Data from: Biostratigraphy and geometric morphometrics of conchostracans (Crustacea, Branchiopoda) from the Late Triassic fissure deposits of Cromhall Quarry, UK

The enigmatic fissure deposits of south-eastern England and southern Wales are famous for their unique assemblage of Late Triassic vertebrates, although their age is contentious. While recent studies of palynomorphs have dated some as Rhaetian, their conchostracan (Crustacea, Branchiopoda) assemblages have not been described in detail nor used in biostratigraphy. We find that species determination of British Late Triassic conchostracans requires detailed observations of size, shape and ornamentation. We provide evidence that although Euestheria brodieana is invariably smaller than E. minuta, with some slight differences in carapace ornamentation, the traditional view that they are very similar is upheld. The use of conchostracans as a biostratigraphical tool is here tested by application to the British Triassic fissures at Cromhall quarry where the usual stratigraphical evidence provided by superposition is absent. We find no distinction between conchostracans from bedded Rhaetian deposits of the UK and specimens collected from the fissure deposits of Cromhall Quarry, Gloucestershire, supporting a late Rhaetian age for these deposits.

英格兰东南部与威尔士南部的神秘裂隙沉积，以其独特的晚三叠世脊椎动物化石组合闻名于世，但其形成年代一直存在争议。尽管近期针对孢粉形态化石（palynomorphs）的研究将部分沉积的年代测定为瑞替阶（Rhaetian），但其中的叶肢介类（Conchostracan，隶属于甲壳纲（Crustacea）、鳃足亚纲（Branchiopoda））化石组合尚未得到详细研究与描述，也未被应用于生物地层学研究。本研究表明，英国晚三叠世叶肢介的物种鉴定需要对其个体大小、壳体形态及壳饰特征开展细致观测。研究提供的证据显示：尽管布罗迪真叶肢介（Euestheria brodieana）的壳体始终小于微小真叶肢介（Euestheria minuta），且在壳瓣纹饰上存在细微差异，但二者高度相似的传统分类观点仍得到了支持。本研究通过将叶肢介作为生物地层学工具，应用于英国克罗姆霍尔采石场的三叠纪裂隙沉积中开展检验——该类沉积缺失了由叠覆关系提供的常规地层学证据。研究发现，英国层状瑞替阶沉积中的叶肢介标本，与格洛斯特郡克罗姆霍尔采石场裂隙沉积中采集的样本并无显著差异，这一结果支持了该类沉积形成于瑞替阶晚期的结论。