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A coleoid gladius (Mollusca, Cephalopoda) from the Albian of Normandy (France): A new squid genus and species
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Annales de Paléontologie 99 (2013) 275–283
Original article
A coleoid gladius (Mollusca, Cephalopoda) from the Albian of Normandy (France): A new squid genus and species Un rostre de coléoïde (Mollusque, Céphalopode) de l’Albien de Normandie (France): un nouveau genre et une nouvelle espèce de calmar Gérard Breton a,∗,b , Jan Strugnell c , Desmond T. Donovan d b
a 6, rue des Réservoirs, 76600 Le Havre, France UMR 6118 Géosciences, université de Rennes 1, 35042 Rennes cedex, France c Department of Genetics, La Trobe Institute for Molecular Science, La Trobe University, Bundoora 3086, Victoria, Australia d 4, North Grove, Wells, Somerset, BA5 2TD, UK
Received 14 August 2012; accepted 2 October 2012 Available online 12 August 2013
Abstract A coleoid gladius (Mollusca, Cephalopoda), well preserved in a phosphate nodule, is described from the lower Albian of Normandy (France). The lateral parts of the gladius are considered as the remains of a primary conus. This fossil is part of a gladius of modern type. It is thought to be included in an evolutionary trend leading to the Recent genera, of narrowing of the gladius associated with greater streamlining of the body. The coleoid gladii are almost unknown from the Cretaceous. This coleoid gladius from the Albian of Normandy differs from any known Mesozoic gladius, and thus is named Normanoteuthis inopinata, new genus, new species, within the family Plesioteuthidae. © 2013 Elsevier Masson SAS. All rights reserved. Keywords: Squid; Coleoid; Gladius; New Taxon; Albian; Paris basin; France
Résumé Un rostre de coléoïde (Mollusque, Céphalopode), bien préservé dans un nodule phosphaté de l’Albien inférieur de Normandie (France), est décrit. Les parties latérales du rostre sont considérées comme les restes d’un cône primaire. Ce fossile est une partie d’un rostre de type moderne. Il est interprété comme faisant
∗
Corresponding author. E-mail address: [email protected] (G. Breton).
0753-3969/$ – see front matter © 2013 Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.annpal.2013.07.004
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partie d’une tendance évolutive menant aux genres actuels, avec raccourcissement du rostre et plus grand fuselage du corps. Les rostres de coléoïdes sont presque inconnus au Crétacé. Ce spécimen de l’Albien de Normandie diffère de tous ceux connus au Mésozoïque, et est baptisé Normanoteuthis inopinata, nouveau genre et nouvelle espèce de la famille des Plesioteuthidae. © 2013 Elsevier Masson SAS. Publié par Elsevier Masson SAS. Tous droits réservés. Mots clés : Calmar ; Coléoïde ; Rostre ; Nouveau taxon ; Albien ; Bassin de Paris ; France
1. Introduction A curious and unusual fossil, collected in October 1981 by Michel Breton in a disused claypit of Normandy (France) remained unidentified until 2008, when one of us (GB) submitted it to the “Mystery fossil” of the Palaeontological Association Newsletter (Breton, 2008: 64–65). DTD identified it as a very rare and exceptionally 3-D preserved squid gladius, which we describe now. The fossil is housed in the collections of the Muséum national d’Histoire naturelle, Paris (France), Département Histoire de la Terre, reg. number MNHN A31826. 2. Geological setting 2.1. Geographic origin The claypit was located at Bully (Seine-Maritime, Normandie, France: x = 531.1; y = 226.8) along the road towards Saint-Martin-l’Hortier. The pit was worked until 1978 by the brick works Ledoigt at Vieux-Manoir (Seine-Maritime), then disused. It was worked again in 1980 by the Muséum d’Histoire naturelle du Havre in order to prepare the visit of the International Geological Congress post-congress field trip. It is today fully overgrown. 2.2. Geology and stratigraphy The Albian Gault facies outcrops in the heart of the Pays de Bray anticline (the so-called “boutonnière du Bray”). The Ledoigt quarry exposed c. 15 m of dark clay of the upper part of the lower Albian and the basal part of the middle Albian. The first lithostratigraphical and biostratigraphical accounts were published by Destombes (1973) and Destombes et al. (1977) and, more recently, included in a wider revision of the Paris Basin Aptian and Albian by Amédro and Matrion, 2004:11. The bed where the fossil was collected (bed “a” Destombes, 1973: 2146) is a black clay with pyrite and phosphatic nodules, dated to the Otohoplites bulliensis ammonite zone, upper part of the lower Albian, c. 105 Ma (Geological Time Scale, 2008). 2.3. Associated fauna and palaeoecology The bed “a” of Bully quarry provided a rich and very well preserved fauna. The taphocoenosis is dominated by molluscs. (1) Ammonites have often their shell preserved, their phragmocone is pyritic and the body chamber phosphatic. The main taxa are: Otohoplites bulliensis Destombes, O. subhilli (Spath),
