[论文解读] The Flexibility and Musculature of the Ostrich Neck: Implications for the Feeding Ecology and Reconstruction of the Sauropoda (Dinosauria:Saurischia)

Matthew James Cobley|arXiv (Cornell University)|Feb 15, 2013

Paleontology and Evolutionary Biology被引用 6

一句话总结

本研究通过分析鸵鸟颈部在逐步去除软组织及比较肌肉附着点的过程中，探究软组织在决定蜥脚类恐龙颈部灵活性和姿势中的作用。研究发现，软组织（而不仅仅是骨骼结构）是限制颈部灵活性的关键因素，这挑战了骨骼中立姿势模型（Osteological Neutral Pose model）的假设，并表明蜥脚类恐龙的取食范围可能比以往认为的更为有限。

ABSTRACT

The Sauropoda were the largest terrestrial animals ever to have lived on this planet. As their nutritional requirements were so huge, their diet holds sway over the ecology of many Mesozoic herbivores. The diet of the sauropods is limited by their feeding envelope, which in turn is governed by the posture and flexibility of their elongate necks. Yet the exact nature of the flexibility and posture of the neck has been a contentious issue. Previous studies have utilised computer models of dry bone, mechanical principles or the flexibility of the necks of extant animals. However, the effect of the musculature of the neck has yet to be investigated. Through measurements of the flexibility of the ostrich neck after cumulative tissue removal, analyses of the muscle attachment sites of the ostrich and sauropods, and testing of the Osteological Neutral Pose model, this study attempts to rectify this situation. The ostrich neck was shown to have three sections of flexibility; a slightly flexible anterior section, a very flexible middle section and a stiff posterior section. The Osteological Neutral Pose did not show these sections, and was shown to potentially overestimate and underestimate flexibility. It was also found that the inter-vertebral space could account for varying estimates of flexibility, and that sauropods would have proportionally more muscle mass at the base of the neck in relation to the ostrich. Ultimately, it was shown that the tissues of the neck place the limits of flexibility, and that zygapophyseal overlap does not indicate the flexibility of the neck. Should the Osteological Neutral Pose affect sauropod flexibility estimates in the same manner as that of the ostrich (a general overestimate), then the sauropods would have a more limited feeding envelope than previously thought, allowing for greater niche partitioning between groups.

研究动机与目标

• 评估软组织（尤其是肌肉和椎间空间）对长颈四足动物颈部灵活性的影响。
• 评估骨骼中立姿势（Osteological Neutral Pose, ONP）模型在预测颈部姿势和活动范围方面的可靠性。
• 通过比较鸵鸟与蜥脚类恐龙的肌肉附着点，推断其颈部肌肉结构与生物力学的差异。
• 确定蜥脚类恐龙椎骨关节突重叠是否能准确反映颈部灵活性。
• 基于软组织分析得出的更准确的灵活性估计，重新评估蜥脚类恐龙的取食范围。

提出的方法

• 对鸵鸟颈部标本进行逐步解剖，测量在顺序移除肌肉、韧带和软组织后灵活性的变化。
• 通过比较骨骼学分析，绘制鸵鸟与蜥脚类恐龙颈椎骨上的肌肉附着点。
• 通过将ONP模型预测的活动范围与实测灵活性进行对比，检验ONP模型的准确性。
• 利用解剖数据的形态测量学测量，量化椎间空间对颈部灵活性的贡献。
• 通过比较解剖学方法，估算鸵鸟与蜥脚类恐龙颈部肌肉质量的比例差异。
• 应用生物力学原理，评估软组织约束如何影响长颈动物的功能活动范围。

实验结果

研究问题

• RQ1 与仅基于干燥骨骼的预测相比，软组织的存在如何影响鸵鸟颈部的灵活性？
• RQ2 骨骼中立姿势模型在多大程度上准确反映了鸵鸟颈部的真实活动范围？
• RQ3 鸵鸟的肌肉附着模式与蜥脚类恐龙相比如何？这对蜥脚类恐龙颈部肌肉结构有何启示？
• RQ4 蜥脚类恐龙椎骨关节突重叠能否作为颈部灵活性的可靠指标？
• RQ5 基于软组织信息的灵活性估计，对蜥脚类恐龙取食生态与生态位分化有何影响？

主要发现

• 鸵鸟颈部表现出三个明显的灵活性区域：前部略具柔韧性，中部高度灵活，后部僵硬，而骨骼中立姿势模型未能捕捉到这一特征。
• 骨骼中立姿势模型在后部区域高估了灵活性，在中部区域则低估了灵活性，表明其预测准确性存在显著局限。
• 椎间空间对整体颈部灵活性有显著贡献，其测量值可能导致活动范围估计值的差异。
• 基于对肌肉附着点的比较分析，蜥脚类恐龙颈部基部的肌肉质量比例可能显著高于鸵鸟。
• 软组织（而不仅仅是骨骼形态）是限制颈部灵活性的主要因素，且关节突重叠不能可靠地指示功能性灵活性。
• 如果骨骼中立姿势模型在蜥脚类恐龙中的表现如同在鸵鸟中一样高估灵活性，那么其取食范围可能比以往模型所假设的更为受限，从而支持蜥脚类恐龙类群之间存在更大的生态位分化。