NEW ORDOVICIAN CORNUTES (ECHINODERMATA, STYLOPHORA ...

NEW ORDOVICIAN C O R N U T E S (ECHINODERMATA, STYLOPHORA) FROM MONTAGNE NOIRE AND BRITTANY (FRANCE) AND A R E V I S I O N OF THE O R D E R CORNUTA J A E K E L 1901 To the memory BERTRAND L E F E B V R E

of Jean

Chauvel

& DANIEL V I Z C A I N O

LEFEBVRE B. & VIZCAINO D. 1999. New Ordovician cornutes (Echinodermata, Stylophora) from Montagne Noire and Brittany (France) and a revision of the order Cornuta Jaekel 1901. [Nouveaux cornutes (Echinodermata, Stylophora) de l'Ordovicien de Montagne Noire et de Bretagne (France) et une r~vision de l'ordre Cornuta Jaekel 1901]. GEOBIOS, 32, 3: 421-458. Villeurbanne, le 30.06.1999. Manuscrit d6posd le 01.12.1997; accept~ d4finitivement le 14.02.1999. ABSTRACT - Plate homologies are identified and discussed in cornute stylophoran echinoderms. The main results are: 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. KEYWORDS: HOMOLOGY, CORNUTA, STYLOPHORA, FRANCE, ORDOVICIAN, MITRATA. Rt~SUMI~ - Les homologies de plaques entre les divers genres de cornutes (~chinodermes stylophores) sent identifi~es et discut~es. Les principaux r~sultats sent: 1) l'homologie de la plaque zygale post~rieure chez tous les cornutes et, 2) la non-homologie de la spinale, susceptible d'etre d4velopp4e par deux plaques marginales distinctes. L'analyse morpho-fonctionnelle des "orifices accessoires" des stylophores en tant que syst~me d'~change permet de les proposer comme structures respiratoires. D'autres moyens de respiration sent dgalement envisages chez les cornutes. Une r~vision syst~matique de l'Ordre Cornuta est 4galement r4alis4e. Le genre nouveau Arauricystis est propos~ pour deux esp~ces de cornutes attributes jusqu'alors au genre Cothurnocystis. Trois nouvelles esp~ces de cornutes sent d4crites dans l'Arenig inf~rieur (Ordovicien infdrieur) de la Montagne Noire (France m~ridionale), Ampelocarpus landeyranensis nov.gen, et nov. sp. et Thoralicystis ubaghsi nov. sp., et dans le Llandeilo (Ordovicien moyen) de Bretagne (Ouest de la France), Scotiaecystis guilloui nov. sp.. Enfin, l'analyse cladistique confirme les r~sultats obtenus par la reconnaissance des homologies de plaques, h savoir que: 1) cornutes et mitrates sent groupes-fr~res, 2) Ceratocystis appartient au groupe-souche des cornutes et des mitrates, 3) Amygdalothecfda et Cothurnocystida sent groupes-fr~res et, 4) Protocystites appartient au groupe-souche des Amygdalothecida et des Cothurnocystida. MOTS-CLES: HOMOLOGIE, CORNUTA, STYLOPHORA, FRANCE, ORDOVICIEN, MITRATA. INTRODUCTION

Stylophoran echinoderms are bizarre-shaped Palaeozoic fossils k n o w n f r o m the e a r l y Middle C a m b r i a n u p to the U p p e r Carboniferous. T h e class S t y l o p h o r a Gill & C a s t e r 1960 consists of the two o r d e r s C o r n u t a J a e k e l 1901 a n d M i t r a t a J a e k e l 1918. C o r n u t e s a n d m i t r a t e s s h a r e the

s a m e basic o r g a n i z a t i o n w i t h a t r i p a r t i t e flexible a p p e n d a g e i n s e r t e d into a f l a t t e n e d a s y m m e t r i c a l theca. T h e s e o r g a n i s m s possess a calcitic s k e l e t o n typical of e c h i n o d e r m s b u t do not show a n y p e n t a m e r a l s y m m e t r y . For this reason, t h e y are considered by m o s t a u t h o r s as p r i m i t i v e n o n - r a d i a t e echin o d e r m s (Gill & C a s t e r 1960; U b a g h s 1975; C h a u v e l 1981; K o l a t a & Jollie 1982; P a r s l e y 1988;

422 FIOURE 1 - Location of the fossiliferous localities. 1. Montagne Noire, localities 1 (les Sources du Foulon, Cessenon) and 2 (Pont-Sup~rieur, Saint-Nazaire-de-Ladarez). 2. Brittany, locality 3 (La Saudrais, Guichen). Situation des gisements fossilif~res. 1. Montagne Noire. 2. Bretagne.

