What a Drawerful of Dung Reveals About the Lives of Ground Sloths

For International Sloth Day, learn about the scientific clues preserved in petrified poop

Several large chunks of fossilized poop that prehistoric ground sloths left in an Arizona cave tens of thousands of years ago. Jack Tamisiea, NMNH

With approximately 148 million specimens and objects in its collection, the vast majority of the National Museum of Natural History’s specimens are off display. But each of these specimens — whether it be a moth, meteorite, moss or mammoth — tells a story that helps museum researchers make sense of the natural world. Each month, the Specimen Spotlight series will highlight a different specimen or object from the world’s largest natural history collection to shed light on why we collect.

With roughly 40 million fossils spanning the entire history of life on Earth, the National Museum of Natural History is home to one of the largest and most comprehensive paleobiology collections in the world. But some of the collection’s most adored specimens are also its strangest.

Several of the museum’s Shasta ground sloth dung specimens. Chip Clark, NMNH

“It’s fun to think about just how many people have seen the contents of these drawers,” said Kathy Hollis, the museum’s paleobiology collections manager. Whenever Hollis gives a tour of the collection, she usually stops here to show off a sampling of the museum’s unparalleled collection of coprolite, or fossilized feces. While these clumps of dung would not look out of place in the elephant enclosure at the National Zoo, these pieces of poop were left behind more than ten thousand years ago by giant ground sloths.

“Maybe people are just being polite, but everyone seems surprised and happy when I show them the drawers of dung,” Hollis said. “I sure find the dung delightful!”

Athena, the National Zoo's Southern two-toed sloth. Unlike their much larger prehistoric predecessors, modern sloths spend most of their time in the rainforest canopy, often only descending to the forest floor once a week to defecate. Roshan Patel, Smithsonian's National Zoo

In celebration of International Sloth Day, Smithsonian Voices dug into the backstory of these drawers of dung to learn why petrified poop is a gold mine of paleontological data.

Coprolite Cave

Located near the western end of the Grand Canyon in Arizona, Rampart Cave is one of the world’s preeminent deposits of dung. When the narrow cavern was discovered in the mid-1930s, most of its floor was composed of coprolite left behind by  the chamber’s previous inhabitants: Shasta ground sloths (Nothrotheriops shastensis). These black bear-sized herbivores lived throughout the southwest during the last ice age. They used their powerful cheek teeth to grind tough desert plants and harnessed their sharp claws to keep dire wolves and sabertooth cats at bay.
An archival image of Rampart Cave in 1938. The rock-like material littering the floor is  actually fossilized clumps of sloth poop. National Park Service

From 40,000 to as recently as 11,000 years ago, lumbering Shasta ground sloths did their business in Rampart Cave. Over the eons, their dung piled up. In some spots, the fossilized excrement accumulated to depths of nearly twenty feet.

The museum’s fossilized droppings were collected by Smithsonian paleontologist Remington Kellogg in 1942. (Kellogg would later become the director of NMNH and the assistant secretary during his nearly 40-year career at the Smithsonian.) Kellog’s team also collected Rampart Cave’s bounty of fossil bones. Most of these bones were from the generations of Shasta ground sloths that frequented the cave. The vast amount of juvenile sloth bones has led some scientists to speculate that the cave was a sloth nursery.
A Shasta ground sloth skull in the Grand Canyon National Park Museum’s collection. National Park Service

In addition to the stockpile of sloth bones, researchers have uncovered remains from dozens of other species in Rampart Cave. These include fossils from still-living critters like desert tortoises, mountain lions, vultures, packrats and bighorn sheep as well as several now-extinct creatures including  an ancient horse, mountain goat and vampire bat. The cave’s arid conditions were perfect for not just the preservation of poop, but also soft tissue, like skin and cartilage, that are often lost in the fossilization process. Researchers have even found bits of sloth fur here.

Kellogg brought many of these specimens back to Washington and deposited them in the museum’s collection for safekeeping. This turned out to be a stroke of luck decades later when vandals broke into Rampart Cave and started a fire in 1976. Roughly 70 percent of the cave’s dung deposits were destroyed in the flame.

A sampling of fossil scat from Rampart Cave in the museum’s collection. The smaller pellets to the bottom left of the drawer are from the site’s ancient mountain goats. Jack Tamisiea, NMNH

Dropping(s) Knowledge

The museum’s drawerful of dung not only fascinates visitors from far and wide, but it provides  insight into the ecology of these prehistoric giants. Because the clumps are so well preserved, scientists can sift through the scat to find pieces of the plants the sloths were eating during the Pleistocene epoch. Researchers have found the remains of seven different plant species in Rampart Cave’s sloth dung. These include rugged desert staples like yucca, saltbush and cacti. Shasta ground sloths also snacked on fruit from Joshua trees and dispersed the plant’s seeds in their dung. The disappearance of these seed-spreading sloths is believed to be one factor impacting the current distribution of the iconic tree.

The mummified dung not only reveals what was on the ground sloth’s menu but also what was wiggling around their guts. Several samples of the site’s sloth poop contain parasites like roundworms and single-celled protozoa that infected these large herbivores. At least one piece of sloth excrement was found to contain parasitic worm eggs.

A sample of mummified sloth poop (right) next to a giant hyena’s fossilized feces (left) appropriately displayed next to a public restroom across from the museum’s FossiLab. Jack Tamisiea, NMNH

Information preserved in coprolites has helped paleontologists understand how all manner of prehistoric animals lived. Scientists have analyzed fossilized scat from Tyrannosaurus rex and other dinosaurs, mammoths and even ancient humans. They have also identified new species in clumps of coprolite, such as a prehistoric species of beetle embedded in a 230-million-year-old prehistoric reptile’s droppings.

Rampart Cave’s dung is particularly rich in ecological clues and may even reveal what drove these mega-herbivores to extinction 11,000 years ago. Some researchers think that because the clumps of dung are packed with the remnants of plant species still living in the area, the ground sloths would have had plenty to eat as a warming climate closed the ice age. Instead, hunting by the region’s early human population likely doomed these sluggish sloths. Thankfully, their ecological legacy is preserved in the museum’s drawers of dung.

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