Project Results

About This Project

Tyrannosaurs are essential components of Late Cretaceous ecosystems, but are generally rare and poorly known, especially in the southern U.S. We discovered a mass mortality site, including tyrannosaurs in multiple growth stages. What caused this mass mortality? How diverse were southern tyrannosaurs? What can we conclude regarding the social structure of these apex predators? Full excavation of the site and preparation of the fossil material will help us answer these critical questions.

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What is the context of this research?

The Late Cretaceous rocks of southern Utah preserve a fairly continuous and detailed record of dinosaur evolution between 88 and 73 million years ago. Much of the fossil material found in the Kaiparowits Formation of Grand Staircase-Escalante National Monument is preserved remarkably well, at times capturing soft tissue. This allows for a very detailed glimpse into the unique paleo-ecosystem of the southern part of Laramidia, the island continent that stretched from Alaska to Mexico. Despite its remoteness, in the last 20 years at least 30 new species of dinosaurs have been unearthed from GSENM, of which about 20 have been found in the Kaiparowits Fm alone. Interestingly, many animals discovered from this region are morphologically distinct and part of a whole new ecosystem.

What is the significance of this project?

Diversity of tyrannosaurs, a group of large carnivorous dinosaurs including T. rex, is still largely unknown, mainly because tyrannosaur skull finds are rare. We discovered a site with the remains of three size classes of tyrannosaur, elements of which are morphologically different from analogous elements of the one tyrannosaur known from the Kaiparowits Fm. Full excavation, preparation and research of this site will help us determine tyrannosaur diversity. The association of multiple tyrannosaurs at different growth stages will allow us to assess possible social structures, evidence for which has been previously lacking in southern Laramidia. This discovery is invaluable for understanding not only tyrannosaur behavior, but also general Late Cretaceous paleoecology of southern Laramidia.

What are the goals of the project?

We would like to fully excavate the site, which will require at least two additional field seasons. The fossil material needs to be transported to our lab in Kanab, Utah, much of which has to be done via airlifting due to jacket size/weight and the GSENM transportation plan that prohibits offroad driving.

To unravel the depositional story and assess the cause for this mass mortality, we would like to conduct a detailed analysis of the site. We have found abundant charcoal associated with the fossil material. Was a forest fire responsible for the deaths?

Once in the lab, we would like to fully prepare the material and make a taxonomic identification of the tyrannosaur. Is it a new species? And if so, what does that tell us about the tyrannosaur diversity this far south on the Laramidian continent?