T. rex’s silly-look­ing arms built for slash­ing

Iran Daily - - Science & Technology -

Tyran­nosaurus rex may have had small arms, but it was no pushover.

This fierce di­nosaur is known for its gi­ant head, pow­er­ful jaws and over­all fear­some ap­pear­ance — ex­cept for those com­i­cal-look­ing arms, sci­ence­news.org wrote.

But the roughly me­ter-long limbs weren’t just ves­ti­gial re­minders of a longer-armed past, pa­le­on­tol­o­gist Steven Stan­ley of the Univer­sity of Hawaii at Manoa said at the Ge­o­log­i­cal So­ci­ety of Amer­ica’s an­nual meet­ing.

He ar­gued, “In­stead, the limbs were well-adapted for vi­cious slash­ing at close quar­ters.”

T. rex an­ces­tors had longer arms that the di­nosaur used for grasp­ing. But at some point, T. rex and other tyran­nosaurs be­gan to use their gi­ant jaws for grasp­ing in­stead, and the limbs even­tu­ally at­ro­phied.

Many peo­ple have hy­poth­e­sized that the shrunken arms were, at best, used for mat­ing or per­haps push­ing the an­i­mal up off the ground; at worst, they were com­pletely func­tion­less.

But Stan­ley noted that the arms were quite strong, with ro­bust bones that could sus­tain the im­pact of slash­ing.

Each arm ended in two sharp claws about 10 cen­time­ters long. Two claws give more slash­ing power than three, be­cause each one can ap­ply heav­ier pres­sure.

Stan­ley con­cluded, “Fur­ther­more, the edges of the claws are beveled and sharp like those of a bear rather than flat like the grasp­ing claws of an ea­gle. Those traits sup­port the slasher hy­poth­e­sis.” Many sci­en­tists aren’t con­vinced. Ver­te­brate pa­le­on­tol­o­gist Thomas Holtz of the Univer­sity of Mary­land in Col­lege Park, said, “While an in­ter­est­ing idea, it’s still un­likely that an adult T. rex would have used its arms as a pri­mary weapon.”

Although strong, the arm of a fully grown T. rex would barely reach past its chest, greatly re­duc­ing its po­ten­tial strike zone.

Holtz added, “But a T. rex’s arms grew more slowly than its body, so younger di­nosaur would have had pro­por­tion­ally longer arms. It’s pos­si­ble the ju­ve­niles might have found them use­ful for slash­ing prey.”

sci­ence­news.org Tyran­nosaurus rex may have used its small arms for slash­ing prey.

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