Search

Radiodonts, a diverse clade of early Palaeozoic stem-group euarthropods, have provided critical information for understanding the evolution of this phylum, and were important constituents of marine ecosystems at this time. The well-known Chengjiang Lagerstätte (Cambrian Stage 3, c. 518 Ma) has yielded the highest known diversity of radiodonts of any Cambrian Konservat-Lagerstätten, and represents a crucial deposit for radiodont research. One important but generally overlooked Chengjiang radiodont taxon, previously identified as Anomalocaris sp. or Radiodont C, is herein designated as the type species of a new monotypic genus, Shucaris ankylosskelos gen. et sp. nov., based on dozens of specimens. Shucaris is distinctive for its combination of several characters, including the presence of two pairs of endites on its proximal-most claw podomere, posteriorly inward curved endites on claw podomeres 2–6, and, most strikingly, the coexistence of gnathobase-like structures and an oral cone. New material of Ramskoeldia consimilis records the first known oral cone in this species, confirming that oral cones and gnathobase-like structures co-occur in multiple radiodont taxa. Phylogenetic analyses retrieve Shucaris as either an early diverging member of Anomalocarididae or as sister to the clade Anomalocarididae + Amplectobeluidae. Moreover, our phylogenetic analyses also support the divergence between hurdiid and non-hurdiid radiodonts. [ABSTRACT FROM AUTHOR]

The Cambrian (Series 2, Stage 3) Qingjiang Lagerstätte of South China is one of the most diverse Burgess Shale‐type deposits around the world, yielding abundant non‐biomineralized fossils. Radiodonta, a taxonomically and ecologically diverse stem‐euarthropod group, has been generally thought to represent the largest consumers in early Palaeozoic marine ecosystems. Here we describe several new radiodont specimens from the Qingjiang Lagerstätte assigned to various groups, including Stanleycaris qingjiangensis sp. nov., a new type of hurdiid head carapace, one possible Hurdia carapace, and two partial appendages with uncertain affinities. These specimens not only extend the geographic and stratigraphic range of these taxa, they also illuminate the diversity of radiodonts (in particular hurdiids) in their early evolutionary history. Radiodont palaeobiogeographic patterns are visualized using network analysis. Laurentia and South China share many members at the genus level, Anomalocaris is the most cosmopolitan taxon, but most genera are endemic. Radiodonts show a high initial diversity that declines through the early Palaeozoic, enabling three diversification phases of radiodonts to be recognized: the thriving phase (Cambrian Series 2), declining phase (Cambrian Miaolingian) and terminal phase (Cambrian Furongian to Ordovician Floian). [ABSTRACT FROM AUTHOR]

A metazoan-dominated biological pump was established early in the Phanerozoic, a time that saw the evolution of the first pelagic euarthropod zooplankton such as some species of the Cambrian bivalved euarthropod Isoxys . Pelagic groups evolved from benthic stock, in many cases through neoteny and retention of characteristics from planktic larval stages. However, Isoxys brooded eggs and did not have a planktic larval stage, precluding this route into the pelagic realm. Computational fluid dynamics was used to quantify hydrodynamic performance through the ontogeny of two hyperbenthic species of Isoxys, Isoxys auritus and Isoxys minor . Coefficients were used to quantify forces for different carapace shapes over a range of biologically relevant sizes and swimming speeds. Streamlining and lift generation were greater for later growth stages, a consequence of carapace asymmetry and elongated anterior and posterior spines. Simulations performed with anterior spines artificially removed demonstrate the importance of this feature for lift generation, with a minimal impact on drag. Elongated spines and faster swimming can also be considered anti-predatory, and the reduction of drag would have reduced the detectability of Isoxys to predators. Taken together, it is likely that pelagic Isoxys species evolved from benthic stock through the co-option of anti-predatory features., Competing Interests: We declare we have no competing interests., (© 2024 The Author(s).)

Tian et al . (Research Articles, 8 July 2022, abm2708) hypothesized that yunnanozoans are stem-group vertebrates on the basis of "cellular cartilage", "fibrillin microfibers", and "subchordal rod" associated with the branchial arches of yunnanozoans. However, we reject the presence of cellular cartilage, fibrillin, and the phylogenetic proposal of vertebrate affinities based on ultrastructure and morphology of yunnanozoans from more than 8000 specimens.