DIVERSIFICATION OF AMMONOIDS AND VERTEBRATES DURING THE DEVONIAN NEKTON REVOLUTION

The Devonian Nekton Revolution, or DNR, has recently been identified as a phenomenon separate from the better known Great Ordovician Biodiversification Event. The DNR is notable for the rapid occupation of the water column by active predators, in contrast to the earlier radiations of more demersal and passive ecologies. This event is particularly important for cephalopods and vertebrates, two of the most prominent groups of nektonic predators in ancient and modern oceans, which are plausible ecological counterparts. The Early Devonian featured both the first appearance of the ammonoids and the transition from “ostracoderm” to gnathostome dominated assemblages (gnathostomes are known from the Ordovician, but rare prior to the Devonian). Identification of the DNR relied on generic stratigraphic ranges compiled from Sepkoski’s Compendium and the Paleobiology Database. Genera, however, may not be monophyletic and their stratigraphic ranges may generate artificial diversity patterns; species-level ranges are preferable. Such data are available for Paleozoic ammonoids on AMMON, but no such database exists for mid-Paleozoic vertebrates. We assembled stratigraphic ranges of vertebrate species compiled from Fossilworks, the PBDB, the Yale Peabody Museum collections, and the primary literature. This information, albeit incomplete, is more comprehensive than any previously available. The data reveal diversity patterns of Silurian to Mississippian ammonoids and vertebrates that illuminate the dynamics of this critical event in the history of the global nekton.