75Bollettino della Società Paleontologica Italiana, 49 (1), 2010, 75-81. Modena, 15 maggio 2010

ISSN 0375-7633

INTRODUCTION

Nautiloid cephalopods of the Carnic Alps are wellknown since the second half of the eighteenth century. In1872, the Austrian geologist Guido Stache (1833-1921)pointed out for the first time the occurrence of theSilurian rocks in the Carnic Alps. Successively herecorded “Orthoceras limestones” in many localities ofthe Carnic area and collected a great number ofcephalopod specimens, but did not produce anysystematic work. In 1887, Fritz Frech (1861-1917), aGerman geologist, in “Über das Devon der Ostalpen, nebstBemerkungen über das Silur und einempaläontologischem Anhang”, described two species ofnautiloid cephalopods: Orthoceras potens andOrthoceras alticola.

The first systematic work on cephalopod fauna, fromthe Silurian outcrops, is dated to 1909: the Italiangeologists Michele Gortani (1883-1966) and PaoloVinassa de Regny (1871-1957) described 18 species ofcephalopods from Italian side of the of the Carnic Alps.

In 1929, Franz Heritsch (1882-1945) published“Faunen aus dem Silur der Ostalpen”, a detailedpalaeontological systematic study on Silurian cephalopodfaunas with specimens collected by himself and withmaterial, stored in the Geological Survey of Vienna, andbelonging to collections of von Gaertner, Geyer andStache.

Palaeontological studies on cephalopod fauna stoppedafter the Second World War. Only in 1968 HeinrichRistedt, from the Bonn University, published an essentialwork on cephalopod early stages and protoconchs, withspecimens coming from the terranes forming thenorthern margin of Gondwana during the Silurian.Renewed interest for the research on cephalopods arose

close to the end of the century thanks to Gnoli & Histon(1998), Histon (1999), Serventi (1999), Serventi et al.(1999), Gnoli et al. (2000), Serventi & Gnoli (2000),Serventi (2002) and Gnoli & Serventi (2006).

The main investigated cephalopod faunas concernmembers of the orders Orthocerida Kuhn, 1940,Oncocerida Flower in Flower & Kummel, 1950,Barrandeocerida Flower in Flower & Kummel, 1950,Discosorida Flower in Flower & Kummel, 1950 andNautilida Agassiz, 1847.

Except few fragmentary specimens reported byServenti & Gnoli (2000) and left in open nomenclature,members of the order Actinocerida Teichert 1933, havenot been studied. The goal of this paper is to describe anew material of actinoceroids collected in the Italian sideof the Carnic Alps in the Mt. Cocco area (Fig. 1) and storedin the Museo Friulano di Storia Naturale, Udine, and inPalaeontological collections of the University of Modenaand Reggio Emilia.

GEOLOGICAL REMARKS

In the Friuli Venezia Giulia region (in the northeasternpart of Italy) three mountain chains are welded together:the Palaeocarnic chain, the eastern section of the SouthAlpine chain and the northwestern part of the OuterDinarides. The Palaeocarnic chain, about 180 km long(from Comelico to Caravanche) and 10-20 km wide,presents a metamorphic part, confined in the northwesternsector, and a non-metamorphic part represented by analmost continuous Palaeozoic sedimentary succession(Carulli, 2006) (Fig. 1). The Palaeozoic outcrops, veryrich in palaeontological remains, range from the UpperOrdovician to Permian.

Actinocerid cephalopods from the Silurian of the Carnic Alps (Italy)

Paolo SERVENTI, Maurizio GNOLI & Luca SIMONETTO

P. Serventi, Dipartimento di Scienze della Terra, Università degli Studi di Modena e Reggio Emilia, L.go S. Eufemia 19, I-41121 Modena, Italy;paolo.serventi@unimore.it

M. Gnoli, Dipartimento di Scienze della Terra, Università degli Studi di Modena e Reggio Emilia, L.go S. Eufemia 19, I-41121 Modena, Italy;maurizio.gnoli@unimore.it

L. Simonetto, Museo Friulano di Storia Naturale, Via Marangoni 39, I-33100 Udine, Italy; mfsn@comune.udine.it

KEY WORDS - Cephalopoda, Actinocerida, Armenoceratidae, Huroniidae, Ormoceratidae, Carnic Alps, Silurian, Italy.

ABSTRACT - Silurian actinocerid cephalopods from the Italian side of the Carnic Alps are reported on the basis of newly collectedmaterial. Three actinocerid taxa, belonging to Armenoceratidae, Huroniidae, and Ormoceratidae families, are described and left in opennomenclature.

