Soon After Dinosaur Decimation, Our Primate Ancestors


A hunger for crunchy insects may have led our early primate ancestors to develop the signature traits that we inherited.

Small primates like Teilhardina, which lived in the forest canopy of ancient China 55 million years ago, were early adopters of some of our evolutionary family’s most famous characteristics. Looking much more like lemurs than monkeys, they had forward-facing eyes, grasping hands and nails that would become hallmarks of many later primate species—including ourselves. How such traits evolved in the first place has long been controversial among fossil primate experts, but a new hypothesis suggests that sneakily hunting up in the treetops had a lot to do with it.

Investigations of human origins often center on our ancient hominin relatives such as “Lucy,” but many of the characteristics that make us unique among mammals are much, much older. “Humans represent a mosaic of traits that have evolved at various points throughout the 66-million-year history of primates,” says University of Toronto paleontologist Mary Silcox.

Our gifts of depth perception, dexterous hands and more can be drawn back to a time much closer to the dinosaurian heyday than the present. The first primate with a grasping toe dates back to 56 million years ago, the first big increase in brain size occurred 55 million years ago and the number of teeth we have can be traced back to 30 million years ago, Silcox points out. But exactly why our early ancestors came to have such telltale traits has been debated by experts for decades.

Working from what’s known about living primates and experiments involving how squirrels climb trees, Yonghua Wu, a biologist at Northeast Normal University in Changchun, China, and colleagues have proposed that many of our classic primate traits came from quietly sneaking up on prey in the trees. Their study, published earlier this year in Science Advances, proposes that key primate traits like nails, the ability to leap and forward-facing eyes all evolved because early primates were ambush hunters. Past researchers have suggested that hunting for insects was crucial to primate origins, but the specific way primates might have captured their meals was left unclear. What the new study adds is the notion that using stealth to hunt small prey, specifically, was the catalyst for some big primate changes. “I really like that paper, because it introduced some new ideas to a topic that was getting a bit stale,” Silcox says.

Taken individually, many of our primate traits might seem strange. Forward-facing eyes were present in primates by 55 million years ago, but paleoanthropologists have often wondered why. If this ocular innovation was so important to moving in the trees, for example, then why do other arboreal animals like squirrels have eyes on the sides of their heads? Most primates also have nails rather than claws, but these would seem to make climbing harder.

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