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

Abstract

An ostracode 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, ostracodes, spinicaudatans, and a diverse ichnofauna of invertebrates and vertebrates. Four ostracode species, all belonging to the suborder Darwinulocopina, were recovered from these sediments:Suchonellina globosa,S. stricta,Whipplella? sp. 1, andW.? sp. 2. The diversity and composition of the Whitmore Point Member ostracode fauna agree with previous interpretations about Lake Dixie and nearby paleoenvironments as shallow lakes inhabited by darwinulocopine species that survived the effects of the Central Atlantic Magmatic Province and the subsequent end-Triassic extinction and quickly recolonized these areas, thanks to asexual reproduction by parthenogenesis. The Lake Dixie region, in its geographical isolation, could represent the last episode of darwinulocopine dominance in nonmarine environments before the Late Jurassic diversification of the cypridocopine/cytherocopine modern ostracodes.

Evaluation of the ontogeny and sexual dimorphism in a new species of Middle Triassic Darwinulocopina (Crustacea, Ostracoda) from Argentina

“…The work of Antonietto et al . (2018) is an example of the integration of these two approaches, with interesting results, such as the identification of typical Permian–Triassic ostracods in the Lower Jurassic Moenave Formation (Arizona and Utah, USA).…”

“…nov. are referred to Suchonellina and Suchonella (Table 1), both typical Permian genera that survived into the Triassic, the first even up to the Jurassic (Antonietto et al . 2018; Naumcheva & Golubev 2020). The greatest width in Suchonella is displaced ventrally, resulting in a rounded subtriangular cross‐section, it also has a convex dorsal margin.…”

“…Subsequently, the taxonomy of the Permian, Triassic and Jurassic Darwinulocopina was adjusted, and several species previously assigned to Darwinula were reallocated to different genera (Molostovskaya 1980, 1990, 2005; Kashevarova & Neustrueva 1982; Kukhtinov & Voronkova 2015; Antonietto et al . 2018). Similarly, after the work of Rossetti & Martens (1998), several extant and Mesozoic species formerly referred to Darwinula were reassigned (Martens et al .…”