[ad_1]
A fossilized primate skull the size of a chicken egg helped to better understand the evolution of the primate brain, including ours.
The nearly complete skull, 20 million years old, is a rare specimen. It belongs to Chilecebus carrascoensis, a primate who traveled the Chilean Andes during the Miocene.
The species is part of the New World monkeys, or platyrrhins, a group found in Central and South America that today includes marmosets, capuchins and spider monkeys.
The brains do not leave fossils. But the paleontologist Xijun Ni of the Chinese Academy of Sciences Beijing and his colleagues swept the fossilized skull with the help of a high-resolution CT, which captures the general shape of the skull as well than its internal cavities.
From the computed tomography, they recreated an endocast of the cerebral cavity. An endocast resembles the shape of the brain covered by the protective membrane of the dura and may reveal information about the shape, size and folding patterns of the brain on the surface.
"All morphology is very similar to the brain of a living animal," explains Ni, who led the study.
Weighing about eight grams, Chilecebus had a brain about the size of a marmoset. However, unlike the brain of a marmoset, which has a fairly smooth surface, Chilecebus brain had seven pairs of furrows – sulci – on its surface.
The presence of sulci is usually associated with larger, more cognitively advanced brains. the Chilecebus brain suggests that brain size and folds do not go together.
Other anatomical features also seem to evolve independently.
Scientists have often observed a compromise between sight and smell. Species that develop a large visual system typically have olfactory regions detecting smaller odors, and vice versa.
This is not the case for Chilecebuswhich apparently did not particularly excel in both cases; the two regions are relatively small.
The results corroborate the idea that primate brains evolve in a complex "mosaic" with different functional regions evolving independently of each other.
New World monkeys separated from the other main group of primates, catarrhines, more than 40 million years ago. This group includes monkeys from the Old World of Asia and Africa – baboons, mandrils and the like – and great apes, to which our own lineage belongs.
In both groups, brain size increased over time – a converging evolutionary situation.
But the comparison also reveals how strange the human brain is.
"It's only in the human lineage that brains are unusually enlarged," Ni says. Human brains expanded threefold more than would be expected based on the evolutionary trajectory of other lineages.
"It's interesting, it's another fossil that fills a gap in our understanding of primate brain evolution," says evolutionary biologist Robert Barton of Durham University in the United Kingdom. Uni, who did not participate in the study.
"We tend to look at living species and deduce from what had to happen to create these living species," he says, but "you can not be really sure what happened in the historical past by looking at fossils ".
Discoveries on living primates, revealing that important anatomical variations related to the number and function of neurons at the cellular level could improve what could be gleaned from fossilized specimens in the future.
The Royal Institution of Australia has an educational resource based on this article.
You can access it here.
[ad_2]
Source link