A new paper:
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Pneumatic features of the dorsal vertebrae of Unenlagia comahuensis are studied.
Lateral pneumatic foramina are in the centrum from anterior to posterior dorsals.
CT scans revealed camellate tissue in the vertebral centra.
Camellae are also observed in other unenlagiines, such as Unenlagia paynemili.
This study increases the knowledge of pneumaticity of non-avian theropods.
Abstract
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 âpleurocoelsâ) 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.
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