A drawer of ancient sloth dung might not be the first place you would look for an Ice Age story. To a palaeontologist, though, every preserved pellet can be a tiny time capsule filled with traces of lost meals and changing landscapes.
The animal behind some of the best-known specimens was the Shasta ground sloth, Nothrotheriops shastensis. It lived in western North America during the Pleistocene and disappeared around the end of the last Ice Age. Unlike today's tree sloths, it walked on the ground. Yet it was still part of the same extraordinary sloth family tree.
Meet the Shasta ground sloth
The phrase “giant ground sloth” can bring to mind an elephant-sized animal towering over the landscape. Ground sloths were wonderfully varied, however. According to the US National Park Service, the Shasta ground sloth was one of the smaller North American forms, although “small” is doing a lot of work here. It could reach about nine feet in length and weigh up to roughly 550 pounds.
Its fossils have been found across the arid American Southwest. Dry caves were especially important because they could preserve material that would normally decay, including hair, skin and enormous quantities of dung. In a damp environment, most of that evidence would vanish. In a sheltered desert cave, it could survive for thousands of years.
Why old dung is scientific treasure
Fossilised or naturally preserved dung is often called a coprolite. It offers something bones cannot: a direct record of what passed through an animal's digestive system. A skeleton can suggest whether teeth and jaws were suited to browsing or grazing, but plant remains in dung can identify parts of the actual menu.
Researchers can examine tiny pieces of leaf, fibre, seed and pollen under a microscope. They can compare the structures with modern plants, measure which plants appear most often and look for changes between layers deposited at different times. In some cases, molecular techniques can recover ancient DNA as another line of evidence.
That does not make every meal perfectly visible. Soft foods may disappear more readily than tough fibres, and preservation can favour some evidence over others. Coprolites are best understood alongside bones, teeth, cave sediments, pollen and dates. The strength comes from several clues pointing in the same direction.
More than 500 pieces of evidence
One classic study of Shasta ground sloth food habits examined more than 500 pieces of dung from Rampart Cave in Arizona and compared them with material from nearby caves. The study record hosted by the University of South Florida Digital Commons explains that researchers used microhistological analysis to identify and quantify plant remains.
The results did not reveal one monotonous food. An archived San Diego Zoo Wildlife Alliance ground-sloth fact sheet notes that pollen studies connected Rampart Cave dung with dozens of plant genera. Desert globe mallow, saltbushes, agaves and other dry-country plants appear in reconstructions of the Shasta ground sloth's diet.
This turns a pile of dung into a surprisingly detailed portrait: a large herbivore moving through a dry landscape, browsing shrubs and desert plants rather than living like a modern leafy-canopy specialist.
A menu can reveal a changing landscape
Cave deposits build in layers. When scientists compare older and younger samples, changes in the plants can reflect changes in local vegetation, climate or the seasons in which animals used the cave. Dung can therefore tell two stories at once. It records the eater, but it also records the world around the eater.
This is why a specimen does not have to be beautiful to be valuable. A dramatic skull may draw a crowd, while a plain brown coprolite quietly preserves ecological detail that the skull cannot. Museum collections keep that evidence available for new questions and new techniques long after it was first collected.
What ancient dung cannot tell us alone
It is tempting to turn a handful of plant fragments into a complete daily routine, but careful science leaves room for uncertainty. Dung from a cave represents particular animals, places and periods. It may not capture every habitat the species used or every food available across its full range.
Even the word “fossilised” needs care. Some cave dung is mineralised like a classic fossil, while other samples are better described as dried or mummified because arid conditions preserved much of the original material. Both can be ancient and scientifically useful.
The best conclusion is also the most interesting one: these remains give us unusually direct glimpses of individual meals, then researchers combine hundreds of glimpses to test a bigger ecological picture.
A strange link between living and extinct sloths
Today's sloths live mostly in tropical forest canopies and follow a very different way of life. Their extinct relatives included ground-dwelling animals adapted to deserts, woodlands, grasslands and even coastal environments. The sloth story is much larger than the slow green animals we know now.
A piece of Shasta ground sloth dung makes that deep history tangible. It tells us that sloths once browsed agaves and shrubs in North American desert country, and that evidence of those meals could wait in a cave for scientists to find it.
Not every treasure sparkles. Sometimes it sits in a museum drawer, looks suspiciously like old poo and holds an entire Ice Age menu inside.
Sources
- US National Park Service: Giant Ground Sloths
- University of South Florida Digital Commons: Shasta ground sloth food habits, Rampart Cave, Arizona
- San Diego Zoo Wildlife Alliance archived fact sheet: Diet and Feeding of Extinct Ground Sloths
Featured image: reconstruction of Nothrotheriops shastensis by Dmitry Bogdanov, via Wikimedia Commons, licensed under CC BY-SA 4.0.