The aim of this paper is to enlarge the description of the only known complete pes of a Tertiary megatherine and make comparisons with those of other members of the subfamily. The complete pes of the type specimen of Pyramiodontherium bergi (Moreno & Mercerat, 1891) (MLP 2-66) was found at the informally named “Araucanense” s.l. levels of Bajo de Andalhuala, Catamarca Province (late Miocene-Pliocene), Argentina. The elements of the pes show the general characters of other megatherines. However, the astragalar depression is not as deep as in Megatherium americanum Cuvier, 1796; the calcaneum is more slender than Eremotherium laurillardi (Lund, 1842); the navicular has two facets to articulate with the ectocuneiform; there are seven separate tarsal elements (calcaneum, astragalus, navicular, entocuneiform, mesocuneiform, ectocuneiform, and cuboid) while in other megatherines, usually the mesocuneiform and the entocuneiform are fused into a single element termed the mesoentocuneiform complex; the third digit is formed only by the proximal phalanx fused with the second phalanx, and digit IV, unlike Quaternary megatherines, has three phalanges. The presence of separated entocuneiform and mesocuneiform and three phalanges in the digit IV, are interpreted as plesiomorphic condition of the characters present in the Plio-Pleistocene genera. The plesiomorphic character states observed here could be useful to solve the megatherine polytomy proposed by De Iuliis (1996), and indicate more precisely the way the states of the characters were changed.
Mammalia, Xenarthra, Megatheriinae, Pyramiodontherium bergi, Tertiary, pes, morphology