, Volume 82, Issue 1, pp 59-75

Forelimb biomechanics of nonavian theropod dinosaurs in predation

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Theoretical models of theropod forelimb biomechanics are often tainted with preconceived ideas. Actualistic modeling using specimens and casts, coupled with CAT-scans and dissections of extant vertebrate forelimbs, demonstrates that forelimb motion in theropods is considerably less than hypothetical models indicate. The forelimbs ofCoelophysis, cf.Coelurus, Allosaurus, Deinonychus, andTyrannosaurus were investigated. Motion at the shoulder, elbow, wrist, and digits were analyzed and compared with those of birds and crocodiles, then motion of the entire forelimb was examined. The results have considerable implications for forelimb use in predation. Three models of predation are recognized: 1) long armed grasper —Deinonychus, cf.Coelurus; 2) clutcher -Tyrannosaurus; 3) combination grasper-clutcher -Allosaurus. Analysis of the joints ofDeinonychus show that the forelimb could not fold avian fashion. The scapula of the theropodUnenlagia was oriented incorrectly and differs little from the standard theropod scapula.