Did the LCA Have Teeth More Like a Gorilla?

Artificial intelligence is playing a role in understanding human evolution.  From the Australian site News.com comes a story about new work in trying to understand what the last common ancestor to apes and humans might have looked like:

IT’S an image imprinted on our brains: the steady march of evolution from chimp to human. But it’s not quite right.

Monkeys don’t belong on the tree. They have tails.

Chimps, which don’t, are with Bonobos our closest living relatives. And, as such, both should be standing alongside us in the march of life.

Stretching out behind should be a gradually converging branch of earlier variations.

Ultimately, between six and eight million years ago, the branches almost certainly converge on one common ancestor.

We know almost nothing about what that was.

We have reasonably secure evidence of bipedality at around 6 million years in the form of Orrorin tugenensis from Kenya, as well as a crushed skull from Chad called Sahelanthropus that may or may not be 7 million years old, and recently, fossil footprints, purporting to show bipedal walking, from Crete have been uncovered that have been dated to around 5.7 million years ago.  Beyond that, nothing.  That is where the new AI study comes in.

The researchers used machine learning to teach an artificial intelligence to identify and classify fossilised hominid teeth dating from 25 million years ago. It then sifted through these to find patterns of development.

The study published in the science journal PaleoBios found one tantalising tip.

Our common ancestor almost certainly had gorilla-like teeth.

Now, it’s not a lot. And it certainly doesn’t say our ancestor was a gorilla.

But what it does do is add some shape and substance to this nebulous period of our human origins.

The information that is contained in the article is not nearly as cut and dried as is indicated by the news story. From the conclusion:

Given that the divergence of humans and chimpanzees occurred in the late Miocene, and that Miocene apes are much more similar to Gorilla in dental proportions, we assert that gorillas are the more appropriate extant model for the African ape LCA in terms of the relative sizes of the postcanine teeth. This similarity in dental proportions likely has implications for the interpretation of dietary adaptation and possibly phylogenetic relationships in Miocene apes, including the chimpanzee-human last common ancestor.

What this likely means is that, during the Miocene, which was the golden age of the apes, even after the divergence of Gorillas from the main line, there were extant forms that continued to have varying degrees of traits that could be associated with gorillas, presenting a classic case of collateral ancestry.  It is possible that one of the lines eventually led to chimpanzees, while another led to us.  We won't know more until we actually have some fossil remains from that missing time period. 
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