DOCSLIB.ORG

The Structure and Formation of the Siphuncular Tube of Quenstedtoceras Compared with That of Nautilus (Cephalopoda)

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

N. Jb. Gcol. Palaont. Abh. 161 2 153—171 j Stuttgart, Marz 1981 The Structure and Formation of the Siphuncular Tube of Quenstedtoceras compared with that of Nautilus (Cephalopoda) By Klaus Bandel, Erlangen With 9 figures in the text Bandel, K. (1981): The Structure and Formation of the Siphuncular Tube of Quenstedtoceras compared with that of Nautilus (Cephalopoda). — N. Jb. Geol. Palaont, Abh., 161: 153—171; Stuttgart. Abstract: The mode of formation of new chambers of the ammonite Quen­ stedtoceras was analysed in detail and compared with that of Nautilus. The siphuncular tube formed independently from the septum and was attached to the ventral shell wall. The septum was fixed in shape by rapid mineralization and the nacreous septum formed after stabilization of septum morphology. Porous pillar zones that connected chamber liquid with the tissue of the living siphuncle were formed between mineral ends of the organic siphuncular tube within septal necks. K e y words: Perisphinctida (Quenstedtoceras), Nautiloidea (Nautilus), siphun­ cular tube, septum, skeleton, aragonite, organic microstructure. Zusammenfassung: Bei der Neubildung einer Gehausekammer schied Quenstedto­ ceras das Siphonalrohr ab, bevor sich ein neues Septum bildete. Das Rohr wurde der ventralen, inneren Schalenoberfliiche und dem vorherigen Septum mit orga- nischen Lamellen verheftet. Letztere setzen sich in spharolithisch-prismatische Ara- gonitwiilste fort, die auf der mincralischen Schalenoberflache aufgewachsen sind. Das Septum mit seiner komplex verfalteten, randlichen Sutur entstand rasch aus mineralischen und organischen Ausscheidungcn im Schleim der vom Mantelgewebe ausgeschiedenen, extrapallialcn Fliissigkeit. Hierbei wurde die Oberflache des unter Zug stehenden Mantelepithels in seiner Form nachgepriigt nicht aber selbst mineralisiert, wobei der Aufwuchs spharolithisch-prismatischer Aragonit-Kristall- rasen nach hinten erfolgte. Nach der mineralischen Versteifung des Septums und der vollstandigen Abscheidung des organischen Siphonalrohres lostc sich der rtick- wiirtige Mantel von den geregelt verteilten Muskelanheftungspunkten und -linien an der Schaleninnenseitc ab, und erst danach erfolgte die Ausscheidung des Perl- mutterseptums. Nach Beendigung der Perlmutter-Abscheidung wurde die neue Kammer funktionell. Der neue Abschnitt des Siphonalrohres greift in den nach 154 Klaus Bandel vorne gebogenen Septenkragen des vorhergehenden Septums hinein. Hierbei liegt zwischcn spharolithisch-prismatischer Anheftung des hinteren Rohrsegments und der glcichartig strukturierten Anheftung des vorderen Rohrsegmentes eine ausge- dchnte, porose Pfeilerzone, in der eine von der Kammerflussigkeit abgetrennte kleine Fliissigkeitsmenge Platz fand, und die das Gewebe des Siphostranges mit dem Innenraum der abgeschlossenen Rammer in Verbindung brachte. Die Kammer- bildung bei Ammoniten wird mit der von Nautilus verglichen und die Struktur, Bildung und Funktion des Septalapparats diskutiert. Introduction The siphuncular tube is the most characteristic feature of shell bearing cephalopods. It differentiates them from all other members of the phylum Mollusca. In regard to all other shell features, such as planispiral coiling, shell of aragonitic nacreous and prismatic structure, septation of apical shell portions, other mollusc groups may show one or more of these characters, but none are known that have a tube connecting sealed off portions of the shell with the living tissue as is present in the chambered cephalopods. This very ancient acquisition of a septate, benthic limpet-like mollusc that lived in Cambrian times (Y ochelson et ah, 1973) enabled the cephalopod branch of the molluscs to conquer the water above its original benthic habitat and adopt a free swimming mode of life. The tube connecting the soft body situated in the anterior portion of the shell (living chamber) with the sealed off apical portion of the shell and its chambers is filled with living tissue. The sealed off chambers themselves no longer contain living tissue and after formation are filled with water. D enton (1974), D enton & G il pin -B rown (1961, 1966, 1971) and D en­ t o n , G il p in -B rown & H o w a rth (1961, 1967) have shown conclusively that living cephalopods with chambered shell can pump water in and out of the chambers quite easily and can thus adapt their weight to the desired depth of water. They attain neutral buoyancy by changing the amount of liquid held within the chambers by interaction of the cells of the living siphuncle with the liquid held within the chambers. The siphuncular tube of Nautilus is permeable to sea water, imperme­ able to air and able to withstand pressures equivalent to well above 450 m of water depth (C ollins 8c M in to n, 1967). According to these authors a Nautilus shell would fill in about 2 hours if the living siphuncle did not prevent it, since the siphuncular tube acts as a permeable membrane. Gas can enter the chambers by diffusion only. C ham