Prof. Dr. Nadia Fröbisch
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Deep Time Evolution of the Regenerative Program of Fins/Limbs and Tails – Combining Molecular, Morphological and Paleontological Approaches
Quelle ↗Förderer: DAAD Zeitraum: 01/2019 - 12/2020 Projektleitung: Prof. Dr. Nadia Fröbisch
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Publikationen25
Top 25 nach Zitationen — Quelle: OpenAlex (BAAI/bge-m3 embedded für Matching).
Nature · 229 Zitationen · DOI
Ossification patterns in the tetrapod limb – conservation and divergence from morphogenetic events
2008Biological reviews/Biological reviews of the Cambridge Philosophical Society · 90 Zitationen · DOI
Two different patterns of the condensation and chondrification of the limbs of tetrapods are known from extensive studies on their early skeletal development. These are on the one hand postaxial dominance in the sequential formation of skeletal elements in amniotes and anurans, and on the other, preaxial dominance in urodeles. The present study investigates the relative sequence of ossification in the fore- and hindlimbs of selected tetrapod taxa based on a literature survey in comparison to the patterns of early skeletal development, i.e. mesenchymal condensation and chondrification, representing essential steps in the late stages of tetrapod limb development. This reveals the degree of conservation and divergence of the ossification sequence from early morphogenetic events in the tetrapod limb skeleton. A step-by-step recapitulation of condensation and chondrification during the ossification of limbs can clearly be refuted. However, some of the deeper aspects of early skeletal patterning in the limbs, i.e. the general direction of development and sequence of digit formation are conserved, particularly in anamniotes. Amniotes show a weaker coupling of the ossification sequence in the limb skeleton with earlier condensation and chondrification events. The stronger correlation between the sequence of condensation/chondrification and ossification in the limbs of anamniotes may represent a plesiomorphic trait of tetrapods. The pattern of limb ossification across tetrapods also shows that some trends in the sequence of ossification of their limb skeleton are shared by major clades possibly representing phylogenetic signals. This review furthermore concerns the ossification sequence of the limbs of the Palaeozoic temnospondyl amphibian Apateon sp. For the first time this is described in detail and its patterns are compared with those observed in extant taxa. Apateon sp. shares preaxial dominance in limb development with extant salamanders and the specific order of ossification events in the fore- and hindlimb of this fossil dissorophoid is almost identical to that of some modern urodeles.
Nature · 82 Zitationen · DOI
Developmental Dynamics · 82 Zitationen · DOI
The development of the tetrapod limb during skeletogenesis follows a highly conservative pattern characterized by a general proximo-distal progression in the establishment of skeletal elements and a postaxial polarity in digit development. Salamanders represent the only exception to this pattern and display an early establishment of distal autopodial structures, specifically the basale commune, an amalgamation of distal carpal and tarsal 1 and 2, and a distinct preaxial polarity in digit development. This deviance from the conserved tetrapod pattern has resulted in a number of hypotheses to explain its developmental basis and evolutionary history. Here we summarize the current knowledge of salamander limb development under consideration of the fossil record to provide a deep time perspective of this evolutionary pathway and highlight what data will be needed in the future to gain a better understanding of salamander limb development specifically and tetrapod limb development and evolution more broadly.
Evolution & Development · 80 Zitationen · DOI
Despite the wide range of shapes and sizes that accompany a vast variety of functions, the development of tetrapod limbs follows a conservative pattern of de novo condensation, branching, and segmentation. Development of the zeugopodium and digital arch typically occurs in a posterior to anterior sequence, referred to as postaxial dominance, with a digital sequence of 4-3-5-2-1. The only exception to this pattern in all of living Tetrapoda can be found in salamanders, which display a preaxial dominance in limb development, a de novo condensation of a basale commune (distal carpal/tarsal 1+2) and a precoccial development of digits I and II. These divergent patterns have puzzled researchers for over a century leading to various explanatory hypotheses. Despite many advances in research on tetrapod limb development, the divergent evolution of these two pathways and its causes are still not understood. Based on an extensive ontogenetic series we investigated the pattern of limb development of the 300 Ma old branchiosaurid amphibian Apateon. This revealed a preaxial dominance in limb development that was previously believed to be unique and derived for modern salamanders. The Branchiosauridae are favored as close relatives of extant salamanders in most phylogenetic hypotheses of the highly controversial origins and relationships of extant amphibians. The findings provide new insights into the evolution of developmental pathways in tetrapod limb development, the relationships of modern amphibians with possible Paleozoic antecedents, and their initial timing of divergence.
