A new, diminutive, heterodont neosuchian from the Vaughn Member of the Blackleaf Formation (Cenomanian), southwest Montana, and implications for the paleoecology of heterodont neosuchians

Although crocodyliforms from the Campanian–Maastrichtian of North America have received considerable attention, taxa occurring earlier in the Cretaceous have only recently begun to be more thoroughly studied. Of particular interest amongst these recent discoveries is the heterodont neosuchian <i>Wannchampsus kirpachi</i> Adams 2014 and the similar, undescribed ‘Glen Rose Form’ (USNM 22039). Both hold an unclear phylogenetic position, either forming a clade sister to Atoposauridae, a group of small, heterodont neosuchians from the Jurassic and Cretaceous of Laurasia, or to Paralligatoridae, a clade of larger, platyrostral, homodont neosuchians from the Cretaceous of Asia and North America. Here we describe a new species of diminutive, heterodont neosuchian, <i>Thikarisuchus xenodentes</i> gen. et sp. nov., from the early–middle Cenomanian Vaughn Member of the Blackleaf Formation of southwest Montana. The specimen includes cranial, mandibular, axial, and appendicular elements in articulation and dense concentration. It is recovered in a sister relationship with <i>Wannchampsus</i> and USNM 22039. We propose the name Wannchampsidae (clade nov.) for this group of small, heterodont neosuchians endemic to the Cretaceous of North America. Wannchampsidae is more confidently recovered sister to Atoposauridae due to the recognition of new synapomorphies. The new taxon provides greater clarity on the potential diet and paleoecology of Wannchampsidae and Atoposauridae and displays similar craniomandibular and dental characteristics to the notosuchian group Uruguaysuchidae, strongly suggesting these neosuchian groups were also omnivorous or insectivorous and terrestrially adapted, respectively representing a unique diet and reversion to terrestriality within Neosuchia.