Exceptionally Preserved Cambrian Trilobite Digestive System Revealed in 3D by Synchrotron-Radiation X-Ray Tomographic Microscopy

The Cambrian ‘Orsten’ fauna comprises exceptionally preserved and phosphatised microscopic arthropods. The external morphology of these fossils is well known, but their internal soft-tissue anatomy has remained virtually unknown. Here, we report the first non-biomineralised tissues from a juvenile polymerid trilobite, represented by digestive structures, glands, and connective strands harboured in a hypostome from the Swedish ‘Orsten’ fauna. Synchrotron-radiation X-ray tomographic microscopy enabled three-dimensional internal recordings at sub-micrometre resolution. The specimen provides the first unambiguous evidence for a J-shaped anterior gut and the presence of a crop with a constricted alimentary tract in the Trilobita. Moreover, the gut is Y-shaped in cross section, probably due to a collapsed lumen of that shape, another feature which has not previously been observed in trilobites. The combination of anatomical features suggests that the trilobite hypostome is functionally analogous to the labrum of euarthropods and that it was a sophisticated element closely integrated with the digestive system. This study also briefly addresses the preservational bias of the ‘Orsten’ fauna, particularly the near-absence of polymerid trilobites, and the taphonomy of the soft-tissue-harbouring hypostome.寒武纪“奥斯坦（Orsten）”化石群包含经磷酸盐化且特异保存的微型节肢动物。学界对该类化石的外部形态已有充分认知，但其内部软组织解剖结构却几乎未被探明。本文首次报道瑞典奥斯坦（Orsten）化石群中一件幼年多节三叶虫类（polymerid trilobite）标本，其唇瓣（hypostome）内保存有消化结构、腺体及结缔组织束等非矿化组织。本研究借助同步辐射X射线断层扫描显微镜（Synchrotron-radiation X-ray tomographic microscopy），实现了亚微米分辨率的三维内部成像。该标本为三叶虫纲（Trilobita）存在J形前肠以及带有缩窄消化道的嗉囊提供了首个明确证据。此外，该消化道的横截面呈Y形，这大概率由内腔塌陷所致，也是此前在三叶虫中未被观测到的特征。上述解剖学特征的组合表明，三叶虫的唇瓣在功能上类似于真节肢动物的上唇，是一类与消化系统紧密整合的精密结构。本研究还简要探讨了奥斯坦（Orsten）化石群的保存偏差（尤其体现在多节三叶虫类的近乎缺失）以及携带软组织的唇瓣标本的埋藏学特征。