Newly discovered fossilised bones for the world's oldest and most primitive known primate, Purgatorius, reveal a tiny, agile animal that spent much of its time eating fruit and climbing trees.
The fossils are the first known below-the-head bones for Purgatorius and previously, only teeth revealed its existence.
"The ankle bones show that it had a mobile ankle joint like primates today that live in trees," co-author Stephen Chester, a Yale University vertebrate paleontologist, told the Discovery News.
"This mobility would have allowed for rotating the foot in different directions as it adjusted to different angles presented by tree trunks and branches," Chester said.
"It also shows that the first primates did not have elongate ankles that you see in many living primates today that are thought to be related to leaping behaviours," added Chester.
He conducted the study with colleagues Jonathan Bloch of the Florida Museum of Natural History and William Clemens, a professor emeritus at the University of California.
Researchers believe that the specialised ankle bones of Purgatorius played a key role in the evolutionary success of early primates.
"These new fossils support the idea that the first 10 million years of primate evolution happened in the context of an intense period of similar diversification in flowering plants, including the ability to climb in branches and collect fruits and other products of the trees at the very beginning," Bloch said.
While many questions remain unanswered about Purgatorius, this and other studies are shedding more light on the animal.
Purgatorius lived during the Paleocene, shortly after the extinction of non-avian dinosaurs. Given the end of the Age of Dinosaurs, the new era began the mammal-dominated era.
This mammal is generally believed to have been small and brown, and had a bushy tail.
Purgatorius weighed about 1.3 ounces, making it roughly the size of the smallest living primates: the mouse lemurs of Madagascar, researchers said.
The mammal had a lot of teeth, including relatively low-crowned molars, which were specialised for eating fruit, although it probably ate other things too.
Tree living served this and other primates well, such that all but a few existing species remain at least partly arboreal. Humans are part of the rare exceptions, since our more recent ancestors left the trees some 60 million years after Purgatorius' lifetime.
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