Search

A juvenile orthocerid Dolorthoceras sp. from the Frasnian (Late Devonian) of the Polar Urals in NW Russia is the first recorded ectocochleate cephalopod showing fibrous structures and the first Devonian cephalopod preserving nacreous structures within its conch. Like Nautilus, Dolorthoceras sp. has columnar nacre in its shell wall and septa, which are composed of differentiated nacreous tablets that are c. 3 µm and 10 µm in diameter. The central, small, cylindrical, hollow siphonal tube—studied in median section using scanning electron microscope—comprises short columnar-nacreous suborthochoanitic septal necks and thin, apparently primarily chitinous, connecting rings; swollen, lens-shaped in median section, two-part fibrous non-biomineralized structures—here named clutches—envelope the posterior parts of the septal necks. Together with the adjacent connecting ring, the outer part of the clutch may extend onto adapical septal surfaces; their inner part and adjoining from inside next connecting ring line the septal neck. The clutches are comparable, to some degree, to the auxiliary deposits and cuffs of the siphonal tubes found in ammonoids; these are interpreted as being protective structures of the conjunctions between the connecting rings and septal necks reinforcing it against hydrostatic pressure, which was probably also the case in Dolorthoceras. Tracing the Silurian to Cretaceous longiconic cephalopods with narrow, central to eccentric, hollow siphonal tubes and swollen posterior portions of the septal necks shows that the Dolorthoceras-type siphonal tube may represent a conch structure that persisted throughout about 370 million-year-long evolutionary history of orthocerid cephalopods.

The Ypresian Antarcticeras Doguzhaeva has an internal conch and a central siphuncle that have been recently found also in the Late Devonian longicone. The Antarcticeras-related concept of t...

The limited record of the bactritoid-like coleoid cephalopods is here expanded due to discovery of a late Carboniferous (Moscovian) orthocone comprising a phragmocone and a body chamber with a proostracum-like structure, a sheath-like rostrum, an ink sac, and a muscular mantle preserved on top of the conch. The specimen comes from the Wewoka Formation in the vicinity of the city of Okmulgee, Oklahoma, which previously yielded an orthocone indicative of an evolutionary branch of the Carboniferous cephalopods described as the order Donovaniconida Doguzhaeva, Mapes, and Mutvei, 2007a within the subclass Coleoidea Bather, 1888. Here, we describe from that site a bactritoid-like coleoid,Oklaconus okmulgeensisn. gen. n. sp. in Oklaconidae n. fam. A broad lateral lobe of the suture line and a compressed conch with a narrowed dorsal side and a broadly rounded ventral side distinguish this genus fromDonovaniconusDoguzhaeva, Mapes, and Mutvei, 2002b. The muscular mantle is preserved as a dense sheet-like structure, with a crisscross pattern and a globular-lamellar ultrastructure. Recent knowledge on the early to late Carboniferous coleoids is discussed. Carboniferous coleoids show a high morphological plasticity with a capacity for being altered to create the diverse combinations of ‘bactritoid’ and ‘coleoid’ structures. This could be the principle evolutionary driver of their radiation in the late Carboniferous.

Here we report the discovery of an Early Carboniferous (Late Visean) 3D cephalopod beak displaying significant similarity to the lower beak of Recent coleoids. It was uncovered in a fragmentarily preserved, longiconic shell from the Moorefield Formation in Arkansas, USA. This shell comprises a fractured 29-mm-long body chamber having a maximum diameter of ~14 mm and showing an indistinct pro-ostracum-like structure. The beak-bearing shell could easily have been mistaken for a bactritid or orthocerid if it were not for a coleoid-type, weakly mineralized, evidently organic-rich shell wall which shows a lamello-columnar ultrastructure of a bulk of shell wall thickness and plate ultrastructure of thin outer layer. The specimen is assigned to an as-yet unnamed shelled coleoid of a so far unknown high-level taxonomic group. A partially exposed, 4.0-mm-long portion of the beak is the lower beak in oblique view from its left side. It exhibits fractured anthracite-like black, apparently originally chitin material, helmet-like general shape, broad hood with narrow shallow median groove and small notch posteriorly, pronounced pointed, non-biomineralized upside belt rostrum, high shoulder and about a 90–100 degrees jaw angle. A broad hood and massive rostrum emphasize its similarity to the lower mandible of Recent Vampyroteuthis and signify that its unique, among living coleoids, structure has been existed for at least since Late Visean time (~333 my).

