Daniel Vizcaïno

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.

New Early Cambrian bivalved arthropods from southern France

The Lower Cambrian Pardailhan Formation of the Montagne Noire (Southern France) has yielded a diverse fossil assemblage including bivalved arthropods (the bradoriids Monceretia erisylvia gen. et sp. nov., Cambria danvizcainia sp. nov. and Matthoria ? sp., together with Isoxys sp.) associated with trilobites, hyolithids, inarticulate brachiopods, sponge spicules, ichnofossils and chancelloriid sclerites. This assemblage provides new evidence about the biodiversity of Early Cambrian marine communities in palaeocontinental Gondwana. The bradoriids are Cambriidae, a family with widespread distribution in offshore shelf marine environments during Early Cambrian times. The present study confirms the presence of cambriids within a subtropical latitudinal belt that encompasses Laurentia, Siberia and the Gondwanan margins from Southern France to South China. Although knowledge of the distribution of fossil cambriids is patchy, at the generic level they appear to be provincial, with Petrianna from Laurentia, Shangsiella and Auriculatella from South China, Cambria from Siberia and Gondwana (Armorica), and Monceretia gen nov. from Gondwana (Armorica). The presence of Isoxys in the Montagne-Noire confirms the cosmopolitan distribution of this genus in the Early and Middle Cambrian tropics. Cambriid bradoriids occupy a biostratigraphically narrow time interval, probably equating to part of the Atdabanian and Botomian stages of Russian terminology. Their presence in the Pardailhan Formation supports the notion of a Botomian age, determined from archaeocyathan evidence. The North American bradoriid genus Matthoria , also possibly present in the Pardailhan Formation, is reassigned to the Cambriidae.

Paleogeographic patterns of the Cambrian-Ordovician transition in the southern Montagne Noire (France) : preliminary results

The Cambrian-Ordovician transition in the southern Montagne Noire records a major siliciclastic regressive trend of prograding shoaling complexes (the La Dentelle Formation), separating two transgressive storm-dominated sedimentary systems of mixed (carbonate-siliciclastic) deposits. The latter comprise the underlying La Gardie and Val d’Homs Formations, and the overlying Mounio Formation, all of them displaying evidence of an important synsedimentary tectonic activity. Isolated settings of carbonate productivity, located on intra-shelf ramps and horsts, contain the richest and diversified faunistic communities comprising trilobites, echinoderms, conodonts, carbonate- and phosphate-shell brachiopods, sponge spicules, etc. Although the Cambrian-Ordovician transition of the southern Montagne Noire did not record volcanic events but a rather distensive regime inducing paleotopographies, the latter may reflect a distinct extensional regime recorded in other earliest Ordovician platforms of the French Massif Central, involving oceanization and a major magmatic activity.

Chapter 13 Cambrian echinoderm diversity and palaeobiogeography

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

Morphology and Ontogeny of the Cambrian Edrioasteroid Echinoderm Cambraster cannati from Western Gondwana

A review of the Cambrian edrioasteroid echinoderm Cambraster cannati is made based on new collections from the Iberian Chains (NE Spain) and Montagne Noire (France). New morphological data include a completely articulated oral area and details of ambulacra. Specimens ranging from 4 to 26 mm in diameter provide detailed information concerning the full ontogeny. Important changes through ontogeny mainly affect the marginal ring and the plating pattern of the aboral surface. Comparison with other species of Cambraster indicates that the aboral surface of Cambraster tastudorum from Australia shows strong resemblance to juvenile specimens of C. cannati. Cambraster cannati was attached directly to the substrate and inhabited relatively high energy, offshore environments from the west margin of Gondwana. Abnormalities in the skeleton are described for the first time in a Cambrian edrioasteroid.

