The New Ichnogenus Flagrichnus - A Paleoenvironmental Indicator for Cold-Water Settings?

The new marine microboring ichnogenus Flagrichnus is described from Pleistocene mollusc shell beds of Rhodes (Greece) and the Costa Brava (Spain). Recent equivalents are studied in detail from the cold-temperate setting of the Swedish Kosterfjord area. Two ichnospecies are recognized: Flagrichnus profundus consists solely of a deeply penetrating gallery with a basal swelling while Flagrichnus baiulus comprises a single to multiple sack-shaped cavity at the base of a branching filamentous gallery that is penetrating deeply into the substrate. The traces are distributed from the euphotic zone down to aphotic depths suggesting (chemo)heterotrophic microendoliths and more specifically marine fungi as the trace makers. For Flagrichnus profundus, the thraustochytrid fungus Schizochytrium is recognized as its trace maker; for Flagrichnus baiulus, no definite candidate has been identified. While Flagrichnus profundus is distributed from tropical to arctic waters, Flagrichnus baiulus is only known from fossil and Recent non-tropical settings suggesting an applicability of this ichnospecies as an indicator for low paleotemperatures