A new species of the enigmatic mammal Bondesius from the Late Cretaceous of Patagonia

Abstract

The fossil record of Mesozoic mammals in the Southern Hemisphere is much less well-known than that from the Northern Hemisphere. In the last two decades, more complete skulls and skeletons of dryolestoids and gondwanatherians have shed light on the established lineages of South American Mesozoic mammals. These remains have improved understanding of functional and comparative morphology. Yet, one of the most enigmatic taxa, Bondesius ferox, was erected on a single tooth from the Maastrichtian Los Alamitos Formation of northern Patagonia, Argentina. Here, we describe a new species of Bondesius from the same locality and horizon. This new species lacks character states shared by Mesozoic gondwanatherians, meridiolestidans, and docodonts. On the other hand, it shows striking similarities to extinct stem-therians, such as adapisoriculids. The paucity of available specimens precludes a definitive taxonomic referral. Nevertheless, unique character states exhibited by the new species of Bondesius hint at a cryptic lineage of South American Mesozoic mammals.