Demuth Oliver E, Wiseman Ashleigh L A, Hutchinson John R
Structure and Motion Laboratory, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hatfield, UK.
Department of Earth Sciences, University of Cambridge, Cambridge, UK.
R Soc Open Sci. 2023 Jan 25;10(1):221195. doi: 10.1098/rsos.221195. eCollection 2023 Jan.
Birds and crocodylians are the only remaining members of Archosauria (ruling reptiles) and they exhibit major differences in posture and gait, which are polar opposites in terms of locomotor strategies. Their broader lineages (Avemetatarsalia and Pseudosuchia) evolved a multitude of locomotor modes in the Triassic and Jurassic periods, including several occurrences of bipedalism. The exact timings and frequencies of bipedal origins within archosaurs, and thus their ancestral capabilities, are contentious. It is often suggested that archosaurs ancestrally exhibited some form of bipedalism. is a central taxon for the investigation of locomotion in archosaurs due to its phylogenetic position and intermediate skeletal morphology, and is argued to be representative of facultative bipedalism in this group. However, no studies to date have biomechanically tested if bipedality was feasible in . Here, we use musculoskeletal models and static simulations in its hindlimb to test the influences of body posture and muscle parameter estimation methods on locomotor potential. Our analyses show that the resulting negative pitching moments around the centre of mass were prohibitive to sustainable bipedality. We conclude that it is unlikely that was facultatively bipedal, and was probably quadrupedal, rendering the inference of ancestral bipedal abilities in Archosauria unlikely.
鸟类和鳄目动物是主龙类（统治性爬行动物）仅存的成员，它们在姿势和步态上表现出重大差异，就运动策略而言，二者截然相反。它们更广泛的谱系（鸟跖类和假鳄类）在三叠纪和侏罗纪时期演化出了多种运动模式，包括多次两足行走的情况。主龙类中两足起源的确切时间和频率，以及它们的原始能力，存在争议。人们常认为主龙类在祖先时期就表现出某种形式的两足行走。由于其系统发育位置和中间的骨骼形态，它是研究主龙类运动的核心分类单元，并且被认为是该类群中兼性两足行走的代表。然而，迄今为止，尚无研究从生物力学角度测试两足行走在它身上是否可行。在这里，我们使用其后肢的肌肉骨骼模型和静态模拟来测试身体姿势和肌肉参数估计方法对运动潜力的影响。我们的分析表明，围绕质心产生的负俯仰力矩阻碍了可持续的两足行走。我们得出结论，它不太可能是兼性两足动物，可能是四足动物，这使得推断主龙类的祖先两足能力不太可能。
