Well, That Was Anti-Climactic: Gorilla Ancestor Redux

As I mentioned here various and sundry media organizations are having a field day with the recently announced discovery of some fossil teeth belonging to a new species of Miocene ape. The find in itself is quite interesting, but:

New Fossil Ape May Shatter Human Evolution Theory says National Geographic. The finds from the Afar rift, in eastern Ethiopia, raise questions on current theories of human evolution. says the more sedate BBC article. However this is not quite what the article in Nature says. The article announces the find of a new species of Miocene ape – called Chororapithecus abyssinicus in the form of nine teeth. The paper compares to teeth to a number of extant and extinct species and notes some similarities to modern gorillas – among others. The controversy comes because the authors argue that this species is related to the gorilla – kind of – and, therefore, the timing of the gorilla, chimp and human split needs to be pushed back. Here is Suwa et al on the issue:

The similarities seen between the two genera raise the possibility that Chororapithecus is a Miocene member of the Gorilla clade. Alternatively, with its combination of thick enamel and distinct molar cresting pattern, Chororapithecus may represent a unique adaptation that is convergent with gorillas in molar structure and function. Although the evidence for phylogenetic affinity between Chororapithecus and Gorilla is inconclusive, it may be that the basal members of the gorilla clade shared large tooth size and incipiently enhanced molar shear as a part of an herbivorous diet that accompanied (presumed) larger body size. Chororapithecus may then represent one example of adaptational (and perhaps phyletic) differentiation within that clade.

The evidence for a phlyogenetic link with gorillas is scanty, but if true, say Suwa et al, then we would need to take another look at the fossil and molecular evidence. Just shatters human evolutionary theory don’t it? Interestingly, they argue more strongly for a revised timeline in the supplemental material. Having said that I do like the way they try to bring genetic and developmental data into the study and I especially liked this:

Because recent experimental and quantitative genetic studies suggest significant degrees of morphogenetic independence between corresponding upper and lower molar structures.. the presence of a functionally integral inter-jaw pattern of morphological expression, as seen in the Chororapithecus molars, suggests adaptation by natural selection, as opposed to chance emergence of neutral morphological minutia.

In other words, neutral theory doesn’t explain it…
You would have thought paleoanthropology would have learned something from Ramapithecus. Dental gorillas don’t mean actual gorillas. Just like being a dental hominid didn’t make Ramapithecus a real hominid.
A new species of great ape from the late Miocene epoch in Ethiopia
Gen Suwa et al.
doi:10.1038/nature06113