Megalonyx

Kingdom: Animalia
Phylum: Chordata
Order: Pilosa
Family: Megalonychidae
Genus: Megalonyx
Species: M. matthisi
               M. wheatieyi
               M. leptostomus
               M. jeffersonii

Conservation Status: Extinct
Temporal Range: Miocene to Pleistocene 

Megalonyx is an extinct genus of giant 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 around 10. 3 Million years ago to 11,000 years ago, existing for approximately 10.289 million years.

DESCRIPTION

Megalonyx certainly does not look like a sloth, it was a large, heavily built animal about 9.8 feet (3m) long. Its maximum weight is estimated at 1000 kg. This is medium-sized among the giant ground sloths. It is of the size of an American Bison. Like other ground sloths it had a blunt snout, massive jaw, and large peg-like teeth.

 HIND LEGS

It was not like the usual sloths what we have seen in the jungles of South America, it was built for living on the ground. Their hind was built like human feet, i.e. Megalonyx walked with heel, foot and toe bones all on the ground just what we do. This provided good surface area for carrying weight and better balance when the stood up. This is called 'Plantigrade' by the biologists. This provided good surface area for carrying weight and better balance when Megalonyx stood up. And Megalonyx probably spend a lot of time standing in order to eat. To give this giant ground sloth added stability and to ease the stress on its massive hind legs.

 TAIL

Except their massive legs the have a thick, muscular tail which is very rare for the land mammals. Its massive hips gave ample area for strong muscles, while Megalonyx spent time ripping down and feasting on soft leaves and fruit from the trees.

ARM

Bending down those huge branches to reach its mouth was the job of the Megalonyx's powerful arms. The arm and shoulder bones are large and have wide wings and large knobs where big muscles attached. Each of the three fingers on the hand was equipped with large, powerful claws upto 8 inches or 20 cm long. Unlike the claws of the modern lion these giant claws were mostly used to grasp and tear up branches and leaves. However, they also made for a very effective defense against the predators. One swipe of the arm of the Megalonyx may have been more powerful than a grizzly bear.

TEETH

One of the most peculiar anatomical  feature of sloths is their teeth, which lack the hard enamel found in the humans and nearly all other mammals. Instead, sloths possess simple peg-like molar (back) teeth made primarily of the material dentin. Dentin is much softer than enamel and wears out faster. The sloths teeth never stop growing. Because of this, Megalonyx could keep on eating even if a tooth was damaged, since the damaged part would wear out and be replaced by healthy dentin over time. Inlike nearly all other mammals, Megalonyx never had to worry about a chipped tooth.

TAXONOMY

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 Harian in 1825.

 

EVOLUTION

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). It belongs to the genus Megalonyx, a name proposed by Thomas Jefferson, future president of the United States, in 1797. M. jeffersoni was probably descended from M. wheatieyi, which was in turn was probably derived from M. leptostomus. This was named by Cope (1893). This species lived from Florida to Texas, north to Kansas and Nebraska, and west to New Mexico, Nevada, Oregon, and Washington. It is about half the size of M. jeffersoni.

 

HABITAT

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 first specimen  ever found in the Colorado was discovered at the Ziegler Reservoir site near Snowmass Village. The Firelands ground sloth fossils dated between 11,727and 11,424 B.C. represents the earliest known hunting activity by Ohioan Paleoindians.

SOCIAL BEHAVIOR

Aside from the basics of the size, food choice and general mobility it is often difficult to learn details of the life habits of animals from their fossils. But recently from an ongoing excavations at Tarkio valley in southwest lowa may reveal something of the familial life of Megalonyx. An adult was found in direct association with two juveniles of different ages, suggesting that adults cared for young of different generations.