Phoebeannaia mossae, Caron & Venkataraman & Tietjen & Fls, 2023

Phoebeannaia mossae

The otic wall extends from the otico-occipital fissure to the post-orbital processes. The roof of this region is partially obscured by displaced frontal and parietal bones, although the semicircular canals and fossa bridgei are evident on the right side of the specimen (ant.ssc, pos.ssc, f.br; Fig. 9B). The ridge overlying the anterior semicircular canal is longer than the posterior, as is common in Carboniferous actinopterygians, and extends forward to the level of the post-orbital process. Consequently, the circumscribed fossa bridgei is large and contiguous with the dorsal exit of the spiracular canal (spir.f; Fig. 9B). There does not appear to be any connection between the intracranial space and fossa bridgei, nor could the fossa bridgei have housed epaxial musculature due to the height of the neurocranial roof overlying the posterior semicircular canal.

In lateral aspect, a well-defined triangular parampullary fossa (pa.f; Figs 7A, 8A) spans the area between the rear of the hyoid facet (overlying the external semicircular canal ampulla) and the prominence capping the posterior ampulla. This is the likely site of opercular adductor muscle origin. The crest forming the roof of the parampullary fossa descends anteriorly, aligned with the dorsal margin of the kidney-shaped, posteroventrally directed hyomandibular facet (hm.fa; Figs 7A, 8A, 9A). A narrow spiracular bridge (spir.br; Figs 7A, 9A) ascends from the anterior rim of the hyoid facet to the posterior of the post-orbital process (po.p; Figs 7A, 9A, 10A), enclosing (canalizing) a shallow spiracular groove. The free posterior surface of the post-orbital process likely provided the attachment surface for the hyoid constrictor muscles in the absence of a clearly defined dilatator fossa.

The ventral rim of the post-orbital process tapers smoothly into a broad lateral commissure. The groove for the efferent hyoid artery, anterior to the projection for the first infrapharyngobranchial, ascends the lateral commissure and joins the jugular canal via a foramen (e.hy.a; Figs 7A, 8A, 9A). On the left side of the neurocranium there are three posterior exits from the jugal canal: a large medial opening primarily for the jugular vein (j.c; Figs 7A, 8A, 9A, 10A), and two small lateral foramina that might have transmitted branches of the facial nerve (VII.hy, VII.op; Fig. 8A). There is only one lateral foramen on the right side, which could indicate plasticity of this feature or merely post-mortem breakage. The groove for the jugular vein continues posteriorly ventral to the exit of the vagus nerve and is roofed by a broad horizontal shelf with an anterior concavity—the subtemporal fossa (st.f; Figs 7A, 8A, 9A). The glossopharyngeal nerve foramen, ventral to the jugal groove, is closely associated with a broad lateral projection for articulation with the first suprapharyngobranchial. Both the foramen and the articulation are aligned with the rear of the vestibular fontanelle, which is bounded posteriorly by a ventral tongue-like projection from the otic wall (v.t; Figs 7A, 8A, 9A). Similar examples are present in Kansasiella , Kentuckia deani and Pteronisculus .