RIASSUNTO - [Cefalopodi actinoceridi nel Siluriano delle Alpi Carniche (versante italiano)] - Materiale raccolto nel corso di recenticampagne di studio condotte nel versante italiano delle Alpi Carniche ha permesso di individuare alcuni esemplari di cefalopodi appartenentiall’ordine Actinocerida Teichert,1933. Si tratta di tre specie attribuibili ai generi Elrodoceras Foreste,1924, Huroniella Foreste,1024 e OrmocerasStokes,1840 che, a causa del precario stato di conservazione, sono temporaneamente lasciate in nomenclatura aperta. La presenza nelle AlpiCarniche di cefalopodi actinoceridi permette di aumentare le conoscenze relative alla distribuzione paleogeografica della fauna a cefalopodidurante il Siluriano.

07 S ti t l P65 09/06/10 13 4075

76 Bollettino della Società Paleontologica Italiana, 49 (1), 2010

The Silurian deposits show wide lateral faciesdiversity, a limited total thickness (50-100 m) and areirregularly distributed within the Carnic Alps. It is possibleto find bioclastic limestones testifying a shallow water

environment, cephalopod-bearing limestones,intercalations of limestones with shales and finally blackgraptolitic shales and cherts testifying deep water basinalenvironment (Corradini & Simonetto, 2006). Thisjustifes the subdivision of the Silurian rocks in four majorfacies (Selli, 1963; Schönlaub, 1997, 1998; Wenzel,1997), reflecting the depths and the differenthydrodynamic conditions of the environments (Fig. 1).Proceeding from North-West towards South-East, it ispossible to find: the Wolayer facies, characterized byshallow-water sediments, the Plocken and the Findenigfacies, with intermediate conditions, and finally theBischofalm facies with deep-water sediments. FromLlandovery to Ludlow, Silurian sedimentation showsgenerally a transgressive trend, whereas a diffuse Pridolicarbonate sedimentation shows a more steady conditions(Schönlaub, 1997). Most of Llandovery and sometimesalso the lower Wenlock are lacking due to a significantgap between Ordovician and Silurian sediments (Histon& Schönlaub, 1999).

SOME REMARKS ON ACTINOCERIDA

The order Actinocerida ranging from MiddleOrdovician to late Carboniferous is represented bycephalopods having mainly slender and straight or in somecases slightly curved orthoconic shell. The specimens ofthis order are medium to large in size, ranging from 90cm to 6 m (genus Rayonnoceras Teichert, 1964). Thecross section is generally circular to subcircular, thoughsome specialized genera have the conch stronglycompressed and flattened. The inner features aredistinctive and diagnostic: siphuncle is large, subcentralto marginal in position with broadly expanded segments.The septal necks in actinocerids are cyrtochoanitic. Inmany families (e.g. Armenoceratidae) the septal neck isstrongly recumbent and the brim is near to or in contactwith the inferior part of the septa. Epi/hyposeptalcalcareous cameral deposits are well developed, as wellas endosiphuncular deposits. In mature stage of the conchthe endosiphuncular deposits may fill the space, producinga typical endosiphuncular canal system, which is “… aprimary organic feature” (Flower, 1955; Teichert, 1964).

Teichert (1933) elevated this taxon to ordinal leveland attempted to link actinocerids to endocerids because

Fig. 1 - Location of the Carnic Alps (A), locality map of the Mt.Cocco area outcrop (indicated by an asterisk) (B), lithology of Siluriansediments of the four different lithofacies of the Carnic Alps (C)(after Wenzel, 1997).

EXPLANATION OF PLATE 1

Fig. 1 - Elrodoceras sp. ind. A. Specimen IPUM 27969.1a - Polished oblique section preserving the last chamber of phragmocone, x 1.5;1b - detail showing the central siphuncle with annular deposits more developed on the ventral side, x 3;1c - enlarged detail showing the dorsal annular deposit, the recumbent septal neck and the trend of the connecting ring in its proximal

part, x 8.5;1d - enlarged detail of the above reported features in the ventral side of the septal foramen, x 7;1e - schematic draft showing the septal neck.

Fig. 2 - Huroniella? sp. ind. Specimen IPUM 27970.2a - Longitudinal polished section showing three chambers, the wide sub-central siphuncle and the preserved inner features, x 2;2b - enlarged detail of the strongly recumbent actinocerid septal neck with funnel-like huronionid adnation area, x 10;2c - schematic draft showing the transversal section with the shaded area indicates available material;2d - schematic draft showing the septal neck.

