A unique example of the Late Cretaceous horseshoe crab Tachypleus syriacus preserves transitional bromalites

Bromalites are the group of ichnofossils that record the consumption, processing, and elimination of material through digestive systems. Each main stage of processing has been ascribed to distinct bromalite subgroups, such as cololites, coprolites, and regurgitates, with little evidence for transitions between these stages. To expand this limited record, we consider a fossil horseshoe crab—Tachypleus syriacus—from the Cenomanian Hjoula Lagerst€atte (Sannine Formation, Lebanon) that showcases one such transition. The specimen illustrates a bromalite both within the animal’s guts (cololite) and as expelled faecal matter (coprolite). This demonstrates a link between these two conditions for fossil chelicerates and highlights the level of exceptional preservation within the Hjoula Lagerst€atte. Additionally, the specimen features prosomal nodules unique to limulids, suggesting new automorphic morphologies for T. syriacus.