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Fossils found in Utah indicate tyrannosaurs were social predators, not solitary

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Posted at 3:49 PM, Apr 19, 2021

KANAB, Utah — New research from paleontologists in Utah found evidence that tyrannosaurs may have been social — hunting in packs like wolves — rather than solitary as previously believed.

In 2014, Dr. Alan Titus of the Bureau of Land Management (BLM) discovered what was later named the "Rainbows and Unicorns Quarry" site in Grand Staircase Escalante National Monument.

Scientists discovered a "tyrannosaur mass death site" there — the first of its kind to be found in the southern United States, according to a press release from the BLM.

Tyrannosauridae is a family in dinosaur taxonomy that includes several different species, including the well-known Tyrannosaurus rex, as well as the species whose fossils were found in the southern Utah quarry: Teratophoneus curriei.

“We realized right away this site could potentially be used to test the social tyrannosaur idea," said Titus, a paleontologist with the BLM Utah Paria River District. "Unfortunately, the site’s ancient history is complicated."

PHOTO GALLERY: Excavation and findings from "tyrannosaur mass-burial site" in southern Utah

Titus explains that the bones found at the site appeared to have been exhumed and reburied by river activity, so the way in which they were found was not how they were originally buried.

However, further research concluded that the group of Teratophoneus died together in a seasonal flood. Their carcasses were washed into into a lake, where they sat "largely undisturbed" until the river stirred them up.

“Traditional excavation techniques, supplemented by the analysis of rare earth elements, stable isotopes and charcoal concentrations convincingly show a synchronous death event at the Rainbows site," world-renowned tyrannosaur expert Dr. Philip Currie said.

Currie first hypothesized more than 20 years ago that tyrannosaurs were social and had complex hunting strategies. His ideas were based on findings from a site in Alberta, Canada where at least 12 tyrannosaurs were found.

"Localities [like Rainbows and Unicorns Quarry] that produce insights into the possible behavior of extinct animals are especially rare and difficult to interpret,” he added.

Still, Currie and other experts are confident that these four or five tyrannosaurs were together when they died.

"Undoubtedly, this group died together, which adds to a growing body of evidence that tyrannosaurids were capable of interacting as gregarious packs," he said.

Titus added: "I consider this sort of a once-in-a-lifetime discovery... I probably won't find another site this exciting and scientifically significant during my career."

The research findings were published Monday and can be read in full on PeerJ, an open-access scientific journal.

Full list of contributors to the study:

  • Alan L. Titus​
  • Katja Knoll
  • Joseph J.W. Sertich
  • Daigo Yamamura
  • Celina A. Suarez
  • Ian J. Glasspool
  • Jonathan E. Ginouves
  • Abigail K. Lukacic
  • Eric M. Roberts