Cephalopod Fauna Research Articles

Long-term annual trawl data show shifts in cephalopod community in the western Barents sea during 18 years

Climate change is threatening marine ecosystems on a global scale but particularly so in the Arctic. As a result of warming, species are shifting their distributions, altering marine communities and predator-prey interactions. This is known as the Atlantification of the Arctic. Warming may favor short-lived, opportunistic species such as cephalopods, marine mollusks that previously have been hypothesized to be winners in an ocean of change. To detect temporal regional trends in biodiversity, long-term annual surveys in hotspots of climate change are an unparalleled source of data. Here, we use 18 years of annual bottom trawl data (2005–2022) to analyse cephalopods in the western Barents Sea. More specifically, our research goals are to assess temporal trends in cephalopod fauna composition, abundance and biomass, and to relate these trends to climate change in the western Barents Sea. Main changes in cephalopod diversity and distribution occurred in mid-2000s and early 2010s, which corresponds with a period of warming in the Arctic since the late 1990s/early 2000s. Repeated increased occurrence of the boreal-subtropical cephalopods was recorded from 2005–2013 to 2014–2022. Moreover, the abundance of cephalopods in the area (in general and for most taxa) increased from 2005–2013 to 2014–2022. These observations suggest that the cephalopod community of the Barents Sea is subjected to Atlantification since the 2005–2013 period. This corresponds with previously reported evidence of the Atlantification in fishes and benthic invertebrates in the Barents Sea and benthic invertebrates. ‘Typical’ Arctic cephalopod species such as Bathypolypus spp., Gonatus fabricii and Rossia spp., however, are still much more abundant in the western Barents Sea compared to the deep-sea and the boreal-subtropical species. We also found indirect indications for body-size reduction in Bathypolypus spp. from 2005–2013 to 2014–2022. Overall, the temporal trends in the Barents Sea cephalopod fauna provide evidence for changing marine communities in the Arctic.

Rare Middle Triassic coleoids from the Alpine-Carpathian system: new records from Slovakia and their significance

Two stratigraphically well constrained (by ammonites and conodonts) coleoid remains have been recorded from the Triassic (Anisian) dark-grey organodetritic limestones (Ráztoka Limestone) of Western Carpathians (Hronic Nappe). The limestones deposited at the periphery of a former carbonate platform. It yields a highly diverse cephalopod fauna including nautiloids (2 taxa), ammonoids (7 taxa) and indetermined aulacoceratids. Two unusual coleoid specimens are referred to genus Mojsisovicsteuthis (M. boeckhi) and probably to a new taxon (described as Breviconoteuthis aff. breviconus herein) possessing similar morphological features of genus Breviconoteuthis (Phragmoteuthida) and/or Zugmontites. Based on index ammonites and conodonts, both records are of the uppermost Trinodosus through the lowermost Reitzi zones (Anisian—lower Illyrian). While the genus Mojsisovicsteuthis has been widely dispersed (however its records are rare), the occurrence of Breviconoteuthis and Zugmontites is strictly limited to the Alpine-Carpathian region. Comparing with the holotype and additional specimens stored in the Hungarian Natural History Museum, the overal shell of Mojsisovicsteuthis and its size has been reconstructed. Its relationship to aulacoceratids and phragmoteuthids is briefly discussed. Geochemical record (n-alkanes from the bulk rock) provided a relevant signal of the existence of algal meadows.

