The influence of speed and size on avian terrestrial locomotor biomechanics: Predicting locomotion in extinct theropod dinosaurs

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.

Trunk Pitch Oscillations for Joint Load Redistribution in Humans and Humanoid Robots

“…In biomechanics, gaits can be characterized by the duty factor (DF). DF is the ratio of the leg contact time to the stride period and is correlated to the magnitude of the GRF [28]. We tune control gains to match DFs of simulated gaits to the data in Fig.…”

“…Control parameters and damping are adjusted so that the simulation's duty factor lie in the grey shaded region estimated from biomechanical experiments [28,29]. [28,29]. Consequently, the DF, leg angle at TD, and damping coefficient decrease with speed ( Fig.…”

Spring-loaded inverted pendulum goes through two contraction-extension cycles during the single stance phase of walking

“…We imposed two constraints on VGRF. First, VGRF rarely goes below 30% of the weight of the animal [25,4]. To capture this constraint, we define "VGRF ratio", G r ≡ (minimum VGRF)/mg, and impose the constraint…”

“…Second, for mammals, including humans [12,29], certain birds [4,14], and most quadrupeds [43,9,27], the VGRF has a mid-stance minimum and is flanked on each side by two local maxima thereby producing a characteristic M-shape, see Fig. 1C.…”

Peer Review #2 of "Cancellous bone and theropod dinosaur locomotion. Part III—Inferring posture and locomotor biomechanics in extinct theropods, and its evolution on the line to birds (v0.1)"

“…Most of the above changes also occurred in tandem with a progressive (Lee et al 2014) or multistep (Benson et al in press) reduction in body size along the theropod stem lineage. A decrease in body size -either along the theropod stem lineage, or by directly comparing Daspletosaurus, 'Troodon' and the chicken -might be expected in and of itself to bring about changes in posture, since posture correlates with body size in extant parasagittal tetrapods (Biewener 1989;Biewener 1990;Bishop et al 2018;Gatesy & Biewener 1991). However, since many other aspects of theropod anatomy and locomotor biomechanics also change in tandem with body size along the theropod stem lineage, it is presently not possible to disentangle the relative importance of body size (or any other single feature) on posture.…”