Non-dental odontodes in the masticatory apparatus of †pycnodonts (Osteichthyes, Actinopterygii)

Two specimens of the pycnodont Haquelpycnodus picteti from the Cenomanian (Late Cretaceous) of Lebanon possess small non-dental odontodes flanking the teeth inside the oral cavity. These odontodes are distributed labially with respect to the vomerine and prearticular dentition, corresponding to the internal face of the cheek and in front of the maxilla. They have no relation to any of the bones in the mouth region and were situated in the endo-oral mucosa. This dentition pattern resembles that of the earliest osteichthyans and stem-gnathostomes. SEM-investigation of the non-dental odontodes demonstrates a thick layer of orthodentine covered by two thin outer layers of acrodin. The microchemical composition of these odontodes corresponds to those of the dermal scales (derived from odontodes) that are distributed in the integument of the same examined specimen. Both morphology, ultrastructure, and topographic relationships demonstrate that these structures are dermal and not dental odontodes. The reappearance of dermal odontodes in the dentition of individual specimens of Haquelpycnodus thus reflects the latent capacity of the endo-oral mucosa to form non-dental odontodes. These odontodes probably exerted lateral pressure to the content within the oral cavity, which took place synchronously with the prehensile movements of the incisors.