Giant Sloths Died Wallowing in Their Own Feces, Paleontologists Suggest

Evidence collected from an ice age boneyard suggests a group of giant ground sloths died wallowing in their own feces, say scientists.

In a study published in Palaeogeography, Palaeoclimatology, Palaeoecology, scientists led by Emily Lindsey, from the La Brea Tar Pits and Museum, California, describe the remains of at least 22 sloths of the now-extinct species Eremotherium laurillardi.

They were discovered at Tanque Loma, a site on the Santa Elena Peninsula in southwest Ecuador. The bones are between 18,000 and 23,000 years old.

The site includes the fossilized remains of other animals, including a horse, a deer, an elephant-like creature called a gomphothere and another species of ground sloth, a Mylodon. However, E. laurillardi dominates. According to the researchers, 575 of the 667 fossils analyzed in the study belonged to members of this species.

A closer analysis of the bones reveals the sloths buried in Tanque Loma were part of a multigenerational group, containing at least 15 adults, one subadult and six juveniles. The combination of age groups and the arrangement of the remains is indicative of a mass mortality event where a group of individuals died at around the same time, the researchers say.

Before they went extinct, giant ground sloths were among the most common large vertebrates living in the Americas. According to a paper published in Science Advances last year, E. laurillardi could reach lengths of 19 feet and was widely distributed across the Americas. Its ranged extended from southern Brazil to North America's Gulf and Atlantic coast.

But while they frequently pop up on South America's fossil record, the Lindsey and colleagues say little is known about their behavior and social structure.

According to the latest paper, the fossils at Tanque Loma suggest the E. laurillardi may have been social and "gregarious" creatures that congregated near water sources. Sediment from the soil suggests the site used to be a shallow marsh where the sloth wallowed to cool off, much like rhinos, warthogs and other large herbivores living in arid and tropical habitats do today.

The assemblage of the bones and the chemical composition of the sediment also offers clues to the circumstances of the deaths. Because sloths of all ages are present, the team say disease or an attack by a predator are unlikely, as in this case you would see a greater prevalence of young and old.

A natural disaster, such as a volcano or a tsunami, can also be ruled out because the sediments do not contain ash or charcoal. They also say entrapment is unlikely because of the terrain.

Instead, the researchers say the most likely scenario is that the sloths died as a result of drought, disease, poisoning or a combination of the above—and possibly as a result of contamination from their own fecal matter.

The researchers compare the extinct sloths to the modern day hippopotamus to explain how this die-off may have occurred.

In the early 1970s, scientists monitoring a group in the Selous Game Reserve, Tanzania, noted a population of around 140 hippos, which had gathered around a singular watering hole at the beginning of the dry season. The behavior was not unusual. Hippos frequently congregate in large groups in water to wallow, remaining submerged to protect themselves against the glaring sun and from biting insects.

On this occasion, drought caused the water hole to start drying up, but the hippos continued to wallow in the water. The drought continued and the amount of water fell, while feces piled up, contaminating the surroundings. In the space of a week, herd numbers fell from 140 to around 40 individuals.

The researchers suspect something similar may have occurred to the giant sloth at Tanque Loma 18,000 years ago.

"Taking observations from modern megafaunal ecosystems as an analogue, we suggest that this death event could have resulted from drought and/or disease stemming from the contamination of the wallow, paralleling situations observed among hippopotamus populations in watering holes on the present-day African savannah," they wrote.