Leidyosuchus (Crocodylia: Alligatoroidea) from the Upper Cretaceous Kaiparowits Formation (late Campanian) of Utah, USA

Abstract

Several crocodyliform lineages inhabited the Western Interior Basin of North America during the late Campanian (Late Cretaceous), with alligatoroids in the Kaiparowits Formation of southern Utah exhibiting exceptional diversity within this setting. A partial skeleton of a previously unknown alligatoroid taxon from the Kaiparowits Formation may represent the fifth alligatoroid and sixth crocodyliform lineage from this unit. The fossil includes the lower jaw, numerous osteoderms, vertebrae, ribs, and a humerus. The lower jaw is generally long and slender, and the dentary features 22 alveoli with conical, non-globidont teeth. The splenial contributes to the posterior quarter of the mandibular symphysis, which extends posteriorly to the level of alveolus 8, and the dorsal process of the surangular is forked around the terminal alveolus. Dorsal midline osteoderms are square. This combination of character states identifies the Kaiparowits taxon as the sister taxon of the early alligatoroid Leidyosuchus canadensis from the Late Cretaceous of Alberta, the first verified report of the Leidyosuchus (sensu stricto) lineage from the southern Western Interior Basin. This phylogenetic placement is consistent with at least occasional faunal exchanges between northern and southern parts of the Western Interior Basin during the late Campanian, as noted for other reptile clades.