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October 29, 2015

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T. rex may have been a cannibal

Oct. 29, 2015
Courtesy of Geological Society of America
and World Science staff

A re­cently un­earthed ty­ran­no­saur bone has re­vealed a nas­ty lit­tle 66-million-year-old family se­cret, sci­en­tists claim: the bone has pe­cu­liar tooth marks strongly sug­gest­ing it was gnawed by an­oth­er ty­ran­no­saur. 

A recently unearthed tyrannosaur bone with tooth marks that scientists say point to cannibalism. (Photo by Matthew McLain)


The find could be some of the best ev­i­dence yet that ty­ran­no­saurs were not shy about eat­ing their own kind, re­search­ers say.

“We were out in Wy­o­ming dig­ging up di­no­saurs in the Lance Forma­t­ion,” said pa­le­on­tol­ogist Mat­thew McLain of Lo­ma Lin­da Un­ivers­ity in Cal­i­for­nia.

“Some­one found a ty­ran­no­saur bone that was bro­ken at both ends. It was cov­ered in grooves. They were very deep grooves.”

The grooves were clearly those of an an­i­mal pulling the flesh off the bone—pulling at right angles to the bone, as hu­mans eat fried chick­en, he said. But one groove stood out. It was at the larg­er end of the bone and con­tained smaller par­al­lel grooves caused by the din­er’s head turn­ing, so that the ser­rat­ed edges of its teeth dragged across the bone.

Ser­rat­ed teeth rule out crocodiles and point to a di­no­saur like Ty­ran­no­sau­r­us rex, which is part of a line­age of di­no­saurs called thero­pods, he added. 

The only large thero­pods found in the Lance Forma­t­ion are two ty­ran­no­saurs—T. rex or Nan­otyran­nus lan­cen­sis—elim­in­at­ing all in­ter­preta­t­ions but can­ni­bal­ism, ex­plained McLain, who is to pre­sent the findings on Nov. 1 at the an­nu­al meet­ing of the Ge­o­log­i­cal So­ci­e­ty of Amer­i­ca in Bal­ti­more.

“This has to be a ty­ran­no­saur,” said McLain. “There’s just noth­ing else that has such big teeth.”

The di­rec­tion of the grooves is con­sist­ent with get­ting flesh from bones off an an­i­mal that was quite dead at the time, he added. The bones don’t re­veal wheth­er the can­ni­bal was scav­eng­ing or was al­so the kill­er of the ty­ran­no­saur.

“Ex­actly who did the eat­ing that day, in the Late Cre­ta­ceous, could still be sorted out by the same grooves,” McLain said.

The serra­t­ion grooves are a val­u­a­ble clue to the size of the an­i­mal who owned the teeth, he added. Pre­vi­ous work us­ing Ko­modo drag­on teeth has shown the rela­t­ion­ship be­tween serra­t­ion sizes and the size of the an­i­mal. This ap­proach has been used on ty­ran­no­saurs, and McLain thinks it will work in this case, too.

“It only works if you know what spe­cies it is,” he said. “And since ty­ran­no­sauruses are the only large preda­tors in these forma­t­ions, it’s pret­ty straight­for­ward.”

Even with­out know­ing the size of the eat­er, it may be easy to say which spe­cies of ty­ran­no­saur was eat­ing, be­cause, ac­cord­ing to McLain, many pa­le­on­tol­ogists be­lieve Nan­otyran­nus were really ju­ve­nile T. rex.


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A recently unearthed tyrannosaur bone has revealed a nasty little 66-million-year-old family secret, scientists claim: the bone has peculiar tooth marks strongly suggesting it was gnawed by another tyrannosaur. The find could be some of the best evidence yet that tyrannosaurs were not shy about eating their own kind, researchers say. “We were out in Wyoming digging up dinosaurs in the Lance Formation,” said paleontologist Matthew McLain of Loma Linda University in California. “Someone found a tyrannosaur bone that was broken at both ends. It was covered in grooves. They were very deep grooves.” The grooves were clearly those of an animal pulling the flesh off the bone—pulling in a direction perpendicular to the bone, as humans eat fried chicken, he said. But one groove stood out. It was located at the larger end of the bone and contained smaller parallel grooves caused by the diner’s head turning, so that the serrated edges of its teeth dragged across the bone. Serrated teeth rule out crocodiles and point to a dinosaur like T. rex, which is part of a lineage of dinosaurs called theropods, he added. The fact that the only large theropods found in the Lance Formation are two tyrannosaurs—Tyrannosaurus rex or Nanotyrannus lancensis—eliminates all interpretations but cannibalism, explained McLain, who will be presenting the discovery on Nov. 1 at the annual meeting of the Geological Society of America in Baltimore. “This has to be a tyrannosaur,” said McLain. “There’s just nothing else that has such big teeth.” The direction of the grooves is consistent with getting flesh from bones off an animal that was quite dead at the time, he added. The bones don’t reveal whether the cannibal was scavenging or was also the killer of the tyrannosaur. “Exactly who did the eating that day, in the Late Cretaceous, could still be sorted out by the same grooves,” McLain said. The serration grooves are a valuable clue to the size of the animal who owned the teeth, he added. Previous work using Komodo dragon teeth has shown the relationship between serration sizes and the size of the animal. This approach has been used on tyrannosaurs, and McLain thinks it will work in this case, too. “It only works if you know what species it is,” he said. “And since tyrannosauruses are the only large predators in these formations, it’s pretty straightforward.” Even without knowing the size of the eater, it may be easy to say which species of tyrannosaur was eating, because, according to McLain, many paleontologists believe Nanotyrannus were really juvenile T. rex.