Deltatheroides—like mammals from the Upper Cretaceous of North America

Abstract

THE family Deltatheridiidae¹ has been redifined to include primitive therian mammals of tribosphenic grade referrable to only two genera Deltatheridium¹ and Deltatheroides², from the Djadokhta and Barun Goyot Formations, of uncertain age within the Upper Cretaceous of Mongolia². The Deltatheridiidae, long considered Eutheria, although of disputed taxonomic dimensions and phyletic position within the infraclass^1–5, seem now best classified as therians of metatherian–eutherian grade, but referrable to neither Metatheria nor Eutheria². A combination of apparent marsupial-like and placental-like features in the known parts of the dentition and skull of members of the Deltatheridiidae insures that the family will be of continuing interest.