Geologically Oldest Pediomyoidea (Mammalia, Marsupialiformes) from the Late Cretaceous of North America, with Implications for Taxonomy and Diet of Earliest Late Cretaceous Mammals

Terrestrial faunas of Turonian age are poorly known due to the paucity of the fossil record in North America and globally. The Smoky Hollow Member of the Straight Cliffs Formation, southern Utah, has yielded a rich assemblage of terrestrial vertebrates; among these, we herein recognize the geologically oldest members of Pediomyoidea. Two new species, <i>Scalaria martini</i>, gen. et sp. nov. and <i>Scalaria aquilana</i>, gen. et sp. nov., are recovered as members of Aquiladelphidae, sharing upper molar characters such as a subdivided B cusp, round and inflated cusps, and an anteroposteriorly expanded protocone. A fragmentary specimen is recognized as an indeterminate pediomyid with morphological similarities to <i>Leptalestes</i>. The occurrence of these distinctive groups in the Turonian prompted a re-evaluation of possible antecedents from earlier faunas, and a review of specimens referred to Aquiladelphidae. A phylogenetic analysis suggests that the Cenomanian tribosphenidan <i>Dakotadens</i> may belong within Aquiladelphidae. Of specimens referred to Aquiladelphidae, we recognize <i>Aquiladelphis laurae</i> as a valid species within the genus, and describe a new species of <i>Aquiladelphis</i> from the Judith River Formation of Montana, <i>Aquiladelphis analetris</i>, sp. nov. Two specimens from the ‘Edmontonian’ Williams Fork Formation, previously identified as <i>Aquiladelphis</i>, are here referred to a new species of <i>Glasbius</i>, <i>G. piceanus</i>, sp. nov. The presence of dentally derived marsupialiforms in the Turonian suggests that ecological drivers credited with dietary specializations among later Cretaceous taxa, such as proliferation of angiosperms and pollinating insects, were at work earlier than previously thought. http://zoobank.org/urn:lsid:zoobank.org:pub:E938B685-7F91-4BC2-85D6-3CDD501D5D88