Middle Jurassic Nautit,Oidea from \Testern France

Home , Cadomites, Cenoceras, Dorsetensia, Grypoceras, Peltoceras, Zigzagiceras

Rivista Italian,r di Paleontologia e Stratigrafia volume I I u no. I J prs, pp. 141-149 Apflt luuî

MIDDLE JURASSIC NAUTIT,OIDEA FROM \TESTERN FRANCE

PATRICK BRANGER

Receiz'ed Septetnber 19,2002; dccepted October 23, 2003

Kq, irords : Nautilida, Cephalopod, Middle Jurassic, Biostratig- Introduction raPh)', Poitou, Frrnce. \Well known for its rich ammonite fauna, the Mid- Abstract. The Middle shelf margin limestones and nrarly Jurassic dle Jurassic shelf margin limestones and marly limestones limestones of Vesrern France vield quite numerous Nautilida. This record from the Seuil du Poitou (\Western France) were inten- is here described for the first time in detaì1, nine genera and more than sively last years. spite fre- fortl' species, whose range rarely exceeds one or two ammonite biozones, studied during the forty In of constitute a rather precise tool to date Middle Jurassic beds. Each taxon quent discontinuities throughout the succession, most is placed in an accurate biostratigraphical chart; a new genus, Pictonautilus biozones recognised elsewhere in Western Europe have nov. gen., is described. The strxtìfgrphical nnge of Cenoceras, Digonioceras been found, except for the Middle Bathonian, where the and Gen. B n. ? (sensu Chirat 1997) is extended up to the Middle Callovian. Tulites subcontractus Morrisiceras morrisi Zones are In the Jurassic successions of Poitou, Nautilida always represent a mrnor ^nd missing (Mangold et 1971). Many biohorizons and p,rrt of the fossil record and thev ;lre nrore abundant in four levels: Mid- ^1. dle Aalenìan, base of Upper Bajocian, Lox,er Bathonian and top of Mid- subzones of large extension (Gabilly 1964; Gabilly et al. dle Bathonian. Ds'arf Nautilida (Paracenoceras) and species showing nrore 1921; Cariou 1974;1984) have been defined here. From fofded septa and a subventral siphuncle (Pseutlaganides) or strongly ribbed Aalenian to Callovian, these levels also yield quite nu- specinrens (C),matonautilus) are characteristic of stable open-shelf environ- merous Nautilida that have never been studied by these nrents (Callovian), whereas large shelled nautilus would be mostly present authors. few of these fossils were described by Tin- during deepening episodes. The geographical extension of many tîxa ìndi- Only cates a provincialisnr that fits with that of amn.ronites of the same period. tanr (1969; 1980; 1987; 1994). For the last twenty years, beside the other fossils, I carefully collected and identi- Riassunto. I calcari e le marne calcaree del margine di piattafor- fied more than forty species of Nautilida, mostly on the ma del Giurassico medio della Francia occidentale hanno fornito Nau- North Aquitaine border of the Seuil du Poitou. This pa- tilida abbastanza nunrerosi. Questa documentazione è qui descritta in per presents the first results of such a research. dettaglio per la prin.ra volta, nove !Ìeneri e più di quaranta specie, la cui distribuzione raranrente supera una o due biozone ad anrmoniti, e costi- tuisce uno strumento piuttosto preciso per datare gli strati del Giurassico medio. Ogni taxon è posto in un accurato diagramma biostratigrafico; Systematics and stratigraphic distribution viene descritto un nuovo genere, Pìctonautilus nov, gen. La distribuzione stratìgrafica di Cenoceras, Digonioceras e Gen. B n. ? (sensu Chirat) viene Most of the Middle Jurassic fossiliferous beds of esteso fino al Calloviano medio. Nelle successioni giurassiche del Poitou, Poitou contain Nautilida. Fig. 1 indicates the biostrati- i Nlutilida rappresentano sempre una parte minore della documentazlone graphical range for each genus and species, in a detailed fossile, e sono più abbondanti ìn quattro livelli: Aaleniano medio, base del Bajociano superiore, Bathoniano inferiore e sommità del Bathoniano biostratigraphical chart based on ammonites. Most Nau- nredio. I Nautilida nani (Paracenocer4J), le specie che mostrano setti piìl tilida are adults and always associated with ammonites. piegati ed un sifone subventrale (Pseudaganides), e gli esemplari forte- Their frequency increases throughout four levels: Lower nrenre cosrari (C),matonautilus) sono caratteristici di ambienti stabili di and Middle Aalenian, base of Upper Bajocian, Lower Ba- piattaforn.ra aperta (Calloviano), mentre i nautili con grandi conchiglie thonian and top of Middle Bathonian, which correspond sono nraggiormente presenti durrnte gli episodi di approfondimento. Lestensione geografica di molti t:rxa indica un provincialismo che coin- to transgressive units (Gonnin er al. 1,992; 1993) . Till now, cide con quello degli ammoniti durante lo stesso periodo. the Graphocerds concdaum (Late Aalenian), Hyperlioce-

