Diverse cuticular remains in Cambrian (Series 2) SSF assemblages from China and the pioneer metazoan colonization of offshore environments

Abstract

Our understanding of the early Cambrian bioradiation is largely driven by the contrasting information obtained from small skeletal fossils (SSF) and various types of exceptionally preserved fossils from different parts of the world. In this study, a new 'Orsten'-type fossil Lagerstätte is reported from the Cambrian Series 2 upper Shuijingtuo Formation in the eastern Three Gorges area, South China. The Shuijingtuo Formation yielded a range of microscopic fragments of metazoan cuticles as well as fragments of possible epithelial tissue. Seventeen different types of micro-ornamentation patterns are recognized on the surface of these cuticular fragments. Based on comparisons with fossil organisms recorded from coeval strata elsewhere, as well as extant relatives, possible affinities with arthropods, palaeoscolecids, acrotretid brachiopods and mollusks are discussed. This 'Orsten'-type fossil assemblage was deposited in offshore environments, and the lack of evidence for long-distance transportation indicates that a highly diverse fauna was present in, or very close to, the relatively deep shelf settings in the Three Gorges area during the early Cambrian (Series 2, Stage 3). The invasion of metazoans into deeper, offshore environments could have closely followed, or even been coeval, with their radiation in relatively shallow water settings. Thus, albeit highly fragmented, such cuticular fossils can aid in providing a more complete picture of the Cambrian bioradiation.