Department of Musculoskeletal Biology, Institute of Aging and Chronic Disease , University of Liverpool , The Apex Building, 6 West Derby Street, Liverpool L7 8TX , UK.
Department of Earth Science and Engineering , Imperial College London , South Kensington Campus, London SW7 2AZ , UK.
R Soc Open Sci. 2016 Mar 30;3(3):150636. doi: 10.1098/rsos.150636. eCollection 2016 Mar.
The colossal size and body plan of sauropod dinosaurs are unparalleled in terrestrial vertebrates. However, to date, there have been only limited attempts to examine temporal and phylogenetic patterns in the sauropod bauplan. Here, we combine three-dimensional computational models with phylogenetic reconstructions to quantify the evolution of whole-body shape and body segment properties across the sauropod radiation. Limitations associated with the absence of soft tissue preservation in fossils result in large error bars about mean absolute body shape predictions. However, applying any consistent skeleton : body volume ratio to all taxa does yield changes in body shape that appear concurrent with major macroevolutionary events in sauropod history. A caudad shift in centre-of-mass (CoM) in Middle Triassic Saurischia, associated with the evolution of bipedalism in various dinosaur lineages, was reversed in Late Triassic sauropodomorphs. A craniad CoM shift coincided with the evolution of quadrupedalism in the Late Triassic, followed by a more striking craniad shift in Late Jurassic-Cretaceous titanosauriforms, which included the largest sauropods. These craniad CoM shifts are strongly correlated with neck enlargement, a key innovation in sauropod evolution and pivotal to their gigantism. By creating a much larger feeding envelope, neck elongation is thought to have increased feeding efficiency and opened up trophic niches that were inaccessible to other herbivores. However, we find that relative neck size and CoM position are not strongly correlated with inferred feeding habits. Instead the craniad CoM positions of titanosauriforms appear closely linked with locomotion and environmental distributions, potentially contributing to the continued success of this group until the end-Cretaceous, with all other sauropods having gone extinct by the early Late Cretaceous.
蜥脚类恐龙的巨大体型和身体结构在陆地脊椎动物中是无与伦比的。然而，迄今为止，对于蜥脚形类动物的建筑计划，只有有限的尝试来研究时间和系统发育模式。在这里，我们将三维计算模型与系统发育重建相结合，以量化整个身体形状和身体节段特性在蜥脚类动物辐射中的进化。由于化石中缺乏软组织保存，与平均绝对身体形状预测相关的局限性很大。然而，对所有分类群应用任何一致的骨骼：体体积比，确实会导致身体形状的变化，这些变化似乎与蜥脚类动物历史上的主要宏观进化事件同时发生。中三叠世蜥脚类动物质心（CoM）的尾向移动，与各种恐龙谱系中双足行走的进化有关，在晚三叠世蜥脚形类动物中被逆转。CoM 的颅向移动与晚三叠世四足行走的进化同时发生，随后在晚侏罗世-白垩纪泰坦巨龙类中发生了更为显著的颅向移动，其中包括最大的蜥脚类动物。这些颅向 CoM 移动与颈部增大密切相关，这是蜥脚类动物进化中的一个关键创新，对其巨型化至关重要。通过创建一个更大的进食范围，颈部伸长被认为提高了进食效率，并开辟了其他食草动物无法进入的营养位。然而，我们发现相对颈部大小和 CoM 位置与推断的食性没有很强的相关性。相反，泰坦巨龙类的颅向 CoM 位置似乎与运动和环境分布密切相关，这可能有助于该群体的持续成功，直到白垩纪末期，而所有其他蜥脚类动物在早白垩纪末期已经灭绝。
