Walking—and Running and Jumping—with Dinosaurs and their Cousins, Viewed Through the Lens of Evolutionary Biomechanics

Abstract

Archosauria diversified throughout the Triassic Period before experiencing two mass extinctions near its end∼201 Mya, leaving only the crocodile-lineage (Crocodylomorpha) and bird-lineage (Dinosauria) as survivors; along with thepterosaurian flying reptiles. About 50 years ago, the “locomotor superiority hypothesis” (LSH) proposed that dinosaurs ultimatelydominated by the Early Jurassic Period because their locomotion was superior to other archosaurs’. This idea has beendebated continuously since, with taxonomic andmorphological analyses suggesting dinosaurs were “lucky” rather than survivingdue to being biologically superior. However, the LSH has never been tested biomechanically. Here we present integrationof experimental data from locomotion in extant archosaurs with inverse and predictive simulations of the same behavioursusing musculoskeletal models, showing that we can reliably predict how extant archosaurs walk, run and jump. These simulationshave been guiding predictive simulations of extinct archosaurs to estimate how they moved, and we show our progressin that endeavour. The musculoskeletal models used in these simulations can also be used for simpler analyses of form andfunction such as muscle moment arms, which inform us about more basic biomechanical similarities and differences betweenarchosaurs. Placing all these data into an evolutionary and biomechanical context, we take a fresh look at the LSH as part of acritical review of competing hypotheses for why dinosaurs (and a few other archosaur clades) survived the Late Triassic extinctions.Early dinosaurs had some quantifiable differences in locomotor function and performance vs. some other archosaurs, butother derived dinosaurian features (e.g., metabolic or growth rates, ventilatory abilities) are not necessarily mutually exclusivefrom the LSH; or maybe even an opportunistic replacement hypothesis; in explaining dinosaurs’ success.