Article: The conchostracan fauna of the Great Estuarine Group, Middle Jurassic, Scotland
The Great Estuarine Group contains the most diverse conchostracan fauna so far described from the Jurassic or Cretaceous of Europe, comprising twelve species in seven genera. Estheria murchisoniae Jones was described in the last century; it is now referred to Pseudograpta Novojilov and is the youngest member (latest Bathonian?) of the fauna described here. Euestheria trotternishensis and Neopolygrapta lealtensis spp. nov. occur near the base of the Great Estuarine Group and probably close to the Bajocian-Bathonian boundary. Dendrostracus hebridesensis sp. nov. occurs towards the top of the Kildonnan Member, Lealt Shale Formation. In the overlying Lonfearn Member, Skyestheria intermedia sp. nov. appears (probably descended from Neopolygrapta) and itself gives rise to Antronestheria praecursor sp. nov. The higher parts of the Great Estuarine Group, including most of the Kilmaluag Formation, are dominated by Antronestheria kilmaluagensis sp. nov., with one occurrence of Fibrestheria puncta sp. nov. The Pseudograpta fauna (containing P. orbita Chen, P. morrisi sp. nov., P.jonesi sp. nov. and P. murchisoniae (Jones)) occurs in beds probably near the top of the Kilmaluag Formation. All the conchostracans inhabited shallow, freshwater to oligohaline, near-coastal, lagoons. Biogeographic comparisons with China show that the earlier faunas were distinct in the two areas, but the Pseudograpta fauna occurs in both. Details of the construction of conchostracan growth bands are revealed by stereo scanning electron micrographs.