The black layer in cephalopods from the German Muschelkalk (Triassic)

Thin, dark, probably phosphatic coatings were found on the dorsum in front of and sometimes behind the aperture of 50 specimens of Paraceratites and Ceratites (Ammonoidea) belonging to 14 species and subspecies and in three specimens of Germanonautilus , all from the Middle Triassic of Germany. The proportions, occurrences, position, outline, and preservation in fossil Nautiloidea and Ammonoidea (originally organic matter) of this structure support the hypothesis that it is homologous with the black layer in Recent Nautilus and Allonautilus . It is not yet possible to test whether these cephalopods show homologous styles of the development of these structures or whether the black layer can be identified in a common ancestor. In contrast to many ammonoids, Ceratites and Paraceratites , most Palaeozoic ammonoids, and some Mesozoic ammonoids probably did not have lower mandibles that were suitable for the closure of the aperture. They probably possessed a dorsally extending mantle (supracephalic mantle fold) and a hood, as in Recent Nautilus and Allonautilus , that was attached to the black layer. This interpretation is corroborated by a similar morphology of the black layer in an adult specimen of the nautilid Cenoceras from the South German Middle Jurassic and three specimens of Germanonautilus from the South German Middle Triassic (both Nautiloidea).     

Soft‐tissue imprints in fossil and Recent cephalopod septa and septum formation

Several soft‐tissue imprints and attachment sites have been discovered on the inside of the shell wall and on the apertural side of the septum of various fossil and Recent ectocochleate cephalopods. In addition to the scars of the cephalic retractors, steinkerns of the body chambers of bactritoids and some ammonoids from the Moroccan and the German Emsian (Early Devonian) display various kinds of striations; some of these striations are restricted to the mural part of the septum, some start at the suture and terminate at the anterior limit of the annular elevation. Several of these features were also discovered in specimens of Mesozoic and Recent nautilids. These structures are here interpreted as imprints of muscle fibre bundles of the posterior and especially the septal mantle, blood vessels as well as the septal furrow. Most of these structures were not found in ammonoids younger than Middle Devonian. We suggest that newly formed, not yet mineralized (or only slightly), septa were more tightly stayed between the more numerous lobes and saddles in more strongly folded septa of more derived ammonoids and that the higher tension in these septa did not permit soft‐parts to leave imprints on the organic preseptum. It is conceivable that this permitted more derived ammonoids to replace the chamber liquid faster by gas and consequently, new chambers could be used earlier than in other ectocochleate cephalopods, perhaps this process began even prior to mineralization. This would have allowed faster growth rates in derived ammonoids.     

Dark bands on pyritic internal moulds of the Early Jurassic ammonites Oxynoticeras and Cheltonia from Gloucestershire,England: interpretation and significance to ammonite growth analysis

Abstract: Thin, radiating, darker bands occur on pyritic internal moulds of the Early Jurassic ammonites Oxynoticeras and Cheltonia from Bishop’s Cleeve, Gloucestershire. They closely resemble true colour patterns preserved in Early Jurassic Calliphylloceras from Kutch, India, and false colour patterns reported in Carboniferous and Triassic ammonoids. Up to five dark bands occur within the body chamber, suggesting that they do not represent serially repeated anatomical structures, but the same feature repeatedly formed during growth. Dark bands are interpreted as traces of black bands deposited on the inside of the shell at the aperture during pauses in growth. The angles between dark bands and between septa correlate strongly in Cheltonia, suggesting that pauses in growth coincided with septal secretion during the chamber formation cycle. There are, however, no other indications that growth was episodic in either genus.     

AMMONOIDS ACROSS THE PERMIAN/TRIASSIC BOUNDARY: A CLADISTIC PERSPECTIVE

Abstract:  The rapid diversification of ceratitid ammonoids during the earliest Mesozoic has been taken at face value as an example of explosive radiation following the Permian/Triassic mass extinction. However, the validity of this interpretation has never been tested within a phylogenetic framework. A total evidence cladistic analysis of Mid–Late Permian and Induan (earliest Triassic) ammonoids confirms the monophyly of the Ceratitida. Partitioned phylogenetic analysis of suture line characters vs. shell shape and ornament characters confirms the importance of suture-line characters for resolving the higher taxonomy of ammonoids. When the cladogram is compared with the observed fossil record, the resultant tree implies that the divergence of a number of early Triassic lineages actually occurred during the latest Permian. If these range extensions are taken into account the ammonoid per-genus extinction rate across the Permian/Triassic boundary drops from c. 85 per cent to c. 60 per cent.     

