Jaws and dentition in an Early Triassic, 3-dimensionally preserved eugeneodontid skull (Chondrichthyes)

Abstract

Neutron scans of a concretion with a 3-dimensionally preserved partial skull from the Lower Triassic Vega Phroso Siltstone Member of the Sulphur Mountain Formation (western Canada), previously assigned to Caseodus, reveal that upper jaws were absent in this eugeneodontid. Large, anteriorly deep lower jaws housed relatively few and large tooth files and enclosed a narrow anterior mouth cavity together with the symphysial tooth whorl, which is situated on the mandibular rostrum. The symphysial teeth are slender-conical in antero-occlusal view and do not appear to possess a transversal crest. The taxonomic significance of tooth morphology and absence of upper jaws is discussed. This eugeneodontid yields evidence of another group of rather primitive fishes surviving the end-Permian extinction event. The architecture of oral cavity and dentition suggests these chondrichthyans were specialized on preying on disc-shaped or flat, presumably shelled organisms.