A review of the Mesozoic mammalian record of South America

Abstract

Almost 25 years ago, an isolated mammalian molar from the Late Cretaceous Los Alamitos Formation, Patagonia, Argentina was reported by Bonaparte and Soria (1985). The specimen served as the type of Mesungulatum houssayi and was originally interpreted as a condylarth-eutherian. However, it was promptly re-interpreted as a non-tribosphenic mammal possibly related to dryolestoids (Bonaparte and Soria, 1985, postscript). The exploration for and discovery of Mesozoic mammals developed rapidly from that initial discovery and the fauna from Los Alamitos Formation became foundational for our views of the Cretaceous mammalian fauna in South America and Gondwana. Bonaparte and colleagues eventually described 17 taxa from that formation (Bonaparte, 1986a, 1990, 2002), although several of them are likely not valid. Almost immediately, new mammalian remains were discovered in the Hauterivian-Barremian La Amarga Formation (Bonaparte 1986a). This last discovery furnished the rudiments to begin to understand the evolution of the mammalian fauna in South America from a historical perspective. A few more localities, filling other temporal and systematic gaps, have been discovered recently, helping to piece together a framework in which mammalian evolution can be studied in the general context of a large scale phylogeny. We review here the Mesozoic mammalian record in South America and explore its biogeographic implications. To facilitate a historical perspective, we present a chronological review of the localities and taxa, followed by its discussion. See also Kielan-Jaworowska et al. (2004) for an earlier summary of the world-wide mammalian Mesozoic record.