490 research outputs found

    How many ontogenetic points are needed to accurately describe the ontogeny of a cephalopod conch? A case study of the modern nautilid Nautilus pompilius

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    Recent advancements in tomographic techniques allow for detailed morphological analysis of various organisms, which has proved difficult in the past. However, the time and cost required for the post-processing of highly resolved tomographic data are considerable. Cephalopods are an ideal group to study ontogeny using tomography as the entire life history is preserved within a conch. Although an increasing number of studies apply tomography to cephalopod conchs, the number of conch measurements needed to adequately characterize ontogeny remains unknown. Therefore, the effect of different ontogenetic sampling densities on the accuracy of the resultant growth trajectories needs to be investigated. Here, we reconstruct ontogenetic trajectories of a single conch of Nautilus pompilius using different numbers of ontogenetic points to assess the resulting accuracies. To this end, conch parameters were measured every 10°, 30°, 45°, 90°, and 180°. Results reveal that the overall patterns of reconstructed growth trajectories are nearly identical. Relatively large errors appear to occur where growth changes occur, such as the points of hatching and the onset of morphogenetic countdown before the attainment of maturity. In addition, a previously undocumented growth change before hatching was detected when measurements were taken every 10°, 30°, and 45°, though this growth change was obscured when fewer measurements were used (90° and 180°). The lower number of measurements also masks the subtle fluctuating patterns of conch parameters in middle ontogeny. We conclude that the measurements of a conch every 30° and 45° permit a reasonably precise description of conch ontogeny in nautilids. Since ammonoids were likely more responsive to external stimuli than to nautilids, a much denser sampling may be required for ammonoids. Subjects Developmental Biology, Marine Biology, Paleontology, Taxonomy, Zoology Keywords Cephalopods, Nautiloidea, Morphometrics, Ontogeny, Conch, Tomograph

    Historical significance and taxonomic status of Ischyrodon meriani (Pliosauridae) from the Middle Jurassic of Switzerland

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    Ischyrodon meriani is an obscure pliosaurid taxon established upon an exceptionally large tooth crown of a probable Callovian (Middle Jurassic) age that originates from Wölflinswil, Canton of Aargau, Switzerland. Despite being known for almost two centuries, the specimen remains poorly researched. Historically, I. meriani has been associated, or even considered conspecific, with Pliosaurus macromerus and Liopleurodon ferox. However, neither of the two hypotheses have been tested through detailed comparisons or using modern quantitative methods. Here, we redescribe the type of Ischyrodon meriani, illustrate it, and compare to teeth of thalassophonean pliosaurids, with special focus on Jurassic representatives of the clade. Multivariate analyses show close similarities to L. ferox but comparable structures to those of I. meriani, including a distinctive pattern of the apicobasal ridges, are also observable in some mid-Cretaceous brachauchenines from the ‘Polyptychodon’ assemblage of East and South East England. While it is likely that I. meriani represents a Liopleurodon-like taxon, or is indeed conspecific with L. ferox, which would make I. meriani the proper name for the species, any such taxonomic considerations are hindered by the fragmentary nature of the type specimens of both these taxa as well as limited knowledge of the dental variability within and between individual jaws of L. ferox. Currently, I. meriani is best treated as a nomen dubium. Finally, we discuss the potential implications of I. meriani being conspecific with L. ferox, and additionally provide a commentary on the taxonomic status of Liopleurodon

    Evolutionary development of the cephalopod arm armature: a review

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    The cephalopod arm armature is certainly one of the most important morphological innovations responsible for the evolutionary success of the Cephalopoda. New palaeontological discoveries in the recent past afford to review and reassess origin and homology of suckers, sucker rings, hooks, and cirri. Since a priori character state reconstructions are still ambiguous, we suggest and discuss three different evolutionary scenarios. Each of them is based on the following assumptions: (1) Neocoleoidea uniting extant Decabrachia and Octobrachia is monophyletic (= proostracum-bearing coleoids); (2) extinct Belemnitida and Diplobelida are stem decabrachians; (3) proostracum-less coleoids (Hematitida, Donovaniconida, Aulacoceratida) represent stem-neocoleoids; (4) Ammonoidea and Bactritoidea are stem coleoids. We consider a scenario where belemnoid hooks derived from primitive suckers as well-supported. Regarding belemnoid hooks and suckers as homologues implies that belemnoid, oegopsid, and probably ammonoid arm hooks arose through parallel evolution. Our conclusions challenge the widespread opinion, whereupon belemnoid hooks evolved de novo, and instead support earlier ideas formulated by Sigurd von Boletzky

