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  • 1.
    Bremer, Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Distribution of Silurian vertebrates on Gotland, Sweden2016Conference paper (Other academic)
  • 2.
    Bremer, Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Geology, stratigraphy, and fossil vertebrates of Gotland, Sweden: a review2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The Silurian limestones of Gotland, Sweden, and their exceptionally well-preserved fossils have attracted the interest of scientists for more than 200 years. The sedimentary rocks represent approximately 10 million years of time, and were deposited in a shallow, equatorial inland sea named the Baltic Basin. The majority of the sediments are composed of reef-associated strata, but a general transition can be seen along the strike from shallow water in the northeast to deeper shelf environments in the southwest. The understanding of the stratigraphy and the geology of Gotland has greatly improved during the last decades. This research on Gotland has also led to the discovery of a series of stable isotope excursions and extinctions among several faunal groups. These events were probably linked to cycles in atmospheric and oceanic states, and three of them have been recognized globally. The Baltic Basin was also home to a variety of early vertebrates. The first fossil vertebrates from Gotland were reported in 1861, but the most extensive study of these early fishes was performed in the late 1900s. More recently it was shown that the vertebrates were also affected by one of the extinction events. This thesis is an extensive review of previous work and will form a geological basis for future studies. In this work, all previous reports of vertebrates have been gathered, reviewed, and the old samples have been placed in an updated stratigraphical framework. The scale taxonomy of Gotland vertebrates, including the Baltic acanthodians, has been evaluated and partly revised. Additionally, the depositional environments of the sampled areas have been investigated. Studying the vertebrates of Gotland is important for understanding the distribution of vertebrates through time and in different environments during the Silurian. Initial results indicate environmental preferences among vertebrates on both group and species-level, which may prove useful for testing the vertebrate biozonation developed for the Silurian.

    List of papers
    1. An updated stratigraphic and environmental framework for the distribution of Silurian vertebrates on Gotland
    Open this publication in new window or tab >>An updated stratigraphic and environmental framework for the distribution of Silurian vertebrates on Gotland
    2015 (English)In: Estonian journal of earth sciences, ISSN 1736-4728, E-ISSN 1736-7557, Vol. 64, no 1, p. 13-18Article in journal (Refereed) Published
    Keywords
    vertebrate distribution, stratigraphy, facies, Silurian events, Gotland, Sweden
    National Category
    Developmental Biology Earth and Related Environmental Sciences
    Identifiers
    urn:nbn:se:uu:diva-251824 (URN)10.3176/earth.2015.03 (DOI)000351327700004 ()
    Available from: 2015-04-27 Created: 2015-04-24 Last updated: 2017-08-21
    2. Vertebrate microremains from the upper Silurian Winnica Formation of the Holy Cross Mountains, Poland
    Open this publication in new window or tab >>Vertebrate microremains from the upper Silurian Winnica Formation of the Holy Cross Mountains, Poland
    Show others...
    2018 (English)In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 155, no 7, p. 1523-1541Article in journal (Refereed) Published
    Abstract [en]

    Vertebrate microremains from the upper Silurian Winnica Formation in the Holy Cross Mountains, Poland are described from the Winnica and Rzepin sections. Both sites record the uppermost part of the Supianka Member, but represent different depositional environments. The Winnica samples come from a low-energy environment, while the Rzepin sample was taken from a high-energy, oolitic facies. Both sites contain thelodonts Thelodus parvidens, Thelodus trilobatus, an anaspid cf. Liivilepis and a number of acanthodian scales of 'nostolepid', poracanthodid and 'gomphonchid' types. Notable differences between the sites are the addition of the osteostracan Tahulaspis cf. ordinata, the thelodont Paralogania ludlowiensis and acanthodian scales identified as Nostolepis gracilis in the Rzepin section. Placing the vertebrate faunas within the vertebrate biozonation established for the Silurian proved difficult. The suggested late Ludlow age for the Supianka Member based on sequence stratigraphical and chemostratigraphical correlations cannot be definitely confirmed or refuted, but a late Ludfordian age seems the most plausible based on invertebrate and vertebrate faunas. The much lower abundance of poracanthodid acanthodians in the Rzepin sample supports the notion of Poracanthodes porosus Zone as a deep-water equivalent to a number of vertebrate biozones. The presence of P. ludlowiensis only in the oolitic sample confirms a long temporal range, but restricted environmental distribution for this taxon.

