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

PASCUAL, R.; GOIN, F.; BALARINO, L.; UDRIZAR SAUTHIER, D. E.

ACTA PALAEONTOLOGICA POLONICA

INST PALEOBIOLOGII PAN

Año: 2002 vol. 47 p. 487 - 492

0567-7920

We described 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 molariforms were “pseudo-triangulate” without a true trigonid, and that the monotreme pseudo-triangulate pattern did not arise through rotation of the primary molars cusps. Monotreme lower molars lack of talonid, and consequently there is no basin with facets produced by the wearing action of a “protocone” ; a cristid oblique connecting the “talonid” to the “trigonid” is also absent. We hypothesized that  acquisition of the molar pattern see 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.