Meeting Abstract
Archosauria (birds, crocodiles and all descendants of their common ancestor) is characterized by remarkable locomotor variation across its evolution since the Triassic. More sprawling, quadrupedal crocodiles and more erect, bipedal birds are prime examples of this variation. The functional implications of musculoskeletal anatomy have been widely studied, but more experimental data are needed on how muscles control locomotor movements in extant archosaurs. We present new electromyographic measurements from key appendicular muscles across a range of walking and running speeds in Nile crocodiles and numerous species of birds (tinamous, emus, guinea fowl, pheasants, turkeys and quail). We consider how extant archosaurs control limb movements, and how neuromotor control has likely evolved. Crocodiles, like most other tetrapods, use their pectoral muscles in an antigravity role. Crocodiles’ iliotibial, digital flexor and gastrocnemius muscles are activated similarly to birds (including Palaeognathae); likely ancestral for Archosauria. Birds, regardless of clade or ontogenetic status, show conservatism among the hindlimb muscles studied; these motor patterns appear ancestral for Aves. Our analysis is important for revealing which muscles display neuromotor conservation vs. evolutionary specialization. These findings are vital for testing the validity of computer simulations and reconstructing how locomotor disparity evolved in Archosauria.
