Paleontological study on the early phase of Cambrian Explosion based on the small shelly fossils and ichnofossils

根据从纽芬兰、加拿大、贵州、云南、中国和蒙古戈壁-阿拉泰等地采集或观察到的遗迹化石和小壳化石，探讨了早寒武世后生动物的快速演化模式。结果，澄清了以下三件事。1.在下寒武统最低的生物带--足爪金线虫带和阿瓦隆氏沼泽带，生物多样性和层理生物扰动指数呈现两阶段递增的趋势。在这些带中，没有根据不同的沉积相发育明显的遗迹化石，在微生物垫的上表面也没有发现明显的遗迹化石。2.通过对云南梅树村下段原牙形石的详细形态研究，认为其中有一些为纤毛虫(箭虫)的抓刺。这一发现反过来又表明，在早寒武世，远洋环境的中水柱中存在着捕食性动物。3.对比了秦岭组和巴郎组两个早寒武世晚期的遗迹化石，前者的沉积环境比后者略浅。在这一时期，遗迹化石已经根据不同的环境进行了分化，这一特征在纽芬兰最早的寒武纪遗迹化石中是没有发现的。

We investigated pattern of rapid evolution of metazoa occurred in the Early Cambrian, based on the ichnofossils and small shelly fossils sampled or observed from Newfoundland, Canada, Guizhou and Yunnan provinces, China and Gobi-Altai, Mongolia. As a result, following three things were clarified. 1. Two-staged, stepwise increase in the diversity and bedding plane bioturbation index were detected in the Treptichnus pedum and the Rusophycus avalonensis zones, the lowest biozones in the Lower Cambrian. In these zones, there were no development of a clear differentiation of ichnofossils according to different sedimentary facies, and also there is no clear ichnofossils detected on the upper surface of microbial mats. 2. Based on the detailed morphological studies on the protoconodonts from the lower Meishucun Stage in Yunnan Province, some of these are considered as grasping spines of chaetognaths(arrow worms). This discovery in turn suggests that there were predatory animals present in the mid-water column of the pelagic environment in the Early Cambrian. 3. We compared ichnofossils from two late Early Cambrian formations(Chintingshan and Balang), the former formation deposited slightly shallower environment than the latter. In this time, there was already differentiation of ichnofossils according to the different environments, which character was not detected in the ichnofossils from the earliest Cambrian of Newfoundland.