Faculté des Sciences, Universitó de Poitiers, Laboratoire de Géobiologie, Biochronologie et Paléontologie Humaine, ,lO Avenue du Recteur Pineau, 86022 Poitiers cedex, France. E-mail: patrick.branger@,n'anadoo.fr 142 P Branget

.l :l'l I .ll'l ìta rl :lsli ':tÈt;t_= c ÈtìtÌ zot\fts Slil-rl: : | ì t,: F Èlì lÉ ,1, :lì Èlil'lj li \-l ' :l: l( lr -ìlu l!1. ililì i[H.l.|: -l il,l.!'l: Èl,l,l, -l -tlst t1 li l. l, l. l, lrl, l* l'1, lil. lil. È1. | | l:l z \\t Bl TIILIJI o I J \( I:!S l,'* rl r I Ir*' t l, t)t5( tt llkl:\11 kl I z t, c Nf)RRtSt t *rfrl"* I F lR()(iR\( lt ls o I I IIL l,' \R(t\sr)\l tî tl lr r î l? tf c { \tPtiRiliSt \Nl I I'r l*u l,li îtt z : IR \I)f()RDI:NSIS lr ut R( llts0\^t. il \Western Fi,, 1 Stratigraphic distribution of the Nautilida rvithin the Middle Jurassic of Frlnce, lccording to tl.re biozon;rl scheme proposed by the Groupe FranEais d'Etudes du Jurassique ( 1 997).

ras discites (Early Bajocian) and Clydoniceras discus (Late show the characteristic sulcate venter and their ventral Bathonian) Zones have not yielded any specimen. The lobe is not deep enough. Inner whorls are involute, show- adopted classification is that proposed by Tintant & ing their close relationship with other Cenoceras. The last Kabamba f 1983). whorl becomes very evolute. The closest species for these fossils rs Cenoceras mazardrikense (Sarkar, 1964) from Baluchistan. Another interesting aspect of such specimens Cenoceratidae Tintant 8r Kabamba, 1983 is their perfect sin-rilarity with contemporary Procyma- Cenoceras Hyatt, 1883 toceras pictonicumTintanr (1969), the only difference be- ing the ribbing that is missin g on Cenoceras mazardribense Cenoceras, a world-wide taxon which appears in shells. As the lack of ribbing may depend on fossilisation, the Upper Triassic from New-Zealand (Kummel 1956), Procymatoceras pictonicum Tinrant is here regarded as a is here restricted to shells with rounded section, usually junior synonym for Cenoceras mazardrikense (Sarkar); wider than high; their suture line shows shallow ventral at most P. pictonicum could be kept as a subspecies of and lateral lobes. The body chamber section often widens Sarkar's taxon. Cenoceras survived at least until Middle and its ventral part flattens in the adult stage. Callovian (Reinecheia anceps Zone) (Fig. 1).

