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Gerald Mayr - One of the best experts on this subject based on the ideXlab platform.

  • Avian higher level biogeography: Southern Hemispheric origins or Southern Hemispheric relicts?
    Journal of Biogeography, 2017
    Co-Authors: Gerald Mayr
    Abstract:

    A recent analysis of a comprehensive phylogenetic data set suggested Southern Hemispheric origins for various higher level taxa of neornithine (Crown Group) birds. These results contrast with hypotheses derived from the fossil record, with the occurrence of successively branching stem Group representatives of many “Southern Hemispheric” bird Groups in the early Cenozoic of Europe and North America suggesting relict extant distributions. However, a selective consideration of the fossil record and the merging of extant ranges may have resulted in a skewed picture of the past biogeographical history of birds. For future studies, it is proposed that multiple taxa of successively branching Northern Hemispheric stem Group representatives are considered to narrow down the ancestral areas of the Crown Group representatives.

  • Skeletal morphology of the middle Eocene swift Scaniacypselus and the evolutionary history of true swifts (Apodidae)
    Journal of Ornithology, 2015
    Co-Authors: Gerald Mayr
    Abstract:

    Skelettmorphologie des mitteleozänen Seglers Scaniacypselus und die Evolutionsgeschichte echter Segler (Apodidae) Es werden neue Fossilfunde von Scaniacypselus beschrieben, einem mitteleozänen Stammgruppenvertreter der Apodidae (Segler) aus Messel. Die neuen Belege zeigen, dass sich Scaniacypselus in einigen Skelettmerkmalen deutlich von heutigen Apodidae unterscheidet. Insbesondere ist das Brustbein von Scaniacypselus kürzer als das heutiger Segler, die Ulna länger, der Carpometacarpus kürzer und der Processus internus indicis der proximalen Phalanx des Hauptfingerstrahls des Flügels weniger stark entwickelt. In einigen Details der Morphologie des Humerus unterscheidet sich Scaniacypselus von allen rezenten apodiformen Vögeln. Der Tarsometatarsus von Scaniacypselus ist zudem viel kürzer als derjenige der meisten Kronengruppen-Vertreter der Apodidae. Vermutlich sind kurze Läufe plesiomorph für Pan-Apodidae (Stammgruppe und Kronengruppe), während eine Verlängerung des Tarsometatarsus primitiv für die Kronengruppe ist und eine Anpassung an das Klammern an vertikalen Oberflächen darstellt. Die weniger spezialisierte Flügelmorphologie von Scaniacypselus legt nahe, dass das Taxon weniger an das Leben in der Luft angepasst war als heutige Segler. Die Unterschiede in der Morphologie der Füße weisen darauf hin, dass Scaniacypselus in höherem Maße baumbewohnend war und von heutigen Seglern und Baumseglern abweichende Brut- und Ruhegewohnheiten hatte. Die Kronengruppenvertreter der Apodidae spalteten sich vermutlich erst weit nach dem mittleren Eozän ab, und das abgeleitete Brutverhalten dieser Vögel dürfte zu ihrem evolutionären Erfolg beigetragen haben. New specimens of Scaniacypselus szarskii , a stem Group representative of the Apodidae (true swifts) from the middle Eocene Messel oilshale in Germany, are described. These fossils show that Scaniacypselus differs from Crown Group Apodidae in a number of distinct and previously unrecognized osteological features. Notably, the sternum of Scaniacypselus is shorter than that of extant true swifts, the ulna proportionally longer, the carpometacarpus shorter, and the internal index process on the proximal phalanx of the major wing digit less developed. In details of its humerus morphology, Scaniacypselus is distinguished from all extant apodiform birds. Scaniacypselus further has a much shorter tarsometatarsus than most Crown Group Apodidae. It is hypothesized that short legs are plesiomorphic for Apodidae as a total Group (stem Group and Crown Group representatives), but that Crown Group Apodidae primitively have an elongated tarsometatarsus as an adaptation for clinging to vertical surfaces. The less specialized wing and pectoral girdle morphology suggests that Scaniacypselus was probably not as aerial as extant Apodidae. The differences in foot morphology indicate that it was more arboreal than its living relatives and had different breeding and roosting habits. Crown Group Apodiformes probably diverged well after the middle Eocene, and the derived nesting behavior may have contributed to their evolutionary success.

