An epipodite-bearing crown-group crustacean from the Lower Cambrian

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 periods. Finds in Lower Cambrian rocks of the Phosphatocopina, the fossil sister group to eucrustaceans, 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 Cambrian. 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: they occur in a set of three, derive from setae and are a ground-pattern feature of Eucrustacea.

Hexapoda: Comparative Aspects of Later Embryogenesis and Metamorphosis

“…In one hypothesis, the outer and inner lobes of the mandible are homologous to the outer and inner endites of more posterior mouthparts (Machida 2000 ). In a second hypothesis, the outer mandibular lobe is homologous to a single endite, while the inner lobe is homologous to the proximal segment of other appendage types (Zhang et al 2007 ). Expression data from multiple genes in Tribolium support the presence of a single endite derivative in the mandible (Figs.…”

The developmental trend of labrum and median eyes of Orsten-type preserved Phosphatocopina (Crustacea)

“…At last, Dong et al [17] reported the very well-preserved fossils of Orsten-type preservation represented by Phosphatocopina and Skaracarida recovered from the Upper Cambrian of Hunan in 2005. Zhang et al [18] reported an epipodite-bearing crown-group crustacean Yicaris from the Lower Cambrian of Yunnan in 2007.…”

The Cambrian Explosion: How Do We Use the Evidence

“…Moreover, an emerging picture of Early Cambrian arthropods suggests that primitive forms, bearing characters ancestral to many euarthropods (Waloszek and Maas 2005), coexisted with definitive crown-group (meaning that they have characters of derived groups) crustacea, a modern group that dominates the oceans today (Zhang et al 2007). Arthropods described from southern China, and three-dimensionally preserved Orsten-type fossils from the Lower to the Upper Cambrian, demonstrate a remarkable coexistence of different stages of evolution, from ancestors to derived groups such as crustaceans and their sister group (Siveter et al 2001, Hou et al 2004).…”