Seventy-four million years ago, tyrannosaurs hunted in the jungles of the late Cretaceous period – but they weren’t alone. Fossils from a family of drowned tyrannosaurs suggest these giants formed cohesive groups that hunted in packs.
The fossils come from a site at Grand Staircase-Escalante National Monument in southern Utah. In 2014, Alan Titus at the US Bureau of Land Management stumbled upon the remains of a group of tyrannosaurs. “The first discovery bone was an ankle bone, and within minutes of brushing around, we uncovered dozens of other tyrannosaur bones,” he said in a press conference.
In total, five tyrannosaur skeletons of the genus Teratophoneus were unearthed. Based on their sizes, the team estimated that the group is composed of one adult, one sub-adult and three juveniles.
Celina Suarez at the University of Arkansas performed a stable isotope analysis on samples taken from each of the skeletons to determine the environment these dinosaurs lived in, how they were fossilised and a potential cause of death. She found that they died together in a single catastrophic event – a flood.
The tyrannosaur family died and fossilised at the same time, which provides more evidence that these dinosaurs were gregarious animals that lived and hunted in groups, much like wolves do today.
Group hunting by large predators like tyrannosaurs is rare. “Predators don’t instinctively become gregarious as easily as plant eaters,” says Titus. Notable exceptions such as wolves, orcas and lions come to mind, but most hunters hunt alone.
This finding adds to previous evidence of social behaviour among tyrannosaurs, including trackways of multiple Tyrannosaurus rex in one location which suggest they may have hunted together. The new evidence of group life among these predators is rare, but builds on previous findings from a fossil site in Canada hypothesised to be the site of a mass death of tyrannosaurs.
Journal reference: PeerJ, DOI: 10.7717/peerj.11013
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