Laboratório de Paleontologia, Departamento de Ciências Biológicas, Centro de Ciências Humanas e Naturais, Universidade Federal do Espírito Santo, Vitória, ES, Brazil.
Laboratório de Mastozoologia, Departamento de Zoologia, Universidade Federal do Estado do Rio de Janeiro, Rio de Janeiro, RJ, Brazil.
PLoS One. 2019 Oct 25;14(10):e0224165. doi: 10.1371/journal.pone.0224165. eCollection 2019.
Birds and pterosaurs have pneumatic bones, a feature likely related to their flight capabilities but whose evolution and origin is still poorly understood. Pneumatic foramina are present on the external surface of the bone and are reliable indicators of post-cranial skeletal pneumatization present in Pterosauria, Eusauropoda, and Neotheropoda. Here, we carried out a qualitative analysis of the position, size and number of pneumatic foramina of the cervical and thoracic/dorsal vertebrae of pterosaurs and birds, as they have the potential to challenge hypotheses about the emergence and evolution of the respiratory trait in these groups. We also discussed differences between pneumatic and vascular foramina for identification purposes. Besides phylogenetic representativeness, the pterosaur taxonomic sampling considered the preservation of specimens and, for birds, their life habit, as this relates to the level of pneumatization. Pneumatic foramina on the lateral faces of the centrum of the mid-cervical vertebrae of pterosaurs and birds differ in position and size, and those adjacent to the neural canal additionally differ in number. The avian posterior cervical vertebrae show a higher number of pneumatic foramina in comparison to their mid-cervicals, while the opposite is true for pterosaurs, suggesting differences in the cervical air sac of these clades. Pneumatic foramina were found at the base of the transverse processes of the notarial vertebrae of birds, while they were absent from some of the pterosaurs analyzed here, revealing the presence of a pneumatic hiatus in the vertebral column that might be explained due to the distance of this structure to the cervical air sac. These findings indicate that, although the overall skeletal pneumatization of pterosaurs and birds present deep homologies, some pneumatic features occurred convergently because variation in the number of pneumatic foramina along the vertebral column is related to the position of the air sacs in pterosaurs and birds and/or the habit of each species. There is an evident reduction of the pneumatic foramina in birds that have aquatic foraging and an increase in the ones which perform static soaring. Although we did not find any external anatomical difference between pneumatic and vascular foramina, we observed that vascular foramina occur at specific sites and thus identification on the basis of location is reliable.
鸟类和翼龙具有充气骨骼，这一特征可能与它们的飞行能力有关，但它们的进化和起源仍知之甚少。充气骨孔存在于骨骼的外表面，是翼龙类、eusauropoda 和 neotheropoda 后颅骨充气的可靠指标。在这里，我们对翼龙和鸟类的颈椎和胸/背椎的骨孔位置、大小和数量进行了定性分析，因为它们有可能挑战关于这些群体呼吸特征出现和进化的假说。我们还讨论了为识别目的而区分充气骨孔和血管骨孔的差异。除了系统发育代表性之外，翼龙的分类采样考虑了标本的保存情况，以及鸟类的生活习性，因为这与充气程度有关。翼龙和鸟类的中颈椎侧骨孔在位置和大小上存在差异，而靠近神经管的骨孔在数量上也存在差异。与中颈椎相比，鸟类的后颈椎具有更多的充气骨孔，而翼龙则相反，这表明这两个类群的颈椎气囊存在差异。在鸟类的枢椎横突基部发现了充气骨孔，而这里分析的一些翼龙则没有，这表明在脊椎柱中存在一个充气间隙，这可能是由于该结构与颈椎气囊的距离造成的。这些发现表明，尽管翼龙和鸟类的整体骨骼充气具有很深的同源性，但一些充气特征是趋同进化的，因为沿着脊椎骨的充气骨孔数量的变化与气囊在翼龙和鸟类中的位置以及每个物种的习性有关。具有水生觅食习性的鸟类的充气骨孔明显减少，而进行静态翱翔的鸟类的充气骨孔增加。虽然我们没有发现充气骨孔和血管骨孔之间存在任何外部解剖差异，但我们观察到血管骨孔出现在特定的位置，因此基于位置的识别是可靠的。