MIDDLE TRIASSIC (ANISIAN) CEPHALOPODS FROM THE MECSEK MOUNTAINS, HUNGARY

Recent nautiloid and ammonoid finds from the Middle Triassic Zuhánya Limestone Formation in the Mecsek Mountains (south Hungary) proved that the formation encompasses the whole Pelsonian and the lower Illyrian substages of the Anisian Stage. On the basis of 11 identified ammonoid species, the Balatonicus and Trinodosus zones have a complete record. The stratigraphical position of the Zuhánya Limestone on the whole corresponds to the Felsőörs Limestone in the Balaton Highland. The palaeobiogeographical evaluation of the cephalopod fauna showed that the elements of the nautilid fauna point mostly to Germanic and partly to Sephardic affinity. On the other hand, the ammonoid fauna has no Germanic elements; most of the species are Alpine in character, while the species Procladiscites brancoi indicates Dinaridic connection, or at least an occasional appearance of pelagic organisms. These results endorse the previous palaeogeographical assumption and suggest that during the Middle Triassic the Mecsek succession was situated along the European shelf, between the Vindelician-Bohemian Land and the open Tethyan Ocean.

Cephalopoda (Mollusca) of the Colombian Caribbean Sea

The cephalopod fauna in Colombian Caribbean waters is poorly known. This work gives an overview of the species found in the area. For elaborating this list, the most relevant natural history collections where the material of the area’s is material is deposited were consulted, identifications were verified compared with type material and original descriptions and redescriptions. In the Colombian Caribbean Sea 48 cephalopod species are present in different environments, represented in 17 families and 33 genera. There is one Spirula, seven sepiolids, 21 squids, and 19 octopod species. Most animals are from shallow coastal waters.

Cephalopod fauna of the Pacific Southern Ocean using Antarctic toothfish (Dissostichus mawsoni) as biological samplers and fisheries bycatch specimens

Cephalopods are an important component of Southern Ocean food webs but studies analysing their habitat and trophic ecology are scarce. Here, we use the Antarctic toothfish Dissostichus mawsoni as a biological sampler of Southern Ocean's cephalopods in the Ross, Amundsen, and D'Urville Seas. Ten cephalopod taxa were identified in the diet of the Antarctic toothfish, with Pareledone turqueti and Moroteuthopsis longimana being the only species present in all the three studied areas. DNA analysis conducted on squid flesh samples allowed identification of eight and two specimens of Mesonychoteuthis hamiltoni and M. longimana, respectively, proving this technique as a potential tool to improve the knowledge of cephalopods biodiversity and biogeography in the Southern Ocean. Stable isotopes were used to compare the habitat (δ13C) and trophic ecology (δ15N) between two life-stages of the two most abundant squid species (M. longimana and Psychroteuthis glacialis) from the D'Urville Sea (both squid species) and Amundsen Sea (only P. glacialis). Higher δ13C values in M. longimana suggest that this species inhabits waters near the Antarctic Polar Front, with incursions into sub-Antarctic waters, whilst P. glacialis spends its entire life in Antarctic waters. The most recently deposited part of the beak is enriched in 15N suggesting an increase in trophic level during squid growth. These results give us the first insights into the bathyal distribution of cephalopods in the Amundsen and D'Urville Seas, as well as into the ontogenetic changes of two of the most consumed squid species by top predators in this region. Such results are an important step towards improving the biogeography of Antarctic cephalopods, being of utmost importance to understand the biodiversity, food web structure, and functioning of this region.

Reappraisal of the latest Albian (Mortoniceras fallax Zone) cephalopod fauna from the classical Salazac locality (Gard, southeastern France)

The Salazac locality (Gard, southeastern France) is renowned for the richness of its cephalopod fauna (especially ammonites) from the Mortoniceras fallax Zone (uppermost Albian, Lower Cretaceous). However, most ammonite species have paradoxically been scarcely illustrated up to now. Furthermore, the rare assessments of ammonite taxonomic diversity are presumably inaccurate, as they either result from a drastic typological approach or could not benefit from the most recent advances in modern concepts of ammonoid intraspecific and ontogenetic variations. In this work, we document an original cephalopod assemblage from Salazac represented by abundant, well-preserved specimens (564 studied ammonites, including ca. 50% of heteromorphs) constituting a high diversity. The sample size and quality of this new material allowed some extensive morphological and biometric analyses whenever possible (i.e., for subdatasets in which a significant number of measurements is available) and to thoroughly assess intraspecific and ontogenetic variations for a few species. This led to determine the diagnostic value of various shell characters commonly used to characterize both well-documented and poorly-defined species. In particular, we show that a significant part of the variation in the number of ribs per whorl within the heteromorphic genera Mariella and Turrilitoides is directly related to shell size and that the strength of tubercles covaries negatively with the number of ribs in Mariella, therefore challenging the diagnostic value of these characters. We further suggest that rib density covaries with whorl shape in Mariella, following Buckman’s first rule of covariation. In total, one species of nautilid and 38 taxa (25 genera) of ammonites are described, among which five species are documented from Salazac for the first time. In turn, this study provides valuable data for future phylogenetic, biostratigraphical, biogeographical and broad-scale diversity studies.

