Sloth Dung: Hints of the Ice Age Past Dropped in a West Texas Cave
By Andrew Stuart
Limestone mesas dominate the foreground, the pale strata angling skyward above what, even by West Texas standards, is a rough dirt road. Above the mesas, higher still, is the Sierra Vieja, red mountains, molten in appearance, though the volcanic eruptions that laid them ended 30 million years ago.
Here, on the Pinto Canyon Ranch in Presidio County, researchers are traveling by all-terrain vehicle to Spirit Eye Cave. Collectors and looters dug the cave for a century. But what remains – in foodstuffs and fibers, in pot shards and tools – is broadening our understanding of Big Bend prehistory.
But cultural artifacts aren’t the purpose of this outing. Archeologist Bryon Schroeder, of Alpine’s Center for Big Bend Studies, is escorting a different kind of scientist. Jim Mead is a paleontologist – and the self-described “number 1 number 2 man.”
Spirit Eye is an impressive cave system. Its vast central chamber was targeted by artifact-hunters. But narrow shafts deep in the cave remain undisturbed. It was in one of these shafts that Schroeder uncovered a curious layer of reddish-brown organic material.
He didn’t know what it was, but he knew it was old, that it dated to the Ice Age, when people first arrived here. He asked specialists in this “Paleoindian” period what he might be overlooking.
“And the resounding answer was: sloth poop,” Schroeder said. “’We would all ask you why it’s not sloth poop.’ ‘Who do I talk to about that?’ And Jim’s name came up every single time, that you’ve got to talk to Jim. His poo precedes him.”
Mead is an expert in Ice Age dung.
“A PhD does mean ‘pile it higher and deeper,’” Mead said, “and in this case, it’s spot on.”
Mead is the chief scientist at the Mammoth Site in Hot Springs, South Dakota. He’s excavated caves in the Grand Canyon, with sloth dung deposits 5 feet thick. Schroeder mailed him a sample of what he’d found. Mead made the ID – this was the 13,000-year-old dung of a Shasta ground sloth, the first proof they lived in the Big Bend.
Mead wanted more – and Schroeder thought of a bolus – a turd – he’d seen in another shaft, and which he’d taken for a donkey apple. This too was ground sloth dung, and it was 30,000 years old.
Mead is here today to collect more samples.
Shasta ground sloths were browsers in canyons and mountains. They were smaller than the plains-dwelling Megalonyx sloths, but still weighed in at 500 pounds. Spirit Eye may have been a nesting cave.
There may have been dung deposits in the main chamber, removed when collectors dug. This poo endured because of another creature – the packrat.
In assembling their debris piles, or middens, packrats gather rocks, plants – and poop. Diverse dung smells can confuse predators. Packrats often cement the debris together with their own urine. It was Pleistocene packrats that spirited this dung into the cave’s recesses.
Mead has a nose for middens. He can estimate the age from texture, and smell.
It’s a specialty that invites puns. But it’s also powerful science.
Even a casual glance at the midden is revelatory. There are juniper berries. Today, juniper is found at much higher elevations. But plant communities were different in the cooler, wetter span of the Ice Age.
By analyzing plant material, as well as microscopic pollen in the dung, Mead will be able to create a picture of what the Pleistocene Big Bend looked like.
“So this is the kind of empirical data that we needed,” Mead said. “We don’t have the bones, but we have the dung, so we can say, this is what they’re eating here. That tells us what the environment is here. That’s reconstruction of the Ice Age environment.”
The insight is a testament to Spirit Eye’s rich record. It’s also a testament to collaboration, Mead said.
“This is opening up a new door,” he said, “because a lot of times archeology stops when the cultural [material] stops. My message is, every archeologist who digs in a dry cave, if you have sediments below cultural, please dig down and tell me what you have, because there’s probably a record that is incredibly interesting. And Bryon has done that. He knows his sh**.”
Nature Notes is supported by the Shield-Ayres Foundation and produced by Marfa Public Radio with the Sibley Nature Center. The program can be heard each Tuesday and Thursday, at 7:45 a.m. and 4:45 p.m., Central time, on KRTS Marfa, 93.5 FM, and KXWT Odessa/Midland, 91.3 FM. This episode was written by Andrew Stuart.