The terrible tyrannosaurs were social animals – sciencedaily

The dreaded Tyrannosaur dinosaurs that ruled the northern hemisphere during the Late Cretaceous Period (66-100 million years ago) may not have been solitary predators as is commonly believed, but similar social carnivores. wolves, according to a new study.

The find, based on research at a unique fossil bone site inside Utah’s Grand Staircase-Escalante National Monument containing the remains of several dinosaurs of the same species, was made by a team of scientists, including Celina Suarez, associate professor of geosciences at the University of Arkansas.

“This confirms our hypothesis that these tyrannosaurs died at 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,” said Suarez.

The research team also includes scientists from the United States Bureau of Land Management, the Denver Museum of Nature and Science, Colby College of Maine, and James Cook University in Australia. The study examines a unique fossil bone site inside the Grand Staircase-Escalante National Monument called the ‘Rainbow and Unicorn Quarry’ which they say exceeded expectations even raised by the nickname high site.

“Localities [like Rainbows and Unicorns Quarry] that provide information on the possible behavior of extinct animals are particularly rare and difficult to interpret, “tyrannosaur expert Philip Currie said in a BLM press release.” Traditional excavation techniques, supplemented by 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. Without a doubt, this group died together, adding to a growing body of evidence that tyrannosaurids were able to interact as gregarious packs. “

In 2014, BLM paleontologist Alan Titus discovered the Rainbows and Unicorns Quarry site at the Grand Staircase-Escalante National Monument and conducted further research on the site, which is the first site of tyrannosaur mass death found in the south. the United States. The researchers carried out a battery of tests and analyzes on the remains of the original site, now preserved as small fragments of rock and fossils in their final resting place, and the sandbank deposits of the ancient river.

“We realized right away that this site could potentially be used to test the idea of ​​the social tyrannosaurus. Unfortunately, the ancient history of the site is complicated,” said Titus. “As the bones appear to have been exhumed and buried again by the action of a river, the original context in which they rested has been destroyed. However, not all was lost.” As details of the site’s history emerged, the research team concluded that the tyrannosaurs died together in a seasonal flood that washed their carcasses into a lake, where they sat, largely intact until the river made its way through the bone bed.

“We used a truly multidisciplinary approach (physical and chemical evidence) to piece together the history of the site, the end result being that the tyrannosaurs died together in a seasonal flood,” said Suarez.

Using analysis of stable carbon and oxygen isotopes and rare earth element concentrations in bone and rock, Suarez and his then doctoral student, Daigo Yamamura, were able to provide a chemical footprint of the site. . Based on the geochemical work, they were able to conclusively determine that the site remains were all fossilized in the same environment and were not the result of an attrition assemblage of fossils from various areas.

“None of the physical evidence conclusively suggested that these organisms fossilized together, so we turned to geochemistry to see if that could help us. said Suarez.

Excavation of the quarry site has been ongoing since its discovery in 2014 and due to the size of the site and the volume of bones found there, excavation will likely continue for the foreseeable future. In addition to tyrannosaurs, the site has also produced seven species of turtles, several species of fish and rays, two other types of dinosaurs, and an almost complete skeleton of a juvenile Deinosuchus alligator (12 feet long), although they do not appear. to be all dead together like tyrannosaurs.

“The new Utah site adds to the growing body of evidence showing that tyrannosaurs were large, complex predators capable of social behaviors common to many of their living relatives, the birds,” said Joe Sertich, project contributor, curator of dinosaurs at the Denver Museum. of nature and science. “This finding should be the tipping point to reconsider how these large carnivores behaved and hunted in the northern hemisphere during the Cretaceous.”

Future research plans for the rainbow and unicorn quarry fossils include additional trace elements and isotopic analysis of tyrannosaur bones, which paleontologists hope will determine the mystery of the behavior with more certainty. social of Teratophoneus.

Unlike social interaction between humans and between many species of animals, paleontologists have long debated whether tyrannosaurs lived and hunted alone or in groups.

Based on findings at a site in Alberta, Canada with more than 12 individuals, the idea that tyrannosaurs were social with complex hunting strategies was first formulated by Philip Currie over 20 years ago. . This idea has been widely debated, with many scientists doubting that giant killing machines have the brains to organize themselves into something more complex than what is seen in modern crocodiles. Because the Canadian site appeared to be an isolated case, skeptics claimed it represented unusual circumstances that did not reflect normal tyrannosaur behavior. The discovery of a second site of massive tyrannosaur death in Montana again raised the possibility of social tyrannosaurs, but this site was still not widely accepted by the scientific community as evidence of social behavior. The unicorn and rainbow quarry researcher’s findings provide even more compelling evidence that tyrannosaurs may have lived usually in groups.

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