Palaeogeographical and palaeoecological aspects of the Cambro–Ordovician radiation of echinoderms in Gondwanan Africa and peri-Gondwanan Europe

Abstract Ecology and tempo of the Lower Palaeozoic radiation of echinoderms are discussed in this paper based on comparison of the diversity patterns observed in Cambro–Ordovician faunas from Laurentia and the northern Gondwana margin. The Cambrian ‘agronomic revolution’ triggered a global radiation of echinoderms, with the progressive disappearance of biomat-related lifestyles, and the colonisation of new environments. Both in Laurentia and on the northern Gondwana margin, soft-substrate echinoderm assemblages related to cold and/or deep environments were dominated by blastozoans and stylophorans. These assemblages show a pattern of continuous diversification from the Middle Cambrian to th…

Quoi de neuf en paléontologie du Paléozoïque ?

7 pages; National audience; En paléontologie,les XIXe et XXe siècles corres-pondentà la mise en place de l’anatomie comparée pour interpréter les fossiles, des corrélations stratigraphiques pour dater les terrains sédimentaires etd e l’usage de la biostratigraphie, de la paléoécologie et de la paléogéographie, plus tardivementde la paléobiologie etd e sacontribution à l’étude des crises de biodiversité, comme composantes des sciences de la Terre. La paléontologie du Paléozoïque n’a pas échappé à cesgrandes tendances. Elle a connu en particulier l’âge d’or dela biostratigraphie paléobotanique et paléopalynologique appliquée à l’exploration età l’exploitation des bassinshouillers du Nord – Pa…

ABNORMALITIES IN THE LOWER ORDOVICIAN CORNUTE PHYLLOCYSTIS THORAL, 1935 (ECHINODERMATA: STYLOPHORA) FROM MONTAGNE NOIRE (SOUTHERN FRANCE): IMPLICATIONS FOR PLATE HOMOLOGY AND PHYLOGENY

9 pages; International audience; Two specimens of the cornute Phyllocystis crassimarginata Thoral, 1935 from the Lower Ordovician of Southern Montagne Noire (Languedoc, France) showing abnormal numbers of marginal plates are described. The first one (UM 310) is characterized by the insertion of one extra plate between the fourth right marginal and the zygal plate Z. Comparison with a new, undescribed Tremadoc boot-shaped cornute suggests that 1) the extra plate of UM 310 is equivalent to M4, and 2) the three right marginals located between M1 and Z in ‘‘normal'' specimens of Phyllocystis can be identified as M2, Mc, and M3. Plate configurations of the right thecal margin are thus identical …

Athenacrinus n. gen. and other early echinoderm taxa inform crinoid origin and arm evolution

AbstractIntermediate morphologies of a new fossil crinoid shed light on the pathway by which crinoids acquired their distinctive arms. Apomorphies originating deep in echinoderm history among early nonblastozoan pentaradiate echinoderms distinguish Tremadocian (earliest Ordovician) crinoid arms from later taxa. The brachial series is separated from the ambulacra, part of the axial skeleton, by lateral plate fields. Cover plates are arrayed in two tiers, and floor plates expressed podial basins and pores. Later during the Early Ordovician, floor plates contacted and nestled into brachials, then were unexpressed as stereom elements entirely and cover plates were reduced to a single tier. Inco…

Preliminary report on new echinoderm Lagerstatten from the Upper Ordovician of the eastern Anti-Atlas, Morocco.

8 pages (p.23-30); International audience; Four distinct echinoderm Lagerstatten have recently been discovered in the Upper Ordovician of the eastern Anti-Atlas, Morocco. They have yielded hundreds of exquisitely preserved specimens. Their taphonomy and associated lithology both suggest rapid, in situ burial. Here we discuss the diverse range of assemblages represented and their significance to the diversity of echinoderms in the Lower Palaeozoic. The oldest assemblage (Izegguirene Formation, lowermost Caradoc) is dominated by eocrinoids, large ophiuroids, and mitrate stylophorans associated with rare crinoids. It shows strong similarities with slightly older faunas described from the under…

First report of the mitrate Peltocystis cornuta Thoral (Echinodermata, Stylophora) in the Lower Ordovician of central Anti-Atlas (Morocco)

The mitrate Peltocystis cornuta is one the best known and most abundant stylophoran echinoderms in the Lower Ordovician (upper Tremadoc - lower Arenig) of Montagne Noire (southern France). It is here documented outside this region for the first time, in coeval deposits of central Anti-Atlas (Morocco). This report confirms the strong faunal affinities between Montagne Noire and Moroccan assemblages in the Ordovician. Twenty-eight individuals of P. cornuta are described from two distinct localities of the Zagora region. Their overall morphology is very comparable to that of Montagne Noire specimens. However, the Moroccan Peltocystis differ from the French ones in their smaller mean size, and …

