链状心网虫(Cardiodictyon catenulum)是寒武纪澄江生物群中较为常见的叶足动物, 其躯干骨板的形态一直存在较大争议。本项研究显示该叶足动物的躯干具有一纵列马鞍状骨板, 每个体节具有单一的骨板, 每个骨板从背部延伸至躯干两侧。因此该叶足动物的骨板与其余具有成对或环状分布的躯干骨板的叶足动物存在显著的区别。骨板中央存在一个圆锥形凸起, 骨板边缘显著增厚且呈锯齿状。链状心网虫的躯干骨板边缘增厚和鞍点的凸起提升了整体的刚性; 锯齿状边缘也指示了更优的保护及防御功能。本项研究还发现链状心网虫骨板表面具有显微筛状结构, 筛孔被充填并保存为众多等距离分布的黄铁矿化瘤突, 与微网虫、怪诞虫及爪网虫躯干骨板的显微网状结构类似, 可能为纤细乳突的出口。本文认为: 寒武纪叶足动物的躯干骨板普遍具有显微筛状结构; 这些骨板除了保护与防御, 可能还有感觉的功能。每个躯干体节对应骨板为寒武纪叶足动物的独有衍征, 可能为背骨板的早期形态, 也可能由成对骨板愈合而来。

Cardiodictyon catenulum is a common lobopodian in the early Cambrian Chengjiang fauna. The functional morphology of its trunk sclerites has long been controversial. Here, we show that the trunk of C. catenulum has a longitudinal series of saddle-shaped sclerites, each corresponding to a body segment and extending from the dorsum to both sides of the trunk. Thus, its trunk sclerites are significantly different from those of other Cambrian lobopodians which possessed paired or circular trunk sclerites. The trunk sclerite of C. catenulum has a conical dorsal projection at the center. The brim of each sclerite is obviously thickened and serrated, which may have in creased its overall rigidity and indicate an enhanced function of protection and defense. In this study, we also report a sieve-like microstructure on the surface of the sclerites, resembling the net-like microstructure on sclerites of Hallucigenia, Microdictyon, and Onychodictyon. The equidistantly arrayed pores are diagenetically permineralizsed with pyrite and preserved as numerous pyritized micro-tubercles. These pores might have served as exits for micro-papillae. We consider that the trunk sclerites of Cambrian lobopodians are in general with a sieve-like microstructure, which may have had protective sensory function. A single sclerite corresponding to a trunk segment in C. catenulum is an autapomorphy of the Cambrian lobopodians. The distinctive arrangement of trunk plates in C. catenulum might represent the prototype of trunk sclerites, or alternatively a derived trait, i.e., secondary fusion of paired sclerites, of early lobopodians.

国家自然科学基金面上项目(41972009, 42372027)、中国地质调查局项目(DD20230219)和中国地质大学北京大学生创新创业训练计划项目(202011415492)联合资助