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

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 the pterosaurian flying reptiles. About
50 years ago, the ‗locomotor superiority hypothesis‘ (LSH) proposed that dinosaurs
ultimately dominated by the Early Jurassic Period because their locomotion was superior to
other archosaurs‘. This idea has been debated continuously since, with taxonomic and
morphological analyses suggesting dinosaurs were ―lucky‖ rather than surviving due to being
biologically superior. However, the LSH has never been tested biomechanically. Here we
present integration of experimental data from locomotion in extant archosaurs with inverse
and predictive simulations of the same behaviours using musculoskeletal models, showing
that we can reliably predict how extant archosaurs walk, run and jump. These simulations
have been guiding predictive simulations of extinct archosaurs to estimate how they moved,
and we show our progress in that endeavour. The musculoskeletal models used in these
simulations can also be used for simpler analyses of form and function such as muscle
moment arms, which inform us about more basic biomechanical similarities and differences
between archosaurs. Placing all these data into an evolutionary and biomechanical context,
we take a fresh look at the LSH as part of a critical 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, but other derived dinosaurian features (e.g., metabolic or growth rates,
ventilatory abilities) are not necessarily mutually exclusive from the LSH; or maybe even an
opportunistic replacement hypothesis; in explaining dinosaurs‘ success.