Abstract
Xandarellida is a well-defined clade of Lower Palaeozoic non-biomineralized artiopodans that is exclusively known from the early Cambrian (Stage 3) Chengjiang biota of South China. Here we describe a new member of this group, Xandarella mauretanica sp. nov., from the middle Cambrian (Stage 5) Tatelt Formation of Morocco, making this the first non-trilobite Cambrian euarthropod known from North Africa. X. mauretanica sp. nov. represents the youngest occurrence of Xandarellida – extending its stratigraphic range by approximately 10 million years – and expands the palaeobiogeographic distribution of the group to the high southern palaeolatitudes of West Gondwana. The new species provides insights into the lightly sclerotized ventral anatomy of Xandarellida, and offers stratigraphically older evidence for a palaeobiogeographic connection between Burgess Shale-type euarthropod communities in North Africa and South China, relative to the (Tremadocian) Fezouata biota.
Highlights
The Xandarellida Chen et al.[1] are an enigmatic group of non-biomineralized artiopodan euarthropods whose distinctive features include the possession of stalked ventral eyes, a posterior extension of the cephalon covering the anterior trunk tergites, and the occurrence of dorsoventral segmental mismatch on the trunk[1,2,3,4,5,6,7]
The new taxon can be assigned to Artiopoda based on the preserved ventral morphology[23], notably the antenniform first appendage pair attached at either side of a strongly sclerotized ventral hypostome, followed by numerous pairs of homonomous walking legs that gradually decrease in size along the body, and the possession of hourglass-shaped sternites
Hourglass-shaped sternites rule out comparisons with non-artiopodan Cambrian euarthropods – which lack sternites altogether – such as fuxianhuiids[24,25], bivalved stem-group euarthropods[26,27], megacheirans[28,29], and marrellomorphs[30,31]
Summary
The Xandarellida Chen et al.[1] (sensu2,3) are an enigmatic group of non-biomineralized artiopodan euarthropods whose distinctive features include the possession of stalked ventral eyes, a posterior extension of the cephalon covering the anterior trunk tergites, and the occurrence of dorsoventral segmental mismatch on the trunk[1,2,3,4,5,6,7]. Within the diverse Palaeozoic clade Artiopoda Hou and Bergström[2], xandarellids have been regarded as members of a more inclusive group known as the Petalopleura Hou and Bergström[2] (Table 1), which includes the lower Cambrian forms Sinoburius lunaris[4] from Chengjiang, and (potentially) Phytophilaspis pergamena[8] from the (Stage 4) Sinsk Formation in Siberia[9,10]. Unlike other monophyletic groups in Artiopoda, a clade that includes trilobites as its most familiar members (Fig. 1), the spatial distribution and temporal occurrence of xandarellids suggests a high degree of endemicity. The new taxon represents the youngest stratigraphic occurrence of Petalopleura, the first palaeobiogeographic record of Xandarellida outside South China, and clarifies the organization of the lightly sclerotized ventral morphology in this poorly known group of non-biomineralized euarthropods
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