ABSTRACT

Here we investigate megaspores from 10 Triassic‒Jurassic localities of southern Sweden and Bornholm, Denmark, based on collections housed in the Swedish Museum of Natural History. We identify and describe 19 megaspore taxa belonging to three stratigraphically constrained assemblages, representing the Rhaetian, Hettangian and Pliensbachian, respectively. Megaspores are abundant and diverse (12 taxa) in the Rhaetian assemblage. Diversity markedly decreases across the Triassic–Jurassic boundary (TJB), with species richness reducing from 12 to two taxa. The Hettangian assemblage is well-preserved but depauperate, and is overwhelmingly dominated by Nathorstisporites hopliticus. A subsequent recovery of lycopsid diversity followed, recorded by an increase in richness to six taxa in the Pliensbachian assemblage. The disappearance of the hygrophilous and diverse heterosporous lycophyte communities across the TJB, suggests a shift to drier conditions in the earliest Jurassic. This is supported by lithological changes from coal-forming environments in the Rhaetian to sandstone-dominated fluvial-estuarine facies in the Hettangian. Throughout this study, we analysed the megaspores using fluorescence microscopy, which revealed detailed morphological features on specimens that were otherwise opaque under visible light. This non-destructive technique is particularly useful for examining opaque megaspores embedded in permanent mounting media, such as epoxy resin, and may provide new insights into historical megaspore collections elsewhere.

摘要

在这里，我们根据瑞典自然历史博物馆的藏品调查了来自瑞典南部和丹麦博恩霍尔姆的 10 个三叠纪-侏罗纪地区的大孢子。我们识别并描述了 19 个大孢子分类群，它们分别属于三个地层约束组合，分别代表 Rhaetian、Hettangian 和 Pliensbachian。大孢子在雷氏组合中丰富多样（12 个分类群）。三叠纪-侏罗纪边界（TJB）的多样性显着下降，物种丰富度从 12 个减少到两个类群。Hettangian 组合保存完好，但已枯竭，主要由Nathorstisporites hopliticus占主导地位. 随后石蒜素多样性恢复，记录到 Pliensbachian 组合中的丰富度增加到六个分类群。整个 TJB 的潮湿和多样化的异孢石松群落的消失表明在最早的侏罗纪向干燥条件的转变。这得到了从 Rhaetian 的成煤环境到 Hettangian 以砂岩为主的河流河口相的岩性变化的支持。在整个研究过程中，我们使用荧光显微镜分析了大孢子，这揭示了在可见光下不透明的标本的详细形态特征。这种非破坏性技术对于检查嵌入永久性封固剂（如环氧树脂）中的不透明大孢子特别有用，