Development of the paratympanic pneumatic system of Japanese quail

Abstract

Avian heads are characterized as having two extensive air‐filled systems lined with epithelia; the paranasal and paratympanic sinuses. Many diverticula derived from the paratympanic sinus system are known to reticulate with each other to form a single merged pneumatic space within the adult braincase. However, the development of these complex branching and reticulating epithelia has not been examined in detail. In this study, we describe the comprehensive developmental pattern of the paratympanic sinus and its associated soft tissues in a model bird, Japanese quail (Coturnix japonica). The data are derived from three‐dimensional reconstructions based on histological sections and soft tissue enhanced micro‐CT data. Those data provide the foundation of the complex hierarchical developmental pattern of the paratympanic sinus system. Moreover, associations with other tissues help establish key morphologies that identify each pneumatic entity. This study clarifies the developmental relationships of the ventral portions of the paratympanic sinus system, the siphoneal diverticulum and marginal sinus, based on the ligaments associated with the Eustachian tube. In addition, detailed histological pneumatic morphologies reveal hitherto unknown epithelial diversity, which may be indicative of equally complex developmental processes. We use the pneumatization of the quadrate as an example to support a close relationship with vascular growth and pneumatic epithelia invasion into ossified bone. We confirm pneumatic diverticula never enter into cartilages, possibly due to the absence of vasculature in these tissues. Lastly, we use the concept of a morphogenetic tree as a tool to help present the complex developmental pattern of the paratympanic sinus system and apply it toward inferring pneumatic morphologies in a nonavian theropod braincase.

Computed tomographic and gross anatomy of the head of the blue‐fronted Amazon parrot (Amazona aestiva)

“…The paratympanic sinus could also not be identified in bluefronted Amazon parrots in this study, as this structure is thought to be topographically related to middle ear structures (Tahara & Larsson, 2019a), which could not be clearly demarcated in conventional CT images.…”

“…Pneumatic foramina could not be identified in CT images in this study; therefore, the origin of skull bone pneumatization could not be determined. The paratympanic sinus could also not be identified in blue‐fronted Amazon parrots in this study, as this structure is thought to be topographically related to middle ear structures (Tahara & Larsson, 2019a), which could not be clearly demarcated in conventional CT images.…”

“…However, intrinsic limitations aside, conventional CT may still be useful for otitis diagnosis (Delk et al, 2014). The use of high‐resolution modalities such as micro‐CT for visualization of these structures has been suggested (Bonsmann, Stoffel, Burkhart, & Hatt, 2016; Tahara & Larsson, 2019a, 2019b).…”

“…The use of high-resolution modalities such as micro-CT for visualization of these structures has been suggested (Bonsmann, Stoffel, Burkhart, & Hatt, 2016;Tahara & Larsson, 2019a, 2019b.…”

The skull of the Miocene Spheniscus urbinai (Aves, Sphenisciformes): osteology, brain morphology, and the cranial pneumatic systems

“…In birds, cranial pneumatization occurs when epithelial diverticula (from two main systems) invade the bone (Witmer, 1997). The paranasal and paratympanic sinuses (Starck, 1995; Tahara & Larsson, 2019b), which together comprise the head sinuses (sensu Tahara & Larsson, 2019a), include two extensive air‐filled systems that characterize the avian head. The paranasal sinuses extend within the upper beak forming a set of variable nasal conchae and diverticula.…”