1 75 Bollettino della Società Paleontologica Italiana, 49 (1), 2010, Modena, 15 maggio 2010 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 Modena, Italy; M. Gnoli, Dipartimento di Scienze della Terra, Università degli Studi di Modena e Reggio Emilia, L.go S. Eufemia 19, I Modena, Italy; L. Simonetto, Museo Friulano di Storia Naturale, Via Marangoni 39, I Udine, Italy; 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 collected material. Three actinocerid taxa, belonging to Armenoceratidae, Huroniidae, and Ormoceratidae families, are described and left in open nomenclature. RIASSUNTO - [Cefalopodi actinoceridi nel Siluriano delle Alpi Carniche (versante italiano)] - Materiale raccolto nel corso di recenti campagne di studio condotte nel versante italiano delle Alpi Carniche ha permesso di individuare alcuni esemplari di cefalopodi appartenenti all ordine Actinocerida Teichert,1933. Si tratta di tre specie attribuibili ai generi Elrodoceras Foreste,1924, Huroniella Foreste,1024 e Ormoceras Stokes,1840 che, a causa del precario stato di conservazione, sono temporaneamente lasciate in nomenclatura aperta. La presenza nelle Alpi Carniche di cefalopodi actinoceridi permette di aumentare le conoscenze relative alla distribuzione paleogeografica della fauna a cefalopodi durante il Siluriano. INTRODUCTION Nautiloid cephalopods of the Carnic Alps are well known since the second half of the eighteenth century. In 1872, the Austrian geologist Guido Stache ( ) pointed out for the first time the occurrence of the Silurian rocks in the Carnic Alps. Successively he recorded Orthoceras limestones in many localities of the Carnic area and collected a great number of cephalopod specimens, but did not produce any systematic work. In 1887, Fritz Frech ( ), a German geologist, in Über das Devon der Ostalpen, nebst Bemerkungen über das Silur und einem paläontologischem Anhang, described two species of nautiloid cephalopods: Orthoceras potens and Orthoceras alticola. The first systematic work on cephalopod fauna, from the Silurian outcrops, is dated to 1909: the Italian geologists Michele Gortani ( ) and Paolo Vinassa de Regny ( ) described 18 species of cephalopods from Italian side of the of the Carnic Alps. In 1929, Franz Heritsch ( ) published Faunen aus dem Silur der Ostalpen, a detailed palaeontological systematic study on Silurian cephalopod faunas with specimens collected by himself and with material, stored in the Geological Survey of Vienna, and belonging to collections of von Gaertner, Geyer and Stache. Palaeontological studies on cephalopod fauna stopped after the Second World War. Only in 1968 Heinrich Ristedt, from the Bonn University, published an essential work on cephalopod early stages and protoconchs, with specimens coming from the terranes forming the northern 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 concern members of the orders Orthocerida Kuhn, 1940, Oncocerida Flower in Flower & Kummel, 1950, Barrandeocerida Flower in Flower & Kummel, 1950, Discosorida Flower in Flower & Kummel, 1950 and Nautilida Agassiz, Except few fragmentary specimens reported by Serventi & Gnoli (2000) and left in open nomenclature, members of the order Actinocerida Teichert 1933, have not been studied. The goal of this paper is to describe a new material of actinoceroids collected in the Italian side of the Carnic Alps in the Mt. Cocco area (Fig. 1) and stored in the Museo Friulano di Storia Naturale, Udine, and in Palaeontological collections of the University of Modena and Reggio Emilia. GEOLOGICAL REMARKS In the Friuli Venezia Giulia region (in the northeastern part of Italy) three mountain chains are welded together: the Palaeocarnic chain, the eastern section of the South Alpine chain and the northwestern part of the Outer Dinarides. The Palaeocarnic chain, about 180 km long (from Comelico to Caravanche) and km wide, presents a metamorphic part, confined in the northwestern sector, and a non-metamorphic part represented by an almost continuous Palaeozoic sedimentary succession (Carulli, 2006) (Fig. 1). The Palaeozoic outcrops, very rich in palaeontological remains, range from the Upper Ordovician to Permian. ISSN
