Ebert M.,Leibniz Institute For Evolutions Und Biodiversitatsforschung |
Hecht L.,Leibniz Institute For Evolutions Und Biodiversitatsforschung |
Deutsch A.,University of Munster |
Kenkmann T.,Albert Ludwigs University of Freiburg
Meteoritics and Planetary Science | Year: 2013
In the context of the MEMIN project, a hypervelocity cratering experiment has been performed using a sphere of the iron meteorite Campo del Cielo as projectile accelerated to 4.56kms-1, and a block of Seeberger sandstone as target material. The ejecta, collected in a newly designed catcher, are represented by (1) weakly deformed, (2) highly deformed, and (3) highly shocked material. The latter shows shock-metamorphic features such as planar deformation features (PDF) in quartz, formation of diaplectic quartz glass, partial melting of the sandstone, and partially molten projectile, mixed mechanically and chemically with target melt. During mixing of projectile and target melts, the Fe of the projectile is preferentially partitioned into target melt to a greater degree than Ni and Co yielding a Fe/Ni that is generally higher than Fe/Ni in the projectile. This fractionation results from the differing siderophile properties, specifically from differences in reactivity of Fe, Ni, and Co with oxygen during projectile-target interaction. Projectile matter was also detected in shocked quartz grains. The average Fe/Ni of quartz with PDF (about 20) and of silica glasses (about 24) are in contrast to the average sandstone ratio (about 422), but resembles the Fe/Ni-ratio of the projectile (about 14). We briefly discuss possible reasons of projectile melting and vaporization in the experiment, in which the calculated maximum shock pressure does not exceed 55GPa. © The Meteoritical Society, 2013.
Hipsley C.A.,Leibniz Institute For Evolutions Und Biodiversitatsforschung |
Muller J.,Leibniz Institute For Evolutions Und Biodiversitatsforschung |
Muller J.,Berlin Brandenburg Institute of Avanced Biodiversity Research
Frontiers in Genetics | Year: 2014
Molecular-based divergence dating methods, or molecular clocks, are the primary neontological tool for estimating the temporal origins of clades. While the appropriate use of vertebrate fossils as external clock calibrations has stimulated heated discussions in the paleontological community, less attention has been given to the quality and implementation of other calibration types. In lieu of appropriate fossils, many studies rely on alternative sources of age constraints based on geological events, substitution rates and heterochronous sampling, as well as dates secondarily derived from previous analyses. To illustrate the breadth and frequency of calibration types currently employed, we conducted a literature survey of over 600 articles published from 2007 to 2013. Over half of all analyses implemented one or more fossil dates as constraints, followed by geological events and secondary calibrations (15% each). Vertebrate taxa were subjects in nearly half of all studies, while invertebrates and plants together accounted for 43%, followed by viruses, protists and fungi (3% each). Current patterns in calibration practices were disproportionate to the number of discussions on their proper use, particularly regarding plants and secondarily derived dates, which are both relatively neglected in methodological evaluations. Based on our survey, we provide a comprehensive overview of the latest approaches in clock calibration, and outline strengths and weaknesses associated with each. This critique should serve as a call to action for researchers across multiple communities, particularly those working on clades for which fossil records are poor, to develop their own guidelines regarding selection and implementation of alternative calibration types. This issue is particularly relevant now, as time-calibrated phylogenies are used for more than dating evolutionary origins, but often serve as the backbone of investigations into biogeography, diversity dynamics and rates of phenotypic evolution. © 2014 Hipsley and Müller.
Schobben M.,Leibniz Institute For Evolutions Und Biodiversitatsforschung |
Joachimski M.M.,Friedrich - Alexander - University, Erlangen - Nuremberg |
Korn D.,Leibniz Institute For Evolutions Und Biodiversitatsforschung |
Leda L.,Leibniz Institute For Evolutions Und Biodiversitatsforschung |
Korte C.,Copenhagen University
Gondwana Research | Year: 2014
The end-Permian mass extinction has been associated with severe global warming. Main stage volcanism of the Siberian Traps occurred at or near the extinction interval and has been proposed as a likely greenhouse catalyst. In this study, a high-resolution δ18O record is established using diagenetically resistant apatite of conodonts and low-Mg calcite of brachiopods from stratigraphically well-constrained Permian-Triassic (P-Tr) boundary successions in northwestern Iran. A new evaluation is made for previously published conodont δ18O values from South China and revised palaeotemperatures are presented together with new data from Wuchiapingian to Griesbachian sections in Iran. δ18O data from P-Tr sections in Iran document tropical sea surface temperatures (SST) of 27-33°C during the Changhsingian with a negative shift in δ18O starting at the extinction horizon, translating into a warming of SSTs to over 35°C. The results are consistent with re-calculated SSTs of the South Chinese sections. Warming was associated with an enhanced hydrological cycle involving increased tropical precipitation and monsoonal activity in the Tethys Sea. Global warming, intensification of the hydrological cycle and associated processes, vertical water column stratification, eutrophication and subsequent local anoxia may all have facilitated an extinction event. © 2013 International Association for Gondwana Research.