Ventral bite marks in Mesozoic ammonoids

Reports on the predators of ammonoids are rare, although ammonoids were abundant and diverse invertebrates in many Paleozoic and Mesozoic marine ecosystems. Most previous work on lethal ammonoid predation has focused on (sub)circular tooth marks which resulted from fish and mosasaur attacks. In the present study we discuss a relatively common type of bite mark in ammonoid shells, the ‘ventral bite mark’. This typically occurs in a restricted position on the ventral side of the outer body chamber whorl and does not affect either the aperture or the phragmocone. Ammonoid specimens revealing ventral bite marks used in this study were collected from a wide range of strata which range in age from the Lower Jurassic to the uppermost Cretaceous (close to the Cretaceous–Paleogene boundary). These ventral bite marks are absent in the Paleozoic collections studied. The vast majority of ventral bite marks are situated at the end of the body chamber, close to the phragmocone. This is interpreted as the result of predatory attacks on the back or blind side of ammonoids in their living position. The predators aimed for the vital parts and muscle attachments to obtain the edible soft tissues. The agents for most of the ventral bite marks to ammonoids are probably coleoid cephalopods (especially teuthoids) and predatory fishes to a lesser extent.     

The ammonitella: a model of formation with the aid of the embryonic shell of archaeogastropods

Recent archaeogastropoda secrete their first conch (primary shell) without producing increments of growth. This conch remains attached to the epithelium responsible for its production until completed. Only afterwards does tissue detach from the edge of the shell and the conch begins to function as a protective exoskeleton. After a potential swimming phase by the veliger larva, the organic primary shell is deformed by mechanical means through muscular tension from the inside and the outside of the conch. It then becomes mineralized by aragonitic crystallites and, thus, functional for the use of a benthic animal. The embryonic conch of ammonites (ammonitella) is devoid of increments of growth. The inner lip (dorsal side) of the aperture became flattened after the evenly rounded primary conch had been secreted. The primary organic shell was mineralized by aragonitic crystallites from within. All these features of the formation of the ammonitella can be interpreted in the light of early shell formation of recent archaeogastropods.     

Evolutionary rates of the Triassic marine macrofauna and sea-level changes: Evidences from the Northwestern Caucasus,Northern Neotethys (Russia)

A diverse Triassic marine macrofauna from the Northwestern Caucasus sheds new light on the biotic evolution after the end-Permian mass extinction. In the early Mesozoic, the study area was located on the northern margin of the Neotethys Ocean. Data on stratigraphic ranges of 130 genera of brachiopods, bivalves, ammonoids, corals, and sponges have been used to calculate the changes in two evolutionary rates, namely faunal transformation rate (FTR) and rate of transformation of the taxonomic diversity structure (TTDSR). The FTR demonstrates the changes in the generic composition of assemblages through geologic time, whereas the TTDSR indicates changes in the generic control of the species diversity. The Triassic marine macrofauna of the Northwestern Caucasus was characterized by very high FTR and TTDSR during the Early Triassic through early Late Triassic. The FTR slowed in the Middle Triassic, and accelerated again in the Carnian–Norian. In contrast, the FTR was abnormally slow in the Norian–Rhaetian. A remarkable turnover among macrofauna occurred at the Carnian–Norian transition. Regional sea-level changes were similar to the global eustatic fluctuations. It is difficult to establish their direct connections with changes in the evolutionary rates, although the turnover at the Carnian–Norian boundary coincided with a prominent regressive episode. In general, high evolutionary rates reported for the Triassic marine macrofauna of the Northwestern Caucasus may be explained as a consequence of the devastating end-Permian mass extinction.     

Connecting stripes: An organic skeletal structure in Sepia from Red Sea

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.     

