陕南寒武系纽芬兰统幸运阶宽川铺组中大量高精度形态结构特征的小壳化石在磷酸盐化作用下得以保存, 该地也成为了研究“寒武纪生命大爆发事件”的重要化石宝库。Olivooides (橄榄蛋属)是第一小壳化石组合带 Anabarites trisulcatus—Protohertzina anabarica中一类特征鲜明、易于识别的刺胞类动物化石。过去40多年来报道的绝大部分Olivooides (橄榄蛋属)化石被厘定归并为2个种: O. multisulcatus (多沟橄榄蛋)和O. mirabilis (奇异橄榄蛋)。该属化石的形态分异度以及生长发育模式还有待进一步研究。本文描述了陕南宁强圆宝山剖面寒武系幸运阶宽川铺组中以次生磷酸盐化方式保存的Olivooides化石。本研究发现了一种新类型的O. mirabilis化石, 它与传统类型O. mirabilis的主要区别为: 布满星状棘突的胚胎期组织部分只发育一圈横向环带、胚胎后期组织部分发育五列纵向的“V”型褶皱、口部发育两组不同形态特征和不同褶皱程度的口叶。

Three-dimensionally phosphatized small shelly fossils with phylogenetic affinities of multiple animal phyla from the Fortunian strata of the Cambrian witnessed a pivotal evolutionary episode in the Cambrian Explosion. Olivooides is a morphologically distinctive and easily identifiable taxon in the small shelly fossil Anabarites trisulca tus–Protohertzina anabarica assemblage zone with a widely accepted phylogenetic placement within the Cnidarian. The great majority of Olivooides fossil specimens reported in the last 40 years have been primarily assigned to two species: O. multisulcatus and O. mirabilis. Morphological disparity and growth mode of Olivooides, however, need further study for better clarification. Here we describe phosphatized Olivooides fossils from the basal Cambrian Kuanchuanpu Formation (Fortunian Stage, Terreneuvian Series) at the Yuanbaoshan section in Ningqiang County, southern Shaanxi Province, South China. We report a new type of Olivooides mirabilis, characterized by only one transverse band in the embryonic tissue, five rows of tightly and sharply arranged longitudinal folds in the post-embryonic tissue, and two sets of oral lobes with two distinct degrees of folding. The distinct features between the new and the traditional O. mirabilis may represent intraspecific variation. The new fossil material adds to the diversity of Olivooides and sheds palaeobiological as well as embryological insights into our understanding of these enigmatic fossils in the earliest Cambrian Period.

国家自然科学基金项目(42372015, 42372012)；大陆动力学国家重点实验室项目；三秦学者创新团队项目；西北大学研究生科研创新项目(CX2024226)联合资助