First monotreme from the Late Cretaceous of South America

An isolated tooth from the Late Cretaceous of Argentina indicates a monotreme presence in South America by the end of the Mesozoic. Monotremata is a clade of egg-lying mammals, represented by the living platypus and echidnas, which is endemic to Australia, and adjacent islands. Occurrence of basal monotremes in the Early Cretaceous of Australia has led to the consensus that this clade originated on that continent, arriving later to South America. Here we report on the discovery of a Late Cretaceous monotreme from southern Argentina, demonstrating that monotremes were present in circumpolar regions by the end of the Mesozoic, and that their distinctive anatomical features were probably present in these ancient forms as well.

Automated summary

A tooth from the Late Cretaceous in Argentina suggests the presence of monotremes in South America at the end of the Mesozoic Era. Monotremata, a group of egg-laying mammals represented by the platypus and echidnas, is endemic to Australia and nearby islands. The discovery of a Late Cretaceous monotreme in southern Argentina indicates their presence in circumpolar regions and suggests that their distinctive anatomical features were already present in ancient forms.