Frommolt K.-H.,Leibniz Institute For Evolutions Und Biodiversitatsforschung |
Tauchert K.-H.,BfUL Sachsische Vogelschutzwarte Neschwitz
Ecological Informatics | Year: 2014
Bioacoustic monitoring is becoming more and more popular as a non-invasive method to study populations and communities of vocalizing animals. Acoustic pattern recognition techniques allow for automated identification of species and an estimation of species composition within ecosystems. Here we describe an approach where on the basis of long term acoustic recordings not only the occurrence of a species was documented, but where the number of vocalizing animals was also estimated. This approach allows us to follow up changes in population density and to define breeding sites in a changing environment. We present the results of five years of continuous acoustic monitoring of Eurasian bittern (Botaurus stellaris) in a recent wetland restoration area. Using a setup consisting of four four-channel recorders equipped with cardioid microphones we recorded vocal activity during entire nights. Vocalizations of bitterns were detected on the recordings by spectrogram template matching. On basis of time differences of arrival (TDOA) of the acoustic signals at different recording devices booming bitterns could be mapped using hyperbolic localization. During the study period not only changes in the number of calling birds but also changes in their spatial distribution connected with changes in habitat structure could be documented. This semi-automated approach towards monitoring birds described here could be applied to a wide range of monitoring tasks for animals with long distance vocalizations. © 2013 Elsevier B.V.
Witzmann F.,Leibniz Institute For Evolutions Und Biodiversitatsforschung |
Schoch R.R.,Staatliches Museum fur Naturkunde
Journal of Morphology | Year: 2013
The cranial and hyobranchial muscles of the Triassic temnospondyl Gerrothorax have been reconstructed based on direct evidence (spatial limitations, ossified muscle insertion sites on skull, mandible, and hyobranchium) and on phylogenetic reasoning (with extant basal actinopterygians and caudates as bracketing taxa). The skeletal and soft-anatomical data allow the reconstruction of the feeding strike of this bottom-dwelling, aquatic temnospondyl. The orientation of the muscle scars on the postglenoid area of the mandible indicates that the depressor mandibulae was indeed used for lowering the mandible and not to raise the skull as supposed previously and implies that the skull including the mandible must have been lifted off the ground during prey capture. It can thus be assumed that Gerrothorax raised the head toward the prey with the jaws still closed. Analogous to the bracketing taxa, subsequent mouth opening was caused by action of the strong epaxial muscles (further elevation of the head) and the depressor mandibulae and rectus cervicis (lowering of the mandible). During mouth opening, the action of the rectus cervicis muscle also rotated the hyobranchial apparatus ventrally and caudally, thus expanding the buccal cavity and causing the inflow of water with the prey through the mouth opening. The strongly developed depressor mandibulae and rectus cervicis, and the well ossified, large quadrate-articular joint suggest that this action occurred rapidly and that powerful suction was generated. Also, the jaw adductors were well developed and enabled a rapid mouth closure. In contrast to extant caudate larvae and most extant actinopterygians (teleosts), no cranial kinesis was possible in the Gerrothorax skull, and therefore suction feeding was not as elaborate as in these extant forms. This reconstruction may guide future studies of feeding in extinct aquatic tetrapods with ossified hyobranchial apparatus. © 2012 Wiley Periodicals, Inc.
Mietchen D.,Leibniz Institute For Evolutions Und Biodiversitatsforschung
PLoS Biology | Year: 2014
Central to research funding are grant proposals that researchers send in to potential funders for review, in the hope of approval. A survey of policies at major research funders found that there is room for more transparency in the process of grant review, which would strengthen the case for the efficiency of public spending on research. On that basis, debate was invited on which transparency measures should be implemented and how, with some concrete suggestions at hand. The present article adds to this discussion by providing further context from the literature, along with considerations on the effect size of the proposed measures. The article then explores the option of opening to the public key components of the process, makes the case for pilot projects in this area, and sketches out the potential that such measures might have to transform the research landscape in those areas in which they are implemented. © 2014 Daniel Mietchen.
Schoch R.R.,Staatliches Museum fur Naturkunde |
Witzmann F.,Leibniz Institute For Evolutions Und Biodiversitatsforschung
Acta Zoologica | Year: 2011
The issue of which breathing mechanism was used by the earliest tetrapods is still unsolved. Recent discoveries of stem tetrapods suggest the presence of internal gills and fish-like underwater breathing. The same osteological features were used by Bystrow to infer a salamander-like breathing through external gills in temnospondyl amphibians. This apparent contradiction - here called Bystrow's Paradox - is resolved by reviewing the primary fossil evidence and the anatomy of the two gill types in extant taxa. Rather unexpectedly, we find that internal gills were present in a range of early crown tetrapods (temnospondyls), based on the anatomy of gill lamellae and location of branchial arteries on the ventral side of gill arch elements (ceratobranchials). Although it remains to be clarified which components are homologous in external and internal gills, both gill types are likely to have been present in Palaeozoic tetrapods - internal gills in aquatic adults of some taxa, and external gills in the larvae of these taxa and in larvae of numerous forms with terrestrial adults, which resorbed the external gills after the larval phase. Future developmental studies will hopefully clarify which mechanistic pathways are involved in gill formation and how these might have evolved. © 2010 The Authors. Acta Zoologica © 2010 The Royal Swedish Academy of Sciences.