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Sprinkle 1992) or as primitive chordates still retaining an echinoderm stereomic skeleton: the "calcichordates" (Jefferies 1968; Cripps 1991; Daley 1992; Gil Cid et al. 1996; Ruta 1997). The "calcichordate" interpretation of these fossils has been convincingly rejected elsewhere (Ubaghs 1975, 1981; Philip 1979; Kolata & Jollie 1982; Lefebvre et al. 1998) and Stylophora are here considered merebers of the Echinodermata. This paper focuses on the order Cornuta (early Middle Cambrian - Upper Ordovician). One of the main aims of the present study is to recognize homologous plates in cornutes (see Lefebvre et al. 1998). This identification is the preliminary absolute necessity to any systematic revision, description or cladistic analysis of cornutes. In addition, many cornutes possess curious "accessory orifices" (Ubaghs 1968) on their upper surface. A functional analysis of these structures as respiratory devices will also be realized. Three new cornutes from the Ordovician of Montagne Noire and B r i t t a n y (France) are described and a cladistic analysis of cornutes is proposed. The material referred to in this paper is preserved in the following collections: Vizca~no collection, Carcassonne (VOMN, VCBH); CourtessoleVizcaino collection, Carcassonne (OE); N~rodni Muzeum, Prague (L); Institut de G~ologie, Rennes (IGR); Universit~ Claude Bernard-Lyon I, UFR Sciences de la Terre, Villeurbanne (FSL).

STRATIGRAPHY A N D LOCALITIES MONTAGNE NOIRE (Fig. 1.1) The first detailed studies on stylophoran echinoderms from the Lower Ordovician of Montagne Noire were carried out by Thoral (1935) and Ubaghs (1961, 1969). All of their material came from sandy concretions collected in the pelites and siltites of faunal zones f and g, in the SaintChinian Formation.

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In recent years, a rising interest in these organisms has lead us to look assiduously for them particularly in all Tremadocian and Arenigian formations in Montagne Noire. Recent investigations in the Saint-Chinian Formation (faunal zones e to g) have lead to the descriptions of new stylophorans (Ubaghs 1983, 1994; Daley 1992; Ruta 1997). In the limonitic calcareous concretions of faunal zone e, characterized by the abundance of the gastropod Peelerophon oehlerti, Phyllocystis crassimarginata has been collected, in association with some rare echinoderms (Minervaecystis vidali, Macrocystella azaisi), hyoliths, brachiopods, bivalves and trilobites: Megistaspis (Ekeraspis) filacovi,

Symphysurus angustatus angustatus, Euloma filacovi, Prionocheilus languedocensis, Aocaspis macrophtalma and agnostids. In faunal zone f, stylophorans are most common at the bottom of the sections (Euloma filacovi faunal zone, Dolambi & Gond 1991) and highly diversified: Phyllocystis crassimarginata, P. blayaci,

Peltocystis cornuta, Cothurnocystis fellinensis, Trigonocarpus singularis, Chauvelicystis spinosa, C. vizcainoi, Galliaecystis ubaghsi, Thoralicystis griffei, Chinianocarpos thorali, Amygdalotheca griffei, Vizcainocarpus dentiger and some rare Kirkocystidae associated with other echinoderms such as Aethocrinus moorei, Minervaecystis vidali, Balantiocystis thorali, Macrocystella azaisi, somasteroids, ophiuroids and edrioasteroids. At the bottom of faunal zone f, the trilobite assemblage consists of the same species as in the previous fauhal zone with, in addition, "Paramegalaspis" guiraudi. At the top of faunal zone f, Asaphelina bar-

roisi, Asaphellus frequens, Paramegalaspis immarginata and Euloma sp. are also present. A rich fauna of molluscs, orthocone nautiloids, brachiopods and hyoliths characterizes faunal zone f. In the next faunal zone (faunal zone g), characterized by Taihungshania miqueli associated with

