21-Million-Year Old Monkey Fossils Are Oldest Ever Found in North America

The upper molar of 21-million-year-old Panamacebus transitus. Image credit: Aldo Rincon

During an ongoing fossil salvage project at the Las Cascadas Formation in the Panama Canal Basin, scientists from the Smithsonian Tropical Research Institute (STRI), the University of Florida, and the New Mexico Museum of Natural History and Science found seven fossil teeth that belong to a previously unknown species of monkey that lived 21 million years ago. The findings, recently published in the journal Nature, may change what we know about the early biology of the Americas.

The Las Cascadas formation, located on the shore of the Panama Canal, where the fossils of 21-million-year-old Panamacebus were found. Image credit: Jason Head

The new species was named Panamacebus transitus because of its believed movement between continents some 18 million years before the Isthmus of Panama formed 3.5 million years ago. Jonathan Bloch, the lead author of the study, said in a press release that P. transitus is a relative of South and Central America’s capuchin and squirrel monkeys.

“Prior to this discovery, New World monkeys were thought to have evolved in isolation on South America, cut off from North America by a wide seaway,” Bloch said. High-resolution images of the teeth, which were a combination of upper molars, premolars, canines, and incisors, were studied for two years to determine where the species fits into the evolution of the primates.

It is still unclear how the monkeys made the continental voyage or what happened thereafter, but the existence of P. transitus on the continent does pose important questions that researchers are eager to answer. 

The capuchin monkey (Cebus capucinus) is thought to be closely related to Panamacebus transitus. Image credit: Kristen Grace

Bloch tells Nature that the plan now is to return to the place where the teeth were found to hopefully discover more P. transitus fossils. “I would really like to find a skull or parts of the rest of the skeleton,” he said.