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Scientists reveal the brain structure of a 20 million year old monkey



The monkey skull.
Photo: AMNH / N. Wong and M. Ellison

Paleontologists using CT scanners have discovered the structure of a 20 million-year-old primate brain thanks to an extremely well preserved fossil skull.

Understanding the Development of Our Wildly Complex Human Brain It's not easy, and there are no old brains that just sit in the dirt to compare with. Instead, researchers must indirectly search for clues to brain forms based on the way the brain leaves imprints on the skulls. That's what makes this discovery exciting – it's a glimpse of what the primate brain was like long before man evolved.

"It's quite remarkable," said John Flynn, one of the authors of the study and curator of fossil mammals at the American Museum of Natural History in New York, Gizmodo said. "We tried to convince ourselves that it was anything but a primate, but it showed a bulbous area where the brain was supposed to be … The cleansing and subsequent CT analysis underpinned all this and the importance of the findings . " The evolutionary tree is divided into two groups: the New World monkeys called Platyrrhines, and the Old World monkeys and apes (including humans) called catarrhines. Scientists believe that the split occurred at least 36 million years ago. The fossil skull studied here belongs to the conserved early platyrrhins named Chilecebus carrascoensis, perhaps the first platyrrhines to deviate from the common ancestors of the group, as published in Science Advances. The creature would be similar in size to a modern tamarin or marmoset, but a smaller brain.

A 3D scan of the monkey skull.
GIF: X. Ni / AMNH / MNHN

The researchers, led by Xijun Ni at the Chinese Academy of Sciences, measured the fossil with high-energy X-rays, allowing them to differentiate between bone and rock in the sample. They combine the scans into a 3D image showing the structure of the brain imprinted on the fossilized bone. They estimated that such a brain would weigh about 8 grams. They also estimated the size of the monkey's olfactory bulb (the region of the brain responsible for processing odors) and the shape of the optic canal and optic nerve. The brain also had some surprisingly complicated folds, said Flynn.

C. The proportions of the brain of carrascoensis provide an insight into the history of the evolution of the brain and primates. The olfactory lamp was surprisingly small, but was not compensated by more complex or larger optical components. This tells researchers that the brain of primates is unlikely to develop as a whole, but changes take place piecemeal.

Although it is an exciting specimen, it is still a million-year-old and badly weathered over time. More fossils of more species are needed to understand the whole picture. Nevertheless, these brain-case scans are important tools for the reconstruction of the primate pedigree that go beyond what brain scans of living monkeys can provide. New scans like the one presented here can provide us with information about which features escaped evolution, which originated from a common ancestor and which emerged independently of each other in different groups. For example, newer platyrrhines such as marmosets and tamarins appear to have less brain fold than C. carrascoensis, said Flynn.

The team hopes to continue to analyze the structure of this brain in higher resolution.


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