Medusas del Cámbrico inferior de Constantina (Sevilla)

Résumé

Ninety giant, discoid structures occurring on a bedding plane of Corduban arkosic greywackes in the Spanish regional stages, from southwestern Spain are described. Crosscutting relationships between discoid structures and associated trace fossils, as well as evidence for penecontemporaneous deformation of sediment laminae below the discoids, permit to interprete these structures as impressions of ancient, soft-bodied marine organisms. Taphonomic, biometric, and morphological studies suggest that they are outer moulds of ancient jellyfish of hydrozoan coelenterates similar to the extant genus Aequorea. Palaeoichnological, lithological and sedimentological features indicate that these organisms were deposited in extremely shallow water stranded on a sandy beach. The palaeontological site described here is noticeable because its anomalous record of hydrozoans in coarse siliciclastic rocks, and the high number of specimens on a single surface. Since soft-bodied biotas of Corduban ages are very scarce, this site may provide a better understanding of the important biological events across the Neoproterozoic/Phanerozoic transition, particularly the evolution of hydrozoans.