Morphological disparity and systematic revision of the eocrinoid genus Rhopalocystis (Echinodermata, Blastozoa) from the Lower Ordovician of the central Anti-Atlas (Morocco)

The genus Rhopalocystis (Eocrinoidea, Blastozoa) is characterized by both a short stratigraphic range (Fezouata Shale, middle Tremadocian to middle Floian, Lower Ordovician) and a reduced geographic extension (Agdz-Zagora area, central Anti-Atlas, Morocco). Since the original description of its type species (R. destombesi Ubaghs, 1963), three successive revisions of the genus Rhopalocystis have led to the erection of nine additional species. The morphological disparity within this genus is here critically reassessed on the basis of both historical material and new recently collected samples. The detailed examination of all specimens, coupled with morphometric and cladistic analyses, points toward a relatively strong support for five morphotypes. A systematic revision of Rhopalocystis is thus suggested, with only five valid taxa: R. destombesi, R. fraga Chauvel, 1971, R. grandis Chauvel, 1971, R. havliceki Chauvel, 1978, and R. zagoraensis Chauvel, 1971. The five others are considered as junior synonyms (R. dehirensis Chauvel and Régnault, 1986, R. lehmani Chauvel and Régnault, 1986, R. sp. A, R. sp. B, and R. sp. C).Fil: Allaire, Ninon. Université de Lille; FranciaFil: Lefebvre, Bertrand. Université Claude Bernard Lyon 1; FranciaFil: Nardin, Elise. Géosciences Environnement Toulouse; FranciaFil: Martin, Emmanuel L.O.. Université Claude Bernard Lyon 1; FranciaFil: Romain, Vaucher. Université Claude Bernard Lyon 1; FranciaFil: Escarguel, Gilles. Université Claude Bernard Lyon 1; Franci

New Middle and Late Ordovician cornute stylophorans (Echinodermata) from Morocco and other peri-Gondwanan areas

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New Middle and Late Ordovician cornute stylophorans (Echinodermata) from Morocco and other peri-Gondwanan areas

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Exceptionally preserved soft parts in fossils from the Lower Ordovician of Morocco clarify stylophoran affinities within basal deuterostomes.

10 pagesInternational audienceThe extinct echinoderm clade Stylophora consists of some of the strangest known deuterostomes. Stylophorans are known from complete, fully articulated skeletal remains from the middle Cambrian to the Pennsylvanian, but remain difficult to interpret. Their bizarre morphology, with a single appendage extending from a main body, has spawned vigorous debate over the phylogenetic significance of stylophorans, which were long considered modified but bona fide echinoderms with a feeding appendage. More recent interpretation of this appendage as a posterior “tail-like” structure has literally turned the animal back to front, leading to consideration of stylophorans as ancestral chordates, or as hemichordate-like, early echinoderms. Until now, the data feeding the debate have been restricted to evaluations of skeletal anatomy. Here, we apply novel elemental mapping technologies to describe, for the first time, soft tissue traces in stylophorans in conjunction with skeletal molds. The single stylophoran appendage contains a longitudinal canal with perpendicular, elongate extensions projecting beyond hinged biserial plates. This pattern of soft tissues compares most favorably with the hydrocoel, including a water vascular canal and tube feet found in all typical echinoderms. Presence of both calcite stereom and now, an apparent water vascular system, supports echinoderm and not hemichordate-like affinities

Fossilized appendages and guts in three phacopid triobites from the Tremadocian lower Fezouata Konservat-Lagerstätte (Lower Ordovician, Morocco)

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Worm-lobopodian assemblages from the Early Cambrian Chengjiang biota: Insight into the "pre-arthropodan ecology"?