  • Skeletal morphology of the middle Eocene swift Scaniacypselus and the evolutionary history of true swifts (Apodidae)
    Journal of Ornithology, 2014
    Co-Authors: Gerald Mayr
    Abstract:

    New specimens of Scaniacypselus szarskii, a stem Group representative of the Apodidae (true swifts) from the middle Eocene Messel oilshale in Germany, are described. These fossils show that Scaniacypselus differs from Crown Group Apodidae in a number of distinct and previously unrecognized osteological features. Notably, the sternum of Scaniacypselus is shorter than that of extant true swifts, the ulna proportionally longer, the carpometacarpus shorter, and the internal index process on the proximal phalanx of the major wing digit less developed. In details of its humerus morphology, Scaniacypselus is distinguished from all extant apodiform birds. Scaniacypselus further has a much shorter tarsometatarsus than most Crown Group Apodidae. It is hypothesized that short legs are plesiomorphic for Apodidae as a total Group (stem Group and Crown Group representatives), but that Crown Group Apodidae primitively have an elongated tarsometatarsus as an adaptation for clinging to vertical surfaces. The less specialized wing and pectoral girdle morphology suggests that Scaniacypselus was probably not as aerial as extant Apodidae. The differences in foot morphology indicate that it was more arboreal than its living relatives and had different breeding and roosting habits. Crown Group Apodiformes probably diverged well after the middle Eocene, and the derived nesting behavior may have contributed to their evolutionary success.

  • The origins of Crown Group birds: molecules and fossils
    Palaeontology, 2014
    Co-Authors: Gerald Mayr
    Abstract:

    Knowledge of the evolutionary history of Crown Group birds (Neornithes) has significantly improved through emerging congruence among phylogenetic hypotheses and the description of numerous new Palaeogene stem Group representatives. However, controversies still persist about the precise interrelationships of many extant and fossil taxa and about the timing of the diversification of the neornithine Crown Group. Using the example of Phaethontiformes (tropicbirds) and Psittaciformes (parrots), it is shown how new sequence-based phylogenies may shed light on the relationships of fossils with an unexpected character mosaic, and how such fossils can improve our understanding of character evolution in morphologically disparate avian taxa. The earliest occurrences of neornithine birds are plotted on a current phylogeny. As noted by previous authors, an extensive diversification of neornithine birds before the latest Cretaceous is not supported by the fossil record, and the existence of essentially modern-type representatives of Telluraves (the clade including most arboreal birds) in the Cretaceous, such as suggested from molecular calibrations, is highly unlikely.

  • the age of the Crown Group of passerine birds and its evolutionary significance molecular calibrations versus the fossil record
    Systematics and Biodiversity, 2013
    Co-Authors: Gerald Mayr
    Abstract:

    Based on calibrations of molecular phylogenies and biogeographic considerations, it has been argued that the basal divergences of Crown Group Passeriformes occurred in the late Cretaceous, following the break-up of eastern Gondwana. Some implications of this hypothesis have, however, not yet been adequately addressed. In particular, a Cretaceous divergence of Crown Group passerines would imply an unprecedented evolutionary stasis for more than 80 million years in one of the most species-rich Group of endothermic vertebrates. The temporal distribution and phylogenetic affinities of northern hemispheric fossils further conflicts with current hypotheses on the historical biogeography of passerines, and is in better concordance with a Cenozoic divergence of Crown Group Passeriformes.

Pavel P. Skutschas - One of the best experts on this subject based on the ideXlab platform.

  • A new Crown-Group salamander from the Middle Jurassic of Western Siberia, Russia
    Palaeobiodiversity and Palaeoenvironments, 2015
    Co-Authors: Pavel P. Skutschas
    Abstract:

    A new Crown-Group salamander, Kiyatriton krasnolutskii sp. nov., from the Middle Jurassic (Bathonian) Itat Formation of the Berezovsk Quarry locality in Western Siberia, Russia, is described on the basis of new material and a dentary fragment previously referred to the undescribed salamander taxon “Berezovsk salamander B” (sensu Skutschas2013). Kiyatriton krasnolutskii sp. nov. differs from K. leshchinskiyi (type species of the genus Kiyatriton) in that the ventrolateral ridges on the atlas are sharper anteriorly, more ventrally oriented and reach the anterior cotylar rims and that the dentary has a relatively taller dental parapet. Kiyatriton krasnolutskii sp. nov. is one of the oldest salamanders in the fossil record. The finding of Kiyatriton krasnolutskii sp. nov. in Berezovsk Quarry is significant for: (1) clarifying that the previously reported “Berezovsk salamander B” is a Crown-Group salamander of the genus Kiyatriton; (2) extending the stratigraphic range of the genus Kiyatriton backward some 40 million years into the Bathonian, from the previously youngest record in the Aptian–Albian; (3) indicating that K. leshchinskiyi from the Aptian–Albian Shestakovo locality in Western Siberia, Russia, survived as a relic into the Early Cretaceous of present-day Western Siberia; (4) supporting the hypothesis that Bathonian vertebrate faunas of Europe and Western Siberia were homogeneous; and (5) suggesting that all Bathonian Crown-Group salamanders in Asia could be members of one cryptobranchoid clade and could represent the first radiation of Cryptobranchoidea.