07 S ti t l P65 19/05/10 12 5376

77P. Serventi et al. - Silurian nautiloid cephalopods from the Carnic Alps Pl. 1

07 S ti t l P65 19/05/10 12 5377

78 Bollettino della Società Paleontologica Italiana, 49 (1), 2010

large siphuncles and long septal necks. According toKobayashi (1935) and Schindewolf (1935) actinocerids,with small siphuncles (species belonging to generaOrmoceras or Sactoceras), arose from Michelino-ceratida. In 1941, Flower proposed that Actinoceridaoriginated from Bathmoceras inside the Ellesme-roceratida (Upper Canadian), through Polydesmia “as theoldest and most primitive genus” (Flower, p. 12) starts inmiddle Arenigian (Teichert, 1933; Flower, 1957, 1968).

Some authors discussed the systematic position ofactinocerids (see, e. g., Mutvei, 1997, 2002a, 2002b;Evans, 2005; Kröger & Mapes, 2007), for exampleMutvei stressed out the importance of connecting ringstructure and of muscle scars.

In our opinion the distinctive peculiar features ofactinoceroid cephalopods among others seem thoseconcerning the wide siphuncle and in particular the shapeof long curved septal necks, the endosiphuncular canalssystem and associated primary deposits.

FOSSIL PRESERVATION

All the studied specimens, with few exceptions, arefragmentary and affected by dissolution and/or stronglyrecrystallized. This occasionally makes impossible tostudy internal structures - connecting rings or siphuncularand cameral deposits - important in cephalopodtaxonomy. Preparation of fossils, consequently, has beenquite difficult as the majority of specimens are embeddedin a hard matrix with high iron-manganese mineralization.

Institutional abbreviations - IPUM: Museo diPaleontologia dell’Università di Modena e Reggio Emilia;MFSNgp: Museo Friulano di Storia Naturale, collezionegeologica-paleontologica.

SYSTEMATIC PALAEONTOLOGY

The taxonomic scheme adopted here is mainly thatreported in the Treatise Part K, Mollusca 3 (Teichert,1964) with integrations from the Data Retrieval SystemNautiloidea by T. Engeser, available on CD ROM thanksto the courtesy of the author. Proposed systematics byDzik (1984) is also taken into account.

The terminology employed is essentially thatadvocated by Flower (1964) including the terms adapical(towards the apex of the shell) and adoral (towards theaperture).

Order ACTINOCERIDA Teichert, 1933Family ARMENOCERATIDAE Troedsson, 1926

Genus Elrodoceras Foerste, 1924

Type species - Cyrtoceras indianense Miller, 1892by original designation.

Remarks - The genus Elrodoceras Foerste, 1924 wasregarded by Dzik (1984: p. 147) as a junior subjectivesynonym for Ormoceras Stokes, 1840 and later re-established by Holland (1998: p. 189). In the opinion ofthe writers the main difference between the reportedgenera is the wider adnation area shown by the siphuncularfeatures of Elrodoceras.

Elrodoceras sp. ind. A(Pl. 1, fig. 1)

2000 Ormoceras sp. A SERVENTI & GNOLI, p. 11, pl. 1, fig. 1a-b.

Material studied - One fragment of phragmoconeregistered under the number IPUM 27969.

Description - The material consists of one shortfragment of phragmocone, 54 mm long, of orthoconic(presumably slender) shell where only one chamber ispreserved. Chamber long being 2/5 its diameter; septadepth corresponds to 0.45 diameter; wide centralsiphuncle whose diameter is 4.6 mm at septal foramen.Barrel-like connecting rings reaching a diameter of about13 mm in its middle part. Very short actinoceridrecumbent septal necks being of length 0.4 mm with 1mm long brim. Endosiphuncular deposit in form of annulimainly developed on the ventral side (Pl. 1, fig. 1b),showing alternate light and dark growth layers. No outerornamentation is preserved.