berlain (1978) estimated the permeability of the siphuncular tube of Nautilus and fossil ectocochleate cephalopods using previously published data on the siphuncle composition for his calculations. Thus he used the assumption that liquid must move through the horny tube of the Nautilus siphuncle only. He therefore came to results which were controversial to C ollins & M in to n ’s experiments. C ham berlain concluded that the rate of fluid removal from the chambers Structure and Formation of the Siphuncular Tube of Quenstedtoceras 155 is low, lower than suggested by C ollins & M inton (1967) and D fn ton Sc G il p in -B row n (1966). The living siphuncle and the chambered portion of the shell that has been sealed off from the living tissue in Sepia and Spirula remains through­ out life the most important apparatus for buoyancy control. The contact between living tissue and the liquid held in the chambers thus lies within the siphuncular tube. This tube is not permeable throughout, but only at certain places, as Bandel Sc B oletzky (1979) have shown conclusively for the living members of chambered, shell-bearing cephalopods (Sepia, Spirula, Nautilus). According to these authors the function of the siphun­ cular system in general has most probably never changed in the chambered shells of recent and fossil cephalopods. Bandel Sc Boletzky (1979, Figs. 25, 26) also demonstrated that the siphuncular tube of the Ammonoidea and its attachment to the septum differs in several respects from that of recent Nautilus and Spirula. The data for their reconstruction of the siphuncular tube of ammonites had been extracted from the available literature. Thanks to Prof. Dr. A. Z eiss (Inst, fiir Palaontologie, Erlangen) it was now pos­ sible to study extremely well-preserved Jurassic material of the ammonite Quenstedtoceras from the Polish locality Lukow, and to verify and correct this reconstruction. Quenstedtoceras Previous data: Bandel Sc B oletzky (1979, Figs. 23, 24, 25, 26) combining literature data of G ra nd jean (1910), M iller Sc U nklesbay (1943), M utvei (1967), E rben Sc R eid (1971), B ayer (1975) and others came to the following reconstruction of the relationship of siphuncular tube and septum in ammonoids. The septal neck of semi-adult and adult ammonoids always points towards the living chamber (apertural). The walls of the siphuncular tube are not continuous with this septal neck, but are made of organic material similar to the horny tube of the Nautilus siphuncle. The siphuncular tube consists of portions, each of which has the same length as the corresponding chamber. These individual portions are not fused with one another so as to form one continuous organic tube; instead they are connected to each other by calcareous material. The apical part of each tube segment is narrower than the apertural part in the seg­ ment formed before. The siphuncular tube of the ammonoids is covered by an organic pellicle that separates from the tube near its ends. With these organic sheets the siphuncular tube is attached to the ventral shell wall. The siphuncular tube in most ammonoids becomes independent from the septum during ontogenesis and M utvf.i (1975) suggested that if formed after the septum is completed. K ulicki (1979), in contrast, presented convincing evidence that a new tube section forms before the septum 156 Klaus Bandel Fig. 1—6 (Legend see p. 157) Structure and Formation of the Siphuncular Tube of Quenstedtoceras 157 is completed. The siphuncular tube is attached to the septal neck by sur­ rounding calcareous deposits. In the course of their ontogeny the aramo- noids develop a new porous zone in their siphuncular tube, when the septal necks changed from a retro- to prosiphonate arrangement. B a n d e l Sc B o l e t z k y thought that it might be possible that chamber liquid could be drained on both ends of the tube segment crossing the chamber. N e w data: The septum of Quenstedtoceras in construction is mainly nacreous. At the place where the siphuncle penetrates through the septum, a round aperture is bent towards the living chamber forming the so-called prochoanitic septal neck. The position of the siphuncular tube is close to the outside of each whorl (ventral) in the individuals that have grown after hatching from the egg case. Thus the siphuncular tube runs marginally, almost in contact with the inner side of the outer shell (Fig. 1). The nacreous layer composing most of the outer shell is overlain by a thin inner prismatic layer throughout. Along the insertion of the nacreous septum onto the inner side of the outer shell this prismatic layer increases in thickness, attaining greatest thickness just posterior of the attachment of the septum (Fig. 4). This increased thickness is due to the fact that a prismatic ramp attaches a thick organic pellicle here, which further back­ wards (apically) merges with the organic siphuncular tube (Fig. 1), forming its outermost layer. There may be not only one such sheet, but several, in which case each of these pellicles shows an individual attachment to the inner prismatic layer of the mineral shell.
Recommended publications
  • Nautiloid Shell Morphology

    Nautiloid Shell Morphology

    MEMOIR 13 Nautiloid Shell Morphology By ROUSSEAU H. FLOWER STATEBUREAUOFMINESANDMINERALRESOURCES NEWMEXICOINSTITUTEOFMININGANDTECHNOLOGY CAMPUSSTATION SOCORRO, NEWMEXICO MEMOIR 13 Nautiloid Shell Morphology By ROUSSEAU H. FLOIVER 1964 STATEBUREAUOFMINESANDMINERALRESOURCES NEWMEXICOINSTITUTEOFMININGANDTECHNOLOGY CAMPUSSTATION SOCORRO, NEWMEXICO NEW MEXICO INSTITUTE OF MINING & TECHNOLOGY E. J. Workman, President STATE BUREAU OF MINES AND MINERAL RESOURCES Alvin J. Thompson, Director THE REGENTS MEMBERS EXOFFICIO THEHONORABLEJACKM.CAMPBELL ................................ Governor of New Mexico LEONARDDELAY() ................................................... Superintendent of Public Instruction APPOINTEDMEMBERS WILLIAM G. ABBOTT ................................ ................................ ............................... Hobbs EUGENE L. COULSON, M.D ................................................................. Socorro THOMASM.CRAMER ................................ ................................ ................... Carlsbad EVA M. LARRAZOLO (Mrs. Paul F.) ................................................. Albuquerque RICHARDM.ZIMMERLY ................................ ................................ ....... Socorro Published February 1 o, 1964 For Sale by the New Mexico Bureau of Mines & Mineral Resources Campus Station, Socorro, N. Mex.—Price $2.50 Contents Page ABSTRACT ....................................................................................................................................................... 1 INTRODUCTION
  • Siphuncular Structure in the Extant Spirula and in Other Coleoids (Cephalopoda)

    Siphuncular Structure in the Extant Spirula and in Other Coleoids (Cephalopoda)

    GFF ISSN: 1103-5897 (Print) 2000-0863 (Online) Journal homepage: http://www.tandfonline.com/loi/sgff20 Siphuncular Structure in the Extant Spirula and in Other Coleoids (Cephalopoda) Harry Mutvei To cite this article: Harry Mutvei (2016): Siphuncular Structure in the Extant Spirula and in Other Coleoids (Cephalopoda), GFF, DOI: 10.1080/11035897.2016.1227364 To link to this article: http://dx.doi.org/10.1080/11035897.2016.1227364 Published online: 21 Sep 2016. Submit your article to this journal View related articles View Crossmark data Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=sgff20 Download by: [Dr Harry Mutvei] Date: 21 September 2016, At: 11:07 GFF, 2016 http://dx.doi.org/10.1080/11035897.2016.1227364 Siphuncular Structure in the Extant Spirula and in Other Coleoids (Cephalopoda) Harry Mutvei Department of Palaeobiology, Swedish Museum of Natural History, Box 50007, SE-10405 Stockholm, Sweden ABSTRACT ARTICLE HISTORY The shell wall in Spirula is composed of prismatic layers, whereas the septa consist of lamello-fibrillar nacre. Received 13 May 2016 The septal neck is holochoanitic and consists of two calcareous layers: the outer lamello-fibrillar nacreous Accepted 23 June 2016 layer that continues from the septum, and the inner pillar layer that covers the inner surface of the septal KEYWORDS neck. The pillar layer probably is a structurally modified simple prisma layer that covers the inner surface of Siphuncular structures; the septal neck in Nautilus. The pillars have a complicated crystalline structure and contain high amount of connecting rings; Spirula; chitinous substance.
  • Schmitz, M. D. 2000. Appendix 2: Radioisotopic Ages Used In