2 76 Bollettino della Società Paleontologica Italiana, 49 (1), 2010 The Silurian deposits show wide lateral facies diversity, a limited total thickness ( m) and are irregularly distributed within the Carnic Alps. It is possible to find bioclastic limestones testifying a shallow water environment, cephalopod-bearing limestones, intercalations of limestones with shales and finally black graptolitic shales and cherts testifying deep water basinal environment (Corradini & Simonetto, 2006). This justifes the subdivision of the Silurian rocks in four major facies (Selli, 1963; Schönlaub, 1997, 1998; Wenzel, 1997), reflecting the depths and the different hydrodynamic conditions of the environments (Fig. 1). Proceeding from North-West towards South-East, it is possible to find: the Wolayer facies, characterized by shallow-water sediments, the Plocken and the Findenig facies, with intermediate conditions, and finally the Bischofalm facies with deep-water sediments. From Llandovery to Ludlow, Silurian sedimentation shows generally a transgressive trend, whereas a diffuse Pridoli carbonate sedimentation shows a more steady conditions (Schönlaub, 1997). Most of Llandovery and sometimes also the lower Wenlock are lacking due to a significant gap between Ordovician and Silurian sediments (Histon & Schönlaub, 1999). SOME REMARKS ON ACTINOCERIDA Fig. 1 - Location of the Carnic Alps (A), locality map of the Mt. Cocco area outcrop (indicated by an asterisk) (B), lithology of Silurian sediments of the four different lithofacies of the Carnic Alps (C) (after Wenzel, 1997). The order Actinocerida ranging from Middle Ordovician to late Carboniferous is represented by cephalopods having mainly slender and straight or in some cases slightly curved orthoconic shell. The specimens of this order are medium to large in size, ranging from 90 cm to 6 m (genus Rayonnoceras Teichert, 1964). The cross section is generally circular to subcircular, though some specialized genera have the conch strongly compressed and flattened. The inner features are distinctive and diagnostic: siphuncle is large, subcentral to marginal in position with broadly expanded segments. The septal necks in actinocerids are cyrtochoanitic. In many families (e.g. Armenoceratidae) the septal neck is strongly recumbent and the brim is near to or in contact with the inferior part of the septa. Epi/hyposeptal calcareous cameral deposits are well developed, as well as endosiphuncular deposits. In mature stage of the conch the endosiphuncular deposits may fill the space, producing a typical endosiphuncular canal system, which is a primary organic feature (Flower, 1955; Teichert, 1964). Teichert (1933) elevated this taxon to ordinal level and attempted to link actinocerids to endocerids because EXPLANATION OF PLATE 1 Fig. 1 - Elrodoceras sp. ind. A. Specimen IPUM a - 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 a - 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.
3 77 P. Serventi et al. - Silurian nautiloid cephalopods from the Carnic Alps Pl. 1
4 78 Bollettino della Società Paleontologica Italiana, 49 (1), 2010 large siphuncles and long septal necks. According to Kobayashi (1935) and Schindewolf (1935) actinocerids, with small siphuncles (species belonging to genera Ormoceras or Sactoceras), arose from Michelinoceratida. In 1941, Flower proposed that Actinocerida originated from Bathmoceras inside the Ellesmeroceratida (Upper Canadian), through Polydesmia as the oldest and most primitive genus (Flower, p. 12) starts in middle Arenigian (Teichert, 1933; Flower, 1957, 1968). Some authors discussed the systematic position of actinocerids (see, e. g., Mutvei, 1997, 2002a, 2002b; Evans, 2005; Kröger & Mapes, 2007), for example Mutvei stressed out the importance of connecting ring structure and of muscle scars. In our opinion the distinctive peculiar features of actinoceroid cephalopods among others seem those concerning the wide siphuncle and in particular the shape of long curved septal necks, the endosiphuncular canals system and associated primary deposits. FOSSIL PRESERVATION All the studied specimens, with few exceptions, are fragmentary and affected by dissolution and/or strongly recrystallized. This occasionally makes impossible to study internal structures - connecting rings or siphuncular and cameral deposits - important in cephalopod taxonomy. Preparation of fossils, consequently, has been quite difficult as the majority of specimens are embedded in a hard matrix with high iron-manganese