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Douvilleiceras mammillatum (Schlotheim), Beudanticeras dupinianum (d’Orbigny), and swarms of Protanisoceras spp. (2) Other cephalopods include very rare nautiloids, a unique phragmocone of Neohibolites minimus (Lister), and the squid gladius described below. (3) Macrogastropods are finely preserved, with their shell and aperture. Moreover, an interesting and diverse mesofauna of very small gastropods was described by Destombes, 1984: 41–57. (4) Bivalves are abundant, their shell is preserved and the internal mould is phosphatic, pyritic or both. They include epifaunal (Inoceramus spp.) and endofaunal taxa, e.g. Pectinucula pectinata (J. Sowerby) or Nanonavis carinatus (J. Sowerby) (Destombes and Mongin, 1976). (5) Small sized scaphopods (Dentalium sp.) are abundant. (6) Echinoderms. The test of large endofaunal echinoids (Hemiaster sp.) is always crushed. Destombes (1985) described three species of planktonic microcrinoids roveacrinid from the bed “a”. (7) The fauna of decapod crustaceans is far less diverse than in the eastern part of the Paris Basin or the London basin at the same time (Breton, 2010 in Colleté; Breton, 2011): the lobsters Hoploparia longimana (G.B. Sowerby) and the rare Mecochirus houdardi Van Straelen, abundant claws of a thalassinoid burrower Callianassa agae Breton, and crabs as Notopocorystes stokesii (Mantell), sometimes with a bopyriform swelling, and three scarce species Joeranina broderipii (Mantell), Homolopsis edwardsii (Bell) and Etyus martini Mantell (Breton, 1965). (8) Micropalaeontology has been investigated by Teste (1974) for the foraminifers and Damotte (1976) for the ostracodes. (9) Teeth of Selachians and fish otolithes are common. (10) Wood is frequent, preserved as pyritic charcoal. The macrotaphocoenosis is thus composed of nectobenthic (ammonites), epibenthic (crabs and lobsters, gastropods and inoceramids) and endobenthic (other bivalves, scaphopods and thalassinoids) animals. The squid belongs to the nectobenthic population. The sedimentology denotes a quiet sedimentation, far from the margins of the basin where high-energy conditions, at the same time, led to the Upper Greensand deposits. Notwithstanding the anoxic condition in the sediment, with pyrite formation, the benthic populations were flourishing and diverse. 2.4. Taphonomy The fossil is preserved in a phosphatic nodule. As with most of the fossils preserved in such nodules, the very early phosphate precipitation and hardening prevented any important subsequent deformation, for instance during the compaction of the sediment. As the phosphate precipitation was induced by the decay of organic material, it is supposed that the gladius fell on the sea bottom together with, at least, a part of the flesh of the squid. The nodule is elongated and looks like phosphatic burrows which can be found in the same level, but nothing, apart this resemblance, allows us to say that the corpse of the squid has been buried in a burrow, before phosphatization. 3. Systematic palaeontology Subclass COLEOIDEA Bather, 1888. Order TEUTHOIDEA Naef, 1916. Family PLESIOTEUTHIDAE Naef, 1921. Genus Normanoteuthis gen. nov. Type species. Normanoteuthis inopinata sp. nov., by monotypy.
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Fig. 1. Normanoteuthis inopinata gen. nov., sp. nov. Gladius. MNHN A31826. Lower Albian, Bulliensis Zone, Bully (Seine-Maritime, Normandy, France). Specimen preserved in a phosphatic nodule, uncoated. Above: dorsal view, below: lateral view. Scale bar: 1 cm. Normanoteuthis inopinata gen. nov., sp. nov. Rostre. MNHN A31826. Albien inférieur, Zone à Bulliensis, Bully (SeineMaritime, Normandie, France). Spécimen préservé dans un nodule phosphaté, non blanchi. En haut : vue dorsale ; en bas : vue latérale. Barre d’échelle : 1 cm.
Diagnosis. Gladius with a strong, solid, dorsal median rib flanked by grooves. The rib is of nearly semicircular section. The grooves are limited laterally by weaker ridges. The primary conus is conical or cup-shaped with U-shaped ventral rim. Transverse section circular. Dorso-ventral apical angle c. 30◦ . Lateral margins diverging at angle of c. 8◦ –9◦ . Etymology. Norman-: from Normandy; -teuthis a common ending in teuthoids. Gender feminine. Included species. Normanotheuthis inopinata gen. nov., sp. nov. is the only known species. Lower Albian, Normandy (France). Normanoteuthis inopinata sp. nov. Figs. 1–3 Holotype and unique known specimen: MHNH A31826, Figs. 1–3. Diagnosis. As for the genus. Etymology. As no other specimen was known in the Gault of the Paris Basin, its find was unexpected. Description. The fossil represents part of a coleoid gladius (Figs 1 and 2). The total preserved length is 30.0 mm, and both the posterior part and the anterior part are missing. The dorsal view shows a strong median rib flanked by grooves. The rib is of nearly semicircular section. The grooves are limited laterally by weaker ridges. The lateral sides of the ridges are ill-defined as the gladius slopes away; because it has been laterally compressed prior to fossilisation; the original angle of slope is uncertain. Convergence of the lateral ridges indicates that the length of the missing posterior section was about 8–10 mm.