  • Long bone histology of the stem salamander Kokartus honorarius (Amphibia: Caudata) from the Middle Jurassic of Kyrgyzstan.
    Journal of Anatomy, 2015
    Co-Authors: Pavel P. Skutschas, Koen Stein
    Abstract:

    Kokartus honorarius from the Middle Jurassic (Bathonian) of Kyrgyzstan is one of the oldest salamanders in the fossil record, characterized by a mixture of plesiomorphic morphological features and characters shared with Crown-Group salamanders. Here we present a detailed histological analysis of its long bones. The analysis of a growth series demonstrates a significant histological maturation during ontogeny, expressed by the progressive appearance of longitudinally oriented primary vascular canals, primary osteons, growth marks, remodelling features in primary bone tissues, as well as progressive resorption of the calcified cartilage, formation of endochondral bone and development of cartilaginous to bony trabeculae in the epiphyses. Apart from the presence of secondary osteons, the long bone histology of Kokartus is very similar to that of miniaturized temnospondyls, other Jurassic stem salamanders, miniaturized seymouriamorphs and modern Crown-Group salamanders. We propose that the presence of secondary osteons in Kokartus honorarius is a plesiomorphic feature, and the loss of secondary osteons in the long bones of Crown-Group salamanders as well as in those of miniaturized temnospondyls is the result of miniaturization processes. Hitherto, all stem salamander long bong histology (Kokartus, Marmorerpeton and ‘salamander A’) has been generally described as having paedomorphic features (i.e. the presence of Katschenko's Line and a layer of calcified cartilage), these taxa were thus most likely neotenic forms. The absence of clear lines of arrested growth and annuli in long bones of Kokartus honorarius suggests that the animals lived in an environment with stable local conditions.

  • Kiyatriton leshchinskiyi Averianov et Voronkevich, 2001, a Crown-Group salamander from the Lower Cretaceous of Western Siberia, Russia
    Cretaceous Research, 2014
    Co-Authors: Pavel P. Skutschas
    Abstract:

    Abstract Crown-Group salamander Kiyatriton leshchinskiyi , from the Lower Cretaceous (Aptian–Albian) Ilek Formation of the Shestakovo locality in Western Siberia, Russia, was the first “lissamphibian” discovered from the Mesozoic of Russia and it is the only Early Cretaceous salamander from Asia which was found outside China. In this paper a detailed redescription of type and newly collected material on Kiyatriton leshchinskiyi , consisting fragmentary cranial and postcranial bones is presented. The structure of the atlas, trunk vertebrae and femur suggest that Kiyatriton leshchinskiyi may be a member of the Cryptobranchoidea.

  • The spinal cord supports of vertebrae in the Crown-Group salamanders (Caudata, Urodela).
    Journal of Morphology, 2012
    Co-Authors: Pavel P. Skutschas, Nataly V. Baleeva
    Abstract:

    The development of spinal cord supports (bony thickenings which extend into the vertebral canal of vertebrae) in primitive (Salamandrella keyserlingii) and derived (Lissotriton vulgaris) salamanders were described. The spinal cord supports develop as the protuberances of periostal bone of the neural arches in the anteroproximal part of the septal collagenous fibers which connect a transverse myoseptum with the notochord and spinal cord, in the septal bundle inside the vertebral canal. Spinal cord supports were also found in some teleostean (Salmo salar, Oncorhynchus mykiss) and dipnoan (Protopterus sp.) fishes. The absence of the spinal cord supports in vertebrates with cartilaginous vertebrae (lampreys, chondrichthyan, and chondrostean fishes) corresponds to the fact that the spinal cord supports are bone structures. The absence of the spinal cord supports in frogs correlates with the lack of the well developed septal bundles inside the vertebral canal. The spinal cord supports are, presumably, a synapomorphic character for salamanders which originated independently of those observed in teleostean and dipnoan fishes. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.

Adam C Pritchard - One of the best experts on this subject based on the ideXlab platform.

