New Saurorhynchus (Actinopterygii: Saurichthyidae) material from the Early Jurassic of Alberta, Canada

Abstract

Saurichthyidae are a family of elongate, piscivorous actinopterygian fishes with a stratigraphic range extending from the late Permian to the Middle Jurassic. There are four recognized Early Jurassic species, all from Europe and all referred to the genus Saurorhynchus. Only a single non-European Jurassic occurrence has been reported, a partial Saurorhynchus skull from the Fernie Formation of western Alberta, Canada. Here, we evaluate the Saurorhynchus material from Canada, including a new skull from Ya Ha Tinda, Alberta, and a fragmentary mandible from Canyon Creek, Alberta. All diagnostic Canadian Saurorhynchus specimens are consistent with the European species Saurorhynchus acutus, on the basis of external narial morphology and reduced dermal ornamentation. Saurorhynchus acutus was present in the Toarcian of western North America from the tenuicostatum Zone to the late serpentinum – early bifrons Zone, similar to the stratigraphic range documented in Europe. The absence of divergence between eastern Panthalassan and western Tethyan saurichthyids is surprising, given that divergence has been well-documented in coeval invertebrates. Saurorhynchus may have had slower rates of morphological evolution than contemporaneous marine invertebrates; alternatively greater mobility, broader environmental tolerance, or both in these fish may have allowed ongoing gene flow between the two oceanic basins in the early Toarcian.