[论文解读] Postcranial pneumaticity in dinosaurs and the origin of the avian lung

Matt Wedel|arXiv (Cornell University)|Feb 13, 2013

Paleontology and Evolutionary Biology参考文献 214被引用 15

一句话总结

本文提出，蜥臀目恐龙的骨骼气腔化——表现为脊椎中的凹窝、孔洞和腔室——表明其具有气囊和类似鸟类的流动式肺通气。通过空气空间比例（ASP）分析，研究显示腕龙类和兽脚类的气腔化骨骼平均有61%的体积为空气填充，使骨骼质量减少7–10%，并使梁龙的特定重力降低至0.80（当计入气腔时）。

ABSTRACT

In birds, diverticula of the lungs and air sacs pneumatize specific regions of the postcranial skeleton. Relationships among pulmonary components and skeletal regions they pneumatize allow inferences about pulmonary anatomy in non-avian dinosaurs. Fossae, foramina and chambers in the postcranial skeletons of pterosaurs and saurischian dinosaurs are diagnostic for pneumaticity. In basal saurischians only the cervical skeleton is pneumatized, by cervical air sacs. In more derived saurischians pneumatization of posterior dorsal, sacral, and caudal vertebrae indicates abdominal air sacs. Abdominal air sacs in sauropods are also indicated by a pneumatic hiatus (a gap in vertebral pneumatization) in Haplocanthosaurus. Minimally, saurischians had dorsally attached diverticular lungs plus anterior and posterior air sacs, and all the pulmonary prerequisites for flow-through lung ventilation like that of birds. Pneumaticity reduced skeletal mass in saurischians. I propose the Air Space Proportion (ASP) as a measure of proportional volume of air in pneumatic bones. The mean ASP of a sample of sauropod and theropod vertebrae is 0.61, so on average, air occupied more than half the volume of these vertebrae. In Diplodocus, pneumatization lightened the living animal by 7-10 percent, and that does not include extraskeletal diverticula, air sacs, lungs, or trachea. If all these air reservoirs included, the specific gravity of Diplodocus is 0.80, higher than published values for birds but lower than those for squamates and crocodilians. Pneumatization of cervical vertebrae facilitated evolution of long necks in sauropods. Necks longer than nine meters evolved at least four times, in mamenchisaurs, diplodocids, brachiosaurids, and titanosaurs. Increases in the number of cervical vertebrae, their proportional lengths, and their internal complexity occurred in parallel in most of these lineages.

研究动机与目标

• 确定恐龙的骨骼气腔化是否表明存在气囊和流动式肺通气。
• 评估骨骼气腔化在促进腕龙类长颈演化中的作用。
• 利用新指标——空气空间比例（ASP）——量化气腔化对骨骼质量和体密度的影响。
• 基于骨骼气腔化模式重建非鸟类恐龙的肺部解剖结构。

提出的方法

• 识别并分析翼龙和蜥臀目恐龙后段骨骼中的气腔特征（凹窝、孔洞、腔室）。
• 使用空气空间比例（ASP）估算气腔化骨骼中空气体积占比。
• 比较不同恐龙类群的气腔化模式，以推断颈气囊和腹气囊的存在。
• 基于骨骼气腔化分布及哈普洛鱼龙蜥（Haplocanthosaurus）中气腔间隙的存在，推断肺通气机制。
• 通过计入气腔化骨骼、气囊、肺和气管，计算梁龙的特定重力。
• 分析长颈腕龙类类群中，脊椎气腔化与颈长及形态复杂性的关联。

实验结果

研究问题

• RQ1 非鸟类蜥臀目恐龙是否具有类似鸟类的气囊和流动式肺通气？
• RQ2 骨骼气腔化在减轻骨骼质量并促进长颈演化方面具有何种功能意义？
• RQ3 气腔化骨骼的体积中有多少被空气占据？对体密度有何影响？
• RQ4 能否通过脊椎中气腔特征的分布推断气囊的存在及其位置？
• RQ5 当计入骨骼、肺、气囊和气管中的气腔时，梁龙的特定重力是多少？

主要发现

• 腕龙类和兽脚类脊椎的平均空气空间比例（ASP）为0.61，表明这些骨骼平均有超过一半体积为空气占据。
• 气腔化使梁龙的骨骼质量减少了7–10%，显著降低了其整体体密度。
• 当计入骨骼、肺、气囊和气管中的气腔时，梁龙的特定重力估计为0.80，低于鳄类和有鳞目动物。
• 哈普洛鱼龙蜥中气腔间隙的存在支持了腕龙类存在腹气囊。
• 腕龙类颈椎气腔化的程度与颈部长度超过九米的演化相关，此类长颈至少独立演化了四次。
• 在多个长颈腕龙类类群中，颈椎数量增加、比例长度增长及内部结构复杂化同步演化。