423

Asaphelina barroisi, stylophorans are less diversifled: Phyllocystis blayaci, Chauvelicystis vizcainoi and Thoralicystis griffei are still present, with Cothurnocystis courtessolei and the two species of the new genus Arauricystis: A. primaeva and A. occitana. Kirkocystidae are locally very abundant. A specimen of Galliaeystis cf. lignieresi has been collected in the black shales of the Fourbidarias River, near Saint-Chinian; the type and unique known specimen of Galliaecystis lignieresi (FSL 168717) has been collected in the Saint-Chinian Formation, close to the same locality. The Saint-Chinian Formation is consequently characterized by a rich, diversified benthic fauna (Dean 1966), corresponding to a relatively deep outer shelf environment in Montag~e Noire (Henry & Vizca~no !996; Vidal 1996). In the La Maurerie Formation (faunal zones h and i), Kirkocystidae are the only stylophorans that have been collected. They are associated with trilobites (less diversified than in the Saint-Chinian Formation: Taihungshania, Asaphidae, Raphiophoridae and some rare Agnostidae), molluscs, graptolites and other echinoderms (Balantiocystis thorali, Cheirocystella languedociana, and Lingulocystis

elongata). The deposits from La Cluse de l'Orb Formation correspond to a shallow, high energetic environment: coarse terrigenic sediments would have been deposited u n d e r t e m p e s t conditions (Eschard in Courtessole et al. 1985; Courtessole et al. 1991). The fauna is far less diversified. Stylophorans have not been collected in the La Cluse de l'Orb (faunal zone j) and Foulon (faunal zone k) Formations. The shales of the Landeyran Formation (faunal zones 1 and m) and their rich, diversified fauna indicate a deepening of the basin and more favourable environmental conditions. Numerous outcrops in the Orb and Landeyran valleys have yielded a fauna mainly composed of trilobites, brachiopods, molluscs, graptolites, hyoliths and, less frequently, echinoderms. Stylophorans have been found in three fossiliferous horizons: - Faunal zone 1, Orb Valley, Les Sources du Foulon, Pt CS34 (locality 1, Fig. 1.1): Proscotiaecystis rnelchiori, Thoralicystis ubaghsi and Kirkocystidae are present, associated with Ramseyocrinus vizcainoi, Cheirocystella sp., Balantiocystis sp., asterozoans, numerous trilobites (Colpocoryphe thorali, Apatoke-

phalus incisus, Bathycheilus gallicus, Ampyx priscus, Prionocheilus rnatutinus, Selenopeltis binodosus, Geragnostus mediterraneus, G. occitanus and frequently larval stages ofAsaphidae), brachiopods, hyoliths, molluscs and some rare ostracods. Faunal zone 1, L a n d e y r a n Valley, Le PontSup6rieur, Pt SNL2 (locality 2, Fig. 1.1): Nanocar-

pus dolambii, Lagynocystis pyramidalis, Ampelo-

carpus landeyranensis, Kirkocystidae and the crinoid Ramseyocrinus vizcainoi have been collected at this outcrop. The associated fauna is less diversifted and composed of trilobites (Asaphidae, often of great size, Colpocoryphe thorali, Apatokephalus incisus, Bathycheilus gaUicus, Geragnostus), molluscs, some rare graptolites and ostracods. - Faunal zone m, Landeyran Valley, Les Rocs NSgres, Pt CV12 and CV17: Ovocarpus moncereti,

Lyricocarpus courtessolei, Nanocarpus dolambii, Lagynocystis pyramidalis (these three forms being rare), Kirkocystidae, Lingulocystis deani, undetermined eocrinoids, trilobites (Colpocoryphe thorali, Hanchungolithus prirnitivus, Toletanaspis borni, Neseuretus nov. sp., Pradoella antetristani, Basiliella mediterranea and other Asaphidae), brachiopods, molluscs and numerous ostracods. The influence of environmental variations that has been pointed out in recent works on trilobites (Courtessole et al. 1991; Henry & Vizca~no 1996; Vidal 1996), seems to be preponderant as well, as far as stylophorans are concerned. BRITTANY (Fig. 1.2) Stylophorans were first mentioned from the Ordovician of MassifArmoricain by Chauvel (1937, 1941). These echinoderms are particularly abundant in the siltstones with fossiliferous concretions of the Traveusot Formation (Martign~-Ferchaud synclinorium, South of Rennes). Scotiaecystis guilloui nov. sp. has been collected in that Formation, at La Saudrais (locality 3, Fig. 1.2), North of the D39 between Guichen and Laill6 (see Henry 1980, p~ 31, fig. 5). The abundant and diverse fauna is dominated by trilobites (mostly Phacopidina michdi and Colpocoryphe rouaulti, associated with ZeliszkeIla

lapeyrei, Panderia beaumonti, EctilIaneus giganteus, Isabelinia glabrata, Dionide rnareki), in association with stylophorans (Mitrocystella, IZArkocystidae), orthocone cephalopods (internal. and external moulds), and some rare brachiopods (Aegiromena mariana) and ostracods. This faunal assemblage is attributed to the Llandeilo, upper part (probably top) of the P1. (Placoparia) tournemini biozone [with 1% of Pl. (Placoparia) borni in the population; see Henry 1980, p. 52, p. 219].

