Tyrannosaurs Lived in Groups, New Evidence Suggests
Tyrannosaurs — theropod dinosaurs that lived in what is now North America and Asia between 100 and 66 million years ago (Cretaceous period) — may not have been solitary hunters as popularly envisioned.
The idea that tyrannosaurs were social with complex hunting strategies was first formulated by Canadian paleontologist Professor Philip Currie in 1998.
It was based on the discovery of skeletons of over 12 Albertosaurus sarcophagus individuals at a site in Alberta, Canada.
The idea has been widely debated, with many paleontologists doubting the giant predators had the brainpower to organize into anything more complex than what is observed in modern crocodiles.
Because the Alberta site appeared to be an isolated case, skeptics claimed it represented unusual circumstances that did not reflect normal tyrannosaur behavior.
The 2005 discovery of a second tyrannosaur mass death site in Montana again raised the possibility of social tyrannosaurs, but that site was still not widely accepted by the scientific community as evidence for social behavior.
“Localities that produce insights into the possible behavior of extinct animals are especially rare, and difficult to interpret,” Professor Currie said.
In the new research, Bureau of Land Management paleontologist Alan Titus and colleagues examined a recently-discovered large bonebed containing at least four individuals of the tyrannosaur species Teratophoneus curriei.
Called the Rainbows and Unicorns Quarry, the site is located in the northern Kaiparowits Plateau area of Grand Staircase-Escalante National Monument in southern Utah.
Using analysis of stable carbon and oxygen isotopes and concentrations of rare earth elements within the bones and rock, the researchers found that the remains from the site all fossilized in the same environment and were not the result of an attritional assemblage of fossils washed in from a variety of areas.
They concluded that a group of Teratophoneus curriei died together during a seasonal flooding event that washed their carcasses into a lake, where they sat, largely undisturbed until the river later churned its way through the bone bed.
“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 of four or five tyrannosaurids,” Professor Currie said.
“Undoubtedly, this group died together, which adds to a growing body of evidence that tyrannosaurids were capable of interacting as gregarious packs.”
“The new Utah site adds to the growing body of evidence showing that tyrannosaurs were complex, large predators capable of social behaviors common in many of their living relatives, the birds,” said Dr. Joe Sertich, curator of dinosaurs at the Denver Museum of Nature & Science.
“This discovery should be the tipping point for reconsidering how these top carnivores behaved and hunted across the northern hemisphere during the Cretaceous.”
The study was published online in the journal PeerJ.
A.L. Titus et al. 2021. Geology and taphonomy of a unique tyrannosaurid bonebed from the upper Campanian Kaiparowits Formation of southern Utah: implications for tyrannosaurid gregariousness. PeerJ 9: e11013; doi: 10.7717/peerj.11013