mineralization. Institutional abbreviations - IPUM: Museo di Paleontologia dell Università di Modena e Reggio Emilia; MFSNgp: Museo Friulano di Storia Naturale, collezione geologica-paleontologica. SYSTEMATIC PALAEONTOLOGY The taxonomic scheme adopted here is mainly that reported in the Treatise Part K, Mollusca 3 (Teichert, 1964) with integrations from the Data Retrieval System Nautiloidea by T. Engeser, available on CD ROM thanks to the courtesy of the author. Proposed systematics by Dzik (1984) is also taken into account. The terminology employed is essentially that advocated by Flower (1964) including the terms adapical (towards the apex of the shell) and adoral (towards the aperture). Order ACTINOCERIDA Teichert, 1933 Family ARMENOCERATIDAE Troedsson, 1926 Genus Elrodoceras Foerste, 1924 Type species - Cyrtoceras indianense Miller, 1892 by original designation. Remarks - The genus Elrodoceras Foerste, 1924 was regarded by Dzik (1984: p. 147) as a junior subjective synonym for Ormoceras Stokes, 1840 and later reestablished by Holland (1998: p. 189). In the opinion of the writers the main difference between the reported genera is the wider adnation area shown by the siphuncular features 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 phragmocone registered under the number IPUM Description - The material consists of one short fragment of phragmocone, 54 mm long, of orthoconic (presumably slender) shell where only one chamber is preserved. Chamber long being 2/5 its diameter; septa depth corresponds to 0.45 diameter; wide central siphuncle whose diameter is 4.6 mm at septal foramen. Barrel-like connecting rings reaching a diameter of about 13 mm in its middle part. Very short actinocerid recumbent septal necks being of length 0.4 mm with 1 mm long brim. Endosiphuncular deposit in form of annuli mainly developed on the ventral side (Pl. 1, fig. 1b), showing alternate light and dark growth layers. No outer ornamentation is preserved. Remarks - Due to impossibility to extract the specimen from the recrystallized hard matrix, internal features of the shell have been studied in a longitudinal polished section. Outline trend of the proximal parts of the preserved connecting ring allows us to assume with goodness of fit the measurement of the max. middle diameter of the siphuncular segments close to 13 mm. The shape of the strongly recumbent septal necks, the endosiphuncular annular deposits, and wide adnation area allow the assignment to the genus Elrodoceras. Due to the lack of any information either on the outer EXPLANATION OF PLATE 2 Fig.1 - Ormoceras sp. ind. A. Specimen MFSNgp a - 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.
5 P. Serventi et al. - Silurian nautiloid cephalopods from the Carnic Alps 79 Pl. 2
6 80 Bollettino della Società Paleontologica Italiana, 49 (1), 2010 ornamentation or on the most of the inner features, the specimen is left in open nomenclature. Stratigraphy and geographic distribution - Silurian of Mt. Cocco, Carnic Alps. Family HURONIIDAE Foerste & Teichert, 1930 Genus Huroniella Foerste, 1924 Type species - Huronia inflecta Parks, 1915 by original designation. Huroniella? sp. ind. (Pl. 1, fig. 2) Material studied - One fragment of phragmocone registered under the number IPUM Description - Short fragment of phragmocone of a large orthoconic shell 41.5 mm long preserving about three chambers whose length corresponds medially to 14 mm. Sub-central wide actinocerid siphuncle whose diameter reaching 28 mm. Septal necks short and strongly recumbent being 0.4 mm with a brim of 1.4 mm. Funnelshaped adnation area corresponds to 5.3 mm. Barrel-like connecting rings expanded in the chambers in its middle part about 7.2 mm from the line connecting two subsequent septal necks. No other features are preserved. Remarks - Estimated diameter of the specimen is about 80 mm. The characteristic outline of the funnellike adnation area and the strongly recumbent septal necks allow, even dubitatively, to assign this specimen to genus Huroniella. Stratigraphy and geographic distribution - Silurian of Mt. Cocco, Carnic Alps. Family ORMOCERATIDAE Saemann, 1853 Genus Ormoceras Stokes, 1840 Type species - Ormoceras bayfieldi Stokes, 1840 by subsequent 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 phragmocone under the number MFSNgp Description - Available