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Great strides have been made in understanding the phylogeny of the five extant echinoderm classes, however, many Palaeozoic groups have yet to be examined in a rigorous, quantitative framework. The aberrant morphologies of Paracrinoidea, an unusual group of Palaeozoic echinoderms, have hindered their inclusion in large‐scale phylogenetic and morphologic studies. This study uses a combined approach of phylogenetic analysis and morphological disparity to elucidate species relationships within the clade. Findings from this study suggest that Paracrinoidea is a monophyletic group and that respiratory structures, oral plate arrangement, and ambulacral morphologies are important for defining subclades within Paracrinoidea. Examination of paracrinoids in a quantitative framework, facilitates their inclusion in larger projects examining Palaeozoic echinoderm evolution, ecology and biogeography. [ABSTRACT FROM AUTHOR]

The Cambrian and Ordovician radiations marked the origins of all major echinoderm clades and established their Phanerozoic ecological blueprint. Recent claims of modest innovation of early echinoderms and other animals suggest constraints on novelty during the origins of phyla. Here, we document the life‐habit richness, body size, tiering, habitat usage, mobility, diet and foraging habits of 366 Cambrian–Ordovician echinoderm genera across a time‐scaled phylogeny to identify the timing and impact of novelty. Most early echinoderms were sedentary, filter‐feeding microbivores, and their body sizes, diets and modes of locomotion were largely unchanged through time, despite major volatility in taxonomic composition. Cambrian echinoderms lived close to the seafloor, with stylophorans first evolving semi‐infaunality. Many Ordovician echinoderms lived farther from the seafloor, with more complex filter‐feeding organs and tiering structure, often using other organisms as substrates. Mobile carnivores and mass‐feeders emerge then, too, across diverse asterozoans and echinozoans. Most of these novelties coincide with the origins of individual clades during the early and late Cambrian (Terreneuvian/Series 2 and Furongian), and 10–20 million years pass before most become ecologically important. Life‐habit evolution within most taxa involved new variations in these traits, with crinoids and asterozoans better able to shift strategies. The Ordovician radiation records more new variability in pre‐existing Cambrian life habits rather than radical re‐invention, with important novelties (like mobile carnivory and mass‐feeding, increased height off the seafloor, and biotic substrates) becoming ecologically more impactful. Taxa with these strategies were those best able to capitalize on the newly heterogeneous Ordovician world. [ABSTRACT FROM AUTHOR]

Hirnantian (latest Ordovician) localities containing echinoderm fossils are rare; the few that have been discovered primarily contain disarticulated crinoid ossicles. Therefore, relatively little is known about echinoderm evolutionary dynamics across the Late Ordovician--early Silurian boundary, especially noncrinoid echinoderms. New diploporitan echinoderms, Holocystites salmoensis and an unidentified holocystitid, from reefal facies of the Upper Ordovician Ellis Bay Formation of Anticosti Island provide a critical data point concerning diploporitan biogeography and evolutionary pathways undertaken during the Ordovician and Silurian. These fossils also provide a crucial link in understanding the ancestry of the Silurian Holocystites Fauna, an unusual diploporitan fauna from the middle Silurian of North America, whose origination dates back at least 15 million years earlier than previously thought with the discovery of taxa described here. New fossil data such as these stress the importance of uncovering new localities from underrepresented times and places in Earth's history, so that these evolutionary transitions can be better understood. Les localités hirnantiennes (Ordovicien sommital) qui renferment des fossiles d'échinodermes sont rares, et les quelques-unes qui ont été découvertes contiennent principalement des ossicules de crinoïde désarticulés. Les connaissances sur la dynamique de l'évolution des échinodermes à la limite Ordovicien tardif--Silurien précoce sont donc relativement limitées, en particulier en ce qui concerne les échinodermes non-crinoïdes. De nouveaux échinodermes diploporites, Holocystites salmoensis et un holocystitidé non identifié, de faciès récifaux de la Formation d'Ellis Bay de l'Ordovicien supérieur de l'île d'Anticosti fournissent un datum clé sur la biogéographie et les voies d'évolution des diploporites durant l'Ordovicien et le Silurien. Ces fossiles fournissent également un lien crucial pour la compréhension de l'ascendance de la faune à Holocystites silurienne, un assemblage inhabituel de diploporites du Silurien moyen de l'Amérique du Nord, dont les origines, à la lumière de la découverte des taxons décrits dans le présent article, sont au moins 15 millions d'années plus anciennes que ce qui était présumé auparavant. Des telles données sur de nouveaux fossiles soulignent l'importance que revêt la découverte de nouvelles localités pour des périodes et des lieux sous-représentés dans l'histoire de la Terre, afin de mieux comprendre ces transitions évolutives. [Traduit par la Rédaction], Introduction The Great Ordovician Biodiversification Event (GOBE) resulted in a significant increase in lower-level diversity across the entire globe, as well as across phyla (Webby et al. 2004). With this [...]