Late Cretaceous Notogoneus from microvertebrate assemblages of the Dinosaur Park Formation, Campanian of southern Alberta, Canada, and insight into the ecology and evolution of early gonorynchids

We here report the first documented occurrence of a gonorynchiform from the Mesozoic of Canada, represented by disarticulated material recovered from multiple localities in the Lethbridge Coal Zone, in the Late Cretaceous Campanian upper Dinosaur Park Formation of southern Alberta. Despite the preservation of these specimens as disarticulated and isolated microvertebrate material, we can identify this fish as the gonorynchid Notogoneus. Although this material was recovered from estuarine settings, the local environment was freshwater, and this occurrence does not constitute evidence that this species of Notogoneus was amphidromous, as has previously been hypothesized for early gonorynchids. We offer suggestions regarding the whole-body anatomy of the fish represented in our sample through comparisons with articulated specimens of Notogoneus osculus from the Green River Formation as well as with modern comparative material. Such details include a narrow mouth in a ventral position and probable possession of branchial tooth plates, from which aspects of the ecology of this fish can be deduced, such as durophagy and a probable demersal environmental preference. Additionally, these comparisons highlight the mosaic evolution of early gonorynchids, combining a primitively chanid-like vertebral anatomy and a more derived, Gonorynchus-like jaw.