Palaeobiology Group, School of Earth Sciences, University of Bristol, Bristol, United Kingdom.
School of Biological and Environmental Sciences, Liverpool John Moores University, Liverpool, United Kingdom.
PeerJ. 2024 Aug 5;12:e17678. doi: 10.7717/peerj.17678. eCollection 2024.
Take-off is a vital part of powered flight which likely constrains the size of birds, yet extinct pterosaurs are known to have reached far larger sizes. Three different hypothesised take-off motions (bipedal burst launching, bipedal countermotion launching, and quadrupedal launching) have been proposed as explanations for how pterosaurs became airborne and circumvented this proposed morphological limit. We have constructed a computational musculoskeletal model of a 5 m wingspan ornithocheiraean pterosaur, reconstructing thirty-four key muscles to estimate the muscle moment arms throughout the three hypothesised take-off motions. Range of motion constrained hypothetical kinematic sequences for bipedal and quadrupedal take-off motions were modelled after extant flying vertebrates. Across our simulations we did not find higher hindlimb moment arms for bipedal take-off motions or noticeably higher forelimb moment arms in the forelimb for quadrupedal take-off motions. Despite this, in all our models we found the muscles utilised in the quadrupedal take-off have the largest total launch applicable moment arms throughout the entire take-off sequences and for the take-off pose. This indicates the potential availability of higher leverage for a quadrupedal take-off than hypothesised bipedal motions in pterosaurs pending further examination of muscle forces.
起飞是动力飞行的重要组成部分，这可能限制了鸟类的体型，但已灭绝的翼龙的体型却大得多。为了解释翼龙如何飞离地面并避开这种形态限制，人们提出了三种不同的起飞动作假设（双足爆发式起飞、双足反向运动起飞和四足起飞）。我们构建了一个 5 米翼展的鸟掌翼龙的计算肌肉骨骼模型，重建了 34 个关键肌肉，以估计在三种假设的起飞动作中整个肌肉力臂。双足和四足起飞运动的运动范围受约束的假设运动学序列是根据现生飞行脊椎动物建模的。在我们的模拟中，我们没有发现双足起飞运动中后腿的力臂更高，也没有发现四足起飞运动中前腿的力臂明显更高。尽管如此，在我们所有的模型中，我们发现四足起飞所使用的肌肉在整个起飞序列和起飞姿势中具有最大的总起飞可用力臂。这表明在翼龙中，四足起飞比假设的双足运动可能具有更高的杠杆作用，但需要进一步检查肌肉力量。
