INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Is there tropical influence on the origin and diversification of sloths?
PUJOS, F.; DE IULIIS, G.
Congreso; 4th International Palaeontological Congress; 2014
Modern sloths are relatively small, slow-moving mammals utilizing a mainly suspensory posture in arboreal environments of the tropical rainforests of South and Central America and some Antillean islands. However, their fossil kin, generally referred to as ground sloths, displayed a much wider range of body size, diet, and locomotory modes, and a much broader geographic distribution. They colonized much of the Americas (including the West Indies) during the Neogene and Quaternary, extending from Patagonia to Alaska. In South America, the sloths, along with native South American ungulates, dominated the continent until about 10,000 years ago. An unresolved question in xenarthran evolution is the origin of current and fossil sloths. Although they are ultimately of South American origin, the factors and place are still uncertain. The diphyletic origin of the living tree sloths Bradypus and Choloepus has been strongly supported. Many of their remarkable postcranial specializations (e.g. elongation of long bones, simplification of articular facets) are convergent and strikingly different from the condition in ground sloths, so that their relationship to other sloths (Choloepus as a megalonychid, Bradypus as the sister group to all other sloths) is based on skull characters. Abundant discoveries of new Mio-Pliocene tropical localities (e.g., in Brazil, Colombia, Peru, and Venezuela) have not yielded fossil tree sloths. Instead, most tropical fossil lineages exhibit strong affinities with taxa present in other areas of the continent. Some peculiar tropical ground sloths, such as the mylodontoid Octodontobradys, are clearly not closely related phylogenetically to tree sloths. Large ground sloths, particularly among Megatheriidae and Mylodontidae, were apparently well suited to subtropical environments present in northern South America since the Neogene. Megathericulus, the oldest megatheriine genus common in Patagonia and recently discovered in the Peruvian Amazon, was already a very large sloth of several hundred kilograms since the middle Miocene. The evidence indicating 1/ origin and diversification of current sloths is clearly related to tropical influence, 2/ the existence of great taxonomic, dietary, and locomotory diversity in ground sloths, the absence of fossil tree sloths, and of several sloth clades in the southernmost region of South America provide neither any suggestion of a tropical origin for ground sloths nor that the tropics have radically influenced the diversification of these large mammals.