Well-preserved assemblages dominated by scalidophoran worms (Cricocosmia, Mafangscolex) and lobopodians (Paucipodia, Microdictyon, Onychodictyon and undetermined xenusiid) are described from the Early Cambrian Chengjiang biota of China. This fossil material provides the opportunity to reassess key aspects of the functional morphology and lifestyles of the two groups. Both lobopodians exemplified here by Paucipodia and worms relied on a hydrostatic skeleton for support and locomotion and have direct functional analogues in extant onychophorans and priapulids, respectively. Retractor-like muscles attached to terminal claws probably assisted leg elevation in the lobopodians. Whereas lobopodians were essentially walkers and climbers, Cricocosmia and Mafangscolex were most likely subhorizontal burrowers. Their external ornament (phosphatic circular micro plates or spiny sclerites) is interpreted as a possible adaptation for tunnelling close to the water-sediment interface. These assemblages seem to represent in-situ faunal associations and suggest that lobopodians and worms might have shared the same habitat and possibly exploited the same detrital food source. However, no evidence indicates that they interacted in predator-prey relationships. Finally, we hypothesize that during a time interval preceding Cambrian Stage 2, scalidophoran worms and lobopodians were the prevalent ecdysozoan component of early animal communities, and introduce the notion of a possible "pre-arthropodan ecology". (C) 2016 Elsevier B.V. All rights reserved

Palaeoecological aspects of the diversification of echinoderms in the lower Ordovician of Central Anti-Atlas, Morocco

Echinoderms are one of the major components of benthic faunas in the Lower Ordovician sequence near Zagora, central Anti-Atlas, Morocco. The Fezouata Shale (Tremadocian–late Floian) has yielded numerous, exquisitely preserved echinoderm assemblages, ranging through several stratigraphic levels and palaeoenvironmental conditions. These associations offer a unique opportunity to document both evolutionary and palaeoecological aspects of echinoderm diversification in high-latitude, siliciclastic-dominated western Gondwana sediments, where rapid in situ burials facilitated excellent faunal census conditions. Lower shoreface deposits of the Fezouata Shale provide the most complete record of successive echinoderm faunas. In late Tremadocian times, these relatively shallow shelf deposits show the progressive replacement of low-diversity, opportunistic, Cambrian-like, dwarfed communities dominated by cornute stylophorans, in unhospitable, dysoxic environmental conditions by higher diversity benthic assemblages, more typical of the Great Ordovician Biodiversification Event and dominated by blastozoans, on well-oxygenated sea-floors. The turnover of the Ordovician radiation was apparently slightly delayed in more proximal settings. Eocrinoid meadows persisted in shallower environmental conditions up to the middle Floian. In the late Floian, they were replaced by diploporite-dominated communities, typical of later Ordovician high-latitude peri-Gondwanan faunas. From a palaeobiogeographic point of view, low-diversity assemblages display relatively strong affinities with cosmopolitan late Cambrian echinoderm faunas, whereas high-diversity communities are dominated by peri-Gondwanan taxa

The Lower Ordovician Fezouata Konservat-Lagerstatte from Morocco: Age, environment and evolutionary perspectives

International audienceThe Lower Ordovician Fezouata Konservat-Lagerstatte from southern Morocco has been one of the major palaeontological discoveries of the last decade. It provides a unique insight into one of the most critical periods in the evolution of marine life: the Cambrian-Ordovician transition. However, its potential for deciphering key trends in animal diversification was hitherto largely limited by major uncertainties concerning its stratigraphic position, age and environmental setting. Based on extensive fieldwork, fossil evidence, and facies recognition, our study provides clarification on these three crucial issues. Exceptional preservation is limited to two intervals within the Fezouata Shale. Graptolites indicate a late Tremadocian age for the Fezouata Konservat-Lagerstatte as a whole, which is supported by biostratigraphical evidence provided by acritarchs. Sedimentological features and reconstructed patterns of relative sea-level changes indicate relatively shallow-water environmental conditions, under distal storm influence, in an offshore to lower shoreface siliciclastic ramp setting. The Fezouata Biota represents a unique and exceptional window into the palaeobiodiversity in open-marine conditions, thus contrasting with the other Ordovician Konservat-Lagerstatten presently known. In our analyses of this new set of data, we pave the way for accurate temporal, faunal and environmental comparisons with other Lower Palaeozoic Konservat-Lagerstatten, and unlock the full potential of the Fezouata Biota to better understand the processes and scenarios of early animal radiations. (C) 2015 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved