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International audience; The exquisitely preserved, diverse and abundant fossil assemblages yielded by the 'echinoderm meadows' of the Tafilalt region of the eastern Anti-Atlas represent a new Konservat-Lagerstätte, one of the few exceptionally preserved Late Ordovician open marine faunas found globally, giving us an insight into the radiation of life during the later phases of the Great Ordovician Biodiversification Event (GOBE) in high-latitude peri-Gondwana. The GOBE saw most phyla increase exponentially in diversity, at the fastest rate of the entire Phanerozoic and represents one of the most significant events in the evolution of the marine biosphere, preceding the end-Ordovician mass extinction. This volume is the culmination of over 20 years of research by several international teams that integrates sedimentology, palaeobiology and palaeobiogeographic approaches. Nine different phyla and several softbodied problematica are represented in the Tafilalt, including several notable echinoderm

SI Text; Supplementary Figures (S1–S7)

Examined Specimens

The Anti-Atlas contains a thick, volcanic-free Ordovician succession that originally deposited in a passive-margin basin. Three main sedimentary packages are bounded by major unconformities: (i) the Tremadocian–Floian Lower Fezouata and Upper Fezouata formations, which unconformably overlie a palaeorelief of Cambrian rifting volcanosedimentary complexes, and are subsequently topped by a Dapingian para-conformable gap; (ii) the Darriwilian–Katian Tachilla Formation and First Bani and Ktaoua groups, the latter unconformably overlain by a Hirnantian glaciogenic succession; and (iii) the Second Bani Group, which subsequently infilled the former glaciogenic palaeorelief. Due to the scarcity of carbonate interbeds for etching analyses, leading to rare references of conodonts, the global Ordovician chart is interpolated on the basis of microphytoplancton (acritarchs and chitinozoans), regional graptolites and brachiopods. The Ordovician counter-clockwise rotation of Gondwana led its Moroccan margin from mid-to high-latitude positions, leading to the onset of a siliciclastic, wave-and storm-dominated platform. Flooding surfaces are marked by shelly silty carbonate interbeds that reflect the episodic development of echinoderm–bryozoan meadows during Katian times; in areas protected from siliciclastic input, they reached massive and bedded bioaccumulations (Khabt-el-Hajar Formation). The Hirnantian glaciation controlled the incision of numerous tunnel channels, infilled with both alluvial to fluvial sediments and glaciomarine diamictites. The Hirnantian palaeorelief was definitively sealed during Silurian times., The authors thanks the useful and detailed revisions made by J. Colmenar, T. Servais and one 661 anonymous referee. This work is dedicated to the memory of Jacques Destombes who left us 662 during the redaction of this synthesis.This paper is a contribution to Spanish project CGL2017-663 19 87631-P from Spanish Ministry of Science, Innovation and Universities and IGCP 653 (IUGS-664 UNESCO) project ‘The Onset of the Great Ordovician Biodiversification Event’.

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International audience

Trabajo presentado en el 5th International Palaeontological Congress, celebrado en París (Francia) del 9 al 13 de julio de 2018, In recent years, the Upper Ordovician series of the Tafilalt area (eastern Anti-Atlas, Morocco) have yielded several echinoderm Lagerstätten (or ’starfish beds’) providing a relatively continuous record of successive, nearshore, echinoderm-dominated assemblages from the early Sandbian to the Hirnantian. During this time interval, the composition of the Tafilalt echinoderm assemblages shows little change, with the persistence of the same dominating groups: edrioasteroids, eocrinoids, glyptocystitid rhombiferans, ophiuroids, solutans and stylophorans. Asteroids, coronates, crinoids and diploporitans are also present, though generally as minor components of these assemblages. From a palaeobiogeographic point of view, the Tafilalt assemblages share many similarities with Sandbian to early Katian faunas described in other high-latitude (peri)Gondwanan regions of the Mediterranean Province (e.g. Armorican Massif, Bohemia, Spain). During the late Katian time interval, typical ’cool-adapted’ Mediterranean echinoderm assemblages are suddenly replaced, in most peri-Gondwanan areas (e.g. Algeria, Aragón, Armorican Massif, Cantabria, Carnic Alps, Corbières, Montagne Noire, Portugal, Sardinia), by more ’temperate’ faunas, migrating southward from lower palaeolatitudes, and dominated by coronates, crinoids, and both caryocystitid and hemicosmitid rhombiferans. No such dramatic faunal turnover (’Boda Event’) is documented in the Tafilalt area during the late Katian time interval, probably because of its palaeogeographic position at higher palaeolatitudes.