    Schmitz, M. D. 2000. Appendix 2: Radioisotopic Ages Used In

    Appendix 2 Radioisotopic ages used in GTS2020 M.D. SCHMITZ 1285 1286 Appendix 2 GTS GTS Sample Locality Lat-Long Lithostratigraphy Age 6 2s 6 2s Age Type 2020 2012 (Ma) analytical total ID ID Period Epoch Age Quaternary À not compiled Neogene À not compiled Pliocene Miocene Paleogene Oligocene Chattian Pg36 biotite-rich layer; PAC- Pieve d’Accinelli section, 43 35040.41vN, Scaglia Cinerea Fm, 42.3 m above base of 26.57 0.02 0.04 206Pb/238U B2 northeastern Apennines, Italy 12 29034.16vE section Rupelian Pg35 Pg20 biotite-rich layer; MCA- Monte Cagnero section (Chattian 43 38047.81vN, Scaglia Cinerea Fm, 145.8 m above base 31.41 0.03 0.04 206Pb/238U 145.8, equivalent to GSSP), northeastern Apennines, Italy 12 28003.83vE of section MCA/84-3 Pg34 biotite-rich layer; MCA- Monte Cagnero section (Chattian 43 38047.81vN, Scaglia Cinerea Fm, 142.8 m above base 31.72 0.02 0.04 206Pb/238U 142.8 GSSP), northeastern Apennines, Italy 12 28003.83vE of section Eocene Priabonian Pg33 Pg19 biotite-rich layer; MASS- Massignano (Oligocene GSSP), near 43.5328 N, Scaglia Cinerea Fm, 14.7 m above base of 34.50 0.04 0.05 206Pb/238U 14.7, equivalent to Ancona, northeastern Apennines, 13.6011 E section MAS/86-14.7 Italy Pg32 biotite-rich layer; MASS- Massignano (Oligocene GSSP), near 43.5328 N, Scaglia Cinerea Fm, 12.9 m above base of 34.68 0.04 0.06 206Pb/238U 12.9 Ancona, northeastern Apennines, 13.6011 E section Italy Pg31 Pg18 biotite-rich layer; MASS- Massignano (Oligocene GSSP), near 43.5328 N, Scaglia Cinerea Fm, 12.7 m above base of 34.72 0.02 0.04 206Pb/238U
  • Palaeoecology and Palaeoenvironments of the Middle Jurassic to Lowermost Cretaceous Agardhfjellet Formation (Bathonian–Ryazanian), Spitsbergen, Svalbard

    Palaeoecology and Palaeoenvironments of the Middle Jurassic to Lowermost Cretaceous Agardhfjellet Formation (Bathonian–Ryazanian), Spitsbergen, Svalbard

