Integrating the fossil record with computer simulation to reconstruct posture and locomotor evolution in the ancestors of mammals

A distinguishing feature of modern mammals is how they stand and move: they hold their limbs straight underneath their body, and this ‘erect’ mode of locomotion has profoundly influenced their evolutionary success and ecological diversity. The fossil record shows that the early ancestors of mammals (~300 million years ago) looked and moved more like reptiles, using a ‘sprawled’ posture with the limbs held out to the side of the body.

An enduring question in evolutionary biology is how and when the transition from sprawled to erect posture occurred during the rise of mammals. This project will use the exceptional fossil record of mammal ancestors – rivalling that of dinosaurs – and data from modern species to answer this fundamental question. Cutting-edge biomechanical methods, originally developed for aerospace and medical research, will be applied to develop sophisticated computer simulations of locomotion in extinct species, virtually bringing them back to life and deepening our understanding of a quintessentially mammalian characteristic.

The results of this project will provide the foundation for a strong program of outreach that targets increasing diversity in the sciences, and combats misperceptions about paleontologists. Summer workshops, hosted in local communities, will use both physical and virtual interactive displays to encourage those from underrepresented groups to see paleontology, biomechanics, and computer simulation as accessible career fields, stimulating the next generation of scientists.

Paid summer internship programs involving local high school students will also be incorporated, providing interns first-hand experience in research, museum collections management and public communication activities. Students will also act as near-peer role models in helping to deliver workshops in surrounding communities. Research outcomes will be disseminated to the scientific community through conference presentations, open-access publications, and online webinars dedicated to showcasing interdisciplinary research in paleontology and biomechanics.

Modern mammals display remarkable locomotor diversity, which has been facilitated by profound transformation in anatomy and function that occurred in their extinct ancestors, the non-mammalian synapsids. Fundamental to this was a shift in stance and gait, from a reptilian ‘sprawl’ to the ‘erect’ mode used by living terrestrial mammals. Despite its pivotal importance in mammal evolution, how and when the sprawling-to-erect transition occurred remains poorly understood.

Furthermore, it is unclear what anatomical and mechanical factors facilitated or constrained this transition. This project will address these issues by synthesizing the exemplary fossil record of non-mammalian synapsids with cutting-edge analytical and simulation approaches in biomechanics to unravel the history of locomotor transformation on the line to mammals.

The project will: 1) tackle locomotor function at multiple scales, from structural transformation in individual bones through to whole-organism functional integration and performance; 2) produce rigorous and quantitative assessments of limb function, performance, and versatility; 3) develop dynamic simulations of three-dimensional gait cycles in a range of extinct species; and 4) recreate the sequence of events and adaptive drivers that culminated in modern mammalian locomotion. By leveraging exceptional fossil material, detailed anatomical data from modern species and sophisticated computational biomechanical methods, the project will produce the first broad-scale, physics-based assessments of posture and locomotor performance in numerous key taxa spanning the sprawling-to-erect transition.

The methods used and insights gained will provide a powerful, new perspective on how anatomical and mechanical factors can shape macroevolutionary change in a lineage and give rise to new major clades of animals, paving the way forward for rigorous investigation of other major evolutionary transitions in vertebrate history.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.