1. Key Laboratory for Palaeobiology, Yunnan University, Kunming 650091, China
2. Department of Geology, University of Leicester, Leicester LE1 7RH, UK
3. Section for Biosystematic Documentation, University of Ulm, D-98081 Ulm, Germany

Correspondence to: Xi-guang Zhang¹ Correspondence and requests for materials should be addressed to X.-g.Z. (Email: xgzhang@ynu.edu.cn).

Abstract

Crown-group crustaceans (Eucrustacea) are common in the fossil record of the past 500 million years back to the early Ordovician period, and very rare representatives are also known from the late Middle and Late Cambrian periods¹. Finds in Lower Cambrian rocks of the Phosphatocopina, the fossil sister group to eucrustaceans², imply that members of the eucrustacean stem lineage co-occurred, but it remained unclear whether crown-group members were also present at that time. 'Orsten'-type fossils are typically tiny embryos and cuticle-bearing animals, of which the cuticle is phosphatized and the material is three-dimensional and complete with soft parts. Such fossils are found predominantly in the Cambrian and Ordovician and provide detailed morphological and phylogenetic information on the early evolution of metazoans. Here we report an Orsten-type Konservat-Lagerstätte from the Lower Cambrian of China that contains at least three new arthropod species, of which we describe the most abundant form on the basis of exceptionally well preserved material of several growth stages. The limb morphology and other details of this new species are markedly similar to those of living cephalocarids, branchiopods and copepods and it is assigned to the Eucrustacea, thus representing the first undoubted crown-group crustacean from the early Cambrian. Its stratigraphical position provides substantial support to the proposition that the main cladogenic event that gave rise to the Arthropoda was before the Cambrian³. Small leaf-shaped structures on the outer limb base of the new species provide evidence on the long-debated issue of the origin of epipodites^{4, 5}: they occur in a set of three, derive from setae and are a ground-pattern feature of Eucrustacea.

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