Early evolution of limb regeneration in tetrapods: evidence from a 300-million-year-old amphibian
2014Proceedings of the Royal Society B Biological Sciences · 77 Zitationen · DOI
Salamanders are the only tetrapods capable of fully regenerating their limbs throughout their entire lives. Much data on the underlying molecular mechanisms of limb regeneration have been gathered in recent years allowing for new comparative studies between salamanders and other tetrapods that lack this unique regenerative potential. By contrast, the evolution of animal regeneration just recently shifted back into focus, despite being highly relevant for research designs aiming to unravel the factors allowing for limb regeneration. We show that the 300-million-year-old temnospondyl amphibian Micromelerpeton, a distant relative of modern amphibians, was already capable of regenerating its limbs. A number of exceptionally well-preserved specimens from fossil deposits show a unique pattern and combination of abnormalities in their limbs that is distinctive of irregular regenerative activity in modern salamanders and does not occur as variants of normal limb development. This demonstrates that the capacity to regenerate limbs is not a derived feature of modern salamanders, but may be an ancient feature of non-amniote tetrapods and possibly even shared by all bony fish. The finding provides a new framework for understanding the evolution of regenerative capacity of paired appendages in vertebrates in the search for conserved versus derived molecular mechanisms of limb regeneration.
The Anatomical Record · 77 Zitationen · DOI
The ontogeny of the northwestern Atlantic batoid, Leucoraja ocellata, is described with special focus on the development of skate specific morphologies and the development of the fins. The results show that the sequence of events involving the early outgrowth of the paired fins and the initial development of the pharyngeal region is remarkably constant in skates, holocephalians, and sharks. However, differences exist in timing of the reshaping of the mandibular arch region, development of branchial filaments, median fins, denticles, and the order of branchial cleft formation. Despite the similarities of early events related to development of the branchial region and initial outgrowth of the fins, later stages are increasingly characterized by taxon-specific morphologies making a universal staging table for chondrichthyans less applicable. The staging table presented in this study represents an important resource for future studies on batoid embryology.
Proceedings of the National Academy of Sciences · 76 Zitationen · DOI
Salamanders and lungfishes are the only sarcopterygians (lobe-finned vertebrates) capable of paired appendage regeneration, regardless of the amputation level. Among actinopterygians (ray-finned fishes), regeneration after amputation at the fin endoskeleton has only been demonstrated in polypterid fishes (Cladistia). Whether this ability evolved independently in sarcopterygians and actinopterygians or has a common origin remains unknown. Here we combine fin regeneration assays and comparative RNA-sequencing (RNA-seq) analysis of <i>Polypterus</i> and axolotl blastemas to provide support for a common origin of paired appendage regeneration in Osteichthyes (bony vertebrates). We show that, in addition to polypterids, regeneration after fin endoskeleton amputation occurs in extant representatives of 2 other nonteleost actinopterygians: the American paddlefish (Chondrostei) and the spotted gar (Holostei). Furthermore, we assessed regeneration in 4 teleost species and show that, with the exception of the blue gourami (Anabantidae), 3 species were capable of regenerating fins after endoskeleton amputation: the white convict and the oscar (Cichlidae), and the goldfish (Cyprinidae). Our comparative RNA-seq analysis of regenerating blastemas of axolotl and <i>Polypterus</i> reveals the activation of common genetic pathways and expression profiles, consistent with a shared genetic program of appendage regeneration. Comparison of RNA-seq data from early <i>Polypterus</i> blastema to single-cell RNA-seq data from axolotl limb bud and limb regeneration stages shows that <i>Polypterus</i> and axolotl share a regeneration-specific genetic program. Collectively, our findings support a deep evolutionary origin of paired appendage regeneration in Osteichthyes and provide an evolutionary framework for studies on the genetic basis of appendage regeneration.
