11-06-2023

Ekgmowechashala: The last American primate before humans

In the expansive plains of North America, a tale of survival and extinction has been slowly pieced together by paleontologists, and the story centers around a mysterious primate named Ekgmowechashala. This creature, the last primate on the continent before the arrival of humans, thrived approximately 30 million years ago during a period of significant climatic shifts.

A team of experts from the University of Kansas, alongside colleagues from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, have published a report that sheds new light on Ekgmowechashala. The evidence is drawn from dental fossils unearthed in Nebraska and China, which have sparked a revision in the primate’s evolutionary narrative.

Unique morphology 

Ekgmowechashala seems to have endured against all odds during the Eocene-Oligocene transition, a period marked by a cooler and drier climate that was inhospitable for primates.

Study lead author Kathleen Rust is a doctoral candidate in Paleontology at KU’s Biodiversity Institute and Natural History Museum.

“This project focuses on a very distinctive fossil primate known to paleontologists since the 1960s,” said Rust. “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.”

Ancient wanderer 

The discovery of an ancient Chinese primate, named Palaeohodites, or “ancient wanderer,” has helped in solving this puzzle. Professor Chris Beard stumbled upon Chinese fossils in the 1990s that bore a striking resemblance to the North American Ekgmowechashala.

“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,’” said Professor Beard, Rust’s doctoral adviser and and senior curator of vertebrate paleontology.

“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.”

Close evolutionary relationship 

An extensive morphological analysis established a close evolutionary relationship between the two species. “We collected a substantial amount of morphological data to create an evolutionary tree using a phylogenetic reconstruction software and algorithm,” said Rust. 

“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.”

Immigrant species 

The research concluded that Ekgmowechashala did not evolve from an isolated group of North American primates but was an immigrant species. Its ancestors likely migrated over the Beringian land bridge, the route that the first Native Americans would take much later.

“Our analysis dispels the idea that Ekgmowechashala is a relic or survivor of earlier primates in North America,” explained Rust. “Instead, it was an immigrant species that evolved in Asia and migrated to North America during a surprisingly cool period, most likely via Beringia.”

Lazarus effect

According to the researchers, 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 who was raised from the dead.

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

“The first primates came to North America about 56 million years ago at the beginning of the Eocene, and they flourished on this continent for more than 20 million years. But they went extinct when climate became cooler and drier near the Eocene-Oligocene boundary, about 34 million years ago.”

“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. After Ekgmowechashala is gone for more than 25 million years, Clovis people come to North America, marking the third chapter of primates on this continent. Like Ekgmowechashala, humans in North America are a prime example of the Lazarus effect.”

Study significance

Rust pointed out out the significance of Ekgmowechashala’s story, particularly in the context of present-day environmental challenges. She emphasized the importance of understanding past biological responses to climate shifts in the era of human-induced climate change.

“It’s crucial to comprehend how past biota reacted to such shifts,” said Rust. “In such situations, organisms typically either adapt by retreating to more hospitable regions with available resources or face extinction. 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.”

Our evolutionary journey 

The study is also a part of a larger story that represents the earliest chapters of our own evolutionary journey that ultimately led to our own species, Rust said.

“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.”

The study is published in the Journal of Human Evolution.

Image Credit: Kristen Tietjen, scientific illustrator with the KU Biodiversity Institute and Natural History Museum

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