Specimens D H h \(/ w U U $r/H

440 mm 180 mm 0.40 240 mm 0.54 110 mm 0.25 1.33 C. mazardrikense (P849) 200 95 0.47 120 0.60 40 0.20 1.26

380 175 0.46 200 u-)z 80 4.21 1.14 "P pictonicwm" (P865) 280 140 0.50 170 0.60 55 0.19 1.21

D: diameteqH: height,h: H/D,V: vidth, rv =V/D,U = umbilicusn,idth,u: U/D PB = collections of Patrick Br:rnger.

In this taxon I also include large specimens up to Digonioceras Hyatt, 1894 45 cm in diameteq that are often found in the Lower and Middle Callovian and probably already in the Upper Recently rehabilitated by Chirat (1997), the genus Bathonian. These Nautilida cannot belong to the Parace- Digonioceras corresponds to Jurassic Nautilida (Toarcian noceras group because) even at a large size, they never to Bathonian) which section is usually wider than high Nautiloidea from western France t43

and with a wide umbilicus. Characteristic of this genus is The type species has only been figured by Lissa- the existence of an angular margin that borders the um- jous (1923) and cited by Tintant (198ab; 1987). Picto- bilical u'edge and appears more or less early during the nautilws extends from Upper Bajocian to Late Batho- ontogenesis. At present, Digonioceras has not yet been nian. recorded outside Europe and Arabia. The most inreresr- Discussion. Most of the Nautilida here considered ine specin.ren from Poitou (Pl. 1, fig.6) comes fron.r the as a new genus s/ere previously ranged into the genus Pa- lower part of the Ermnoceras coronatum Zone (Middle racenoceras (Tintant 1984b; 1987,p.92) fromwhich they Callovian) of Exoudun; it is very evolute (IJ/V : 0.29) differ sienificantly for their venter that is never grooved and densely septated (2a to 24 in the inner whorls). This and is bordered by sharp angular margins. The shape of new species represents :r still unnamed species and is the the venter is quite sirnilar to the one of Somalinawtilus first record of this genus within the Callovian (Fig. 1). Spath, 1,927, which is probably the closest genus. Nev- ertheless the latter differs mostly in the feature of the Oph ion autilus Spath, 1927 suture line that shows a lateral saddle according to the type species described by Dacqué (1905, pl. III, fig. 3a). Ophionautilus represents r minor part of the Nau- Only known by the type species, Somalinawtilazs is also tilida found in the Seuil du Poitou area. These larse and separated from Pictonawtilus by a important stratigraphic evolute shells are here represented by the single species gap (Kimmeridgian) (Fig. t). Opbionautilus burtonensis (Foord & Crick, 1890) from Species recognised as Pictonautilus the Upper Bajocian layers (Strenoceras niortense and Ga- - Pictonnutilus r;erciacense (Lissajous), Middle and Upper Bathonian rantiana garantiana Zones) (Fig. 1). (Cadontites bremeri a,nd Prohecticoceras reh'ocosta.tuni) Zones: Pl. 1, fi-

Pictonautilus gen. n. - Pictonautilus gr. claz'ifer (Tìntant), Lower and ? Middle Bathonian (Zrg- zagiceras zigzag end Procerites progracilis Zones): Pl. 1, figs. 4, 5. Type species. 1923 Nautilus Derddcensis Lissajous, p. 48, pl. II, - Pictonautilus no\,. sp., Upper Bajocian (Garantiana garantiana Zo- fig. l, l.r. ne): Pl. i, fig.6. Origin of the nanre. From pictonicus, latin vord for Poitou.

Specimens D H h \(/ w U U sí/H

Holotype 123mm 72 0.58 55 4.44 10 0.08 0.76

PB5O 110 58 0.52 64 0.58 7 0.06 1.10 88 53 0.60 50 0.56 o 0.06 0.94 77 ++ 0.57 +J 0.55 5 U.Ur) 0.97

PB51 99 56 0.56 52 0.52 t) 0.06 0.92 67 36 0.53 39 0.s8 b 0.08 1.08

PB52 124 64 0.53 60 n5n 12 0.10 0.93 52 33 0.63 34 0.65 3 0.05 1.03

PB53 120 64 0.s3 59 0.49 b U.Uf 0.92 88 50 0.56 47 0.53 5 U.Uf 0.94 77 45 0.s8 35 n4q 5 0.06 0.77

