54-million-year-old skull may reveal how primates got larger brain

June 23rd, 2009 - 2:31 pm ICT by ANI  

Washington, June 23 (ANI): Following the analysis of a well-preserved skull from 54 million years ago, researchers at the University of Florida and the University of Winnipeg have developed the first detailed images of a primitive primate brain, a finding which could help narrow the possibilities for what caused primates to evolve larger brain sizes.

The analysis of the well-preserved, 1.5-inch-long skull has cast doubt on previous theories about evolution of brain structure.

The skull belongs to an animal, Ignacius graybullianus, cousin of primitive primates known as Plesiadapiforms that evolved in the 10 million years between the extinction of the dinosaurs and the first traceable ancestors of modern primates.

The fully intact skull allowed researchers to make the first virtual mould of a primitive primate brain.

“Most explanations on the evolution of primate brains are based on data from living primates,” said lead author Mary Silcox, an anthropologist at the University of Winnipeg and research associate at UF’s Florida Museum of Natural History.

“There have been all these inferences about what the brains of the earliest primates would look like, and it turns out that most of those inferences are wrong,” she added.

During the study, the researchers used CT scans to take more than 1,200 cross-sectional X-ray images of the skull, which were combined into a 3-D model of the brain.

The detailed images of a primitive primate brain have shown that cousins of our earliest ancestors relied on smell more than sight.

Ignacius graybullianus represents a side branch on the primate tree of life, said Florida Museum vertebrate paleontologist and study co-author Jonathan Bloch.

In previous research, Bloch and Silcox established that Ignacius was similar to modern primates in terms of its diet and tree-dwelling but did not leap from tree to tree like modern fast-moving primates.

In many ways, the early primate behaved like living primates but with a brain that was one-half to two-thirds the size of the smallest modern primates.

This means that factors such as tree-dwelling and fruit-eating can be eliminated as potential causes for primates evolving larger brain sizes, Silcox said, because “the smaller brained Ignacius was already doing those things.”

The mould suggests a “startling combination” of features in the early primate that requires a rethinking of primate brain evolution, said Florida State University anthropologist Dean Falk, who was not involved in the study.

“Hypotheses about early primate brain evolution often link keen smell with nocturnal insect-eating, and a more recently evolved increase in visual processing with fruit-eating in arboreal habitats,” Falk said.

“A large and complex brain has long been regarded as one of the major steps that sets primates apart from the rest of mammals,” said Bloch.

“At our very humble beginnings, we weren’t so special. That happened over tens of millions of years,” he added.

During an evolutionary burst around 10 million years, after the extinction of the dinosaurs, visual features in the brain became much more prominent while the olfactory bulbs became proportionately smaller.

The study will appear in the Proceedings of the National Academy of Sciences. (ANI)

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