Dents de deux théropodes d'Appalachie

Résumé de l'étude:

The faunal changes that occurred in the few million years before the Cretaceous–Palaeogene extinction are of much interest to vertebrate palaeontologists. Western North America preserves arguably the best fossil record from this time, whereas terrestrial vertebrate fossils from the eastern portion of the continent are usually limited to isolated, eroded postcranial remains. Examination of fragmentary specimens from the American east, which was isolated for the majority of the Cretaceous as the landmass Appalachia, is nonetheless important for better understanding dinosaur diversity at the end of the Mesozoic. 

Here, I report on two theropod teeth from the Mount Laurel Formation, a lower-middle Maastrichtian unit from northeastern North America. One of these preserves in detail the structure of the outer enamel and resembles the dentition of the tyrannosauroid Dryptosaurus aquilunguis among latest Cretaceous forms in being heavily mediolaterally compressed and showing many moderately developed enamel crenulations. Along with previously reported tyrannosauroid material from the Mt Laurel and overlying Cretaceous units, this fossil supports the presence of non-tyrannosaurid tyrannosauroids in the Campanian–Maastrichtian of eastern North America and provides evidence for the hypothesis that the area was still home to relictual vertebrates through the end of the Mesozoic. 

The other tooth is assignable to a dromaeosaurid and represents both the youngest occurrence of a non-avian maniraptoran in eastern North America and the first from the Maastrichtian reported east of the Mississippi. This tooth, which belonged to a 3–4 m dromaeosaurid based on size comparisons with the teeth of taxa for which skeletons are known, increases the diversity of the Maastrichtian dinosaur fauna of Appalachia. Along with previously reported dromaeosaurid teeth, the Mt Laurel specimen supports the presence of mid-sized to large dromaeosaurids in eastern North America throughout the Cretaceous.

 

Figure 1. Locality information, Maastrichtian eastern North American dinosaurs and Mount Laurel tyrannosauroid tooth anatomy. (a) Map of New Jersey showing the location of Burlington and Monmouth counties and the Big Brook site (grey dot), (b) possible partial Lambeosaurine forelimb, (c) cast of the manual ungual of Dr. aquilunguis and (d) pedal phalanx of an ornithomimosaur. NJSM GP 14256 in labial (e,f), distal (g) and basal (h) views with a close-up of the enamel wrinkles (i) and distal denticles (j) (arrows show convexity). Map is public domain, access to photograph the cast of the manual ungual of Dr. aquilunguis courtesy of the Yale Peabody Museum (peabody.yale.edu).

Figure 3. Anatomy of the Mt Laurel dromaeosaurid tooth. NJSM GP 22949 in labial (a), lingual (b), basal (c) and distal (d) views, with a close-up (e) of the distal denticles. (f) Teeth of Velociraptor, (g) dentary and teeth of ‘Bambiraptor’, (h) premaxilla and teeth of Utahraptor and (i) dentary and teeth of Dromaeosaurus. r, enamel ridge; tc, twisted mesial carina.