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Fig. 2. Normanoteuthis inopinata gen. nov., sp. nov. Gladius. MNHN A31826. Lower Albian, Bulliensis Zone, Bully (Seine-Maritime, Normandy, France). Specimen is NH4Cl coated. Above: dorsal view, below: lateral view. Scale bar: 1 cm. Normanoteuthis inopinata gen. nov., sp. nov. Rostre. MNHN A31826. Albien inférieur, Zone à Bulliensis, Bully (SeineMaritime, Normandie, France). Le spécimen est blanchi au NH4Cl. En haut : vue dorsale ; en bas : vue latérale. Barre d’échelle : 1 cm.
Fig. 3. Normanoteuthis inopinata gen. nov., sp. nov. Gladius. MNHN A31826. Lower Albian, Bulliensis Zone, Bully (Seine-Maritime, Normandy, France). Diagrammatic reconstruction. From left to right: ventral, lateral, dorsal views. Normanoteuthis inopinata gen. nov., sp. nov. Rostre. MNHN A31826. Albien inférieur, Zone à Bulliensis, Bully (SeineMaritime, Normandie, France). Reconstruction schématique. De gauche à droite : vues ventrale, latérale et dorsale.
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Thickness of the gladius is estimated at about 100 m or less, but the median rib is solid. Growth lines on the gladius lateral to the median structure are well seen and on the left side in particular the original lateral edge appears to be preserved with little damage. The right side is less complete. More ventrally and posteriorly the present edges are clearly broken because they truncate growth lines at a high angle. These edges have been brought close to each other by the post-mortem lateral compression. Two interpretations are possible: the lateral parts of the gladius could be the remains of a primary conus (conical or cup-shaped with U-shaped ventral rim; Toll, 1998: 55) which has been broken ventrally by the lateral compression; or there could have been a mid-ventral gap separating the two wings of a secondary conus. The former interpretation is preferred because there is no sign on the remaining parts of the gladius of a curve in the growth lines towards the posterior end that would be expected if the two remaining sides were parts of separate vanes or wings. As reconstructed (Fig. 3), the conus has a dorso-ventral apical angle of about 30◦ . A conus of circular transverse section is assumed. The apical angle could be greater depending on how much of the ventral wall is missing; the existing ventral edges do not fit together. The apical angle probably decreased slightly with growth. The ventral length of the conus as reconstructed is about 18 mm, but would be less if the conus had a rounded end as in Plesioteuthis (see below). Because the posterior end is missing, it is a matter of conjecture whether it was pointed, as reconstructed here on a purely geometrical basis, or bluntly rounded as in Plesioteuthis (see below). Discussion. It is likely that the median rib and adjacent fields continue forwards. In recent squids, the primary conus is always small in comparison with the total gladius length, its ventral length rarely exceeds 6% of gladius length. The secondary conus can be relatively larger (Toll, 1998: 55). Because the sides of the anterior part of the fossil are damaged the width of the anterior part, and the exact nature of its lateral edges, and its anterior margin, are uncertain. However the lateral margins appear to diverge at an angle of about 8◦ –9◦ . The angle made by the margins of the corresponding part of the gladii of recent squids is invariably less than this, seldom as much as 5◦ (Toll, 1998: figs. 4–40). It is clear that this fossil is part of a gladius of modern type, differing from recent genera by its greater breadth. It is likely that there has been an evolutionary trend, in several parallel lineages leading to the recent genera, of narrowing of the gladius associated with greater streamlining of the body. The only Jurassic gladius with a similar conus is Plesioteuthis from the Lower Tithonian Solnhofen Formation. This has a solid median rib or keel on the posterior part of the gladius, which dies out anteriorly (Fuchs et al., 2007: pp. 244, Figs. 1C, 1D, 1G). Palaeololigo from the same formation has a similar median rib and flanking grooves but the rib is hollow ventrally, and the gladius has a blunt, rounded posterior end (Donovan & Strugnell, 2010). Gladii are almost unknown from the Cretaceous, the best known being in the Upper Cretaceous of the Lebanon (Fuchs, 2006). Dorateuthis (Woodward, 1883), known from both the Upper Cenomanian and Upper Santonian, is a plesioteuthid. The gladius has a small median ridge (Fuchs, 2006: pp. 7, pl. 1 Figs. B, C; pl. 3, Fig. B). It has a pointed posterior end (Woodward, 1883: pl. 1; holotype, refigured by Fuchs, 2006: pl. 3, Fig. B) but unfortunately it is not clear whether there was a conus. Gladii of Upper Cretaceous are also known from the Czech Republic (Kostak, 2002), but do not include any like the present fossil. We may conclude, subject to the limitation that only a small part of the gladius is preserved, that our new fossil was related to the plesioteuthid lineage. It fills a stratigraphical gap, between
