New early Tyrannosaur sheds light on the evolution of later bone-crushing giants

Business News | 6 May |

The Arizona Museum of Natural History and Virginia Tech announce the discovery and publication of a mid-Cretaceous Period tyrannosaur that significantly contributes to understanding tyrannosaur evolution. The find is important because of the scarcity of mid-Cretaceous deposits worldwide. Fossils from such rare deposits offer unique insights into the ancestors of the mighty dinosaurs of the end-Cretaceous.

The find is announced and described today in the journal Nature Ecology and Evolution. Co-discoverer and lead author of the paper, Mesa Arizona native Sterling Nesbitt, Department of Geosciences, Virginia Tech, states that the tyrannosaur “belongs to a dinosaurian fauna that just precedes the iconic dinosaurian faunas in the latest Cretaceous that include some of the most famous dinosaurs.”

The tyrannosaur is named Suskityrannus hazelae. Suski means coyote in the Zuni language (used after consultation with Zuni Tribe). Tyrannus hazelae means tyrant (Latin) of Hazel, or Hazel’s coyote tyrant, and is named after Hazel Wolfe, one of the field project’s critical members.

Two tyrannosaurs of the same species were found within about 50 meters of each other in the Moreno Hill Formation in the Zuni Basin of western New Mexico. Field crews from the Arizona Museum of Natural History recovered the dinosaurs in 1996-1998. The fossils date to the early Middle Turonian, or 92 million years ago, thus predating the massive T. rex by 27 million years.

As the authors state, “This new species is phylogenetically intermediate between the grade of early-diverging, small to medium-sized tryannosauroids that originated in the Middle Jurassic and the enormous, bone-crunching apex predator tyrannosaurids of the final 20 million years of the Cretaceous.”

These mid-Cretaceous gracile animals had a foot shaped for speed and recurved serrated teeth confirming their carnivorous status. Analyses of the skeletons suggest they had not yet completed their growth, i.e. they were juveniles. The dinosaur was about three meters (nine feet) long, stood 2-3 feet tall at the hip, and weighed 20-40 kilograms (about 45-90 pounds).

Dr. Steven Brusatte, University of Edinburgh, author of The Rise and Fall of the Dinosaurs and co-author of the Nature Ecology and Evolution paper, writes that “Suskityrannus is a key link between the enormous bone-crunching dinosaurs like T. rex and the smaller species they evolved from. The new species shows that tyrannosaurs developed many of their signature features like a muscular skull, broad mouth, and a shock-absorbing foot when they were still small, maybe as adaptations for living in the shadows.”

These tyrannosaurs are also significant for our understanding of associated faunas from the Zuni Basin in similar timeframes: the ceratopsian Zuniceratops chistopheri, the hadrosaur Jeyawati rugoculus, the therizinosaur Nothronychus mckinleyi and ankylosaur fossils. In the late Cretaceous, ceratopsians such as Triceratops, numerous large hadrosaurs, ankylosaurs and, of course, the mighty tyrannosaurs roamed the landscapes, only to face the rapid extinction event about 66 million years ago.

Sterling Nesbitt, lead author of the Nature Ecology and Evolution paper, was a teen volunteer at the Arizona Museum of Natural History when he was part of the team that discovered Suskitryannus. Now an assistant professor at Virginia Tech, he writes that “My discovery of a partial skeleton of Suskityrannus put me onto a scientific journey that has framed my career.”

The Arizona Museum of Natural History will permanently house the Suskityrannus fossils. Benjamin Paysnoe, Paleo-artist with the museum, has created a full-scale model of Suskityrannus that is on display at the museum along with a reproduction of the Suskityrannus skeleton. Also on view are Zuniceratops, therazinosaur remains, a partial skeleton and animatronic model of an early ankylosaur, as well as earlier and later dinosaurs.

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