New data on the Paleocene monotreme Monotrematum sudamericanum, and the convergent evolution of triangulate molars

PASCUAL R; GOIN FJ; BALARINO L; UDRIZAR SAUTHIER D

ACTA PALAEONTOLOGICA POLONICA

INST PALEOBIOLOGII PAN

Lugar: Varsovia; Año: 2002 vol. 47 p. 487 - 492

0567-7920

We describe an additional fragmentary upper molar and the first lower molar known of Monotrematum sudamericanum, the oldest Cenozoic (Paleocene) monotreme. Comparisons suggest that the monotreme evolution passed through a stage in which their molars were ?pseudo−triangulate?, without a true trigonid, and that the monotreme pseudo−triangulate pattern did not arise through rotation of the primary molar cusps. Monotreme lower molars lack a talonid, and consequentlythere is no basin with facets produced by the wearing action of a ?protocone?; a cristid obliqua connecting the ?talonid? to the ?trigonid? is also absent.We hypothesize that acquisition of the molar pattern seen in Steropodon galmani (Early Cretaceous, Albian) followed a process similar to that already postulated for docodonts (Docodon in Laurasia, Reigitherium in the South American sector of Gondwana) and, probably, in the gondwanathere Ferugliotherium.