    National Category
    Other Earth and Related Environmental Sciences
    Identifiers
    urn:nbn:se:uu:diva-281657 (URN)10.1017/S0016756817000681 (DOI)000443814900008 ()
    Available from: 2016-03-29 Created: 2016-03-29 Last updated: 2018-11-06Bibliographically approved
  • 3.
    Bremer, Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Silurian vertebrates of Gotland (Sweden) and the Baltic Basin2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    During the Silurian, the Swedish island Gotland was positioned close to the equator and covered by a shallow sea called the Baltic Basin. The sedimentary rocks (predominantly carbonates) comprising most of the island today were initially formed in this warm sea, and the relatively complete succession of rocks often contains fossil fragments and scales from early vertebrates, including heterostracans, anaspids, thelodonts, osteostracans, acanthodians, and a stem-osteichthyan. Fossils of early vertebrates become increasingly more common in younger Silurian rocks, but are mostly represented by fragmentary remains and rarer occurrences of articulated jawless vertebrates (agnathans). However, the record of articulated specimens and jawed vertebrates (gnathostomes) are more numerous in rocks of the following Devonian Period. Isolated peaks of agnathan diversity during the Silurian and disarticulated remains of gnathostomes from this period hint at a cryptic evolutionary history. A micropaleontological approach with broader sampling may provide a better understanding of early vertebrate distribution patterns and hopefully give some insights into this history. The objective of this study was to build upon previous sampling on Gotland and to use established frameworks for disarticulated remains with the aim of making comparisons with similar studies performed in the East Baltic. However, difficulties locating the collections from these previous works necessitated a different focus. Undescribed museum collections and newly sampled material enabled some taxonomical revisions and greatly improved the understanding of vertebrate distribution in the youngest part of the Gotland sequence. It also indicated that this interval may represent the early stages of the diversification of gnathostomes that become increasingly dominant toward the end of the Silurian. Furthermore, the description of samples from partly coeval sections in Poland enabled some preliminary comparisons outside of Gotland, and presented a striking example of restricted environmental occurrences for a thelodont taxon. This is encouraging for future sampling and investigations on Gotland. Together with the establishment of a facies-framework comparable to that developed in the East Baltic and correlations to other areas, this may prove fruitful for an increased understanding of early vertebrate distribution and evolution during the Silurian.

    List of papers
    1. An updated stratigraphic and environmental framework for the distribution of Silurian vertebrates on Gotland
    Open this publication in new window or tab >>An updated stratigraphic and environmental framework for the distribution of Silurian vertebrates on Gotland
    2015 (English)In: Estonian journal of earth sciences, ISSN 1736-4728, E-ISSN 1736-7557, Vol. 64, no 1, p. 13-18Article in journal (Refereed) Published
    Keywords
    vertebrate distribution, stratigraphy, facies, Silurian events, Gotland, Sweden
    National Category
    Developmental Biology Earth and Related Environmental Sciences
    Identifiers
    urn:nbn:se:uu:diva-251824 (URN)10.3176/earth.2015.03 (DOI)000351327700004 ()
    Available from: 2015-04-27 Created: 2015-04-24 Last updated: 2017-08-21
    2. End-Wenlock terminal Mulde carbon isotope excursion in Gotland, Sweden: Integration of stratigraphy and taphonomy for correlations across restricted facies and specialized faunas
    Open this publication in new window or tab >>End-Wenlock terminal Mulde carbon isotope excursion in Gotland, Sweden: Integration of stratigraphy and taphonomy for correlations across restricted facies and specialized faunas
    Show others...
    2016 (English)In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 457, p. 304-322Article in journal (Refereed) Published
    National Category
    Earth and Related Environmental Sciences
    Research subject
    Earth Science with specialization in Historical Geology and Palaeontology
    Identifiers
    urn:nbn:se:uu:diva-299498 (URN)10.1016/j.palaeo.2016.06.031 (DOI)000380598800025 ()
    Available from: 2016-07-21 Created: 2016-07-21 Last updated: 2017-08-21
    3. Vertebrate remains and conodont biostratigraphy in the Ludlow Burgsvik Formation of Gotland, Sweden
    Open this publication in new window or tab >>Vertebrate remains and conodont biostratigraphy in the Ludlow Burgsvik Formation of Gotland, Sweden
    (English)Manuscript (preprint) (Other academic)
    National Category
    Earth and Related Environmental Sciences
    Identifiers
    urn:nbn:se:uu:diva-328226 (URN)
    Available from: 2017-08-20 Created: 2017-08-20 Last updated: 2017-08-25
    4. Vertebrate dermal remains and conodont distribution in the upper Silurian Hamra and Sundre formations of Gotland, Sweden
    Open this publication in new window or tab >>Vertebrate dermal remains and conodont distribution in the upper Silurian Hamra and Sundre formations of Gotland, Sweden
    (English)Manuscript (preprint) (Other academic)
    National Category
    Earth and Related Environmental Sciences
    Identifiers
    urn:nbn:se:uu:diva-328227 (URN)
    Available from: 2017-08-20 Created: 2017-08-20 Last updated: 2017-08-21
    5. Vertebrate microremains from the upper Silurian Winnica Formation of the Holy Cross Mountains, Poland
    Open this publication in new window or tab >>Vertebrate microremains from the upper Silurian Winnica Formation of the Holy Cross Mountains, Poland
    Show others...
    2018 (English)In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 155, no 7, p. 1523-1541Article in journal (Refereed) Published
    Abstract [en]

