The first new polychaete from the Mazon Creek fossil site in 20 years suggests cryptic annelid diversity in the Late Paleozoic

Abstract

The Mazon Creek fossil site is famous for the preservation of diverse animal and plant assemblages. Among these fossils are representatives of animal groups that are rarely preserved with soft tissues. Annelida is one of these groups, and the Mazon Creek polychaete fauna comprises a disproportionately large sample of all known soft-bodied annelid fossils. Here, we describe the first new fossil annelid from Mazon Creek in over 20 years. This new species, Mazovermes magnaterminus , has a unique morphology with notably large posterior segments, giving an overall teardrop-shaped silhouette not found in any other fossil polychaete. It further preserves fine details such as the nanometre-sized chaetae, as well as muscular tissues. Fundamentally, this new species demonstrates not only a unique body organisation within this extremely morphologically and ecologically disparate phylum but also that the Mazon Creek Lagerstätte is likely to yield additional undescribed invertebrates with soft-tissue preservation upon re-investigation.