Rhizocorallites Müller, 1955 from the Triassic and Jurassic of Germany: burrow, coprolite, or cololite?

Rhizocorallites articularis Müller, 1955 are string-shaped sediment aggregates with a homogeneous fill and transverse segmentation, known from marginal-marine deposits of the Middle Triassic (Anisian) of the Germanic Basin. They preferably occur as winding and bent strings at the base of thin storm layers (tempestites). Originally interpreted as the dwellings of a tubiculous annelid or a backfilled burrow similar to Taenidium, a reinvestigation of the type and supplementary material reveals characteristics more conformable with an interpretation as the faecal string (i.e., coprolite) or intestine content (i.e., cololite) left by an epibenthic organism. Comparison with modern analogues suggests holothurians as potential producers of R. articularis. This is confirmed by one of the paratype specimens that, in addition to the segmented string-shaped aggregate, preserved other connecting organs interpreted as stomach, intestine, rectum, and cloaca of a decaying holothurian. Different taphonomic pathways of decaying sea cucumbers result in varying styles of preservation, reaching from conservation (obrution) by burial with sediment to reworking by currents and incorporation into event deposits. Comparable specimens from the Upper Jurassic (Tithonian) lithographic limestone of southern Germany are assigned to Rhizocorallites inaequalis isp. nov. and, due to their exceptional preservation partly within the carcasses of holothurians, confirm an origin as cololites. Several records of Rhizocorallites from different parts of the world indicate its wide distribution from the Upper Ordovician to the Upper Cretaceous.