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The first record of jaws of Boreal Valanginian ammonites (Cephalopoda, Polyptychitidae)
Abstract
Jaws of ammonites which inhabited the Panboreal Superrealm during the Jurassic and Cretaceous are poorly known in comparison to those of Tethyan ammonoid faunas. This paucity may be explained by limited thickness, or even absence of an outer calcitic layer, in lower jaw elements (aptychi) of Boreal ammonites. Here we describe, for the first time, the jaws (both lower and upper) of ammonites of the Boreal family Polyptychitidae, of the Early Cretaceous (Valanginian) age. Polyptychitid lower jaws are of the aptychus type, but have an unusual pointed and convex shape. However, lower jaws of Late Jurassic ancestors of polyptychitids (Craspeditidae) as well as Middle Jurassic cardioceratids (Pseudocadoceras) have a near-identical shape, as do previously described aptychi of the Late Cretaceous genera Neogastroplites and Placenticeras (Hoplitoidea). The close resemblance of lower jaws of evolutionarily distant ammonites may be linked to a similar lifestyle, but more data are needed to substantiate this. Upper jaws of polyptychitid are closely similar to previously described upper jaws of Jurassic ammonites, which indicates the conservatism of this part of the jaw apparatus. Together with shells and jaws of the Valanginian ammonites described herein, jaws of coleoids (likely belemnites) as well as arm hooks (onychites) have been found.
... Klug et al., 2021b). Another important source of finds of cephalopod jaws is various concretions, in which elements of the jaw apparatus are often buried together with accumulations of shells of their hosts, primarily ammonoids (Landman et al., 2006(Landman et al., , 2015Keupp and Mitta, 2013;Tanabe et al., 2015a;Mironenko and Mitta, 2023). The jaws of coleoids can also be preserved in concretions (Dzik, 1986;Tanabe et al., 2008Tanabe et al., , 2015bTanabe et al., , 2017Tanabe and Hikida, 2010;Tanabe 2012;Keupp and Mitta, 2013). ...
... However, this assumption is most likely erroneous since these specimens are almost identical to the outer lamellae of the upper jaw of aptychophoran ammonites (see Mironenko 2021: fig. 7 andMitta 2023: fig. 5A-C) and most likely belonged to the kosmoceratid and cardioceratid ammonites, the inner lamellae of the upper jaw of which are found in the same concretions (Keupp and Mitta, 2013: fig. ...
We report on remains of the buccal apparatus and possible associated structures for the Late Cretaceous ammonite Maorites
seymourianus from the López de Bertodano Formation (Antarctic Peninsula). This is the first description of these structures for the family
Kossmaticeratidae. Further, we discuss the most likely taphonomic processes taking place that allowed this exceptional preservation.
Reflectance Transformation Imaging (RTI) technique was employed in this work to better document the faint structures. We briefly provide a
review of this method and its potential importance for paleontological studies because it seems that this powerful technique has been largely
overlooked by paleontologists.
Boreal and Subboreal ammonite taxa, belonging to the families Cardioceratidae, Aulacostephanidae, Oppeliidae, Aspidoceratidae, Ataxioceratidae, Virgatitidae, Dorsoplanitidae and Craspeditidae which are most characteristic for the Kimmerigian and Volgian stages were revised. Their phylogenetic relationship, geographic and stratigraphic distribution as well as peculiarities of evolution were specified. Key genera of Kimmeridgian and Volgian ammonites are described. Two new genera (Michailoviceras and Arctocrendonites), as well as 10 new species (Suboxydiscites birkelundae, Sutneria perplexa, Virgatites saratovensis, Dorsoplanites callomoni, D. laevis, Praechetaites
schulginae, Kachpurites praefulgens, K. laevis, Laugeites mesezhnikowi, L. muravini) are established. Infrazonal subdivision of the considered stratigraphic interval has been substantially specified (and for some regions it has been proposed for the first time). In the Kimmeridgian and Volgian Stages of the Panboreal Superrealm 42 inter-regionally correlated stratigraphic levels have been traced, allowing for a detailed correlation of zonal and infrazonal scales to be justified. On this basis, a new version of the ammonite scale of the Boreal zonal standard was developed. In the Kimmeridgian and Volgian Stages 31 stratigraphic levels have been identified that allow for detailed Boreal-Tethyan correlation. The lower boundaries of the Kimmeridgian and Volgian Stages are reliably traced in marine facies all over the world, while the upper boundary of the Volgian Stage is clearly fixed within the Panboreal Superrealm, but in the Tethys-Pantalassa Superrealm this level does not correspond to any zonal or subzonal boundary. The description of the key studied sections and the determination of ammonites from boreholes are given in the electronic supplement to the monograph: http://ginras.ru/library/pdf/627_2021_supplement.pdf
Cephalopoda is the only class of molluscs in which virtually all its modern representatives have a pair of powerful jaws. There is little doubt that jaws have contributed to the evolutionary success of cephalopods, but their origin still remains a mystery. Though cephalopods appeared at the end of the Cambrian, the oldest unequivocal jaws have been reported to date from the Late Devonian, though they were initially interpreted as phyllopod crustaceans of the suborder Discinocarina. After their relation with ammonoids was proven, they were considered as opercula, and only later their mandibular nature was recognized and widely accepted. Finds of discinocarins from Silurian deposits are still considered as opercula of ammonoid ancestors ‐ nautiloids of the order Orthocerida. However, according to modern ideas, there is no place within their soft body for the location of such large opercula. Moreover, the repeated appearance of very similar structures in the same evolutionary line at least twice, but in different places of the body and for different purposes seems highly improbable. A new hypothesis is proposed herein, in which the Silurian fossils, earlier assigned to Discinocarina, are not specialized opercula, but protective shields, to defend orthocerids not from the predators, but from their own prey. The chitinous plates around the mouth likely appeared in the Silurian orthocerids for protection from such damage and later, during Silurian and Devonian, most likely gradually evolved into the jaws.