Adequacy of the Early Ordovician trilobite record in the southern Montagne Noire (France): biases for biodiversity documentation

The litho- and biostratigraphical subdivisions of the Tremadocian-Arenigian succession of the southern Montagne Noire are hereby revised. The Lower Ordovician diversity patterns are estimated through statistical analysis of 27 families, 64 genera and 132 species of trilobites across nine interval zones; from bottom to top: the Proteuloma geinitzi, Shumardia (Conophrys) pusilla, Euloma filacovi, Taihungshania miqueli, Taihungshania shui landyranensis, Colpocoryphe maynardensis, Neseuretus (Neseuretus) arenosus, Apatokephalus incisus and Hangchungolithus primitivus zones. Maximum trilobite diversity occurred within the E. filacovi and A. incisus zones, alternating with two sharp declines ( S. ( C. ) pusilla and T.shui landyranensis zones), in both cases drastically related to transgressive-regressive trends. Trilobites attained their highest diversity in muddy outer-platform settings, decreasing in fine-grained sandstones and siltstones of shoreface environments, where trilobites could still be numerically abundant. Four major trilobite turnovers are recognised at the bottom of the P. geinitzi , S.(C.)pusilla, E. filacovi and T. shui landyranensis zones, in which survivors from previous intervals are not reported at specific level, and important generic replacements took place. Despite the relative incompleteness of the Lower Ordovician trilobite record, envisaged after analysing the high proportion of monotypic taxa and discontinuous ranges of some families, the trilobite record is representative enough to estimate diversity patterns, although a better understanding of the palaeoenvironmental control will greatly enhance biodiversity resolution.

Depositional controls on Early Cambrian microbial carbonates from the Montagne Noire, southern France

Lower Cambrian shallow-water carbonates enclosing microbial structures are documented for the first time from the upper Lastours Member of the Montagne Noire (southern France). Microbial organisms constructed self-supported boundstones resulting in the formation of exclusively microbial-accreted buildups, which exhibit three main types of non-skeletal microbialites: planar stratiform stromatolites, dome-shaped stromatolites and nonlaminated (thrombolitic) biostromes. In addition, thrombolitic boundstones display four distinct microbial microstructures: clotted and Renalcis -like forms, branching bushy forms, clusters of unbranching straight filaments and crustose forms. The upper member of the Lastours Formation records an upward transition from a shalydominant open shelf to a protected shelf environment bounded by a surface representing a major subaerial exposure. Initially, at the inception of the highstand systems tract, flat stratiform stromatolites formed on open sea subtidal shaly substrates, while stacked domal stromatolites developed in peritidal areas which record subaerial exposure. In contrast, prograding shoal barriers of the transgressive systems tract favoured the establishment of thrombolitic boundstones in protected (back-shoal) environments.

Biostratigraphical significanceof the genus Ferralsia (Lower Cambrian, Trilobita)

Abstract Ferralsia is known from the southern side of the Montagne Noire (France), the Gorlitz Synclinorium(Germany), and the Ossa-Morena zone (Iberian Peninsula). The finding of Ferralsia saxonica in the reference section of the Marianian stage (a Lower Cambrian chronostratigraphic unit of the Iberian Peninsula) allows us to consider it as a potential taxon for correlation within the Cambrian Mediterranean Subprovince. The stratigraphical position and associated trilobites suggest a middle to late Marianian age for Ferralsia saxonica, whereas a middle Marianian to earliest Bilbilian age may be suggested for Ferralsia blayaci.

Guzhangian (mid Cambrian) trilobites from siliceous concretions of the Valtorres Formation, Iberian Chains, NE Spain

In the carbonate-siliciclastic strata of West Gondwana (e. g. in the Montagne Noire, France), the aftermath of the mid Languedocian (mid Cambrian) regression is characterized by a late Languedocian major turnover of trilobite families and a Furongian-early Tremadocian radiation related to the stepwise immigration of trilobite invaders from East Gondwana under persistent transgressive conditions. The scarcity of upper Languedocian fossil accumulations in clayey substrates has inspired the sampling of the palaeogeographically most distal parts of the Iberian Chains (Spain), where diagenetic dissolution of ubiquitous hexactinellid sponge spicules has favoured the formation of siliceous concretions. These have yielded the trilobites Peronopsis cf. insignis, Oidalagnostus trispinifer, Proampyx difformis (= Proampyx aculeatus), Bailiaspis? glabrata (= Holocephalina agrauloides, by ontogeny), Holasaphus cf. centropyge and a paradoxidid gen. et sp. indet. Despite preservation and sampling biases, the identification of this taphonomic window in offshore clayey substrates of West Gondwana allows the recognition of a strong biogeographical link with Baltica, and the correlation of the global Guzhangian Stage and the Solenopleura? brachymetopa Zone of Scandinavia with part of the Mediterranean upper Languedocian Substage. (Less)