Description. Small to middle size Nautilida Gen. n.? B (sensu Chirat 1997). ."vhose whorls are generally' higher than wide. Juvenile rvhorls are rounded; the section becomes rapidly trap- Discussion. This unnamed genus corresponds to ezoidal. The narrow and flat or slightly rounded venrer middle to large size Nautilida with compressed section is bordered by sharp angular margins sometimes cari- (\W/H < 1) and oval shaped except at the nepionic stage nate. Sides are slightly rounded with maximum secrion where the shells are rounded, suggesting a close phyle- width near the umbilical edge. The umbilicus, very nar- tic link with Cenoceras.The umbilicus is mostly closed. row, is probably closed when the shell is completely A broad lateral lobe spreads on their flanks whereas the preserved. The septrr show a wide, shallow, lateral lobe ventral lobe is shallow or non-existent. These cephalo- and a rather deep ventral lobe. The body chamber of pods probably belong to the "groupe de Nautilus araris the adult widens. Dumortier" (Tintant 1984a) called Gen. nov. ? B araris 144 P. Branger

(Dumortier) by Chirat (1997, p. 27a). This latter author PLATE I did not give any name to the Nautilida of this group, be- Fig. 1,2 - Pictonautilusverciacensis (Lissajous, 1921). PB50,.rdult, D : cause he suggested that they could be related to the ge- I 10 mm (X 0,2). Upper Bathonian (Prohecticoceras retrocostatun Zone), Saint-M;rixent (Deux-Sèvres). 2 : ventral view of nus Grypoceras from the Upper Triassic. the same specimen shon'ing the narrow and flat venter (X 0,6). representatives of nov. ? B In Poitou, the first Gen. Fig. 3 - ? Pictonautilusz,et"ciacensìs (Lìssajous, 1923). P866, adult, D : have been recorded from Lower Bajocian (Stepbanocer- 38 mm (X 1,6). Possible microconch. Upper Bathonian (Pro- as bumphriesianum Zone, Dorsetensia romani Subzone). becticoceras retrocostat um Zone), Saint-Maixent (Deux-Sèvres). : They are specially abundant in the Middle Bathonian Fig.4 - Pictonawtilus gr claoilèr (Tintant, 1994). P854, adult, D 50 rnm (X1,6). Lower Bathonian (Zigzagiceras zigzagZone), (Cadomites bremeri Zone) and extend up to the Middle Tauché (Deux-Sèvres) Callovian (Reinecbeia ancep s Zone). Fig. 5 - Pictonautilus gx clalifer (Tintant, 1994). PB55, adult, D : 45 nr nr (X 1,2 5). Lower Bathoni,r n (Z i gzagi ceras zigzag Zone), Ia Species recognised as Gen. n.? B Crèche (Deux-Sòr,rcs), ventral vìerv. Gen.B cf . pseudolineattts (Foord Ei Crick), l-ower Bajocian (Stephano- Fig.6 - Pictonautilus nov. sp. PB30, adult, D : 160 mm (X 0,42). ceras humpbriesianum Zone): Pl. l, fig. 3. Upper Ba jocìan (G rtrttntiantt garantiana Zone, Garantiana Gen. B cl impedens (Crick), Upper Bajocian (Strzroce ras niortenseZone). subgaranti Subzone), Chauray (Deux-Sèvres). The typical Gen. B nov. sp. 1, Middle and Uppe r Bathonirn (Cadomites bremeri and flrrt ventrrl prrt bordered by angular n-rargins appears only Probecticoceras retrocostatum Zones): Pl. I, fis. 7, Pl. 2, fig. l. on the last half whorl. Gen. B nov. sp. 2, Middle Callovian (Reinecheìa anceps Zone): Pl. 2, fig. 2. Fig. Z - Gen. B nor,. sp. l, PB5Z, adult, D - 440 mm (X 0,3). Middle Bathonian (Cadontites brenmì Zone), Niort (Deux-Sèvres). PB - Branser collectiorr. Para c e n o c er a s Spath, 1 9 27

