Systematics of albanerpetontids and other lissamphibians from the late Cretaceous of western North America

The Cretaceous Period was an important interval in the evolution of lissamphibians, or so-called “modern amphibians,” and one of the best fossil records from this time occurs in the Western Interior of North America. The taxonomic diversity and systematics of Cretaceous lissamphibians from the Western Interior is investigated, with emphasis on occurrences from the Campanian and Maastrichtian stages that span about the last 18 million years of the Cretaceous Period. Lissamphibians from these horizons are more diverse taxonomically than was previously known. Frogs, salamanders, and albanerpetontids are represented and some 20 species, seven of which are new, are recognized among 17 genera and six families. Albanerpetonid and salamander species are assignable to families, but just one frog species can be confidently assigned to a known family. Albanerpetontids were most diverse during the middle Campanian, while salamanders and frogs achieved their maximum diversity later during the late Maastrichtian. New and previously reported material from the Western Interior and elsewhere permit a detailed examination of the Albanerpetontidae, an extinct and enigmatic group of salamander-like amphibians. Seven species, three of which are new, are recognized for the Euramerican type genus Albanerpeton . The first phylogenetic analysis for the genus implies that its early evolution was centered in the Western Interior and that the three North American Campanian and Maastrichtian congeners are members of two sister-clades, the origins of which can be traced back to the Early/Late Cretaceous boundary in the Western Interior. A larger scale analysis for the Albanerpetontidae corroborates monophyly of the clade and nests the family within the Lissamphibia as the sister-taxon of frogs plus salamanders. None of the character states previously advanced as salamander-albanerpetontid synapomorphies convincingly ally the two groups. Albanerpetontids are better regarded not as aberrant salamanders as some workers have argued, but as a distinct clade of lissamphibians in which numerous cranial and vertebral novelties related to feeding and burrowing are superimposed on an otherwise relatively basic lissamphibian body plan.