Scanning electron microscopy, energy dispersive spectrometry and taphonomic analysis are applied for studying of about 250 shells of the pachybelemnopsein belemnites Hibolithes and Pachybelemnopsis ...

15 pages; International audience; We describe an Olenekian (Early Triassic) “fossil squid” belonging to the oldest complex Mesozoic marine biota collected in the Lower Shale unit of the Lower Triassic Thaynes Group in Idaho, USA. The studied specimen shows a tapered structure embedded in a cylindrical soft body. Morphological, ultrastructural and geochemical features of the specimen suggest that it corresponds to an internally-shelled cephalopod exhibiting a tapered micro-laminated gladius with rachis, narrow median and lateral fields and a large conus; a pair of posterior large fin-supported cartilages and fins; ventral and dorsal mantle band-shape structures, the dorsal one being cartilaginous; mantle patches; a stomach containing undigested arm-hooks and sheet-like pieces of potential flooded ink. Coupled SEM/EDS analyses show that (i) arm-hooks and ink were pseudomorphed by nanoparticles (less than 0.6 mm in diameter) of carbon, (ii) gladius and soft tissues were substituted by granules of calcium phosphate, (iii) cartilage canalicula’s were partially filled with calcium phosphate grains and crystals of Zn- and S-containing minerals. The specimen was hence probably fossilized due to metabolism of P- and C-accumulating bacteria. Based on this specimen, Idahoteuthis parisiana Doguzhaeva and Brayard gen. et sp. nov. and Idahoteuthidae Doguzhaeva and Brayard fam. nov. are erected. This family is characterized by an elongated, cylindrical, dorsally cartilaginous muscular mantle; well-developed, about 0.2 mantle length, rounded anteriorly and acute posteriorly, fin-supported cartilages and similarly shaped two fins at conical mantle termination, and thin slender gladius with narrow median and lateral fields, rachis and breviconic conus. This family assumedly falls in Myopsida (Decabrachia). A streamlined body, large fin-supported cartilages and eroded arm-hooks in the stomach of Idahoteuthis Doguzhaeva and Brayard gen. nov. suggest that this was a maneuverable cannibal predator that dwelled in the subequatorial shallow sea of the west coast of Pangaea.

The evolutionary process through which the siphonal zone of the cuttlebone of Sepia replaced the tubular siphuncle seen in other shelled cephalopods is poorly understood. Recently, porous connecting stripes, interpreted as homologous to connecting rings of tubular siphuncles, were revealed in Sepia (Acanthosepion) cf. savignyi (Geobios, 45:13–17, 2012). New data on the siphonal zone structure are herein demonstrated through SEM testing of 16 beach-collected cuttlebones of Sepia officinalis from Vale do Lobo, southern Portugal. In examined cuttlebones, the organic connecting stripes are mineralized along their peripheries where they are attached to septa by inorganic–organic porous contacting ridges. The contacting ridges consist of globular crystalline units within an organic matrix; each globule is a stack of rounded alternating organic and mineralized microlaminas parallel to the septal surface; mineralized microlaminas contain carbonate microgranules. Porous connecting stripes together with the contacting ridges may serve as transport routes for the cameral liquid used in buoyancy regulation. The contacting ridges appear to reinforce contacts between the connecting stripes and septa, and may strengthen shell resistance to changing environments. Lamella–fibrillar nacre in septa is demonstrated in Sepia for the first time. Comparison of Sepia and Spirula reveals the common character of their phragmocones, the slit-like shape of the permeable zones between chambers and the siphuncle. Narrowing of the permeable zones may provide shell resistance to high hydrostatic pressure; however, the essentially dissimilar relative length of the permeable zones may results in different capabilities of two genera for buoyancy regulation. In Sepia, long narrow porous inorganic–organic permeable connecting stripes and contacting ridges may allow for rapid buoyancy regulation which would lead to environmental plasticity and higher species diversity.

Data on the re-examined-type specimens of the Early Permian Glochinomorpha stifeli Gordon 1971 (Coleoidea, Cephalopoda) gives new insight into the evolutionary origination of gladius-bearing coleoids in the Late Palaeozoic and suggests their parallel evolution with the belemnoids and phragmoteuthids. The iron-oxidized arm hooks are found in front of a gladius on an un-illustrated paratype (USNM 170614). They are dispersed in a maximum distance equal to 2.5 the gladius length from the incomplete anterior end of the rachis of the gladius. The hook height ranges from less than 1 mm to as much as 4 mm. They have a massive curved base, and a strongly curved shaft with a long thin distal part. The hooks confirm the cephalopod and the coleoid affiliation of G. stifeli that is widely rejected. The iron-oxidized gladii (preserved length is less than 20 mm) show micro-laminations and a fibrous ultrastructure; the fibre bundles are approximately 0.5 μm thick. Lack of calcium and the high content of nitrogen (up to 12% of total weight) confirm the originally non-biomineralized (apparently chitin) composition of the gladii suggested by their fibrous ultrastructure. These data lead to the conclusion that in the evolutionary history of gladius-bearing coleoids, the biomaterial (biochemical) development of the skeleton preceded its morphological transformation. This phenomenon resulted in a recombination of an advanced composition (being non-biomineralized) with archaic features (sensu morphological structure of the posterior part) in the gladius of G. stifeli. The data cast doubt on the hypothesized origination of a gladius from a phragmoteuthid pro-ostracum as well as the evolutionary origination of the gladius-bearing coleoids from pro-ostracum-bearing phragmoteuthids or belemnitids.

Background The Subclass Coleoidea (Class Cephalopoda) accommodates the diverse present-day internally shelled cephalopod mollusks (Spirula, Sepia and octopuses, squids, Vampyroteuthis) and also extinct internally shelled cephalopods. Recent Spirula represents a unique coleoid retaining shell structures, a narrow marginal siphuncle and globular protoconch that signify the ancestry of the subclass Coleoidea from the Paleozoic subclass Bactritoidea. This hypothesis has been recently supported by newly recorded diverse bactritoid-like coleoids from the Carboniferous of the USA, but prior to this study no fossil cephalopod indicative of an endochochleate branch with an origin independent from subclass Bactritoidea has been reported. Methodology/Principal findings Two orthoconic conchs were recovered from the Early Eocene of Seymour Island at the tip of the Antarctic Peninsula, Antarctica. They have loosely mineralized organic-rich chitincompatible microlaminated shell walls and broadly expanded central siphuncles. The morphological, ultrustructural and chemical data were determined and characterized through comparisons with extant and extinct taxa using Scanning Electron Microscopy/Energy Dispersive Spectrometry (SEM/EDS). Conclusions/Significance Our study presents the first evidence for an evolutionary lineage of internally shelled cephalopods with independent origin from Bactritoidea/Coleoidea, indicating convergent evolution with the subclass Coleoidea. A new subclass Paracoleoidea Doguzhaeva n. subcl. is established for accommodation of orthoconic cephalopods with the internal shell associated with a broadly expanded central siphuncle. Antarcticerida Doguzhaeva n. ord., Antarcticeratidae Doguzhaeva n. fam., Antarcticeras nordenskjoeldi Doguzhaeva n. gen., n. sp. are described within the subclass Paracoleoidea. The analysis of organic-rich shell preservation of A. nordenskjoeldi by use of SEM/EDS techniques revealed fossilization of hyposeptal cameral soft tissues. This suggests that a depositional environment favoring soft-tissue preservation was the factor enabling conservation of the weakly mineralized shell of A. nordenskjoeldi., Facultad de Ciencias Naturales y Museo

A pro-ostracum – the anterior dorsal plate subdivided into three longitudinal fields – isdeveloped in Triassic phragmoteuthids (Phragmoteuthis, Breviconoteuthis) and the belemnotheutid? (Lunzoteuthis) but is missing in aulacocerids which have a pro-ostracum-like structure – the dorsal apertural crest with arched growth lines. Two types of pro-ostraca: a Phragmoteuthis-type, characterized by arched growth lines in each field, and a Lunzoteuthis-type, in which the median field has arched growth lines and lateral fields bear converging longitudinal ridges, are distinguished. The pro-ostracum with the ridged lateral fields evidently obtained further rapid development; in the Sinemurian belemnite Nannobelus the ridged lateral fields are already formed by the longitudinally exposed narrow portions of succeeding, overlapping sublayers of the pro-ostracum. This structure apparently enabled efficient mantle/shell linkage that facilitated effective manoeuvring, an active mode of life and global radiation of Jurassic belemnites. Exceptional, large scale, preservation of pro-ostraca in lower Carnian of Schindelberg, Lower Austria, and Raibl, North Italy, was possibly due to the concurrency of (1) an environment of the northern Tethys that allowed for post-mortem carbon substitution of chitin and other non-biomineralized material, such as ink and mantle tissue, and (2) the inorganic-organic composition of pro-ostracum as indicated by micro-laminations typical of chitin-containing material and characterized by alteration of chitinous and carbonate laminas similar to those in cuttlebones of Recent Sepia.

Morphological features of the shell including internal structures of the phragmocones of three different bactritoid cephalopod taxa assigned to the Order Bactritida: Bactrites quadrilineatus, Ctenobactrites lesliensis (L. Carboniferous) and the Order Parabactritida: Rugobactrites jacksboroensis (U. Carboniferous) were studied. The material comes from South Central USA. The features examined include the conch shape, siphuncle shape and ultrastructure of the shell wall, septa, septal neck and the connecting ring. These traits were then compared with Shimanskya postremus from Upper Carboniferous of Texas, which has been originally referred to bactritids and later placed within the coleoids in the Order Spirulida. Based on similarities and differences observed, B. quadrilineatus and C. lesliensis are now also considered being coleoids similar to S. postremus; R. jacksboroensis remains placed in the Order Parabactritida.

The pro-ostracum of the early Sinemurian belemnite Nannobelus from the Belgian Province of Luxembourg is preserved as a thin, irregularly mineralized (phosphatized and pyritized), finely laminated ...

The skeletal structure, herein termed “connecting stripes”, is demonstrated in dried cuttlebones of Sepia (Acanthosepion) savignyi de Blainville from the Gulf of Aqaba, Red Sea, Eilat, Israel. This structure consists of segmented chitinous strip-like sheets covering the outside opening to the cuttlebone chambers. Scanning electron microscope images demonstrate that the connecting stripes are tightly attached to the neighbouring septa along the septal edges and do not continue from one chamber to the next. When broken, they leave band-like remnants along the attachment sites. The connecting stripes consist of fibrous, organic, possibly mainly chitinous, laminas. Chemical analysis using energy dispersive spectrometry shows that the connecting stripes contain C, O, Na, K but lack Ca and P. The connecting stripes show perceptible, usually barely visible micropores with diameter of ca. 0.1 μm; distances between the micropores are 0.2 to 0.3 μm. The connecting stripes in Sepia are similar to connecting rings in bactritoids and ammonoids in having a segmented structure and a non-mineralized, organic composition. The microporosity of connecting stripes observed in Sepia has been also recorded in three genera of Mesozoic ammonoids. The connecting stripes may serve as a transport route of the cameral liquid in and out of the chambers and are considered to be a homologue of the connecting rings in cephalopods with a fully developed siphonal tube.

An unusual, bilaterally symmetrical black structure that embraces the protoconch and the phragmocone and is overlain by a rostrum has been studied in the Santonian– early Campanian (Late Cretaceous) belemnite genus Gonioteuthis from Braunschweig, north-west Germany. The structure is here named the capsule. Energy dispersed spectrometry analyses of the capsule show a co-occurrence of sulphur with zinc, barium, iron, lead and titanium, suggesting their chemical association. The capsule was originally made of organic material that was diagenetically transformed into sulphur-containing matter. The material of the capsule differs from the chitin of the connecting rings in the same specimens. The capsule has a complex morphology: (1) ventral and dorsal wing-like projections that are repeated in a breviconic shape of the alveolus, (2) an aperture with lateral lobes and ventral and dorsal sinuses copied by growth lines and (3) a ventral ridge that fits with the position of the fissure in the rostrum. The alveolus in the most anterior part of the rostrum is crater-like. It is lined with thin, pyritized, laminated material, which appears to be the outermost portion of the capsule attached to the inner surface of the rostrum. A flare along the periphery of the alveolus marks a region where the rostrum was not yet formed, suggesting that the capsule extended beyond the rostrum. Modification of the skeleton in Gonioteuthis comprises a set of supposedly interrelated changes, such as innovation of the organic capsule, partial elimination of the calcareous rostrum and a diminishing of the pro-ostracum, resulting in the appearance of a new type of pro-ostracum that became narrower and shorter and lost the spatula-like shape and gently curved growth lines of a median field that are typical for the majority of Jurassic and Cretaceous belemnites. The partial replacement of a calcareous rostrum with an organic capsule in belemnitellids may have been an adaptive reaction to an unfavourable environmental condition, perhaps related to difficulties in calcium carbonate secretion during the Late Cretaceous that forced animals to reduce carbonate production and to secret an organic capsule around the protoconch and the phragmocone.