  • a bird like skull in a triassic diapsid reptile increases heterogeneity of the morphological and phylogenetic radiation of diapsida
    Royal Society Open Science, 2017
    Co-Authors: Adam C Pritchard, Sterling J. Nesbitt
    Abstract:

    The Triassic Period saw the first appearance of numerous amniote lineages (e.g. Lepidosauria, Archosauria, Mammalia) that defined Mesozoic ecosystems following the end Permian Mass Extinction, as well as the first major morphological diversification of Crown-Group reptiles. Unfortunately, much of our understanding of this event comes from the record of large-bodied reptiles (total body length > 1 m). Here we present a new species of drepanosaurid (small-bodied, chameleon-like diapsids) from the Upper Triassic Chinle Formation of New Mexico. Using reconstructions of micro-computed tomography data, we reveal the three-dimensional skull osteology of this clade for the first time. The skull presents many archaic anatomical traits unknown in Triassic Crown-Group reptiles (e.g. absence of bony support for the external ear), whereas other traits (e.g. toothless rostrum, anteriorly directed orbits, inflated endocranium) resemble derived avian theropods. A phylogenetic analysis of Permo-Triassic diapsids supports the hypothesis that drepanosaurs are an archaic lineage that originated in the Permian, far removed from Crown-Group Reptilia. The phylogenetic position of drepanosaurids indicates the presence of archaic Permian clades among Triassic small reptile assemblages and that morphological convergence produced a remarkably bird-like skull nearly 100 Myr before one is known to have emerged in Theropoda.

Daniel B. Blake - One of the best experts on this subject based on the ideXlab platform.

  • NEW TRIASSIC ASTEROIDEA (ECHINODERMATA) SPECIMENS AND THEIR EVOLUTIONARY SIGNIFICANCE
    Rivista Italiana Di Paleontologia E Stratigrafia, 2017
    Co-Authors: Daniel B. Blake, Andrea Tintori, Tea Kolar-jurkovšek
    Abstract:

    The Paleozoic-Mesozoic transition saw the disappearance of asteroid stem Groups and the ascent of the Crown Group, but late Paleozoic and Triassic asteroids are rare and transition events are poorly documented. Three new Middle and Late Triassic specimens augment existing data; included are a specimen of Trichasteropsis weissmanni from Germany, a specimen of Trichasteropsis ? sp. indet. from Italy, and a possible member of the extant Poraniidae from Slovenia. Presence of a small ossicle at the interbrachial midline and adjacent to the marginal series of the new T. weissmanni specimen is consistent with similar expressions not only of other trichasteropsids but also occurrence of two interbrachial ossicles in Paleozoic, stem-Group asterozoans; presence is in turn consistent with a hypothesis of derivation of the axillary/odontophore coupling from two ossicles rather than direct derivation of the Crown-Group odontophore from a single stem-Group axillary. Morphology of Trichasteropsis ? sp. indet., including, for example, the evenly-tapering arms are reminiscent of those of diverse Crown-Group asteroids whereas the enlarged distal arms of T. weissmanni are unique, the morphology of T ? sp. indet. thereby potentially indicative of a plesiomorphic, stemward positioning within the Trichasteropsiidae. The range of the Poraniidae is tentatively extended to the Carnian. Similarities shared by the Poraniidae and the Trichasteropsiidae suggest stemward positioning within Crown-Group diversification; however, known Triassic fossils do not appear closely related to extant taxa identified in recent molecular studies as basal within the Crown-Group. A temperate climate is suggested as preferred by the Triassic asteroids rather than a tropical, warmer one.

  • The Complex Morphology of a New Lower Silurian Asteroid (Echinodermata)
    Journal of Paleontology, 2009
    Co-Authors: Daniel B. Blake, Frank R. Ettensohn
    Abstract:

    Abstract Gordonaster brassfieldensis is a new genus and species of Asteroidea (Echinodermata) described from the Lower Silurian Brassfield Formation of east-central Kentucky. Tentatively assigned to the poorly understood Palaeasteridae, Gordonaster shares much with Ordovician asteroids, yet it also exhibits apparent homoplasies that presage the post-Paleozoic Crown Group. Available specimens also indicate that the ontogenetic pattern of ossicular addition seen in the Crown Group was established during the Paleozoic.

  • New early Crown-Group asteroids (Echinodermata; Triassic of Germany)
    Paläontologische Zeitschrift, 2006
    Co-Authors: Daniel B. Blake, Friedrich Bielert, Ulrich Bielert
    Abstract:

    Migmaster angularis n. gen. n. sp. (Trichasteropsiidae, Forcipulatacea, Asteroidea) is described from the German Triassic Lower Muschelkalk of Anisian (Pelsonian) age, and new specimens ofTrichasteropsis bielertorum broaden understanding of this species. Phylogenetic events linking the stem Groups, known only from Paleozoic rocks, with the Crown Group, known only from post-Paleozoic rocks, are problematic; the new fossils partially constrain phylogenetic changes associated with emergence of Crown-Group asteroids.