Although belemnite rostra can be quite abundant in Jurassic and Cretaceous strata, the record of belemnite jaws was limited to a few specimens from Germany and Russia. Here, we describe and figure three cephalopod jaws from the Middle Jurassic Opalinus Clay of northern Switzerland. Although flattened, the carbonaceous fossils display enough
morphological information to rule out an ammonoid, nautiloid or octobrachian origin of the two larger jaws. Their similarities to belemnite jaws from Germany and Russia conforms with our interpretation of these specimens as belemnite jaws. Based on their rather large size, we tentatively assign these two jaws to the megateuthidid Acrocoelites conoideus. The third jaw is a rather small upper jaw of an ammonoid. Since Leioceras opalinum is by far the most common ammonite in this unit in northern Switzerland, we tentatively suggest that the upper jaw belongs to this species.
The short geochronological span and wide geographic distribution of the genus Hectoroceras in the Boreal Paleogeographic Superrealm make it exceptionally important for correlation of the Volgian-Ryazanian boundary beds. The Ogarkovo Section on the Unzha River (Kostroma Region), which is essential for this correlation, is described. The revised genus Hectoroceras includes the type species H. kochi Spath, H. larwoodi Casey, H. tolijense (Nikitin), and its microconch H. pseudokochi (Mesezhnikov), the latter two previously assigned to the genus Shulginites Casey, 1973 which is here considered as a junior subjective synonym of Hectoroceras. The FAD of Hectoroceras kochi is an interregional marker for Panboreal correlation, and the coincidence of this event with the invasion of ammonites of Tethyan origin into the Central Russian ecotone improves the prospects for a Boreal-Tethyan correlation of the Jurassic-Cretaceous boundary interval.
This paper presents the results of the revision of the taxonomic composition and stratigraphic distribution of Central Russian representatives of the Valanginian genus Delphinites. The lower Undaloplicatilis zone of the Valanginian in the basin of the Sura River (Menya River) contains D. undulatoplicatilis (Stchi-rowsky) [subjective synonyms: Oxynoticeras tuberculiferum Stchirowsky, Pseudogarnieria securis Sasonova], D. menensis (Stchirowsky), D. alatyrense (Kemper), D. kurmyschensis (Stchirowsky), D. stchirowskyi (Sason-ova), D. donovani Alsen et Rawson and D. heineae sp. nov. In addition, Delphinites sp. was figured from the Michalskii Zone (terminal Lower Valanginian) of the Kostroma Region (Unzha River). Thus, the interval of distribution of the genus Delphinites is not restricted by the basal zone of the Valanginian.
Nomenclature types of ammonites of the genera Dorsoplanites, Pavlovia, Zaraiskites and Cras-pedites from the Volgian Stage of the Russian platform are discussed; for some species type specimens are designated and illustrated. The date of the establishment of the genus Pavlovia Ilovaisky, 1915 is emended, and it type species is detailed. The name Ammonites panderi Eichwald, 1840 is recognized as nomen dubium; for the species Dorsoplanites panderi auctt. non Eichwald, 1840 the new name D. typicus nom. nov. is proposed; the index species of the Panderi Zone of the Volgian Stage is replaced by Zaraiskites scythicus (Vischniakoff). The species Craspedites ivanovi Gerasimov, the index species of the upper subzone of the Virgatites virgatus Zone is re-described. The interval with Craspedites milkovensis can be only considered as the terminal faunal horizon of the Craspedites nodiger Zone interpreted to include the Mosquensis and Nodiger subzones.
Ammonoidea is a subclass of cephalopod mollusks that existed in the seas from the end of the Devonian to the very end of the Cretaceous. Due to the beauty and variety of the forms of ammonoid shells, they have become the subject of collecting, whereas their rapid evolution and widespread distribution made them an important tool for biostratigraphy. However, in spite of the abundance of ammonoid shells in Paleozoic and Mesozoic deposits, their popularity among professional and amateur paleontologists as well as their significance for stratigraphy, ammonoids themselves had remained highly enigmatic creatures until recently. However, in the last two decades the situation has improved significantly. New findings of well-preserved ammonoid shells shed light on the structure of the muscular system of ammonoids and areas of attachment of soft tissues to the shell, the structure of the siphuncle soft tissues, the digestive system and the jaw apparatus. A detailed study of the embryonic development of modern cephalopods and the latest discoveries in the evolution of the entire Cephalopoda allowed us to draw conclusions about the structure of those parts of the ammonoid soft body that have not yet been found in the fossil state. At present, it can be considered as proven that the ammonoids had well-developed eyes, a complex system of retractor muscles, a powerful hyponome and a wrinkle layer, similar to the black layer of Nautilida, which played an important role in the swimming and manoeuvrability of ammonoids. Ammonoids, like other cephalopods, initially had ten arms. The soft tissues of the siphuncle were similar to those of modern Nautilus, although they differed in some details. This publication summarizes current data on the anatomical structure of ammonoids, including those based on the findings made by the author in the Jurassic localities of Central Russia. It also discusses the paleobiology of ammonoids, such as in vivo orientation of their shells in the water, the mechanism of the swimming and ammonoid reproduction.
