From the paleoprimatology department comes news that a second intact cranium of Aegyptopithecus zeuxis has been found and is, ‘”extraordinarily unusual,” …mainly because it’s complete and uncrushed.’ This fossil cranium is important because tells us a lot about what was going on with primate brain evolution many million years ago.

The fossil cranium was found by Elwyn Simons, a primatologist at Duke University, and his colleagues. Aegyptopithecus zeuxis is around 30 million years old and believed to be an old world monkey. From National Geographic News,

“The completeness of the fossil skull allowed Simons and colleagues to take computerized x-rays and create a virtual model of the specimen’s tiny brain.

Based on analyses of previous fossil skulls collected at the dig site outside Cairo…, scientists had assumed the ancient monkey’s brain was larger and more advanced.

The new fossil indicates Aegyptopithecus had a relatively primitive brain compared to its descendants…

Nevertheless, the brain region responsible for vision, called the visual cortex, was large. This suggests that, like many primates, Aegyptopithecus had good vision.”

Aegyptopithecus zeuxisFrom the x-ray scan, Simons and team also found out there was a great degree of sexual dimorphism… an anatomical size phenomenon between males and females. In this situation the newly discovered fossil was a ‘female, which may have weighed about 5.5 pounds (2.5 kilograms)’ while the older Aegyptopithecus was a male, twice the size.

Dean Falk, an anthropologist that specializes in primate brain evolution, specifically hominid brain evolution, commented on the finding. She said this finding,

“”challenges “perceived truths” that large brain size was required for things like daytime activity and living in large social groups.

“[The new study] is saying you don’t have increased brain size back when you have some of these things,” she said.

In fact, Falk believes the virtual model of Aegyptopithecus’ brain, used in the new study, suggests the brain was even less advanced than the researchers propose.

However, Falk agrees that the brain model does confirm an enlarged area for vision, suggesting good eyesight was important early on for our ancestors.”

From what I am gathering this is an important conclusion that implies the primate brain expanded vision before it enlarged anywhere else. Of course more fossil primate skulls could support that or show that this feature happened in the Aegyptopithecus lineage.

The results of the x-ray analysis of Aegyptopithecus have apparently been published in PNAS, a journal notorious for letting press releases come out way before the actual publication. That being said, I don’t have a link to the actual publication as of now.