The last primate in North America: New fossil analysis reveals a story 30 million years in the making

Illustration of Ekgmowechashala, the last primate to inhabit North America before humans. (Kristen Tietjen, scientific illustrator with the KU Biodiversity Institute and Natural History Museum.)

Today, the only primates that make North America their home are humans. But 30 million years ago, a tiny, scrappy primate represented the last bastion of non-Homo sapiens primates on this continent—and researchers are finally able to piece together its story of survival.

A new study published in the Journal of Human Evolution lays out how a species of primate called Ekgmowechashala, likely came to North America after all other primates died out millions of years before.

Ekgmowechashala is a species that we’ve known about for decades, with its fossil record first unearthed in the 1960s, according to researchers. But this ancient primate’s story has been shrouded in mystery for years.

“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,” Kathleen Rust, a doctoral candidate in paleontology at the University of Kansas’s Biodiversity Institute and Natural History Museum and lead author of the research, said in a press release.

“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.”

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Primates came to North America around 56 million years ago, but after the Eocene-Oligocene transition 34 million years ago, North America became much cooler and dryer, making it a less than optimal home for the primates that used to commonly roam this continent.

“Several million years later Ekgmowechashala shows up like a drifting gunslinger in a Western movie, only to be a flash in the pan as far as the long trajectory of evolution is concerned,” Rust said.

It’s a phenomenon known as the ‘Lazarus effect’—a type of species seemingly going extinct in a region, only to resurface abruptly in the fossil record millions of years later.

For years, researchers have been looking for a definitive answer to this primate’s source. Did some primates survive the Eocene-Oligocene transition and evolve into Ekgmowechashala—or did the primate come from somewhere else entirely?

To put together the pieces of Ekgmowechashala’s puzzle, Rust looked at fossilized teeth and jaws found not only in the U.S. state of Nebraska, but also fossils from China which were collected decades ago.

Co-author Chris Beard, senior curator of vertebrate paleontology at the University of Kansas as well as Rust’s doctoral advisor, had first collected the fossils from the Nadu Formation in the Baise Basin in Guangxi, China in the 1990s.

When he first spotted the fossils, he saw the resemblance to Ekgmowechashala immediately, he said.

“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,’” Beard said in the release. “It’s not like it took a long time, and we had to undertake all kinds of detailed analysis — we knew what it was. Here in KU’s collection, 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.”

However, a more in-depth analysis still needed to be done—and that’s where Rust came in.

Fossils of Ekgmowechashala have been reported in three areas of western U.S., in South Dakota, Oregon and Nebraska. For this analysis, Rust looked at fossils sourced from Nebraska that make up the earliest known North American record of Ekgmowechashala, so as to provide a better comparison to the older Chinese fossils.

Rust’s analysis of these fossils, showing similarities between the teeth and jaws of the Nebraska and Chinese fossils that spell out a clear evolutionary relationship, solidifies a key bridge in Ekgmowechashala’s history, researchers say.

The apparent confirmation of an older “sister taxon” for Ekgmowechashala which originated in China suggests that this is where Ekgmowechashala originally developed. This species discovered in China is named Palaeohodites, which means “ancient wanderer.”

“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 supports this hypothesis.”

This fossil trail suggests that, like many of the occupants of North America today, Ekgmowechashala was an immigrant.

“(It) evolved in Asia and migrated to North America during a surprisingly cool period, most likely via Beringia,” Rust said.

It’s unknown exactly how long Ekgmowechashala was around for—fossils of the primate dating from around 29.5 million years ago to around 27.8 million years ago, suggesting the species endured for at least two million years.

This new research is exciting, Rust says, because it sheds light on primate evolution during a time of huge environmental upheaval in North America.

“It’s crucial to comprehend how past biota reacted to such shifts,” she said. “Around 34 million years ago, all of the primates in North America couldn’t adapt and survive. North America lacked the necessary conditions for survival. This underscores the significance of accessible resources for our non-human primate relatives during times of drastic climatic change.

“Understanding this narrative is not only humbling, but also helps us appreciate the depth and complexity of the dynamic planet we inhabit. It allows us to grasp the intricate workings of nature, the power of evolution in giving rise to life and the influence of environmental factors.”