As the fiercest dinosaur, the Tyrannosaurus rex once roamed the lands that now make up North America with impunity. And if the conclusions of a new research project are correct, their behavior may have been even more terrifying and intimidating than previously thought. This is evident from an article of 19 April in the open access journal PeerJ: life and the environment Tyrannosaurus rex was most likely not a lone hunter, but instead worked in packs to chase, surround, and voraciously consume the animals they depended on, much like wolves.
A circular representation of Tyrannosaurus rex skulls. ( Kumiko from Tokyo, Japan / CC BY-SA 2.0 )
Tyrannosaurus Rex: The Complex Truth finally emerges
This fascinating and somewhat disturbing discovery emerged from a study conducted by a team of paleontologists working with the U.S. Bureau of Land Management (BLM) office in Utah.
The scientists conducted an extensive analysis of a diverse collection of Tyrannosaurus rex bones found at a fertile Cretaceous fossil site in southern Utah, located near the Grand Staircase-Escalante National Monument. This site is popularly known as the “Rainbows and Unicorns Quarry”, in recognition of all the rare fossils (the “unicorns”) that have been excavated there.
Paleontologist Alan Titus, who discovered the Rainbows and Unicorns site in 2014 and is one of the lead authors of the PeerJ study, says the group of deceased and fossilized Tyrannosaurus rex specimens were victims of a massive flood that drowned them and washed their bodies into a lake. They lay on the bottom, grouped and undisturbed for millions of years, until climatic and geological changes dried up the lake and created a river (also now disappeared) that eroded the soil and brought the bones back to the surface of the earth.
“We used a truly multidisciplinary approach (physical and chemical evidence) to piece together the history of the site,” explains Celina Suarez, a geologist and student at the University of Arkansas. “The end result [was] that the tyrannosaurs died together during a seasonal flood. ”
The members of the BLM research team see their findings as circumstantial but clear evidence of group dynamics in action among the Tyrannosaurus rex specimens in question. Their cooperative behavior would have been survival-oriented, centered around group hunting, and perhaps also allow for comprehensive parental care, the scientists argue.
“The new Utah site adds to the growing body of evidence showing that tyrannosaurs were complex, large predators capable of social behaviors that many of their living relatives, the birds, have,” said Joe Sertich, participant. the research project, which is the dinosaur curator at the Denver Museum of Nature and Science. “This discovery should be the tipping point to rethink how these top carnivores behaved and hunted across the Northern Hemisphere during the Cretaceous Period.”
A family of Tyrannosaurus rex dinosaurs on the run. ( Orlando Florin Rosu / Adobe Stock)
Slow and steady wins the race
Earlier evidence to support the claim that Tyrannosaurus rex hunted in groups emerged in 2020, when Canadian scientists published the results of their study of tyrannosaurus physiology and anatomy in the May issue of the journal PLOS One .
Contrary to previous claims, which claimed that Tyrannosaurus rex could travel at speeds of up to 42 miles (70 kilometers) per hour, the Canadian researchers concluded that a sprinting T. rex could not have surpassed 12 miles per hour. hour (20 kilometers per hour) marking. However, the T. rex anatomy would have allowed them to keep sailing at that speed for considerable distances, said Professor Hans Larsson of McGill University.
“If this was their way of hunting, they could cover much greater distances at a reasonably good price [but not great] clip, what kind of lifestyle would that be? The animals that do this today are, like wolves, that hunt in packs, ”noted Larsson.
It should also be mentioned that the bone bed in southern Utah is not the first mass grave of the Tyrannosaurus rex discovered on the North American continent. Two decades ago, more than a dozen different T. rex fossils were found buried together at a site in Red Deer, Alberta, Canada, and another massive T. rex burial was unearthed a few years later in Montana.
If the pack hypothesis is true, no doubt more such discoveries await.
Tyrannosaurus rex attacks an Einiosaurus. ( Elenarts / Adobe Stock)
Imagine countless packages of hungry T. Rexes on the hunt
Had Tyrannosaurus rex hunted in teams, as the growing body of evidence suggests, their group cohesion would have given them evolutionary benefits that would have been reflected in their population numbers.
During their 2.5 million year reign as the king of the dinosaurs, the mighty Tyrannosaurus rex was always the predator, never the prey. As a result, there would have been few controls on their population growth, other than the occasional food shortage (which was probably rare on a prehistoric earth teeming with animal life).
That begs an interesting question: Exactly how many Tyrannosaurus rex specimens lived and died on the North American continent, before the entire species went extinct about 65 million years ago?
A team of scientists and science students from the University of California-Berkeley set out to find the answer to this intriguing question. They collected all of the data on Tyrannosaurus rex obtained from the fossil record and used that information to calculate the mean lifespan of T. rex, along with the creature’s nutritional needs and likely breeding ability.
After compiling all the numbers, the Cal-Berkeley team determined that at any one time, about 20,000 individual animals would have lived on the 1.4 million square miles (2.3 million square kilometers) of available habitat space. They estimate that a new generation would be born every 19 years, and that there would have been about 127,000 generations of T. rex over the course of its 2.5 million-year species lifespan.
If these estimates are correct, and the scientists claim that it is 95 percent certain that they are, it means that 2.5 billion Tyrannosaurus rexes have lived and died on this planet. Had they traveled in groups of 10 to 20, at any given time between 1,000 and 2,000 T. rex packs would roam the continent in search of food.
Assuming it did, the animals that T. rex preyed on would have enjoyed precious moments of rest. Once a thundering herd of the most terrifying predator the planet has ever produced had passed, another would soon arrive from beyond the horizon, and that new herd would be just as hungry as the one that preceded it.
If people ever perfect the science of time travel, we should probably think twice about visiting the North American continent during the late Cretaceous Period.
Top image: Tyrannosaurus rex is hunted in groups like wolves, according to the latest scientific study. Source: warpaintcobra / Adobe Stock
By Nathan Falde