Apidium zuetina: a new Anthropoid Primate From Oligocene Paleogene Libya

During upheaval in Libya in 2013, a window of opportunity opened for scientists from the University of Kansas to perform research at the Zallah Oasis, a promising site for unearthing fossils from the Oligocene period, roughly 30 million years ago.

From that work, the KU-led team last week published a description of a previously unknown anthropoid primate -- a forerunner of today's monkeys, apes and humans -- in the Journal of Human Evolution. They've dubbed their new find Apidium zuetina.

Significantly, it's the first example of Apidium to be found outside of Egypt.

"Apidium is interesting because it was the first early anthropoid primate ever to be found and described, in 1908," said K. Christopher Beard, Distinguished Foundation Professor of Ecology and Evolutionary Biology and senior curator with KU's Biodiversity Institute, who headed the research. "The oldest known Apidium fossils are about 31 million years old, while the youngest are 29 million. Before our discovery in Libya, only three species of Apidium were ever recovered in Egypt. People had come up with the idea that these primates had evolved locally in Egypt."

Beard said evidence that Apidium had dispersed across North Africa was the key facet of the find. He believes shifting climatic and environmental conditions shaped the distribution of species of Apidium, which affected their evolution.

"We've found evidence that climate change -- not warming, but cooling and drying -- across the Eocene-Oligocene boundary probably is the root cause in kicking anthropoid evolution into overdrive," he said. "All of these anthropoids, which were our distant relatives, were living up in the trees -- none of them were coming down. When the world became cooler and dryer in this period, what was previously a continuous belt of forest became more fragmented. This created barriers to gene flow and movement of animals from one part of forest to what used to be adjacent forest."

With a forest broken up, there was an inhibition of gene flow that through time resulted in speciation, or the creation of new species, according to the KU researcher.

"Animals that are sequestered become different species over millions of years," Beard said. "As the climate oscillates again, you've got different species of Apidium. As forests expand and contract, now you've got competition between species of Apidium that have never seen each other before. One species outcompetes the other, the other goes extinct, and we think that's what we're picking up with this Libyan Apidium, which is related to the youngest and largest species of Apidium known from Egypt."

Beard said that Apidium zuetina would have been physically similar to modern-day squirrel monkeys from South America, but with smaller brains, and would have dined on fruits, nuts and seeds.

"We know that Apidium was a very active arboreal monkey, a really good leaper," he said. "We know they actually had fused lower-leg bones just above the ankle joint. That's really unusual for anthropoid primates, and the only reason for it to happen is because you like to jump a lot, as it stabilized the join between those bones and the ankle."

The team identified Apidium zuetina through detailed analysis of its teeth.

link.