The ‘Last Hurrah of the Reigning Darwinulocopines’? Ostracoda (Arthropoda, Crustacea) from the Lower Jurassic Moenave Formation, Arizona and Utah, USA

An ostracod fauna is described from lacustrine sediments of the Hettangian, Lower Jurassic Whitmore Point Member of the Moenave Formation. The Moenave is well known for its rich, Late Triassic?–Early Jurassic fossil record, which includes fossil fishes, stromatolites, ostracods, spinicaudatans and a diverse ichnofauna of invertebrates and vertebrates. Four ostracod species, all belonging to the suborder Darwinulocopina, were recovered from these sediments: Suchonellina globosa, Suchonellina stricta, Whipplella? sp. 1 and Whipplella? sp. 2. The diversity and composition of the Whitmore Point Member ostracod fauna agree with previous interpretations about Lake Dixie and nearby paleoenvironments as shallow lakes, where darwinulocopine species which survived the effects of the Central Atlantic Magmatic Province and the subsequent End-Triassic extinction quickly recolonized these areas thanks to asexual reproduction by parthenogenesis. The Lake Dixie region, in its geographical isolation, may represent the last episode of darwinulocopine dominance in non-marine environments before the Late Jurassic diversification of the cypridocopine/cytherocopine modern ostracods.