MEGATHERIUM CELENDINENSE SP. NOV. FROM THE PLEISTOCENE OF THE PERUVIAN ANDES and THE PHYLOGENETIC RELATIONSHIPS OF MEGATHERIINES

Abstract:  A new Pleistocene megatheriine, Megatherium celendinense sp. nov., is reported from a cave in the north of the Peruvian Andes. It is the largest Andean Megatheriinae and is characterized by a short, massive, Y-shaped premaxilla unfused to the maxilla, a dorsoventrally compressed occiput perpendicular to the dorsal plane of the cranial roof, prominent and posteriorly extended occipital condyles, an extremely reduced deltopectoral crest and a poorly marked musculospiral groove on the humerus, a rectilinear anterior margin of the distal epiphysis of the tibia, a concave lateral margin of the fibula, discoid and ectal facets of the astragalus clearly separated in dorsolateral view, and a pedestaled articular facet for the meso-entocuneiform on the ectocuneiform. The monophyly of the subfamily is confirmed. ( Pyramiodontherium , Megatheriops , Megatherium and Eremotherium ) constitute a monophyletic clade and ( Pyramiodontherium , Megatheriops ) and ( Eremotherium , Megatherium ) are sister groups. The genus Megatherium includes two clades: ( M. altiplanicum , M. americanum ), subgenus Megatherium , and an Andean lineage ( M. sundti , M. urbinai , M. celendinense sp. nov., M. tarijense , M. medinae ), subgenus Pseudomegatherium . Anatomical characters suggest a more quadrupedal stance for Andean Megatheriinae (Ecuador, Peru, Bolivia and Chile) than those from lower altitude regions.