A review of cephalopods (Phylum: Mollusca) of the Canary Current Large Marine Ecosystem (Central-East Atlantic, African coast)

AbstractAn extensive review of cephalopod fauna in the Central and North Atlantic coast of Africa was performed based on material collected during 10 research cruises in these waters. In the Canary Current Large Marine Ecosystem (CCLME) area, a total of 378,377 cephalopod specimens was collected from 1247 bottom trawl stations. Of those specimens, 300 were sampled for subsequent identification in the laboratory and found to belong to 65 different species and 23 families. After an exhaustive review of the existing literature on the cephalopods and new data obtained from the surveys, an updated checklist of 138 species was generated for the CCLME area. Our knowledge of the known geographic distribution ranges of several species has been expanded: Muusoctopus januarii has been sighted from Guinea–Bissau waters, passing through Western Sahara, to Morocco waters for the first time; Lepidoteuthis grimaldii and Octopus salutii have been sighted off Morocco waters for the first time; Austrorossia mastigophora, Abralia (Heterabralia) siedleckyi, Abralia (Pygmabralia) redfieldi and Sepiola atlantica have been cited off Western Sahara waters for the first time; Magnoteuthis magna, Abralia (Asteroteuthis) veranyi and Octopoteuthis megaptera have been sighted off Moroccan and Western Sahara waters for the first time; Ancistroteuthis lichtensteinii, Opisthoteuthis grimaldii, Onykia robsoni, Muusoctopus levis and Bathypolypus valdiviae have been cited in the Guinea–Bissau coast for the first time; the northern geographic limit of Bathypolypus ergasticus has been expanded to Morocco, Western Sahara and Mauritania and southward to Guinea–Bissau waters. The presence of Muusoctopus johnsonianus in Senegalese waters has been reported for the first time. A Chtenopteryx sicula specimen was reported in Western Sahara waters. A specimen belonging to the poorly known Cirrothauma murrayi species was found in South Moroccan waters. Amphitretus pelagicus, a probably cosmopolitan species, has been reported in the Western Sahara and Guinea–Bissau waters. Some species that were previously recorded in the area, Sepia angulata, Sepia hieronis, Heteroteuthis dagamensis, Helicocranchia joubini and Tremoctopus gelatus, were removed from the final checklist and considered to be not present in the CCLME area. Cycloteuthis akimushkini was substituted with Cycloteuthis sirventi, its senior synonym, in the final checklist. Similarly, Mastigoteuthis flammea and Mastigoteuthis grimaldii were substituted with Mastigoteuthis agassizii.

Latest Oxfordian – earliest Kimmeridgian ammonite dominated fauna and microfacies from the ammonitico rosso-type Fonyászó Limestone Formation at Zengővárkony (Mecsek Mountains, Hungary)

