Big brains arose twice in highe...( After taking a fresh look at an old ...)

After taking a fresh look at an old fossil, John Flynn, Frick Curator of Paleontology at the American Museum of Natural History, and colleagues determined that the brains of the ancestors of modern Neotropical primates were as small as those of their early fossil simian counterparts in the Old World. This means one of the hallmarks of primate biology, increased brain size, arose independently in isolated groupsthe platyrrhines of the Americas and the catarrhines of Africa and Eurasia.

"Primatologists have long suspected that increased encephalization may have arisen at different points in the primate evolutionary tree, but this is the first clear demonstration of independent brain size increase in New and Old World anthropoids," says Flynn of the paper that appeared in the Museum's publication Novitates this June. Encephalization is the increase in brain size relative to body size. Animals with large encephalization quotients (E.Q.'s) are those with bigger brains relative to their body size in comparison to the average for an entire group. Most primates and dolphins have high E.Q.'s relative to other mammals, although some primates (especially apes and humans) have higher E.Q.'s than others.

At the heart of the new paper is the development of more accurate equations for estimating body size in platyrrhines, or New World "monkeys." Most fossils are fragments of skulls or teeth so, to help in estimating their body size (and then E.Q.), Flynn and colleagues collected 80 measurements of the skulls, jaws, and teeth of 17 different species of living New World monkeys that ranged across the full spectrum of body sizes. This study is one of the first to estimate body size with platyrrhines instead of their better-studied counterparts from the Old World, and this detailed analysis uses new statistical approaches to tease out which characteristics correlate best with body size. The goal is to apply this equation to fossilized specimens.