A giant tyrannosaur from the Campanian-Maastrichtian of southern North America and the evolution of tyrannosaurid gigantism.

Tyrannosaurid dinosaurs dominated as predators in the Late Cretaceous of Laurasia, culminating in the evolution of the giant Tyrannosaurus rex, both the last and largest tyrannosaurid. Where and when Tyrannosaurini (T. rex and kin) originated remains unclear. Competing hypotheses place tyrannosaurin origins in Asia, or western North America (Laramidia). We report a new tyrannosaurin, Tyrannosaurus mcraeensis, from the Campanian-Maastrichtian Hall Lake Formation of New Mexico, based on a fossil previously referred to T. rex. T. mcraeensis predates T. rex by ~ 6-7 million years, yet rivaled it in size. Phylogenetic analysis recovers T. mcraeensis as sister to T. rex and suggests Tyrannosaurini originated in southern Laramidia. Evolution of giant tyrannosaurs in southern North America, alongside giant ceratopsians, hadrosaurs, and titanosaurs suggests large-bodied dinosaurs evolved at low latitudes in North America.

Osteology and reassessment of Dineobellator notohesperus, a southern eudromaeosaur (Theropoda: Dromaeosauridae: Eudromaeosauria) from the latest Cretaceous of New Mexico.

Dromaeosaurids (Theropoda: Dromaeosauridae), a group of dynamic, swift predators, have a sparse fossil record, particularly at the end of the Cretaceous Period. The recently described Dineobellator notohesperus, consisting of a partial skeleton from the Upper Cretaceous (Maastrichtian) of New Mexico, is the only diagnostic dromaeosaurid to be recovered from the latest Cretaceous of the southwestern United States. Reinterpreted and newly described material include several caudal vertebrae, portions of the right radius and pubis, and an additional ungual, tentatively inferred to be from manual digit III. Unique features, particularly those of the humerus, unguals, and caudal vertebrae, distinguish D. notohesperus from other known dromaeosaurids. This material indicates different physical attributes among dromaeosaurids, such as use of the forearms, strength in the hands and feet, and mobility of the tail. Several bones in the holotype exhibit abnormal growth and are inferred to be pathologic features resulting from an injury or disease. Similar lengths of the humerus imply Dineobellator and Deinonychus were of similar size, at least regarding length and/or height, although the more gracile nature of the humerus implies Dineobellator was a more lightly built predator. A new phylogenetic analysis recovers D. notohesperus as a dromaeosaurid outside other previously known and named clades. Theropod composition of the Naashoibito Member theropod fauna is like those found in the more northern Late Cretaceous North American ecosystems. Differences in tooth morphologies among recovered theropod teeth from the Naashoibito Member also implies D. notohesperus was not the only dromaeosaurid present in its environment.

New Dromaeosaurid Dinosaur (Theropoda, Dromaeosauridae) from New Mexico and Biodiversity of Dromaeosaurids at the end of the Cretaceous.

Dromaeosaurids (Theropoda: Dromaeosauridae), a group of dynamic, swift predators, have a sparse fossil record, particularly at the time of their extinction near the Cretaceous-Paleogene boundary. Here we report on a new dromaeosaurid, Dineobellator notohesperus, gen. and sp. nov., consisting of a partial skeleton from the Upper Cretaceous (Maastrichtian) of New Mexico, the first diagnostic dromaeosaurid to be recovered from the latest Cretaceous of the southern United States (southern Laramidia). The holotype includes elements of the skull, axial, and appendicular skeleton. The specimen reveals a host of morphologies that shed light on new behavioral attributes for these feathered dinosaurs. Unique features on its forelimbs suggest greater strength capabilities in flexion than the normal dromaeosaurid condition, in conjunction with a relatively tighter grip strength in the manual claws. Aspects of the caudal vertebrae suggest greater movement near the tail base, aiding in agility and predation. Phylogenetic analysis places Dineobellator within Velociraptorinae. Its phylogenetic position, along with that of other Maastrichtian taxa (Acheroraptor and Dakotaraptor), suggests dromaeosaurids were still diversifying at the end of the Cretaceous. Furthermore, its recovery as a second North American Maastrichtian velociraptorine suggests vicariance of North American velociraptorines after a dispersal event during the Campanian-Maastrichtian from Asia. Features of Dineobellator also imply that dromaeosaurids were active predators that occupied discrete ecological niches while living in the shadow of Tyrannosaurus rex, until the end of the dinosaurs' reign.

A new slider turtle (Testudines: Emydidae: Deirochelyinae: Trachemys) from the late Hemphillian (late Miocene/early Pliocene) of eastern Tennessee and the evolution of the deirochelyines.

Trachemys (Testudines: Emydidae) represents one of the most well-known turtle genera today. The evolution of Trachemys, while being heavily documented with fossil representatives, is not well understood. Numerous fossils from the late Hemphillian Gray Fossil Site (GFS) in northeastern Tennessee help to elucidate its evolution. The fossil Trachemys at the GFS represent a new species. The new taxon, Trachemys haugrudi, is described, and currently represents the most thoroughly described fossil emydid species known. A phylogenetic analysis, including 31 species, focusing on the subfamily Deirochelyinae is performed that includes the new fossil species, along with numerous other modern and fossil deirochelyine species, representing the first phylogenetic analysis published that includes several fossil deirochelyines. The phylogenetic analysis, utilizing morphological evidence, provides monophyletic clades of all modern deirochelyines, including Chrysemys, Deirochelys, Pseudemys, Malaclemys, Graptemys, and Trachemys. A strict consensus tree finds the recently described fossil species Graptemys kerneri to be part of a clade of Graptemys + Malaclemys. Three fossil taxa, including one previously referred to Pseudemys (Pseudemys caelata) and two to Deirochelys (Deirochelys carri and Deirochelys floridana) are found to form a clade with modern Deirochelys reticularia reticularia, with D. floridana sister to the other members of the clade. Chrysemys is found to be part of a basal polytomy with Deirochelys in relation to other deirochelyine taxa. Two fossil taxa previously referred to Chrysemys (Chrysemys timida and Chrysemys williamsi) form a paraphyly with the modern Chrysemys picta picta and Deirochelys, and may be referable to distinct genera. Additionally, fossil taxa previously attributed to Trachemys (Trachemys hillii, Trachemys idahoensis, Trachemys inflata, and Trachemys platymarginata) and T. haugrudi are found to form a clade separate from clades of northern and southern Trachemys species, potentially suggesting a distinct lineage of Trachemys with no modern survivors. Hypotheses of phylogenetic relationships mostly agree between the present study and previous ones, although the inclusion of fossil taxa provides further clues to the evolution of parts of the Deirochelyinae. The inclusion of more fossil taxa and characters may help resolve the placement of some taxa, and further elucidate the evolution of these New World turtles.