CONICET | Buscador de Institutos y Recursos Humanos

Propyrotherium saxeum Ameghino is one the lesser known member of Pyrotheria, an enigmatic group of giant, endemic South American ungulates. The species was originally described based upon two isolated cheek teeth and two tusk fragments (MACN). Latter authors assigned additional isolated teeth to this taxon, but the position within the tooth row of all these teeth remained uncertain, preventing an accurate dental characterization and taxonomic distinction from other related species. Here we re-examine the type specimens of P. saxeum and additional materials (AMNH) previously reported as belonging to this species, and analyze several lots of still undescribed specimens (MLP), in order to reconstruct the cheek teeth series. Based on comparisons with better known pyrotheres, we conclude that the most probable cheek teeth formula is P2-M3/p2-m3, the cheek teeth series increase in size gradually from front to back, and the upper series has a gradual increase of the lophs curvature, as in Pyrotherium Ameghino. All cheek teeth are bilophodont, but in the premolars (upper and lowers) the anterior loph/id is transversally shorter than the posterior. All cheek teeth have lingual cingulum/id; P3-M3 are sub-quadratic and have three roots; p4-m3 are longer than wide, two rooted, and bear a variably developed vestige of cristid obliqua. Propyrotherium is morphologically distinguishable from Griphodon Antony and Baguatherium Salas et al., but the distinction between the two latter, based on non comparable materials, is unverifiable with the current evidences. A revised cladistic analysis confirms that Propyrotherium is one of the earliest diverging pyrotheriid, but the elucidation of its relationships with Griphodon and Baguatherium requires further evidences.