52-Million-Year-Old Ankle Fossil Suggests Our Ancestors Were High Flying Acrobats

Biologists have long believed the common ancestor of all primates was a small, deliberate animal which used its grasping hands and feet to scamper along thin branches foraging for fruits and insects. They theorized that the leaping skills came later, after the proto-primate evolved into two distinct groups — wet-nosed primates like lemurs and dry-nosed primates that include monkeys, apes, and humans. However, the discovery of a perfectly preserved 52-million-year-old fossil seems to suggest that the first primate might have been leading an impressively acrobatic lifestyle, leaping from one tree to another.

Paleontologists discovered the quarter-inch-long ankle bone on an expedition near Marseilles, in south-eastern France, more than 30 years ago. However, it is only recently that a team led by Duke University assistant professor Doug Boyer, decided to study it in detail.

As it turns out, the fossil belonged to one of the oldest known wet-nosed primates — a chipmunk-sized creature called Donrussellia provincialis. Since the mammal has previously only been identified by its jaws and teeth, the team decided to conduct an extensive analysis, by comparing 3-D scans of the tiny bone with those of other animal species.

To their surprise, they found that the structure of the tiny bone was similar to leaping animals like the tree shrew — a small, agile mammal that can jump distances of up to 60 cm (24 in).

The findings are significant because previous studies have shown that the most primitive dry-nosed primate, the Archicebus Achilles, was also capable of jumping long distances.

Boyer says, “Donrussellia and Archicebus are definitely on opposite sides of the tree. So when they both have the suggestion of leaping traits, it starts to look like acrobatic leaping behaviors were important early in primate evolution.”

This has led the researchers, who published their findings in the October 2017 issue of the Journal of Human Evolution, to conclude that the first primates may have evolved their jumping skills before learning to creep along small branches and twigs. "Being able to jump from one tree to another might have been important, especially if there were ground predators around waiting to snag them," Boyer said.

However, not everyone agrees with Boyer’s team. University of Michigan’s Philip Gingerich says that while he has no doubt Donrussellia was a leaper, he is not convinced it was a wet-nosed primate. Kenneth Rose, a researcher at John Hopkins University School of Medicine in Baltimore, Maryland says that though the ancient mammal may have been able to jump, there is not enough evidence to prove that it was a feature of the common primate ancestor. Hopefully, the discovery of additional fossils from the first primates will shed more light on how our predecessors lived.

Resources: phys.org, today.duke.edu.