Exploring the morphology and taphonomy of Archaeoniscus brodiei—a gregarious, Early Cretaceous isopod

Abstract

Marine isopod fossils represent a small component of the crustacean fossil record, contrasting the exceptional modern diversity of marine representatives of Isopoda. Examination of previously documented isopod species therefore presents an opportunity to derive additional paleobiological and taphonomic insight of these rare fossils. Here we consider two clusters of Archaeoniscus brodiei from the Lower Cretaceous (middle to upper Berriasian) Intermarine Member of the Durlston Formation, England. The individuals within the clusters are mostly complete, of similar size ranges, and are preserved on two different bedding planes. After examining these individuals, we illustrate, for the first time, appendages and eyes of A. brodiei. The appendage morphology supports the interpretation of A. brodiei as an isopod adapted to a benthic lifestyle. We propose that isopods from the Durlston Formation follow similar taphonomic pathways to arthropods preserved within plattenkalk-like deposits, resulting in enrichment in calcium carbonate and phosphate. Finally, the clusters reflect gregarious activities that were preserved during hypoxic events brought on by concurrent decay of algal blooms.