Reappraisal of ambulacral branching patterns in blastozoans

6 pages; International audience; The type of ambulacral bifurcation is an important diagnostic character in primitive echinoderms. However this character is rarely used in blastozoan phylogenetic studies, whereas the corresponding character is well used in crinoid analyses. The main reason for this gap is the absence of definition of patterns for all blastozoans, resulting in terminological confusion. Although crinoid arms and blastozoan ambulacra are not homologous, the well-defined crinoid terminology has been used to describe the different topologies of ambulacral bifurcation. Unilateral and bilateral patterns have been recognized in blastozoans, and associated with the mineralization of…

Stephen J. Gould, les mitrates et les monstres

Resume L'interet de l'analyse des cas teratologiques pour la comprehension des mecanismes du developpement ontogenetique est un theme recurrent dans l'œuvre litteraire de Gould. Cet article aborde le theme des monstres a travers deux problematiques ayant pour sujet des echinodermes paleozoiques atypiques: les stylophores mitrates. Le premier theme s'interesse au debat concernant la position phyletique des stylophores au sein des deuterostomes. Trois interpretations ont ete proposees pour leur appendice articule, dont l'une implique que les mitrates soient des « monstres prometteurs » (modele calcichorde). Une analogie avec differents scenarios proposes pour l'extinction des dinosaures demon…

Are homalozoans echinoderms? An answer from the extraxial-axial theory

Homalozoans include four classes of non-pentamerous Paleozoic echinoderms: Homostelea (cinctans), Ctenocystoidea (ctenoid-bearing homalozoans), Homoiostelea (solutes), and Stylophora (cornutes and mitrates). Their atypical morphologies have historically made it difficult to relate them to other classes. Therefore, their systematic positions have been represented by two hypotheses (H): as stem taxa to echinoderms (H1) or as stem taxa to chordates (H2). These conclusions rest on previous inability to recognize synapomorphies with more crownward echinoderms, resulting in a forcing of the homalozoans down the phylogenetic tree that is more artifactual than evolutionary. The Extraxial-Axial Theo…

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

10 pages; International audience; The 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…

Morphometric analysis of Tremadocian (earliest Ordovician) kirkocystid mitrates (Echinodermata, Stylophora) from the Taebaeksan Basin, Korea

Abstract Abundant isolated remains of stylophoran echinoderms (cornutes and mitrates) are reported for the first time in the late Tremadocian (Asaphellus Zone) Tumugol Formation of Korea. Mitrate remains include numerous adorals of Kirkocystidae. Several new important anatomical features have been observed on these adorals, as an internal calcitic layer that is associated to s2 and possibly also to the palmar complex. This observation suggests that the palmar complex would be present not only in mitrocystitid mitrates, but also in peltocystitids. For the first time, several morphometric analyses have been undertaken based on isolated kirkocystid adorals, so as to explore the morphological d…

Reevaluation of the enigmatic Ordovician genus Bolboporites.

International audience

A critical comment on ‘ankyroids’ (Echinodermata, Stylophora)

Abstract A recent cladistic analysis of stylophoran echinoderms performed by Parsley suggested that mitrates are polyphyletic and derived from symmetrical cornutes. Parsley erected the order Ankyroida to include all derived cornutes and mitrates. The present paper addresses several significant problems in the data matrix of Parsley's cladistic analysis. Detailed morphological comparisons of various stylophorans suggest that important homologies have been ignored: cornute zygal crest and mitrate septum, adorals, glossal and digital. Subanals are not homologous in mitrates. Identification of plate homologies shows that similar-looking symmetrical thecal outlines have been acquired independent…

Tremadocian Stylophoran Echinoderms From The Taebaeksan Basin, Korea.

15 pages; International audience; Abundant isolated elements of cornute and mitrate stylophorans were recovered from the upper Tremadocian Tumugol Formation in the Taebaeksan Basin, Korea. Cornute skeletal elements comprise a diverse assemblage of marginals and brachials of cothurnocystid affinities, suggesting the presence of no fewer than four different species. Mitrate remains include numerous isolated adorals, marginals, and aulacophoral plates with typical peltocystidan morphologies. Two adorals are identified as Anatifopsis sp., while all the others are attributable to A. cocaban. However, the two previously documented peltocystidans of Korea, A. cocaban and A. truncata, are sufficien…

LATEST CAMBRIAN CORNUTES (ECHINODERMATA: STYLOPHORA) FROM THE TAEBAEKSAN BASIN, KOREA

The oldest echinoderms and first cornute stylophorans ever reported from Korea are described, based on more than 40 specimens collected from the Late Cambrian of the Taebaeksan Basin. New material doubles the number of stylophorans described from Asia and the number of specimens of Late Cambrian stylophorans recorded throughout the world. Three different cornutes are identified: Sokkaejaecystis serrata n. gen. and sp. and two genus and species indeterminate forms A and B. Sokkaejaecystis serrata and indeterminate form B are assigned to the Chauvelicystinae, while the systematic position of indeterminate form A within cornutes is difficult to assess. This new material suggests paleobiogeogra…