    NORWEGIAN JOURNAL OF GEOLOGY Vol 99 Nr. 1 https://dx.doi.org/10.17850/njg99-1-02 Palaeoecology and palaeoenvironments of the Middle Jurassic to lowermost Cretaceous Agardhfjellet Formation (Bathonian–Ryazanian), Spitsbergen, Svalbard Maayke J. Koevoets1, Øyvind Hammer1 & Crispin T.S. Little2 1Natural History Museum, University of Oslo, P.O. Box 1172 Blindern, 0318 Oslo, Norway. 2School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom. E-mail corresponding author (Maayke J. Koevoets): [email protected] We describe the invertebrate assemblages in the Middle Jurassic to lowermost Cretaceous of the Agardhfjellet Formation present in the DH2 rock-core material of Central Spitsbergen (Svalbard). Previous studies of the Agardhfjellet Formation do not accurately reflect the distribution of invertebrates throughout the unit as they were limited to sampling discontinuous intervals at outcrop. The rock-core material shows the benthic bivalve fauna to reflect dysoxic, but not anoxic environments for the Oxfordian–Lower Kimmeridgian interval with sporadic monospecific assemblages of epifaunal bivalves, and more favourable conditions in the Volgian, with major increases in abundance and diversity of Hartwellia sp. assemblages. Overall, the new information from cores shows that abundance, diversity and stratigraphic continuity of the fossil record in the Upper Jurassic of Spitsbergen are considerably higher than indicated in outcrop studies. The inferred life positions and feeding habits of the benthic fauna refine our understanding of the depositional environments of the Agardhfjellet Formation. The pattern of occurrence of the bivalve genera is correlated with published studies of Arctic localities in East Greenland and northern Siberia and shows similarities in palaeoecology with the former but not the latter.
  • A Guide to 1.000 Foraminifera from Southwestern Pacific New Caledonia

    A Guide to 1.000 Foraminifera from Southwestern Pacific New Caledonia

    Jean-Pierre Debenay A Guide to 1,000 Foraminifera from Southwestern Pacific New Caledonia PUBLICATIONS SCIENTIFIQUES DU MUSÉUM Debenay-1 7/01/13 12:12 Page 1 A Guide to 1,000 Foraminifera from Southwestern Pacific: New Caledonia Debenay-1 7/01/13 12:12 Page 2 Debenay-1 7/01/13 12:12 Page 3 A Guide to 1,000 Foraminifera from Southwestern Pacific: New Caledonia Jean-Pierre Debenay IRD Éditions Institut de recherche pour le développement Marseille Publications Scientifiques du Muséum Muséum national d’Histoire naturelle Paris 2012 Debenay-1 11/01/13 18:14 Page 4 Photos de couverture / Cover photographs p. 1 – © J.-P. Debenay : les foraminifères : une biodiversité aux formes spectaculaires / Foraminifera: a high biodiversity with a spectacular variety of forms p. 4 – © IRD/P. Laboute : îlôt Gi en Nouvelle-Calédonie / Island Gi in New Caledonia Sauf mention particulière, les photos de cet ouvrage sont de l'auteur / Except particular mention, the photos of this book are of the author Préparation éditoriale / Copy-editing Yolande Cavallazzi Maquette intérieure et mise en page / Design and page layout Aline Lugand – Gris Souris Maquette de couverture / Cover design Michelle Saint-Léger Coordination, fabrication / Production coordination Catherine Plasse La loi du 1er juillet 1992 (code de la propriété intellectuelle, première partie) n'autorisant, aux termes des alinéas 2 et 3 de l'article L. 122-5, d'une part, que les « copies ou reproductions strictement réservées à l'usage privé du copiste et non destinées à une utilisation collective » et, d'autre part, que les analyses et les courtes citations dans un but d'exemple et d'illustration, « toute représentation ou reproduction intégrale ou partielle, faite sans le consentement de l'auteur ou de ses ayants droit ou ayants cause, est illicite » (alinéa 1er de l'article L.
  • Late Jurassic Ammonites from Alaska

    Late Jurassic Ammonites from Alaska

    Late Jurassic Ammonites From Alaska GEOLOGICAL SURVEY PROFESSIONAL PAPER 1190 Late Jurassic Ammonites From Alaska By RALPH W. IMLAY GEOLOGICAL SURVEY PROFESSIONAL PAPER 1190 Studies of the Late jurassic ammonites of Alaska enables fairly close age determinations and correlations to be made with Upper Jurassic ammonite and stratigraphic sequences elsewhere in the world UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1981 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES G. WATT, Secretary GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress catalog-card No. 81-600164 For sale by the Distribution Branch, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 CONTENTS Page Page Abstract ----------------------------------------- 1 Ages and correlations -----------------------------­ 19 19 Introduction -------------------------------------- 2 Early to early middle Oxfordian --------------­ Biologic analysis _________________________________ _ 14 Late middle Oxfordian to early late Kimmeridgian 20 Latest Kimmeridgian and early Tithonian _____ _ 21 Biostratigraphic summary ------------------------- 14 Late Tithonian ______________________________ _ 21 ~ortheastern Alaska -------------------------­ 14 Ammonite faunal setting --------------------------­ 22 Wrangell Mountains -------------------------- 15 Geographic distribution ---------------------------- 23 Talkeetna Mountains -------------------------­ 17 Systematic descriptions ___________________________ _ 28 Tuxedni Bay-Iniskin Bay area ----------------- 17 References
  • Extent and Mechanism of Sealing in Transected Giant Axons of Squid and Earthworms