The somasteroids are Ordovician star-shaped animals widely regarded as ancestors of Asterozoa, the group of extant echinoderms that includes brittle stars and starfish. The phylogenetic position of somasteroids makes them critical for understanding the origin and early evolution of crown group Echinodermata. However, the early evolution of asterozoans, the origin of their distinctive body organization and their relationships with other Cambrian and Ordovician echinoderms, such as edrioasteroids, blastozoans, crinoids, and other asterozoans, remain problematic due to the difficulties of comparing the calcitic endoskeleton of these disparate groups. Here we describe the new somasteroidCantabrigiaster fezouataensisfrom the Early Ordovician (Tremadocian) Fezouata Lagerstätte in Morocco.Cantabrigiastershares with other somasteroids the presence of rod-like virgal ossicles that articulate with the ambulacrals, but differs from all other known asterozoans in the absence of adambulacral ossicles defining the arm margins. The unique arm construction evokes parallels with non-asterozoan echinoderms. Developmentally informed Bayesian and parsimony based phylogenetic analyses, which reflect the homology of the biserial ambulacral ossicles in Paleozoic echinoderms according to the Extraxial-Axial Theory, recoverCantabrigiasteras basal within stem group Asterozoa. Our results indicate thatCantabrigiasteris the earliest diverging stem group asterozoan, revealing the ancestral morphology of this major clade and clarifying the affinities of problematic Ordovician taxa. Somasteroids are resolved as a paraphyletic grade within stem and crown group Asterozoa (starfishes), whereas stenuroids are paraphyletic within stem group Ophiuroidea (brittle stars).Cantabrigiasteralso illuminates the relationship between Ordovician crown group Echinodermata and its Cambrian stem lineage, which includes sessile forms with incipient radial symmetry such as edrioasteroids and blastozoans. The contentious Pelmatozoa hypothesis (i.e. monophyly of blastozoans and crinoids) is not supported; instead, blastozoans represent the most likely sister-taxon of crown group Echinodermata.Author summaryStarfish and brittle stars, collectively known as asterozoans, constitute a diverse and ecologically successful group of echinoderms that first appear in the fossil record some 480Ma. However, the early evolution of asterozoans, the origin of their distinctive body organization, and their phylogenetic relationships with Cambrian echinoderms remain largely unresolved. We describeCantabrigiaster fezouataensisgen. et sp. nov., a primitive asterozoan from the Fezouata Lagerstätte, Morocco, with a unique endoskeletal arm organization that reveals the ancestral morphology of this major clade. Bayesian and parsimony based phylogenetic analyses indicate thatCantabrigiasteris the earliest diverging stem group asterozoan, and resolve the phylogenetic position of Ordovician asterozoans such as somasteroids. Our analyses clarify the origin of crown group echinoderms relative to their problematic Cambrian stem group representatives.