material consists of one fragment of phragmocone of an orthoconic shell, 85 mm long, gradually expanding with an angle close to 4 degrees. Six chambers are preserved. Chambers depth about 2/5 their diameter. Septa moderately concave corresponding to about 1/4 their diameter. Sub-central siphuncle with a mean diameter of 3.5 mm at septal foramina, but reaching its max. value in the middle part of the connecting rings with a diameter of 10 mm representing about 1/3 the shell diameter. Septal foramina are 2.8 mm across, corresponding to about 1/10 the shell diameter. Septal necks of actinocerid type are very short and recumbent being in length 0.6 mm with a 1.8 mm long brim (Pl. 2, fig. 1d). Remarks - This fragmentary specimen is assigned to the genus Ormoceras mainly because of the peculiar siphuncular outlines. In particular the recumbent septal necks and an adnation area are less developed than in the specimen mentioned above and referred to Elrodoceras. The brim shape is similar to that noted in members of Elrodoceras, but the minor development of the adnation area is closer to the genus Ormoceras. Incomplete preservation suggests to leave this form in open nomenclature. Stratigraphy and geographic distribution - Silurian of Mt. Cocco, Carnic Alps. ACKNOWLEDGEMENTS Thanks are due to Dr. Carlo Morandini, director of MFSN for giving 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 the MS, useful suggestions and advises. Dr. Theo Engeser give us available his CD compilation Data Retrieval System Nautiloidea. This research was funded by PRIN Quo vadis, north Gondwana? - Regional palaeogeography and migrational seaways of pelagic organisms in the Early Palaeozoic project grant (responsible Prof. Annalisa Ferretti). REFERENCES Bassler R.S. (1915). Bibliographic index of American Ordovician and Silurian Fossils. Bulletin of the United States National Museum, 92: Carulli G.B. (2006). Inquadramento geologico del Friuli. In Corradini C., Muscio G. &. Simonetto L. (eds.), Escursione in Friuli. Giornate di Paleontologia 2006: Corradini C. & Simonetto L. (2006). Il Siluriano e Devoniano Inferiore carnico: la sezione Rio Malinfier. In Corradini C., Muscio G. & Simonetto L. (eds.), Escursione in Friuli. Giornate di Paleontologia 2006: Dzik J. (1984). Phylogeny of the Nautiloidea. Palaeontologia Polonica, 45: Evans D. (2005). The lower and middle Ordovician Cephalopod faunas of England and Wales. Monograph of the Palaeontographical Society, London: 1-81 (Publ. No. 623, part of vol. 158 for 2004). Flower R.H. (1941). Notes on the structure and phylogeny of eurysiphonate cephalopods. Palaeontographica Americana, 3: Flower R.H. (1955). Status of Endoceroid Classification. Journal of Paleontology, 28(3): Flower R.H. (1957). The Ordovician development of the Actinoceratida. New Mexico Institute of Mines and Technology, State Bureau of Mines and Mineral research, Mem. 2: Flower R.H. (1964). Nautiloid shell morphology. New Mexico Institute of Mines and Technology, State Bureau of Mines and Mineral research, Mem. 13: 1-75.
7 P. Serventi et al. - Silurian nautiloid cephalopods from the Carnic Alps 81 Flower R.H. (1968). The first great expansion of the Actinoceroids. New Mexico Institute of Mines and Technology, State Bureau of Mines and Mineral research, Mem. 19: Foerste A.F. (1924). Silurian Cephalopods of Northern Michigan. Contributions from the Museum of Geology University of Michigan, 2: Foerste A.F. & Teichert, C. (1930). The Actinoceroids of East-central North America. Denison University Bulletin, Journal of the Scientific Laboratories, 25: Frech F. (1887). Uber das Devon des Ostalpen, nebst Bemerkungen uber das Silur und einem paläontologischen Anhang. Zeitschrift der Deutsche Geophysikalische Gesellschaft, 39: Gnoli M. & Histon K. (1998). Silurian Nautiloid cephalopods from the Carnic Alps: a preliminary investigation. Bollettino della Società Paleontologica Italiana, 36: Gnoli M., Histon K. & Serventi P. (2000). Revision of Silurian cephalopods from the Carnic Alps: the Gortani and Vinassa de Regny collection, Bollettino della Società Paleontologica Italiana, 39: Gnoli M. & Serventi P. (2006). Indagine preliminare su stadi giovanili e protoconche di nautiloidi dal Siluriano delle Alpi Carniche. In Fonda G., Melis R. & Romano R. (eds.), Giornate di Paleontologia 2006, Trieste, Abstracts: 