Remarks - Due to impossibility to extract thespecimen from the recrystallized hard matrix, internalfeatures of the shell have been studied in a longitudinalpolished section. Outline trend of the proximal parts ofthe preserved connecting ring allows us to assume withgoodness of fit the measurement of the max. middlediameter of the siphuncular segments close to 13 mm.The shape of the strongly recumbent septal necks, theendosiphuncular annular deposits, and wide adnation areaallow the assignment to the genus Elrodoceras. Due tothe lack of any information either on the outer

EXPLANATION OF PLATE 2

Fig.1 - Ormoceras sp. ind. A. Specimen MFSNgp 23221.1a - Outer view, x 1.2;1b - longitudinal polished section showing about six chambers and the relatively narrow central siphuncle, x 1.3;1c - enlarged detail of the septal foramen area showing the recumbent septal neck and the trend of the connecting rings in their

proximal part, x 10;1d - the same dorsal part enlarged, x 20;1e - schematic draft showing the septal neck.

07 S ti t l P65 09/06/10 13 4078

79Pl. 2P. Serventi et al. - Silurian nautiloid cephalopods from the Carnic Alps

07 S ti t l P65 19/05/10 12 5379

80 Bollettino della Società Paleontologica Italiana, 49 (1), 2010

ornamentation or on the most of the inner features, thespecimen is left in open nomenclature.

Stratigraphy and geographic distribution - Silurianof Mt. Cocco, Carnic Alps.

Family HURONIIDAE Foerste & Teichert, 1930

Genus Huroniella Foerste, 1924

Type species - Huronia inflecta Parks, 1915 byoriginal designation.

Huroniella? sp. ind.(Pl. 1, fig. 2)

Material studied - One fragment of phragmoconeregistered under the number IPUM 27970.

Description - Short fragment of phragmocone of alarge orthoconic shell 41.5 mm long preserving aboutthree chambers whose length corresponds medially to 14mm. Sub-central wide actinocerid siphuncle whosediameter reaching 28 mm. Septal necks short and stronglyrecumbent being 0.4 mm with a brim of 1.4 mm. Funnel-shaped adnation area corresponds to 5.3 mm. Barrel-likeconnecting rings expanded in the chambers in its middlepart about 7.2 mm from the line connecting twosubsequent septal necks. No other features are preserved.

Remarks - Estimated diameter of the specimen isabout 80 mm. The characteristic outline of the funnel-like adnation area and the strongly recumbent septal necksallow, even dubitatively, to assign this specimen to genusHuroniella.

Stratigraphy and geographic distribution - Silurianof Mt. Cocco, Carnic Alps.

Family ORMOCERATIDAE Saemann, 1853

Genus Ormoceras Stokes, 1840

Type species - Ormoceras bayfieldi Stokes, 1840 bysubsequent designation (Bassler, 1915).

Ormoceras sp. ind. A(Pl. 2, fig. 1)

2000 Ormoceras? sp. B SERVENTI & GNOLI, p. 11, pl. 1, figs. 3a-b.

Material studied - One fragment of phragmoconeunder the number MFSNgp 23221.

Description - Available material consists of onefragment of phragmocone of an orthoconic shell, 85 mmlong, gradually expanding with an angle close to 4 degrees.Six chambers are preserved.

Chambers depth about 2/5 their diameter. Septamoderately concave corresponding to about 1/4 their

diameter. Sub-central siphuncle with a mean diameter of3.5 mm at septal foramina, but reaching its max. value inthe middle part of the connecting rings with a diameterof 10 mm representing about 1/3 the shell diameter.Septal foramina are 2.8 mm across, corresponding toabout 1/10 the shell diameter.

Septal necks of actinocerid type are very short andrecumbent being in length 0.6 mm with a 1.8 mm longbrim (Pl. 2, fig. 1d).

Remarks - This fragmentary specimen is assigned tothe genus Ormoceras mainly because of the peculiarsiphuncular outlines. In particular the recumbent septalnecks and an adnation area are less developed than in thespecimen mentioned above and referred to Elrodoceras.The brim shape is similar to that noted in members ofElrodoceras, but the minor development of the adnationarea is closer to the genus Ormoceras. Incompletepreservation suggests to leave this form in opennomenclature.

Stratigraphy and geographic distribution - Silurianof Mt. Cocco, Carnic Alps.

ACKNOWLEDGEMENTS

Thanks are due to Dr. Carlo Morandini, director of MFSN forgiving available for study fossil specimens stored in the Museum.The authors are deeply indebted to Prof. Enrico Serpagli, Dr. V.Turek and an anonymous referees for the critical reading of theMS, useful suggestions and advises. Dr. Theo Engeser give usavailable his CD compilation Data Retrieval System Nautiloidea.

This research was funded by PRIN “Quo vadis, northGondwana? - Regional palaeogeography and migrational seawaysof pelagic organisms in the Early Palaeozoic” project grant(responsible Prof. Annalisa Ferretti).

