An ancient ancestor of ours was mentally less advanced than expected about 29 millions years ago, a new study by a Duke University primatologist has revealed.
Elwyn Simons identified the second and the most intact cranium found till date of the Aegyptopithecus zeuxis and subjected it to micro CT scanning to calculate the approximate dimensions of the brain encased inside the cranium.
Based on previous fossils collected at the same dig site in a quarry outside Cairo, scientists had hypothesized that this early monkey already would have had a relatively large brain. But they were surprised to find that the species "had a brain that might have been even smaller than that of a modern lemur's".
"This means the big-brained monkeys and apes developed their large brains at a later point in time," said Simons, a professor of biological anthropology and anatomy at the university.
Simons said he originally overestimated Aegyptopithecus' likely brain size based on the original 1966 skull, which has a bigger snout and pronounced crests, features that he now attributes to its being male.
"Aegyptopithecus' brain is smaller than once thought. But other features in these skulls, and in many other Aegyptopithecus fossil pieces collected at the Egyptian site over four decades, suggest that this primate was already branching away from its lemurlike ancestry," said Simons.
"We also find that the visual cortex was large, which means that like many primates, this species likely had very acute vision. So the visual sense, which is regarded as a very important feature of anthropoids, or higher primates, had already expanded," he said.
The findings appear online in the journal Proceedings of the National Academy of Sciences (PNAS).