New data on the Paleocene monotreme Monotrematum sudamericanum, and the convergent evolution of triangulate molars
2002; Institute of Paleobiology; Volume: 47; Issue: 3 Linguagem: Inglês
ISSN
1732-2421
AutoresR. Pascual, Francisco J. Goin, María Lucía Balarino, Daniel E. Udrizar Sauthier,
Tópico(s)Ichthyology and Marine Biology
ResumoWe 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 pat− tern 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 Cre− taceous, 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.
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