PLATE 2 In spite of its probably polyphyletic origin (Tin- Fig. I - Gen. B nov. sp. l. PB68, phragmocone and beginning of the tant & Kaban-rba 1983, p. 572 ),I refer to this group all body charlber of an adult, D = 280 mm (X 0,38). Middle Ba- the Nautilida that show a true sulcate venter. Most of the thonian (Cadom ites breneri Zone), Nìort (Deux-Sèvres). The specimens collected from the Doeger beds of Western sides of this specinren rvear fine ribs at any stage of its growth. Fig. 2 - Gen. B nor'. sp. 2. P844, adult, D : 225 mm (X 0,42). Middle France are dwarf species showing this sulcate venter at an Calf ovi:rn (Reinecheia anceps Zone), Pamproux (Deux-Sèvres). early stage (Pl. 3, figs. 4,5,6).These Paracenoceras are Fig.3 - Cenoceras baberi (Morris Er Lycett, 1850). PB27, rdult, D : rare, the oldest one has been collected within the Middle 97 mm (X 0,62). Upper Bathonian (Prohecticoceras retrocos- Bathonian layers (Cadomites bremeri Zone) from Niort. tatum Zone), Niort. Both sides show a shallow groove on Callovian species of Paracenoceras are more numerous their extern.rl pîrt, may be of teratological origrn. Fig. + - Digoniocerusdispansum (Morristi Lycett, 1850).PB28,phragmo- but ever dwarf (Fig. 1). cone of an adult, D : 135 nrm (X0,6). Upper Bathonian (Pro- becticoceras retrocostatun Zone), Srint-Maixent (Deux-Sèvres). : C y m at o n auti lu s Sp ath, 19 27 Fig. 5 - Digonioceras nor'. sp. 1. PB38, edult, D 135 mm (X 0,58). Upper Bathonia n (Prohecticoceras retrocostdtum Zone), Sainr- Maixent (Deux-Sèvres). These strongly ribbed nautiloids studied by Tintant Fig. 6 - Digonioceras nov. sp. 2. PB35, phragmocone, D = 210 mm (1969) are never abundant: only the Callovian beds pro- (X 0,45). Middle Callovian (Er1,mn6svas coronatum Zone, vide such forms (Fig. 1). Cymatonautilus julii (d'Orbigny, Erymnoceras baylei Subzone), Exoudun (Deux-Sèvres). PB 1850) characterises the Bullatimorphites bullatus and Mac- : Branger collection.

ro ceph a lite s graci li s Zones vzhile C. m oj s i s ov i c s i (Neumayt 1870) and C. teixeirai Tintant, 1980 are typical of the Rei- PLATE 3 : neckeia anceps Zone. Fig. 1 - Pseudaganides nov. sp. PB56, adult, D 300 mm (X 0,34). Middle Callovian (Macrocephalites gracilis Zone, Indospbinc- tes paliil.l Subzone), Salles (Deux-Sèvres). Pseudonautilidae Shimansky tr Erlanger, 1,955 Fig.2 - Cenoceras nov. sp. P860, adult, D = 83 mn.r (X 1,lO). Upper Bathonian (Prohecticoceras retrocostatum Zone), Niort (Deux- Sèvres). The body chamber wears clavi that probably corre- This family groups Nautilida with sinuous su- spond to old peristomes. Such an ornamentation have been Paracymatoceras tures. Pseudaganides is ribless whereas observed in other specinrens. is ribbed. Fig.3 - Gen. nov. sp. 1 cf. pseudolineatus (Foord Er Crick, 1890). PBl7, phragmocone, D : 98 mm (X 0,71). Lower Bajocian (Stepbanoceras huntpbriesianum Zone, Dorsetensia romani P s e u dagan i d e s Sp ath, 1 9 27 Subzone), Celles-Sur-Belle (Deux-Sèvres). Fis.4,5- Paracenoceras úf. speciosum Tintant, 1987.P867, phragmo- Pseudaganides is a quite frequent genus in Callovian cone, D = 47 rnn1 (Fig.4: X 1,38; Fig.5: X 1,5) Middle Ba- beds and has been well documented by Marchand & Tin- thonian (Cadomites bremeri Zone), Niort. Fis.6 - Paracenoceras nov. sp. Nl1, phraemocone, D : 38 mm (X ranr (L971). Pseudaganides dimidiatus Marchand & Tin- 1,52). Upper Callovian (Peltoceras athleta Zone),Montreuil- tant is older (Lower and Middle Callovian) than Ps. aga- Bellay (Maine et Loire). The venter part of this dwarf speci- niticws (Schlotheim) (UpperCallovian, Pehoceras athleta men is srooved on the whole last u,horl. N = Rantien col- and Quendstedtoceras lamberti Zones) (Fig. 1). lection., PB : Branger collection.

