A 20 million-year-old monkey skull which can fit in the palm of an adult’s hand may contain clues to the evolution of the brain in ancient primates.
A study has found that the neural landmarks on the skull depict a situation in which certain primate brain regions expanded or contracted independent of other regions. According to researchers, a section of the monkey’s brain involved with perception of smell was not balanced with a visual system of greater size, as present in the primates currently.
Xijun Ni, paleontologist of Chinese Academy of Sciences, Beijing said that the size and complexity of the primate visual systems increased through several million years without major changes in the other sections of the brain. By comparing with the skulls of the fossils belonging to African primates aged more than 30 million years it is revealed that brain structures evolved at different rates in different lineages along with the change in brain size with that of body. The work appears in the Science Advances journal. This shows that the brain of primates did not just expand as a whole but different sections changed at different rates.
An extinct monkey’s skull, Chilecebus carrascoensis was discovered in Andes Mountains, Chile in 1995 by John Flynn, a paleontologist at American Museum of Natural History, New York. They used high-resolution scanning and a three-dimensional cast of the skull’s inner surface to obtain impressions made by neural folds.
It revealed that brain tissue was separated into different areas with specific duties like smell and vision. Estimation of the size of the ancient visual system was done through measuring the eye sockets in the skull and an opening present at the back of the cavities. Placement of key folds on the surface of the brain helped in estimating the size of the region dedicated to smell perception.
Brenda Benefit, a biological anthropologist at New Mexico State University said that the variety of folding patterns of the brain in New World monkeys exceed that of the patterns in the brains of present-day African and Asian monkeys. But their features are not always relevant to the study of ape brain evolution and Old World monkey.
Previously her team identified a 15 million-year-old African monkey which had a large odor-perception region in a brain of a smaller size similar to today’s African monkeys.
Ni said that through comparing fossils of Old World and New World monkeys, they found that through different means of evolution, a gradual increase in the complexity and size of brain were produced.