The huge carnivore inhabited Laramidia, a landmass formed on the western coast of a shallow sea that flooded the central region of North America, isolating western and eastern portions of the continent for millions of years during the Late Cretaceous Period, between 95-70 million years ago.
The newly discovered dinosaur, belonging to the same evolutionary branch as the famous Tyrannosaurus rex, was announced today in the open-access scientific journal PLoS ONE and unveiled on exhibit in the Past Worlds Gallery at the Natural History Museum of Utah at the Rio Tinto Center in Salt Lake City, Utah.
Among tyrannosaurs, a group of small to large-bodied, bipedal carnivorous dinosaurs including T. rex that lived during the Jurassic and Cretaceous periods, the newly discovered species, Lythronax argestes, possesses several unique features, a short narrow snout with a wide back of the skull with forward-oriented eyes. Lythronax translates as “king of gore,” and the second part of the name, argestes, refers to its geographic location in the American Southwest. Previously, paleontologists thought this type of wide-skulled tyrannosaurid only appeared 70 million years ago, whereas Lythronax shows it had evolved at least 10 million years earlier.
The study, funded in large part by the Bureau of Land Management and the National Science Foundation, was led by Mark Loewen, research associate at the Natural History Museum of Utah, and adjunct assistant professor in the department of geology and geophysics at the University of Utah. Additional collaborative authors include Randall Irmis, Natural History Museum of Utah and department of geology and geophysics, University of Utah; Joseph Sertich, Denver Museum of Nature & Science; Philip Currie, University of Alberta; and Scott Sampson, Denver Museum of Nature & Science. The skeleton was discovered by BLM employee Scott Richardson, and excavated by a joint NHMU-GSENM team.
Lythronax lived on Laramidia, along the western shores of the great seaway that separated North America; this landmass hosted a vast array of unique dinosaur species and served as the crucible of evolution for iconic dinosaur groups such as the horned and duck billed dinosaurs. This study also indicates that tyrannosaurid dinosaurs (the group of tyrannosaurs that includes T. rex) likely evolved in isolation on this island continent. Lythronax stands out from its contemporaries in having a much wider skull at the eyes and a narrow short snout, similar to its relative T. rex, which lived 10 to 12 million years later. Mark Loewen, the study’s lead author, noted, “The width of the back of the skull of Lythronax allowed it to see with an overlapping field of view—giving it the binocular vision— very useful for a predator and a condition we associate with T. rex.” Previously, paleontologists thought this type of wide-skulled tyrannosaurid only appeared approximately 70 million years ago, whereas Lythronax shows it had evolved at least 10 million years earlier.
Paleontologists have recently determined that the dinosaurs of southern Laramidia (Utah, New Mexico, Texas and Mexico), although belonging to the same major groups, differ at the species level from those on northern Laramidia (Montana, Wyoming, the Dakotas and Canada). Lythronax and its tyrannosaurid relatives on southern Laramidia are more closely related to each other than the long snouted forms from northern Laramidia. Joseph Sertich, a co-author of the study, stated that, “Lythronax may demonstrate that tyrannosaurs followed a pattern similar to what we see in other dinosaurs from this age, with different species living in the north and south at the same time.”
These patterns of dinosaur distribution across Laramidia lead the researchers to ask what might have caused the divisions between the north and south, given that an enterprising dinosaur could have walked from Alaska to Mexico if given enough time. Randall Irmis, a study co-author, explained that by analyzing the evolutionary relationships, geologic age and geographic distribution of tyrannosaurid dinosaurs, the team determined that "Lythronax and other tyrannosaurids diversified between 95 to 80 million years ago, during a time when North America’s interior sea was at its widest extent. The incursion of the seaway onto large parts of low-lying Laramidia would have separated small areas of land from each other, allowing different species of dinosaurs to evolve in isolation on different parts of the landmass.” As the seaway gradually retreated after 80 million years ago, these differences in dinosaur species may have been reinforced by climate variations, differences in food sources (different prey and plants), and other factors. This hypothesis explains why the iconic Late Cretaceous dinosaurs of western North America are so different from those of the same age on other continents.A Treasure Trove of Dinosaurs on the Lost Continent of Laramidia
During the past 14 years, crews from the Natural History Museum of Utah, GSENM, the Denver Museum of Nature & Science, and several other partner institutions (for example, the Raymond Alf Museum of Paleontology and Utah Geological Survey) have unearthed a new assemblage of more than a dozen species dinosaurs in GSENM. In addition to Lythronax, the collection includes a variety of other plant-eating dinosaurs—among them duck-billed hadrosaurs, armored ankylosaurs, dome-headed pachycephalosaurs, and two other horned dinosaurs—Utahceratops and Kosmoceratops—together with carnivorous dinosaurs great and small, from “raptor-like” predators such as Talos, to another large tyrannosaur named Teratophoneus. Amongst the other fossil discoveries are fossil plants, insect traces, snails, clams, fishes, amphibians, lizards, turtles, crocodiles and mammals. Together, this diverse bounty of fossils is offering one of the most comprehensive glimpses into a Mesozoic ecosystem. Remarkably, virtually all of the identifiable dinosaur remains found in GSENM belong to new species.
Philip Currie, another co-author, stated that, “Lythronax is a wonderful example of just how much more we have to learn about the world of dinosaurs. Many more exciting fossils await discovery in Grand Staircase-Escalante National Monument.”Study Summary
(7) Our analysis indicates that tyrannosaurids originated in northern Laramidia (western North America), with multiple species moving into southern Laramidia over time, and some species immigrating to Asia towards the end of the Cretaceous between 75 to 70 million years ago.Study Design
• We then used this family tree and information about the geologic age and geographic location of different tyrannosaurid dinosaurs to reconstruct the biogeography of the group – that is, the evolution of their distribution across different continental landmasses.New Dinosaur Name: Lythronax argestes
• Lythronax is a member of a group or relatively short-snouted tyrannosaurs that were restricted to the southern part of Laramidia at the same time long-snouted tyrannosaurs were living in the northern parts of Laramidia. This finding presents strong evidence of dinosaur provincialism on Laramidia—that is, the formation of northern and southern dinosaur assemblages during a part of the Late Cretaceous.Discovery
• These discoveries are the result of a continuing collaboration between the Natural History Museum of Utah, the Denver Museum of Nature & Science, and the Bureau of Land Management.Excavation
• Other fossils found along with Lythronax at the site include parts of turtle shell, crab claws, leaf impressions, and a few molluscs. The bizarre horned dinosaur Diabloceratops eatoni was recovered from nearby rocks of the same age.Preparation
• Nearly all preparation was done by NHMU volunteers Marilyn Harris, Jerry Golden and Randy Johnson.Other
• The Bureau of Land Management manages more land—253 million acres—than any other federal agency, and manages paleontological resources using scientific principles and expertise.
Patti Carpenter, Natural History Museum of Utah, 801-707-6138, email@example.com
Charlotte Hurley, Denver Museum of Nature & Science, 303-370-6407, firstname.lastname@example.org
Patti Carpenter | Newswise
Further reports about: > Cretaceous octopus > Cretaceous period > Late Cretaceous > Lythronax > T. rex > Tarbosaurus > Teratophoneus > Tyrannosaurus rex > binocular vision > dinosaur > dinosaur species > evolutionary relationship > food source > genetic analysis > geologic age > new species > phylogenetic analysis > plant-eating dinosaur
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