It missed the 2010 Utah dinosaur rush by nearly a month, but a new tyrannosaur from the southern part of the beehive state makes up for its tardiness by helping to fill a gap in the famous group's evolutionary history.
Almost one year ago, paleontologists Thomas Carr and Thomas Williamson described Bistahieversor sealeyi, a tyrannosaur from New Mexico and the first representative of this group to be described from the American Southwest. Now, in the journal Naturwissenschaften, Carr and Williamson join colleagues Brooks Britt and Ken Stadtman in describing a second southwestern tyrannosaur. They have named it Teratophoneus curriei, and it was a different sort of predator from its larger, northern cousins.
Found in the 75-million-year-old rock of Utah's Grand Staircase-Escalante National Monument, Teratophoneus is known from a partial skull and additional elements from the rest of the skeleton. Its head was short—a departure from the typically long-snouted profiles of other tyrannosaurs—and it was a close relative of the northern forms Daspletosaurus and Tyrannosaurus. Based on its anatomy and its geographic place, Teratophoneus appears to be part of a unique radiation of southern tyrannosaurs.
Paleontologists have seen this pattern before. Just last year scientists described two new horned dinosaurs from the same place—Utahceratops and Kosmoceratops—which indicated that dinosaurs in the American Southwest evolved differently from their cousins to the north. There must have been some sort of barrier that kept dinosaur populations separate and caused the northern and southern groups to evolve in distinct ways. The peculiar anatomy of Teratophoneus adds further support to this idea.
Given its name—Teratophoneus roughly translates as "monstrous murderer"—you might think that this predator was a terrifying giant, but the new tyrannosaur was not quite as imposing as the famous Tyrannosaurus. Although it was a bit larger than the long-snouted genus Alioramus from Asia, Teratophoneus is estimated to have weighed about three quarters of a ton—about one tenth the mass of an adult Tyrannosaurus. (As the authors note, though, this first Teratophoneus specimen was a subadult, so they did grow a little bigger.) Just what it preyed on is as yet unclear, but hadrosaurs and horned dinosaurs have already been described from the same rock formations. Juveniles of these herbivores, at least, would have almost certainly been on the menu.
And Teratophoneus was not the only tyrannosaur found within the fossil-rich Grand Staircase-Escalante National Monument. During the 70th annual Society of Vertebrate Paleontology meeting, Utah Museum of Natural History scientist Mark Loewen introduced attendees to an older and even stranger tyrannosaur found there. This creature has yet to be fully described, but, along with Teratophoneus and Bistahieversor, it is one of the many specimens that is rapidly altering what we thought we knew about the evolution of the tyrant dinosaurs.
Carr, T., Williamson, T., Britt, B., & Stadtman, K. (2011). Evidence for high taxonomic and morphologic tyrannosauroid diversity in the Late Cretaceous (Late Campanian) of the American Southwest and a new short-skulled tyrannosaurid from the Kaiparowits formation of Utah Naturwissenschaften DOI: 10.1007/s00114-011-0762-7