P1.128 Wednesday, Jan. 4 Reconstructing the antebrachial and manual musculature in the basal theropod dinosaur Tawa hallae BURCH, Sara H.*; SMITH, Nathan D.; NESBITT, Sterling J.; IRMIS, Randall B.; TURNER, Alan H.; Stony Brook University; Field Museum; The University of Washington; Utah Museum of Natural History; Stony Brook University firstname.lastname@example.org
Reconstructing limb musculature provides important information about the function and capability of extinct tetrapod limbs, but previous reconstructions of theropod forelimb myology have focused on shoulder musculature in crownward taxa. The antebrachial and manual musculature in particular have remained largely unstudied due to uncertain muscular homologies in archosaurs. The theropod Tawa hallae from the Late Triassic of New Mexico provides a complete osteology of the forelimb, allowing a full reconstruction of the musculature in a basal taxon. Data on the morphology and development of this musculature in extant crocodylians, birds, squamates, and turtles were collected from the literature and dissections, and analyzed to form new hypotheses of antebrachial and manual muscle homology in archosaurs and other reptiles. Integrative phylogenetic methods were used to make well-supported inferences for muscle presence and attachment sites in Tawa. Although muscles of the antebrachium leave few scars on the bone surface, the radius and ulna of Tawa feature distinct, flat faces which serve as correlates for the attachment of muscles such as supinator and pronator teres. A medial flange on metacarpal I likely represents the attachment for abductor pollicis longus, indicating the retention of a plesiomorphic metacarpal insertion as in birds and squamates, rather than a derived insertion on the radiale as in crocodylians. The antebrachial and manual myology of Tawa clarifies the basal conformation of this musculature in Theropoda and is critical for investigations addressing the evolution of specialized forelimb function in this diverse clade.