Megatherium

Abstract: The fossil xenarthrans include giant forms, the ground sloths (Tardigrada), characteristic of the mammal fauna of the Pleistocene of South America. Although most authors agree in considering them as herbivorous, these forms have not been studied in terms of detailed morpho-functional analyses of their masticatory apparatuses. The aim of this work is the study the masticatory apparatus of the large Pleistocene ground sloths Glossotherium robustum, Lestodon armatus, Mylodon darwini and Scelidotherium leptocephalum (Mylodontidae) applying biomecanichal and morphogeometrical methods, and to compare with the information obtained for Megatherium americanum (Megatheriidae). The results are integrated with recent ecomorphological analyses that include three variables (hypsodonty index, dental occlusal surface area and relative width and shape of the muzzle) providing useful information for the inference of dietary habits and to propose a niche partitioning among these species. Glossotherium robustum and Lestodon armatus, the wide-muzzled sloths, were mostly bulk-feeders (i.e. ingest great amounts of food with each bite; probably grass and herbaceous plants). Mylodon darwini and Scelidotherium leptocephalum, the narrow-muzzled sloths, were mixed or selective-feeders (i.e. select plants or plant parts; grass and/or tree and shrubs foliage). The tooth design of mylodontids indicates that teeth were used mainly for crushing and grinding turgid and fibrous items respectively. Megatherium americanum was probably the most selective feeder among these sloths, and selectively fed on particular plants (shrubs) or plant parts (leaves, twigs, fruits). Its dentition was designed mostly for cutting soft but tough items which might include flesh, leaving open the possibility of an omnivorous diet.

Abstract: The traditional point of view that fossil ground sloths (Xenarthra) were a relatively uniform, ecologically little diverse group has been recently challenged. Marine habits have been ascribed to Thalassocnus natans of the Pliocene of Peru. Also, a more diverse diet has been proposed by one of us (R.A.F.) for some Lujanian (late Pleistocene-early Holocene of South America genera of ground sloths. In this paper, an aspect of this latter hypothesis is tested, i.e. that Megatherium americanum had morphological features that are better explained by its having had carnivorous habits rather than by solely herbivorous ones. Specifically, the question of its forearms having been designed for optimizing speed rather than strength of extension is addressed. Such a trait might have been associated with a potentially aggressive use of the animal large claws, whereas a strong extension would be more proper for tearing branches out. On the other hand the high mechanical advantage of the biceps might have made it possible for the animal to have lifted and carried heavy weights. This in turn, suggests the possibility that the animal could have manipulated large prey (for instance, turning dorsally armoured preys or carcasses upside down to expose softer parts and cached large food pieces in a safer place. By this view, Megatherium americanum would be the largest land mammal hunter to have existed.

Abstract: South America’s peculiar extinct mammalian fauna has been a source of fascination since the late 1700’s when a Pleistocene skeleton of the giant ground sloth Megatherium, later described by Cuvier (1796, 1812), was unearthed and sent to Spain by the Dominican Manuel Torres. Strange new Pleistocene discoveries continued to be made throughout the 19th Century (see, for instance, Darwin, 1839; Lund, 1841; Owen, 1842). Toward the end of the 1800’s the Tertiary faunal history of South America began to be documented, notably by the famous Ameghino brothers. The history of 19th- and 20th-Century vertebrate paleontology in South America, however, has been the subject of excellent summaries elsewhere (e.g., Simpson, 1940, 1948, 1967, 1978; Marshall et al., in press a,b) and will only be mentioned briefly where appropriate here. The purpose of this study is to provide a critique of theories of the origin, rather than the full history, of the early mammalian fauna of a southern land mass that has changed its geological affinities profoundly since the Jurassic. I shall not be much concerned with the effects of reconnection of South with Central America during the Pliocene. For discussions of the resulting “Great American Interchange” at the end of the Cenozoic, one is referred to Patterson and Pascual (1968a), Webb (1976, 1978a,b), Marshall and Hecht (1978), Marshall (1979), and Marshall et al. (1979).

Abstract: The extinction of Pleistocene megafauna and the role played by humans have been subjects of constant debate in American archeology. Previous evidence from the Pampas region of Argentina suggested that this environment might have provided a refugium for the Holocene survival of several megamammals. However, recent excavations and more advanced accelerator mass spectrometry radiocarbon dating at Campo Laborde site in the Argentinian Pampas challenge the Holocene survival of Pleistocene megamammals and provide original and high-quality information documenting direct human impact on the Pleistocene fauna. The new data offer definitive evidence for hunting and butchering of Megatherium americanum (giant ground sloth) at 12,600 cal years BP and dispute previous interpretations that Pleistocene megamammals survived into the Holocene in the Pampas.