Cuticular microfragments from the lower Cambrian Yanjiahe Formation, China: insights into ecdysozoan biodiversity at the dawn of animal radiation

Ecdysozoa (molting animals) represent one of the most diverse and ecologically successful animal groups in both extant and fossil ecosystems. This study presents new microfossil cuticular evidence from the lower Cambrian (∼535 Ma) Yanjiahe Formation (southern China) for ecdysozoan diversity during the Fortunian Stage. Six forms are recognized mainly based on their ornamented cuticular patterns, as well as characters of spines and sclerites, including potentially new scalidophorans and possible fragments of appendage-bearing panarthropods. The fossil assemblage, preserved through phosphatization, includes specimens exceeding 2 mm in size and displays a wide array of cuticular ornamentations organized into three main categories: spiny/sclerite-bearing fragments, appendage-like elements, and other undetermined cuticular remains. Remains of possible appendages (e.g., panarthropods) provide tentative but potentially key insights into the tempo of ecdysozoan radiation. The diversity of cuticular structures suggests the co-occurrence of diverse ecdysozoan body plans during the Fortunian, paralleling the early radiation of other metazoan lineages.