Cranial anatomy of a Late Cretaceous aspidorhynchid fish (Neopterygii: Aspidorhynchiformes) from Alberta, Canada.

Belonostomus longirostrisis was named for an isolated jaw fragment from freshwater Upper Cretaceous (Campanian) sediments of the Dinosaur Park Formation of Alberta, Canada. Following the description of the Albertan species, numerous isolated cranial and postcranial elements have been collected from the Dinosaur Park Formation and assigned to B. longirostris, despite the material not overlapping with, and therefore not being comparable to, the holotype. This includes two partial skulls that lack jaws. These two skulls were assigned to the genus based on their clear aspidorhynchid affinities including ganoine-covered dermal bones, and lack of other known taxa from the locality to which they could be ascribed. The two skulls were scanned with micro-computed tomography (μ-CT) to allow description of the cranial elements and their internal structure. The bones of the dermal skull roof are almost entirely fused together, ornamented with conspicuous ridges and tubercles, and bear a pair of supraorbital sensory canals along the lateral sides. Internally, many bones of the skull are fused together, with only a few elements that can be consistently isolated in the μ-CT scans. Notable discoveries in this material include extensive enclosed cranial sensory canals, no fusion between the basioccipital and first vertebra, the anterior myodome restricted to the sphenotic region with complete lack of a posterior myodome, and a canal, presumably for the jugular vein, that does not connect with the trigemino-facialis chamber. These last two features are important in that they would exclude Aspidorhynchidae from belonging to Teleostei.