A NEW SPECIMEN OF ORTHOGENYSUCHUS FROM THE UINTA FORMATION OF UTAH

In 2009, during a paleontological reconnaissance survey in the Uinta B (Wagonhound Member) of the Uinta Formation, a unique Crocodylian was discovered and collected. As reported on at the 2010 Society of Vertebrate Paleontology annual meeting, the specimen (BYU 18904) consists of associated maxilla, partial left and right dentaries, vertebrae, and many loose teeth. Known Crocodylia, from the geographic area of the Uinta Basin, include Allognathosuchus, Procaimanoidea, Brachychampsa, Crocodylus, 3 species of Leidyosuchus, Pristichampsus (Green River Formation), and potentially Borealosuchus. These crocodylians are typically larger, more derived, have distinctive non-bladelike teeth, pitted rugosity, and significantly different skull morphology when compared to BYU 18904.

Preliminary osteological comparisons suggest the specimen belongs to the genus Orthogenysuchus. BYU 18904 displays similar apomorphies with the only known specimen of Orthogenysuchus (AMNH 5178) from Wasatchian Beds of the Big Horn Basin, Wyoming. Similarities include: small, slender, angled teeth; the anterior portions of the dentaries expand and compress latero-ventrally; proximal dentary avoleii expand laterally, not dorsally; and slight, rolling rugose depressions (not pits) on cranial material. The dentaries are tubular when compared to other Uinta Basin Crocodylians.

If the BYU 18904 specimen is an additional specimen of Orthogenysuchus, this discovery increases the temporal range of the genus by ~15 million years and a substantial extension of the geographic region. The new specimen is considered to be an adult based on fusions in the vertebrae and lack of visible sutures on the skull and dentaries, however, it is significantly smaller than the known specimen AMNH 5178. The new specimen’s preserved skull is approximately 187mm long, compared with 333mm of the known. BYU 18904 is only moderately well preserved and sutures may be obstructed. Further taxonomic investigation is needed to determine if BYU 18904 is a paratype to AMNH 5178, or if it represents a derived species. This new specimen has the potential to add significant morphological data to the genus Orthogenosuchus and shed further taxonomic light on basal Crocodylian phylogeny, paleoecology, and paleogeography.