Early Palaeozoic palaeobiogeography and palaeoecology of stylophoran echinoderms

44 pages; International audience; Stylophorans (cornutes, mitrates) represent one of the most diverse classes of Cambro-Ordovician echinoderms. They were freeliving, benthic, non-radiate forms, closely related to asterozoans and crinoids. Taphonomic, sedimentological, and palaeosynecological data provide useful information on key aspects of stylophoran palaeoecology. Such a combined approach suggests that the rarity of stylophorans in proximal environments (above storm-wave base) was probably original and does not exclusively result from the possession of a loosely articulated polyplated calcitic test. Conversely, stylophorans were relatively abundant in deeper settings (below storm-wave ba…

Introduction—A tribute to Prof. Georges Ubaghs (1916–2005)

Functional Morphology of Stylophoran Echinoderms

The life orientation and mode of life of stylophorans are a subject of much ongoing debate. Examination of the ornamentation occurring both on the arm and theca in several cornutes and mitrates strongly supports the view that the life orientation was similar in all stylophorans and was ‘flat-surface down’. The presence of an asymmetrical ornamentation adapted to hinder, or minimize, back slippage of the organism in all stylophorans gives strong support to their interpretation as mostly sessile organisms, feeding with the arm facing the current and the theca downstream. The examination of a wide array of thecal morphologies and sculpture patterns displayed by the various groups of cornutes a…

La radiation des échinodermes au Paléozoïque inférieur, l'exemple des blastozoaires.

10 pages; Le sous-phylum Blastozoa est un des groupes d'échinodermes les plus diversifiés (dix classes) au début du Paléozoïque. Après révision critique de leur squelette, leurs morphologies en apparence très variées sont en fait homogènes. Leur diversité montre deux pics (Drumien, Sandbien) liés par un événement de fortes apparitions génériques au Cambrien supérieur-Ordovicien inférieur. Les blastozoaires montrent un fort endémisme au Cambrien et un important provincialisme à l'Ordovicien inférieur et moyen. Ils deviennent cosmopolites à l'Ordovicien supérieur, par plusieurs événements migratoires. Ils sont restreints à la Laurentia et à Baltica au Silurien inférieur.

Introduction – A tribute to Prof. Georges Ubaghs (1916–2005) – Part 2

Unravelling extrinsic and intrinsic factors of the early Palaeozoic diversification of blastozoan echinoderms

19 pages; International audience; The Subphylum Blastozoa represents more than one third of the early Palaeozoic echinoderm fauna. A comprehensive database including all records of blastozoans was built to provide quantitative analyses of palaeogeography and diversity patterns and processes, for the 10 classes currently included in this subphylum during the early Palaeozoic. The global pattern of taxonomic diversity shows two peaks during the Cambrian Series 3 and the Late Ordovician intervals. In Cambrian times, the high taxonomic diversity seems to be related with a high turnover rate and a high endemicity of blastozoan genera, whereas in Ordovician times, the rise in diversity is associa…

Ordovician echinoderms from the Tabas and Damghan regions, Iran: palaeobiogeographical implications

Abstract Two echinoderm assemblages are described in the Middle Ordovician of Iran (Darriwilian). The Simeh Kuh section (Damghan area, eastern Alborz range) has yielded a rich and diverse blastozoan fauna consisting of fistuliporite (Echinosphaerites, Heliocrinites) and dichoporite rhombiferans (cheirocrinids indet., hemicosmitids indet.), as well as aristocystitid (Sinocystis) and sphaeronitid diploporites (Glyptosphaerites, Tholocystis). Heliocrinites, cheirocrinids, hemicosmitids, Glyptosphaerites, and Tholocystis are reported for the first time in the Ordovician of Iran. A less diverse assemblage was collected in the Shirgesht section (Tabas area, Derenjal Mountains), and represents the…

<p class="HeadingRunIn"><strong>Reinterpretation of the enigmatic Ordovician genus <em>Bolboporites </em>(Echinodermata)</strong></p>

Bolboporites is an enigmatic Ordovician cone-shaped fossil, the precise nature and systematic affinities of which have been controversial over almost two centuries. For the first time, a wide range of techniques (CT-scan, SEM, cathodoluminescence, XPL, UV epifluorescence, EBSD, FT-IR and XRF spectrometry) were applied to well-preserved specimens of Bolboporites from Norway and Russia. Our main finding confirms its echinoderm affinities, as shown by its stereomic microstructure and by the first definitive evidence of its monocrystalline nature. Each cone consists in a single, microporous calcitic crystal with a narrow longitudinal internal canal. These results are combined with all previous …