Tyrannosaurus Kin Had a Toothy Smile
November 12, 2013
Paleontologists in southern Utah have discovered an older dinosaur relative of Tyrannosaurus rex that terrorized the region more than 80 million years ago. Mark Lowen of the Natural History Museum of Utah and his colleagues described the new fossil species, to which they gave the scientific name Lythronax argestes, meaning King of gore from the southwest, in the online scientific journal PLoS ONE. With a mouthful of knife-edged teeth set in powerful jaws, the meat-eating Lythronax was one of the most terrifying predators ever to walk on land.
The fossil skeleton was discovered in the Grand Staircase-Escalante National Monument in the desert region of southern Utah. When Lythronax stalked the landscape 80 million years ago, the region formed the western shore of a shallow sea in central North America. The sea divided the continent into separate land masses with many smaller islands over millions of years during the Late Cretaceous Period, between 95 million and 70 million years ago. The geographic isolation of species due to rising mountains and sea levels led to the evolution of unique dinosaurs adapted to different environments.
In life, the bipedal (two-legged) Lythronax would have been about 30 feet (9.1 meters) in length and would have weighed between 2 and 3 tons (1.8 and 2.7 metric tons). The jaws of Lythronax were short and wide, but they held just as many knife-like teeth as its larger, long-snouted relative, Tyrannosaurus rex, which roamed the same region 10 million years later. The wider skull and forward-facing eyes of Lythronax gave it an overlapping field of vision, known as binocular vision, that provided good depth perception–a valuable characteristic for chasing prey. These traits, combined with powerful limbs and a large size, would have made Lythronax a highly effective and terrifying predator.
These specialized characteristics are puzzling to paleontologists. Many had thought that such traits appeared much later, with Tyrannosaurus rex and its kin, about 70 million years ago. The discovery of Lythronax, however, suggests that the tyrannosaurids developed their predatory features much earlier. Others scientists point out many gaps in the fossil record of tyrannosaurids, suggesting that Lythronax may represent an isolated side branch on the family tree of these fearsome predators.
Additional World Book articles:
- Prehistoric animal
- Tyrannousarus rex: The Tyrant Still Reigns (a special report)