Million-Year-Old Monkey Fossil Discovered In Underwater Cave

2270 Million-Year-Old Monkey Fossil Discovered In Underwater Cave
Antillothrix bones and skull. Journal of Human Evolution

A one-million-year-old fossil shin bone recovered from limestone rocks in an underwater cave belonged to an extinct monkey called Antillothrix bernensis. This Dominican Republic native remained relatively unchanged for over a million years, according to new findings published in the Journal of Human Evolution

The fossil shin bone (or tibia) was discovered a few years ago in the Dominican province of Altagracia on the large island of Hispaniola. Because uranium trapped in rocks decays to form thorium and lead, University of Melbourne’s Robyn Pickering and colleagues were able to date the fossil by measuring the amount of uranium, thorium and lead present in the limestone rocks it was embedded in. The tibia was 1.32 million years old, give or take 110,000 years. 


Then, using a technique known as three-dimensional geometric morphometrics, the team confirmed that the fossil tibia does indeed belong to the Dominican primate Antillothrix bernensis. After modeling the shape of the leg, they were able to reconstruct how the monkey moved around in its environment, and this allowed them to compare it with previously described fossils. This tree-dwelling monkey was about the size of a small cat, and its diet mainly consisted of fruits and leaves. Even though the species was first described in 1977, researchers knew very little about it until now.

Other morphologically consistent material has all been dated to within the last 10,000 years, suggesting the species changed little in over a million years. "Many times when a long-lived species is discovered, there is a shift in its morphology over time," study co-author Melissa Tallman of Grand Valley State University said in a statement. "For these primates, at least in the tibia, they remained remarkably stable morphologically. They obviously adapted to their island environment in such a way that was flexible enough that it allowed them to persist for more than one million years.” In fact, these monkeys were likely still around when humans first colonized the Caribbean's Greater Antilles.