Field work has resulted in the recognition of a previously unknown outcrop in the vicinity of the Zengővárkony lime-kilns (Mecsek Mountains, South Hungary) which has provided a remarkably rich, but poorly preserved, uppermost Oxfordian – earliest Kimmeridgian fauna dominated by ammonites probably representing the Hypselum–Bimammatum zones. This is the first description and illustration of Oxfordian–Kimmeridgian ammonites from the Mecsek Mountains. The cephalopod fauna comprises Phylloceras div. sp., Holcophylloceras div. sp., Sowerbyceras sp., Lytoceras sp., Lissoceratoides erato, Trimarginites cf. trimarginatus, Glochiceras (Coryceras) cf. microdomum, Subdiscosphinctes sp., ?Wegelea sp., Passendorferiinae gen. et sp. ind., ?Orthosphinctes sp., Euaspidoceras cf. radisense, Aspidoceras sp., A. cf. binodum, Physodoceras sp. ex gr. altenense-wolfi, Lamellaptychus sp., Laevaptychus sp. ex gr. hoplisus-obliquus. The fauna has a Mediterranean character (55% of Phylloceratidae and Lytoceratidae) and is similar to the Tethyan assemblages of the Venetian Alps (Italy), and Palma de Mallorca. The spirochaete tube worm Spiraserpula spirolinites is also the first record from the Mecsek Mountains. The Saccocoma wackestone-packstone microfacies is recorded with benthic foraminifera (Lenticulina sp. and Spirillina sp.) indicating well oxygenated and nutrient-rich bottom conditions.

Evolution of Ordovician cephalopod diversity in the Middle Yangtze region of South China and its controlling factors

The evolution of Ordovician cephalopod diversity in the Middle Yangtze region of South China has been analysed. The cephalopods in this region appeared in the earliest Tremadocian, radiated in the Early–Middle Floian and Middle Ordovician, and went through an extinction period during the Late Katian and Hirnantian. The composition of the cephalopod fauna underwent major changes in the Late Floian. Specifically, all the genera occurring in previous time periods disappeared and Tarphyceratida, Actinoceratida, and Orthoceratida appeared and prospered. Differences in the evolution of cephalopod diversity between Middle Yangtze region and other regions were detected, which were caused by differences in the vertical sequence and horizontal combination of controlling factors. Changes in living environments and the distribution of food resources prompted Ordovician cephalopods to evolve adaptations for life in deep-water environments. The low-temperature ocean current near the western coastline of Gondwana created favourable conditions for the Floian peak of cephalopod diversity in South China. The tectonic movements, high rainfall, and relatively closed environment of the Middle Yangtze region led to rapid sea level rise and hindered cephalopod diversification. These processes explain the low cephalopod diversity in the Late Ordovician and the absence of the previously reported Katian radiation peak in this region.

Lituitid cephalopods from the upper Darriwilian and basal Sandbian (Middle–Upper Ordovician) of Estonia

ABSTRACT Cephalopods of the order Lituitida Starobogatov, 1983 from the late Darriwilian and early Sandbian strata of Estonia are revised herein. During that time, the lituitids reached their peak abundance and were among the key components of cephalopod faunas on Baltica, as well as in other mid- and low-latitude palaeogeographic locations. The Estonian lituitids mostly come from localities representing more off-shore environments with deeper-water sedimentation in the Middle Ordovician. This supports previous assumptions that lituitids preferred pelagic environments and were capable of long-distance migration. In the studied lituitid collection, two genera were identified – Lituites Bertrand, 1763 and Ancistroceras Boll, 1857. Three species – Ancistroceras ristnensis sp. nov., Ancistroceras vahikuelaensis sp. nov. and Lituites nehatuensis sp. nov. – were newly established. However, species determinations were often hindered by high intraspecific variability and fragmentary preservation. Investigation of cameral deposits using median sections showed that: connecting rings in chambers with deposits are commonly broken or missing; oriented fragments of connecting rings are present, sometimes overgrown by primary deposits; several generations of primary deposits can be developed; simultaneous presence of both broken and intact connecting rings in the same specimen is usual. These observations elucidate the formation of cameral deposits in lituitids. Currently, this process is explained either by passive deposition from cameral fluids, or active secretion by cameral mantle. The evidence collected herein from Estonian lituitids reveals, however, that both modes of formation might have occurred successively during the lituitid ontogeny and that a gradual, life-time destruction of connecting rings was possibly involved.