    Vertebrate microremains from the upper Silurian Winnica Formation in the Holy Cross Mountains, Poland are described from the Winnica and Rzepin sections. Both sites record the uppermost part of the Supianka Member, but represent different depositional environments. The Winnica samples come from a low-energy environment, while the Rzepin sample was taken from a high-energy, oolitic facies. Both sites contain thelodonts Thelodus parvidens, Thelodus trilobatus, an anaspid cf. Liivilepis and a number of acanthodian scales of 'nostolepid', poracanthodid and 'gomphonchid' types. Notable differences between the sites are the addition of the osteostracan Tahulaspis cf. ordinata, the thelodont Paralogania ludlowiensis and acanthodian scales identified as Nostolepis gracilis in the Rzepin section. Placing the vertebrate faunas within the vertebrate biozonation established for the Silurian proved difficult. The suggested late Ludlow age for the Supianka Member based on sequence stratigraphical and chemostratigraphical correlations cannot be definitely confirmed or refuted, but a late Ludfordian age seems the most plausible based on invertebrate and vertebrate faunas. The much lower abundance of poracanthodid acanthodians in the Rzepin sample supports the notion of Poracanthodes porosus Zone as a deep-water equivalent to a number of vertebrate biozones. The presence of P. ludlowiensis only in the oolitic sample confirms a long temporal range, but restricted environmental distribution for this taxon.

    National Category
    Other Earth and Related Environmental Sciences
    Identifiers
    urn:nbn:se:uu:diva-281657 (URN)10.1017/S0016756817000681 (DOI)000443814900008 ()
    Available from: 2016-03-29 Created: 2016-03-29 Last updated: 2018-11-06Bibliographically approved
  • 4.
    Bremer, Oskar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Blom, Henning
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    An updated stratigraphic and environmental framework for the distribution of Silurian vertebrates on Gotland2015In: Estonian journal of earth sciences, ISSN 1736-4728, E-ISSN 1736-7557, Vol. 64, no 1, p. 13-18Article in journal (Refereed)
  • 5.
    Bremer, Oskar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Blom, Henning
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Biostratigraphy of early vertebrates on Gotland2014In: 4th Annual Meeting of IGCP 591, Estonia, 10 - 19 June 2014.: Abstracts and Field Guide / [ed] Heikki Bauert, Olle Hints, Tõnu Meidla & Peep Männik, Tartu: University of Tartu, 2014, p. 21-21Conference paper (Other academic)
  • 6.
    Bremer, Oskar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Blom, Henning
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Biostratigraphy of Silurian vertebrates from Gotland, Sweden, revisited: understanding spatial and temporal distributions2015In: Abstract volume of the 13th International symposium on Early and Lower Vertebrates / [ed] Kate Trinajstic, Zerina Johanson, Martha Richter and Catherine Boisvert, 2015Conference paper (Other academic)
  • 7.
    Bremer, Oskar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Kear, Benjamin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Reassessment of the ‘last’ goniopholidid: denazinosuchus kirtlandicus from the late cretaceous of New Mexico2013In: Program and Abstract Book, 2013, p. 93-94Conference paper (Other academic)
  • 8.
    Bremer, Oskar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    Kear, Benjamin P.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
    CT-scan of Parasaurolophus tubicen from the Sternberg Collection (Uppsala University)2011In: The 2nd Wiman Meeting. Carl Wiman's Legacy: 100 Years of Swedish Palaeontology / [ed] Benjamin P. Kear and Michael Streng, 2011, p. 4-Conference paper (Other academic)
    Abstract [en]

