Why Megalonyx?

I like giant sloths. Who wouldn't? Although almost all my work has been on Pleistocene and recent felids, the Pleistocene megafauna is so amazingly diverse that there are bound to be genera and species that capture the imagination.  The giant Xenarthra are so unlike anything that's around today that I cant help but wonder how they fitted into the ecology of ancient America, what they looked like in the flesh, and what the people who had the privilege of seeing them 10,000 years ago thought about them.  

A lot of the history of Quaternary study is closely tied to giant sloths. Megalonyx ("great claw"), as well as having a cool name, was the first superstar of American palaeontology. At a time when European palaeontology was starting out and people were impressed by remains of cave bears (Ursus spelaeus), cave lions (Panthera leo spelaea) cave hyaenas (Crocuta crocuta spelaea), Irish Elk (Megaloceros giganteus), and Mammoths (Mammuthus primigenius), these animals were used to argue that the Americas were somehow inferior and lacking in any comparable fauna.  

Megalonyx was named by Thomas Jefferson (American president and polymath) who was given some bones from western Virginia and correctly surmised they belonged to an animal about three times as large as a lion. He was also able to suggest it had some affinity to another recently discovered animal- the Megatherium, which had been dug up from the La Plata river in Paraguay and sent to the King of Spain. 

Megatherium and Megalonyx are both still regarded as valid genera of giant sloth. Jefferson, writing over 200 years ago, was smart enough to work out that his bones came from a giant animal, probably related to the "bradypus, dasypus, and pangolin" (i.e. sloths and pangolins) and very rare (at a time when most of western America was unexplored this seemed a safe bet). Given the state of palaeontology in the 18th century, Jefferson was certainly extremely prescient.  One of the most common Pleistocene Megalonychid sloths is named in his honour- Megalonyx jeffersonii.

See the original fossils that Jefferson described here.

More information on Megalonyx

Great reconstructions here.

Ref:

Jefferson, T. (1799)"A memoir on the discovery of certain bones of a quadruped of the clawed kind in the western parts of Virginia" Trans.Amer.Phil.Soc V4, P246-260