The palaeobiogeographical distribution of the six major clades of Ordovician echinoderms (asterozoans, blastozoans, crinoids, echinozoans, edrioasteroids and stylophorans) is analysed based on a comprehensive and up-to-date database compiling 3701 occurrences (1938 species recorded from 331 localities) of both complete specimens and isolated ossicles. Although historically biased towards a limited number of regions (Europe, North America, Russia), the resulting dataset makes it possible to identify six main palaeobiogeographical provinces for Ordovician echinoderms: Laurentia, Baltica, West Gondwana, East Gondwana, Avalonia and Siberia. At a global scale, the high endemicity of echinoderms during the Early to Middle Ordovician coincides with the time of maximum dispersal of continental masses. Late Ordovician faunas tend to become more cosmopolitan, possibly as a consequence of changing palaeogeography and/or relatively higher sea-levels in the Sandbian–Katian interval. Regional biodiversity patterns of Ordovician echinoderms confirm that their major diversification during the Ordovician is not a single, universal evolutionary event, but rather results from the complex addition of contrasted local evolutionary trends.

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Occurrences of articulated, multi-element skeletons of edrioasteroids provide evidence of sudden burial and an opportunity for detailed paleoecologic analysis. This study examines two catastrophically buried communities of edrioasteroids from Florence, Kentucky and Sharonville, Ohio. In these two occurrences, the edrioasteroids Isorophus cincinnatiensis, Streptaster vorticellatus, and Carneyella pilea utilized brachiopod and mollusk shells as hard substrates for attachment. Age structure analysis for specimens of Isorophus cincinnatiensis on both pavements show right-skewed distributions that are attributed to high juvenile mortality. Thecae on the Florence pavement have slight bimodal preferential orientation, likely in response to current flow, whereas no preferential thecal orientation was noted for specimens on the Sharonville pavement. Spatial analysis of the Florence pavement indicates a clustered edrioasteroid distribution resulting from multiple edrioasteroids attached to single brachiopod shells. Edrioasteroid margin deformation, in response to inter-and intraspecific competition, provides evidence that edrioasteroids were unable to move once attached to the substrate. Spatial analysis for Isorophus cincinnatiensis on the Sharonville pavement shows few instances of multiple edrioasteroids attached to individual shells. Instead, this clustered distribution suggests enhanced encrustation in areas of enhanced survival (i.e., increased feeding opportunity). The high degree of thecal disarticulation on the Sharonville pavement suggests postmortem bloating and rupture.

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