Tiny 20-million-year-old monkey skull points to primate brain areas evolving separately

The brain size of primates, thought to have increased progressively, seems to have followed a more roundabout path. In a study published Wednesday in the journal Science Advances, researchers in China and the US used high-resolution imaging to examine the only known fossilized skull of the extinct Chilecebus, a New World monkey that scampered around ancient mountain forests, feeding on leaves and fruit. One key finding: the brain size of primates, long assumed to have increased progressively over time, now appears to have followed a more roundabout path. “We see multiple episodes of expansion of the brain in each of these major groups, and we see several episodes of actual reduction of relative brain size in certain groups,” co-author John Flynn of the American Museum of Natural History told AFP. Though the Chilecebus was roughly around the size of a modern marmoset or tamarin, in contrast to those monkeys its brain had several grooves known as infolding that suggest a greater degree of cognitive complexity: in other words, brain size is not always linked to advancement.