Biology of the sauropod dinosaurs: the evolution of gigantism.
Biology of the sauropod dinosaurs: the evolution of gigantism.
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DOI：
10.1111/j.1469-185x.2010.00137.x
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发表时间：
2011-02
影响因子：
--
通讯作者：
Witzel U
中科院分区：
文献类型：
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作者：
Sander PM;Christian A;Clauss M;Fechner R;Gee CT;Griebeler EM;Gunga HC;Hummel J;Mallison H;Perry SF;Preuschoft H;Rauhut OW;Remes K;Tütken T;Wings O;Witzel U
侏罗纪和白垩纪的食草性蜥脚类恐龙是有史以来最大的陆地动物，在体重上超过了最大的食草性哺乳动物一个数量级。据保守估计，蜥脚类中的几个进化谱系产生了体重超过50公吨的巨人。随着大体型的选择优势所驱动的体重增加，动物谱系的体型将增加，直到它们达到由包普兰、生物学和资源可获得性相互作用决定的极限。然而，没有证据表明，资源可获得性和全球物理化学参数在中生代的差异足以导致蜥脚类巨人。我们详细回顾了蜥脚类恐龙的生物学，并假设蜥脚类巨型恐龙是由不同水平的拟态特征(系统发育遗传)和进化创新的特定组合而产生的，这引发了显着的进化级联。在这些关键的创新中，最重要的可能是非常长的脖子，这是蜥脚类动物包普兰最显著的特征。与其他食草动物相比，长颈比其他大型食草动物能够更有效地摄取食物，因为它覆盖了一个大得多的觅食信封，并使其他食草动物无法获得的食物得以获取。因此，蜥脚类动物肯定比其他食草动物从环境中吸收了更多的能量。反过来，由于头部较小以及蜥脚类轴骨的广泛气化，长颈得以进化，从而减轻了颈部的重量。小脑袋是可能的，因为食物是在没有咀嚼的情况下摄入的。咀嚼和胃碾磨都会限制食物的摄取率。胃肠道大小和基础代谢率(BMR)之间的比例关系表明，蜥脚类动物即使在高摄取率下，也通过长时间的保留来弥补颗粒减少的不足。轴骨的广泛气化是鸟类呼吸系统进化的结果，据推测是在蜥蜴的底部。鸟式呼吸系统还将降低呼吸成本，降低比重，并可能在排出体内多余热量方面发挥重要作用。另一项继承自基础恐龙的关键创新是高BMR。这是为数吨重的动物存活到生殖成熟所需的高增长率提供燃料所必需的。半形性卵生繁殖模式的保留似乎也是至关重要的，这使得种群恢复的速度比大型食草动物的种群恢复要快得多。蜥脚类在每个季节都会产生数量众多但规模较小的后代，而陆地哺乳动物的繁殖产量与体型呈负相关。这使得蜥脚类动物的种群密度低于大型食草动物哺乳动物，但个体更大。因此，我们对蜥脚类恐龙的研究告诉我们，其他食草性陆地四足动物的体型在进化上是有限的。外温爬行动物受到其低BMR的强烈限制，保持较小的体型。哺乳动物受到它们广泛的咀嚼和胎生的限制，而鸟栖恐龙只受到它们广泛的咀嚼的限制，它们的平均身体尺寸比哺乳动物大。
The herbivorous sauropod dinosaurs of the Jurassic and Cretaceous periods were the largest terrestrial animals ever, surpassing the largest herbivorous mammals by an order of magnitude in body mass. Several evolutionary lineages among Sauropoda produced giants with body masses in excess of 50 metric tonnes by conservative estimates. With body mass increase driven by the selective advantages of large body size, animal lineages will increase in body size until they reach the limit determined by the interplay of bauplan, biology, and resource availability. There is no evidence, however, that resource availability and global physicochemical parameters were different enough in the Mesozoic to have led to sauropod gigantism. We review the biology of sauropod dinosaurs in detail and posit that sauropod gigantism was made possible by a specific combination of plesiomorphic characters (phylogenetic heritage) and evolutionary innovations at different levels which triggered a remarkable evolutionary cascade. Of these key innovations, the most important probably was the very long neck, the most conspicuous feature of the sauropod bauplan. Compared to other herbivores, the long neck allowed more efficient food uptake than in other large herbivores by covering a much larger feeding envelope and making food accessible that was out of the reach of other herbivores. Sauropods thus must have been able to take up more energy from their environment than other herbivores. The long neck, in turn, could only evolve because of the small head and the extensive pneumatization of the sauropod axial skeleton, lightening the neck. The small head was possible because food was ingested without mastication. Both mastication and a gastric mill would have limited food uptake rate. Scaling relationships between gastrointestinal tract size and basal metabolic rate (BMR) suggest that sauropods compensated for the lack of particle reduction with long retention times, even at high uptake rates. The extensive pneumatization of the axial skeleton resulted from the evolution of an avian-style respiratory system, presumably at the base of Saurischia. An avian-style respiratory system would also have lowered the cost of breathing, reduced specific gravity, and may have been important in removing excess body heat. Another crucial innovation inherited from basal dinosaurs was a high BMR. This is required for fueling the high growth rate necessary for a multi-tonne animal to survive to reproductive maturity. The retention of the plesiomorphic oviparous mode of reproduction appears to have been critical as well, allowing much faster population recovery than in megaherbivore mammals. Sauropods produced numerous but small offspring each season while land mammals show a negative correlation of reproductive output to body size. This permitted lower population densities in sauropods than in megaherbivore mammals but larger individuals. Our work on sauropod dinosaurs thus informs us about evolutionary limits to body size in other groups of herbivorous terrestrial tetrapods. Ectothermic reptiles are strongly limited by their low BMR, remaining small. Mammals are limited by their extensive mastication and their vivipary, while ornithsichian dinosaurs were only limited by their extensive mastication, having greater average body sizes than mammals.