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Lower Tithonian and Upper Cenomanian, and is chiefly interesting as showing the well preserved posterior end with a conus. A number of families of recent squids have a primary conus (Toll, 1982, 1998; Young and Vecchione, 2004: website) and these generally have a narrow median structure which often projects anteriorly to form a free rachis. The ventral length of the conus is usually relatively short. The median rib/free rachis in recent families tends to have a complex structure (Toll, 1982; Bizikov, 2008) which is not present, as far as can be seen, in the present genus. 4. Significance of the conus for coleoid phylogeny The primary conus is thought to be a primitive or plesiomorphic character in coleoids. This is certainly the case if it is, as is fairly widely believed (Naef, 1922: 104; Toll, 1982: 149; 1998: 55), homologous with the conotheca or phragmocone wall of cephalopods with a septate shell. This is not easy to prove, however, because no intermediate forms are known between ones with a calcareous conotheca, whose ultrastructure is fairly well known, and the coleoid gladius which is non-mineralized. The plausibility of the hypothesis rests on its being an obvious, ‘commonsense’ interpretation of coleoid phylogeny. Gladii of recent squids are in many cases fragile and difficult to extract from the animal without damage. The appearance of the posterior end can also depend on the angle from which it is viewed (Donovan & Strugnell, 2010). Such considerations may account for the difference of opinion between Toll (1982, 1998) who regards the recent Bathyteuthis as lacking a conus – he draws it with a cup-shaped posterior end – and Bizikov (2008: Fig. 69B) who draws it with a typical primary conus. It may be significant that the Bathyteuthoidea (including Bathyteuthis) is now accepted to be the sister taxon to the Oegopsida (Strugnell, 2004; Strugnell et al., 2005; Strugnell & Nishiguchi, 2007; Lindgren, 2010). Five of the conus-bearing families, Enoploteuthidae, Gonatidae, Neoteuthidae, Ommastrephidae and Onychoteuthidae, group fairly close together in a phylogeny based on morphology (Clarke, 1988 in Clarke and Trueman: Fig. 1). In molecular phylogenies no clear pattern emerges (e.g. Lindgren and Daly, 2007; Lindgren, 2010), and it is likely that a greater number of conserved genes need to be sequenced from additional oegopsid genera before conclusions can be drawn. Assuming that the primary conus is primitive, it is likely that it was modified or lost independently in different lineages. We must emphasize that there is a difference of opinion as to the phylogenetic position of the Plesioteuthidae. German palaeontologists (e.g. Fuchs et al., 2007, pp. 240) regard them as Vampyropoda, while British and American authors (e.g. Donovan & Toll, 1988; Doyle et al., 1994, pp. 6) place them in the Decabrachia and therefore closer to the ancestors of modern squids. Divergence time estimates (Strugnell et al., 2006: 93) concur in the latter opinion. Disclosure of interest The authors declare that they have no conflicts of interest concerning this article. Acknowledgements Our thanks to Michel Breton who donated the specimen.
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References Amédro, F., Matrion, B., 2004. L’Aptien-Albien du Bassin de Paris: un nouveau regard à l’aube du XXIè siècle. Bulletin d’Information des Géologues du Bassin de Paris 41, 3–23. Bizikov, V.A., 2008. Evolution of the shell in Cephalopoda. VNIRO Publishing, Moscow, pp. 448 [in Russian with English summaries]. Breton, G., 1965. Présentation de quelques Crustacés Décapodes fossiles du Pays de Bray. Bulletin de la Société Linnéenne de Normandie 10e série (6), 45–46. Breton, G., 2008. Mystery fossil 14. The Palaeontology Newsletter 69, 64–65. Breton, G., 2010. Crustacés. In: Colleté, C.(coord.) (Ed.), Stratotype Albien. Collection Patrimoine géologique, 2. Muséum national d’Histoire naturelle, Paris, pp. 221–230. Breton, G., 2011. Deux nouvelles espèces de crustacés décapodes de l’Albien du Bassin de Paris. Geodiversitas 33 (2), 279–284. Clarke, M.R., 1988. Evolution of recent cephalopods - a brief review. In: Clarke, M.R., Trueman, E.R. (Eds.), The Mollusca. Paleontology and Neontology of Cephalopods, 12. Academic Press, San Diego, pp. 331–340. Damotte, R., 1976. Ostracodes de l’Albien de Bully. Bulletin d’Information des Géologues du Bassin de Paris 13 (2), 63–65. Destombes, P., 1973. Hoplitidae et zonation nouvelle de l’Albien inférieur de Bully-Saint-Martin (Bray occidental). Comptes Rendus de l’Académie des Sciences, Paris, série D 277, 2145–2148. Destombes, P., 1984. Recherches sur la mésofaune de l’Albien inférieur de Bully–Saint-Martin-L’Hortier (Pays de Bray). Bulletin trimestriel de la Société Géologique de Normandie et des Amis du Muséum du Havre 70 (4), 41–57. Destombes, P., 1985. Roveacrinidae nouveaux de l’Albien du Bassin de Paris. Bulletin trimestriel de la Société Géologique de Normandie et des Amis du Muséum du Havre 71 (2–3), 9–16. Destombes, P., Mongin, D., 1976. L’Albien moyen de Courcelles (Aube). Bulletin d’Information des Géologues du Bassin de Paris 41 (2), 3–23. Destombes, P., Gamble, H.J., Juignet, P., Owen, H.G., 1977. Cretaceous and lower Tertiary of Seine-Maritime, France: a guide to key localities. Proceedings of the Geologists’ Association 88 (1), 15–38. Donovan, D.T., Strugnell, J.M., 2010. A redescription of the fossil coleoid cephalopod genus Palaeololigo Naef 1921 (Decapodiformes: Palaeololiginidae) and its relationship to Recent squids. Journal of Natural History 44, 23–24 [1475–1492]. Donovan, D.T., Toll, R., 1988. The gladius in coleoid (Cephalopoda) evolution. In: Clarke, M.R., Trueman, E.R. (Eds.), The Mollusca. Paleontology and Neontology of Cephalopods, 12. Academic Press, San Diego, pp. 89–101. Doyle, P., Donovan, D.T., Nixon, M., 1994. Phylogeny and systematics of Coleoidea. The University of Kansas Paleontological Contributions, New Series 5, 1–14. Fuchs, D., 2006. Morphology, taxonomy and diversity of vampyropod coleoids (Cephalopoda) from the Upper Cretaceous of Lebanon. Memorie della Società Italiana di Scienze Naturali e del Museo Civio di Storia Naturale di Milano 34 (2), 1–28. Fuchs, D., Klinghammer, A., Keupp, H., 2007. Taxonomy, morphology and phylogeny of plesioteuthidid coleoids from the Upper Jurassic (Tithonian) Plattenkalks of Solnhofen. Neues Jahrbuch für Geologie und Paläontologie Abhandlungen 245, 239–252. 2008. Geological Time Scale, 33rd International Congress of Geology (ICG), Oslo. August. Kostak, M., 2002. Teuthoidea from the Bohemian Cretaceous Basin (Czech Republic) – a critical review. Abhandlungen der Geologischen Bundesanstalt A 57, 359–369. Lindgren, A.R., Daly, M., 2007. The impact of length-variable data and alignment criterion on the phylogeny of Decapodiformes (Mollusca: Cephalopoda). Cladistics 23, 464–476. Lindgren, A.R., 2010. Molecular inference of phylogenetic relationships among Decapodiformes (Mollusca: Cephalopoda) with special focus on the squid Order Oegopsida. Molecular Phylogenetics and Evolution 56, 77–90. Naef, A., 1922. Die fossilen Tintenfische. Gustav Fischer, Jena, 322 p. Strugnell, J., 2004. The molecular evolutionary history of the Class Cephalopoda (Phylum Mollusca). University of Oxford, 221 p. [PhD Thesis, unpublished]. Strugnell, J., Norman, M., Jackson, J., Drummond, A.J., Cooper, A., 2005. Molecular phylogeny of coleoid cephalopod (Mollusca: Cephalopoda) using a multigene approach; the effect of data partitioning on resolving phylogenies in a Bayesian framework. Molecular Phylogenetics and Evolution 37, 426–441.
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Annales de Paléontologie 99 (2013) 275–283
Original article
A coleoid gladius (Mollusca, Cephalopoda) from the Albian of Normandy (France): A new squid genus and species Un rostre de coléoïde (Mollusque, Céphalopode) de l’Albien de Normandie (France): un nouveau genre et une nouvelle espèce de calmar Gérard Breton a,∗,b , Jan Strugnell c , Desmond T. Donovan d b
a 6, rue des Réservoirs, 76600 Le Havre, France UMR 6118 Géosciences, université de Rennes 1, 35042 Rennes cedex, France c Department of Genetics, La Trobe Institute for Molecular Science, La Trobe University, Bundoora 3086, Victoria, Australia d 4, North Grove, Wells, Somerset, BA5 2TD, UK
Received 14 August 2012; accepted 2 October 2012 Available online 12 August 2013
Abstract A coleoid gladius (Mollusca, Cephalopoda), well preserved in a phosphate nodule, is described from the lower Albian of Normandy (France). The lateral parts of the gladius are considered as the remains of a primary conus. This fossil is part of a gladius of modern type. It is thought to be included in an evolutionary trend leading to the Recent genera, of narrowing of the gladius associated with greater streamlining of the body. The coleoid gladii are almost unknown from the Cretaceous. This coleoid gladius from the Albian of Normandy differs from any known Mesozoic gladius, and thus is named Normanoteuthis inopinata, new genus, new species, within the family Plesioteuthidae. © 2013 Elsevier Masson SAS. All rights reserved. Keywords: Squid; Coleoid; Gladius; New Taxon; Albian; Paris basin; France
Résumé Un rostre de coléoïde (Mollusque, Céphalopode), bien préservé dans un nodule phosphaté de l’Albien inférieur de Normandie (France), est décrit. Les parties latérales du rostre sont considérées comme les restes d’un cône primaire. Ce fossile est une partie d’un rostre de type moderne. Il est interprété comme faisant
∗
Corresponding author. E-mail address: [email protected] (G. Breton).