Review of zonal and infrazonal subdivision of the Kimmeridgian and Volgian stage of southern part of the Moscow Syneclise, accompanied by the detailed description of key sections and all stratigraphic units (zones, subzones and biohorizons) of the region, is provided. New biohorizons are introduced: crenulatus (Lower Kimmeridgian), tenuicostatum, arkelli (Lower Volgian), gerassimovi, virgatus, rarecostatus (Middle Volgian), praeokensis, interjectum, transitionis (Upper Volgian), and characteristics of biohorizons mentioned previously by the author but never described in details (evolutus, tenuicostatus, cheremkhensis, subfulgens, involutus, catenulatum, nodiger, milkovensis horizons) is provided. Dimorphism and polymorphism patterns in Kimmeridgian and Volgian ammonites are discussed. Updated diagnoses are provided for Virgatitidae, Garniericeratinae and Craspedites (Trautscholdiceras). New species, which are used as indexes of ammonite horizons, are described: Virgatites rarecostatus sp. nov., Craspedites (C.) praeokenis sp. nov., C. (Trautscholdiceras) transitionis sp. nov., Kachpurites evolutus sp. nov., K. tenuicostatus sp. nov. and K. involutus sp. nov.. Evolution of Late Volgian craspeditids is reviewed. Two eudemic subfamilies which evolved in the Late Volgian in the Middle Russian Sea (Craspeditinae and Garniericeratinae) were characterized by significantly different evolutionary rates through time: at the beginning of Late Volgian time evolutionary rates in garniericeratins was very high, while during the Nodiger Chron craspeditins evolved much quicker than garniericeratins. Although early members of two lineages strongly resemble each other, major trends in evolution of these subfamilies were different. At the beginning of the Late Volgian garniericeratins predominated in ammonoid assemblages, and their shells were quickly evolving from platycones to oxycones; this was accompanied by gradual reduction of variability and loss of sculpture. In the both discussed lineages intraspecific variability and evolutionary rates were positively correlated with relative abundance within ammonite assemblages. However, intraspecific variability of some species was especially high (Kachpurites tenuicostatus) or very low (Garniericeras interjectum). Speciation in Craspeditinae led to the appearance of cadicones, and these changes in shape were accompanied by gradual strengthening of the sculpture (with appearance of strong nodes in C. (Trautscholdiceras)). At the beginning of the Late Volgian craspeditins were relatively uncommon (5-10%), but became predominate during the Nodiger Chron (90-98% of all ammonite records). Changes of shell size through the evolution of garniericeratins were irregular, while craspeditins showed strong trend to decrease of both median and maximal sizes through their evolution. Late Volgian ammonites, belonging to eudemic craspeditid lineages inhabiting the Middle Russian Sea, became extinct in the latest Late Volgian. During the latest Chron of the Late Volgian (Singularis Chron) ammonoid assemblages of the Middle Russian Sea were represented by the immigrant taxa only (Volgidiscus and Shulginites).
Late Berriasian–earliest Valanginian lamellaptychi (Cephalopoda) are described in detail for the first time. With one exception, all species belong to early representatives of Mortilletilamellaptychus. The majority of the well dated aptychi come from the cephalopod-rich sediments of the Vocontian Basin in south-eastern France; others are from south-eastern Spain. Thorolamellaptychus anglesensis sp. nov. is introduced.
A nearly complete radula with seven elements per row preserved inside of an isolated, bivalved, calcitic lower jaw (= aptychus) of the Late Jurassic ammonite Aspidoceras is described from the Fossillagerstätte Painten (Bavaria, southern Germany). It is the largest known ammonite radula and the first record for the Perisphinctoidea. The multicuspidate tooth elements (ctenodont type of radula) present short cusps. Owing to significant morphological differences between known aptychophoran ammonoid radulae, their possible function is discussed, partly in comparison with modern cephalopod and gastropod radulae. Analogies between the evolution of the pharyngeal jaws of cichlid fishes and the ammonoid buccal apparatus raise the possibility that the evolution of a multicuspidate radula allowed for a functional decoupling of the aptychophoran ammonoid jaw. The radula, therefore, represents a key innovation which allowed for the evolution of the calcified lower jaws in Jurassic and Cretaceous aptychophoran ammonites. Possible triggers for this morphological change during the early Toarcian are discussed. Finally, we hypothesize potential adaptations of ammonoids to different feeding niches based on radular tooth morphologies.
Late Valanginian (Early Cretaceous) lamellaptychi of the genus Mortilletilamellaptychus were collected from seven ammonite-controlled sections in south-eastern France demonstrate distinct changes in ribbing during growth. Simpler juvenile ribbing, which is essentially uniform for all of the specimens studied, differs distinctly from the complicated arrangement of the adult ribs. Changes in ribbing morphology were observed in the five species studied, two of which were identified as new (i.e. Mortilletilamellaptychus heterocostatus sp. nov. and M. bicostatus sp. nov.).
Here we are providing a review of aptychi records in ammonites of Boreal origin or that inhabited Boreal/Subboreal basins during the Bathonian - Albian with special focus on new records and the relationship between the evolution of ammonite conch and aptychi. For the first time we figure aptychi that belong to Aulacostephanidae, Virgatitidae, Deshayesitidae, Craspeditinae and Laugeitinae. A strong difference between aptychi of micro- and macroconchs of co-occurring Aspidoceratidae is shown, which, along with their shell morphologies suggests niche divergence of these dimorphs. Aptychi of Aptian Sinzovia (Aconeceratidae) should be tentatively ascribed to Didayilamellaptychus, while their previous assignment to rhynchaptychi was caused by misidentification. Aptychi of Middle Jurassic - Early Cretaceous Boreal and Subboreal ammonites are characterized by a very thin calcareous non-porous outer layer lacking distinct ribs and tubercles (only radial striae sometimes occur), and mainly should be assigned to Praestriaptychus. Some ammonoid groups (i.e. Ancylocerina and Desmoceratoidea) are characterized by the presence of different aptychi types irrespective of their shell shape. This fact could indicate that bivalved praestriaptychi could have easily transformed into single-valved "anaptychi" and vice versa. Size and form of aptychi in relation to those of the aperture of ammonite conchs vary within different lineages and at least some Stephanoceratoidea and Perisphinctoidea have aptychi significantly smaller than the aperture diameter.
Current knowledge on the ammonoid buccal mass and jaw apparatus is synthesized based on in situ fossil records from 109 genera that are distributed in 30 superfamilies of 8 suborders of Devonian to Cretaceous age. As in those of modern cephalopods, the jaw apparatus of ammonoids consists of upper and lower elements. Comparative anatomical examination of the attachment scars of chitin-secreting cells (beccublasts) on the jaw lamellae allow us to reconstruct the buccal mass structure of ammonoids. The jaw apparatuses of ammonoids can be classified into the normal, anaptychus, aptychus, intermediate, and rhynchaptychus types based mainly on the differences in overall morphology and lamellar composition in the lower jaws. The fairly large variation of the jaw morphology and the variety of food remains preserved in the digestive tract and buccal cavities in Mesozoic ammonoids may reflect diversity of feeding and diets ranging from predatory via scavenging to microphagous habits.
