Brachychampsa sp.

Brand, Nickolas A., Heckert, Andrew B., Sanchez, Israel, Foster, John R., Hunt-Foster, Rebecca K. & Eberle, Jaelyn J., 2022, New Late Cretaceous microvertebrate assemblage from the Campanian-Maastrichtian Williams Fork Formation, northwestern Colorado, USA, and its paleoenvironmental implications, Acta Palaeontologica Polonica 67 (3), pp. 579-600 : 590-591

cf. Brachychampsa sp.

Fig. 6A–C .

Material.— MWC 9577, tooth; MWC 9578, tooth; MWC 9579, tooth; MWC 9592, numerous teeth; from the Campanian–Maastrichtian, Williams Fork Formation, J&M site, northwest Colorado, USA.

Description.—Crocodyliform teeth of small to intermediate size. Gracile teeth are taller, more triangular, and less blunt, while robust teeth are proportionately lower, less conical, more blunt and are larger in both width and crown height.

These teeth are very similar to those of Brachychampa ( Williamson 1996).

Remarks.—We assign relatively low-crowned, blunt, striated alligatoroid teeth that vary from gracile and recurved to a robust morphotype we refer to cf. Brachychampsa sp. These teeth are relatively common at the J&M site and are similar to those of the species of alligatoroid Brachychampsa , although precise identification is rendered impossible by a lack of diagnostic skull material. We have collected a variety of morphotypes, with taller, triangular, gracile teeth, intermediate, more conical teeth, and lower blunt teeth. The latter of these teeth strongly suggest a durophagous diet.

Dinosauria Owen, 1842

Theropoda Marsh, 1881

Coelurosauria Huene, 1914

Dromaeosauridae Matthew and Brown, 1922 Dromaeosauridae gen. et sp. indet.

Fig. 7B .

Material.— MWC 8872 , tooth; from the Campanian–Maastrichtian , Williams Fork Formation, J &M site, northwest Colorado, USA .

Description.—We assign one tooth to Dromaeosauridae indet. This specimen is, unfortunately, broken both towards the tip of the crown and towards the root but is laterally compressed and finely serrated. The tooth is recurved, has very fine denticles on both the mesial and distal surfaces of the crown, and compares favorably to the dromaeosauridae morphotype A as figured by Williamson and Brusatte (2014).

Remarks.—Recurved, laterally compressed teeth where the serrations are uniform in size and shape from base to tip of the crown have been assigned to the Dromaeosauridae ( Williamson and Brusatte 2014) . Based on the uniform shape and small size of the serrations, we suspect that this specimen most likely represents an indeterminate dromaeosaur. Without more material, more precise identification is impossible.

Figures

Fig. 6. Representative reptile (A–C, E) and amphibian (D) teeth from the J&M site, Colorado, USA,Williams Fork Formation, Campanian–Maastrichtian, Upper Cretaceous. A–C. cf. Brachychampsa sp. A. MWC 9577, gracile morph tooth crown in lateral (A1) and occlusal (A2) views. B. MWC 9578, robust morph tooth crown in lateral (B1) and occlusal (B2) views. C. MWC 9579, robust morph tooth crown in lateral (C1) and occlusal (C2) views. D. Tetrapoda indet., MWC 8877, jaw fragment with teeth in lateral (D1) and occlusal (D2) views. E. Peneteius sp., MWC 8871, tooth crown with root in mesial (E1), lateral (E2), and occlusal (E3) views.

Fig. 7. Representative theropod dinosaur teeth from the J&M site,Colorado, USA, Williams Fork Formation, Campanian–Maastrichtian, Upper Cretaceous. A. cf. Richardoestesia sp., MWC 8865, tooth crown in labial view (A1), mesial (A2) and distal (A3) serration detail views.B. Dromaeosauridae indet., MWC 8872, tooth crown fragment in lingual (B1), distal (B2) and mesial (B3) serration detail views. C. Hadrosauridae indet., MWC 8896, tooth crown in occlusal (C1) and lateral (C2) views.