0753-3969/$ – see front matter © 2013 Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.annpal.2013.07.004
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partie d’une tendance évolutive menant aux genres actuels, avec raccourcissement du rostre et plus grand fuselage du corps. Les rostres de coléoïdes sont presque inconnus au Crétacé. Ce spécimen de l’Albien de Normandie diffère de tous ceux connus au Mésozoïque, et est baptisé Normanoteuthis inopinata, nouveau genre et nouvelle espèce de la famille des Plesioteuthidae. © 2013 Elsevier Masson SAS. Publié par Elsevier Masson SAS. Tous droits réservés. Mots clés : Calmar ; Coléoïde ; Rostre ; Nouveau taxon ; Albien ; Bassin de Paris ; France
1. Introduction A curious and unusual fossil, collected in October 1981 by Michel Breton in a disused claypit of Normandy (France) remained unidentified until 2008, when one of us (GB) submitted it to the “Mystery fossil” of the Palaeontological Association Newsletter (Breton, 2008: 64–65). DTD identified it as a very rare and exceptionally 3-D preserved squid gladius, which we describe now. The fossil is housed in the collections of the Muséum national d’Histoire naturelle, Paris (France), Département Histoire de la Terre, reg. number MNHN A31826. 2. Geological setting 2.1. Geographic origin The claypit was located at Bully (Seine-Maritime, Normandie, France: x = 531.1; y = 226.8) along the road towards Saint-Martin-l’Hortier. The pit was worked until 1978 by the brick works Ledoigt at Vieux-Manoir (Seine-Maritime), then disused. It was worked again in 1980 by the Muséum d’Histoire naturelle du Havre in order to prepare the visit of the International Geological Congress post-congress field trip. It is today fully overgrown. 2.2. Geology and stratigraphy The Albian Gault facies outcrops in the heart of the Pays de Bray anticline (the so-called “boutonnière du Bray”). The Ledoigt quarry exposed c. 15 m of dark clay of the upper part of the lower Albian and the basal part of the middle Albian. The first lithostratigraphical and biostratigraphical accounts were published by Destombes (1973) and Destombes et al. (1977) and, more recently, included in a wider revision of the Paris Basin Aptian and Albian by Amédro and Matrion, 2004:11. The bed where the fossil was collected (bed “a” Destombes, 1973: 2146) is a black clay with pyrite and phosphatic nodules, dated to the Otohoplites bulliensis ammonite zone, upper part of the lower Albian, c. 105 Ma (Geological Time Scale, 2008). 2.3. Associated fauna and palaeoecology The bed “a” of Bully quarry provided a rich and very well preserved fauna. The taphocoenosis is dominated by molluscs. (1) Ammonites have often their shell preserved, their phragmocone is pyritic and the body chamber phosphatic. The main taxa are: Otohoplites bulliensis Destombes, O. subhilli (Spath),
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Douvilleiceras mammillatum (Schlotheim), Beudanticeras dupinianum (d’Orbigny), and swarms of Protanisoceras spp. (2) Other cephalopods include very rare nautiloids, a unique phragmocone of Neohibolites minimus (Lister), and the squid gladius described below. (3) Macrogastropods are finely preserved, with their shell and aperture. Moreover, an interesting and diverse mesofauna of very small gastropods was described by Destombes, 1984: 41–57. (4) Bivalves are abundant, their shell is preserved and the internal mould is phosphatic, pyritic or both. They include epifaunal (Inoceramus spp.) and endofaunal taxa, e.g. Pectinucula pectinata (J. Sowerby) or Nanonavis carinatus (J. Sowerby) (Destombes and Mongin, 1976). (5) Small sized scaphopods (Dentalium sp.) are abundant. (6) Echinoderms. The test of large endofaunal echinoids (Hemiaster sp.) is always crushed. Destombes (1985) described three species of planktonic microcrinoids roveacrinid from the bed “a”. (7) The fauna of decapod crustaceans is far less diverse than in the eastern part of the Paris Basin or the London basin at the same time (Breton, 2010 in Colleté; Breton, 2011): the lobsters Hoploparia longimana (G.B. Sowerby) and the rare Mecochirus houdardi Van Straelen, abundant claws of a thalassinoid burrower Callianassa agae Breton, and crabs as Notopocorystes stokesii (Mantell), sometimes with a bopyriform swelling, and three scarce species Joeranina broderipii (Mantell), Homolopsis edwardsii (Bell) and Etyus martini Mantell (Breton, 1965). (8) Micropalaeontology has been investigated by Teste (1974) for the foraminifers and Damotte (1976) for the ostracodes. (9) Teeth of Selachians and fish otolithes are common. (10) Wood is frequent, preserved as pyritic charcoal. The macrotaphocoenosis is thus composed of nectobenthic (ammonites), epibenthic (crabs and lobsters, gastropods and inoceramids) and endobenthic (other bivalves, scaphopods and thalassinoids) animals. The squid belongs to the nectobenthic population. The sedimentology denotes a quiet sedimentation, far from the margins of the basin where high-energy conditions, at the same time, led to the Upper Greensand deposits. Notwithstanding the anoxic condition in the sediment, with pyrite formation, the benthic populations were flourishing and diverse. 2.4. Taphonomy The fossil is preserved in a phosphatic nodule. As with most of the fossils preserved in such nodules, the very early phosphate precipitation and hardening prevented any important subsequent deformation, for instance during the compaction of the sediment. As the phosphate precipitation was induced by the decay of organic material, it is supposed that the gladius fell on the sea bottom together with, at least, a part of the flesh of the squid. The nodule is elongated and looks like phosphatic burrows which can be found in the same level, but nothing, apart this resemblance, allows us to say that the corpse of the squid has been buried in a burrow, before phosphatization. 3. Systematic palaeontology Subclass COLEOIDEA Bather, 1888. Order TEUTHOIDEA Naef, 1916. Family PLESIOTEUTHIDAE Naef, 1921. Genus Normanoteuthis gen. nov. Type species. Normanoteuthis inopinata sp. nov., by monotypy.