This paper presents the results of a study of the aptychi collected from nine Lower Cretaceous sections belonging to the Subbetic Zone in SE Spain. The aptychi were collected together with stratigraphically significant Late Berriasian/Early Valanginian, Late Valanginian and Late Hauterivian
ammonites. In this collection of aptychi, 18 species of three genera are identified; three species are new: Mortilletilamellaptychus undulatiformis n. sp., Thorolamellaptychus subangulatus n. sp., and Didayilamellaptychus praeangulatus n. sp.
The jaw apparatus of the genus Kachpurites (Ammonoidea, Craspeditidae), consisting of a pair of aptychi and a beak-shaped upper jaw is described and figured for the first time. A new aptychus species Praestriaptychus fulgens sp. nov. is established. Aptychi of this species are elongated-triangular, weakly ribbed, with a well-developed inner organic layer and a considerably thinner, often poorly preserved external calcite layer. Specimens of the type series were found in the body chamber of ammonites Kachpurites fulgens (Trautschold), from the Upper Jurassic (Upper Volgian) Kachpurites fulgens Zone of Moscow and the Moscow Region.
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Unfortunately there is an error in the translation from Russian to English in this article. On page 583 the external (outer) lamella of the upper jaw was named twice as the inner lamella. As printed in the article: "It should be said that quite often the upper jaws of Jurassic and Cretaceous ammonites (belonging to Aptychophora) are found without the INNER lamella". However, "without the OUTER lamella" should have been printed. Somewhat further in the same paragraph, the error persists: "suggest that the records of jaws lacking the INNER lamella are the product of separation of two loosely connected elements in the jaw, rather than the reduction of the outer lamella", whereas it should have stated that: "suggest that the records of jaws lacking the OUTER lamella are the product...".
The distribution of the Central Russian representatives of the genus Delphinites is discussed. Apart from the Lower Valanginian Delphinites undulatoplicatilis Zone in the type region (Menya River, Chuvashia, Middle reaches of the Volga River), they are found in the Kostroma Region, in the basin of the Unzha River, together with Euryptychites ex gr. astieriptychus, Siberites cf. ramulicosta and Buchia keyserlingi var. sibirica. This assemblage indicates the Lower Valanginian, most likely the upper part of the Hoplitoides Zone to the lower part of the Michalskii Zone.
This paper presents the taxonomic revision of Late Jurassic and Early Cretaceous aptychi housed at the National Museum of Natural History, Sofia (Bulgaria). The aptychi came from the pelagic, flysch-like and flysch deposits of Central and North Bulgaria, and most of them have been initially described by STEFANOV (1961). The taxonomic revision has led to the determination of 23 species and subspecies of six genera. A new species named Mortilletilamellaptychus stefanovi is described. The collection contains also the holotype of Didayilamellaptychus filicostatus (STEFANOV), which was previously elevated from a variety to species level by MECHOVA et al. (2010). A valve of Didayilamellaptychus cf. didayi preserved in the body chamber of a Neolissoceras supports the hypothesis that lamellaptychi and perhaps punctaptychi belong to the natural system of ammonites of family Haploceratidae ZITTEL, 1884. It became evident that the state of preservation may strongly affect the taxonomic determination of the aptychi. Only in exceptional cases (occurrence of both valves in a pair with different state of preservation) this preservation phenomenon can be revealed and erroneous determination of any of the valves could be possibly avoided.
Two findings of ammonoid jaw aparatusses from the Callovian of Russia are described and classed with the genera Costacadoceras and Kosmoceras, respectively. Their different morphology confirm the opinion that both genera do not belong to the same superfamily Stephanoceratoidea as mentioned by ARKELL et al. (1957), rather the Kosmoceratids have to classify with the Perisphinctoidea.
Three-dimensionally preserved ammonoid and coleoid jaw elements are described from
the Lower Callovian of the Unzha-river region. Isolated praestriaptychi are attributed to the kosmoceratid
ammonites Kepplerites/Sigaloceras based on correlation between their shape with the
outlines of aperture of ammonite conchs found in the same strata. The width/length-ratios of the
aptychi cluster into four morphotypes representing macro- and microconchs of two species. Only one
incomplete praestriaptychus valve may represent a perisphinctid. The praestriaptychi of Kepplerites/
Sigaloceras exhibit a thin lamellar calcite coating composed of rosette-like calcification centres. Two
complete jaw apparatuses of the aptychophoran kosmoceratid Kepplerites show reduced rostra of
their upper jaws of the same length as the lower jaws. The reduced or complete absence of a rostrum
suggests that the aptychus bearing ammonits did not eat large prey, because they could not hold and
cup up it. Therefore, we suggest that the Middle Jurassic aptychophoran ammonoids fed on plankton
or other minute organisms. We find the function of aptychi as an operculum more important than as a
specialized feeding apparatus. In contrast to the simplified morphology of upper ammonoid jaws, the
associated upper jaws of coleoids, probably belonging to belemnites, are characterized by prominent
rostra. A small isolated shovel-like jaw element may represent the lower jaw of a vampyromorph
coleoid.
The book summarizes information on taxonomic diversity, stratigraphic confinement and geographic differentiation of the Jurassic belemnites of the family Cylindroteuthidae. The range of species and genera, their diag-noses and systematic assignment are revised and according to the revision there are suggested modified system of family and the charts showing phylogeny of species, subgenera and genera developed by the authors. Special emphasis is laid on morphologic features and change of characters of rostrum ontogeny as well as on the main courses in evolution of cylindroteuthids, geographic and stratigraphic distribution, that allowed us to suggest a fresh evaluation of taxonomic importance of the features. Detailed charts for biostratigraphic subdivision based on the Callovian and Upper Jurassic belemnites from West and East Siberia are proposed. Correlation charts for reference sections were developed with consideration for the revision of taxonomic composition of belemnite assemblages from these sections.
The book is meant for the geologists studying the Mesozoic deposits, paleontologists and stratigraphers.
