Systematic review and evolution of the early Cytheruridae (Ostracoda)

Abstract. A review of the literature on the taxonomy of Triassic and Early Jurassic cytheracean Ostracoda reveals that the validity of many genera is questionable. A number of studies of the Triassic microfaunas from eastern European sequences have, in particular, obscured the true generic and suprageneric classification of many ostracod taxa. The present study concentrates on the diverse extant cytheracean family the Cytheruridae, whose origins are in the earliest Mesozoic–latest Palaeozoic, but it is clear that many contemporary cytheracean families present similar problems. This review clarifies the previous taxonomic confusion and obfuscation by demonstrating that many of these genera are spurious having been erected on specific rather than generic morphological criteria. Many of them are best accommodated within the extant genus Eucytherura Müller, 1894. Most of the cytherurid genera known from the Liassic deposits of NW Europe can be traced back to these Triassic assemblages. In considering the origin and earliest evolution of the Cytheruridae, we note that some Triassic taxa share characteristics typical of both the Cytheruridae and the Bythocytheridae and it is suggested that the former may have arisen from the latter family during the latest Permian or earliest Triassic. We also note that the palaeoenvironmental interpretation of many of the Triassic deposits is brackish-water, marginal marine.