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Fig. 1. Normanoteuthis inopinata gen. nov., sp. nov. Gladius. MNHN A31826. Lower Albian, Bulliensis Zone, Bully (Seine-Maritime, Normandy, France). Specimen preserved in a phosphatic nodule, uncoated. Above: dorsal view, below: lateral view. Scale bar: 1 cm. Normanoteuthis inopinata gen. nov., sp. nov. Rostre. MNHN A31826. Albien inférieur, Zone à Bulliensis, Bully (SeineMaritime, Normandie, France). Spécimen préservé dans un nodule phosphaté, non blanchi. En haut : vue dorsale ; en bas : vue latérale. Barre d’échelle : 1 cm.
Diagnosis. Gladius with a strong, solid, dorsal median rib flanked by grooves. The rib is of nearly semicircular section. The grooves are limited laterally by weaker ridges. The primary conus is conical or cup-shaped with U-shaped ventral rim. Transverse section circular. Dorso-ventral apical angle c. 30◦ . Lateral margins diverging at angle of c. 8◦ –9◦ . Etymology. Norman-: from Normandy; -teuthis a common ending in teuthoids. Gender feminine. Included species. Normanotheuthis inopinata gen. nov., sp. nov. is the only known species. Lower Albian, Normandy (France). Normanoteuthis inopinata sp. nov. Figs. 1–3 Holotype and unique known specimen: MHNH A31826, Figs. 1–3. Diagnosis. As for the genus. Etymology. As no other specimen was known in the Gault of the Paris Basin, its find was unexpected. Description. The fossil represents part of a coleoid gladius (Figs 1 and 2). The total preserved length is 30.0 mm, and both the posterior part and the anterior part are missing. The dorsal view shows a strong median rib flanked by grooves. The rib is of nearly semicircular section. The grooves are limited laterally by weaker ridges. The lateral sides of the ridges are ill-defined as the gladius slopes away; because it has been laterally compressed prior to fossilisation; the original angle of slope is uncertain. Convergence of the lateral ridges indicates that the length of the missing posterior section was about 8–10 mm.
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Fig. 2. Normanoteuthis inopinata gen. nov., sp. nov. Gladius. MNHN A31826. Lower Albian, Bulliensis Zone, Bully (Seine-Maritime, Normandy, France). Specimen is NH4Cl coated. Above: dorsal view, below: lateral view. Scale bar: 1 cm. Normanoteuthis inopinata gen. nov., sp. nov. Rostre. MNHN A31826. Albien inférieur, Zone à Bulliensis, Bully (SeineMaritime, Normandie, France). Le spécimen est blanchi au NH4Cl. En haut : vue dorsale ; en bas : vue latérale. Barre d’échelle : 1 cm.
Fig. 3. Normanoteuthis inopinata gen. nov., sp. nov. Gladius. MNHN A31826. Lower Albian, Bulliensis Zone, Bully (Seine-Maritime, Normandy, France). Diagrammatic reconstruction. From left to right: ventral, lateral, dorsal views. Normanoteuthis inopinata gen. nov., sp. nov. Rostre. MNHN A31826. Albien inférieur, Zone à Bulliensis, Bully (SeineMaritime, Normandie, France). Reconstruction schématique. De gauche à droite : vues ventrale, latérale et dorsale.