MORPHOLOGY, ANATOMY & TERMINOLOGY GENERAL ORGANIZATION IN CORNUTES As all stylophoran echinoderms, cornutes consist of a flexible, articulated appendage, or aulacophore, inserted into a massive flattened theca (Fig. 2). They are known from the early Middle Cambrian (undescribed form from the Spence Shale of Utah, Sprinkle 1992) to the Upper Ordovician: Cothurnocystis elizae, Scotiaecystis curvata from the Ashgill of Scotland (Bather 1913), and Scotiaecystis collap-

424 FIGURE 2 - General organization of the cornute Phyllocystis blayaci THORAL,1935 [x 2] (after Ubaghs 1969). 1. Upper surface. 2. Lower surface. 3. Lateral view; with AP: anal pyramid, COTH: cothurnopores (respiratory structures), DA : distal aulacophore, INF: inferolaterals, LIA: left infracentral area, LMG: longitudinal median groove, MA: main axis, MF: marginal frame, OCP: open cover plates, OSS: ossicles, PA: proximal aulacophore, RIA: right infracentral area, SIA: supracentra] integumentary area, STR: strut, STY : stylocone, TEC: tectals. Organisation gdndrale du cornute Phyllocystis blayaci THORAL, 1935. 1. Face supdrieure. 2. Face infgrieure. 3. Vue latgrale.

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sa from the Ashgill of Northern Ireland (Cripps 1988). In cornutes, the organization of the aulacophore is always tripartite and similar to that of other stylophorans (Ubaghs 1968, 1981; Chauvel 1981; Philip 1981; Kolata & Jollie 1982; Lefebvre et al. 1998). It consists of a proximal, a middle and a distal part. The proximal part is broad, highly flexible and composed of numerous, articulated, overlapping calcitic rings enclosing a large lumen. The lumen of the proximal aulacophore could communicate with the intrathecal cavity. The middle and distal parts of the aulacophore consist of unpaired elements (stylocone and ossicles, respectively), and articulated with them, a variable number of paired cover plates. The stylocone probably results from the fusion of two (or more) ossicles. The stylocone and ossicles show numerous internal structures on their inner surface, protected by the cover plates: a longitudinal median groove with, on each side, lateral channels leading to lateral depressions. In primitive forms, cover plates which are not paired, but arranged in right and left series, are alternating. In Ceratocystis perneri and Protocystites menevensis for example, there is no direct relationship between the ossicles and the number of associated (left and right) cover plates (Jefferies 1969, p. 515; Woods & Jefferies 1987, p. 469). In more derived species, cover plates tend to become paired and opposite each other on the ossicles. The structures on the upper surface of ossicles and stylocone, as well as the pattern of alternating cover plates (at least in some primitive forms) allow the interpretation of the aulacophore as a single brachial process bearing a unique ambulacrum: the longitudinal median groove corresponding to an ambulacral canal, with side branches (lateral channels) leading to tube feet (housed in the lateral depressions). This appendage would be