    Extent and Mechanism of Sealing in Transected Giant Axons of Squid and Earthworms

    The Journal of Neuroscience, November 1994, 14(11): 6636-6651 Extent and Mechanism of Sealing in Transected Giant Axons of Squid and Earthworms Todd L. Krause,1*2 Harvey M. Fishman, Martis L. Ballinger,’ and George D. BittneC2J ‘Department of Zoology, %stitute for Neuroscience, and Xollege of Pharmacy, University of Texas, Austin, Texas 78712 and 4Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston, Texas 775550841 Transected axons are often assumed to seal at their cut After transection, the proximal portion of a severed axon may ends by the formation of continuous membrane barriers that survive and even regenerate;the distal portion degenerateswith- allow for the restoration of function in the axonal stumps. in hours to days in mammals and birds, but often survives for We have used several electrophysiological measures (mem- weeks to years in lower vertebrates and invertebrates (seeBitt- brane potential, input resistance, injury current density) and ner, 1991, for a review). To survive, the proximal or distal several morphological measures (phase-contrast, video-en- portion of a severed axon must form a barrier (seal) at the hanced differential interference contrast, light, and electron transection site to prevent toxic changesin the internal concen- microscopies) of living and fixed material to assess the ex- trations of ions or macromolecules.Such a seal should be dis- tent and mechanism of sealing within hours after transecting cernible both functionally and morphologically. giant axons of squid (Loligo pealeiand Sepioteuthis lesson- This article reports data from a set of electrophysiological iana) and earthworms (Lumbricus terrestris). Our electro- measures[membrane potential (v,), input resistance(&), and physiological data suggest that the proximal and distal ends injury-induced current density (Zinj)] and morphological mea- of transected squid giant axons do not completely seal within suresof living [phase-contrast microscopy, or video-enhanced 2.5 hr in physiological saline.
  • The Evolution of the Jurassic Ammonite Family Cardioceratidae

    The Evolution of the Jurassic Ammonite Family Cardioceratidae

    THE EVOLUTION OF THE JURASSIC AMMONITE FAMILY CARDIOCERATIDAE by J. H. CALLOMON ABSTRACT.The beginnings of the Jurassic ammonite family Cardioceratidae can be traced back rather precisely to the sudden colonization of a largely land-locked Boreal Sea devoid of ammonites by North Pacific Sphaer- oceras (Defonticeras) in the Upper Bajocian. Thereafter the evolution of the family can be followed in great detail up to its equally abrupt extinction at the top of the Lower Kimmeridgian (sensu onglico). Over a hundred successive assemblages have been recognized, spanning some four and a half stages, twenty-eight standard ammonite zones and sixty-two subzones, equivalent on average to time-intervals of perhaps 250,000 years. Material at most levels is sufficiently abundant to delineate intraspecific variability and dimorphism. Both vary with time and can be very large. They point strongly to an important conclusion, that the assemblages found at any one level and place are monospecific. Morphological overlap between successive assemblages then identifies phyletic lineages. Evolution was on the whole gradualistic, with noise, although the principal lineage can be seen to have undergone phylogenetic division at least twice, followed by a major geographic migration of one or both branches. At other times, considerable mierations. which could be eeologicallv tns~antancous,did not lead to phylogenetic rpeciation. Thc habxtat 07 the famtly remaned broadly 'Horeil thro~phout,local endemlsmr hrinz infrequent and short-livcd Mot~holoeicall\,- .~the family evolved through almost the complete spectrum ofcoiling and sculpture to be found in ammonites as a whole, excluding heteromorphs. The nature of the selection-pressure, if any, remains totally obscure.
  • PDF Figs. 2-27