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Thickness of the gladius is estimated at about 100 m or less, but the median rib is solid. Growth lines on the gladius lateral to the median structure are well seen and on the left side in particular the original lateral edge appears to be preserved with little damage. The right side is less complete. More ventrally and posteriorly the present edges are clearly broken because they truncate growth lines at a high angle. These edges have been brought close to each other by the post-mortem lateral compression. Two interpretations are possible: the lateral parts of the gladius could be the remains of a primary conus (conical or cup-shaped with U-shaped ventral rim; Toll, 1998: 55) which has been broken ventrally by the lateral compression; or there could have been a mid-ventral gap separating the two wings of a secondary conus. The former interpretation is preferred because there is no sign on the remaining parts of the gladius of a curve in the growth lines towards the posterior end that would be expected if the two remaining sides were parts of separate vanes or wings. As reconstructed (Fig. 3), the conus has a dorso-ventral apical angle of about 30◦ . A conus of circular transverse section is assumed. The apical angle could be greater depending on how much of the ventral wall is missing; the existing ventral edges do not fit together. The apical angle probably decreased slightly with growth. The ventral length of the conus as reconstructed is about 18 mm, but would be less if the conus had a rounded end as in Plesioteuthis (see below). Because the posterior end is missing, it is a matter of conjecture whether it was pointed, as reconstructed here on a purely geometrical basis, or bluntly rounded as in Plesioteuthis (see below). Discussion. It is likely that the median rib and adjacent fields continue forwards. In recent squids, the primary conus is always small in comparison with the total gladius length, its ventral length rarely exceeds 6% of gladius length. The secondary conus can be relatively larger (Toll, 1998: 55). Because the sides of the anterior part of the fossil are damaged the width of the anterior part, and the exact nature of its lateral edges, and its anterior margin, are uncertain. However the lateral margins appear to diverge at an angle of about 8◦ –9◦ . The angle made by the margins of the corresponding part of the gladii of recent squids is invariably less than this, seldom as much as 5◦ (Toll, 1998: figs. 4–40). It is clear that this fossil is part of a gladius of modern type, differing from recent genera by its greater breadth. It is likely that there has been an evolutionary trend, in several parallel lineages leading to the recent genera, of narrowing of the gladius associated with greater streamlining of the body. The only Jurassic gladius with a similar conus is Plesioteuthis from the Lower Tithonian Solnhofen Formation. This has a solid median rib or keel on the posterior part of the gladius, which dies out anteriorly (Fuchs et al., 2007: pp. 244, Figs. 1C, 1D, 1G). Palaeololigo from the same formation has a similar median rib and flanking grooves but the rib is hollow ventrally, and the gladius has a blunt, rounded posterior end (Donovan & Strugnell, 2010). Gladii are almost unknown from the Cretaceous, the best known being in the Upper Cretaceous of the Lebanon (Fuchs, 2006). Dorateuthis (Woodward, 1883), known from both the Upper Cenomanian and Upper Santonian, is a plesioteuthid. The gladius has a small median ridge (Fuchs, 2006: pp. 7, pl. 1 Figs. B, C; pl. 3, Fig. B). It has a pointed posterior end (Woodward, 1883: pl. 1; holotype, refigured by Fuchs, 2006: pl. 3, Fig. B) but unfortunately it is not clear whether there was a conus. Gladii of Upper Cretaceous are also known from the Czech Republic (Kostak, 2002), but do not include any like the present fossil. We may conclude, subject to the limitation that only a small part of the gladius is preserved, that our new fossil was related to the plesioteuthid lineage. It fills a stratigraphical gap, between
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Lower Tithonian and Upper Cenomanian, and is chiefly interesting as showing the well preserved posterior end with a conus. A number of families of recent squids have a primary conus (Toll, 1982, 1998; Young and Vecchione, 2004: website) and these generally have a narrow median structure which often projects anteriorly to form a free rachis. The ventral length of the conus is usually relatively short. The median rib/free rachis in recent families tends to have a complex structure (Toll, 1982; Bizikov, 2008) which is not present, as far as can be seen, in the present genus. 4. Significance of the conus for coleoid phylogeny The primary conus is thought to be a primitive or plesiomorphic character in coleoids. This is certainly the case if it is, as is fairly widely believed (Naef, 1922: 104; Toll, 1982: 149; 1998: 55), homologous with the conotheca or phragmocone wall of cephalopods with a septate shell. This is not easy to prove, however, because no intermediate forms are known between ones with a calcareous conotheca, whose ultrastructure is fairly well known, and the coleoid gladius which is non-mineralized. The plausibility of the hypothesis rests on its being an obvious, ‘commonsense’ interpretation of coleoid phylogeny. Gladii of recent squids are in many cases fragile and difficult to extract from the animal without damage. The appearance of the posterior end can also depend on the angle from which it is viewed (Donovan & Strugnell, 2010). Such considerations may account for the difference of opinion between Toll (1982, 1998) who regards the recent Bathyteuthis as lacking a conus – he draws it with a cup-shaped posterior end – and Bizikov (2008: Fig. 69B) who draws it with a typical primary conus. It may be significant that the Bathyteuthoidea (including Bathyteuthis) is now accepted to be the sister taxon to the Oegopsida (Strugnell, 2004; Strugnell et al., 2005; Strugnell & Nishiguchi, 2007; Lindgren, 2010). Five of the conus-bearing families, Enoploteuthidae, Gonatidae, Neoteuthidae, Ommastrephidae and Onychoteuthidae, group fairly close together in a phylogeny based on morphology (Clarke, 1988 in Clarke and Trueman: Fig. 1). In molecular phylogenies no clear pattern emerges (e.g. Lindgren and Daly, 2007; Lindgren, 2010), and it is likely that a greater number of conserved genes need to be sequenced from additional oegopsid genera before conclusions can be drawn. Assuming that the primary conus is primitive, it is likely that it was modified or lost independently in different lineages. We must emphasize that there is a difference of opinion as to the phylogenetic position of the Plesioteuthidae. German palaeontologists (e.g. Fuchs et al., 2007, pp. 240) regard them as Vampyropoda, while British and American authors (e.g. Donovan & Toll, 1988; Doyle et al., 1994, pp. 6) place them in the Decabrachia and therefore closer to the ancestors of modern squids. Divergence time estimates (Strugnell et al., 2006: 93) concur in the latter opinion. Disclosure of interest The authors declare that they have no conflicts of interest concerning this article. Acknowledgements Our thanks to Michel Breton who donated the specimen.
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