Comparative morphology of porpoise (Cetacea: Phocoenidae) pterygoid sinuses: Phylogenetic and functional implications

Abstract

High-resolution X-ray computed tomographic scans were used to examine pterygoid sinus morphology within extant porpoise species and one delphinid (Tursiops truncatus), in order to consider: 1) intraspecific and interspecific variation among the studied species; 2) the most parsimonious sequence of character acquisition; and 3) the potential functional roles of the preorbital lobes of the sinuses in sound reflection. Scans revealed that the pterygoid/palatine regions are mediolaterally broader in the earliest diverging phocoenid (Neophocaena phocaenoides) and Tursiops truncatus than the dorsoventrally elongated sinuses observed in other species. Rostrocaudal lengths of the sphenoidal regions of the sinuses in all individuals studied are proportionally similar, indicating conservatism in this region across species. The neonate Phocoena phocoena has shorter preorbital lobes than adults, but they are still proportionally longer than Neophocaena phocaenoides and Phocoena spinipinnis. The preorbital lobes broaden mediolaterally to varying degrees across species; in particular, Phocoenoides dalli has the largest dorsal and lateral expansion of this region. Assuming the highest pulse frequency produced by porpoises is 150 kHz, all regions of the preorbital lobes are thick enough to reflect the wavelengths produced. In addition, the neonate preorbital lobes are not as elongated as they are in adults, and the dorsal third of this region may not reflect sound to the same extent. This study reinforces the importance of using nondestructive methods to quantify variation in endocranial anatomy and the value of CT data for recovering phylogenetically useful information, as well as functional roles sinuses play in concert with the soft tissue head anatomy for biosonar.

Morphology and Variation in Porpoise (Cetacea: Phocoenidae) Cranial Endocasts

“…Extant phocoenids are traditionally viewed as showing little external asymmetry compared to other odontocetes (Barnes, ; Ichishima and Kimura, ), in line with what we observe in linear and volumetric measurements. The asymmetry observed visually in this study is superficially correlated with shape of the pterygoid sinuses (Racicot and Berta, ), hinting at the complex relationship during ossification with soft‐tissues. Significant volume differences between the hemispheres is not necessarily expected (Toga and Thompson, ), and perhaps analyses recently developed for primate skulls would perform better in documenting the asymmetry in endocasts or skulls of other taxa (Balzeau and Gilissen, ).…”

“…They are homologous with parts of the circle of Willis; however, they supply the brain independently because they are not interlinked subdurally. Vasculature relevant to the current study involves the endocranial vasculature listed above, although extracranial and endocranial retia are complex and interconnected (Fraser and Purves, ; Geisler and Luo, ; Costidis and Rommel, ; Racicot and Berta, ).…”

A Study of the Head during Prenatal and Perinatal Development of Two Fetuses and One Newborn Striped Dolphin (Stenella coeruleoalba, Meyen 1833) Using Dissections, Sectional Anatomy, CT, and MRI: Anatomical and Functional Implications in Cetaceans and Terrestrial Mammals

“…Reference [1] said that there are no paranasal sinuses in Tursiops truncatus, and that in the remaining odontocetes, the maxillary sinus is described (Figure 3) (probably without functionality), though it is not well studied in whales. On the other hand, [10] described the ethmoidal sinus and [50] the pterygoid sinuses, which we have not observed in our specimens studied. We have located in striped dolphin some small orifices in the frontal wall of the nasal skull that clearly connect the nasal cavity with the maxillary sinus; however, we do not know if nasal mucosa closes these orifices completely or are vascular nutrition orifices.…”

Mycotic Infections in Free-Ranging Harbor Porpoises (Phocoena phocoena)

“…It is assumed that the three cases with severe Aspergillusinduced otitis (#1, #13, and #15) suffered of unilateral hearing loss as a direct consequence. The inner ear of harbor porpoises carry expanded accessory tympanoperiotic air sinuses called pterygoid sacs (Racicot and Berta, 2013). These are homologous to guttural pouches in horses (Cozzi et al, 2017) representing air-filled extensions of the Eustachian tube that have openings into both the middle ear and oropharynx (Couetil and Hawkins, 2013).…”