Ekgmowechashala, the last primate to inhabit North America before humans

Ekgmowechashala is a poorly documented but very distinctive species of ancient primate that lived in western North America during the Early Oligocene epoch, some 30 million years ago.

“Our project focuses on a very distinctive fossil primate known to paleontologists since the 1960s,” said Kathleen Rust, a doctoral candidate with Biodiversity Institute and Natural History Museum at the University of Kansas.

“Due to its unique morphology and its representation only by dental remains, its place on the mammalian evolutionary tree has been a subject of contention and debate.”

“There’s been a prevailing consensus leaning towards its classification as a primate. But the timing and appearance of this primate in the North American fossil record are quite unusual.”

“It appears suddenly in the fossil record of the Great Plains more than 4 million years after the extinction of all other North American primates, which occurred around 34 million years ago.”

In the 1990s, University of Kansas Professor Chris Beard collected fossils from the Nadu Formation in the Baise Basin in Guangxi, China, that closely resembled the Ekgmowechashala material known from North America.

By that time, Ekgmowechashala was notoriously enigmatic among North American paleontologists.

“When we were working there, we had absolutely no idea that we would find an animal that was closely related to this bizarre primate from North America, but literally as soon as I picked up the jaw and saw it, I thought, ‘Wow, this is it’,” Professor Beard said.

“It’s not like it took a long time, and we had to undertake all kinds of detailed analysis — we knew what it was.”

“We have some critical fossils, including what is still by far the best upper molar of Ekgmowechashala known from North America. That upper molar is so distinctive and looks quite similar to the one from China that we found that it kind of seals the deal.”

Map showing known Ekgmowechashala localities in the United States

The authors conducted the morphological analysis that tied Ekgmowechashala and its cousin Palaeohodites from China in a phylogenetic tree to establish their evolutionary relationships.

In the course of the work, they were able to draw conclusions about how Ekgmowechashala came to be discovered in Nebraska, millions of years after its fellow primates died out in the continent’s fossil record.

“We collected a substantial amount of morphological data to create an evolutionary tree using a phylogenetic reconstruction software and algorithm,” Rust said.

“This evolutionary tree suggests a close evolutionary relationship between North American Ekgmowechashala and Palaeohodites from China, which Chris and his colleagues discovered in the 1990s.”

“The results from our analysis unequivocally support this hypothesis.”

According to the researchers, Ekgmowechashala did not descend from an older North American primate that somehow survived the cooler and drier conditions that caused other North American primates to go extinct.

Rather, its ancestors crossed over the Beringian region millions of years later, anticipating the route followed by the first Native Americans much later in time.

“Our analysis dispels the idea that Ekgmowechashala is a relic or survivor of earlier primates in North America,” Rust said.

“Instead, it was an immigrant species that evolved in Asia and migrated to North America during a surprisingly cool period, most likely via Beringia.”

“Species like Ekgmowechashala that show up suddenly in the fossil record long after their relatives have died off are referred to as ‘Lazarus taxa’ after the Biblical figure.”

“The ‘Lazarus effect’ in paleontology is when we find evidence in the fossil record of animals apparently going extinct — only to reappear after a long hiatus, seemingly out of nowhere,” Professor Beard said.

“This is the grand pattern of evolution that we see in the fossil record of North American primates.”

Sources:

Published November 6, 2023 in the Journal of Human Evolution; doi: 10.1016/j.jhevol.2023.103452

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