Associated conchs and opercula of Triplicatella disdoma (Hyolitha) from the early Cambrian of South Australia

Internal moulds of complete shells, including conch and associated opercula, of the hyolith Triplicatella disdoma from Cambrian Series 2, Stages 3–4 of South Australia are described. The conch of T. disdoma is shown to be narrow and cone-shaped, and with a rounded triangular cross-section. The conch shows a gentle dorsal curvature in lateral view. The fossils lack evidence of helens, and the operculum was smaller than the apertural diameter of the conch and could be withdrawn a short distance into the conch. Triplicatella was probably closely related to orthothecid hyoliths.Origin and early evolution of major animal clades in the Cambrian Perio

Biostratigraphical and palaeogeographical implications of Early Cambrian hyoliths from the North China Platform

A succession of diverse hyolith assemblages comprising 10 genera and 14 species are reported from the lower Cambrian Shangwan and Sanjianfang sections of the Xinji Formation, and Xiaomeiyao section of the Houjiashan Formation, which crop out along the southern margin of the North China Platform. Most of the specimens are represented by both conchs and opercula. The identified orthothecids include Conotheca australiensis, Cupitheca holocyclata, C. costellata, Neogloborilus applanatus, N. spinatus, Tegminites hymenodes, Triplicatella disdoma, T. xinjia sp. nov. and Paratriplicatella shangwanensis gen. et sp. nov. The hyolithids comprise Protomicrocornus triplicensis gen. et sp. nov., Microcornus eximius, M. petilus, Parkula bounites and Parakorilithes mammillatus. Some anomalous taxa possess characteristics of both Hyolithida and Orthothecida, such as C. australiensis, Neogloborilus and P. triplicensis. Protomicrocornus may constitute a sister group of other hyolithids. The teeth of Parkula bounites and clavicles of Parakorilithes mammillatus are documented for the first time. The hyolith assemblages from North China are probably coeval, and can be correlated with the Cambrian upper Stage 3–lower Stage 4. Many taxa are also globally distributed and have significant potential for biostratigraphical correlations. In accordance, the hyoliths from North China reveal closest compositional similarities to faunas from eastern Gondwana, and especially South Australia. However, some taxa are shared with Laurentian assemblages suggesting cosmopolitanism, and possibly planktonic larval dispersal