REFERENCES

Bassler R.S. (1915). Bibliographic index of American Ordovicianand Silurian Fossils. Bulletin of the United States NationalMuseum, 92: 1-1521.

Carulli G.B. (2006). Inquadramento geologico del Friuli. In CorradiniC., Muscio G. &. Simonetto L. (eds.), Escursione in Friuli.Giornate di Paleontologia 2006: 65-66.

Corradini C. & Simonetto L. (2006). Il Siluriano e DevonianoInferiore carnico: la sezione “Rio Malinfier”. In Corradini C.,Muscio G. & Simonetto L. (eds.), Escursione in Friuli. Giornatedi Paleontologia 2006: 114-115.

Dzik J. (1984). Phylogeny of the Nautiloidea. PalaeontologiaPolonica, 45: 3-203.

Evans D. (2005). The lower and middle Ordovician Cephalopodfaunas of England and Wales. Monograph of the Palaeontog-raphical Society, London: 1-81 (Publ. No. 623, part of vol. 158for 2004).

Flower R.H. (1941). Notes on the structure and phylogeny ofeurysiphonate cephalopods. Palaeontographica Americana, 3:5-51.

Flower R.H. (1955). Status of Endoceroid Classification. Journalof Paleontology, 28(3): 329-371.

Flower R.H. (1957). The Ordovician development of theActinoceratida. New Mexico Institute of Mines and Technology,State Bureau of Mines and Mineral research, Mem. 2: 1-62.

Flower R.H. (1964). Nautiloid shell morphology. New Mexico Instituteof Mines and Technology, State Bureau of Mines and Mineralresearch, Mem. 13: 1-75.

07 S ti t l P65 19/05/10 12 5480

81

Flower R.H. (1968). The first great expansion of the Actinoceroids.New Mexico Institute of Mines and Technology, State Bureau ofMines and Mineral research, Mem. 19: 1-120.

Foerste A.F. (1924). Silurian Cephalopods of Northern Michigan.Contributions from the Museum of Geology University ofMichigan, 2: 19-120.

Foerste A.F. & Teichert, C. (1930). The Actinoceroids of East-centralNorth America. Denison University Bulletin, Journal of theScientific Laboratories, 25: 201-296.

Frech F. (1887). Uber das Devon des Ostalpen, nebst Bemerkungenuber das Silur und einem paläontologischen Anhang. Zeitschriftder Deutsche Geophysikalische Gesellschaft, 39: 659-738.

Gnoli M. & Histon K. (1998). Silurian Nautiloid cephalopods fromthe Carnic Alps: a preliminary investigation. Bollettino dellaSocietà Paleontologica Italiana, 36: 311-330.

Gnoli M., Histon K. & Serventi P. (2000). Revision of Siluriancephalopods from the Carnic Alps: the Gortani and Vinassa deRegny collection, 1909. Bollettino della Società PaleontologicaItaliana, 39: 3-12.

Gnoli M. & Serventi P. (2006). Indagine preliminare su stadi giovanilie protoconche di nautiloidi dal Siluriano delle Alpi Carniche. InFonda G., Melis R. & Romano R. (eds.), Giornate di Paleontologia2006, Trieste, Abstracts: 42.

Gortani M. & Vinassa de Regny P. (1909). Fossili neosilurici delPizzo di Timau e dei Pal nell’Alta Carnia. Memorie della RealeAccademia dell’Istituto di Scienze, Bologna: 183-217.

Heritsch F. (1929). Faunen aus dem Silur der Ostenalpen.Abhandlungen der Geologischen Bundesanstalt, 23: 1-183.

Histon K. (1999). Revision of Silurian nautiloid Cephalopods fromthe Carnic Alps (Austria) - The Heritsch (1929) Collection inthe Geological Survey of Austria. Abhandlungen derGeologischen Bundesanstalt, 56 (1): 229-258.

Histon K. & Schönlaub H.P. (1999). Taphonomy, Palaeocology andTaphonomy implications of the Nautiloid fauna from the Silurianof the Cellon Section (Carnic Alps, Austria). Abhandlungen derGeologischen Bundesanstalt, 54: 259-274.

Holland C.H. (1998). The Nautiloid cephalopod Order Actinoceridain the British Silurian. Palaeontology, 41: 183-192.

Kobayashi T. (1935). Restudy on Manchuroceras with a brief noteon the classification of the endoceroids. Journal of theGeological Society of Japan, 42: 736-752.