FIRST RECORD OF THE UPPER ILLYRIAN AMMONOID SUBZONE MARKER REITZIITES REITZI IN THE KARST DINARIDES

Middle Triassic deposits in the Karst Dinarides (south Lika area, near Gracac) were investigated for petrological, sedimentological and biostratigraphic determinations. Within two continuously recorded sections of sedimentary carbonates and interlayered pyroclastic rocks (Mali Kunovac and Kunovac sections) reflecting variable sedimentary-magmatic environments, valuable cephalopod fauna ranging from the middle Illyrian to the upper Illyrian age was found. The most significant was the recovery of the ammonoids Asseretoceras sp., indicating the upper part of the Illyrian Paraceratites trinodosus Zone, and Reitziites reitzi species which marks the upper part of the Illyrian Reitziites reitzi Zone. The discovery of the Reitziites reitzi species was not known from the Karst Dinarides until this finding.

Early Devonian ammonoid faunas in the Zeravshan Mountains (Uzbekistan and Tadjikistan) and the transition from a carbonate platform setting to pelagic sedimentation

Thick Early Devonian carbonatic sedimentary successions, exposed in the Zeravshan Mountains of Uzbekistan, display a transition from a reefal to a pelagic facies. This allows us to document and analyze the history of sedimentation and changes in marine faunas of this region. The late Pragian succession of Bursykhirman Mountain is documented with the transition from platform carbonates to pelagic sediments. Lithology and microfacies through the early Emsian sedimentary sequence of two ammonoid-bearing sections were investigated with a focus on the Dzhaus Beds. In addition to this sedimentological analysis, we discuss the palaeobiogeographically peculiar situation of Uzbekistan (palaeocontinent Kazakhstania). Many species found in the Kitab State Geological Reserve are endemic and at least restricted to the South Tien Shan. We suggest a moderately close relationship to southern Chinese and Vietnamese faunas, even though more palaeontological data from the latter two regions is needed for a test. We also revise the cephalopod fauna from the Kitab Reserve and introduce the following new taxa: Beckeroceras gen. nov., Uzbekisphinctes gen. nov., Ivoites meshchankinae sp. nov., Kitabobactrites salimovae gen. et sp. nov., and Metabactrites rakhmonovi sp. nov. • Key words: Pragian, Emsian, carbonate microfacies, endemism, Ammonoidea, palaeogeography

South American sea lions Otaria byronia as biological samplers of local cephalopod fauna in the Patagonian shelf marine ecosystem

AbstractCephalopods are important prey in the diet of top predators, such as marine mammals and seabirds. However, detailed information on their trophic relationships in the Patagonian marine ecosystem is scarce, including those cephalopod species with commercial interest. The aims of this study were to evaluate the composition of the cephalopod component in the diet of Otaria byronia and determine the habitat use and trophic levels of their main cephalopod prey by measuring the stable isotopic signature of cephalopod beaks. Between May 2005 and February 2009, fresh faecal samples were collected from two sea lions rookeries in San Matias Gulf. Cephalopods occurred in 39.4% of the 1112 samples collected during the whole period of study. The dominant prey species was Octopus tehuelchus, which occurred in 45.8% of scats containing cephalopod remains, and represented 58.7% in terms of numerical abundance and 52.0% in mass of cephalopods consumed. The second species most consumed was the myopsid Doryteuthis gahi. The significant higher δ15N values of O. tehuelchus beaks in comparison with those of D. gahi showed that these two species have different trophic levels while occupying similar habitat (δ13C values) in neritic waters of the Patagonian shelf.