Delphinites (Family Neocomitidae, Subfamily Platylenticeratinae) is described from Traill Ø and Wollaston Forland in North-East Greenland, where it is represented by two new species of the subgenus Pseudogarnieria: Delphinites (Pseudogarnieria) christenseni n.sp. and Delphinites (Pseudogarnieria) donovani n. sp. The material indicates the presence of equivalents of the Delphinites (Pseudogarnieria) undulatoplicatilis Zone of the Russian Platform, and of the Thurmanniceras pertransiens Zone of South-East France. These Greenland occurrences are therefore correlatable with the lowest biozones of the Valanginian Stage in both the Boreal and the Tethyan realms. The genus was previously known almost exclusively from the Russian Platform, and it has an essentially marginal Boreal distribution.
The fauna of Mesozoic epicontinental seas that existed on the territory of the present-day Arctic margin of Eurasia, North America, and islands in the Arctic Ocean is dominated by
stenohaline mollusks (ammonoids, coleoids, bivalves, gastropods, brachiopods, foraminifers,
ostracodes, radiolarians, etc.). The marine biota consists of cosmopolitan taxa of the boreal
Pacific and boreal Atlantic origin, Tethyan immigrants, and endemics, including hundreds
of endemic species, tens of endemic genera, and six endemic families. Numerous lines of
invertebrates in the Arctic basin evolved sustainably for tens of millions of years. The high
taxonomic diversity of the specific marine biota and the ways of its panboreal migration
could have been maintained by an oceanic basin occupying the territory of the present-day
Arctic throughout the Mesozoic, as a great volume of oceanic water was necessary to provide
stable salinity and temperature in the surrounding epicontinental basins through 180 Ma.
Long and sustainable development of the specific Mesozoic marine biota was provided by
the South Anyui ocean in the Triassic and Jurassic and by the Amerasian ocean in the
Cretaceous. This evidence substantiates the hypothesis of the presence of oceans in the Arctic
throughout the Mesozoic which was suggested proceeding from geodynamic reconstructions.
Mesozoic, paleoocean, paleontology, geodynamics, paleobiogeography, Arctic
We describe upper and lower jaws of Placenticeras Meek, 1876, from the Upper Cretaceous (upper Campanian) Bearpaw Shale and Pierre Shale of the Western Interior of North America and lower jaws of the related ammonite Metaplacenticeras Spath, 1926, from the Campanian Yasukawa Formation of Hokkaido, Japan. One lower jaw is preserved inside the body chamber of Placenticeras costatum Hyatt, 1903. The other jaws are isolated but are generally associated with fragments of placenticeratid shells. The jaws from North America are attributed to Placenticeras meeki Böhm, 1898, and P. costatum, while those from Japan are attributed to Metaplacenticeras subtilistriatum (Jimbo, 1894). All of the jaws are presumed to be from adults. The jaws of Placenticeras attain lengths of up to 95 mm. They are preserved as steinkerns with a thin film of black material, representing diagenetically altered chitin. X-ray diffraction analysis of samples of this material indicates that it consists of magnesium-rich calcite, pyrite, and amorphous material (organic compounds). The upper jaw is approximately the same length as the lower jaw and is U-shaped, with narrow wings that converge anteriorly to a dome-shaped hood. The lower jaw is composed of two lamellae. The outer lamella is broad and consists of two wings terminating in a bilobate posterior margin. The inner lamella is one-half the length of the outer lamella. The two lamellae are separated except in the apical region and along the sides. The junction between the lamellae appears as a U or V-shaped outline on the anterior portion on the ventral surface of the jaw. This junction is especially conspicuous in specimens in which part of the inner lamella has eroded away. In crushed specimens, the lower jaw is subquadrate in shape. In specimens that retain some or all of their original curvature, the central portion is gently convex and the sides bend steeply dorsally. The rostrum projects slightly anteriorly and dorsally and there is a thickened rim of chitin along the anterior margin where the two lamellae are doubled over. A small indentation appears at the apical end and, in most specimens, develops into a midline slit that extends posteriorly 10–15 mm. However, as shown in well-preserved specimens and based on comparisons with the jaws of closely related ammonites, this slit represents the remnants of a narrow ridge on the ventral side of the inner lamella. This ridge is surrounded by an elongate boss of thickened chitin, which corresponds to a depression on the dorsal side. The ventral surface of the outer lamella bears a midline ridge with a central groove, which essentially forms a continuation of the ridge on the inner lamella. The ventral surface of the outer lamella is ornamented with thin, radial striations and irregular broad undulations paralleling the posterior margin. The posterior end is generally incomplete, probably as a result of predation or postmortem degradation, and the lateral margins are commonly creased, indicating postmortem plastic deformation. The lower jaws of Metaplacenticeras subtilistriatum are much smaller than those of Placenticeras but are otherwise similar in morphology. However, they retain pieces of a very thin, fibrous outer layer comprising two plates. X-ray diffraction analysis of samples of this layer indicates that it consists of calcite enriched in magnesium. Each plate covers the ventral surface of one of the wings and terminates at the midline ridge. Based on the close affinity of Metaplacenticeras and Placenticeras, and in comparison with published descriptions of placenticeratid jaws from elsewhere, we hypothesize that similar plates covered the lower jaws of all placenticeratids, although these plates have not been found in any Placenticeras material from North America. The thin nature and fibrous microstructure of this layer would have made it susceptible to mechanical breakage and chemical dissolution. Furthermore, jaws are internal structures embedded in the buccal bulb. The micro-environment within this bulb may have promoted dissolution of the outer calcitic layer of the lower jaw. The presence of a pair of calcitic plates (aptychi) and a midline ridge with a central groove on the outer lamella of the lower jaw are unique features of the lower jaws of the Aptychophora Engeser and Keupp, 2002. Although differences in preservation obscure this similarity, the lower jaws of placenticeratids conform to the description of aptychus-type jaws. However, unlike the thick calcitic aptychi of other Ammonitina, the thin calcitic aptychi of placenticeratids probably did not function as opercula and would have served simply to strengthen the lower jaw. The jaws of placenticeratids were probably designed for biting and cutting food rather than for passively collecting and straining plankton. Other data about the habitat and mode of life of placenticeratids are consistent with this interpretation. These ammonites probably inhabited surface waters and were capable of pursuing and attacking sluggish prey. An ecological analog of placenticeratids may be the modern ocean sunfish Mola mola (Linnaeus, 1758), which inhabits surface waters and feeds on gelatinous zooplankton.
