Supplemental data from: Taphonomy and environmental distribution of <em>Pseudophillipsia</em> in the Middle Permian Kamiyasse Formation of the Southern Kitakami Terrane, Japan

Evidence suggests that trilobites experienced moderate diversification during the Middle Permian, of which Pseudophillipsia is the most successful with an unusually high number of species. However, it remains unclear whether their abundance reflects a stratigraphic trend or is specific to their habitat. To address this, we conducted a taxonomic study of Pseudophillipsia from the Middle Permian (Capitanian) Kamiyasse Formation of the Southern Kitakami Terrane, Japan, and examined the burial processes to understand their habitat. Careful taxonomic analysis identified two species, Pseudophillipsia (Pseudophillipsia) spatulifera and Pseudophillipsia (Carniphillipsia) sp. cf. P. (C.) raggyorcakaensis. The trilobites occur in both sandstone and mudstone, preserved as complete outstretched and enrolled specimens as well as disarticulated specimens, the majority of which are pygidia. Sedimentary facies indicate that the sandstone layer is formed in a shallow marine environment close to the lower shoreface, whereas the mudstone layer represents a slightly deeper environment, occasionally altered by storm flows. Based on biostratinomic features, the outstretched specimens with convex-up orientation must be autochthonous, while the enrolled specimens are interpreted as para-autochthonous likely transported by storm flows. The greater the bioturbation, the greater the likelihood of the trilobite skeleton being disarticulated, particularly in the mudstone layers. These findings suggest that P. (P.) spatulifera inhabited both sandy and muddy substrates, while P. (C.) sp. cf. P. (C.) raggyorcakaensis was restricted to sandy environments. Given the limited geographic extent of the Kamiyasse Formation, we hypothesize that the appearance of Pseudophillipsia reflects a change in the sedimentary environment.现有证据表明，三叶虫（trilobites）在中二叠世（Middle Permian）期间经历了中等程度的演化辐射，其中假菲利普三叶虫属（Pseudophillipsia）物种数量异常庞大，是该时期最为繁盛的类群。然而目前仍不清楚其种群繁盛究竟是地层学的普遍趋势，还是仅与其栖息环境相关。为解答这一问题，我们针对日本北上地体南部中二叠世卡皮坦期（Capitanian）神谷濑组（Kamiyasse Formation）的假菲利普三叶虫属开展了分类学研究，并通过分析其埋藏过程以探究其栖息环境。经细致的分类学分析，共识别出两个物种：铲状假菲利普三叶虫（Pseudophillipsia (Pseudophillipsia) spatulifera，假菲利普三叶虫亚属），以及假菲利普三叶虫属（肉食菲利普三叶虫亚属）相似于P. (C.) raggyorcakaensis的未定种（Pseudophillipsia (Carniphillipsia) sp. cf. P. (C.) raggyorcakaensis）。该三叶虫化石同时产于砂岩与泥岩地层中，保存状态包括完整伸展的标本、卷曲的标本以及离散的标本，其中绝大多数为尾甲（pygidia）。沉积相（sedimentary facies）分析表明，砂岩形成于接近前滨下部的浅海环境，而泥岩则代表稍深的水体环境，偶尔受到风暴流的改造。基于生物埋藏学特征，呈凸面向上状态的伸展标本应为原地埋藏，而卷曲标本则被认为是准原地埋藏，可能经风暴流搬运而来。生物扰动（bioturbation）程度越高，三叶虫骨骼发生离散的概率就越大，这一现象在泥岩地层中尤为显著。上述研究结果表明，P. (P.) spatulifera 可栖息于砂质与泥质两种底质环境，而P. (C.) sp. cf. P. (C.) raggyorcakaensis则仅局限于砂质环境。鉴于神谷濑组的地理分布范围有限，我们推测假菲利普三叶虫属的出现反映了沉积环境的变化。