Acta Palaeontologica Polonica

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

Rosendo Pascual, Francisco J. Goin, Lucía Balarino, and Daniel E. Udrizar Sauthier

Acta Palaeontologica Polonica 47 (3), 2002: 487-492

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 consequently there 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.

Key words: Monotremata, Monotrematum, pseudo−triangulate molars, molar structure, Gondwana, Patagonia, Paleocene

Rosendo Pascual [], Francisco Goin [], Lucía Balarino, and Daniel Udrizar Sauthier, Departamento Paleontología Vertebrados, Museo de la Plata, Paseo del Bosque s/n, 1900 La Plata, Argentina.

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