42. Gortani M. & Vinassa de Regny P. (1909). Fossili neosilurici del Pizzo di Timau e dei Pal nell Alta Carnia. Memorie della Reale Accademia dell Istituto di Scienze, Bologna: Heritsch F. (1929). Faunen aus dem Silur der Ostenalpen. Abhandlungen der Geologischen Bundesanstalt, 23: Histon K. (1999). Revision of Silurian nautiloid Cephalopods from the Carnic Alps (Austria) - The Heritsch (1929) Collection in the Geological Survey of Austria. Abhandlungen der Geologischen Bundesanstalt, 56 (1): Histon K. & Schönlaub H.P. (1999). Taphonomy, Palaeocology and Taphonomy implications of the Nautiloid fauna from the Silurian of the Cellon Section (Carnic Alps, Austria). Abhandlungen der Geologischen Bundesanstalt, 54: Holland C.H. (1998). The Nautiloid cephalopod Order Actinocerida in the British Silurian. Palaeontology, 41: Kobayashi T. (1935). Restudy on Manchuroceras with a brief note on the classification of the endoceroids. Journal of the Geological Society of Japan, 42: Kröger B. & Mapes R. (2007). Carboniferous actinoceratoids Nautiloidea (Cephalopoda) a new perspective. Journal of Paleontology, 81 (4): Miller S. A. (1892). Palaeontology: Indiana Department of Geology and Natural Resources, 17th Annual Report (1891): Mutvei H. (1997). Characterization of actinoceratoid cephalopods by their siphuncular structure. Lethaia, 29: Mutvei H. (2002a). Connecting ring structure and its significance for classification of the orthoceratid cephalopods. Acta Palaeontologica Polonica, 47 (1): Mutvei H. (2002b). Nautiloid systematics based on siphuncular structure and position of the muscle scars. Abhandlungen der Geologischen Bundesanstalt, 57: Parks W. A. (1915). Palaeozoic fossils from a region southwest of Hudson Bay; a description of the fossils collected by Joseph B. Tyrrel, Esq., F.R.S.C. in the Discrit of Patricia, Ontario, and in norther Manitoba during the summer of Transaction of the Royal Canadian Institute, 11: Saemann L. (1854). Über die Nautiliden. Palaeontographica, 3: Schindewolf O.H. (1935). Bemerkungen zur Ontogenese der Actinoceren und Endoceren (Ceph. Nautil.). Neues Jahrbuch für Mineralogie, Geologie und Paläontologie, Beilage-Band, 74B: Schönlaub H.P. (1997). The Silurian of Austria. In Schönlaub H.P. (ed.), IGCP-421 Inaugural Meeting Vienna. Berichte der Geologischen Bundesanstalt, 33: Schönlaub H.P. (1998). Review of the Paleozoic Paleogeography of the Southern Alps - The perspective from the Austrian side. In Perri M.C. & Spalletta C. (eds.) Giornale di Geologia, s.3, 60 Special Issue: Selli R. (1963). Schema geologico delle Alpi Carniche e Giulie occidentali. Giornale di Geologia, s.2, 30: Serventi P. (1999). Some new Silurian cephalopods from the Italian side of the Carnic Alps. In Histon K. (ed.), V International Symposium Cephalopods - Present and Past, Vienna. Abstract volume. Berichte der Geologischen Bundesanstalt, 46: 103. Serventi P. (2002). Nuova segnalazione di Cefalopode ortocono dal Siluriano delle Alpi Carniche. Giornate di Paleontologia 2002, Abstracts: 50. Serventi P. & Gnoli M. (2000). Nuovi ritrovamenti di Cefalopodi nautiloidei nelle Alpi Carniche. Giornale di Geologia, s. 3, 62, Suppl.: Serventi P., Gnoli M. & Histon K. (1999). Revision of Silurian Nautiloid cephalopods from the Carnic Alps from various museum collections. In Histon K. (ed.), V International Symposium Cephalopods - Present and Past, Vienna. Abstract volume. Berichte der Geologischen Bundesanstalt, 46: 104. Stache G. (1872). Der Graptolithenschiefer am Osternig-Berge in Kärnten. Jahrbuch der Geologischen Reichsanstalt, A., 23: Stokes C On some species of Orthocerata. Transactions of the Geological Society of London, s. 2, 5: Teichert C. (1933). Der Bau der actinoceroiden Cephalopoden. Palaeontographica A, 78: Teichert C. (1964). Actinoceratoidea. In Moore, R.C. (ed.), Treatise on Invertebrate Paleontology, Part K, Mollusca 3, K190-K216 pp., The Geological Society of America and The University of Kansas Press. Troedsson G. T. (1926). On the Middle and Upper Ordovician faunas of northern Greenland. I. Cephalopods. Meddelelser om Grönland, 71: Wenzel B. (1997). Isotopenstratigraphische Untersuchungen an silurischen Abfolgen und deren paläozeanographisce Interpretation. Erlanger geologischen Abheilungen, 129: Manuscript received 17 October 2009 Revised manuscript accepted 10 February 2010