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UI researchers present findings on Ice Age sloth found in southwest Iowa

A man assembles a giant sloth skeleton at the University of Iowa
University of Iowa
The Tarkio Valley Sloth Project helped researchers understand more about Page County during the Ice Age.

The bones of a giant ground sloth are giving a better picture of Iowa in the Ice Age.

University of Iowa researchers have pieced together the bones of three ancient giant ground sloths found in southwest Iowa. The researchers’ recently published findings in the Journal of Vertebrate Paleontology journal reveal a bit about the region’s wildlife more than one hundred thousand years ago.

In 2001, researchers and student volunteers headed to a site near Shenandoah to excavate the bones of the now extinct giant sloth. The 10 foot tall Ice Age mammal, known as the Megalonyx jeffersonii, was much bigger than the sloths of today, weighing up to 3,000 pounds.

The volunteer diggers expected to find just one skeleton. But, University of Iowa professor emeritus Holmes Semken said instead they found an entire family unit.

“So we have an adult, a sub adult and an infant living together. This is spectacular that nobody's ever seen this before,” he said. “It’s some sort of social unit. We like to think of it as mom and her kids.”

It’s one of the most complete giant sloth skeletons ever discovered, Semken said.

A diagram of the giant ground sloth shows which bones were discovered and analyzed by UI researchers
University of Iowa
The researchers found one of the most complete giant sloth skeletons to date.

Semken said they also collected and analyzed microfossils and sediments to learn about the animal’s environment and behavior. He said they were able to translate the discoveries of smaller species – like mollusks, sea clams and turtles – into a picture of the ecosystem and vegetation at the time.

“Paleontology is a lot of chance. You don't know what you're going to find when you start.” he said. “ When you find all of these areas of interest, surrounding the sloth, start putting it together it gets really exciting.”

The creatures roamed during the interglacial period in woodlands along a stream of marshes very similar to southwest Iowa today. The species became extinct around 10,000 years ago.

UI anthropology administrator Sarah Horgen helped coordinate the excavation for the Tarkio Valley project. She said she left the project with a greater appreciation of Iowa’s past.

“It wasn't just learning about giant ground sloths, which are these somewhat mysterious animals of the Ice Age, we learned so much about the actual environment of Iowa 100,000 years ago,” Horgen said.

Two people stand in the center of a large dig in southwest Iowa in 2001.
University of Iowa
Researchers collaborated with students to uncover the fossils of three giant ground sloths.

The sloth remains will be kept in the University of Iowa’s Paleontology Repository, overseen by collections manager Tiffany Adrain. The skeleton will be available for other researchers to look at and study from different perspectives.

Adrian said it’s important that the bones be preserved and made available to the public, in case technological advances allow even more information to be gleaned from the artifacts.

“You don't know what's going to be available to analyze them in the future,” Adrain said. “I've already had people calling me wanting to come and look at it as well to do their own studies.

Kendall was Iowa Public Radio’s western Iowa reporter based in Sioux City, IA until Jan. 20, 2023.