Craniodental anatomy of late Oligocene archaeohyracids (Notoungulata, Mammalia) from Bolivia and Argentina and new phylogenetic hypotheses

The rich Deseadan fauna from the locality of Salla Luribay (Bolivia) documents the last occurrence of archaeohyracids, a poorly known group of small typotherian notoungulates. Exceptionally, archaeohyracid remains are extremely abundant in the Salla deposits and are assigned to a single new species Archaeohyrax suniensis sp. nov. The anatomy of the new taxon is presented and the ontogeny of the cheek teeth is described. Archaeohyrax patagonicus Ameghino, 1897 from the Deseadan of Patagonia is also redescribed and compared with the new Bolivian species. Additionally, juvenile teeth of Sallatherium altiplanense (Hegetotheriidae) are described because they provide crucial phylogenetic information for understanding the phylogeny of archaeohyracids. A cladistic analysis performed on archaeohyracids and hegetotheriids supports for the first time the existence of a clade of late archaeohyracids (post-Mustersan), which is the sister taxon of all hegetotheriids. It also argues for the origin of mesotheriids within archaeohyracids and for the existence of a hegetotheriine clade. These conclusions fit well with temporal data known for each taxa. Nevertheless, the present analysis also underlines the fact that the lack of data concerning the cranial anatomy of many archaeohyracids (Eohyrax, Pseudhyrax, Archaeotypotherium, Protarchaeohyrax) weakens the phylogenetic signal. (C) 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155, 458-509.