Structure & Motion Lab, Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hertfordshire AL9 7TA,UK.
J Exp Biol. 2021 Jun 1;224(11). doi: 10.1242/jeb.217463. Epub 2021 Jun 8.
Giant land vertebrates have evolved more than 30 times, notably in dinosaurs and mammals. The evolutionary and biomechanical perspectives considered here unify data from extant and extinct species, assessing current theory regarding how the locomotor biomechanics of giants has evolved. In terrestrial tetrapods, isometric and allometric scaling patterns of bones are evident throughout evolutionary history, reflecting general trends and lineage-specific divergences as animals evolve giant size. Added to data on the scaling of other supportive tissues and neuromuscular control, these patterns illuminate how lineages of giant tetrapods each evolved into robust forms adapted to the constraints of gigantism, but with some morphological variation. Insights from scaling of the leverage of limbs and trends in maximal speed reinforce the idea that, beyond 100-300 kg of body mass, tetrapods reduce their locomotor abilities, and eventually may lose entire behaviours such as galloping or even running. Compared with prehistory, extant megafaunas are depauperate in diversity and morphological disparity; therefore, turning to the fossil record can tell us more about the evolutionary biomechanics of giant tetrapods. Interspecific variation and uncertainty about unknown aspects of form and function in living and extinct taxa still render it impossible to use first principles of theoretical biomechanics to tightly bound the limits of gigantism. Yet sauropod dinosaurs demonstrate that >50 tonne masses repeatedly evolved, with body plans quite different from those of mammalian giants. Considering the largest bipedal dinosaurs, and the disparity in locomotor function of modern megafauna, this shows that even in terrestrial giants there is flexibility allowing divergent locomotor specialisations.
巨型陆地脊椎动物已经进化了 30 多次，特别是在恐龙和哺乳动物中。这里考虑的进化和生物力学观点统一了现存和已灭绝物种的数据，评估了当前关于巨型动物的运动生物力学是如何进化的理论。在陆地四足动物中，骨骼的等长和异速生长模式在整个进化历史中都很明显，反映了随着动物进化为大型体型的一般趋势和谱系特异性差异。加上关于其他支持组织和神经肌肉控制的缩放数据，这些模式阐明了巨型四足动物的谱系如何各自进化为适应巨型化限制的强壮形式，但具有一些形态变异。从四肢杠杆的缩放和最大速度趋势中获得的见解，进一步强化了这样一种观点，即超过 100-300 公斤的体重后，四足动物会降低其运动能力，最终可能会失去奔跑或甚至疾驰等整个行为。与史前相比，现存的巨型动物在多样性和形态差异上都较为匮乏；因此，研究化石记录可以让我们更多地了解巨型四足动物的进化生物力学。种间变异以及对现存和已灭绝分类群中未知形态和功能方面的不确定性，仍然使得我们无法使用理论生物力学的第一原理来严格限制巨型化的极限。然而，蜥脚类恐龙表明，超过 50 吨的体重多次进化，其身体计划与哺乳动物的大型动物截然不同。考虑到最大的两足恐龙和现代巨型动物在运动功能上的差异，这表明即使在陆地巨型动物中，也存在允许不同运动专业化的灵活性。
