By Jason Matthews

The Tyrannosaurus-Rex is probably the most well-known of all dinosaurs. Almost every child remembers the twisted mix of emotions the first time they saw one on screen. The combination of fear and fascination that the T-Rex invoked, as they mindlessly rampaged and ate any creature they came across, seared this particular "terrible lizard" into our memories, and often, nightmares. However, a new study on a recent fossil discovery suggests this lonesome apex hunter of the cretaceous period was not the solitary predator we believed.

Imiage Credit: Herschel Hoffmeyer via Shutterstock / HDR tune by Universal-Sci

Uncovering the past

A team of researchers and scientists, including Celina Suarez, an associate professor of geosciences from the University of Arkansas, studied the "Rainbows and Unicorns Quarry" dig site in Utah's Grand Staircase-Escalante National Monument, where they have uncovered four to five T-Rex fossils. The reason for all the excitement is they appear to have all died together at the same time. A group death of Tyrannosaurs goes against everything we thought we knew about the behavior of these beasts.

The ultimate "cold case"

All the T-Rex fossils appear to have been disturbed over the eons. After looking at all the evidence, the team believes the animals died simultaneously, probably due to a seasonal flash flood. Their bodies were washed downstream to the bottom of a lake. Their bones were likely disturbed several times by more floods and changes in the watercourse before they were eventually fossilized. The team used a plethora of techniques to piece together the final journey of these ancient monsters.

Suarez explained that none of the material evidence conclusively suggested that these organisms came to be fossilized together, so they turned to geochemistry to see if that would help them. The similarity of rare earth element patterns is highly suggestive that these organisms died and were fossilized together."

She continued, "We used a truly multidisciplinary approach (physical and chemical evidence) to piece the history of the site together, with the end result being that the tyrannosaurs died together during a seasonal flooding event."

"This supports our hypothesis that these tyrannosaurs died in this site and were all fossilized together, they all died together, and this information is key to our interpretation that the animals were likely gregarious in their behavior," concluded Suarez.

Vindicated hypothesis.

Two decades ago, Phillip Currie, a Canadian palaeontologist, suggested tyrannosaurs were pack hunters with a complex social structure. He raised this hypothesis based on a similar discovery in Alberta, Canada. Most scientists dismissed this idea. They doubted tyrannosaurs had the mental capacity to form these behaviors and behaved in a similar way to modern reptiles like crocodiles. Curries peers suggested the Alberta site was an isolated event. However, this new discovery seems to support Currie's idea and indicates tyrannosaurs had a much more complex social behavior, more like birds than reptiles.

"Localities [like Rainbows and Unicorns Quarry] that produce insights into the possible behavior of extinct animals are especially rare and difficult to interpret," said Currie in a press release from the U.S. Bureau of Land Management. "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. Undoubtedly, this group died together, which adds to a growing body of evidence that tyrannosaurids were capable of interacting as gregarious packs."

Future discoveries

The Rainbows and Unicorns Quarry site continues to yield more fossil discoveries, including several new aquatic species and other types of dinosaurs, so it should keep the team and other paleontologists busy for years to come.

Be sure to check out the paper listed below for more information about the study.

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