The discovery of a very large ophiuroid (disk diameter of 80 mm) in the early Permian (Kungurian) Cundlego Formation in the Southern Carnarvon Basin of Western Australia extends the stratigraphical range of ‘archaic’ ophiuroids unequivocally into the Permian, unlocking a lost fossil record of this group. Hitherto such ophiuroids have been discovered preserved articulated from strata no younger than the late Carboniferous. Herein we describe the new ophiuroid as Teleosaster creasyi gen. et sp. nov. Although existing temporally with Permian ophiuroids with a ‘modern’ morphological architecture, Teleosaster was biogeographically separated. This ‘archaic’ ophiuroid persisted in high latitude seas, suggesting such ‘archaic’ forms were displaced from the shallow-water, low latitude niches by the ‘modern’ ophiuroids. In modern oceans, ophiuroid gigantism similar to that in Teleosaster creasyi is typically only expressed in cold, high latitude oceans. It has been argued that the frequent occurrence of gigantism in such environments is due to the much lower levels of predation pressure. Unlike other echinoderm classes, the morphological and ecological transformation that resulted in the evolution of ‘modern’ ophiuroids had already taken place well before the events of the Permo–Triassic mass extinction. With the increase in diversity of durophagous predators in low latitude shallow-water communities during the mid-Palaeozoic Marine Revolution, we argue that ‘archaic’ ophiuroids were more susceptible to these higher levels of predation than the ‘modern’ forms and were displaced into regimes of lower predation pressure in high latitude oceans. http://zoobank.org/urn:lsid:zoobank.org:pub:E4FD9264-127D-4995-AD12-C9721F212FCD

The palaeobiogeographical distribution of the six major clades of Ordovician echinoderms (asterozoans, blastozoans, cri- noids, 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 Ordo- vician 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, Access to important specimens housed in several European collections was provided to E. N. by the European Synthesys project ES-TAF-2991 (Museo Nacional de Ciencias Naturales, Madrid) and to B. L. by both the ‘Vltava program’ of the French Embassy in the Czech Republic (Narodni Museum, Prague) and the European Synthesys projects DE-TAF-4766 (Museum fur Naturkunde, Berlin), GB-TAF-4565 (The Natural History Museum, London) and SE-TAF-4765 (Naturhistoriska Riksmuseet, Stockholm).

International audience; Le site de Bou Nemrou, situé dans le Tafilalt occidental (Anti-Atlas oriental, Maroc) compte parmi les rares gisements à préservation exceptionnelle (Lagerstätten) connus actuellement dans l'0rdovicen supérieur à avoir livré des restes d'organismes peu ou pas minéralisés, associés à une faune marine benthique abondante et diversifiée. Ce même gisement a également livré plusieurs niveaux trèsè riches en échinodermes (starfish beds), dont la préservation est tout à fait remarquable. Elle résulterait de l'enfouissement rapide, in situ et de leur vivant, de véritables "prairies" à échinodermes par des dépôts de tempête. Les starfish bes de Bou Nemrou sont dominés par les éocrinoïdes et les stylophores, auxquels sont associés des crinoïdes, des cyclocystoïdes, des édriastéroïdes et des ophiures. Il s'agit d'un assemblage caractéristique des eaux froides de la Province méditerranéenne. Ces niveaux peuvent témoigner de la colonisation opportuniste du fond marin par des populations denses d'échinodermes suite à des pertubations environnementales

16 pages; In the abandoned slate quarry of Guernanic, Gourin (Morbihan, France), a single horizon (Upper Member of the Schistes de Postolonnec Formation) has yielded an exquisitely preserved Llandeilian (Middle Ordovician) echinoderm assemblage composed of the ophiuroid Taeniaster armoricanus sp. nov. and the mitrate Mitrocystella incipiens. These two groups of echinoderms represent the first fossils formally described from the Middle Ordovician of the Gourin area. The brittlestar T. armoricanus sp. nov. is the third and oldest ophiuroid reported so far in the Palaeozoic of the Armorican Massif. The mitrate Mitrocystella is also described for the first time from western Brittany. Taphonomic features of this ophiuroid–stylophoran aggregation suggest that it probably corresponds to the rapid burial of a life assemblage in an otherwise quiet and moderately deep setting (shelf) below, but close to, storm wave base. This echinoderm association represents the oldest evidence for a gregarious mode of life for ophiuroids, as well as the oldest indisputable example of a mixed ophiuroid–stylophoran meadow.