Bertrand Lefebvre

New Ordovician cornutes(Echinodermata, Stylophora) from Montagne Noire and Brittany (France) and a revision of the order Cornuta Jaekel 1901

Abstract Plate homologies are identified and discussed in cornute stylophoran echinoderms. The main resultsare: 1) the homology of the posterior zygal plate in all cornutes and, 2) the non-homology of the spinal process, which can be borne by two distinct plates from the marginal frame. A functional analysis of stylophoran “accessory orifices” as exchange systems is realised: they are interpreted as respiratory structures. Sutural pores of Phyllocystis blayaci and cothurnopores could represent exothecal pore-structures, and lamellipores endothecal pore-structures. Other possible means of respiration are also envisaged in cornutes. A systematic revision of the Order Cornuta is also presented. The new genus Arauricystis is proposed for two species of cornutes previously assigned to the genus Cothurnocystis.. Two new species of cornutes from the Lower Arenig (Lower Ordovician) of Montagne Noire (Southern France) are described, Ampelocarpus landeyranensis nov. gen. et nov. sp. and Thoralicystis ubaghsi nov. sp.. A new cornute from the Llandeilo (Middle Ordovician) of Brittany (Western France), Scotiaecystis guilloui nov. sp. is also described. Finally, a cladistic analysis of cornutes confirms the results obtained by the identification of plate homologies: 1) cornutes and mitrates are sister-groups, 2) Ceratocystis belongs to the stem-group of both cornutes and mitrates, 3) Amygdalothecida and Cothurnocystida are sister-groups and, 4) Protocystites belongs to the stem-group of both Amygdalothecida and Cothurnocystida.

Les échinodermes du Paléozoïqueinférieur de Montagne Noire: Biostratigraphie et paléodiversité

Early Palaeozoic echinoderm faunas from Montagne Noire represent some of the richest and most diversified assemblages known so far. This situation results from their interest and from more than one century of active research. Study of echinoderms and associated faunas allows us to place them in a well-defined regional stratigraphical framework extending from the Middle Cambrian up to the Arenig, and to illustrate the influence of palaeoenvironnents in the distribution and diversity of echinoderms. Montagne Noire faunas show strong affinities with other assemblages from the northern margin of Gondwana (palaeogeographical implications). Variations in the biodiversity of Cambro-Ordovician echinoderms from Montagne Noire indicate that the radiation observed at the base of the Ordovician may result, at least partly, from a too imperfect knowledge of Upper Cambrian faunas.

Homologies in stylophora:A test of the ‘calcichordate theory’

Abstract Stylophora (cornutes and mitrates) are controversial Paleozoic fossils, variously interpreted as ‘bizarre’echinoderms or as ‘calcichordates’ (primitive chordates). The calcichordate theory is based on the identification of left/right asymmetries supposed to be homologous in stylophorans and modern chordates. This theory imposes the homology of the plano-concave surface of the cornute test with the convex surface of the mitrate test. A detailed analysis of numerous internal and external structures exhibited by the appendage and the test demonstrates the homology of the plano-concave surface of the test in all stylophorans. The basic assumption of the calcichordate theory is thus not valid. Comparison of left/right asymmetries in these organisms with those of modem chordates is not grounded. Stylophora do not represent `calcichordates but actual echinoderms.

Laurentian origin of solutan echinoderms: new evidence from the Guzhangian (Cambrian Series 3) Weeks Formation of Utah, USA

A new solutan echinoderm, Pahvanticystis utahensi s gen. et sp. nov. is described from the upper part of the Weeks Formation (Guzhangian). The Cambrian (Series 3) succession of the central House Range in western Utah documents the early diversification of the class Soluta, which is characterized by a major ecological transition from sessile, ‘pelmatozoan’ primitive taxa ( Coleicarpus , Wheeler Formation), to more and more vagile, temporarily attached ( Castericystis , Marjum Formation), to mostly unattached, ‘homalozoan’ derived forms ( Pahvanticystis , Weeks Formation). The morphology of Pahvanticystis is remarkably intermediate between those of Castericystis and Minervaecystis . Its twisted, flattened dististele possibly represents an adaptation for a more efficient crawling atop soft substrates. This morphological feature also questions the phylogenetic relationships between syringocrinid and dendrocystitid solutans, and the possible evolution of the latter from basal, Pahvanticystis - or Minervaecystis -like syringocrinids by paedomorphosis.

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

Abstract. n 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).