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T. rex, the clumsy giant?

June 5, 2007
Courtesy Communications Management
and World Science staff

New re­search chal­lenges the no­tion that the di­no­saur Ty­ran­no­saur­us rex—the pred­a­to­ry “tyrant liz­ard king”—could turn quickly and chase down fast, ag­ile di­no­saurs.

Two Ty­ran­no­saur­us rex adults are alert and ready to hunt. (Paint­ing © Mark Hal­lett)


John Hutch­in­son of the Roy­al Vet­er­i­nary Col­lege at Herts, U.K. and col­leagues used com­put­er mod­el­ing to fig­ure out what a typ­i­cal T. rex’s body mass would have been, how fast it could run and how quickly it could turn. 

The team de­vel­oped a mod­el­ling sys­tem that es­ti­mates the di­no­saur’s cen­tre of mass, a point at which all its weight can be con­sid­ered to be con­cen­trat­ed in an­a­lyz­ing its mo­tion. 

They al­so es­ti­mat­ed its in­er­tia, the ex­tent to which its turn­ing is slowed down by its own mass. The re­search­ers es­ti­mat­ed that a live T. rex weighed six to eight tons, though some larg­er in­di­vid­u­als could have weighed up to 10 tons, they said.

The mod­el­ing sys­tem en­abled Hutch­in­son to es­ti­mate the rep­tile’s turn­ing abil­ity, some­thing nev­er done be­fore, he said. The bru­te would have turned in­credibly slowly due to its mas­sive in­er­tia, he added, tak­ing a sec­ond or two to turn 45 de­grees—far slower than a hu­man. The spe­cies cer­tainly could not have pir­ou­et­ted rap­idly on one leg, Hutch­in­son added, as some il­lustra­t­ions have pic­tured it and oth­er large di­no­saurs do­ing. 

This re­search al­so adds new sup­port, with bet­ter cal­cula­t­ions, for a no­tion that T. rex and its rel­a­tives, called tyran­nosaurs, could­n’t run at 45 miles per hour as of­ten pic­tured in movies, the re­search­ers said. Twenty-five miles per hour seems the ex­treme max­i­mum speed, they claimed.

“Pre­vi­ous stud­ies have tried to find one or two num­bers to es­ti­mate the mass, where­as we did over 30 dif­fer­ent com­put­er mod­els, giv­ing a much more def­i­nite pre­dic­tion,” said Hutch­in­son. “From this we now know that a T. rex would have been front-heavy, turned slowly and could man­age no more than a lei­surely jog.”

Biome­chan­i­cal stud­ies in­to large liv­ing an­i­mals such as ele­phants of­ten in­form palaeon­tol­o­gists of how di­no­saurs would have moved. But this study found that T. rex wouldn’t have walked like an el­e­phant, with ver­ti­cal, pillar-like legs. To keep its cen­tre of mass over its feet and thus avoid fall­ing over, T. rex had to bend its legs con­si­der­ably, Hutch­in­son ex­plained. The re­search ap­pears in the June 21 is­sue of the Jour­nal of The­o­ret­i­cal Bi­ol­o­gy.


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New research challenges the time-honored notion that the dinosaur Tyrannosaurus rex, the predatory “tyrant lizard king,” could turn quickly and chase down fast, agile dinosaurs. John Hutchinson of the Royal Veterinary College at Herts, U.K. and colleagues used computer modeling to figure out what a typical T. rex’s body mass would have been, how fast it could have run and how quickly it could turn. The team developed a modelling system that estimates the dinosaur’s centre of mass, a point at which all its weight can be considered to be concentrated in analyzing its motion. They also estimated its inertia, the extent to which its turning is slowed down by its own mass. The researchers estimated that a live T. rex weighed six to eight tons, though some larger individuals could have weighed up to 10 tons, they added. The modeling system enabled Hutchinson to estimate the reptile’s turning ability, something never done before, he said. The brute would have turned incredibly slowly due to its massive inertia, he added, taking a second or two to turn 45 degrees—far slower than a human. The species certainly could not have pirouetted rapidly on one leg, Hutchinson added, as some illustrations have pictured it and other large dinosaurs doing. This research also adds new support, with better calculations, for the notion that T. rex and its relatives, called tyrannosaurs, couldn’t run at 45 miles per hour as often pictured in movies, the researchers said. Twenty-five miles per hour seems the extreme maximum speed, they claimed. “Previous studies have tried to find one or two numbers to estimate the mass, whereas we did over 30 different computer models, giving a much more definite prediction,” said Hutchinson. “From this we now know that a T. rex would have been front heavy, turned slowly and could manage no more than a leisurely jog.” Biomechanical studies into large living animals such as elephants often inform palaeontologists of how dinosaurs would have moved. But this study found that T. rex would not have walked in the same way as an elephant does, with vertical, pillar-like legs. To keep its centre of mass over its feet, and avoid falling over, T. rex needed to bend its legs considerably, Hutchinson explained. The research appears in the June 21 issue of the Journal of Theoretical Biology.