  • RECOGNITION OF THE ASTEROID (ECHINODERMATA) Crown Group: IMPLICATIONS OF THE VENTRAL SKELETON
    Journal of Paleontology, 2004
    Co-Authors: Daniel B. Blake, Frederick H. C. Hotchkiss
    Abstract:

    Abstract All known post-Paleozoic asteroids belong to the Crown Group, and no Crown-Group asteroid is known from the Paleozoic. A scanty fossil record provides limited data on morphology of both Paleozoic stem-Group sister lineages and on the Triassic Crown Group diversification. Timing of events is weakly constrained. Interpretations based on this meager record are tentative. Within limitations of the record, recent work suggests that skeletal arrangement of the ventral surface offers apomorphies of Crown-Group diversification. Enlarged disk size is common in the Crown Group. Large disks are constructed in part by addition of many ventral and ventral-lateral so-called “actinal” ossicles. Actinals in the Crown Group are comparatively uniform in size, shape, and arrangement within each species. Actinal alignment is of one of two patterns, parallel to adambulacrals or parallel to marginals. Actinals in the Crown Group are tentatively considered to be an apomorphy of the Crown Group, although the incomplete ...

  • CARNIASTER ORCHARDI NEW GENUS AND SPECIES (ECHINODERMATA: ASTEROIDEA), THE FIRST TRIASSIC ASTEROID FROM THE WESTERN HEMISPHERE
    Journal of Paleontology, 2004
    Co-Authors: Daniel B. Blake, John Paul Zonneveld
    Abstract:

    Carniaster orchardi n. gen. and sp. (Echinodermata: Asteroidea) is only the fourth Triassic asteroid known from material complete enough to warrant a generic name. Data indicating familial and ordinal positions are not available. All four Triassic genera belong to the exclusively post-Paleozoic Crown Group. Carniaster does not appear to differ significantly from other described Triassic genera, and it probably represents a broadly basal lineage within the Crown Group diversification. Available morphological data suggest no ecologic parameters that would be unusual among living asteroids. Carniaster is the first complete Triassic asteroid known from beyond Europe.

Sterling J. Nesbitt - One of the best experts on this subject based on the ideXlab platform.

  • The earliest equatorial record of frogs from the Late Triassic of Arizona.
    Biology Letters, 2019
    Co-Authors: Michelle R. Stocker, Sterling J. Nesbitt, Ben T. Kligman, Daniel J. Paluh, Adam D. Marsh, David C. Blackburn, William G. Parker
    Abstract:

    Crown-Group frogs (Anura) originated over 200 Ma according to molecular phylogenetic analyses, though only a few fossils from high latitudes chronicle the first approximately 60 Myr of frog evoluti...

  • a bird like skull in a triassic diapsid reptile increases heterogeneity of the morphological and phylogenetic radiation of diapsida
    Royal Society Open Science, 2017
    Co-Authors: Adam C Pritchard, Sterling J. Nesbitt
    Abstract:

    The Triassic Period saw the first appearance of numerous amniote lineages (e.g. Lepidosauria, Archosauria, Mammalia) that defined Mesozoic ecosystems following the end Permian Mass Extinction, as well as the first major morphological diversification of Crown-Group reptiles. Unfortunately, much of our understanding of this event comes from the record of large-bodied reptiles (total body length > 1 m). Here we present a new species of drepanosaurid (small-bodied, chameleon-like diapsids) from the Upper Triassic Chinle Formation of New Mexico. Using reconstructions of micro-computed tomography data, we reveal the three-dimensional skull osteology of this clade for the first time. The skull presents many archaic anatomical traits unknown in Triassic Crown-Group reptiles (e.g. absence of bony support for the external ear), whereas other traits (e.g. toothless rostrum, anteriorly directed orbits, inflated endocranium) resemble derived avian theropods. A phylogenetic analysis of Permo-Triassic diapsids supports the hypothesis that drepanosaurs are an archaic lineage that originated in the Permian, far removed from Crown-Group Reptilia. The phylogenetic position of drepanosaurids indicates the presence of archaic Permian clades among Triassic small reptile assemblages and that morphological convergence produced a remarkably bird-like skull nearly 100 Myr before one is known to have emerged in Theropoda.