Proceedings of the National Academy of Sciences · 71 Zitationen · DOI
The biotic recovery from Earth's most severe extinction event at the Permian-Triassic boundary largely reestablished the preextinction structure of marine trophic networks, with marine reptiles assuming the predator roles. However, the highest trophic level of today's marine ecosystems, i.e., macropredatory tetrapods that forage on prey of similar size to their own, was thus far lacking in the Paleozoic and early Mesozoic. Here we report a top-tier tetrapod predator, a very large (>8.6 m) ichthyosaur from the early Middle Triassic (244 Ma), of Nevada. This ichthyosaur had a massive skull and large labiolingually flattened teeth with two cutting edges indicative of a macropredatory feeding style. Its presence documents the rapid evolution of modern marine ecosystems in the Triassic where the same level of complexity as observed in today's marine ecosystems is reached within 8 My after the Permian-Triassic mass extinction and within 4 My of the time reptiles first invaded the sea. This find also indicates that the biotic recovery in the marine realm may have occurred faster compared with terrestrial ecosystems, where the first apex predators may not have evolved before the Carnian.
Systematic Biology · 71 Zitationen · DOI
Among the diverse clade of Paleozoic dissorophoid amphibians, the small, terrestrial amphibamids and the neotenic branchiosaurids have frequently been suggested as possible antecedents of either all or some of the modern amphibian clades. Classically, amphibamids and branchiosaurids have been considered to represent distinct, but closely related clades within dissorophoids, but despite their importance for the controversial lissamphibian origins, a comprehensive phylogenetic analysis of small dissorophoids has thus far not been attempted. On the basis of an integrated data set, the relationships of amphibamids and branchiosaurids were analyzed using parsimony and Bayesian approaches. Both groups represent miniaturized forms and it was tested whether similar developmental pathways, associated with miniaturization, lead to an artificial close relationship of branchiosaurids and amphibamids. Moreover, the fit of the resulting tree topologies to the distribution of fossil taxa in the stratigraphic rock record was assessed as an additional source of information. The results show that characters associated with a miniaturized morphology are not responsible for the close clustering of branchiosaurids and amphibamids. Instead, all analyses invariably demonstrate a monophyletic clade of branchiosaurids highly nested within derived amphibamids, indicating that branchiosaurids represent a group of secondarily neotenic amphibamid dissorophoids. This understanding of the phylogenetic relationships of small dissorophoid amphibians provides a new framework for the discussion of their evolutionary history and the evolution of characters shared by branchiosaurids and/or amphibamids with modern amphibian taxa.
Journal of Vertebrate Paleontology · 67 Zitationen · DOI
ABSTRACT The fissure fills of Richards Spur, Oklahoma, together constitute the most productive Paleozoic continental fossil locality in the world, having produced a wealth of terrestrial vertebrates, including occasional articulated skeletons. A new dissorophoid amphibian is represented by two skulls: an exquisitely preserved, complete small skull and the posterior part of a second skull, almost twice the size of the holotype. The specimens provide detailed information about the skull roof, palate, braincase, and mandible, showing that this new taxon is characterized by a relatively elongate skull with large tabulars and postparietals, and monocuspid, recurved teeth that show no sign of pedicelly. The large, laterally expanded interpterygoid vacuities are covered by a mosaic of small dermal plates, each carrying more than a dozen strongly recurved teeth. A phylogenetic analysis of 17 ingroup taxa and 62 cranial and postcranial characters yielded a single most-parsimonious tree with the new taxon in a monophyletic Amphibamidae as the sister taxon to the Lower Triassic Micropholis from South Africa. In addition, the new analysis supports a basal split of Amphibamidae into two distinct clades, one containing the new taxon, Micropholis, along with Tersomius, and the other comprising Amphibamus, Gerobatrachus, Doleserpeton, Platyrhinops, Plemmyradytes, Eoscopus, and Georgenthalia. The data retrieved from this new taxon provides insights into the evolution and diversity of the Amphibamidae.
JAMA Oncology · 58 Zitationen · DOI
Triassic Cancer-Osteosarcoma in a 240-Million-Year-Old Stem-Turtle Paleopathology, the study of ancient disease, is a vital way by which we understand the evolution of pathogens, immune systems, healing physiology, and ultimately the environment. Cancer research has focused on its prevalence in various organisms and has found that although some animals have a high propensity for cancer, 1 others seem to be resistant. The prevalence of cancer in the tree of life is certainly interesting, but its antiquity should be regarded with equal interest considering the increase in human cancer, which has been related to environmental and genetic changes, and the extreme rarity of cancer in the fossil record. Herein, we present a case study of an osteosarcoma, a highly malignant bone tumor, on the femur of the shell-less stem-turtle Pappochelys rosinae 4 (Figure The appearance of the tumor on this specimen conforms with presentday periosteal osteosarcoma in humans.
