Abstract
Reconstructing the locomotion of extinct vertebrates offers insights into their palaeobiology and helps to conceptualize major transitions in vertebrate evolution1-4. However, estimating the locomotor behaviour of a fossil species remains a challenge because of the limited information preserved and the lack of a direct correspondence between form and function5,6. The evolution of advanced locomotion on land-that is, locomotion that is more erect, balanced and mechanically power-saving than is assumed of anamniote early tetrapods-has previously been linked to the terrestrialization and diversification of amniote lineages7. To our knowledge, no reconstructions of the locomotor characteristics of stem amniotes based on multiple quantitative methods have previously been attempted: previous methods have relied on anatomical features alone, ambiguous locomotor information preserved in ichnofossils or unspecific modelling of locomotor dynamics. Here we quantitatively examine plausible gaits of the stem amniote Orobates pabsti, a species that is known from a complete body fossil preserved in association with trackways8. We reconstruct likely gaits that match the footprints, and investigate whether Orobates exhibited locomotor characteristics that have previously been linked to the diversification of crown amniotes. Our integrative methodology uses constraints derived from biomechanically relevant metrics, which also apply to extant tetrapods. The framework uses in vivo assessment of locomotor mechanics in four extant species to guide an anatomically informed kinematic simulation of Orobates, as well as dynamic simulations and robotics to filter the parameter space for plausible gaits. The approach was validated using two extant species that have different morphologies, gaits and footprints. Our metrics indicate that Orobates exhibited more advanced locomotion than has previously been assumed for earlier tetrapods7,9, which suggests that advanced terrestrial locomotion preceded the diversification of crown amniotes. We provide an accompanying website for the exploration of the filters that constrain our simulations, which will allow revision of our approach using new data, assumptions or methods.
Highlights
*: Corresponding author +: These authors contributed 1: AG Morphologie und Formengeschichte, Institut für Biologie, Humboldt Universität zu Berlin, Berlin, Germany. 2: Bild Wissen Gestaltung
The framework uses in vivo assessment of locomotor mechanics in four extant species to guide an anatomically informed kinematic simulation of Orobates as well as dynamic simulations and biorobotics to filter the parameter space for plausible gaits
Analyzing the anatomy of fossils suffers from joint ranges of motion much larger than those used during locomotion and redundancy in appendages10,11,12
Summary
In light of the extant animal data, we linked both simulations (kinematic Orobates and dynamic OroBOT) by focussing on body height, spine bending, and LAR of the humerus and femur, and visualising these in SGS plots (Fig. 3a-c) to systematically vary these parameters, resulting in different gaits. The physical OroBOT model is a robotic system whose design and control was based on a previous biomimetic platform which successfully replicated kinematics and dynamics of a walking salamander, but here matching the Orobates morphology (Supplementary Information 3-11 and Methods)23 Independent of their score in the SGS, 15 different gaits were tested in OroBOT, closely matching the dynamic simulation in terms of forward speed, body orientation over time, and foot steps (see accompanying interactive website and Supplementary Video 14). Similar integrative approaches may be adopted for comparable research questions concerning major transitions in vertebrate evolution such as the origin of bipedality or active flight using quantitative metrics based on empirical data and/or validated simulations to exclude unlikely locomotor reconstructions while accounting for uncertainty
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
