Megatherium

Megatherium (/mɛɡəˈθɪəriəm/ meg-ə-THEER-ee-əm from the Greek mega [μέγας], meaning "great", and therion [θηρίον], "beast") was a genus of elephant-sized cenozoic ground sloths endemic to South America, sometimes called the giant ground sloth, that lived from the Early Pliocene through the end of the Pleistocene. Only a few other land mammals equaled or exceeded Megatherium in size, such as large proboscideans (e.g., elephants) and the giant rhinoceros Paraceratherium. Megatherium was first discovered in 1788 on the bank of the Luján River in Argentina. The holotype specimen was then shipped to Spain the following year wherein it caught the attention of the esteemed paleontologist Georges Cuvier, who was the first to determine, by means of comparative anatomy, that Megatherium was a sloth.

Sid

Megatherium is one of the largest land mammals known to have existed, weighing up to 4 tonnes and measuring up to 6 m (20 ft) in length from head to tail. It is the largest-known ground sloth, as big as modern elephants, and would have only been exceeded in its time by a few species of mammoth . The group is known primarily from its largest species, M. americanum. Megatherium species were members of the abundant Pleistocene megafauna, large mammals that lived during the Pleistocene epoch.
It had a robust skeleton with a large pelvic girdle and a broad muscular tail. Its large size enabled it to feed at heights unreachable by other contemporary herbivores. Rising on its powerful hind legs and using its tail to form a tripod, Megatherium could support its massive body weight while using the curved claws on its long forelegs to pull down branches with the choicest leaves. This sloth, like a modern anteater, walked on the sides of its feet because its claws prevented it from putting them flat on the ground. Although it was primarily a quadruped, its trackways show that it was capable of bipedal locomotion. Biomechanical analysis also suggests it had adaptations to bipedalism.

Megatherium had a narrow, cone-shaped mouth and prehensile lips that were probably used to select particular plants and fruits. While some evidence suggests the animal could use its tongue to differentiate and select its foliage, the lips probably had a more important role in this. Like other sloths, Megatherium lacked the enamel, deciduous dentition, and dental cusp patterns of other mammals. Instead of enamel, the tooth displays a layer of cementum, orthodentine, and modified orthodentine, creating a soft, easily abraded surface. The teeth of M. americanum exhibit extreme hypsodonty, indicative of its gritty, fibrous diet. Their teeth laterally show interlocking V-shaped occlusion surfaces, though they are nearly square in cross-section and exhibit bilophodonty. The teeth are spaced equidistantly in a series, located posteriorly in the mouth, which leaves space at the predentary; there is no diastema, though the length of this tooth row and of the predentary spout can vary by species. Analysis of wear and the biomechanics of the masticatory muscles suggests that they chewed vertically. Megatheres displayed deeper jaws than other sloth clades. Some of the elements in the oral cavity of Megatherium were fused together: a rigidly articulated stylohyal and epihyal, and the apparatus lies farther anteriorly, which together with the elongated, steeply inclined mandibular symphysis, indicates a relatively shorter geniohyoid muscle and thus more limited capacity for tongue protrusion. It was well adapted for strong, predominantly orthal (up-down) movement for eating rough vegetation.[citation needed] Megatherium possessed the narrowest muzzle of all ground sloths from the Pleistocene. This leads paleobiologists to believe that it was a very selective eater. It had the ability to pick and choose which leaves and twigs it would consume. Megatherium had a large narrow prehensile lip that was capable of grabbing and tearing off particular leaves and twigs and other sorts of vegetation.

According to one study, Megatherium was probably mostly hairless (like modern elephants) due to its large mass making it susceptible to overheating.