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Data Dump: West Texas Sloth Dung Find Brings the Ice Age to Life

photograph by Andrew Stuart. Paleontologist Jim Mead collecting the dung of a now-vanished ground sloth, in a Presidio County cave. Analysis of the dung has expanded knowledge of the region's Ice-Age past.

West Texas has a rich history in paleontology. Scientists have made finds here that have illumined the story of life on Earth.  

Now, an important new find has dropped. 

In remote Spirit Eye Cave, near Pinto Canyon in Presidio County, researchers found something rare – the preserved dung of an extinct ground sloth. It's nothing to pooh-pooh – in the right hands, ancient dung is powerful stuff. The scientists published their findings in fall 2021 – and they bring to life a vanished world.

Jim Mead is a paleontologist and chief scientist at the Mammoth Site, in Hot Springs, South Dakota.

“For somebody who wants to reconstruct diet and environment,” Mead said, “getting animals that eat different plants – well, you take a look at all of them, and then you get a great story, that's kind of funny, because it's all poop.”

Mead discovered his passion – the study of Ice Age dung – in 1969, on a scientific journey through the Grand Canyon. He's now the country's go-to expert for Pleistocene dung.

“As people work in various caves,” Mead said, “and they find dung, I guess it's good that they think of me, I don't know.”

Once targeted by collectors and looters, Spirit Eye Cave is now owned by businessman Jeff Fort, who supports research there. In 2019, archeologist Bryon Schroeder, director of Alpine's Center for Big Bend Studies, was excavating the cave's recesses when he encountered some unusual organic material. 

Another archeologist – interested only in the human past – might have dismissed it. But Schroeder knew better, Mead said.

“Thankfully, Bryon Schroeder – he had the knowledge to say even though it's not an artifact, it may be saying something,” Mead said, “and of course it does.”

Mead and Schroeder ultimately found two dung deposits – one dated to almost 13,000 years old, the other to more than 30,000 years old. Both belonged to a now-vanished creature called a Shasta ground sloth.

Four ground sloths roamed North America in the late Ice Age. Two species grazed the plains and grasslands, while the other two – including the Shasta sloth – browsed the hills and mountains. The Shasta sloth was the smallest – but still weighed in at a thousand pounds. And while it was slow-moving, it had powerful claws. An adult Shasta sloth probably wasn't easy pickings – even for such fierce predators of ancient West Texas as the short-faced bear or dire wolf. 

For sloths, it seems, the cave was a destination for morning ablutions. But the dung's preservation was thanks to another creature – the packrat. Packrats build their middens, or homes, using other creatures' dung – to conceal their own scent and confuse predators. One sloth dung sample was found in a packrat midden.

The find made Spirit Eye one of only 12 known Shasta dung sites. And it was the first proof these sloths lived in the area. But Mead knew the dung had other stories to tell.

Chad Yost is an “archaeobotanist,” specializing in the analysis of microscopic plant remains. 

“What I tell people is that, number 2 is often number 1 with me,” Yost said. “Because the preservation in fossilized dung for micro-fossils is usually really, really good.”

Mead brought Yost on to the project, and, in his lab, Yost analyzed dung samples – specifically to identify tiny fossilized plant remains called phytoliths.  

The findings shed light on the sloth's diet. And combined with Mead's analysis of larger plant remains in the dung, and the packrat midden, they reveal a Big Bend landscape different from the one we know today.

Both dung samples included grasses and sedges. And the more recent one – the 12,900-year-old dung – included remains from hackberries and oaks, and a little creosote. The sloth in question had also feasted on yucca leaves. 

Strikingly, the 30,000-year-old packrat midden contained juniper twigs and seeds, and pine needles. Packrats don't venture far from home. While the area around Spirit Eye is rough desert today, the findings show that in the Ice Age it was a piñon-juniper woodland – akin to the mid-elevations of the Chisos or Davis mountains. The presence of yucca and creosote in the younger dung could mean conditions were drying by the late Ice Age.

The work is just beginning. With Schroeder, Mead plans to return to Spirit Eye, and to visit other Big Bend caves. Mead is particularly keen to hunt the dung of the extinct shrub-ox – a bovine with the look of a wildebeest. 

Scientific insight can come from unexpected places. And when it comes to understanding the Ice Age – one creature's dung is a scientist's treasure.

Drew Stuart is the producer for the Marfa Public Radio series Nature Notes.