Seminars in Cell and Developmental Biology · 54 Zitationen · DOI
Journal of Vertebrate Paleontology · 49 Zitationen · DOI
ABSTRACT A new species of Cacops, C. woehri, is described on the basis of a well-preserved skull from the Dolese Quarry locality in Oklahoma (Leonardian). Although its relatively small size and pattern of sculpturing indicate that the specimen probably represents a sub-adult individual, C. woehri differs from other members of the genus in the shallower shape of the skull, more dorsally located orbits, a distinct sculpturing pattern of radial ridges and grooves, and an ‘L’-shaped, narrow opening in the tympanic embayment. In addition, it differs from C. morrisi, the other anatomically well-known species of the genus, in the presence of a small posterior process of the postorbital contacting the supratemporal, in the presence of an ectopterygoid fang, large occipital flanges of the postparietal and tabular, and in the shape of the basal plate of the parasphenoid. This new taxon highlights the morphological diversity of species within the enigmatic genus Cacops, with variation encompassing a distinct cranial morphology. ACKNOWLEDGMENTS We would like to thank N. Wong Ken for the preparation of the drawings in Figures 1–4 and D. Scott for help with the preparation of the specimen. We thank D. Woehr, B. May, B. Dunn, and M. Feese for their enthusiastic support of research on the Dolese Fauna. We also wish to thank the staff of the Sam Noble Natural History Museum of Oklahoma for their continued support. Research was supported by a research fellowship of the German Research Foundation (DFG) to N.B.F. and an NSERC Discovery Grant to R.R.R. Handling editor: Jason Anderson
Comptes Rendus Palevol · 48 Zitationen · DOI
The accuracy of the taxonomic assignment of three skulls in the collections of the Museum of Comparative Zoology (Harvard University) to the Early Permian taxon Tersomius texensis has been called into question. Here, we re-evaluate the holotype of T. texensis and the three MCZ specimens within the context of discoveries made over the last few years. The results of our phylogenetic analyses corroborate our morphological assessments, revealing that only one of the three skulls (MCZ 1912) is assignable to T. texensis. We identify MCZ 1415 as Pasawioops cf. P. mayi, otherwise known only from Oklahoma, and MCZ 1911 as a new genus and species of dissorophid. Study of the three MCZ skulls reveals previously unrecognized diversity of temnospondyls in the coastal fauna represented in the Archer City Formation of Texas. La précision de l’attribution taxonomique de trois crânes dans les collections du Museum of Comparative Zoology (université de Harvard) à un taxon du Permien inférieur, Tersomius texensis, a posé question. Ici, nous réévaluons l’holotype de T. texensis et les trois spécimens MCZ dans le contexte des découvertes effectuées ces dernières années. Les résultats de nos analyses phylogénétiques corroborent nos estimations morphologiques, à savoir que seul l’un des trois crânes (MCZ 1912) est attribuable à T. texensis. Nous avons identifié MCZ 1415 comme étant Pasawioops cf. P. mayi, par ailleurs, déjà connu dans l’Oklahoma, et MCZ 1911 comme étant un nouveau genre et une nouvelle espèce de dissorophidé. L’étude de ces trois crânes révèle une diversité, non reconnue précédemment, des Temnospondyles dans la faune côtière de la formation Archer City au Texas.
