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

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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.