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Australosphenidans

2021; Springer Nature; Linguagem: Inglês

10.1007/978-3-030-63862-7_4

2197-960X

Guillermo W. Rougier, Agustín G. Martinelli, Analía M. Forasiepi,

Paleontology and Stratigraphy of Fossils

As presently understood Australosphenida is a clade of Gondwanan taxa, including an array of Jurassic and Cretaceous extinct forms and the extant monotremes as the sole survivors. Mesozoic Australosphenida show plesiomorphic features in the lower jaw and derived tribosphenic, or tribosphenic-like, dentition, possibly acquired independently from boreal tribosphenic taxa, namely, therians and their immediate relatives. However, non-monotreme australosphenidans are known by rare and incomplete material making alternative hypotheses of dental homologies viable. Fossil and extant monotremes are hard to relate to Mesozoic non-monotreme australosphenidans, but a few dental and mandibular characters support them as members of the group. South American australosphenidans are the oldest currently known undisputed mammals, highlighting the early acquisition of complex tribosphenic dentitions and the importance of the fossil record from southern continents in the history of early mammals.