Tyrannosaurs are bipedal carnivores which range in length from 5 to 12 meters. T. rex was the largest known species. It was thought that advanced tyrannosaurs with forward facing eyes lived around 70 million years ago but the discovery of the Lythronax specimen suggests that they could have emerged 10 million years earlier. This adds a new branch on the tyrannosaur phylogenetic tree and places Lythronax approximately in the role of a distant uncle to T. rex. The paper was published on PLOS ONE.
Lythronax had a wide skull which would have accommodated binocular vision, giving it very keen eyesight that would have been useful for hunting. It also had large, sharp teeth capable of taking down nearly any kind of prey. At 9 meters in length, Lythronax is slightly smaller than T. rex. However, T. rex lived 10 million years later, making Lythronax the largest predator in its habitat. The dinosaur’s ferocity has been honored in its name, which translates to “king of gore.”
The process of identifying the dinosaur’s species began in 2009, when a portion of the skull and a few other bones were discovered. The samples were found in Utah’s Grand Staircase-Escalante National Monument, which is a hotbed of dinosaur fossils. During the late Cretaceous period, that area was a very green, tropical island known as Laramidia. Laramidia encompassed the west coast of North America with its easternmost border in modern day New Mexico. It existed from 99-65.5 million years ago until the Western Interior Seaway went away and the islands of Laramidia and Appalachia were joined as one continent.
There are distinct differences in skull morphology of dinosaurs in the same group between different regions on the island, leading the researchers to believe tyrannosaurs may have been isolated throughout their evolution due to alterations in the sea level. Information gathered for Lythronax’s discovery could also give clues about the landscape and weather just before dinosaurs went extinct.
This discovery also helps to clarify where tyrannosaurs originated. It appears that most of the evidence places the emergence in North America, not Asia as some had thought.