Abstract 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 resulted in an unprecedented increase in the diversity of families, classes and orders, 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. Nine different phyla and several soft-bodied problematica are represented in the Tafilalt, including several notable echinoderm Lagerstätten. This volume is the culmination of over 20 years of research by several international teams and integrates a series of contributions that look at diverse aspects of the biota, including the stratigraphic distribution of the faunas, depositional environments, systematic palaeontology, preservation, palaeobiogeography and the nature and impact of the international fossil trade on these exceptionally preserved fossil faunas.

Abstract The extensive, predominantly siliciclastic deposits of the Upper Ordovician of the Tafilalt have long been the subject of scientific investigation. In the past 25 years, intensified collecting for commercial purposes has resulted in the discovery of several exceptionally-preserved faunas (Konservat-Lagerstätten) in the Tafilalt region, preserving a range of non-biomineralized and soft-bodied organisms. The preservation of these fossils in the coarse clastic sediments of the Tafilalt is surprising, and in the case of soft-bodied organisms, remarkably similar to the preservational mode of typical Ediacaran biotas. These relatively recent discoveries have increased the scientific significance of the Tafilalt Biota, providing an unparalleled insight into the composition and temporal evolution of the shallow, open-marine ecosystems and their denizens during the later stages of the Great Ordovician Biodiversification Event. At least nine different phyla, in addition to several soft-bodied problematica are represented in the Tafilalt. While the highly diverse and remarkably well-preserved echinoderm and euarthropod faunas are most emblematic for the Tafilalt Biota, further studies have revealed a relatively high diversity of molluscs and brachiopods. Among soft-bodied fossils, the problematic paropsonemid eldonids are iconic for the Tafilalt and stand out both through their abundance, and their wide temporal and geographical range throughout the area.

Abstract 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 paraconformable 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.

Abstract Edrioasteroids from the Katian, Lower Ktaoua and Upper Tiouririne formations provide new data on several previously described species and two new species of edrioasteroids. Ontogenetic and palaeoecological data are provided for Moroccopyrgus matacarros . Well-preserved oral areas and internal views of the oral frame show Euryeschatia reboulorum to be an unusual lebetodiscinid rather than an isorophinid. The pyrgocystid Spinadiscus lefebvrei n. gen. and sp. and the highly inflated isorophinid Panidiscus tamiformis n. gen. and sp. are described. Specimens of Moroccopyrgus matacarros and Euryeschatia reboulorum are only found attached to echinosphaeritid rhombiferans and conulariids, respectively, suggesting commensal relationships. Other species attach to a variety of different surfaces.

Abstract Hexedriocystis is a very unusual echinoderm with a puzzling combination of morphological features. The two described species H. inexpectatus and H. mimus occur in Upper Ordovician siliciclastic rocks from Morocco, North Africa. They show a striking combination of isorophid edrioasteroid, paedomorphic crinoid and blastozoan characteristics including a domed thecal shape with a peripheral rim-like attachment structure, imbricate thecal plates. However, both species developed feeding appendages covered by large peristomial cover plates and six oral plates. Hexedriocystis lived intimately associated with edrioasteroid colonies and its strange morphology is probably the result of convergence with isorophid edrioasteroid.

Abstract New Upper Ordovician Echinoderm–Lagerstätten from the Anti-Atlas of Morocco have provided large collections of blastozoan echinoderms. The echinosphaeritid Echinosphaerites dianae n. sp. preserves the oral region, stem and brachioles, characteristics absent in many species of the same genus. Homocystites adidiensis n. sp. is represented by almost 50 specimens that provide details on the growth in this taxon. This is the only species of Homocystites with granules in the external ridge of the outer proximal stem columnals. The genus Rhombifera is recognized for the first time in Morocco based on one partially preserved thecal plate. Assemblages are characterized by low diversity of rhombiferan blastozoan echinoderms that provide further palaeogeographical links at genus level with Gondwana, Baltica and Avalonia.

Abstract The distribution of all known Cambrian echinoderm taxa, encompassing both articulated specimens and taxonomically diagnostic isolated ossicles, is documented for the first time. The database described by 2011 comprises 188 species recorded from 65 formations from around the world. Formations that have yielded articulated echinoderms are unequally distributed in space and time. Only Laurentia and West Gondwana provide reasonably complete records at the resolution of Stage. The review of the biogeographical distributions of the eight major echinoderm clades shows that faunas from Laurentia and Northeast Gondwana (China and Korea) are distinct from those of West Gondwana and Southeast Gondwana (Australia); other regions are too poorly sampled to make firm palaeobiogeographical statements. Analysis of alpha diversity (species per formation) shows that diversity rose initially to Cambrian Stage 5, declined into Guzhangian and Paibian before returning to Stage 5 levels by the end of the Cambrian. This pattern is replicated in Laurentia and West Gondwana. We show that taxonomically diagnostic ossicles found in isolation typically occur significantly earlier than the first articulated specimens of the same taxa and provide important information on the first occurrence and palaeobiogeographical distribution of key taxa, and of the phylum as a whole. Supplementary material: Articulated Cambrian echinoderms and Isolated plates of Cambrian echinoderms are provided at: http://www.geolsoc.org.uk/SUP18668