    PDF Figs. 2-27

    Carnets de Géologie / Notebooks on Geology - Memoir 2006/02 (CG2006_M02) Figure 2: Adapertural depression and toothplate with serrated margin. SEM, from HOTTINGER et alii, 1993. A: Bulimina elongata d'ORBIGNY; B: Loxostomina cf. africana (SMITTER). a: aperture; ad: adapertural depression; li: lip; tp: toothplate with its serrated margin. 44 Carnets de Géologie / Notebooks on Geology - Memoir 2006/02 (CG2006_M02) Figure 3: Advolute whorl in agglutinated planispiral shell of Labrospira jeffreysii (WILLIAMSON). SEM, from HOTTINGER et alii, 1993. ws: whorl suture. Figure 4: Embryonic and periembryonic chambers in Orbitoides spp. according to VAN HINTE's 1966 concept. I: protoconch; II: deuteroconch; PAC: principal auxiliary chamber; PEC: principal epi-auxiliary chamber; AEC: accessory epi-auxiliary chamber. In our view, we prefer to call PAC an auxiliary and AEC an adauxiliary chamber. 45 Carnets de Géologie / Notebooks on Geology - Memoir 2006/02 (CG2006_M02) Figure 5: Standard dimorphic or trimorphic reproductive cycle in benthic, medium- to large-sized foraminifera according to GOLDSTEIN, 1999. Schizogeny, eventually repeated several times, may be widespread in larger foraminifera from oligotrophic habitats. Planktic foraminifera seem to have no dimorphic life cycle. Life cycles are linked in various ways to seasonal cycles. Example: Heterostegina depressa d'ORBIGNY, equatorial sections, Gulf of Aqaba, Red Sea (from HOTTINGER, 1977). 46 Carnets de Géologie / Notebooks on Geology - Memoir 2006/02 (CG2006_M02) Figure 6: Agglutination in foraminiferan walls; Gulf of Aqaba, Red Sea; Recent. A-C: Textularia sp. C in HOTTINGER et alii, 1993. A: Lateral view showing coarse grains producing a rugged shell surface exept on apertural face. SEM. B: axial thin section of the biserial test showing distribution of agglutinated grains within the shell walls.
  • An Eocene Orthocone from Antarctica Shows Convergent Evolution of Internally Shelled Cephalopods

    An Eocene Orthocone from Antarctica Shows Convergent Evolution of Internally Shelled Cephalopods

    RESEARCH ARTICLE An Eocene orthocone from Antarctica shows convergent evolution of internally shelled cephalopods Larisa A. Doguzhaeva1*, Stefan Bengtson1, Marcelo A. Reguero2, Thomas MoÈrs1 1 Department of Palaeobiology, Swedish Museum of Natural History, Stockholm, Sweden, 2 Division Paleontologia de Vertebrados, Museo de La Plata, Paseo del Bosque s/n, B1900FWA, La Plata, Argentina * [email protected] a1111111111 a1111111111 a1111111111 a1111111111 Abstract a1111111111 Background The Subclass Coleoidea (Class Cephalopoda) accommodates the diverse present-day OPEN ACCESS internally shelled cephalopod mollusks (Spirula, Sepia and octopuses, squids, Vampyro- teuthis) and also extinct internally shelled cephalopods. Recent Spirula represents a unique Citation: Doguzhaeva LA, Bengtson S, Reguero MA, MoÈrs T (2017) An Eocene orthocone from coleoid retaining shell structures, a narrow marginal siphuncle and globular protoconch that Antarctica shows convergent evolution of internally signify the ancestry of the subclass Coleoidea from the Paleozoic subclass Bactritoidea. shelled cephalopods. PLoS ONE 12(3): e0172169. This hypothesis has been recently supported by newly recorded diverse bactritoid-like doi:10.1371/journal.pone.0172169 coleoids from the Carboniferous of the USA, but prior to this study no fossil cephalopod Editor: Geerat J. Vermeij, University of California, indicative of an endochochleate branch with an origin independent from subclass Bactritoi- UNITED STATES dea has been reported. Received: October 10, 2016 Accepted: January 31, 2017 Methodology/Principal findings Published: March 1, 2017 Two orthoconic conchs were recovered from the Early Eocene of Seymour Island at the tip Copyright: © 2017 Doguzhaeva et al. This is an of the Antarctic Peninsula, Antarctica. They have loosely mineralized organic-rich chitin- open access article distributed under the terms of compatible microlaminated shell walls and broadly expanded central siphuncles.
  • The Upper Jurassic of Europe: Its Subdivision and Correlation

