New artiopodan arthropods from the early Cambrian Emu Bay Shale Konservat-Lagerstätte of South Australia

Abstract

The Emu Bay Shale Konservat-Lagerstätte (Cambrian Series 2, Stage 4) on Kangaroo Island, South Australia, is the source of two new non-biomineralized artiopodan arthropods. Squamacula buckorum n. sp. is the first record outside of China of a genus otherwise known only from its type species, S. clypeata, from the Chengjiang biota. The Australian species displays the long cephalic doublure and spiniform exopod setae that are apomorphic for this genus, provides new information on the alimentary tract and midgut glands (the latter preserved as three-dimensional, permineralized structures), and indicates interspecific variability in trunk segment numbers. The distribution of Squamacula strengthens the biogeographic connections between early Cambrian “Burgess Shale-type” biotas of Australia and South China. Australimicola spriggi n. gen. n. sp. represents a monotypic genus resolved in a cladistic analysis of Cambro-Ordovician artiopodans as most closely related to or within Conciliterga (a clade containing Helmetia, Kuamaia, Kwanyinaspis, Rhombicalvaria, Saperion, Skioldia, and Tegopelte). Compared with other members of this clade from Chengjiang and the Burgess Shale, the new genus is diagnosed by an elongate trunk with 23 thoracic tergites having spatulate pleural tips and a small pygidium possessing a single, elongate pair of pleural spines, with specimens also showing a hypostome attached to an anterior (or prehypostomal) sclerite, antennae, short endopods, an annulated alimentary tract, and a series of three-dimensional, permineralized midgut glands. An alternative relationship between Australimicola and the Early Ordovician–Early Devonian Cheloniellida explains the shared anterior flexure of trunk pleurae but forces dubious homologies in other characters, such as dorsally-articulated furcae versus spines.