Evolution and migration of conodonts and ammonoids near the end of Devonian recorded in distant localities

Abstract

The Devonian-Carboniferous boundary is allegedly marked by one of the most catastrophic global extinctions associated with sedimentation of the Hangenberg black shale. A dense sampling of the Kowala section in the Holy Cross Mountains, Poland, challenges this view, showing that the faunal dynamics across the Hangenberg black shalewas not more dramatic than that across the preceding Kowala black shale. Quantitative analysis and biologically meaningful conodont apparatus study of the Kowala material offer probably the most complete record of faunal change in the latest Famennian and earliest Tournaisian among those sampled bed-by-bed for ammonoids and conodonts. It appears that the faunal dynamics of both cephalopods and conodonts was controlled by environmental changes that resulted in numerous immigrations and disappearances of particular lineages. Only a small fraction of lineages persisted long enough at the place, and transformed their morphology fast enough, to leave a record of their evolution. Most of the evolution apparently took place elsewhere. Locations of remote refugia where these lineages evolved in the time span bracketed by the Kowala and Hangenberg black shale events remain to be identified. Conodont apparatus study on geographically distant Vietnamese locality Cat Ba provides evidence that at least in the latest Famennian some conodont species unknown from Poland were present in Vietnam. Moreover, the contribution of species known from both localities to Polish and Vietnamese fossil assemblages was dramatically different.