Late Oligocene mesotheriids (Mammalia, Notoungulata) from Salla and Lacayani (Bolivia): implications for basal mesotheriid phylogeny and distribution

摘要: The oldest known mesotheriids are referred to the genus Trachytherus, a taxon traditionally included in its own subfamily ‘Trachytheriinae’. ontogeny, morphological variation and systematics of Trachytherus still poorly understood monophyly this is questionable. For first time, large collection basal (belonging Trachytherus) yielded by Bolivian Salla beds (Deseadan, late Oligocene) previously T. spegazzinianus was large-scale analysis. This has led recognition unique new species locality Salla-Luribay, distinct from T. spegazzinianus: alloxus sp. nov. Skulls described cheekteeth range throughout ontogeny discussed. These data incorporated parsimony analysis mesotheriids. most probable hypothesis clade T. spegazzinianus-mesotheriines distinction Patagonian confirms faunal differences observed between these Deseadan localities. Moreover, assignment spegazzinianus mesotheriid remains Lacayani deposits complicates problem differences. Further systematic investigations on fauna age localities needed. © 2008 Linnean Society London, Zoological Journal Society, 2008, 152, 153–200.