IANIGLA   20881
INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Is there tropical influence on the origin and diversification of sloths?
Autor/es:
PUJOS, F.; DE IULIIS, G.
Lugar:
Mendoza
Reunión:
Congreso; 4th International Palaeontological Congress; 2014
Institución organizadora:
IPA
Resumen:
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.