A new species of Cardiocarpus from the Sim River Basin in the southern Urals of Russia is the first anatomically preserved cardiocarpalean ovule from the Permian of the Angara floral province. Specimens are preserved in a soft organic limestone with large numbers of juvenile bactritoid protoconchs. Ovules are roughly ellipsoidal in the major plane, up to 6.0–7.5 mm in length and 5.3 mm in width, with a diminutive wing and a rounded chalaza. The outer surface of the ovules is smooth. In longitudinal sections, two vascular tissue channels traverse the sclerotesta at the chalaza, and appear to extend to near the apex within each wing. There is a simple, dome-shaped pollen chamber at the apex, which lies below a narrow micropyle. The sclerotesta consists of one or two layers of longitudinally orientated cells at the interior, and sclereids that are radially elongated towards the periphery. The sarcotesta is incompletely preserved, but displays an outer layer of cells that are somewhat elongated towards the long axis of the ovule. Numerical cladistic analysis reveals little correlation between the structure of cardiocarpalean morphotaxa and the phylogenetic relationships of the plants that produced them, where affinities are known. Cardiocarpus angarensis sp. nov. enriches our understanding of Permian spermatophytes in temperate climates of the Northern Hemisphere, and reveals that ovules similar to those of Euramerican and Cathaysian provinces characterized an Angaran spermatophyte. Journal compilation © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155, 297–305. No claim to original US government works.

The varying body chamber lengths and the different attachment of muscles and mantle to conch wall belong to the major adaptations to their diverse modes of locomotion. Therefore, these traits are indirect indicators of different life styles. The sparse record of ammonoid body chamber lengths and attachment marks has impeded the understanding of this aspect of ammonoid paleobiology. The examination of body chamber length revealed that the decrease of the ammonitella body chamber lengths shows is the long-term trend characterizing the evolutionary development of the Goniatitida–Prolecanitida–Ceratitida–Phylloceratida branch of the Ammonoidea. The analysis of the body chamber lengths and the attachment marks leads to conclusion that a precondition for the jet-powered swimming of ammonoids is less than one whorl body chamber length and the position of the attachment marks in sites from where the cephalic retractor and funnel retractor muscles would be able to extend straight across to the head and to the funnel. This is the case of goniatitids and ammonitids possessing moved forward large ventrolateral muscle marks; jet-powered swimming is highly probable for them. None of the universal small dorsal, umbilical and ventral marks may be left in the attachment sites of the cephalic retractor and funnel retractor muscles. In the hook-shaped terminal body chambers of heteromorph ammonoids, like Audouliceras, the long tongue-like umbilical marks perhaps indicate the moved forward strong umbilical muscles adapted for regular change of the mantle cavity volume for sucking and filtering seawater. This suggests that such ammonoids fed on fine plankton or suspended organic rich substance. Their irregular coiled spiral shells, best suited to floating and perhaps vertical (diurnal) migrations, support the view above. The fossilized mantle so far described in the ceratitid ammonoid Austrotrachyceras has a laminated structure fibrous seen in internally shelled Jurassic belemnotheutis and Loligosaepia.

The present chapter is a review on the aberrant shell wall structures of some ammonoids characterized by additional external layers. Secondary deposits of shell on the outside of the conchs of some ammonoid species suggest that the body exceeded the body chamber volume and the mantle coated the shell.

