tableS1_femora list_20220610.xlsx from The morphogenetic process for the dinosaurian femoral head shape shifted in evolution

Significant evolutionary shifts in locomotor behaviour often involve comparatively subtle anatomical transitions. In particular for dinosaurian locomotor apparatus, considerable medial overhang of the proximal end of the femur has been central to discussions for their locomotion. However, there is an apparent conflict with regard to the evolutionary origin of the dinosaurian femoral head, with neontological and palaeontological data suggesting seemingly incongruent hypotheses. To reconcile this, we reconstructed the evolutionary history of morphogenesis of the proximal end of the femur from early archosaurs to crown birds. Embryological comparison of living archosaurs (crocodylians and birds) suggests the acquisition of the greater overhang of the femoral head in dinosaurs results from additional growth of the proximal end in the medial-ward direction. On the other hand, the fossil comparison suggests this overhang was acquired by torsion of the proximal end, which projected to more rostral direction in ancestors. We reconcile this apparent conflict by inferring that the medial overhang of the dinosaur femoral head was initially acquired by torsion, which was then superseded by mediad growth. Details of anatomical shifts in fossil forms support this hypothesis, and their biomechanical implications are congruent with the general consensus regarding broader morpho-functional evolution on the avian stem.

运动行为的重大演化转变往往伴随相对细微的解剖学过渡。就恐龙的运动系统而言，股骨近端的显著内侧悬突（medial overhang）长期以来都是其运动方式研究的核心议题。然而，关于恐龙股骨头的演化起源，现生生物学与古生物学数据所提出的假说看似存在明显冲突。为调和这一矛盾，我们重建了从早期主龙类到冠群鸟类的股骨近端形态发生演化历史。对现生主龙类（鳄形类与鸟类）的胚胎学比较研究显示，恐龙股骨头的显著内侧悬突源于股骨近端向内侧方向的额外生长。而化石对比研究则表明，该悬突是通过股骨近端的扭转获得的——在祖先类群中，股骨近端曾向更靠前的颅侧方向突出。我们通过推断解决了这一明显冲突：恐龙股骨头的内侧悬突最初通过扭转形成，随后被向内侧生长的方式所取代。化石类群的解剖学转变细节支持这一假说，其蕴含的生物力学意义也与鸟类干群更广泛的形态功能演化的主流共识相符。