Postcranial skeletal pneumaticity (PSP) characterizes extant birds. This feature is related to a series of air sacs connected to the lungs and prolonged in diverticula that invade bones internally. Previous works revealed that PSP was present along the line to birds, being distinctive of pterosaurs and saurischian dinosaurs. PSP is profuse in the vertebral column of sauropods and theropods and was very studied in sauropods, although scarcely in non-avian theropods. Here we analyze the vertebral pneumaticity of the unenlagiine theropod Unenlagia comahuensis, including the observation through CT scans. Unenlagiinae is a clade of southern dromaeosaurid theropods that is closely related to birds. The vertebral centra have lateral pneumatic foramina (lpf) within fossae (commonly termed ‘pleurocoels’) in middle and posterior dorsals, an unusual feature among extant birds and many non-avian theropods. Another possibly pneumatic fossa stands out at both sides of the neural spine base, which is not present in dorsals of other non-avian theropods, except the unenlagiine Unenlagia paynemili. CT scans revealed camellate tissue in the centra, consisting of small chambers separated by thin trabeculae. Camellae are also observed in the unenlagiines U. paynemili and Austroraptor cabazai, other dromaeosaurids, other coelurosaurs, and some non-coelurosaurian tetanurans. Instead, more primitive groups generally have camerae (larger chambers separated by scarce thick septa). Thus, a possible trend of the vertebral inner pneumaticity types is observed throughout non-avian theropod evolution, as indicated by previous authors. This study provides valuable information that helps to clarify this trend, not only in dromaeosaurids but also throughout theropod evolution.

颅后骨骼充气（PSP）是现存鸟类的特征。该特征与一系列连接到肺部并在憩室中延长的气囊有关，这些气囊侵入内部骨骼。之前的研究表明，PSP 与鸟类一起存在，是翼龙和蜥脚类恐龙的独特之处。PSP 在蜥脚类动物和兽脚类恐龙的脊柱中大量存在，并且在蜥脚类恐龙中得到了大量研究，尽管在非鸟类兽脚类动物中很少。在这里，我们分析了 unenlagiine 兽脚亚目Unenlagia comahuensis 的椎骨充气性，包括通过 CT 扫描观察。Unenlagiinae 是南部驰龙科兽脚类恐龙的一个分支，与鸟类关系密切。脊椎中央在背部中部和背部的窝（通常称为“胸膜腔”）内具有侧向充气孔 (lpf)，这是现存鸟类和许多非鸟类兽脚亚目动物的不寻常特征。另一个可能是充气的窝在神经棘基部的两侧突出，除了 unenlagiine Unenlagia paynemili外，其他非鸟类兽脚亚目动物的背部不存在。CT 扫描显示中央有驼状组织，由细小梁隔开的小室组成。在 unenlagiines U. paynemili和Austroraptor cabazai中也观察到了山茶花、其他驰龙科、其他虚骨龙类和一些非虚骨龙类的破伤龙类。相反，更原始的群体通常有照相机（更大的房间被稀少的厚隔膜隔开）。因此，正如之前的作者所指出的，在整个非鸟类兽脚亚目进化过程中都观察到了椎骨内部充气类型的可能趋势。这项研究提供了有价值的信息，有助于阐明这一趋势，不仅在驰龙科动物中，而且在整个兽脚亚目进化过程中也是如此。