Early Jurassic belemnites are of particular interest to the study of the evolution of skeletal morphology in Lower Carboniferous to the uppermost Cretaceous belemnoids, because they signal the beginning of a global Jurassic–Cretaceous expansion and diversification of belemnitids. We investigated potentially relevant, to this evolutionary pattern, shell features of Sinemurian–Bajocian Nannobelus, Parapassaloteuthis, Holcobelus and Pachybelemnopsis from the Paris Basin. Our analysis of morphological, ultrastructural and chemical traits of the earliest ontogenetic stages of the shell suggests that modified embryonic shell structure of Early–Middle Jurassic belemnites was a factor in their expansion and colonization of the pelagic zone and resulted in remarkable diversification of belemnites. Innovative traits of the embryonic shell of Sinemurian– Bajocian belemnites include: (1) an inorganic–organic primordial rostrum encapsulating the protoconch and the phragmocone, its non-biomineralized component, possibly chitin, is herein detected for the first time; (2) an organic rich closing membrane which was under formation. It was yet perforated and possessed a foramen; and (3) an organic rich pro-ostracum earlier documented in an embryonic shell of Pliensbachian Passaloteuthis. The inorganic–organic primordial rostrum tightly coating the protoconch and phragmocone supposedly enhanced protection, without increase in shell weight, of the Early Jurassic belemnites against explosion in deepwater environment. This may have increased the depth and temperature ranges of hatching eggs, accelerated the adaptation of hatchlings to a nektonic mode of life and promoted increasing diversity of belemnoids. This study supports the hypothesis that belemnite hatchlings were ‘a miniature of the adults’.

Pinaceae is the most species rich and geographically dispersed group of living gymnosperms (Florin, 1963), and comprise a dominant component of modern mountain and boreal forests throughout the northern hemisphere (Florin, 1963). Although there are a few records of possible pinaceous species extending back to the Upper Triassic (Delevoryas and Hope, 1987), unequivocal evidence for the family does not appear until the Cretaceous, and Pinaceae may be the most recently derived conifer family. During the Early Cretaceous, pinaceous remains became common components of terrestrial plant communities, and a diverse array of ovuliferous cones signals an explosive evolutionary radiation within the family (Miller, 1976a). Most of this diversity is chronicled by cones that are clearly representatives of the Pinaceae, but are not assignable to a genus with living species. Cones of these types are assigned to the genera Pityostrobus Dutt, Pseudoaraucaria Fliche, and Obirastrobus Ohsawa, Nishida and Nishida, and have been discovered in a circumpolar distribution from North America, through Europe and Russia, to eastern Asia (Miller, 1976a; Ohsawa et al., 1992; Falder et al., 1998). The purpose of this paper is to extend further the known diversity of the early Pinaceae by the description of a new species of the genus Pityostrobus. This cone is the second Pityostrobus species from southwestern Russia, and it further documents the remarkable Cretaceous evolutionary radiation of Pinaceae. The ovuliferous cone is preserved in a Lower Cretaceous calcareous marine nodule from east of the Black Sea in the northwestern Caucasus of Russia. This nodule also contains an osmundaceous (?) fern rachis, a dispersed Pinus -like conifer needle, and a wood fragment. The nodule was recovered from a stream bed at the Hokodz locality (Hokodz River Basin), that has previously provided well-preserved specimens of both plant and animal fossils, including Pityostrobus milleri, wood fragments, …

A new species of permineralized Pityostrobus cone, Pityostrobus milleri Falder et al., sp. nov. has been discovered in a calcareous nodule from shallow marine sediments of Early Cretaceous (latest Aptian; Clansenian) age in the Caucasus Mountains in southwestern Russia. Nodules of this type also contain wood fragments, gastropods, bivalves, and an extremely rich assemblage of well preserved cephalopods. Russian spore and pollen analyses indicate that deposition in this region may have occurred during a temperate climate regime. The cone is cylindrical, about 2.5 cm in diameter and individual scales contain up to 17 resin canals and 18 vascular strands. Although the fossil displays many features of modern Pinus cones, including inflated scale apexes, resin canals abaxial to vascular tissue in scale base, and scale strands curved on the adaxial side, it cannot be assigned to Pinus because the bract and scale trace are not united at their origin. Tunneled borings in the cortex of the cone axis are tightly packed with frass, and resemble tunnels of modern cone boring beetles such as Conophthorus. This cone further documents the worldwide diversity of pinaceous conifers during the Cretaceous, and demonstrates a well developed syndrome of insect herbivory in the Pinaceae by the late Mesozoic.

