- Megalonyx jeffersonii
- Pleistocene Age
- Dixie County, Florida
- This specimen measures approx. 2″ long and even retains a portion of the sheath.. Specimen will come in the 3.25″ x 4.25″ Riker Mount with Label as Shown
Megalonyx (Greek, “large claw”) is an extinct genus of ground sloths of the family Megalonychidae endemic to North America from the Hemphillian of the Late Miocene through to the Rancholabrean of the Pleistocene, living from ~10.3 Mya—11,000 years ago, existing for approximately 10.289 million years. Type species, M. jeffersonii, measured about 3 m (9.8 ft) and weighted up to 1000 kilograms.
Megalonyx was a large, heavily built animal about 9.8 feet (3 m) long. Its maximum weight is estimated at 1,000 kg (2,205 lb). This is medium-sized among the giant ground sloths. Like other ground sloths it had a blunt snout, massive jaw, and large peg-like teeth. The hind limbs were plantigrade (flat-footed) and this, along with its stout tail, allowed it to rear up into a semi-erect position to feed on tree leaves. The forelimbs had three highly developed claws that were probably used to strip leaves and tear off branches.
Megalonyx ranged over much of North and Central America. Their remains have been found as far north as Alaska and the Yukon.
M. jeffersonii was apparently the most wide ranging giant ground sloth. Fossils are known from many Pleistocene sites in the United States, including most of the states east of the Rocky Mountains as well as along the west coast. It was the only ground sloth to range as far north as the present-day Yukon and Alaska.
The generic name Megalonyx was proposed by future U.S. President Thomas Jefferson in 1797, based on fossil specimens of what later came to be called Megalonyx jeffersonii that he had received from western Virginia. His presentation to the American Philosophical Society that year is often credited as the beginning of vertebrate paleontology in North America. However, Jefferson’s name has no validity in zoological nomenclature, and Megalonyx was first formally named by Richard Harlan in 1825.
Megalonyx evolved from ancestors that island-hopped across the Central American Seaway from South America, where ground sloths arose, prior to formation of the Panamanian land bridge. Its appearance in North America thus predates the bulk of the faunal exchange between North and South America. Its immediate predecessor was Pliometanastes and its closest living relatives are the two-toed sloths (Choloepus).
M. jeffersoni lived from the Illinoian Stage during the Middle Pleistocene (150,000 years BP) through to the Rancholabrean of the Late Pleistocene (11,000 BP).