2008. Double alignments of ammonoid aptychi from the Lower Cretaceous of Southeast France: Result of a post−mortem transport or bromalites? Acta Palaeontologica Polonica 53 (2): 261–274. A new preservation of aptychi is described from the Valanginian limestone−marl alternations of the Vergol section (Drôme), located in the Vocontian Basin (SE France). Aptychi are arranged into two parallel rows which are generally 50 mm in length and separated by 4 mm. The alignments are very often made by entire aptychi (around 10 mm in length), oriented following their harmonic margin. Aptychi show the outside of valve to the viewer: they are convex−up. This fos− silization of aptychi is successively interpreted as the result of post−mortem transport by bottom currents (taphonomic− resedimentation process) or the residues (bromalites: fossilized regurgitation, gastric and intestinal contents, excrement) from the digestive tract of an ammonoid−eater (biological processes). Both the parallel rows of aptychi are more likely in− terpreted as a coprolite (fossil faeces) and they could be considered as both halves (hemi−cylindrical in shape) of the same cylindrical coprolite which would have been separated in two parts (following the long axis) just after the animal defe− cated. Considering this hypothesis, a discussion is proposed on the hypothetical ammonoid−eater responsible for them. Stéphane Reboulet [stephane.reboulet@univ−lyon1.fr], Université de Lyon, (UCBL1, La Doua), UFR des Sciences de la Terre, CNRS−UMR 5125 PEPS, Bâtiment Géode, 2 Rue Raphaël Dubois, 69622 Villeurbanne cedex, France; Anthony Rard [anthony.rard@cc−thouarsais.fr], Centre d'interprétation géologique du Thouarsais, Réserve Naturelle Géologique du Toarcien, Les Ecuries du Château, 79100 Thouars, France.
The older system for classification of ribbed calcareous Early Cretaceous aptychi consisted of two genera: Punctaptychus and Lamellaptychus . Later, I. Turculet divided Lamellaptychus into several subgenera. Within the frameworkof both the genera, species and subspecies were distinguished, which resulted in binominal and trinominal nomenclature.With regard to the richness of newly described species and subspecies in recent years, is not possible to continueusing the original system. It is the basic ribbing that plays the decisive role in the generic and subgeneric classificationof ribbed aptychi. In the case of subspecies systematics, all details on the valve surface are used with the exceptionof the sigmoidal bend (fractocostatus) and radial lines (radiatus) . The ribbed aptychi are newly divided into the followingfamilies: Punctaptychidae fam. nov. and Lamellaptychidae fam. nov. Within the family Punctaptychidae we are ableto distinguish two genera: Punctaptychus Trauth, 1927 and Cinctpunctaptychus gen. nov. The family Lamellaptychidaeincludes five genera differing in the basic arrangement of the ribs: Lamellaptychus Trauth, 1927, Beyrichilamellaptychus Turculet, 1994, Mortilletilamellaptychus gen. nov., Thorolamellaptychus Turculet, 1994 and Didayilamellaptychus Turculet, 1994. Eight species and one subspecies are established as new: Cinctpunctaptychusundulatus, Beyrichilamellaptychus pseudostuderi, Mortilletilamellaptychus mortilletioides, M. submortilleti noricus,M. stanislavi, Didayilamellaptychus hennigi, D. andrusovi and D. renzi
Elements of the jaw apparatuses of the ammonite genus Kepplerites (Ammonoidea: Stephanoceratoidea, Kosmoceratidae, Keppleritinae) are described from two Upper Bathonian and one Lower Callovian localities of the Russian Platform. The lower jaws (aptychi), based on their size and shape can be assigned to two groups and certainly belonged to the co-occurring macroconchs K. (Kepplerites) and theirs microconchs K. (Toricellites). It is established that the presence or absence of tuberculate ornamentation on the surface calcite layer in the studied kosmoceratid aptychi (and accordingly the assignment of the aptychi of kosmoceratids to Granulaptychus-type or Praestriaptychus-type) is a result of burial and fossilization in different settings. Most likely all Kosmoceratidae had lower jaws of the Granulaptychus-type, apparently like the related subfamily Garantianinae (family Stephanoceratidae). For the first time, upper jaws of cephalopods supposedly also belonging to the ammonites of genus Kepplerites are described from the Bathonian Stage.
The discovery of a hermit crab (superfamily Paguroidea) preserved in the likely immature shell of an ammonite, Craspedites nekrassovi is reported from the Upper Jurassic of Moscow, Russia. This is the oldest undoubtable symmetrical hermit crab to date which is known from non-reefal environments. This new occurrence combined with the documentation of numerous sublethal and lethal injuries on ammonite shells in the same beds (probably produced by such paguroids), all suggest that the hermit crabs not only lived in ammonite shells but also hunted these animals. The proportion of damaged shells (including healed ones) varies in different Upper Jurassic ammonite genera from 1.2% in Kachpurites up to 9.3% in Craspedites. Among damaged Kachpurites only 6.25% survived attacks whereas among Craspedites the percentage of survivors was 87.5%. These data imply that Craspedites likely lived near the sea bottom and often encountered hermit crabs, whereas Kachpurites likely lived in the water column.