About one hundred goniatite beaks (jaws) and five radulae from the Late Mississippian (Early Carboniferous) of Arkansas wgere studied with light and scanning electron microscopy (SEM). Four beaks were found within the body chamber of the goniatite Girtyoceras. Owing to the three-dimensional preservation, these oldest known beaks could be studied in detail and compared with those in living coleoids. The beaks are univalved, and the lower one is larger than the upper. Each beak consists of an organic outer and inner lamella; only the rostrum is weakly calcified. In the lower beak the outer and inner lamellae are about the same length, but in the upper beak the outer lamella is considerably shorter than the inner lamella. The goniatite beaks resemble those in living coleoids in the relative length of the outer and inner lamellae in the upper beak, which probably indicates similarity in muscle insertion. Concerning the length of the inner and outer lamellae, the lower beak is similar to that in Vampyroteuthis and the pelagic octopod Tremoctopus. Late Mississippian goniatite beaks dealt with here are similar to those of Carboniferous and Permian goniatites in general morphology, but differ from those of Mesozoic ammonoids. In the latter ammonoids, the lower beak has a long outer lamella and a short inner lamella, whereas both lamellae have about equal length in the goniatites. Goniatite radulae remain stable during ammonoid evolution and demonstrate a more or less distinct similarity with those in living coleoids.

A new family, Mississaepiidae, from the Sepia-Spirula branch of decabrachian coleoids (Cephalopoda), is erected on the basis of the following, recently revealed, morphological, ultrastructural and chemical traits of the cuttlebone in the late Eocene Mississaepia, formerly referred to Belosaepiidae: (i) septa are semi-transparent, largely chitinous (as opposed to all other recorded cephalopods having non-transparent aragonitic septa); (ii) septa have a thin lamello-fibrillar nacreous covering (Sepia lacks nacre altogether, Spirula has fully lamello-fibrillar nacreous septa, ectochochleate cephalopods have columnar nacre in septa); (iii) a siphonal tube is present in early ontogeny (similar to siphonal tube development of the Danian Ceratisepia, and as opposed to complete lack of siphonal tube in Sepia and siphonal tube development through its entire ontogeny in Spirula); (iv) the lamello-fibrillar nacreous ultrastructure of septal necks (similar to septal necks in Spirula); (v) a sub-hemispherical protocon...

Background: Preservation of original organic components in fossils across geological time is controversial, but the potential such molecules have for elucidating evolutionary processes and phylogenetic relationships is invaluable. Chitin is one such molecule. Ancient chitin has been recovered from both terrestrial and marine arthropods, but prior to this study had not been recovered from fossil marine mollusks. Methodology/Principal Findings: Organics consistent with b-chitin are recovered in cuttlebones of Mississaepia mississippiensis from the Late Eocene (34.36 million years ago) marine clays of Hinds County, Mississippi, USA. These organics were determined and characterized through comparisons with extant taxa using Scanning Electron Microscopy/Energy Dispersive Spectrometry (SEM/EDS), Field Emission Scanning Electron Microscopy (Hyperprobe), Fourier Transmission Infrared Spectroscopy (FTIR) and Immunohistochemistry (IHC). Conclusions/Significance: Our study presents the first evidence for organics consistent with chitin from an ancient marine mollusk and discusses how these organics have been degraded over time. As mechanisms for their preservation, we propose that the inorganic/organic lamination of the cuttlebone, combined with a suboxic depositional environment with available free Fe2+ ions, inhibited microbial or enzymatic degradation. shell morphology and ultrastructure as a key to coleoid cephalopod phylogeny

Ultrastructural study of a longiconic cephalopod, formerly described as Bactrites postremus (Miller, 1930; Mapes, 1979), reveals that the shell wall, consisting of two prismatic layers and lacking a nacreous layer, differs strongly from that of bactritoids. In the bactritoids, the shell wall after hatching is composed of the principal nacreous and thin outer prismatic layers, and only the embryonic shell, or bactritella, has a prismatic ultrastructure (Doguzhaeva, 1996a-c). Phragmocones possessing a marginal siphuncle and a prismatic shell wall are known in Recent Spirula and Cretaceous members of Spirulida: Groenlandibelus, Naefia and Adygeya (Doguzhaeva, 1996d). Ultrastructural comparison of the shell wall in so-called B. postremus and the four spirulid genera listed above supports the conclusion that the two distinctly separated prismatic layers of the shell wall represent the outer and inner plates sensu Appellof (1893), which were secreted as an internal shell. Thus, the form described as B. postremus cannot be assigned to Bactritoidea. It is redescribed as Shimanskya gen. nov. postremus (Miller, 1930), and is considered to be the earliest known member of the order Spirulida. On the basis of this form the family Shimanskyidae fam. nov. is established.

