Appendicular myology of Skorpiovenator bustingorryi : A first attempt to reconstruct pelvic and hindlimb musculature in an abelisaurid theropod

Abstract

We present the pelvic and hindlimb musculature of the abelisaurid Skorpiovenator bustingorryi, constituting the most comprehensive reconstruction to date in ceratosaur theropods. Using extant phylogenetic bracket method, we reconstructed 39 muscles that can commonly found in extant archosaurs, including intrinsic pedal muscles. Through the identification of bone correlates, we recognized thigh and hindlimb muscles like knee extensors, m. iliofibularis, m. flexor tibialis externus, mm. caudofemorales, mm. puboischiofemorales, and crus muscles important in foot extension and flexion (e.g., m. tibialis anterior, mm. gastrocnemii). Also, autopodial intrinsic muscles were reconstructed whose function involve extension (m. extensor digiti 2-4), flexion (mm. flexor digitorum brevis superficialis), interdigital adduction (m. interosseus dorsalis) and abduction (m. abductor 4). Abelisaurids like Skorpiovenator show a deep pre- and postacetabular blade of the ilium and enlarged cnemial crest, which would have helped increasing the moment arm of muscles related to hip flexion and hindlimb extension. Also, pedal muscles related to pronation and supination were probably present but reduced (e.g, m. adductor hallucis dorsalis). Despite some gross differences in the autopodial morphology in extant outgroups (e.g., crocodilian metatarsus and avian tarsometatarsus), the present study allows us to hypothesize several pedal muscles in Skorpiovenator. These muscles would not be arranged in tendon bundles as in neornithes, but rather the condition would be more like that of crocodilians with several layers formed by fleshy bellies on the metatarsus. The musculature of Skorpiovenator is key for future studies concerning abelisaurid biomechanics, including the integration of functional morphology and ichnological data.