PREPIDOLOPIDAE, NUEVA FAMILIA DE MARSUPIALIA DIDELPHOIDEA DEL EOCENO SUDAMERICANO

Abstract

New and almost complete Prepidolops didelphoides mandibular fragments, with teeth, and fragments of the skull articulated to a mandibular ramus are described. Some other mandibular fragments, with teeth, are recognized as representing a different species, P. molinai. The new remains come from the sarne locality and Early Eocene levels than the holotype, thus Completing the knowledge of this peculiar South American marsupial taxon, modifying its original taxonomical assignment and affeeting the taxonomical arrangement of the South American marsupials best known at presento The principal eonclusions are as follows: (1) Prepidolops represents a new family (Prepidolopidae) of the Didelphoidea nec Polydolopoidea; (2) this new family is considered to be a surviving taxon of the dídelphoíd group, from some species thereof arose the first Polydolopoidea; (3) the unquestionable Didelphoidea and Polydolopoidea relationship is best expressed including both in the eommon suborder Didelphimorphia and order Polyprotodontia; as a eonsequenee the order Paucituberculata is invalidated; (4) Prepidolops represents a "transitional" genus from the "polyprotodont" to the "diprotodont" marsupial types. As sueh most of its eharaeters are eoincident with those of the Macropodidae "hypothetieal ancestor" envisioned by Ride; (5) the presenee of a speeialized lower deciduous eheeek tooth has led me to new eonsiderations of its homology, including the possibility that the original, eo-marsupial, dental formula was compounded by eight post-canine teeth.