Non-mammaliaform cynodonts from western Gondwana and the significance of Argentinean forms in enhancing understanding of the group

Abstract

Terrestrial Triassic assemblages are an important component of the heritage of Argentina, particularly because of their diverse record of fossil vertebrates. Triassic basins from western Argentina have a good representation of therapsids, a lineage that includes a series of stem extinct groups plus crown Mammalia. Because of their diversity and abundance, non-mammaliaform cynodonts are the most conspicuous therapsids in the Argentinean Triassic. Cynodonts have been intensively researched in Argentina since the 1960s and continue to provide key advances in the understanding of the evolution and biology of the lineage. Here we offer a summary of Triassic Argentinean non-mammaliaform cynodonts, presenting a historical context of research on this group, and highlighting seminal contributions of Triassic Argentinean cynodonts to the global knowledge of the group. To provide a Gondwanan context we review the cynodont record in the two other places where the lineage is best represented: Brazil and southern Africa (including Madagascar), highlighting commonalities in the Argentinean record with these places. Considering the important role of non-mammaliaform cynodonts in the interpretation of the origin of mammals, we provide a historical account on the contribution of Argentinean, and Gondwanan, cynodonts to the understanding of this topic. This is supplemented with a summary of the progression of phylogenetic ideas and hypotheses for all non-mammaliaform cynodonts and for the most prolific subgroups represented in western Gondwana.