Palaeoenvironmental changes across the Permian/Triassic boundary at Shangsi (N. Sichuan,China)

The section at Shangsi in Sichuan contains one of the most detailed and best records of events during the Permian/Triassic (P/T) mass extinction. Continuous deep water deposition is only punctuated by a minor shallowing in the late Changxingian. The micritic mudstones and wackestones of the Changxingian Dalong Formation contain abundant ammonoids and radiolaria and diverse and common benthic taxa (mostly bivalves and brachiopods) in a thoroughly bioturbated sediment. The presence of a well developed tiered burrow profile is just one line of evidence for a fully oxygenated water column in the late Permian. The faunal crisis occurs in the top few decimetres of the Dalong Formation and severely affected all groups (benthos, nekton and plankton). The extinction coincides precisely with the development of anaerobic and dysaerobic facies. The basal Triassic sediments of the Feixanguan Formation are thinnly‐bedded or laminated silicic marls and contain pyrite and several levels of elevated organic carbon concentrations. The fauna is restricted to rare ammonoids and a few bedding planes covered in Claraia. The presence of abundant coccoid cyanobacteria in these sediments may indicate an unusually simple trophic web in the early Triassic seas as these picoautotrophs are normally grazed by zooplankton, they are rarely directly incorporated into seafloor sediment. The recent discovery of black shales in P/T pelagic sediments of Japan indicates that the anoxic event also affected deep ocean waters and further strengthens the link between extinction and anoxia.     

Phylogeny of the Cardiidae (Mollusca, Bivalvia): Protocardiinae, Laevicardiinae, Lahilliinae, Tulongocardiinae subfam. n. and Pleuriocardiinae subfam. n.

In a preliminary cladistic analysis of the bivalve family Cardiidae (Schneider 1992), members of the subfamilies Protocardiinae, Lahilliinae, and Laevicardiinae, plus the genus Nemocardium , were found to be the least derived taxa of cardiids. A cladistic analysis is undertaken of the genera and subgenera of these cardiid taxa, plus several Mesozoic taxa which have never been assigned to any subfamily. The Late Triassic Tulongocardium , which is placed in Tulongocardiinae subfam. n., is the sister taxon to all other cardiids. Protocardiinae is restricted to the genus Protocardia. Most other Mesozoic taxa which have been placed in the Protocardiinae are found to be members of the Lahilliinae. Nemocardium is placed in the Laevicardiinae. Incacardium, Pleuriocardia , and Dochmocardia form a monophyletic group, Pleuriocardiinae subfam. n. Pleuriocardiinae, Laevicardiinae, and the remaining members of the Cardiidae (herein informally termed "cucardiids") form a monophyletic group.     

Reconstitution du substratum jurassique-crétacé basal du domaine des Sellaoua (marge sud-téthysienne,Algérie nord-orientale) à partir des galets du bassin mio-pliocène d’Hamman N’Baïls

The Mio-Pliocene series filling up the intermontane basin of Hammam N’Baïls (Guelma region, NE Algeria) corresponds to a fluviatile sequence beginning by polygenic conglomerates that contain several Mesozoic carbonate pebbles. The inventory and the micropalaeontological study of these pebbles attest the occurrence, at the base of the Sellaoua unit (southern Tellian foreland of Maghrebides), of a Jurassic–Berriasian carbonate-dominated series, unknown in outcrops, showing some affinities with the synchronous North-Atlasic Algerian and Tunisian ones respectively to the W-SW and to the E-NE. This series was deposited on the South-Tethyan margin, to the south of the ‘Tethyan trough’ joining the incipient Atlantic Ocean and the Ligurian Ocean. The Upper Miocene and Pliocene extensional tectonics and the halokinetic motions, induced by the presence of large Triassic evaporites masses, have probably uplifted towards the surface this Mesozoic Sellaoua-type material, which, after erosion, has supplied the herein studied fluviatile conglomerates.     

