Have you ever noticed how in pictures and movies, such as the Jurassic Park series, plant-eating dinosaurs are always portrayed as grazing together in groups, while the apex predator of the meat eaters, the Tyrannosaurs, are always portrayed as hunting alone?
The scientific thinking for well over a century has been that tyrannosaurs like T-Rex hunted alone, but now that theory is being turned on its head, after scientists released new findings at a virtual press conference on April 19, 2021.
A spectacular find
In 2014, at the Kaiparowits Plateau area of Utah's Grand Staircase-Escalante National Monument, paleontologist Dr. Alan Titus, who is with the Bureau of Land Management (BLM), discovered the mass grave of five Tyrannosaurus Teratophoneus, who had roamed southern Utah around 76.4 million years ago.
The group was comprised of individuals ranging in size and in age from four to 22-years-old, with one adult, one subadult and three juveniles. The group was engulfed in a flood that was drowning them, and their bodies settled onto the bottom of a prehistoric lake which has long dried up.
Based on the fossil evidence, Dr. Titus came to a conclusion earlier put forth by Canadian paleontologist Philip J. Currie, that the Tyrannosaurs had formed a family group and had been hunting together, however, there was also the possibility that the T-Rexes had died at separate times and locations, then been washed down into the lake.
To bolster his case that the Tyrannosaurs were together when they were enveloped by the flood, Dr. Titus enlisted the help of two scientists at the University of Arkansas, Dr. Celina Suarez and Dr. Daigo Yamamura.
They analyzed the stable carbon and oxygen isotopes within the dinosaur's bones and the surrounding rock. It showed that they were all from the same time period, and had died at the same location. Further evidence was found in the patterns of rare earth elements found in the deposits.
A social species
This was not the first discovery of a mass grave of Tyrannosaurs. Over a dozen Tyrannosaurs had been discovered at a site in Alberta, Canada, and another T-Rex mass grave had been found in Montana. Dr. Titus's find, located in a spot nicknamed the "Rainbows and Unicorns Quarry" due to its abundance of rare fossils, is the third such find.
Alongside the Tyrannosaurus fossils, paleontologists working at the Rainbows and Unicorns Quarry have also discovered two other types of dinosaurs, a near-complete skeleton of a juvenile crocodilian, seven species of turtles, and multiple fish and rays. Unlike the T-Rexes, these other animals do not appear to have died together.
During the press conference, which was attended by scientists from the Bureau of Land Management, the University of Arkansas, Miles Community College, Colby College, James Cook University (Australia), and Denver Museum of Nature & Science, Dr. Titus pointed out that the evidence suggests that Tyrannosaurs banded together in herds and were "gregarious."
He went on to say, "So the idea that large predators like T. rex could have actually been socially complex hunters with role playing and division of the hunt, with ambushers and chasers, and then sharing in the kills is somewhat controversial because a lot of researchers feel like these animals simply didn’t have the brainpower to engage in such complex behavior."
However, Dr. Titus described similar behavior in a descendant of the dinosaurs — the Harris Hawk. "They form groups of multiple individuals; they have communal raising of the young; they share in kills, and they actually have a division of labor when they hunt."
Another theory was put forward by Kristi Curry Rogers, a biology professor at Macalester College, who said that “It is a little tougher to be so sure that these data mean that these tyrannosaurs lived together in the good times. It’s possible that these animals may have lived in the same vicinity as one another without traveling together in a social group, and just came together around dwindling resources as times got tougher.”
Protecting the quarry
At the press conference, Dr. Titus added, "The (Bureau of Land Management) is protecting these fossils as national treasures. They’re part of the story of how North America came to be and how ultimately we came to be."
However, in December 2017, then-President Trump severely reduced the size of two of Utah's national monuments, Grand Staircase-Escalante and Bears Ears, by some two million acres. This was the largest rollback of federal land protection in the history of the U.S.
Earlier this month, Interior Secretary Deb Haaland visited southern Utah in order to gather information so she could submit a recommendation to President Biden on whether to reverse the Trump administration's decision to downsize the two national monuments.
When the first Jurassic Park film came out in 1993, the phrase "Clever Girl" became a meme, used to express respect or admiration for something that has demonstrated substantial intelligence. While in the film, the character Muldoon uses the phrase to refer to a Velociraptor, if T-Rex did indeed hunt in packs, we may have to expand the phrase to include them as well.