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Testing the locomotor superiority hypothesis for early dinosaurs

Periodic Reporting for period 3 - DAWNDINOS (Testing the locomotor superiority hypothesis for early dinosaurs)

Reporting period: 2019-10-01 to 2021-03-31

The “DAWNDINOS” study combines evolutionary and biomechanical research that tests how the anatomy of extinct dinosaurs and their relatives (archosaurs; “ruling reptiles”) was related to their behaviour. We are testing the old “locomotor superiority” hypothesis that early, bipedal dinosaurs evolved advantages in their locomotor performance over other Late Triassic archosaurs. This hypothesis was first proposed to explain what made dinosaurs distinct from other Triassic species, perhaps aiding their survival into the Jurassic period. However, the hypothesis remains untested or unfairly dismissed. We are directly testing this question for the first time, but first we are focusing on developing the best tools to do so.

Extant archosaurs (crocodiles and birds) have allowed us to experimentally measure key factors (such as 3D skeletal motions and limb forces) that are involved in walking, running, jumping, standing up, and turning behaviours. We have finished using biomechanical computer simulations to estimate how these behaviours were achieved, or whether more extreme behaviours (e.g. faster speeds) might still have been feasible but not observed. This has refined our simulations by testing major assumptions, and validated them for studying extinct archosaurs. Additionally, we are now simulating extinct archosaurs.

In the final Period of the study, we will be using our simulation tools to predict how ten Triassic/early Jurassic archosaurs may have moved, and to compare how their performance in the behaviours related to locomotor traits, testing if the results fit expected patterns for “locomotor superiority.”
In the first four years of the DAWNDINOS project, we completed our experimental studies of the locomotor behaviours of crocodiles and birds and finished analyses of these data, resulting in six publications (on crocodile gaits, muscle physiology and hindlimb muscle leverage; and on tinamou bird muscle activity and simulations of walking and running, and jumping). This work led to the development of new protocols for analgesia and anaesthesia in crocodiles and tinamou birds disseminated to the veterinary community in three publications, benefitting animal care and welfare. Furthermore, valuable data and methods we developed led to serendipitous unanticipated benefits in the form of three other publications as invited collaborations with external experts (on giant fossil caimans, gorilla modelling, and ostrich/alligator respiratory systems), and special related outputs from our group as three publications (simulating coordinated wing-leg function in growing birds, simulating sit-to-stand behaviours in dogs; and simulating claw functions in carnivorous dinosaurs).

We also have collected 3D digital scans of the skeletons of all 10 of our fossil archosaur subjects for our modelling and simulation studies and have been modelling and simulating these taxa; in addition to publishing three key studies explaining and refining relevant simulation approaches. We completed two key digital modelling studies of the dinosaur Mussaurus, which was closely related to the giant sauropod dinosaurs but was still of moderate size; showing that its forelimbs could not be planted on the ground for usage in quadrupedalism and that it shifted from a quadruped to a biped as it grew from hatchling to adult. Furthermore, we conducted a pioneering evolutionary study of the biomechanical actions of 35 major hindlimb muscles in 13 musculoskeletal models of archosaurs spanning their 250 million year history, showing how muscular leverage experienced “pulses” of change in some Triassic-Jurassic bipedal dinosaurs. We also studied the early archosaur relative Euparkeria with 3D modelling to reveal that its hindlimbs could adopt a wide variety of postures, as in living crocodiles.

Our simulation framework for the final Period of the study is now sufficiently ready and we have refined and implemented it with experimental data for extant birds and crocodiles, with the six papers on those data giving us strong confidence for our simulations of fossil archosaurs. We also conducted numerous outreach efforts at local schools (and internationally via “Skype A Scientist” and other efforts), engaged with the public repeatedly via diverse efforts, and brought the project to a global audience via the project website including numerous explanatory videos and do-it-at-home activities: as well as via social media (e.g. Twitter’s #DAWNDINOS hashtag), and we presented findings from the project at many technical scientific and public (university/museum) events.
This study pushes the frontiers of analysis of movement by combining the best measurements of performance with the best digital tools, to predict how form and function are coordinated to achieve maximal athletic behaviours. Our rigorous, integrative analyses are moving the field of evolutionary biomechanics forward, enabling new inquiries into how behaviour relates to underlying traits or even palaeoecology, environments or other factors.

Our palaeontological research is moving forward quickly now; for example, we have assembled a 3D model of the skeleton of the early crocodile-relatives Batrachotomus and Euparkeria and found that they clearly were quadrupedal as expected, but both show hints of the bipedal locomotor capacity that later members of their lineage (e.g. Poposaurus) evolved. Importantly, along the way we have tested key assumptions of such digital models, such as that muscle sizes can be predicted from attachment areas evident on the skeleton, and that 3D orientations of joint axes can be estimated from bones alone, enabling rigorous tests of joint mobility or even passive stiffness. These data are informed but not dictated by our studies of extant archosaurs.

We are at a critical juncture in the project. We are focussing on simulating the locomotion of bipedal and quadrupedal extinct archosaurs, generating new 3D behaviours whose initial results are very exciting, including dynamic usage of the tail to maintain balance, limb forces that compare well with independent empirical predictions from living bipeds, and limb muscle recruitment patterns that are similar to those used in living archosaurs (without being forced by the simulations to be so). This bodes well for the project answering its major, comparative/evolutionary questions about whether the crocodile- and dinosaur-lineages had key locomotor differences that might help explain the dominance of the latter after the Triassic Period.

This project is important because dinosaurs fascinate scientists and public alike. The early history of dinosaurs and their kin remains murky. Yet the fossil record from this time is wonderful and quickly improving, so there is untapped potential for addressing major questions such as the locomotor superiority hypothesis; or how and why bipedalism evolved in archosaurs. Furthermore, the DAWNDINOS project is advancing the usage of computer simulation methods for estimating behaviours and linking form with function in the musculoskeletal systems of organisms. This advancement will build confidence in and spread adoption of these methods, ultimately enhancing our understanding of how animals work (even leading to applications such as clinical improvements or robotics/AI) as well as furthering the replacement of experimental methods with digital simulations where appropriate .