Neogene ground sloth footprints from the Beazley basin, San Luis Province, Argentina: paleoenvironmental setting and probable producers

Abstract

This work documents a new finding of ground sloth footprints from the Neogene Las MulitasFormation, San Luis Province, Argentina. The footprints have been preserved in a siliciclasticmudflat adjacent to a perennial saline lake. The trackways are quadrupedal with alternatingmanus and pes prints, exhibiting slight overprinting of pes over manus prints. Based on theirmorphology and footprint characteristics, we assign the trackways to the ichnospeciesMegatherichnum agilis. Although the size of the footprints is smaller than previously describedspecimens of this ichnospecies, the similar size of manus and pes prints, the alternate symmetry ofmanus–pes sets and moderate pace angulation are distinctive. The broad oval outline of the pesprints, the presence of a marked marginal ridge and impression of a single claw indicatea pedolateral posture. The size and slightly arched outline of the footprints point to a small- tomedium-sized member of Megatheriinae or Mylodontinae as potential producer. Although there isno known ground sloth from the Neogene of Argentina that matches the footprints, the morelikely producers are Anisodontherium or Plesiomegatherium (Megatheriinae) or an unknown mylodontine.This discovery provides further evidence of the role of ground sloth in the Neogeneecosystems of South America.