    In 1922, Carl Wiman, head of the then Palaeontological Institute at Uppsala University, received a series of crates containing dinosaur remains from the Upper Cretaceous (upper Campanian–Maastrichtian) Kirtland Formation of New Mexico, U.S.A. The specimens had been collected in 1921 by the famous American fossil hunter, Charles H. Sternberg, during a commissioned 5 month field expedition to the in the San Juan Basin. Arguably, one of the most significant specimens recovered was the partial skull of the spectacular crested hadrosaur Parasaurolophus tubicen. The holotype (PMU 24925) comprises the massive crest and neurocranium, together with parts of the pareital, frontal, prefrontals, postorbitals, squamosals and exoccipitals. The right quadrate is also preserved in articulation with the quadratojugal and pterygoid; the right jugal, maxilla, pterygoid, ectopterygoid and the anterior section of the lacrimal make up the facial region of the skull. Wiman was the first to propose that the crest of Parasaurolophus functioned as a vocalization structure. This study aims to investigate the functional morphology of the crest in this hadrosaur, in conjunction with endocranial anatomy, using CT-scanning and 3D modelling of the intracranial chambers. Comparisons with other specimens of Parasaurolophus will permit reconstruction of sensory capabilities in this 'classic' dinosaur taxon.

  • 9.
    Bremer, Oskar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Niedzwiedzki, Grzegorz
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Blom, Henning
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Dec, Marek
    Polish Acad Sci, Inst Paleobiol, Twarda 51-55, PL-00818 Warsaw, Poland.
    Kozłowski, Wojciech
    Univ Warsaw, Inst Geol, Zwirki & Wigury 93, PL-02089 Warsaw, Poland.
    Vertebrate microremains from the upper Silurian Winnica Formation of the Holy Cross Mountains, Poland2018In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 155, no 7, p. 1523-1541Article in journal (Refereed)
    Abstract [en]

    Vertebrate microremains from the upper Silurian Winnica Formation in the Holy Cross Mountains, Poland are described from the Winnica and Rzepin sections. Both sites record the uppermost part of the Supianka Member, but represent different depositional environments. The Winnica samples come from a low-energy environment, while the Rzepin sample was taken from a high-energy, oolitic facies. Both sites contain thelodonts Thelodus parvidens, Thelodus trilobatus, an anaspid cf. Liivilepis and a number of acanthodian scales of 'nostolepid', poracanthodid and 'gomphonchid' types. Notable differences between the sites are the addition of the osteostracan Tahulaspis cf. ordinata, the thelodont Paralogania ludlowiensis and acanthodian scales identified as Nostolepis gracilis in the Rzepin section. Placing the vertebrate faunas within the vertebrate biozonation established for the Silurian proved difficult. The suggested late Ludlow age for the Supianka Member based on sequence stratigraphical and chemostratigraphical correlations cannot be definitely confirmed or refuted, but a late Ludfordian age seems the most plausible based on invertebrate and vertebrate faunas. The much lower abundance of poracanthodid acanthodians in the Rzepin sample supports the notion of Poracanthodes porosus Zone as a deep-water equivalent to a number of vertebrate biozones. The presence of P. ludlowiensis only in the oolitic sample confirms a long temporal range, but restricted environmental distribution for this taxon.

