ABSTRACT

The Camenellan tommotiid Lapworthella bornholmiensis is systematically revised based on the original type material and collections of Small Shelly Fossils at the Swedish Museum of Natural History. The species is clearly differentiated from all other species of Lapworthella by its unique surface ornamentation. Variability in sclerite shape is analyzed among the 39 specimens and four sclerite morphotypes are recognized: bilaterally subsymmetrical A sclerites with straight apertural margin and subrectangular to subelliptical cross-section; asymmetrical B sclerites with oblique to curved apertural margin and subrectangular to subelliptical cross-section; asymmetrical C sclerites with one concave surface resulting in elliptical to sub-triangular cross section; elongated asymmetrical D sclerites with subcircular cross section. The C sclerites are further divided into two sub-types. The sclerite morphotypes of Lapworthella bornholmiensis allow a detailed comparison with other lapworthellid taxa and we identify a pattern of recurring sclerite morphotypes across a range of species, allowing a new understanding of the lapworthellid scleritome structure. The stratigraphic range of Lapworthella bornholmiensis includes the Cambrian Stage 4 Gislöv Formation, the Wuliuan-Drumian Forsemölla and Exsulans Limestones in the Alum Shale Formation and Guzhangian limestone fill in Proterozoic basement fissures in Bohuslän, making this long ranging species the youngest known tommotiid in the fossil record.

摘要

Camenellan tommotiid Lapworthella Bornholmiensis根据瑞典自然历史博物馆的原始类型材料和小型雪莱化石收藏品进行了系统修订。该物种与所有其他Lapworthella物种明显不同通过其独特的表面装饰。分析了 39 个标本中的骨片形状的变异性，并确认了四种骨片形态类型：双侧不对称 A 骨片，具有直孔边缘和亚矩形至亚椭圆形横截面；不对称的 B 型巩膜，具有倾斜到弯曲的孔径边缘和亚矩形到亚椭圆形的横截面；具有一个凹面的不对称 C 型硬晶石导致椭圆形到亚三角形横截面；具有亚圆形横截面的细长的不对称 D 型硬骨。C sclerites 进一步分为两个亚型。Lapworthella Bornholmiensis的巩膜形态型允许与其他 lapworthellid 分类群进行详细比较，我们确定了一系列物种中重复出现的 sclerite 形态类型，从而对 lapworthellid scleritome 结构有了新的理解。Lapworthella Bornholmiensis的地层范围包括寒武纪第 4 期 Gislöv 组、Alum 页岩组中的 Wuliuan-Drumian Forsemölla 和 Exsulans 石灰岩以及 Bohuslän 元古界基底裂隙中的 Guzhangian 石灰岩填充物，使该物种成为已知分布最远的化石中最年轻的物种记录。