Bifungites from the Ordovician of Crozon Peninsula (Kermeur Formation, Brittany, France): environmental tolerance and evolutionary trajectory of an extinct animal behaviour

Bifungites is an inverted π-shaped vertical burrow that was recovered from 52 stratigraphic levels in the Upper Ordovician (Katian) Kermeur Formation of Crozon Peninsula in northwestern France. Its excellent quality and abundance in various sedimentary facies allow re-evaluations of the ichnotaxonomy, taphonomy, ethology, environmental tolerance, and evolutionary patterns of this curious ichnotaxon. Analysis of 68 specimens permitted the identification of five ichnospecies in Brittany: Bifungites cf. bisagitta, B. cf. bisagittula, B. fezzanensis, B. halli, and Bifungites isp. Bifungites was found both in restricted bay and open marine environments, with peaks of abundance in low-energetic settings while it is totally absent from high-energetic environments. Although preservation of Bifungites on true substrates is theoretically possible, most records (i.e. dumbbell-shaped semi-reliefs) are associated with shallow-tier trace fossils on erosional surfaces that represent constructed bedding planes. A compilation of worldwide records demonstrates that Bifungites was a product of the Ordovician radiation that thrived especially in the offshore until the lower Carboniferous. Its extinction after the Visean may be related to the Serpukhovian biodiversity crisis and global environmental changes that took place across the Carboniferous-Permian interval.