Tooth, jaw fossils tell tale of North America’s last nonhuman primates

Oregon discovery points to lemurlike animals crossing a land bridge from Asia

A few teeth and a jaw fragment discovered in Oregon have helped to flesh out lemurlike features of an enigmatic ancient North American primate.

These creatures probably crossed a land bridge from Northeast Asia to North America around 29 million years ago, say paleontologist Joshua Samuels of the National Park Service in Kimberly, Ore., and his colleagues. That intercontinental journey occurred 6 million years after other North American primates had died out and 7 million years after African monkeys reached South America (SN: 3/7/15, p. 14).

Scientists classify North America’s last nonhuman primates as members of the genus Ekgmowechashala, from a Sioux term for monkey. After these animals vanished around 26 million years ago, no primates inhabited North America until humans arrived well over 25 million years later, Samuels’ team reports June 29 in the American Journal of Physical Anthropology.

From 2011 to early 2015, the researchers discovered two complete teeth, two partial teeth and a jaw fragment eroding out of rocky sediment at Oregon’s John Day Formation. A tooth and jaw fragment from the same species had been found there previously. All the Oregon specimens belong to a new Ekgmowechashala species, the researchers say. Partial jaws and teeth of another Ekgmowechashala species have been found at sites in South Dakota and Nebraska.

The new fossils date to between 28.7 million and 27.9 million years ago, based on their position between dated volcanic ash layers.

Ekgmowechashala’s remains are similar to those of a 34-million-year-old primate from Thailand and a 32-million-year-old primate from Pakistan, Samuels says. Paleontologist Erik Seiffert of Stony Brook University in New York suggested the same Asian–North American primate connection in 2007. Samuels and his colleagues “have laid out the evidence in more detail,” Seiffert says.

Some researchers suspect that Ekgmowechashala had a particularly close evolutionary connection to tarsiers. But paleontologist K. Christopher Beard of the University of Kansas in Lawrence agrees with Samuels’ team that Ekgmowechashala apparently belonged to an extinct primate family with ties to modern lemurs. Finding ankle fossils of these mysterious North Americans primates would clearly show whether they were more closely related to modern lemurs or to tarsiers, Beard says.  

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