CRETACEOUS LUNGFISH (DIPNOI: CERATODUS) DIVERSITY OF NORTH AMERICA

Lungfishes of the form genus Ceratodus represent a widespread yet minor component in most late Mesozoic terrestrial ecosystems of North America (NA). Until recently, most species were known from the Late Jurassic Morrison Formation, with a few specimens documenting presence in Cretaceous assemblages. Early evolutionary hypotheses espoused an anagenetic relationship between Jurassic and Cretaceous Ceratodus species. We report new occurrences demonstrating that many of the Jurassic species (or species groups) survive well into the Cretaceous. On this basis, we propose a simplified terminology for Jurassic–Cretaceous NA lungfish, wherein all species are split into two separate morphotypes based on tooth crown height. Cretaceous taxa can then be recognized as belonging to subcategories, based on similarities shared with known Jurassic species. Because most species are only known from isolated teeth, we make no implications regarding the phylogenetic relationships between these groupings. New fossils extend the known range of C. fossanovum, C. guentheri, and C. robustus into the Cretaceous; multiple new specimens represent novel species similar to C. frazieri and C. robustus. These data suggest certain evolutionary, ecological, and biogeographical patterns. Both crushing and slicing morphotypes co-occur in many Late Jurassic and Early Cretaceous rock units; some taxa in the C. guentheri and C. frazieri morphotypes show general size increase through time. The new fossils and groupings provide a better appreciation of lungfish diversity through the late Mesozoic of NA, and suggest that diversity began to decline in NA after the early Late Cretaceous.