Iterative ontogenetic development of ammonoid conch shapes from the Devonian through to the Jurassic

We measured longitudinal growth in conch cross‐sections of 177 Devonian to Jurassic ammonoid species to test whether conch ontogenetic development parallels the iterative evolution of pachyconic or globular conch shapes. Ontogenetic trajectories of two cardinal conch parameters, conch width index and umbilical width index, show a few common recurring ontogenetic pathways in terms of the number of ontogenetic phases. The most common, with three phases in the conch width index (decrease–increase–decrease) and umbilical width index (increase–decrease–increase), is termed here C‐mode ontogeny (after the Carboniferous genus Cravenoceras). Many of the studied globular Palaeozoic and Triassic species (of the latter, particularly the arcestid ammonoids) share principal patterns in the triphasic C‐mode conch ontogeny in closely related groups but also between unrelated groups as well. The repetition of conch growth patterns is an example of convergent evolution of the entire life history of globular ammonoids. The studied Jurassic globular shaped ammonoids deviate from the growth patterns seen in earlier groups showing less pronounced ontogenetic trajectories with nearly isometric or weakly asymmetric growth without distinct phases. This trajectory is termed here M‐mode ontogeny (after the Jurassic genus Macrocephalites). No major change in the ontogenetic modes of pachyconic and globular ammonoids occurred moving from the Palaeozoic into the Mesozoic; the survivors of the end‐Permian extinction event iteratively developed conch ontogenies similar to those of Palaeozoic forms. In contrast, the Triassic–Jurassic boundary marks the major event with the evolution of some cardinal conch parameters relating to globular ammonoid ontogeny.     

Life-cycles of some Devonian ammonoids

Whorl expansion rates of six representative ammonoid genera from late Emsian and Eifelian strata of Morocco were calculated for each whorl. The corresponding body chamber lengths and the orientations of the apertures were computed based on these values. The resulting body chamber length and orientation of the aperture graphs were compared with other conch features, ecology of Recent cephalopods, and sedimentological data of the host rocks in the Tafilalt (eastern Anti-Atlas, Morocco). A subdivision of the ontogeny of these ammonoids was achieved comprising the early and late embryonic periods, the juvenile period, the preadult, and the adult growth period. All growth periods are defined by specific changes in growth, conch morphology, and mode of life. According to this reconstruction, hatchlings were probably already capable of active movements. Differentiation in two main modes of life of the examined taxa occurred in the late juvenile or early preadult period. As preadult animals, most of the Mimagoniatitoidea and Agoniatitoidea became active swimmers (Nektonic), whereas the representatives of the Anarcestoidea were capable of slow movements only (Planktonic). As adults, most representatives of the three superfamilies had an approximately horizontally oriented aperture, allowing active swimming and possibly active choice of spawning sites. Additionally, the new ammonoid taxon Rherisites tuba gen. nov., sp. nov. from the late Emsian is introduced.     

The mode of life in ammonoids

The following structural features clearly indicate that ammonoid shells were adapted to withstand considerably higher hydrostatic pressures thanNautilus shells: (1) the corrugated and marginally fluted septa gave the shell wall efficient support against implosion; (2) the secondary connecting rings could grow a great deal in thickness; and (3) the last formed chambers remained full of liquid which supported the last septum. On the basis of the following characters it is concluded that ammonoids were incapable of swimming efficiently by jet-propulsion: (1) the retractor muscles were weakly developed; (2) the life position was unstable and highly variable; and (3) in animals with a ventral apertural rostrum the hyponome was probably absent. Ammonoids are considered here as having been pelagic cephalopods which lived in the upper 1000 m of the oceans, and which probably undertook considerable diurnal vertical migrations, similar to those inSpirula. Only some groups may have adopted a life in shallow epicontinental seas. In the late Mesozoic, ammonoids have been replaced by modern oceanic squids which are extremely numerous in the corresponding pelagic environment.     

Diversity variation and tempo-spatial distributions of the Dipteridaceae ferns in the Mesozoic of China

The extant family Dipteridaceae is a remarkable leptosporangiate fern because it includes only one genus with a restricted distribution to tropical regions. The fossil record of this family has been widely reported from the Mesozoic strata in Eurasia, America, Australia, and Greenland. In China, numerous fossils of the Dipteridaceae have been documented, in total, about 74 species of 6 genera. Geographically, they are distributed both in the Southern and Northern Floristic Provinces, and were particularly well developed in the Southern Floristic Province during the Late Triassic and the Early Jurassic intervals. Fossil diversity of Dipteridaceae varies in the different episodes of the Mesozoic in China. It is shown that Dipteridaceae has undergone a diversity development process and a distinct turnover during the Mesozoic. They appear to have diversified in the warm and humid Late Triassic–Early Jurassic, but declined sharply as aridity developed in the Middle Jurassic, and became extinct at the end of the Early Cretaceous. The diversity variation and tempo-spatial distribution pattern is suggested to be linked with paleoclimatic variations during the Mesozoic.     