Fossil Record · 39 Zitationen · DOI
<strong class="journal-contentHeaderColor">Abstract.</strong> Two distinct developmental trajectories, metamorphosis and neoteny (the retention of larval somatic features in adult animals), have been reported for the small gill-bearing branchiosaurids of the Late Carboniferous and Early Permian of central Europe. Based on a very large specimen of the species <i>Apateon caducus</i> (Ammon, 1889), anatomical features characteristic for the neotenic phenotype of branchiosaurids are described. Large neotenes lack changes that occur during a short phase of transformation into terrestrial adults (metamorphosis), such as ossification of the braincase and palatoquadrate and intercentra, further ossification of the girdles and formation of muscle attachment scars and processes on the limb bones. They also lack a distinct sculpturing of the dermal skull roofing elements with deep polygonal ridges and grooves. Instead, larval somatic features are retained including ossified branchial denticles indicative of open gill slits and accentuated larval-type sculpturing of the dermal skull roof. Large size, high degree of ossification as compared to the larvae, and the presence of uncinate processes on the ribs clearly demonstrate an adult ontogenetic stage. Neotenes remained in the aquatic environment throughout their life and were most likely not capable of effective terrestrial locomotion. The frequency distribution of the two phenotypes in modern salamander populations and the environmental cues that influence the development of them provide a comparative framework for the discussion of the evolution of the two life history pathways in branchiosaurids. <br><br> doi:<a href="http://dx.doi.org/10.1002/mmng.200800012" target="_blank">10.1002/mmng.200800012</a>
PLoS ONE · 37 Zitationen · DOI
Basal tetrapods display a wide spectrum of vertebral centrum morphologies that can be used to distinguish different tetrapod groups. The vertebral types range from multipartite centra in stem-tetrapods, temnospondyls, and seymouriamorphs up to monospondylous centra in lepospondyls and have been drawn upon for reconstructing major evolutionary trends in tetrapods that are now considered textbook knowledge. Two modes of vertebral formation have been postulated: the multipartite vertebrae formed first as cartilaginous elements with subsequent ossification. The monospondylous centrum, in contrast, was formed by direct ossification without a cartilaginous precursor. This study describes centrum morphogenesis in basal tetrapods for the first time, based on bone histology. Our results show that the intercentra of the investigated stem-tetrapods consist of a small band of periosteal bone and a dense network of endochondral bone. In stereospondyl temnospondyls, high amounts of calcified cartilage are preserved in the endochondral trabeculae. Notably, the periosteal region is thickened and highly vascularized in the plagiosaurid stereospondyls. Among "microsaur" lepospondyls, the thickened periosteal region is composed of compact bone and the notochordal canal is surrounded by large cell lacunae. In nectridean lepospondyls, the periosteal region has a spongy structure with large intertrabecular spaces, whereas the endochondral region has a highly cancellous structure. Our observations indicate that regardless of whether multipartite or monospondylous, the centra of basal tetrapods display first endochondral and subsequently periosteal ossification. A high interspecific variability is observed in growth rate, organization, and initiation of periosteal ossification. Moreover, vertebral development and structure reflect different lifestyles. The bottom-dwelling Plagiosauridae increase their skeletal mass by hyperplasy of the periosteal region. In nectrideans, the skeletal mass decreases, as the microstructure is spongy and lightly built. Additionally, we observed that vertebral structure is influenced by miniaturization in some groups. The phylogenetic information that can be drawn from vertebral development, however, is limited.
Zoological Journal of the Linnean Society · 36 Zitationen · DOI
Fröbisch, Nadia B., Sander, P. Martin, Rieppel, Olivier (2006): A new species of Cymbospondylus (Diapsida, Ichthyosauria) from the Middle Triassic of Nevada and a re-evaluation of the skull osteology of the genus. Zoological Journal of the Linnean Society 147 (4): 515-538, DOI: 10.1111/j.1096-3642.2006.00225.x, URL: https://academic.oup.com/zoolinnean/article-lookup/doi/10.1111/j.1096-3642.2006.00225.x
A NEW BASAL PTEROSAUR GENUS FROM THE UPPER TRIASSIC OF THE NORTHERN CALCAREOUS ALPS OF SWITZERLAND
2006Palaeontology · 28 Zitationen · DOI
Abstract: A lower jaw with multicusped teeth and a number of unique characteristics was discovered in an extensive exposure of the Upper Triassic Kössen Formation in the Northern Calcareous Alps. The ramus of the jaw is high and dominated by a row of large, oval foramina that lies parallel to the tooth row. In addition, the anterior portion of the dentary exhibits a large number of nutritive foramina and small pits, which might indicate an association with a soft tissue structure and/or the presence of a keratinous cover of that area during life. All elements of the jaw are thin-walled and hollow, possibly pneumatic. Two teeth are preserved within the dentary. One is tricuspid and the other bears four cuSPS. The teeth are noticeably small in comparison with the overall size of the ramus, being only one-third of the height of the ramus. The teeth show a strong similarity to those of the well-known basal pterosaur genus Eudimorphodon, whose jaw morphology, however, clearly differs from the specimen described in this study. The dentition and the pneumatic bone structure make an assignment to the Pterosauria plausible. Based on the great number of distinct morphological characters the specimen is described as Caviramus schesaplanensis gen. et sp. nov.
