Did great apes start small? Our best guess for the size of the last common ancestor of hominoids – humans, great apes and gibbons – just got a lot daintier, thanks to a fossil primate unearthed at a landfill site in Spain.

This ancestor would have lived around 14 million years ago, when lesser apes, the gibbons, split from the great ape lineage.

An earlier hominoid, Proconsul, lived in East Africa about 23 million years ago and had a body mass of up to 50 kilograms – about the same as a chimpanzee, and not much smaller than a human.


Proconsul is thought to be typical of early hominoids, so the consensus was that today’s great apes would have evolved from creatures that were about the same size. That would also mean that gibbons, the only living small-bodied hominoids, must have evolved from a large-bodied ancestor.

But in 2011, palaeontologists in Spain dug up the partial skeleton of an 11.6-million-year-old ape that would have had a body mass of about 5 kilograms – roughly the same as a modern gibbon.

David Alba at the Catalan Institute of Palaeontology in Barcelona, Spain, and his colleagues have now named the skeleton Pliobates cataloniae, and analysed where it might fit in the ape evolutionary tree. They say it is undoubtedly a hominoid – and one that is evolutionarily closer to the last common ancestor of all living hominoids than Proconsul is.

Pliobates shares several features of its wrist with living hominoids. Like gibbons and great apes, it could rotate its wrist for easier clambering around its forested environment. Proconsul‘s wrist is more primitive.

Other parts of the Pliobates skeleton look primitive, though, which complicates the challenge of deciding where to slot it into the evolutionary tree.

“I can actually see some of my colleagues fuming over the Alba paper’s interpretation,” says Brenda Benefit at the New Mexico State University in Las Cruces. “For one thing, the elbow is just too primitive.” Living hominoids have a bony ridge in the elbow that stabilised the joint while the animal is dangling from a branch. Pliobates lacks this feature.

Pliobates‘s ears are even more peculiar: it had a bony ear canal that isn’t seen in living hominoids or in Proconsul. This feature is seen in an extinct family of primates called the pliopithecids. Benefit and her New Mexico State colleague, Monte McCrossin, think Pliobates might actually belong here.

And then there’s Pliobates‘s face (see reconstruction above). It had bony rims around its eyes, rather like a pair of goggles. That’s a feature seen only in gibbons – so perhaps Pliobates belongs in this part of the tree, as a gibbon ancestor that evolved after the gibbons and great apes diverged.

But regardless of where Pliobates belongs in the primate tree, it clearly shows an odd mosaic of features of different groups. This isn’t a complete surprise. “Independent evolution of similar features is a common phenomenon, but it seems to be particularly rampant [in primates],” says Alba.

“We want to find a simple logical progression for primate and human evolution, but evolution was a very messy process,” says Benefit.

Journal reference: Science, DOI: 10.1126/science.aab2625

(Image credits: Marta Palmero/Institut Català de Paleontologia Miquel Crusafont (ICP))

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