Thursday 7 June 2012

A new Ground Sloth from the Late Miocene of Argentina.

Ground Sloths (Megatheridae) were large, robust, ground-dwelling herbivores related to the extant Tree Sloths. They first appeared in South America about 23 million years ago, and spread to North America over the Panama Land Bridge about 2.2 million years ago. The went extinct abruptly at the end of the Pleistocene about 11 000 years ago; just as human beings were colonizing the Americas.

In a paper published in the journal Acta Palaeontologica Polonica on 20 May 2012, Diego Brandoni of the Laboratorio de Paleontología de Vertebrados at the Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción, and Jaime Powell and Osvaldo González of the Facultad de Ciencias Naturales e Instituto Miguel Lillo at the Universidad Nacional de Tucumán, describe a new Ground Sloth specimen from the Late Miocene Saladillo Formation near Cerro Castillo de Las Brujas in Tucumán Province, Argentina.

Right: Map of Argentina showing the distribution of fossil Megatheriinae during the Late Miocene–Pliocene. (1) Abra Pampa (Jujuy Province); (2) Saladillo Formation (Tucumán Province); (3) Andalhuala and Corral Quemado formations (Catamarca Province); (4) Toro Negro Formation (La Rioja Province); (5) Huayquerías de San Carlos (Mendoza Province); (6) “conglomerado osífero”, Ituzaingó Formation (Entre Ríos Province); (7) Arroyo Chasicó Formation (Buenos Aires Province); (8) Río Negro Formation (Río Negro Province). Top Left: Geologic map of Cerro Castillo de Las Brujas area (Tucumán Province). Bottom Left: Schematic profile of the sequence indicating the position of the fossiliferous level. Brandoni et al. (2012).

The new specimen is described from a mandible (jawbone) and partial digit only. It is placed in the genus Anisodontherium on the basis of the mandible (Anisodontherium has narrower jaws and teeth than any similar species of Ground Sloth) but no attempt at species level classification is made, due to the limited nature of the available material.

Anisodontherium sp. (A) Mandible in left lateral view. (B) Mandible in right lateral view. (C) Mandible in occlusal view. (D)Digit III of the manus in lateral view. Brandoni et al. (2012).

To date only three species of Ground Sloth have been described from the Late Miocene-Early Pliocene of northwest Argentina, all of which have been placed within the genus Pyramiodontherium. Even though this new specimen is not complete enough to allow for a full classification, which leaves the possibility of future reclassification very much open, it clearly does not belong to an of these previously described species, indicating a more diverse Sloth population in the area at that time than has previously  been understood.

See also The origin of domestic dogsThree new species of Tapir from the Early Eocene of PakistanGenetic diversity in Grey WhalesThe Dwarf Pachyderms of Crete, Mammoths or Straight-Tusked Elephants? and Mammals on Sciency Thoughts YouTube.

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