Deltatheridia, a new order of mammals. Bulletin of the AMNH ; v. 132, article 1

126 p., 8 p. of plates : ill. ; 27 cm.Includes bibliographical references (p. 113-123) and index."A reconsideration of the phylogeny of some early placental mammals, especially the creodonts, has resulted in the removal of all creodonts except the Miacidae from the Carnivora. The Arctocyonidae and their descendants, the Mesonychidae, are placed in the Condylarthra, and a new order, the Deltatheridia, is created for the Oxyaenoidea, the Palaeoryctidae, the Didymoconidae, and Micropternodus. The zalambdodont insectivores may or may not also be referable to the Deltatheridia. A survey of taxonomically significant characters indicates that the Miacidae are apparently closer to the Arctocyonidae than to the Pantolestinae or to the Deltatheridia. The whales were probably derived from mesonychids in the Paleocene. A detailed consideration of the morphology, systematics, and evolution of the Didelphodontinae is presented, and observations are made on many other mammalian genera, mainly, but not exclusively, of the Deltatheridia. Greatest emphasis is placed on the evolution of dental structure and occlusion, and cranial circulation. A detailed terminology is proposed for the structures of primitive therian teeth. Teeth of possible Tiffanian and Puercan oxyaenoid ancestors are described. Apterodon is tentatively referred to the Mesonychidae; Micropternodus, Nyssodon, and Sarcodon are referred to the Palaeoryctidae; Kochictis and Kopidodon, to the Mioclaeninae; Argillotherium is referred to the Oxyaeninae; and Praolestes, Opisthopsalis, Hyracolestes, and Xenacodon are referred to the Erinaceoidea. New genera are Avunculus in the Didelphodontinae, Pararyctes in the Palaeoryctinae, Mongoloryctes in the Didymoconidae, and Epapheliscus in the Apheliscinae. A new species of Palaeoryctes is described from the late Paleocene, one of Oxyaena, from the early Eocene; and one of Oxyaenodon, from the late Eocene. A possible case of geographic speciation in Didelphodus is presented, and comments are made on determining the relative adaptiveness of different characters, conditions of competitive exclusion, criteria of taxonomic definitions, and other theoretical matters"--P. 112