bioRxiv (Cold Spring Harbor Laboratory) · 19 Zitationen · DOI
Many species regenerate lost body parts following amputation. Most limb regeneration research has focused on the immediate injury site. Meanwhile, body-wide injury responses remain largely unexplored but may be critical for regeneration. Here, we discovered a role for the sympathetic nervous system in stimulating a body-wide stem cell activation response to amputation that drives enhanced limb regeneration in axolotls. This response is mediated by adrenergic signaling, which coordinates distant cellular activation responses via the α<sub>2A</sub>-adrenergic receptor, and local regeneration responses via β-adrenergic receptors. Both α<sub>2A</sub>- and β-adrenergic signaling act upstream of mTOR signaling. Notably, systemically-activated axolotls regenerate limbs faster than naïve animals, suggesting a potential selective advantage in environments where injury from cannibalism or predation is common. This work challenges the predominant view that cellular responses underlying regeneration are confined to the injury site and argues instead for body-wide cellular priming as a foundational step that enables localized tissue regrowth.
Journal of Experimental Zoology Part B Molecular and Developmental Evolution · 18 Zitationen · DOI
Salamanders show unparalleled capacities of tissue regeneration amongst tetrapods (four-legged vertebrates), being able to repair and renew lost or damage body parts, such as tails, jaws, and limbs in a seemingly perfect fashion. Despite countless studies on axolotl (Ambystoma mexicanum) regeneration, only a few studies have thus far compared gross morphological and histological features of the original and regenerated limb skeleton. Therein, most studies have focused on nerves or muscles, while even fewer have provided detailed information about bones and cartilage. This study compares skeletal tissue structures of original and regenerated limbs with respect to tissue level histology. Histological serial sections of 55 axolotl larvae were generated, including 29 limbs that were severed by conspecifics, and 26 that were subject to targeted amputations. Amputations were executed in several larval stages (48, 52, and 53) and at different limb positions (humeral midshaft, above the mesopod). In addition, 3D reconstructions were prepared based on X-ray microtomography scans. The results demonstrate that regenerated forelimbs show a diversity of limb and digit abnormalities as a result of imperfect regeneration. Furthermore, abnormalities were more severe and more frequent in regenerated forelimbs caused by natural bites as compared with regenerated forelimbs after amputation. The results indicate that abnormalities occur frequently after regeneration in larval axolotls contradicting the notion of regeneration generally resulting in perfect limbs.
Journal of Morphology · 18 Zitationen · DOI
A variety of vertebral centrum morphologies have evolved within early tetrapods which range from multipartite centra consisting of intercentra and pleurocentra in stem-tetrapods, temnospondyls, seymouriamorphs, and anthracosaurs up to monospondylous centra in lepospondyls. With the present study, we aim to determine the formation of both intercentrum and pleurocentrum and asked whether these can be homologized based on their bone histology. Both intercentra and pleurocentra ossified endochondrally and periosteal bone was subsequently deposited on the outer surface of the centra. Our observations indicate low histological variation between intercentrum and pleurocentrum in microstructural organization and growth which inhibits the determination of homologies. However, intercentrum and pleurocentrum development differs during ontogeny. As previously assumed, the intercentrum arises from ventrally located and initially paired ossification centers that fuse ventromedially to form the typical, crescentic, rhachitomous intercentrum. In contrast, presacral pleurocentra may be ancestrally represented by four ossification centers: a ventral and a dorsal pair. Subsequently, two divergent developmental patterns are observed: In stem-tetrapods and temnospondyls, the pleurocentrum evolves from the two dorsally located ossification centers which may occasionally fuse to form a dorsal crescent. In some dvinosaurian temnospondyls, the pleurocentrum may even ossify to full rings. In comparison, the pleurocentrum of stem-amniotes (anthracosaurs, chroniosuchids, seymouriamorphs, and lepospondyls) arises from the two ventrally located ossification centers whereby the ossification pattern is almost identical to that of temnospondyls but mirror-inverted. Thus, the ring-shaped pleurocentrum of Discosauriscus ossifies from ventral to dorsal. We also propose that the ossified portions of the intercentrum and pleurocentrum continued as cartilaginous rings or discs that surrounded the notochord in the living animals.