Replacements of Major Cephalopod Faunas in Late Cambrian and Ordovician in South China

Replacements of Major Cephalopod Faunas in Late Cambrian and Ordovician in South China

Az első kréta időszaki nautilida-előfordulás (Eutrephoceras ex gr. boissieri) a Mecsekből

Fieldwork around the lime-kilns at Zengővárkony (southern Hungary, eastern Mecsek Mts.) has led to the discovery of previously unknown beds of the Hidasivölgy Marl Formation. Based on bio- and lithostratigraphic considerations, here a Valanginian (Hauterivian?) age is assumed. This recently discovered section consists of thin-bedded, greybrownish turbiditic marls and limestones laid down in rhythmic alterations. Excavations of the marl beds have yielded a poorly-preserved, but rich cephalopod fauna. Furthermore, Eutrephoceras ex gr. boissieri has been identified here, and this is the first record of Cretaceous nautiloids from the Mecsek Mountains.

Surveying cephalopod diversity of the Amazon reef system using samples from red snapper stomachs and description of a new genus and species of octopus

The cephalopod fauna of the southwestern Atlantic is especially poorly-known because sampling is mostly limited to commercial net-fishing operations that are relatively inefficient at obtaining cephalopods associated with complex benthic substrates. Cephalopods have been identified in the diets of many large marine species but, as few hard structures survive digestion in most cases, the identification of ingested specimens to species level is often impossible. Samples can be identified by molecular techniques like barcoding and for cephalopods, mitochondrial 16S and COI genes have proven to be useful diagnostic markers for this purpose. The Amazon River estuary and continental shelf are known to encompass a range of different substrates with recent mapping highlighting the existence of an extensive reef system, a type of habitat known to support cephalopod diversity. The present study identified samples of the cephalopod fauna of this region obtained from the stomachs of red snappers, Lutjanus purpureus, a large, commercially-important fish harvested by fisheries using traps and hook-and-line gear that are capable of sampling habitats inaccessible to nets. A total of 98 samples were identified using molecular tools, revealing the presence of three squid species and eight MOTUs within the Octopodidae, representing five major clades. These include four known genera, Macrotritopus, Octopus, Scaeurgus and Amphioctopus, and one basal group distinct from all known octopodid genera described here as Lepidoctopus joaquini Haimovici and Sales, new genus and species. Molecular analysis of large predatory fish stomach contents was found to be an incredibly effective extended sampling method for biodiversity surveys where direct sampling is very difficult.

Sinemurian biostratigraphy of the Tannscharten section near Reichraming (Lower Jurassic, Schneeberg Syncline, Northern Calcareous Alps)

Abstract Lower Jurassic ammonites were collected from deep-water limestones of the Tannscharten section, southwest of Reichraming (Northern Calcareous Alps, Upper Austria). The outcrop provides a rich Upper Sinemurian (Lower Jurassic) ammonite fauna of the Allgäu Formation. The area is situated in the westernmost part of the Schneeberg Syncline in the north of the Reichraming Nappe (High Bajuvaric Unit). The ammonite fauna consists of seven different genera, each apparently represented by 1-2 species. Echioceratids are the most frequent components (Echioceras, Leptechioceras, Paltechioceras), followed by the phylloceratids (Juraphyllites, Partschiceras) and oxynoticeratids (Gleviceras, Paroxynoticeras). Juraphyllites libertus, Partschiceras striatocostatum, Gleviceras paniceum, Echioceras quenstedti, Echioceras raricostatoides, Paltechioceras boehmi, Leptechioceras meigeni, Leptechioceras macdonnelli and Paltechioceras oosteri are new for the Schneeberg Syncline and allow for the first time a detailed biostratigraphy of the Echioceras raricostatum zone. The assemblage is correlated with other faunae from Austria, Germany, United Kingdom, France, Switzerland and Romania. The cephalopod fauna consists of a mix of elements from the Northwest European Province and the Mediterranean Province. The detailed biostratigraphy based on ammonites is presented here.