The apical end of Rayonnoceras shell forms a cup-shaped shell primordium with cicatrix. The morphology of the cicatrix is similar to that in recent Nautilus, Shell primordium is flattened ventrally where its margin forms a bilobed structure, which is absent in recent Nautilus and Carboniferous “Orthoceras”, The first segment of the siphuncle is large, pear-shaped and in contact with the shell apex. The first endosiphuncular annular ring fills the entire first siphuncular segment, with the exception of the narrow central canal. The endosiphuncular rings consist of radial lamellae, each of which is composed of crystallites with a feather-like arrangement.

Several exceptionally well-preserved phragmocones of the belemnite Conobelus, with approximately 20 chambers preserved, were collected from the Valanginian of the Crimean Peninsula (Black Sea). The shell structure was studied with SEM. The prismatic wall of the protoconch wedges out near the mural part of the first septum, a short distance after the closing membrane. The prismatic protoconch wall consists of sublayers. In the extremely thin shell wall at the apex, there is a single sublayer. Additional sublayers appear on the inner shell surface at some distance from the apex. The closing membrane, about as thick as the shell wall, is not continuous with wall of the protoconch and conotheca. The primordial rostrum is structurally different from the rostrum, and separated from it by an organic membrane. The first 20 chambers, at least, seem to lack the conotheca proper. The shell wall is here composed of long mural parts of the septa and/or of the prismatic layer of the primordial rostrum. The first septum is prismatic; others are formed by the nacreous layer Type 2 (Mutvei, 1970), which in sections gives an impression of a granular structure; the mural parts of the septa show tabular nacre. At early ontogenetic stages, starting from the sixth septal neck, the transformation from retro- to prochoanitic septal necks occurs. The replacement of retrochoanitic septal necks by prochoanitic (or transitional) necks in Conobelus is similar to that in am- monoids and in some other branches of cephalopods, and, consequently, represents an example of homeomorphy in cephalopod evolution. In addition, the present paper includes an ultrastructural comparison of early shell ontogeny in belemnites and bactritoids.

One of the most intriguing paleobiological problems in ammonoids is to interpret the organization of their muscular system in order to obtain a better understanding of their locomotion and, ultimately, their mode of life. Despite the effects of diagenesis, many ammonoid shells have surprisingly retained visible muscle, ligament, and mantle attachment scars. These scars have been extensively investigated over the last 30 years; in fact, during the quarter of a century that has passed since the classical paper by Jordan (1968), the number of genera exhibiting preserved attachment scars has doubled and is now approximately 80.

The wrinkle layer the inner prismatic layer are described in three Triassic ceratid genera: Phyllocludiscites. Megaphyllites Proarcestes. Both layers have their counterparts in the shell wall of the recent Nautilus: the wrinkle layer corresponds to the mantle-adhesive layer the inner prismatic layer to the myostracal layer in Nautilus. A detailed structural functional comparison between these layers is given. The wrinkle layer is also compared with the oblique prismatic layer in recent gastropods.

From measurements of the thickness of successive growth rings shell growth curves were constructed for seven ammonoid genera of different taxonomic position and geological age. All the curves have ‘sinusoidal’ aspect due to the alternation of maximum and minimum growth increments of the shell tunc. Growth curves made for two ammonoid shells belonging to the genera Proloxyclymenia (D3fm) and Euphylloceras (K1a) show regularly recurring minima and maxima at intervals of 14–16 growth rings. The fact that the minima and maxima of the growth curves recur exactly at intervals of 14–16 growth rings seems to reflect the relationship between the shell tube secretion and the formation of septa. This fact also seems to support the views about fortnightly or 28-day cycles in the construction of ammonoid hydrostatic chambers. By counting the total number of septa in the phragmocones, the duration of phragmocone secretion for 23 shells was estimated. Preliminary inferences on the presence in ammonoid shells of daily, bidaily and weekly growth rings are made. □Ammonoidea, growth rhythms.