Inner Ear Predicts Evolution of Mobility in Primates

The inner ear may hold the key to ancient primate behavior, according to researchers from Pennsylvania State University.

According to a report by university officials,compared 16 X-ray Computed Tomography (CT) scans of fossilized primate skulls or skull fragments from the Old World to the New Worlds with scans of living primates to clarify how these extinct animals moved, especially for those species without any known remains, and to what extent have the mobility patterns of primates changed overtime.

"Almost in every case where there is a fossilized skull, the semicircular canals are present and well preserved," said Timothy Ryan, assistant professor of anthropology, geosciences and information sciences and technology, Penn State. "They are embedded in a very dense part of the skull and so are protected."

The report explains that the complicated labyrinth of bone and marrow of the inner ear is made up of "the cochlea -- the major organ of hearing -- the vestibule and the three semicircular canals which sense head motion and provide input to synchronize movement with visual stimuli."

Studying the inner anatomy of the ear can help researchers piece together the locomotive patterns and behaviors of monkeys and their ancestors.

Research shows that New World monkeys, dating from 12 to 20 million years ago, were relatively agile similar to cebus monkeys or tamarins.

"The last common ancestor of Old World monkeys and apes would have been an animal of medium agility, much like living macaques," said Ryan. "But what is really surprising is that the early ape, Proconsul, appears more agile than expected, "Ryan told university correspondents.

The results suggest that living, larger bodied apes, such as gorillas and orangutans, developed slower gait overtime, different from their agile ancestors.

The study is published in today's (June 13) issue of the journal Proceedings of the Royal Society B: Biological Sciences.