Lower Bathonian Belemnites and Biostratigraphy of the Central and Southern Parts of the East European Platform: Part 2. Cylindroteuthididae and Belemnotheutididae

Belemnites from the lower Bathonian deposits of the Russian Plate are revised and discussed on the basis of study of the two reference sections—Pletnyovka and Sokur quarries. This is the second part of the investigation dealing with representatives of the family Cylindroteuthididae, and “rostrum-less” belemnites of the family Belemnotheutididae, while members of the family Megateuthididae were discussed in detail in the first part (Ippolitov, 2018). The cylindroteuthidids are found only in the Sokur Quarry and comprise four species all assigned to the genus Pachyteuthis, including a new species, Pachyteuthis mittai sp. nov. For Belemnotheutididae, the presence of a single species Acanthoteuthis foliorostris sp. nov. is recorded, which is the first confirmed record of the genus Acanthoteuthis in the pre-Callovian strata. The study of morphological changes within Cylindroteuthididae across the succession allowed two biohorizons to be recognized and the existing belemnite-based scheme for the lower Bathonian of the Volga Region and its correlation with sections in the Pechora River basin to be updated. As the result of the revision, a complex zonal and infrazonal belemnite-based stratigraphic scheme of the lower Bathonian of the Volga Region is introduced. The presence of an endemic genus deriving from Arctic-Boreal immigrants in the lower Bathonian of the Middle Russian Sea allows the belemnite fauna of this age to be interpreted as the first isolated episode of differentiation of the Boreal-Atlantic Province in belemnites. The study of the development of the cephalopod fauna in the early Bathonian of the Russian Plate indicates a biphase formation of the meridional strait connecting the Middle Russian Sea with the Arctic basins and also supports the hypothesis of a short-term opening of a sublatitudinal Pripyat Strait during the maximum highstand.

New record of Abralia (Heterabralia) siedleckyi Lipinski, 1983 (Cephalopoda: Enoploteuthidae) from south-eastern Arabian Sea with some remarks about its biology

Specimens of oceanic squid, Abralia (Heterabralia) siedleckyi Lipinski, 1983 were collected from the south-eastern Arabian Sea using midwater trawl (horizontally at 200 m depth) during night operations in two cruises on 18 April 2015 and 26 February 2017. Description and morphological measurements of the specimens are provided. The record of this mesopelagic squid from the Arabian Sea is an addition to the cephalopod fauna of the Indian Ocean and India. The statolith based age analysis indicates that a 29.1 mm dorsal mantle length specimen had 93 day’s age with a growth rate of 0.31 mm DML/day.

A Study of Bioerosion of Belemnites and Taphonomy of Cephalopods from Kuldhar Member of Jurassic Jaisalmer Formation from Jaisalmer, Rajasthan

ABSTRACT The Callovian-Oxfordian Kuldhar Member of Middle-Upper Jurassic Jaisalmer Formation, Rajasthan is characterized by a rich cephalopod (ammonites and belemnites) fauna along with other invertebrates. They are embedded in oolitic limestone, at places in nodular limestone, grey shale and occasional red mud. The belemnite rostra bear bioerosions in the form of borings of circular or elliptical type. The present study identified those as Trypanites isp. and Rogerella isp. and characterized the hitherto unnoticed bioerosions of these belemnite rostra to be post-mortal. Different dispositions of major diameter of belemnite rostra has been interpreted to represent churning effect of ichnofossil producing organisms which put evidences of several generations of omission surfaces. Vertical and horizontal orientations of stephanoceratid ammonites side by side have been critically analysed in the light of lithology and prevailing environmental condition and inferred to be an artifact of gravity and thixotropic property of clay. Ammonites like Stephanoceratids and Macrocephalitids inhabit within 110m depth which is also permissible depth of belemnites as well as probable depth of formation of oolites, carbonate mud and aluminosilicate mud. Considering the lithology of the rocks like oolites, carbonate mud, aluminosilicate, the habitat of stephanoceratid and habitat of acrothoracid barnacles (organisms responsible for Rogerella isp.), the environment has been delineated to be sublittoral which was previously designated as shoreface zone to offshore transition zone.