First cladoceran fossils from the Carboniferous: Palaeoenvironmental and evolutionary implications

A new cladoceran crustacean, Ebullitiocaris elatus sp. nov., is described from the Carboniferous. This unusual occurrence originates from an ex situ chert-mineralised cobble collected from beach shingle at Sandsend, Whitby, North Yorkshire. Previous biostratigraphic analysis of the micro- and megaspores from fertile plant remains associated with E. elatus restricts the fossils to an Early Mississippian to Middle Pennsylvanian age. The fossil cladocerans occur individually and in clusters and consist of a thin, oval carapace, elliptical in longitudinal section, bilaterally symmetrical, with an anterior cavity. The head overlaps the anterior cavity and is external to the carapace. Soft tissues preserved within the anterior cavity include thin, delicate thoracic appendages within the carapace and paired second antennae that extend anteriorly from the dorsal carapace cavity. These have at least six branches with segmented hair-like protrusions. The head bears a single oval compound eye with a vertically orientated long axis. A cladoceran identity is demonstrated by the univalve carapace and external head that differentiates it from the Ostracoda and Conchostraca. This is only the second record of a Palaeozoic fossil cladoceran, both recognised from sites of exceptional preservation in wetland ecosystems where they constitute an important faunal element. E. elatus is significant as it documents additional diversity during the early evolutionary history of the Cladocera, but also confirms morphological stasis within the group, sharing many of its characteristics with extant Cladocera adapted to algal grazing in freshwater habitats.