Ichnological insights into mitrate palaeobiology

Mitrates are a controversial group of extinct deuterostomes; there is little agreement over their affinities, functional morphology or even the orientation of their upper and lower surfaces. Four slabs of slate from the Lower Devonian Hunsruck Slate (Bundenbach, Germany) are here described, showing trace fossils (Vadichnites transversus igen. et isp. nov.) associated with the mitrate Rhenocystis latipedunculata. These new findings clearly demonstrate that the mitrate appendage was used in locomotion and that this movement took place appendage-first. Such a functional interpretation suggests that mitrates were oriented with the flat body surface upwards in life and argues against a phylogenetic position in the echinoderm crown-group.