Nawtiloidea from western France t47

PLATE 3 Para cy m ato c era s Spath, 1 927 lowing the schen.res known for ammonites at the same tirre (Cariou et al. 1990). These rare Nautilida are represented in the Lorv- er Callovian beds by two species (Fie. 1): Paracl,n1d7o6s- ras ariniense Tintant fronr the Bullatimorpbites bullatus Conclusion Zone :rnd Parctcytnatoceras mondegoense Tintant from the In West-Central France, the first general approach tr(acrocephalites gracilìs Zone. Comparing nly speciruens of this scantily studied group improves our knowledge u.ith this latter and Nautilus clerci described by Petitclerc about and shows their great during (1915, pl. XII, fig. 1) from the Callovian of Pamproux, Nautilida diversity the Middle More than forty species whose range Paracymtttocerds lnondegoense Ttntant could be regarded Jurassic. rarrely exceeds one or two arnmonite biozones constitute as a junior synonym o[ Nautilus clercibecause their shells a rather precise tool for chronostratigraphicai interpre- present the strme shape and the same ribbing. Neverthe- tations. The geoeraphical extension of many nautiloids less r.nore studies are needed before reaching any defini- indic:rtes a provincialism that fits with these of ammo- tive st2ltenrent on the sDecies of Paraatmatocerds. nites. Fron.r a paleontological point of view, the new genus Pictonautilus clarifres the systematic of Bathonian Affinities of nautiloid assemblages nautiloids. The stratigraphical range of Cenoceras, Di- gortioceras and Gen. B n. ? is extended up to the Middle Most of the Nautilida coilected fror-n tl.re Aale- Callovian and we have a better knowledge of the succes- niern, Bzrjocian and Bathonian of Vest-Central France sion of the different species of Cymatonawtilus. Dwarf show mirny affinities with contemporary firunas fror.n Nautilida (Paracenoceras), showing n-rore folded septa and Eneland (Morris & Lycett 1850; Foord & Crick 1890; a subventral siphuncle (Pseudaganides), strongly ribbed Crick 1898), Normandy (Chirat 1997) and South-East- specin-rens (Cymatonautilus and Paracy mato cerds), seem ern France (Tintant 1984 b).lVithin the Lower and Mid- to be characteristic of the stable open shelves environ- dle C:rllovian, Paracenoceras callot-iertse, P dorsoexcaaa- ments of the Callovian. But more studies s/ill be neces- tun, Cyntatonautilus, Pseudaganides, Cenocerds mazard- sary before considering this group as a tool to understand rikettse (: Paracenoceras noetlingi Halder, pers. comn1. paleoenvironmental changes. frorr.r K. Halder) and C. marzLlrdribense pictotticunt are also represented Kutch, India 2000) in (Halder ; in fact, Aknouledgmentls. The author would like to th,rnk the reviewers these Callovian forms seem to be characteristic of the J. Thierry (Dijon) ;rnd G. Pavia (Torino) for their critical reviews and Submecliterr,rnean and Indo-East African provinces, fol- susqestions th;rt improved the nranuscript.

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