The Megatherium and the Mylodon by Édouard Riou from Chatterbox Magazine, 1880, pg. 349

Today's animal of the day is Mylodon darwini!

Image credit: Carlost1205 on DeviantArt

This species of ground sloth lived during the Late Pleistocene in what is now the southernmost region of South America. While not the largest species of ground sloth, that would be Megatherium americanum, they were still fairly large animals and had a total body length between 9 to 13 ft long and could weigh around 1 to 2 tons. Its remains were first found by Charles Darwin embedded in a cliffside in Argentina, during his infamous expedition on the HMS Beagle in the year 1832. However, it wasn't until 1840 that the species was officially described and named by paleontologist Sir Richard Owen. The genus name Mylodon means "molar tooth", while the species name was chosen to honor Darwin for discovering the first specimen.

Image credit: prehistoric-wildlife.com

Since the fossils of this species were discovered in 1832, many more fossils belonging to this ground sloth have been discovered. There is even a cave in Chile called the Cueva del Milodón, where tons of extremely well-preserved Mylodon fossils have been discovered, including fossilized dung, skin fragments, and bits of fur! In fact, these specimens were so well-preserved that in the early 20th century, they were mistaken for fresh dung and fur samples, and there were multiple serious expeditions sent out to find living Mylodons!

Photo credit: FunkMonk

Sadly, Mylodon darwini is confirmed to have gone extinct sometime between 10,000 to 12,000 years ago, around the start of the Holocene epoch, and the reason why these remains looked so fresh is thought to have been because of a combination of the extremely cold temperature, as well relatively unchanging environment inside the cave where they were found. Despite this, Mylodon is thought to have co-existed alongside the first humans to inhabit the Americas, but went extinct very soon after they first arrived in South America. While ancient humans very likely did hunt these ground sloths, it's likely that the species was already going extinct due to climate change, so while hunting by humans certainly didn't help the Mylodon, they also probably weren't the sole cause for them going extinct.

Image credit: agustindiazart on DeviantArt

The shape of Mylodon's teeth, as well as analysis of the materials found in fossilized dung, suggest that Mylodon's diet mostly consisted of grasses and sedges. Which would make sense since the environment it lived in was fairly cold with lots of grasses and only a few large trees and bushes scattered about. That's not to say that grass was the only thing that Mylodon ate. The skull of Mylodon has a closed nasal arch that is quite rough, which suggests that it had a lot of muscle attachments in this area when the animal was alive. Some paleontologists think this suggests that Mylodon would have had a flexible upper lip that it could use to pull tree branches and other larger plants into its mouth. A study in 2021 that looked at the isotope ratios found in fossilized Mylodon dung also suggests that these ground sloths would occasionally eat meat when the opportunity presented itself.

Image credit: Jorge Blanco

While it's more likely that Mylodon would have scavenged off the leftovers of other predators, rather than actively hunt their own prey, the large, sharp claws on their front limbs wouldn't have just been for show. They were likely used to help defend themselves against predators. Fossils found with teeth marks embedded i them show that Mylodon would have had a wide variety of predators such as cougars, jaguars, Smilodon, and even Arctotherium, a genus of giant extinct bears! Like many modern-day xenarthrans (sloths, anteaters, and armadillos), Mylodon's claws could have been used to fight off attackers. There's also some evidence that suggests Mylodon may have used its claws to help dig burrows, which we know some other species of ground sloths did. However, analysis of Mylodon's wrist strength suggests that they wouldn't be super good at it. So, while they could probably dig their own burrows if they needed to, they probably would prefer to take over abandoned burrows made by other animals or seek shelter in naturally occurring caves and caverns.

Image credit: Carlost1205 on DeviantArt

Mylodon from The Ancient World or, Picturesque sketches of Creation by D. T. Ansted (John Van Voorst, London, 1847), after François Jules Pictet 1844