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comparable to a single crinoid or ophiuroid arm (Ubaghs 1961, 1968, 1975; Nichols 1972; Chauvel 1981; Parsley 1988). The mouth would be internal and located at the proximal end of the longitudinal median groove. From this interpretation of the stylophoran appendage results the orientation of the fossils: the aulacophore is anterior and the theca, posterior. Other interpretations of the appendage have been tentatively proposed: stem similar to that of solutes (Barrande 1887; Bather 1913; Jaekel 1918; Chauvel 1941; Gill & Caster 1960; Philip 1979; Kolata & Jollie 1982) or chordate-like tail (Jefferies 1968, 1981, 1986; Cripps 1991; Daley 1992). The theca is more or less asymmetrical and flattened, with a convex upper surface and a flat to slightly concave lower surface. Cornutes are characterized by a general tendency towards more symmetrical outlines. The theca is framed by a ring of marginal plates. In primitive forms, upper and lower surfaces of the theca are rigid, composed of a few large plates. In more derived cornutes, they become much more flexible, with large integumentary areas. In some Cambrian fossils the upper side of the theca is strengthened by a strong triradiate ridge (Ceratocystis, Protocystites, Nevadaecystis). Most cornutes present more or less strong downward pointing protuberances on the lower surface of their anterior and lateral marginal plates. The theca usually slopes gently posteriorly with more or less long projections of some marginal plates. These projections have been called (comparing the theca with a medieval boot) "toe-spine', "tongue" and "tag" (Bather 1913) or "spinal", "glossal" and "digital" respectively (Jaekel 1918). The lower thecal surface is usually divided into two by the "strut" (Bather 1913) or "zygal bar" (Ubaghs 1963) associating and joining two opposite marginal plates of the frame. The strut sepa-

425 rates two integumentary areas: the left and right infracentral areas. An obvious structure in most cornutes is a small anal pyramid, at the opposite end of the aulacophore insertion. All cornutes share the same basic body organization (internal structures, aulacophore). They only differ in their general morphology (boot-shaped, heart-shaped, bottle-shaped), and in the number and arrangement of their marginal plates. The identification of homologous plates thus represents the necessary preliminary to any attempt at systematic or cladistic analysis. PLATE TERMINOLOGY IN CORNUTES Four different plate nomenclatures have been proposed for cornutes (Fig. 3). Three of them are purely descriptive (Bather 1913; Ubaghs 1963; Jefferies 1968). Plates are identified following their position, but without any implication of homology between plates sharing the same name. The only terminological system based on plate homology rather than plate topology is that proposed by J.efferies & Prokop (1972). The first attempt to identify cornute plates was that of Bather (1913) in his description of Cothurnocystis elizae and Scotiaecystis curvata. His approach is only descriptive and based on the comparison of the general morphology of the theca with that of a medieval boot: "ball of foot", "heel", "toe-spine". Each plate is designated by a number, following its position on the marginal frame and counting clockwise (on the upper surface): plate 1 is that supporting the "tag", left of the anus, and plate 11, that supporting the "tongue", right of the anus (Fig. 3.1). This system has been followed by Jaekel (1918), Thoral (1935) and Gigout (1954). 5, of

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Another system has been proposed by Jaekel (1901) to identify marginal plates in mitrates: the aulacophore insertion is used as landmark (Fig. 3.2). All marginal plates right of the aulacophore insertion are designated Mn and marginals left of the aulacophore insertion, M'~ (where n is a number indicating the position of the plate, away from the origin). This system, applied to cornutes for the first time by Ubaghs (1963), has been largely followed (Ubaghs 1967, 1968, 1969, 1981, 1983, 1987, 1994; Ubaghs & Robison 1988; Chauvel 1966, 1971; Parsley 1988; Lefebvre et al. 1998). The choice of the aulacophore insertion as a landmark is interesting and convenient, because plates M1 and M'I are very peculiar plates, easily recognizable as homologous in all stylophorans (Ubaghs 1.968, 1981). Three (or two) small plates, the adoral or adaulacophoral plates, located on the upper surface of the theca and framing with M1 and M'I the aulacophore insertion, are also homologized in all cornutes (Ubaghs 1968, 1981). The possible homology between the two "horns" of Ceratocystis with the glossal and the digital is only suggested (Ubaghs 1967, p. 22; 1968, p.508). In a general way, if some obvious homologies have been pointed out (M1, M'I, adoral plates), strict topological application of this system has obscured the recognition of homologous plates. For example, all cornutes possess a posterior zygal plate with a typical triradiate, Y-shaped morpholog}: This plate is identified (Ubaghs 1994) successively as M3 (Lyricocarpus courtessolei), M4 (Cothurnocystis occitana) and M,~

(Trigo nocarp us singularis ). A third plate terminology, also inspired by Jaekel's system for mitrates, has been developed and extended to cornutes by Jefferies (1968, 1969, 1986). The 4 3, " h e e l "

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1913 (lower surface) Ix 1,3]. P l a t e n o m e n clature. 1. A f t e r Bat h e r (1913). 2. A f t e r Ubaghs (1963). 3. A f t e r Jefferies (1969). 4. A f t e r Jefferies et al. (1987). Terminologie

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