Largest sloth ever

The title for the largest sloth that ever lived is currently shared between Eremotherium and Megatherium, two prehistoric giant ground sloths that weighed in at around 4 tonnes (4.4 tons), and when standing on two legs could tower to more than 3.5 m (11 ft 6 in) in height. For a comparative scale, a modern three-toed tree sloth (Bradypus spp.) has a body length of 45 cm (1 ft 6 in), and weighs up to 4.5 kg (9 lb 15 oz).

The ancestor of both tree sloths and ground sloths first appeared in South America over 40 million years ago. The term “tree” and “ground sloths” reflect the build and lifestyle of the beasts, as opposed to formalized categories of classification (taxonomy). Today’s three-toed sloths, for instance, are far more closely related to Eremotherium and Megatherium than to the modern two-toed sloth. That said, the two-toed sloths are equally endowed in their kinships by gigantic prehistoric cousins, with the South American ground sloths Lestodon and Mylodon, which weighed up to 3.75 and 2 tonnes (4.1 and 2.2 tons), respectively. The diverse landscapes of South America had an influence on the ecology and distribution of ground sloths. Megatherium and Mylodon preferred the badlands of Uruguay and Patagonia, not to be found in the tropics of Brazil which saw the domain of Eremotherium; whereas Lestodon was common to the Uruguayan Pampas east of La Plata River, where Megatherium was rare.

Despite their similar size, the skeleton of Eremotherium differs most notably from Megatherium by its longer limbs and more gracile skull, consistent with modern tropical mammals that are typically less robustly constructed than their cousins inhabiting cooler regions, for ease of heat loss by having a greater total surface area to volume ratio. Such tropical adaptation allowed Eremotherium to expand its range further northwards into Panama and Mexico, reaching as far north as Florida, Georgia, South Carolina and New Jersey in the USA, earning the beast the occasionally used vernacular name of the "pan-American giant ground sloth".

Eremotherium was one of several ground sloths to have enjoyed fresh frontiers up north after the Panamanian Land Bridge fully joined North and South America around 2.5 million years ago. The most northerly distributed of these South American migrants was the Jefferson’s ground sloth Megalonyx, with remains found all over the USA, as far north as Alaska and the Canadian Yukon.