Are the Deltatheriidae marsupials? Their upper molar patterns, with broad stylar shelf and well developed stylocone, resemble some late Cretaceous Didelphidae more than Palaeoryctidae.
The deltatheriid postcanine formula is logically irrelevant to refutation of the hypothesis of marsupial affinities for the Pediomyidae … It is clear … that the reduction in the stylar [area] on upper molars of the Pediomyidae and ‘dog-like marsupials [i.e., borhyaenoids] was generated independently, from very different demands of natural selection in the two groups, and that the one pattern had nothing whatever to do with the other in either a functional or genealogical sense’.c
North America, Europe, Asia, and Africa
The convincing case made recently by Kielan-Jaworowska and Nessov (1990) for the metatherian affinities of the Deltatheroida of the Early to Late Cretaceous of Asia (and possibly also of North America) will be reviewed in Chapter 8 along with the less convincing suggestion of Kielan-Jaworowska (1992) for aegialodontian-deltatheroidan ancestor-descendant relationships. The postcranial anatomy of some deltatheroidan species is currently being described (Szalay & Nessov, in preparation), and a new group of Asian metatherians represented by the late Cretaceous Asiatherium (nomen nudum, Trofimov & Szalay, 1993) is discussed elsewhere (in preparation). A discussion of the relationships of the described taxa is presented in Chapter 8 under “Theria” and “Metatheria.”