A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system
Thomas D. Carr, David J. Varricchio, Jayc C. Sedlmayr, Eric M. Roberts & Jason R. Moore
Scientific Reports 7, Article number: 44942 (2017)
Received: 04 October 2016 Accepted: 14 February 2017 Published online: 30 March 2017
Figure 4: The craniofacial epidermis of Daspletosaurus horneri sp. nov., based on comparison with its closest living relatives, crocodylians and birds.
A new species of tyrannosaurid from the upper Two Medicine Formation of Montana supports the presence of a Laramidian anagenetic (ancestor-descendant) lineage of Late Cretaceous tyrannosaurids. In concert with other anagenetic lineages of dinosaurs from the same time and place, this suggests that anagenesis could have been a widespread mechanism generating species diversity amongst dinosaurs, and perhaps beyond. We studied the excellent fossil record of the tyrannosaurid to test that hypothesis. Phylogenetic analysis places this new taxon as the sister species to Daspletosaurus torosus. However, given their close phylogenetic relationship, geographic proximity, and temporal succession, where D. torosus (~76.7–75.2 Ma) precedes the younger new species (~75.1–74.4 Ma), we argue that the two forms most likely represent a single anagenetic lineage. Daspletosaurus was an important apex predator in the late Campanian dinosaur faunas of Laramidia; its absence from later units indicates it was extinct before Tyrannosaurus rex dispersed into Laramidia from Asia. In addition to its evolutionary implications, the texture of the facial bones of the new taxon, and other derived tyrannosauroids, indicates a scaly integument with high tactile sensitivity. Most significantly, the lower jaw shows evidence for neurovasculature that is also seen in birds.
Source/Fonte: Thomas D. Carr
T.D.C. thanks the following people for access to specimens under their care: D. Brinkman, J. Horner, P. Makovicky, M. Norell, X. Wu, and S. Brusatte for assistance with obtaining the bootstrap values of the phylogenetic analysis. T.D.C. was supported by a Faculty Research & Development Grant from Carthage College. D.J.V. and J.R.M. thank the Bahamas crews of 2000 and 2001. D.J.V. thanks E. Metz, E. Przybyszewski, and A. Takekawa for help in the field and B. Harmon and J. Jette for preparation of specimens. J.C.S. thanks L. M. Witmer for guidance as his advisor during his dissertation work. J.C.S. was supported by a Dissertation Improvement Grant. E.M.R. thanks P. C. Owusu Agyemang and R. Holm for assistance with heavy mineral separations and U-Pb LA-ICPMS analysis. We thank D. A. Eberth for discussion on Belly River Group geochronology. J.R.M. thanks Channel 4 production company for contributing funding for fieldwork on MOR 1130. All authors thank D. Pulerà for rendering the life reconstruction of D. horneri, S. Williams for the photo of the quadratojugal of MOR 1130, S. Brusatte and an anonymous reviewer for their constructive comments, and R. McCrea for handling the manuscript.
Carthage College, 2001 Alford Park Drive, Kenosha, WI 53140, USA
Thomas D. Carr
Department of Earth Sciences, Montana State University, P.O. Box 173480, Bozeman, MT 59717-3480, USA
David J. Varricchio
Louisiana State University Health Sciences Centre - School of Medicine, 1901 Perdido Street, New Orleans, LA 70112, USA
Jayc C. Sedlmayr
Geosciences, College of Science and Engineering, James Cook University, Townsville, QLD 4811, Australia
Eric M. Roberts
Honors College, University of New Mexico, Albuquerque, NM 87131, USA.
Jason R. Moore
T.D.C. wrote the description of the new taxon, collected and analyzed the phylogenetic and ontogenetic data, and wrote the corresponding parts of the manuscript. D.J.V. collected specimens MOR 553 and 1130 and analyzed the stratigraphic data in the field, and wrote the corresponding methods and results. T.D.C and J.C.S. collected and analyzed the data on epidermal soft tissue and associated neurovasculature; T.D.C. wrote the results. E.M.R. analyzed the geochronological data and wrote the corresponding methods and results. J.R.M. obtained funding for 2001 fieldwork on MOR 1130, helped excavate the specimen in 2000 and 2001, and helped write the manuscript.
The authors declare no competing financial interests.
Correspondence to Thomas D. Carr.