. Body sized averaged at 4kg in weight, about the size of a modern guenon monkey. They likely would have lived similarly to guenons too, which means a diet rich in fruit supplemented periodically by insects and leaves. These animals were sexually dimorphic (males were larger with bigger canines than females) which indicates the sort of polygynous lifestyle endemic to living monkeys.

Thus, in the Propliopithicines you have species with teeth like apes (they are called ‘dental apes’) and lifeways remarkably like modern arboreal monkeys. To understand the full significance of this, you have to have a bit of context from the later Miocene epoch. Old World monkeys initially evolved to exploit open, wooded environments on the edges of forests. From their earliest days (species such as Proconsul), apes, on the other hand, were masters of the deep forest. Thus, in order to out-compete the apes in the forests, monkeys evolved to live much the same life that the very most primitive apes lived in the Oligocene.

You can view Catarrhine evolution as proceeding in two twisting lines from its beginnings in the Oligocene of the Fayum. One track continued to evolve in the forest and culminated in the great forest ape radiation of the late Miocene; the other evolved originally in the forest fringe before radiating explosively into the apes’ domain and driving them nearly to extinction.

My (pretty highly) schematic representation of the ecological adaptations of apes and OW monkeys since their divergence

So that’s the long and short of it. P. chirobates was a largish representative of a genus that would have lived similarly to modern guenons, but with teeth more like those of modern apes. It is one of the best represented species of the genus, so when talking about Propliopithecus as a whole you are largely talking about this species. P. chirobates was keeper of that flame which someday would burn in our own breasts during one of the most interesting and definitive periods of our development. It was truly our ancestor.

References

Fleagle, John G. Primate Adaptation and Evolution. 2^nd ed. 1998. Academic Press.

Fleagle, John G.; Kay, Ricard F.; Simons, Elwyn L. “Sexual dimorphism in early anthropoids.” September, 1980. Nature. http://www.nature.com/nature/journal/v287/n5780/abs/287328a0.html

Fleagle, John G.; Simons, Elwyn L. “Skeletal remains of Propliopithecus chirobates from the Egyptian Oligocene.” 1982. Folia Primatoligica. http://www.ncbi.nlm.nih.gov/pubmed/6819985

Kirk, Christopher E.; Simons, Elwyn L. “Diets of fossil primates from the Fayum Depression of Egypt: a quantitative analysis of molar shearing.” 2000. Journal of Human Evolution.

Walker, Alan; Shipman, Pat. The Ape in the Tree: An Intellectual and Natural History of Proconsul. 2005. Belknap.

This entry was posted on Monday, March 17th, 2008 at 7:36 pm and is filed under Meet an Ancestor. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.