Reconstructing the lost cartilaginous epiphyses in extinct archosaurs' limbs

Locomotion is among the most important function involved in tetrapod evolutionary success. Understanding how locomotion in current species evolved implies to study their fossil record. Evolutionary biomechanics tackles this topic, by estimating locomotor abilities of extinct organisms by observing their extant relatives. Particular efforts have been made to infer the locomotion in non- avian dinosaurs and other extinct archosaurs. However, as in most other tetrapods, archosaur limb bones have cartilaginous epiphyses that do not fossilise. This leads to high levels of uncertainty when conducting biomechanical analyses on such animals. Surprisingly, corrective strategies remained rather subjective and simplistic, failing to propose a robust way to account for missing cartilage. Here I propose to answer to this critical issue by concretely REconstructing the LOst CArTilaginous Epiphyses of extinct archosaurs, using cutting-edge quantitative methods. Focusing on the femur, the three-dimensional characteristics of a large sample of archosaurs will be used to estimate the missing epiphyses of fossil species. Subsequently to the study of modern morphological diversity, I will develop the protocol by assessing its accuracy to reconstruct epiphyses in a controlled virtual experimentation on extant species. I will also stress robustness to sampling variability to give the degree of confidence to put on the reconstruction. Finally, the impact of reconstructions will be tested by conducting a comparative biomechanical analysis. At the crossroads of quantitative vertebrate palaeontology, evolutionary biology and biomechanics, the project ambitions to develop the most objective and reliable way to date to reconstruct the lost epiphyses in extinct archosaurs. The unprecedented outcomes of the project should deeply impact inferences about how extinct archosaurs could locomote, and will open perspectives to generalise the approach to any other tetrapod group.