The Early Cambrian Huayuan Biota Illuminates the First Phanerozoic Mass Extinction

The Cambrian Burgess Shale-type (BST) fossil biotas offer nearly complete representations of the earliest marine ecosystems in the Phanerozoic. Nevertheless, because high-diversity BST deposits are rarely found, our understanding of the evolutionary and ecological processes of the Cambrian explosion has remained constrained. The Huayuan biota is a BST Lagerstätte from the lower Cambrian (Stage 4, ~512 Ma) located in a deep-water, outer shelf environment on the Yangtze Block in Hunan, China. This biota displays extraordinary taxonomic diversity, with 153 animal species belonging to 16 phylum-level groups, predominantly arthropods, sponges, and cnidarians; among these, 59% are previously unknown species. The biota is largely composed of soft-bodied organisms, some of which preserve cellular tissues. Its ecosystem features a variety of radiodonts and pelagic tunicates. The Huayun biota closes a gap in records of top-tier BST biotas from the Cambrian Stage 4. In multivariate ordination using a global dataset of Cambrian BST biotas, the Huayuan biota falls within a key transitional phase in marine animal ecosystems between Cambrian Age 3 and Age 4. Network analysis indicates strong faunal similarities between the Huayuan biota and that of the Burgess Shale, suggesting dispersal of animals across oceans. Following the Sinsk event, the Huayuan biota reveals the differences in the impacts on shallow-water versus deep-water environments during the first mass extinction of the Phanerozoic, and provides crucial perspectives on the transformation of global ecosystems in the early Cambrian.