Witzmann F.,Leibniz Institute For Evolutions Und Biodiversitatsforschung
Acta Zoologica | Year: 2011
The gastral scales of limbed tetrapodomorphs evolved from the 'elpistostegid'-type of scale by an enlargement and differentiation of the articulation facets and a shortening and broadening of the keel. These changes caused a tighter connection between gastral scales within a scale row and a greater overlap between the rows. Dorsal round scales of limbed tetrapodomorphs developed from a gastral scale-type by an alteration of the ontogenetic pathway. The posterolateral direction of scale rows in 'elpistostegids' was retained in the gastral scalation of most limbed tetrapodomorphs, whereas the arrangement of round dorsal scales is modified to a transverse orientation. Both gastral and dorsal scales of limbed tetrapodomorphs consist solely of parallel-fibred bone with circumferential growth marks. The proportionally larger overlap surfaces of gastral scales and their mode of articulation in the ventral midline indicate that the body of limbed tetrapodomorphs might have been more flexible than that of their finned relatives. The alteration of dermal scales was one of the most rapid morphological changes during the fish-to-tetrapod transition. Once established, gastral and dorsal scales were retained as a conservative character in different lineages of basal tetrapods, in both the amphibian and the amniote lineages. © 2010 The Author. Acta Zoologica © 2010 The Royal Swedish Academy of Sciences.
Greshake A.,Leibniz Institute For Evolutions Und Biodiversitatsforschung
Meteoritics and Planetary Science | Year: 2014
Hydrous carbonaceous microclasts are by far the most abundant foreign fragments in stony meteorites and mostly resemble CI1-, CM2-, or CR2-like material. Their occurrence is of great importance for understanding the distribution and migration of water-bearing volatile-rich matter in the solar system. This paper reports the first finding of a strongly hydrated microclast in a Rumuruti chondrite. The R3-6 chondrite Northwest Africa 6828 contains a 420 × 325 μm sized angular foreign fragment exhibiting sharp boundaries to the surrounding R-type matrix. The clast is dominantly composed of magnetite, pyrrhotite, rare Ca-carbonate, and very rare Mg-rich olivine set in an abundant fine-grained phyllosilicate-rich matrix. Phyllosilicates are serpentine and saponite. One region of the clast is dominated by forsteritic olivine (Fa<2) supported by a network of interstitial Ca-carbonate. The clast is crosscut by Ca-carbonate-filled veins and lacks any chondrules, calcium-aluminum-rich inclusions, or their respective pseudomorphs. The hydrous clast contains also a single grain of the very rare phosphide andreyivanovite. Comparison with CI1, CM2, and CR2 chondrites as well as with the ungrouped C2 chondrite Tagish Lake shows no positive match with any of these types of meteorites. The clast may, thus, either represent a fragment of an unsampled lithology of the hydrous carbonaceous chondrite parent asteroids or constitute a sample from an as yet unknown parent body, maybe even a comet. Rumuruti chondrites are a unique group of highly oxidized meteorites that probably accreted at a heliocentric distance >1 AU between the formation regions of ordinary and carbonaceous chondrites. The occurrence of a hydrous microclast in an R chondrite attests to the presence of such material also in this region at least at some point in time and documents the wide distribution of water-bearing (possibly zodiacal cloud) material in the solar system. © The Meteoritical Society, 2014.
Fahlke J.M.,Leibniz Institute For Evolutions Und Biodiversitatsforschung
Palaeontologia Electronica | Year: 2012
Basilosauridae are cosmopolitan fully-aquatic archaeocete whales, represented by larger Basilosaurus isis and smaller Dorudon atrox in the middle-to-late Eocene Gehannam and Birket Qarun Formations of Egypt (ca. 38-36.5 Ma). Adult and juvenile Dorudon but only adult Basilosaurus are found in these shallow-marine deposits. Lethal bite marks on juvenile Dorudon skulls sparked the idea that adult Basilosaurus invaded calving grounds of D. atrox to prey on their young. However, there has been no direct evidence to support this idea. In this study, bite marks on specimens of juvenile D. atrox that have previously been described but not assigned to a particular trace-maker are reinvestigated, and additional bone modifications are analyzed. Applying computed tomography (CT), digital surface scanning, and three-dimensional (3D) reconstruction, the juvenile D. atrox specimens were digitally placed into the mouth of an adult B. isis. Bite marks match the dentition of B. isis. Imprints of tooth casts of B. isis in modeling clay furthermore resemble bite marks on these D. atrox specimens in shape and size. B. isis was likely a predator that included juvenile D. atrox in its diet. Prey was predominantly captured from a lateral position across the head and sometimes adjusted in the mouth prior to a more powerful bite. Scavenging of B. isis on D. atrox calves is also possible. The diet of Basilosaurus and dietary differences within the genus resemble those known in modern killer whales (Orcinus orca). B. isis is the only archaeocete known to date that possibly preyed on other cetaceans. © Society for Vertebrate Paleontology November 2012.