Callistoe vincei, a new Proborhyaenidae (Borhyaenoidea, Metatheria, Mammalia) from the Early Eocene of Argentina

Callistoe vincei nov. gen., nov. sp. is a new South American carnivorous marsupial (Proborhyaenidae, Borhyaenoidea) from Salta Province (Argentina). It is preliminarily described and its phylogenetic relationships with other borhyaenoids are analyzed. The holotype is a complete skull with almost complete postcranial skeleton (missing the pelvis and the tail). It is from the Lumbrera Formation (Early Eocene of northwestern Argentina). It represents the most complete proborhyaenid specimen ever discovered and one of the best-preserved borhyaenoid. In the present paper we analyze the major cranial and dental features, the essential elements to compare C. vincei to Arminiheringia auceta, a Casamayoran proborhyaenid of Patagonia. C. vincei is smaller, much more gracile; its skull is narrower; its lower canines are not procumbent; the metacrista of M3 is U-shaped; the postmetacrista of M4 is present and the mandibular symphysis is shorter. This new material allows reconsideration of some dental traits proposed to diagnose the Proborhyaenidae such as the number of incisors and the open-rooted canines.     

A new turtle from the Palaeogene of Patagonia (Argentina) sheds new light on the diversity and evolution of the bizarre clade of horned turtles (Meiolaniidae,Testudinata)

In this contribution we present a new species of horned turtle, G affneylania auricularis gen. et sp. nov. , from the Paleogene of Patagonia. The specimens come from the lower section of the Sarmiento Formation (Middle Eocene) at Cerro Verde (Cañadón Hondo area, Province of Chubut, Argentina). The level containing turtles and crocodyliforrmes is located at the base of the section and it consists of laminated, fine tuffs interpreted as shallow pond sediments. It underlies another fossiliferous level comprising lenticular, massive sandstones bearing skeletal remains of mammals, referred by previous authors to the Casamayoran SALMA. Gaffneylania auricularis represents one of the most complete meiolaniids from South America found to date and it is distinguished from other meiolaniids by the presence of a peculiar half‐moon‐shaped, thick rim surrounding the cavum tympani, the presence of three cranial scutes K and an unenclosed canalis chorda tympani mandibularis, among others. This new species sheds new light on the evolution and palaeobiogeographical history of the clade Meiolaniidae in Australasia and South America during the Cainozoic. The break up of southern Gondwana provoked major global climatic changes during the Cainozoic that probably influenced the evolution of meiolaniid turtles. The co‐evolution of meiolaniids with other amniotes (e.g. chelid turtles, mammals) suggests a common palaeobiogeographical history of those clades in southern Gondwana. © 2015 The Linnean Society of London