A New Genus of Rhynchonellid Brachiopod from the Lower Triassic of South China and Implications for Timing the Recovery of Brachiopoda After the End-Permian Mass Extinction

A new genus, Meishanorhynchia , is proposed based on new material from the Lower Triassic of the Meishan section, South China. It is of a late Griesbachian age based on both associated biozones (ammonoids and bivalves) and radiometric dates of the intercalated volcanic ash beds. Comparison with both Palaeozoic and Mesozoic–Cenozoic-related genera suggests that it may represent the first radiation of progenitor brachiopods in the aftermath of the end-Permian extinction. The lowest brachiopod horizon that contains the genus is estimated to be about 250.1 ± 0.3 Ma. This implies that the initial stage of recovery of Brachiopoda in the Early Triassic was probably about 1.3 ± 0.3 myr after the major pulse of the end-Permian mass extinction (dated as 251.4 ± 0.3 Ma). This is in agreement with Hallam's expectancy that biotic recovery typically begins within one million years or so of major mass extinctions, in contrast to current views on the end-Permian extinction event which propose that the recovery of most if not all biotic groups in the Early Triassic was severely delayed and only began about five million years after the end-Permian extinction.     

On the genus Tomaxellia (Coniferae) from the Lower Cretaceous of Patagonia (Argentina) and its male and female cones

This paper reports the organic attachment of male and female cones to twigs previously described as Tomaxellia biforme Archangelsky. The male cones produce Classopollis pollen, while the scales of the female structures are comparable to the Rhaeto-Liassic northern genus Cheirolepidium. A new interpretation of the possible female cone of Cheirolepidium is presented, based on the new evidence now available with the knowledge of Tomaxellia cones. Other female cones found in Mesozoic formations may be comparable to some extent with Tomaxellia , such as Indostrobus (Cretaceous of India) or Pararaucaria (Jurassic of Argentina), and they may be grouped in the family Cheirolepidiaceae. Comparisons with older conifer genera with known female cones are also included (Voltziaceae). Some morphological changes of the female cones, which probably took place during the Mesozoic (in these particular groups) are also inferred.     

Some rare helical Ammonoidea from the lower Aptian (Lower Cretaceous) of the Paris Basin (NE France)

In the present paper, we describe and figure some rare lower Aptian (Lower Cretaceous) helical ammonoids from the Deshayesites deshayesi Zone of the Argiles à Plicatules Formation (Paris Basin, NE France). Those are the only helical ammonoids known in this zone so far. They were only occasionally evoked in literature and this is probably on the basis of the specimens here described that, according to us, the genus Toxoceratoides (Helicancylidae) was wrongly regarded as possessing an early helical spiral part. We demonstrate here that these specimens are not belonging to Toxoceratoides nor Helicancylidae: they are interpreted as ‘abnormally’ helical representatives of the genus Ancyloceras (Ancyloceratidae) or a new taxon of Ancyloceratidae.     

Occluded Umbilicus In The Pinacitinae (Devonian) And Its Palaeoecological Implications

Eifelian (Middle Devonian) ammonoids of the Pinacitinae Hyatt, 1900 ( Exopinacites , Pinacites )with preserved shell structures from the eastern Anti–Atlas (Morocco) have revealed unusual morphological features. The Pinacitinae belong to the earliest ammonoids which closed their umbilici. As an approach to an interpretation of these structures, the representatives of the subfamily Pinacitinae ( Exopinacites singularis , Pinacites jugleri , P. eminens ) are compared with other ammonoids, e.g. Acrimeroceras , Araucanites , Clistoceras , Gaudryceras , Nathorstites , Prolobites , and Synpharciceras , which produced umbilical plugs and covers. Some of these are comparable in structure to Nautilus pompilius and N. belauensis . In contrast to all of these taxa, the lateral shell wall of the Pinacitinae reached the centre of the umbilicus and formed an umbilical lid. The umbilical shell wall rests on the umbilical lid of the previous whorl. This construction probably had the advantage that it improved the hydrodynamic properties of the conch, along with the oxyconic conch shape and the approximately horizontal orientation of the aperture.