Fossil record · 18 Zitationen · DOI
Abstract. The Lower Permian Dolese locality has produced numerous exquisitely preserved tetrapod fossils representing members of a lower Permian upland fauna. Therein, at least nine taxa of the clade Dissorophoidea, ranging in size from the large predaceous trematopid Acheloma to the miniaturized amphibamid Doleserpeton, highlight the great taxic and ecological diversity of this anamniote clade. Here we describe a large specimen of the dissorophid Cacops woehri, which was previously only known from the juvenile or subadult holotype skull. Another member of the genus Cacops present at the Dolese locality, Cacops morrisi, is also represented by specimens spanning juvenile, subadult, and adult stages, allowing for a comparison of morphological changes taking place in the late phases of the ontogenetic trajectory of cacopine dissorophids. The new find shows that, in contrast to C. morrisi and C. aspidephorus, C. woehri only undergoes relatively subtle changes in skull morphology in late ontogeny and retains the overall more gracile morphology into adult stages. This includes retention of the rather shallow skull shape as well as a pattern of sculpturing consisting of elongate ridges and grooves and a large occipital flange. This suggests somewhat different functional demands in C. woehri than in other known species of Cacops, possibly associated with a different ecology paralleling the great taxic diversity of dissorophoids at the Dolese locality.
Journal of Zoology · 17 Zitationen · DOI
Abstract The origin of lissamphibians remains unresolved and different origins within Paleozoic early tetrapods have been proposed. Both the vertebral morphology as well as the ossification sequence of the vertebrae are potentially important character traits to test these different hypotheses. Here, we aim to determine if vertebral formation and ossification sequence in lissamphibians and early tetrapods are valuable indicatives of phylogenetic relationships. To answer this question, we examined the vertebral development in growth series of different salamander taxa and compared the results with literature data on vertebral development in frogs, caecilians and early tetrapods. In salamanders, caecilians and early tetrapods, the vertebral centrum develops by chordacentral and perichordal centrum formation, whereas in frogs, no chordacentral centrum formation has been observed so far. In the salamander taxa studied here, the following chondrification and ossification sequences are observed: chondrification first of the neural arches and then of the centra followed by ossification first of the centra and then of the neural arches. In frogs, in contrast, the neural arches ossify prior to the centra and it can be assumed that this developmental sequence represents the ancestral condition for tetrapods, as it characterizes some stem‐tetrapods and all temnospondyls from which growth series are known. However, the ossification sequence of the vertebral column is only incompletely known in stem‐amniotes which makes a comparison with extant lissamphibians difficult. This indicates that the mode of centrum formation and the ossification sequence are highly variable and cannot be used to determine the origin of lissamphibians within early tetrapods.
Evolution · 16 Zitationen · DOI
The Branchiosauridae was a clade of small amphibians from the Permo-Carboniferous with an overall salamander-like appearance. The clade is distinguished by an extraordinary fossil record that comprises hundreds of well-preserved specimens, representing a wide range of ontogenetic stages. Branchiosaurids had external gills and weakly ossified skeletons, and due to this larval appearance their status as neotenic (perennibranchiate) forms has long been accepted. Despite their extensive fossil record large specimens with an adult morphology appeared to be lacking altogether, but recently two adult specimens were identified in a rich sample of Apateon gracilis collected in the 19th century from a locality near Dresden, Saxony. These specimens are unique among branchiosaurids in showing a high level of ossification, including bones that have never been reported in a branchiosaur. These highlight the successive formation of features believed to indicate terrestrial locomotion, as well as feeding on larger prey items. Moreover, these transformations occurred in a small time window (whereas the degree of size increase is used as a proxy of time) and the degree of concentration of developmental events in branchiosaurids is unique among tetrapods outside the lissamphibians. These specimens are compared with large adults of the neotenic branchiosaurid Apateon caducus from the Saar-Nahe Basin, which despite their larger body size lack the features found in the adult A. gracilis specimens. These specimens give new insight into patterns of metamorphosis (morphological transformation) in branchiosaurids that are believed to be correlated to a change of habitat, and clearly show that different life-history pathways comparable to those of modern salamanders were already established in this Paleozoic clade.
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- Prof. Dr. Nadia Fröbisch
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- Institut für Biologie
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- Entwicklung und Evolution (S)
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