重型动物在其四肢骨骼上承受巨大的力量,由于体重和地面反作用力的传递,和四肢各种肌肉的收缩。对于犀牛来说尤其如此,能够疾驰的现存最重的动物。一些研究已经检查了他们的肌肉骨骼系统和骨骼所产生的力量,但从未尝试过详细的量化。这种量化可以帮助更好地理解巨型陆地动物的形式和功能之间的联系。在这里,我们构建了Ceratotheriumsimum的前肢和后肢的三维肌肉骨骼模型,现存最重的犀牛物种,并使用静态优化(反向)模拟来估计静止站立时施加在骨骼上的力,包括幅度和方向。总的来说,不出所料,最活跃的肌肉是反重力肌肉,产生与体重相反的力矩(从而产生地面反作用力),从而保持关节伸展,通过屈曲避免关节塌陷。一些肌肉在几个关节周围有反重力作用,因此被发现是高度活跃的,可能专门从事体重支持(尺侧肌;数字屈肌)。肱骨受到的力的总量最大;此外,肱骨上的力来自各种各样的方向。半径主要受到高量级的压缩联合反作用力,但是肌肉紧张,而尺骨观察到相反的模式。股骨有类似于肱骨的图案,胫骨的模式是中间的,在其尾侧受到很大的压缩,但在其颅侧受到很大的张力(即弯曲)。腓骨受到迄今为止最低的力大小。总的来说,估计的力量与记录的C.simum的长骨的形态功能适应一致,与较轻的犀牛相比,它们具有更大的插入区域和更强的整体鲁棒性,可能反映了我们在这里估计的强烈力量。我们对这种巨型四足动物的肌肉和骨骼(关节)载荷方式的估计提高了对支持组织中形式和功能之间联系的理解,并且可以扩展到骨骼形态的其他方面。比如显微解剖学。
Heavy animals incur large forces on their limb bones, due to the transmission of body weight and ground reaction forces, and the contractions of the various muscles of the limbs. This is particularly true for rhinoceroses, the heaviest extant animals capable of galloping. Several studies have examined their musculoskeletal system and the forces their bones incur, but no detailed quantification has ever been attempted. Such quantification could help understand better the link between form and function in giant land animals. Here we constructed three-dimensional musculoskeletal models of the forelimb and hindlimb of Ceratotherium simum, the heaviest extant rhino species, and used static optimisation (inverse) simulations to estimate the forces applied on the bones when standing at rest, including magnitudes and directions. Overall, unsurprisingly, the most active muscles were antigravity muscles, which generate moments opposing body weight (thereby incurring the ground reaction force), and thus keep the joints extended, avoiding joint collapse via flexion. Some muscles have an antigravity action around several joints, and thus were found to be highly active, likely specialised in body weight support (ulnaris lateralis; digital flexors). The humerus was subjected to the greatest amount of forces in terms of total magnitude; forces on the humerus furthermore came from a great variety of directions. The radius was mainly subject to high-magnitude compressive joint reaction forces, but to little muscular tension, whereas the opposite pattern was observed for the ulna. The femur had a pattern similar to that of the humerus, and the tibia\'s pattern was intermediate, being subject to great compression in its caudal side but to great tension in its cranial side (i.e. bending). The fibula was subject to by far the lowest force magnitude. Overall, the forces estimated were consistent with the documented morphofunctional adaptations of C. simum\'s long bones, which have larger insertion areas for several muscles and a greater robusticity overall than those of lighter rhinos, likely reflecting the intense forces we estimated here. Our estimates of muscle and bone (joint) loading regimes for this giant tetrapod improve the understanding of the links between form and function in supportive tissues and could be extended to other aspects of bone morphology, such as microanatomy.