New data about ammonites and high-resolution ammonite-based biostratigraphy of all Boreal areas are provided. For some regions succession of biohorizons are proposed for the first time. This Thesis is illustrated by 110 plates with ammonites
Since the last review of Jurassic—Cretaceous ammonoid ecology (Westermann, 1990), much additional work has been done on ammonoid autecology (architecture or macrostructure) as well as on the associations and occurrences of ammonoids in the field (synecology). Important works on Paleozoic through Triassic ammonoids, dispersed in the literature, have not been reviewed previously. Quantitative autecological studies, begun in the mid-1980s, concerned buoyancy and orientation. Electron and light microscopic studies of the shells have also contributed to an understanding of the soft parts. Research on shell fabrication, strength, and hydrodynamics has increased greatly, also contributing to ammonoid autecology. Intraspecific morphological variation has been studied intensively but remains poorly understood ecologically; most authors still fail to consider variation in the functional interpretation of shell shape. Ammonoid synecology was significantly advanced in recent years by the renewed interest in Paleozoic and Mesozoic dysoxic black-shale facies and their relation to eustasy and orbitally enforced cycles. Other recent studies in synecology have emphasized the interrelations among sediment, eustasy, and biofacies. Finally, ammonoid taxonomy has been summarized in The Ammonoidea (Special Volume 18, The Systematics Association, 1981).
The Late Ryazanian - Early Hauterivian ammonite fauna of North-East Greenland is unusually rich, diverse, and dominated by Boreal polyptychitids but also contains a significant number of Tethyan taxa. The fauna is best known from highly fossiliferous localities on Traill 0, but only a small part of the fauna was described more than 50 years ago. The original material and additional collections from Traill 0 and the Wollaston Forland form the basis of a full description and revision of the fauna. Over 70 ammonite species are described and include 13 new species and one new subgenus: Tollia (Neocraspedites) pentagonalis sp. nov., T. (N.) piaseckii sp. nov., T. (N.) rutila sp. nov., Menjaites (Menjaites) groenlandicus sp. nov., M. (Surlykites) surlyki subgen. nov. et sp. nov., Polyptychites (Polyptychites) robertsi sp. nov., P. (P.) rawsoni sp. nov., P. (P.) copiocostatus sp. nov., P. (P.) rubricosussp. nov., P. (Euryptychites) molsbergensissp. nov., P. (E) subcoronatus sp. nov., P. (E.) roemeri sp. nov., and Dichotomies? mackneyi sp. nov. One new nautiloid species, Paracymatoceras rufum sp. nov., is also described. The first Upper Ryazanian - Lower Hauterivian ammonite zonation in North-East Greenland is established, with 11 zones, partly adopted from extant schemes elsewhere. The Upper Ryazanian is represented by the Analogus, Tzikwinianus, and Albidum Zones adopted from the Russian Platform and Siberia. The Lower Valanginian is represented by the Undulatoplicatilis, Hoplitoides, and Michalskii Zones adopted from the Russian Platform. The Upper Valanginian is represented by the Hollwedensis, Crassus, and Bidichotomoides Zones adopted from the NW European (German) zonation. The Lower Hauterivian is represented by the first Simbirskites recorded in North-East Greenland. The fauna occurs in a thin interval of grey and red mudstones of the Albrechts Bugt and Rødryggen Members, respectively. The interval is characterized by major changes in the depositional environment, ecology, and biogeography, and represents a time of major palaeoceanographic change. Possibly, deep water formed in the Polar Boreal Sea and resulted in a southwards-flowing bottom current, which ventilated the water masses in the narrow epeiric seaway between Eastern Greenland and Norway. In response, a surface counter-current flowing towards the north allowed ammonite taxa to migrate thousands of kilometres from Tethys and become important elements in the North-East Greenland fauna.
Some ammonoids have been found with structures still in the living chamber that are now recognized as jaws (beaks or mandibles) because small teeth, characteristic of those of the radula of extant Cephalopoda, lie between upper and lower jaws. The radulae so far found in ammonoids have the same number of teeth in each transverse row as do those of living Coleoidea, and the teeth are of similar shape and form. The first discovery was of just a few teeth in Eoasianites (Closs and Gordon, 1966), a member of the taxon Goniatitina. A year later, eight specimens of the same species, in which the radula and jaws were preserved together, were reported (Gloss, 1967). The jaws and radulae of two adult microconchs of Eleganticeras elegantulum, a Liassic ammonite, were found by Lehmann (1967); other descriptions have followed, mostly of jaws but also of radulae (for reviews see Lehmann, 1971a, 1981a,b, 1988, 1990; Dagys et al.,1989).
Latest Jurassic–earliest Cretaceous hydrocarbon seeps from Spitsbergen, Svalbard, are
known to contain unusual fauna, lacking most of the species characteristic for roughly
coeval seep deposits. This study summarizes and analyses the fauna from 16 seep carbonate
bodies from Spitsbergen to explain its composition. The seeps formed in a
shallow epicontinental sea with widespread deposition of fine-grained, organic-rich
sediments. They are spread over a relatively large area and are positioned roughly in
the same interval, indicating seepage over extensive areas of the palaeo-Barents Sea.
The seep fauna is very species rich and with low dominance, comprising 54 species,
with a composition similar to that of Jurassic–Cretaceous normal-marine environments
of other Boreal seas. Seep-restricted fauna is not abundant and is represented
by four species only. Hokkaidoconchids and possible siboglinid worm tubes characteristic
for high sulphide fluxes are rare. Apart from seep-restricted sulphide-mining lucinid
and thyasirid bivalves, chemosymbiosis was also a source of nourishment for
background solemyid and nucinellid bivalves, all of which take sulphide from infaunal
sources. This all suggests a relatively weak sulphide flux. The high diversity and low
dominance of the fauna and significant richness and abundance of background species
is typical for shallow water seeps. □
The Westermann Morphospace method displays fundamental morphotypes and hypothesized life modes of measured ammonoid fossils in a ternary diagram. It quantitatively describes shell shape, without assumption of theoretical coiling laws, in a single, easy-to-read diagram. This allows direct comparison between data sets presented in Westermann Morphospace, making it an ideal tool to communicate morphology. By linking measured shells to hypothesized life modes, the diagram estimates ecospace occupation of the water column. Application of this new method is demonstrated with Mesozoic data sets from monographs. Temporal variation, intraspecies variation, and ontogenetic variation are considered. This method can address hypothetical ecospace occupation in collections with tight stratigraphie, lithologie, and abundance control, even when taxonomy is in dispute.
