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Washington, Feb 23 (ANI): A new study has found that Tyrannosaurus Rex was an opportunistic feeder, not a top predator.

Palaeontologists John “Jack” Horner from the Museum of the Rockies and Mark B. Goodwin from the University of California, Berkeley, say that a new census of all dinosaur skeletons unearthed over a large area of eastern Montana shows that T. rex survived on both carrion and fresh-killed prey and exploiting a variety of animals, not just large grazers.

“In our census, T. rex came out very high, equivalent in numbers to Edmontosaurus, which many people had thought was its primary prey,” said Horner.

“This says that T. rex is not a cheetah, it’s not a lion. It’s more like a hyena.”

“This putative apex predator is as abundant in the upper layers of the Hell Creek Formation as the herbivores, its reputed primary food source,” added Goodwin.

“And it’s even more plentiful in the other two-thirds of the formation. This supports the view that T. rex benefited from a much wider variety of food sources than live prey.”

Goodwin explained that top predators are one-third or one-fourth as abundant as their prey, because of the larger energy needs of carnivores but opportunistic hunters like hyena can be twice as abundant as the top predators.

“If you count the lions and the leopards and the cheetahs in the Serengeti, the number still does not equal the number of hyenas, because hyenas have a much wider food source,” Horner said.

“There’s no evidence that T. rex could run very fast, so it wasn’t out there being a cheetah. If it could get a sick animal, it would.”

The census included only skeletal remains, not teeth, because the paleontologists wanted a record of the maturity of each specimen, and teeth tell little about the age of a dinosaur at death, Goodwin said.

A census of older sediments - the lower Hell Creek formation - turned up 11 Triceratops, 11 T. rex and six Edmontosaurus partial skeletons, along with fossil bones of three other dinosaurs: Thescelosaurus and Ornithomimus, two bird-like, bipedal meat-eaters reaching some 12 feet in length at maturity; and Ankylosaurus, an armored, four-legged plant-eater with a club tail.

“Small juveniles and older adults were relatively rare compared to large juveniles and subadults for all the dinosaurs,” Goodwin said.

“This adds to an emerging picture of what the dinosaur fauna looked like during the late Cretaceous,” he said.

“Definitely there was a change in population leading up to the Cretaceous-Tertiary boundary, so something was happening to the faunas prior to the impact,” Goodwin said.

“During the 10 million years after dinosaur diversity peaked 75 million years ago, the dinosaurs dwindled pretty fast, and there weren’t many left at the end.”

The results were published Feb. 9 in the open-access journal PLoS ONE. (ANI)