A new toxodont (Mammalia, Panperissodactyla, Notoungulata) from the Oligocene of Patagonia, Argentina, and systematic considerations on the paraphyletic ‘Notohippidae’

MARTÍNEZ, GASTÓN; DOZO, MARÍA T.; GELFO, JAVIER N.; CIANCIO, MARTÍN R.; GONZÁLEZ-JOSÉ, ROLANDO

JOURNAL OF SYSTEMATIC PALAEONTOLOGY

CAMBRIDGE UNIV PRESS

Año: 2021 p. 1 - 24

1477-2019

Notoungulates were the most diverse group of South American native ungulates during the Cenozoic. They ranged from small rodent-like to heavy rhino-like forms and, despite such a morphological diversity, their monophyly is widely accepted. Within Notoungulata, Typotheria and Toxodontia (the two major clades) are well supported, whereas phylogenetic relationships between early diverging lineages (formerly grouped as Notioprogonia) are still matter of debate. Among Toxodontia, Notohippidae (a paraphyletic group lacking systematic consensus) is represented by small to medium-sized taxa registered from middle Eocene to early/middle Miocene, but especially diverse during the late Oligocene. In this context, we describe a new toxodont (Teushentherium camaronensis gen. et sp. nov.) found in Barrancas Blancas, an Oligocene locality in the Southeast of Chubut (Patagonia, Argentina). It is represented by the anterior portion of the skull (palate and anterior snout) and the associated horizontal rami of the mandible. The phylogenetic analysis placed the new taxon closely related to taxa traditionally regarded as Notohippidae. In addition, an extensive taxonomic sampling allowed us to assess phylogenetic relationships among other representatives. As expected, only Homalodotheriidae, Leontiniidae and Toxodontidae were recovered as monophyletic groups, whereas neither ?Notohippidae? nor Isotemnidae were supported. We also identified a superfamily-level node (that defines a clade sister to Homalodotheriidae) for which we propose the name Eutoxodontoidea. It includes most of the Notohippidae (except for Puelia, Plexotemnus and Pampahippus), Leontiniidae and Toxodontidae, and provides a more accurate definition to refer to middle and later diverging toxodonts avoiding ambiguous terminology as advanced or derived. We hope to contribute to stabilize the toxodontian taxonomy, to highlight main gaps in this respect, and to promote future contributions dealing with such an intricate issue.