The Caveman’s Corner

As I rather suspected would be the case, our very first “Meet an Ancestor” ancestor isn’t strictly a human ancestor. More of an extinct, collateral cousin. It is, however, a fairly well known species on which there is a good amount of information. I was afraid I’d get some obscure Plesiadapid that didn’t even register on Google.

T. oswaldi reconstruction from DKimages

Theropithecus oswaldi is an extinct, giant relative of the modern day gelada, T. gelada. Details of their teeth indicate that the two likely don’t have an ancestor-descendent relationship; they shared a separate common ancestor from 2 to 3 million years ago. Modern geladas live only in the Ethiopian highlands in huge 200+ monkey groups (herds, really), where they graze like cattle (except by sitting down and picking the grass up with their hands). During most of the Pliocene and Pleistocene, however, Theropithecus reigned supreme in the baboon niche across Africa (and into India with T. delsoni). It wasn’t until the Pleistocene that Thereopithecus began to recede and Papio take its present, dominant position in baboondom.

A female T. gelada being uncharacteristically frugivorous.

The analogy between the extinct Theropithecus and modern baboons isn’t exact, however. Theropithecus were generally larger and demonstrated the same specializations for intensive mastication of tough, fibrous grasses and tubers that their modern relatives do. Geladas have massive, deeply crenulated molars with sharp crests to eviscerate the stringy grasses. They also have short fingers and powerful thumbs which they use to collect their fodder.

Right upper dental arcade of T. gelada.

T. oswaldi is in particularly notable for its enormous size, topping out at around 100 kg, the same as a small gorilla. It is ubiquitous in Plio-Pleistocene fossil deposits ranging throughout east and southern Africa. There is some highly circumstantial evidence that Homo ergaster, one of our more direct antecedents, might have butchered T. oswaldi and the two did certainly inhabit the same range. Biomechanical analysis suggests T. oswaldi would have been relatively more arboreal than modern geladas, indicating the diversity of fossil Theropithecus was much higher than it is today but besides that, we have little to go on to reconstruct T. oswaldi’s plausible behavior other than modern geladas and baboons. To that effect, ecological models based on the modern gelada suggest that T. oswaldi would have lived sporadically distributed near large water sources (perhaps in riverine gallery forest) in social groups organized around one male-multifemale harems and groups of unattached males. Imagine great swarms of giant baboons moving through the scrub and you’ll get a picture of what our ancestors might have seen every time they went to take a drink.

A T. oswaldi skull with some assorted other bones in situ from Kenya http://anthropology.si.edu/humanorigins/aop/olorg2004/dispatch/16jul04/16jul04.htm

The great mystery of all the Theropithecus is what happened to them. Why, by the end of the Pleistocene, had they been completely replaced by Papio in everywhere but their montane Ethiopian fortress? The answer might lie in the changing habitats brought on by the ice ages. Perhaps the baboons maintained a more variable diet and were thus better able to adapt. There are definite parallels between the decline and fall of Theropithecus and of the genus of human ancestors Australopithecus, who went by the wayside at around the same time. I’d personally be interested in studying that further.

References

Elton, Sarah. “A reappraisal of the locomotion and habitat preference of Theropithecus oswaldi.”2002. Folia Primatologica. http://cat.inist.fr/?aModele=afficheN&cpsidt=14487623

Faulk, Dean. “Sulcal patterns of fossil Theropithecus baboons: Phylogenetic and functional implications.” 1981. International Journal of Primatology. http://www.springerlink.com/content/0tn08673h8q5u157/

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

This entry was posted on Saturday, February 9th, 2008 at 10:09 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.