    Middle Anisian (Bithynian to Illyrian?, Middle Triassic) Ammonoidea from Rüdersdorf (Brandenburg, Germany) with a revision of Beneckeia Mojsisovics, 1882 and notes on migratory pathways

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    Bithynian and Pelsonian (Anisian, Middle Triassic) Ammonoidea are generally rare in the Germanic Basin. Here, we describe ammonoids from the Jena and Rüdersdorf formations (Lower Muschelkalk) of Rüdersdorf (Brandenburg, Germany). This locality is peculiar in its isolated situation and its comparatively high diversity in ammonoids. This outcrop yielded several assemblages encompassing eight species: Balatonites ottonis (Buch, 1849), B. balatonicus (Mojsisovics, 1873), B. egregius (Arthaber, 1896), Beneckeia buchi (Alberti, 1834), Bulogites zoldianus (Mojsisovics, 1882), “Ceratites” antecedens (Beyrich, 1858), Discoptychites dux (Giebel, 1853) and Noetlingites strombecki (Griepenkerl, 1860). When the geographic distribution of these species are compared, it becomes evident that immigrants from the southeast and the southwest met in that region. Such immigrations were only possible during transgressions. Balatonites balatonicus, B. egregius and B. zoldianus are recorded from the area for the first time. Beneckeia is revised with a focus on Ben. buchi, one of the few true endemites of the Germanic Basin, using synchrotron data to describe its early ontogeny. The holotype of “Ceratites” antecedens is figured for the first time and a lectotype for Balatonites egregius is designated

    Extreme abundance of ammonoids in mass accumulations from the Late Devonian of the Moroccan Anti-Atlas

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    The eastern Anti-Atlas is renowned for its highly fossiliferous outcrops of Devonian rocks. Ammonoids occur in rock-forming numbers at many localities in the Tafilalt and Maïder. This study addresses the questions of how many ammonoids are preserved within a standardized area as well as over the whole Tafilalt and Maïder basins, and how these mass occurrences formed. Five samples from the Tafilalt and Maïder were analysed. The ammonoids contained therein were prepared, measured and counted as a base for estimates of the orders of magnitude of the total number of preserved ammonoids and their biomass within the respective Famennian strata in the eastern Anti-Atlas. Two samples were stratigraphically assigned to the lower Famennian, two samples to the middle Famennian and one sample to the upper Famennian. For these samples, estimates for a standardized area of 1 km2 and a layer thickness of 100 mm lie between 19.9×109 and 1.25×1010 ammonoids. The estimated numbers for the whole study area with a retrodeformed size of 15 512.5 km2 and a sediment thickness of 100 mm, ranges from 30.9×1013 to 19.4×1014 ammonoids and a annual accumulation of 15.4×109 to 97.1×109 ammonoid conchs. This corresponds to a annual total palaeo-biomass that ranges from 25 954 t to 47 058 t within the whole study area and from 1.67 t to 3.03 t within an area of 1 km2. Based on these results and size-distribution in the samples, the ecological role of the small and highly abundant, subspherical ammonoids from the early and middle Famennian is discussed and reproductive rates are estimated. With ca. 230 eggs produced by an adult female, cheiloceratids and small maeneceratids from the early Famennian deposits are at the lower end of ammonoid reproductive rates. Key words: Cephalopoda, Ammonoidea, palaeoecology, biomass, fecundity, Famennian, Anti-Atla

    First African thylacocephalans from the Famennian of Morocco and their role in Late Devonian food webs

