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Thursday, July 29, 2021

T. rex preferred left-overs, not fresh meals

If you are familiar with the Jurassic Park movies, you probably know that the Tyrannosaurus rex – T. rex – is portrayed as a fearsome hunter after any piece of meat. But what if this dinosaur was a scavenger and not a hunter?

Paleontologists John Horner, Mark Goodwin and Nathan Myhrvold conducted a census in the Hell Creek Formation in Montana that revealed new evidence that the T. rex was more like a modern-day hyena – a scavenger. The census, which began in 1999 and lasted through 2009, found T. rex skeletons to be as abundant as the Edmontosaurus – an herbivorous dinosaur. According to the published findings, this suggested that the T. rex was not a typical predator, but the beneficiary of a wide selection of food rather than exclusive live prey.

“We counted skeletons of all kinds of dinosaurs. Triceratops came out as the most prevalent, while T. rex came in a very close second with Edmontosaurus; based on the numbers, T. rex was highly unlikely to have just been a predator,” said John “Jack” Horner, curator of paleontology and professor at Museum of the Rockies, Montana State University.

Horner said that when comparing T. rex numbers to lion numbers in the Serengeti Plain – an African region that hosts the world’s largest mammal migration – one can see that the number of hyenas is significantly higher than the number of lions, something which is contrary to evidence found with the T. rex in the Hell Creek formation. The T. rex numbers seem to be more closely-related to the hyena numbers, which indicates that the T. rex was more likely to have been a scavenger. The T. rex occupied the same ecological niches that the hyena occupies now.

Horner pointed to evidence that shows bite marks in bones, as something important in differentiating between the T. rex being a predator or a scavenger.

“Hunters eat the good parts and leave the rest alone; bite marks in the bones suggest that the T. rex was tearing the carcass apart, something scavengers do,” Horner said.

“I’ve been arguing that point for a long time; it always seemed odd that they had different characteristics than other predatory dinosaurs,” Horner said.

He said that the T. rex’s short arms were extremely disadvantageous for catching prey. If you stretch your arm out and look at the halfway point, that is how long a T. rex’s arms were.

According to reports by the United States Geological Survey (USGS), an adult T. rex was slow. In fact, a recent estimate states that an average human could outrun an adult T. rex, adding to Horner’s belief of the T. rex not being an apt hunter.

Richard Cowen, a UC Davis lecturer emeritus of geology, described Horner’s research as well-documented and believable.

“It’s a major change at the way we look at T. rex,” Cowen said.

He said that Horner’s census is the biggest one ever done, and that the evidence that T. rex’s numbers were very close to Edmontosaurus reveals that T. rex is nowhere near as rare as people thought.

According to Cowen, an adult T. rex weighed between 5 and 10 tons – 10 to 20 thousand pounds – had teeth with ridges that could tear through meat, an enormous skull and was the largest carnivorous dinosaur of its time. It lived during the late Cretaceous period, 60 to 65 million years ago.

Cowen mentioned that hyenas are supposed to be scavengers, but that they will actually kill something if they can.

“They are opportunists, they take what they can get,” Cowen said.

This comparison provides a way at looking at T. rex as a scavenger first and a hunter second. Nevertheless, Cowen believes that the census evidence is a “game-changer” in thinking about the T. rex.

Horner, who worked on the Jurassic Park films as an advisor, said he would depict T. rex as a scavenger if he was the director of a dinosaur film, but that his advising roles have just been focused on making the dinosaurs look as close to actuality as possible.

“People just want the T. rex to be a killer rather than just look at the evidence,” Horner said.

He said that he does not worry about the reaction he receives to his research and that he will continue to publish evidence he finds.

ERIC C. LIPSKY can be reached at science@theaggie.org.

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