Zusammenfassung Funde von zusammengehörigen Ober- und Unterkiefern der GattungenPsiloceras, Pleuroceras undArnioceras beweisen, daß die sogenannten «Anaptychen» der Lias-Ammoniten im Gegensatz zu früheren Annahmen keine Deckel sind, sondern
Kieferelemente. Es wird ein nach Serienschliffen angefertigtes Modell des Kieferapparates einesPsiloceras sp. gezeigt.
Species ofNeogastroplitesdisplay a wide range of morphological variability such that withouta prioriknowledge of the stratigraphical location of some individuals, it is not possible to make an unequivocal specific determination on familiar traditional grounds. Using new techniques of geometric morphometric analysis it is possible to narrow down the margin for error in determining isolated specimens. We have also demonstrated that there are slight though significant differences in average lateral shape of the three species studied in this note:N. americanus,N. muelleriandN. cornutus. If counts of rib-frequencies are admitted into the analysis, the discriminatory effect is heightened. Unexpectedly, the addition of maximum whorl-breadth, a standard distance measure, to the analysis has a relatively slight positive effect on the results. A canonical analysis of the full data-set provides evidence of a gradual shift in shape and ornament over time.
The different forms of the aptychi (opercula, homologous with lower jaws) of the Ammonoidea are used for the first time in a phylogenetic analysis of part of the classic Ammonoidea phylogeny. The results indicate that the aptychi-possessing ammonoids form a monophylum for which we propose the informal name Aptychophora nov. Among the Jurassic ammonoids, it is possible to recognize several monophyletic groups. In part, our results support existing superfamilies (e.g. Hildocerataceae, Haplocerataceae) by new synapomorphies. However, the Perisphinctaceae can now be much more clearly differentiated than in the previously established phylogenetic tree. The Upper Cretaceous ammonoid superfamilies cannot be derived from the Haplocerataceae, but are descendants of a ‘primitive’ perisphinctacean possessing a praestriaptychus. Nor can they be derived from the ‘higher’ perisphinctaceans (family Perisphinctidae) because that clade is characterized by granulaptychi. The consequence of these results is that the quadrilobate primary suture of the ‘Ancyloceratina’ must have evolved more than once by reduction from an ancestral quinquelobate primary suture. The Ancyloceratidae have praestraptychi or aptychi types which can be derived from praestriaptychi, whereas the Crioceratitinae have longitudinally striated anaptychi.
Die Kieferapparate der Ammoniten-GattungenEleganticeras, Hildoceras, Normannites, Scaphites, Physodoceras andQuenstedtoceras (beiQuenst. nur Unterkiefer) werden beschrieben. Dabei zeigt sich die Identität von Unterkiefer und Aptychen dieser Gattungen. Es wird
gefolgert, daß die Aptychen allgemein auch funktionell Unterkiefer waren und höchstens in besonders gelagerten Fällen zusätzlich
eine Schutzfunktion als Deckel ausgeübt haben können.
The jaws of the ammonite generaEleganticeras, Hildoceras, Normannites, Scaphites, Physodoceras, andQuenstedtoceras (ofQuenst. lower jaws only) are described. Lower jaws and aptychi of these genera are shown to be identical. They consist of an inner
layer of organic material, which corresponds to the complete anaptychi of liassic ammonites, and an outer layer of calcitic
material deposited on both flancs of the lower jaw, giving rise, after decay of the organic layer, to the aptychi.
Previously published interpretations of aptychi as opercula or hoods are discussed and rejected. It is concluded that they
certainly functioned as jaws or possibly shovel-like devices.
The Upper Substage of the Volgian Stage of Central Part of the Russian Platform
- P A Gerasimov
Gerasimov, P.A., 1969. The Upper Substage of the Volgian Stage of Central Part of the
Russian Platform. Nauka, Moscow, p. 144 (in Russian).
A unique record of aptychi in ammonites from the subfamily Simbirskitinae Spath
- E Baraboshkin
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- I A Shumilkin
Baraboshkin, E.Yu., Shumilkin, I.A., 2010. A unique record of aptychi in ammonites
from the subfamily Simbirskitinae Spath, 1924. In: Sadovnichiy, V.A.,
Smurov, A.V. (Eds.), Life of the Earth. Geology, Geodynamics, Ecology, Museology. Collection of Scientific Papers by Earth Science Museum at Moscow State
University. MSU, Moscow, pp. 132e136. Moscow (in Russian).
Boreal Late Jurassic belemnites (Cylindroteuthinae) of the Russian platform
- Gustomesov
Gustomesov, V.A., 1964. Boreal Late Jurassic belemnites (Cylindroteuthinae) of the
Russian platform. Transactions of the Geological Institute, Academy of Sciences
of the USSR 107, 91e218 (in Russian).
Paleontology of the Upper Missouri
- Meek
Meek, F.B., Hayden, F.V., 1864. Paleontology of the Upper Missouri. Smithsonian
Contributions to Knowledge 172, 1e135.
Berriasian and Lower Valanginian ammonites of the Russian Platform
- Sasonova
Aptychi and stratigraphy of the Lower Cretaceous in the Western Carpathians
- Vašíček
Va sí cek, Z., 1996. Aptychi and stratigraphy of the Lower Cretaceous in the Western
Carpathians. Mitteilungen aus dem Geologisch-Pal€ aontologischen Institut der
Universit€ at Hamburg 77, 221e241.
Ammonites and infrazonal stratigraphy of the Kimmeridgian and Volgian stages of Panboreal Superrealm
- M A Rogov
Rogov, M.A., 2021. Ammonites and infrazonal stratigraphy of the Kimmeridgian and
Volgian stages of Panboreal Superrealm. Transactions of the Geological Institute
627, 1e732 (in Russian with English summary).
Berriasian and Lower Valanginian ammonites of the Russian Platform. Transactions of All-Russian Geological Oil Institute (VNIGNI)
- I G Sasonova
Sasonova, I.G., 1971. Berriasian and Lower Valanginian ammonites of the Russian
Platform. Transactions of All-Russian Geological Oil Institute (VNIGNI) 110,
3e110 (in Russian).
A unique record of aptychi in ammonites from the subfamily Simbirskitinae Spath, 1924
- Baraboshkin