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    Thylacocephalans are enigmatic arthropods with an erratic Palaeozoic and Mesozoic fossil record. In many of the few localities where they occur, they are quite abundant. This also holds true for the Famennian Thylacocephalan Layer in the Maider (eastern Anti-Atlas of Morocco), a small epicontinental basin hosting some strata with taphonomic properties of a conservation deposit yielding exceptionally preserved gnathostomes and non-vertebrates. In a thin argillaceous interval in the earliest middle Famennian, thylacocephalans occur in such great numbers that they became eponyms of this unit. Therein, we discovered a new taxon of thylacocephalans, Concavicaris submarinus sp. nov., which represent the oldest records of thylacocephalans from Africa. In the CT-imagery, the holotype of Concavicaris submarinus sp. nov. revealed anatomical details including its eyes, appendages and other soft parts. Sedimentary facies and faunal composition of the Thylacocephalan Layer suggest that these animals populated the water column above the low-oxygen sea floor. Thus, thylacocephalans likely represented an important component of the diet of chondrichthyans and placoderms, which are quite common as well. The abundance of thylacocephalans in other conservation deposits like the Cleveland Shale (USA) and the Gogo Formation (Australia) underline their pivotal role in Late Devonian pelagic food webs

    A new Meckel’s cartilage from the Devonian Hangenberg black shale in Morocco and its position in chondrichthyan jaw morphospace

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    Fossil chondrichthyan remains are mostly known from their teeth, scales or fin spines only, whereas their cartilaginous endoskeletons require exceptional preservational conditions to become fossilized. While most cartilaginous remains of Famennian (Late Devonian) chondrichthyans were found in older layers of the eastern Anti-Atlas, such fossils were unknown from the Hangenberg black shale (HBS) and only a few chondrichthyan teeth had been found therein previously. Here, we describe a Meckel’s cartilage from the Hangenberg black shale in Morocco, which is the first fossil cartilage from these strata. Since no teeth or other skeletal elements have been found in articulation, we used elliptical Fourier (EFA), principal component (PCA), and hierarchical cluster (HCA) analyses to morphologically compare it with 41 chondrichthyan taxa of different size and age and to evaluate its possible systematic affiliation. PCA and HCA position the new specimen closest to some acanthodian and elasmobranch jaws. Accordingly, a holocephalan origin was excluded. The jaw shape as well as the presence of a polygonal pattern, typical for tessellated calcified cartilage, suggest a ctenacanth origin and we assigned the new HBS Meckel’s cartilage to the order Ctenacanthiformes with reservations

    Is the relative thickness of ammonoid septa influenced by ocean acidification, phylogenetic relationships and palaeogeographic position?

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    The impact of increasing atmospheric CO2 and the resulting decreasing pH of seawater are in the focus of current environmental research. These factors cause problems for marine calcifiers such as reduced calcification rates and the dissolution of calcareous skeletons. While the impact on recent organisms is well established, little is known about long-term evolutionary consequences. Here, we assessed whether ammonoids reacted to environmental change by changing septal thickness. We measured the septal thickness of ammonoid phragmocones through ontogeny in order to test the hypothesis that atmospheric pCO2, seawater pH and other factors affected aragonite biomineralisation in ammonoids. Particularly, we studied septal thickness of ammonoids before and after the ocean acidification event in the latest Triassic until the Early Cretaceous. Early Jurassic ammonoid lineages had thinner septa relative to diameter than their Late Triassic relatives, which we tentatively interpret as consequence of a positive selection for reduced shell material as an evolutionary response to this ocean acidification event. This response was preserved within several lineages among the Early Jurassic descendants of these ammonoids. By contrast, we did not find a significant correlation between septal thickness and long-term atmospheric pCO2 or seawater pH, but we discovered a correlation with palaeolatitude

    Special issue: recent advances in Cambrian to modern cephalopod research I

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    In September 2014, the 9th International Symposium Cephalopods—Present and Past was held at the Universitz of Zurich in combination with the 5th International Coleoid Symposium. Here, give a short account of these two events
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