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| Thikarisuchus xenodentes Allen, Wilberg, Turner & Varricchio, 2025 Illustration by Dane Johnson/Museum of the Rockies |
ABSTRACT
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 Wannchampsus kirpachi 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, Thikarisuchus xenodentes 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 Wannchampsus 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.
SYSTEMATIC PALEONTOLOGY
CROCODYLOMORPHA Hay, 1930 (sensu Nesbitt, 2011)
CROCODYLIFORMES Hay, 1930 (sensu Clark, 1986)
NEOSUCHIA Clark in Benton and Clark, 1988
WANNCHAMPSIDAE, family nov.
Type Genus—Wannchampsus kirpachi Adams, 2014.
Etymology—'The family of Wannchampsus.’ The stem Wannchamps- is based on the designated type genus Wannchampsus. -idae, is a Latin patronymic suffix.
Under Article 29.2 of the Zoological Code, the suffix -idae denotes a family rank within the family-group.
Phylogenetic Definition—Branch-based clade comprising all taxa more closely related to Wannchampsus kirpachi Adams, 2014 than to Theriosuchus pusillus Owen, 1878 or Shamosuchus djadochtaensis Mook, 1924.
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| Skeletal diagram of preserved elements of Thikarisuchus xenodentes (MOR 11969). Preserved ribs and osteoderms are not shown. Silhouette based off Araripesuchus spp., illustrating the convergence in craniodental characteristics and terrestrial affinities between these distantly related crocodyliform taxa. |
THIKARISUCHUS XENODENTES, gen. et sp. nov.
Locality, Horizon, and Age—Vaughn Member of the upper portions of the Blackleaf Formation (early–middle Cenomanian). Material originates from The Mound (BL-9) in the Lima Peaks area of southwest Montana, southeast of the town of Lima, MT and was recovered on the surface in float or was surface screened, sifted, and later identified/recovered within the lab.
Diagnosis—A small neosuchian crocodyliform with the following unique combination of characters (autapomorphies denoted by an asterisk): longitudinal groove on posterior dentary laterally adjacent to dentary toothrow for reception of posterior maxillary teeth*; extreme mesiodistal elongation and low apicobasal height of posterior ‘low crowned’ maxillary and dentary teeth*; development of frontoparietal midline ridge into a symmetric, elongate hexagonal boss at frontal-parietal suture*; extension of lateral angular ridge onto lateral surface of posterior dentary*; oreinirostral snout; anteriorly oriented external nares; small, anteroposteriorly aligned sulcus present posterior to triple junction of sutures of the premaxilla, maxilla, and nasals; orbitonasal sulcus (sensu Turner, 2015) on lateral surface of maxilla; occlusal pit on palatal process of maxilla adjacent to 4th and 5th maxillary teeth; ventral surface of posterolateral portion of palatal process of maxilla possesses a shallow groove that accommodates some posterior dentary teeth; internal choana bounded almost entirely by pterygoids, with palatines contributing to anterior margin; procoelous cervical, dorsal, and caudal vertebrae; humeral head convex, with the center of the humeral head positioned proximally above the rest of the surface; humerus proximal to deltopectoral crest strongly deflected medially at ∼45° compared with humeral shaft; highly reduced postacetabular process of ilium; elongate proximal process on fibula.
Etymology—After “thikari,” the diminutive form of the Greek word “thiki” meaning sheath, referring to the way in which the posterior maxillary teeth ‘sheath’ within the longitudinal groove on the dentary adjacent to the dentary toothrow as well as the diminutive size of the specimen, and “suchus,” from the Latinized form of “soukhos,” Greek for crocodile. After “xeno,” Greek for strange, and “dentes,” Latin for teeth, referring to the strange heterodont dentition and extremely mesiodistally elongate and apicobasally low posterior teeth.
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| An artistic rendering of Thikarisuchus xenodentes, an extinct crocodyliform from the Cretaceous of Montana. Illustration by Dane Johnson/Museum of the Rockies |
Harrison J. Allen, Eric W. Wilberg, Alan H. Turner and David J. Varricchio. 2025. A New, diminutive, heterodont Neosuchian from the Vaughn Member of the Blackleaf Formation (Cenomanian), southwest Montana, and Implications for the Paleoecology of heterodont neosuchians. Journal of Vertebrate Paleontology. e2542185. DOI: doi.org/10.1080/02724634.2025.2542185 [22 Sep 2025]
