Cretaceous mammals of southern Utah. II. Marsupials and marsupial-like mammals from the Wahweap Formation (early Campanian)

ABSTRACT

The Wahweap Formation of southern Utah is probably early Campanian in age. Its mammalian fauna is generally similar to that of the Aquilan upper Milk River Formation, Alberta, but differs substantially from that and all other known Late Cretaceous mammalian local faunas. Wahweap taxa referable to the Marsupialia include a new, somewhat derived species of Protalphadon and an unidentified taxon. Two new genera and species of advanced therian mammals are described. The status of these taxa is uncertain, because in some respects (such as the “twinning” of lower molar hypoconulid with entoconid) they share advanced morphology with undoubted Cretaceous marsupials, while in others (such as the variable or complete absence of stylar cusp D on upper molars) they may be more primitive than known marsupials and, in fact, would be excluded from the group using most currently-accepted criteria. Although these two Wahweap species could represent members of advanced lineages in which characteristic marsupial specializations were lost, a simpler explanation is that they are primitive in these regards, and represent either primitive marsupials or marsupial sister-taxa, depending on how the group is defined.