Limb length, cursoriality and speed have long been areas of significant interest in theropod paleobiology as locomotory capacity, especially running ability, is critical in not just in prey pursuit but also to avoid become prey oneself. One aspect that is traditionally overlooked is the impact of allometry on running ability and the limiting effect of large body size. Since several different non-avian theropod lineages have each independently evolved body sizes greater than any known terrestrial carnivorous mammal, ∼1000kg or more, the effect that such larger mass has on movement ability and energetics is an area with significant implications for Mesozoic paleoecology. Here using expansive datasets, incorporating several different metrics to estimate body size, limb length and running speed, to calculate the effects of allometry running We test both on traditional metrics used to evaluate cursoriality in non-avian theropods such as distal limb length, relative hindlimb length as well as comparing the energetic cost savings of relative hindlimb elongation between members of the Tyrannosauridae and more basal megacarnivores such as Allosauroids or Ceratosauridae. We find that once the limiting effects of body size increase is incorporated, no commonly used metric including the newly suggested distal limb index (Tibia + Metatarsus/ Femur length) shows a significant correlation to top speed. The data also shows a significant split between large and small bodied theropods in terms of maximizing running potential suggesting two distinct strategies for promoting limb elongation based on the organisms’ size. For small and medium sized theropods increased leg length seems to correlate with a desire to increase top speed while amongst larger taxa it corresponds more closely to energetic efficiency and reducing foraging costs. We also find, using 3D volumetric mass estimates, that the Tyrannosauridae show significant cost of transport savings compared to more basal clades, indicating reduced energy expenditures during foraging and likely reduced need for hunting forays. This suggests that amongst theropods while no one strategy dictated hindlimb evolution. Amongst smaller bodied taxa the competing pressures of being both a predator and a prey item dominant while larger ones, freed from predation pressure, seek to maximize foraging ability. We also discuss the implications both for interactions amongst specific clades and Mesozoic paleobiology and paleoecological reconstructions as a whole.

中文翻译：

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快速节俭：不同的运动策略驱动兽脚类恐龙的肢体延长

肢体的长度，粗略性和速度一直以来都是兽脚类动物古生物学的重要领域，因为运动能力，尤其是奔跑能力，不仅对追捕猎物至关重要，而且对于避免自己成为猎物也至关重要。传统上被忽略的一个方面是异速运动对跑步能力的影响以及大尺寸车身的局限性。由于几种不同的非禽兽脚类动物谱系各自独立进化的体形要大于任何已知的陆生食肉哺乳动物，约1000kg或更多，因此这种较大的体形对运动能力和能量的影响对中生代古生态学意义重大。在这里，我们使用了广泛的数据集，并结合了多种不同的指标来估算身体尺寸，肢体长度和跑步速度，计算跑步法的影响力我们测试了用于评​​估非禽类兽脚类动物的粗度的传统指标，例如远端肢体长度，相对后肢长度，以及比较了霸王龙成员之间相对后肢伸长的能量成本节省等基底大型食肉动物，例如异头龙或角鼻龙科。我们发现，一旦合并了增加体型的限制因素，就没有包括新建议的远端肢体指数（胫骨+ tar骨/股骨长度）在内的常用度量指标与最高速度显着相关。数据还显示，在最大发挥潜能方面，大型和小型肢体兽脚类动物之间存在显着差异，表明根据生物体的大小，两种不同的促进肢体伸长的策略。对于中小型兽脚类动物而言，增加腿的长度似乎与增加最高速度的愿望相关，而在较大的生物分类中，它与能量效率和降低觅食成本更紧密地对应。我们还发现，使用3D体积质量估算，与更多的基础进化枝相比，霸王龙显示出可节省大量的运输成本，这表明觅食过程中的能源消耗减少了，狩猎的需求可能减少了。这表明在兽脚类动物中，没有一种策略指示后肢的进化。在较小的身体分类单元中，竞争压力既是掠食者又是猎物，而较大的则摆脱了捕食压力，力图使觅食能力最大化。