title: A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system.
abstract: 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.
authors.affiliation: Carthage College, 2001 Alford Park Drive, Kenosha, WI 53140, USA.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Carr
authors.affiliation: Department of Earth Sciences, Montana State University, P.O. Box 173480, Bozeman, MT 59717-3480, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Varricchio
authors.affiliation: Louisiana State University Health Sciences Centre - School of Medicine, 1901 Perdido Street, New Orleans, LA 70112, USA.
authors.forename: Jayc C
authors.initials: JC
authors.lastname: Sedlmayr
authors.affiliation: Geosciences, College of Science and Engineering, James Cook University, Townsville, QLD 4811, Australia.
authors.forename: Eric M
authors.initials: EM
authors.lastname: Roberts
authors.affiliation: Honors College, University of New Mexico, Albuquerque, NM 87131, USA.
authors.forename: Jason R
authors.initials: JR
authors.lastname: Moore
mesh_terms: D000489:Alligators and Crocodiles / Q000033:anatomy & histology* / Q000502:physiology*; D000818:Animals; D025061:Dinosaurs / Q000033:anatomy & histology* / Q000145:classification / Q000502:physiology*; D005580:Fossils; D010163:Paleontology; D010802:Phylogeny