A new exceptionally preserved phosphatocopid crustacean from the Furongian of Laurentia and a synthesis of Cambrian phosphatocopid distribution patterns

Planamandibulus nevadensis n. gen n. sp. is a newly discovered exceptionally preserved Laurentian phosphatocopid crustacean described from the upper Windfall Formation (Furongian, Stage 10) in Nevada. Planamandibulus nevadensis has closest affinity with the Baltic and Avalonian taxon Cyclotron. Its occurrence in sedimentary facies associated with dysoxia on the Laurentian paleocontinent fills in a gap in the global distribution of phosphatocopid crustaceans, facilitating a paleoenvironmental synthesis of this Cambrian group. We assess 75 taxa from nine paleocontinental areas spanning Cambrian stages 3 to 10 (~521–486.9 Ma). Comparison of these data with paleoclimate model simulations suggests that phosphatocopid distribution is explained partly by biogeography and ocean temperature patterns. Dabashanella species (e.g., D. hemicyclica Huo et al., 1983) are found across the low paleolatitude (<35°) paleocontinents of East Gondwanan (Australia), South China, and the central Asian terranes, spanning marine shelf carbonates to deeper marine black shale lithofacies, but are absent from mid- and high-paleolatitude sites, suggesting a warmer water preference. A similar warm-water preference is inferred for endemic taxa (e.g., Ulopsis, Parashergoldopsis) of East Gondwana, and perhaps for the newly described Laurentian Planamandibulus. By contrast, the mid- to high-paleolatitude paleocontinents Baltica and Avalonia are characterized by Veldotron, Cyclotron, Bidimorpha, Waldoria, Vestrogothia, Falites, and Trapezilites species, which occur in deep-shelf, cooler-water settings, typically below storm wave base. Hesslandona species sensu lato occur in mid-depth (likely above storm-wave base) warm tropical marine waters but are more typically found in deeper shelf and cooler waters in mid to high paleolatitudes. Phosphatocopids are also associated with sedimentary deposits characteristic of low environmental oxygen concentrations; this is emphasized by a peak in occurrences in the Guzhangian (Miaolingian) and Paibian (Furongian) stages, around the interval of the Steptoean Positive Carbon Isotope Excursion (SPICE) and its associated expansion of anoxic water masses onto shallow marine shelves. Our data compilation and data–model comparison support the environmental preference of phosphatocopids for low-oxygen, but not anoxic, water masses, and the new occurrence of Planamandibulus is consistent with this pattern.