Mass mortality of juvenile antiarchs (Bothriolepis sp.) from the Catskill Formation (Upper Devonian, Famennian Stage), Tioga County, Pennsylvania

Abstract

We analyze a new sample of very small Bothriolepis from the Catskill Formation (Upper Devonian, Famennian Stage) in Tioga County, Pennsylvania, USA. The material was collected in a series of rock slabs, each of which carries as many as thirty-one individuals in densely-packed groups with little to no overlap and with a preferred orientation. Although the taxonomy of Catskill Bothriolepis does not allow for a species diagnosis, morphometric comparison between the new sample and a growth series of Bothriolepis canadensis supports the juvenile status of the individuals in the new Catskill sample. By comparing the new material with other worldwide occurrences of small antiarchs, we recognize anatomical features that indicate juvenile status in antiarchs, including a large median ventral fenestra lacking a median ventral skeletal element, especially large medial serrations on the pectoral appendages, and a strongly convex rostral margin of the postpineal element. The geological and taphonomic context of the new material suggests death events of Bothriolepis hatchlings due to anoxia and desiccation in marginal aquatic environments. We highlight the implications for reproductive strategy in antiarchs.