Kröger B. & Mapes R. (2007). Carboniferous actinoceratoidsNautiloidea (Cephalopoda) – a new perspective. Journal ofPaleontology, 81 (4): 714-724.

Miller S. A. (1892). Palaeontology: Indiana Department of Geologyand Natural Resources, 17th Annual Report (1891): 611-705.

Mutvei H. (1997). Characterization of actinoceratoid cephalopodsby their siphuncular structure. Lethaia, 29: 339-348.

Mutvei H. (2002a). Connecting ring structure and its significancefor classification of the orthoceratid cephalopods. ActaPalaeontologica Polonica, 47 (1): 157-168.

Mutvei H. (2002b). Nautiloid systematics based on siphuncularstructure and position of the muscle scars. Abhandlungen derGeologischen Bundesanstalt, 57: 379-392.

Parks W. A. (1915). Palaeozoic fossils from a region southwest ofHudson Bay; a description of the fossils collected by Joseph B.

Tyrrel, Esq., F.R.S.C. in the Discrit of Patricia, Ontario, and innorther Manitoba during the summer of 1912. Transaction ofthe Royal Canadian Institute, 11: 1-95.

Saemann L. (1854). Über die Nautiliden. Palaeontographica, 3: 121-167.

Schindewolf O.H. (1935). Bemerkungen zur Ontogenese derActinoceren und Endoceren (Ceph. Nautil.). Neues Jahrbuchfür Mineralogie, Geologie und Paläontologie, Beilage-Band, 74B:89-113.

Schönlaub H.P. (1997). The Silurian of Austria. In Schönlaub H.P.(ed.), IGCP-421 Inaugural Meeting Vienna. Berichte derGeologischen Bundesanstalt, 33: 1-124.

Schönlaub H.P. (1998). Review of the Paleozoic Paleogeography ofthe Southern Alps - The perspective from the Austrian side. InPerri M.C. & Spalletta C. (eds.) Giornale di Geologia, s.3, 60Special Issue: 59-68.

Selli R. (1963). Schema geologico delle Alpi Carniche e Giulieoccidentali. Giornale di Geologia, s.2, 30: 1-136.

Serventi P. (1999). Some new Silurian cephalopods from the Italianside of the Carnic Alps. In Histon K. (ed.), V° InternationalSymposium Cephalopods - Present and Past, Vienna. Abstractvolume. Berichte der Geologischen Bundesanstalt, 46: 103.

Serventi P. (2002). Nuova segnalazione di Cefalopode ortocono dalSiluriano delle Alpi Carniche. Giornate di Paleontologia 2002,Abstracts: 50.

Serventi P. & Gnoli M. (2000). Nuovi ritrovamenti di Cefalopodinautiloidei nelle Alpi Carniche. Giornale di Geologia, s. 3, 62,Suppl.: 9-14.

Serventi P., Gnoli M. & Histon K. (1999). Revision of SilurianNautiloid cephalopods from the Carnic Alps from variousmuseum collections. In Histon K. (ed.), V° InternationalSymposium Cephalopods - Present and Past, Vienna. Abstractvolume. Berichte der Geologischen Bundesanstalt, 46: 104.

Stache G. (1872). Der Graptolithenschiefer am Osternig-Berge inKärnten. Jahrbuch der Geologischen Reichsanstalt, A., 23: 175-248.

Stokes C. 1840. On some species of Orthocerata. Transactions ofthe Geological Society of London, s. 2, 5: 705-714.

Teichert C. (1933). Der Bau der actinoceroiden Cephalopoden.Palaeontographica A, 78: 111-230.

Teichert C. (1964). Actinoceratoidea. In Moore, R.C. (ed.), Treatiseon Invertebrate Paleontology, Part K, Mollusca 3, K190-K216pp., The Geological Society of America and The University ofKansas Press.

Troedsson G. T. (1926). On the Middle and Upper Ordovician faunasof northern Greenland. I. Cephalopods. Meddelelser omGrönland, 71: 1-157.

Wenzel B. (1997). Isotopenstratigraphische Untersuchungen ansilurischen Abfolgen und deren paläozeanographisceInterpretation. Erlanger geologischen Abheilungen, 129: 1-117.

Manuscript received 17 October 2009Revised manuscript accepted 10 February 2010

P. Serventi et al. - Silurian nautiloid cephalopods from the Carnic Alps

07 S ti t l P65 19/05/10 12 5481