Abstract
How extinct, non-avian theropod dinosaurs moved is a subject of considerable interest and controversy. A better understanding of non-avian theropod locomotion can be achieved by better understanding terrestrial locomotor biomechanics in their modern descendants, birds. Despite much research on the subject, avian terrestrial locomotion remains little explored in regards to how kinematic and kinetic factors vary together with speed and body size. Here, terrestrial locomotion was investigated in twelve species of ground-dwelling bird, spanning a 1,780-fold range in body mass, across almost their entire speed range. Particular attention was devoted to the ground reaction force (GRF), the force that the feet exert upon the ground. Comparable data for the only other extant obligate, striding biped, humans, were also collected and studied. In birds, all kinematic and kinetic parameters examined changed continuously with increasing speed, while in humans all but one of those same parameters changed abruptly at the walk-run transition. This result supports previous studies that show birds to have a highly continuous locomotor repertoire compared to humans, where discrete ‘walking’ and ‘running’ gaits are not easily distinguished based on kinematic patterns alone. The influences of speed and body size on kinematic and kinetic factors in birds are developed into a set of predictive relationships that may be applied to extinct, non-avian theropods. The resulting predictive model is able to explain 79–93% of the observed variation in kinematics and 69–83% of the observed variation in GRFs, and also performs well in extrapolation tests. However, this study also found that the location of the whole-body centre of mass may exert an important influence on the nature of the GRF, and hence some caution is warranted, in lieu of further investigation.
Highlights
What would an eight tonne Tyrannosaurus rex have looked like moving at 5 m s-1? Could it have managed to move as fast as 10 m s-1, or faster? A perennial question of interest for palaeontologists is how extinct animals appeared and behaved when they were alive
Through the comparative analysis across speed and body size, the results of this study have reiterated the fact that ground-dwelling birds use a highly continuous terrestrial locomotor repertoire
Unlike humans and many other terrestrial animals that have been investigated to date, birds exhibit a continuous change with respect to speed in terms of kinematics
Summary
What would an eight tonne Tyrannosaurus rex have looked like moving at 5 m s-1? Could it have managed to move as fast as 10 m s-1, or faster? A perennial question of interest for palaeontologists is how extinct animals appeared and behaved when they were alive. Perhaps more than any other animal group, theropod dinosaurs have received considerable attention as to how they stood and moved, owing to their carnivorous lifestyle and the gigantic sizes that many species attained, despite their bipedal stance [1]. One way of better understanding how extinct theropods moved is to examine locomotion in extant theropods, birds, because birds retain many (homologous) anatomical similarities to their ancestors [12,13,14,15,16,17,18]. Humans, as the only other extant obligate, striding biped, serve as an important source of information concerning bipedal locomotion in extinct theropods. By identifying and understanding the similarities and differences between bird and human locomotion, it is possible to elucidate fundamental aspects of obligate striding bipedalism, and those that are influenced by anatomical or postural differences
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