Good tidings and well-wishes!
Even when one takes into consideration the incredibly diverse menagerie of Pleistocene megafauna known to science, an irrefutable charm accompanies the epoch’s famed ground sloths. Since the xenarthra is my second favorite superorder of mammals (following the afrotheria), I’m well acquainted with this phenomenon. After all, unlike other well known megafaunal beasts of this fascinating chapter in Earth’s history, there’s really nothing presently alive one could compare to a Megalonyx or Paramylodon. Adding to this prestige is the little-known fact that ground sloths were actually a highly diverse bunch. Thalassocnus was a genus designed for a heavily sub-aquatic lifestyle, Megalonyx may have sucked the blood of fellow megamammals on occasion, whilst the famed Megatherium possibly killed creatures as large as a glyptodont to provide further sustinence to its diet. Given the group’s South American origins, ground sloths have also become arguably the best-known northern acquisition of the great American faunal interchange which began approximately 3 million years ago.
Like their modern kin, ground sloths belong to the order pilosa which includes all living sloths and ant-eaters. Pilosa is further subdivided into two suborders: vermilingua (which contains the ant-eaters) and folivora (which contains the sloths). The modern families of this latter group are the Choloepidae and Bradypodidae, or two-toed and three-toed sloths respectively. The extinct ground sloths were divided into the following families: Megatheriidae (the ‘flat-footed’ ground sloths such as Megalonyx), Megalonychidae (the ‘browsing’ ground sloths such as Megatherium), Mylodontidae (the ‘grazing ground sloths’ such as Mylodon), Scelidotheriidae (the ‘long-faced’ ground sloths like Scelidotherium), and Orphodontidae (information concerning which strangely eludes me, does anyone have some references on these guys?). I could spend a few week’s worth of posts describing these various families, but once again, I’ve gone multiple paragraphs into a post without discussing the creature at hand: Eremotherium sp.
Before I can do this, however, a little further attention geared towards the Megatheriidae, to which Eremotherium belonged, is necessary. In his book “Ice Age Mammals Of North America”, life-long Pleistocene enthusiast and professor of economic geology at the University of Montana at Missoula Ian Lange explains:
“In the earliest Oligocene time, about 36 million years ago, browsing ground sloths made their debut in South America, where they shared a common ancestry with the flat-footed ground sloths, family Megalonychidae. The two major groups of Megatheriidae are the megatheres and nothrotheres, which had similar skull structure and shared many other aspects but differed greatly in size. The nothrotheres, such as the Shasta ground sloth [Nothrotheriops], were slightly built, reaching a length of approximately 4 feet (1.2 meters). The megatheres, Megatherium and Eremotherium, in comparison, were huge animals that could weigh up to 3 tons (2,700 kilograms) and attain lengths of more than 20 feet (6 meters).”
Despite the obvious similarities of the two genera, one of the easiest ways to distinguish an Eremotherium from a Megalonyxis to count the creature’s hands and feet. While the former genus had three well-developed digits on each forelimb with claws located on III and IV, the latter sported four such refined digits and three claws found on numbers II through IV. Like all Megatheriids, Eremotheriumwalked on the sides of its hindlimbs in a stance known as pedolateralism. Similarly, all members of this family supported nearly all of their weight on digit V (with some of it placed on digit IV), though Nothrotheriops and Megatherium did so to a much greater extent. For more information on North American ground sloth locomotion, do go here (the site’s accompanying picture is displayed below).
Geographically, while Megatherium (most likely) remained in South America, Eremotheriummade its way north and has subsequently been unearthed in Georgia, South Carolina, Texas, Florida, and various regions in Central America, including El Hatillo, Panama, which boasts what are often considered to be the best specimens.
‘Megatheres’ are believed to have been browsers primarily because of their massive tails with which they could have either stood upright or sat in order to devour arboreal treats. This scenario is given further credibility when one considers individuals hailing from lagerstatte. According once again to Ian Lange:
“Remains of vegetation from the stomachs of Eremotherium found in Peruvian and Ecuadorian tar pits show these animals browsed on twigs including thorn bushes, which are typical of a savanna environment.”
Furthermore, many paleontologists reconstruct ground sloths with large, giraffe-like tongues, which povides additional plausibility to this niche.
For more Eremotherium goodness, check out this link at the University of Florida.
May the fossil record continue to enchant us all.