By using X-ray imaging and CT scans to study the skulls of ancient monkeys, researchers from Duke University and the Max Planck Institute for Evolutionary Anthropology in Germany have discovered that brain complexity can evolve before brain size in primates.
As the authors report in a new study published Friday in the journal Nature Communications, the Old World monkeys known as Victoriapithecus had a relatively small brain compared to its body size and a brain volume less than half of the volume of same-sized modern monkeys.
The researchers created 3D computer models of these brains and revealed that Victoriapithecus had a brain volume of approximately 36 cubic centimeters, which is about the size of a plum. Even so, the monkey’s brain was surprisingly complex.
Brain size, complexity can evolve independently
Using their CT scans, co-authors Fred Spoor from the Max Planck Institute and Duke’s Lauren Gonzales found that the olfactory bulb, which is used to perceive and analyze odors, was three-times larger than expected, and the brain had several distinctive folds and wrinkles.
“It probably had a better sense of smell than many monkeys and apes living today,” Gonzales explained in a statement. “In living higher primates you find the opposite: the brain is very big, and the olfactory bulb is very small, presumably because as their vision got better their sense of smell got worse… instead of a trade-off between smell and sight, Victoriapithecus might have retained both capabilities.”
Co-author Brenda Benefit of New Mexico State University, who originally discovered the skull with co-author Monte McCrossin (also of NMSU), said that the skulls come from a period in which there are few fossils, and that the skull is the oldest ever discovered from an Old World monkey. As such, the fossil provides new insights into primate brain development.
Among primates like humans and apes, “the thinking is that brains got bigger and then they get more folded and complex,” Gonzalez said. “But this study is some of the hardest proof that in monkeys, the order of events was reversed – complexity came first and bigger brains came later.” Benefit added that the findings reveal that “brain size and brain complexity can evolve independently; they don’t have to evolve together at the same time.”