The Evolutionary Mystery of Ekgmowechashala, the Last Primate in North America

Sunday - November 12 2023, 21:34 UTC - 1 year ago

The recently published evidence on the Journal of Human Evolution shed light on the evolutionary story behind Ekmowechashala, the last primate in North America before Homo sapiens or Clovis people. The study was based on fossil teeth and jaws found in both China and Nebraska. The researchers determined Ekgmowechashala's family tree using a new species of Palaeohodites (or "ancient wanderer") they found in China, and used morphological analysis to reconstruct the primate's estimated appearance.

The story of Ekgmowechashala, the last primate in North America before Homo sapiens or Clovis people, reads like a spaghetti western: A grizzled and mysterious loner, against the odds, ekes out an existence on the American Plains.

Except this tale unfolded about 30 million years ago, just after the Eocene-Oligocene transition during which North America saw great cooling and drying, creating an increasingly inhospitable landscape for warmth-loving primates.

Now, paleontologists from the University of Kansas and the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing have recently published evidence in the Journal of Human Evolution shedding light on the long-standing saga of Ekgmowechashala, based on fossil teeth and jaws found in both Nebraska and China.

To do so, the researchers first had to reconstruct its family tree, a job helped by the discovery of an even more ancient Chinese "sister taxon" of Ekgmowechashala the team has named Palaeohodites (or "ancient wanderer"). The Chinese fossil discovery resolves the mystery of Ekgmowechashala’s presence in North America, showing it was an immigrant rather than the product of local evolution.

"This project focuses on a very distinctive fossil primate known to paleontologists since the 1960s," said lead author Kathleen Rust, a doctoral candidate in paleontology at KU’s Biodiversity Institute and Natural History Museum. "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, Rust’s doctoral adviser and co-author Chris Beard, KU Foundation Distinguished Professor and senior curator of vertebrate paleontology, 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,’" 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. 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." .

Beard left it to Rust to conduct the morphological analysis that tied Ekgmowechashala and its cousin Palaeohodites from China in a phylogenetic tree to establish the primate’s family tree. Then she gathered data from other fossil findings from the same formations in Nebraska.

The analysis suggested Palaeohodites and Ekgmowechashala were related since, based on their skeleton structure, these primates must have shared a common ancestor. But the Ekgmowechashala remained something of an evolutionary loner. The arrival of the mysterious primate in North America appears to have been a fluke — the product of a dispersal pattern caused by a fleeting moment of environmental coincidence about 30 million years ago.

To conclude their research, the scientists used a computer approach founded on the fossil evidence to envision what the primate might have looked like. The result, a digital reconstruction, showed a 3-D fitting of a small snub-nosed primate that fit the description of the Ekgmowechashala, but which revealed nothing remarkable.

This offered a fitting footnote to the tale, as rare are the stories that satisfy as much as puzzled. After all, such is the brunt of biology.