ABSTRACT A long history of geological research on the island of Gotland, Sweden, has resulted in a detailed biostratigraphy based on conodonts for the Gotland sedimentary succession, but the relation between the Hamra and Sundre formations, the youngest strata on southern Gotland, has remained poorly resolved. These formations have also remained relatively poorly described in terms of vertebrates compared to other parts of the succession. A survey of museum collections and newly sampled material reveal that the taxonomical compositions and richness of vertebrate faunas remain similar compared to the underlying Burgsvik Sandstone and Oolite members. However, the relative abundance of the respective groups changes: Paralogania ludlowiensis and rare osteostracan remains of Tahulaspis sp. only occur in samples from the lower Hamra Formation, while Thelodus sculptilis becomes more common in samples from Sundre Formation. Conodont and isotope data give support to previous suggestions that the Hamra and Sundre formations may be largely isochronous, and it is possible that the observed differences in vertebrate faunas reflect changes in depositional setting. This interval on Gotland has been suggested to represent a hiatus in the East Baltic sections, where younger strata show an increased importance of acanthodians in the vertebrate faunas. Gotland could therefore give insights into the early stages of this diversification of gnathostomes during late Silurian times. However, this has to be done in combination with data from other areas, as well as with a review and revision of the scale-based taxonomy of Silurian acanthodians from the Baltic Basin.

中文翻译：

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瑞典哥特兰岛志留纪 Hamra 和 Sundre 地层的脊椎动物遗骸和牙形石

摘要 瑞典哥特兰岛的地质研究历史悠久，根据牙形石对哥特兰岛沉积序列进行了详细的生物地层学研究，但哈姆拉地层与哥得兰岛南部最年轻的地层 Sundre 地层之间的关系仍然很差。解决。与序列的其他部分相比，这些地层在脊椎动物方面的描述也相对较少。对博物馆藏品和新采样材料的调查显示，与潜在的 Burgsvik 砂岩和鲕岩成员相比，脊椎动物群的分类组成和丰富度仍然相似。然而，各组的相对丰度发生了变化：Paralogania ludlowiensis 和 Tahulaspis sp. 的稀有osteostracan 遗骸。仅出现在来自哈姆拉地层下部的样品中，而 Thelodus sculptilis 在来自 Sundre 地层的样本中变得更常见。牙形石和同位素数据支持先前的建议，即 Hamra 和 Sundre 地层可能在很大程度上是等时的，并且观察到的脊椎动物群差异可能反映了沉积环境的变化。哥特兰岛的这一区间被认为代表了东波罗的海地区的一个中断，那里较年轻的地层显示脊椎动物群中棘鱼的重要性增加。因此，哥特兰岛可以深入了解志留纪晚期有颌类动物的这种多样化的早期阶段。然而，这必须结合来自其他地区的数据以及对波罗的海盆地志留纪棘鱼的基于尺度的分类法的审查和修订来完成。