Reconstructing the lost cartilaginous epiphyses in extinct archosaurs' limbs

运动是四足动物进化成功中最重要的功能之一。了解当今物种的运动是如何进化的，意味着要研究它们的化石记录。进化生物力学解决了这个问题，通过观察灭绝生物的现存亲属来估计它们的运动能力。人们特别努力去推断非鸟类恐龙和其他已灭绝的祖龙的运动方式。然而，像大多数其他四足动物一样，祖龙的肢体骨骼有软骨骺，不会变成化石。这导致在对这些动物进行生物力学分析时存在很大的不确定性。令人惊讶的是，矫正策略仍然相当主观和简单，未能提出一个强有力的方法来解释软骨缺失。在这里，我建议通过具体重建已灭绝的祖龙的软骨骨骺，使用尖端的定量方法来回答这个关键问题。以股骨为重点，大量祖龙样本的三维特征将用于估计化石物种缺失的骨骺。随后，在现代形态多样性的研究中，我将通过评估其在现存物种的受控虚拟实验中重建骨骺的准确性来开发该协议。我还将强调对采样可变性的鲁棒性，以给予重建的置信度。最后，重建的影响将通过进行比较生物力学分析来测试。在定量脊椎动物古生物学、进化生物学和生物力学的交叉路口，该项目旨在开发迄今为止最客观、最可靠的方法来重建已灭绝的祖龙的骨骺。这项史无前例的研究成果将会深刻影响人们对已灭绝的始祖龙如何移动的推断，并将为推广其他四足动物群体的研究方法开辟新的视角。

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.