    The Upper Jurassic of Europe: Its Subdivision and Correlation

    The Upper Jurassic of Europe: its subdivision and correlation Arnold Zeiss In the last 40 years, the stratigraphy of the Upper Jurassic of Europe has received much atten- tion and considerable revision; much of the impetus behind this endeavour has stemmed from the work of the International Subcommission on Jurassic Stratigraphy. The Upper Jurassic Series consists of three stages, the Oxfordian, Kimmeridgian and Tithonian which are further subdivided into substages, zones and subzones, primarily on the basis of ammonites. Regional variations between the Mediterranean, Submediterranean and Subboreal provinces are discussed and correlation possibilities indicated. The durations of the Oxfordian, Kimmeridgian and Tithonian Stages are reported to have been 5.3, 3.4 and 6.5 Ma, respectively. This review of the present status of Upper Jurassic stratigraphy aids identification of a num- ber of problems of subdivision and definition of Upper Jurassic stages; in particular these include correlation of the base of the Kimmeridgian and the top of the Tithonian between Submediterranean and Subboreal Europe. Although still primarily based on ammonite stratigraphy, subdivision of the Upper Jurassic is increasingly being refined by the incorporation of other fossil groups; these include both megafossils, such as aptychi, belemnites, bivalves, gastropods, brachiopods, echino- derms, corals, sponges and vertebrates, and microfossils such as foraminifera, radiolaria, ciliata, ostracodes, dinoflagellates, calcareous nannofossils, charophyaceae, dasycladaceae, spores and pollen. Important future developments will depend on the detailed integration of these disparate biostratigraphic data and their precise combination with the abundant new data from sequence stratigraphy, utilising the high degree of stratigraphic resolution offered by certain groups of fos- sils.
  • Ammonoid Intraspecific Variability

    Ammonoid Intraspecific Variability

    Zurich Open Repository and Archive University of Zurich Main Library Strickhofstrasse 39 CH-8057 Zurich www.zora.uzh.ch Year: 2015 Ammonoid Intraspecific Variability De Baets, Kenneth ; Bert, Didier ; Hoffmann, René ; Monnet, Claude ; Yacobucci, Margaret M;Klug, Christian Abstract: Because ammonoids have never been observed swimming, there is no alternative to seeking indirect indications of the locomotory abilities of ammonoids. This approach is based on actualistic com- parisons with the closest relatives of ammonoids, the Coleoidea and the Nautilida, and on the geometrical and physical properties of the shell. Anatomical comparison yields information on the locomotor muscu- lar systems and organs as well as possible modes of propulsion while the shape and physics of ammonoid shells provide information on buoyancy, shell orientation, drag, added mass, cost of transportation and thus on limits of acceleration and swimming speed. On these grounds, we conclude that ammonoid swim- ming is comparable to that of Recent nautilids and sepiids in terms of speed and energy consumption, although some ammonoids might have been slower swimmers than nautilids. DOI: https://doi.org/10.1007/978-94-017-9630-9_9 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-121836 Book Section Accepted Version Originally published at: De Baets, Kenneth; Bert, Didier; Hoffmann, René; Monnet, Claude; Yacobucci, Margaret M; Klug, Christian (2015). Ammonoid Intraspecific Variability. In: Klug, C; Korn, D; De Baets, K; Kruta, I; Mapes, R H. Ammonoid Paleobiology: From anatomy to ecology. Dordrecht: Springer, 359-426. DOI: https://doi.org/10.1007/978-94-017-9630-9_9 Chapter 9 Ammonoid Intraspecific Variability Kenneth De Baets, Didier Bert, René Hoffmann, Claude Monnet, Margaret M.