  • 10.
    Bremer, Oskar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Niedźwiedzki, Grzegorz
    Blom, Henning
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Dec, Marek
    Kozłowski, Wojciech
    Vertebrate microremains from the upper Silurian Winnica Formation of the Holy Cross Mountains, Poland2017Conference paper (Other academic)
  • 11. Jarochowska, Emilia
    et al.
    Bremer, Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Heidlas, Daniel
    Pröpster, Stephanie
    Vandenbroucke, Thijs
    Munnecke, Axel
    Multielement skeletal taphonomy in conodonts: are robust species more common or selectively preserved in shallow-water facies?2016Conference paper (Other academic)
  • 12.
    Jarochowska, Emilia
    et al.
    GeoZentrum Nordbayern, Fachgruppe Paläoumwelt, University of Erlangen-Nuremberg, Loewenichstr. 28, 91054 Erlangen, Germany.
    Bremer, Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Heidlas, Daniel
    GeoZentrum Nordbayern, Fachgruppe Paläoumwelt, University of Erlangen-Nuremberg, Loewenichstr. 28, 91054 Erlangen, Germany.
    Pröpster, Stephanie
    GeoZentrum Nordbayern, Fachgruppe Paläoumwelt, University of Erlangen-Nuremberg, Loewenichstr. 28, 91054 Erlangen, Germany.
    Vandenbroucke, Thijs R.A.
    Department of Geology, Ghent University, Krijgslaan 281-S8, B-9000 Ghent, Belgium;Evo-Eco-Paléo UMR 8198, Université de Lille, Avenue Paul Langevin, Bâtiment SN5, 59655 Villeneuve d'Ascq Cedex, France.
    Munnecke, Axel
    GeoZentrum Nordbayern, Fachgruppe Paläoumwelt, University of Erlangen-Nuremberg, Loewenichstr. 28, 91054 Erlangen, Germany.
    End-Wenlock terminal Mulde carbon isotope excursion in Gotland, Sweden: Integration of stratigraphy and taphonomy for correlations across restricted facies and specialized faunas2016In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 457, p. 304-322Article in journal (Refereed)
  • 13. Jarochowska, Emilia
    et al.
    Viira, Viive
    Einasto, Rein
    Nawrot, Rafal
    Bremer, Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Männik, Peep
    Munnecke, Axel
    Conodont Diversity Across The Onshore-Offshore Gradient: Cozy In Brine2016In: Geological Society of America Abstracts with Programs., 2016, Vol. 48Conference paper (Other academic)
  • 14. Jarochowska, Emilia
    et al.
    Viira, Viive
    Einasto, Rein
    Nawrot, Rafał
    Bremer, Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Männik, Peep
    Munnecke, Axel
    Conodonts in Silurian hypersaline environments: specialized an dunexpectedly diverse2017In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 45, no 1, p. 3-6Article in journal (Refereed)
    Abstract [en]

    Hypersaline environments are commonly assumed to be barren of metazoans and therefore are avoided by paleontologists, yet a number of early Paleozoic jawless vertebrate groups specialized to live in such settings. Sampling bias against restricted settings resulted in substantial underestimation of their diversity. Rare studies venturing into such environments yielded multiple new species of conodonts, suggesting that the diversity and habitat range of these hyperdiverse predators of the early oceans are equally underestimated. We describe here autochthonous conodont fauna from evaporite-bearing horizons from the middle Silurian of Estonia that provide evidence for efficient osmoregulation in this group. Based on a global compilation of coeval conodont assemblages, we show that marginal-marine, periodically emergent environments were characterized by higher conodont diversity than open-marine shallow settings. This diversity is due to a high number of species occurring in these environments only. The high degree of specialization is also reflected by the highest within-habitat variability (β diversity) in marginal settings. Most conodont species had narrow environmental niches and, unlike in marine invertebrates, extreme environments were inhabited by the most specialized taxa. Such environments represent a large proportion of early Paleozoic tropical epicratonic basins. Our analysis allows quantification of the degree to which mid-Silurian conodont diversity is underestimated as a result of sampling bias against marginal-marine settings.

  • 15.
    Jerve, Anna
    et al.
    Imperial Coll London, Biol Dept, Silwood Pk Campus,Buckhurst Rd, Ascot SL5 7PY, Berks, England.
    Bremer, Oskar
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Sanchez, Sophie
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology. Uppsala University, Science for Life Laboratory, SciLifeLab. European Synchrotron Radiat Facil, 71 Ave Martyrs, F-38000 Grenoble, France.
    Ahlberg, Per E.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Organismal Biology, Evolution and Developmental Biology.
    Morphology and histology of acanthodian fin spines from the late Silurian Ramsåsa E locality, Skåne, Sweden2017In: Palaeontologia Electronica, ISSN 1935-3952, E-ISSN 1094-8074, Vol. 20, no 3, article id 56AArticle in journal (Refereed)
    Abstract [en]

    Comparisons of acanthodians to extant gnathostomes are often hampered by the paucity of mineralized structures in their endoskeleton, which limits the potential preservation of phylogenetically informative traits. Fin spines, mineralized dermal structures that sit anterior to fins, are found on both stem-and crown-group gnathostomes, and represent an additional potential source of comparative data for studying acanthodian relationships with the other groups of early gnathostomes. An assemblage of isolated acanthodian fin spines from the late Silurian Ramsasa site E locality (southern Sweden) has been reconstructed in 3D using propagation phase contrast synchrotron X-ray microtomography (PPC-SR mu CT). The aim is to provide morphological and taxo-nomical affinities for the spines by combining morphology and histology with the taxo-nomical framework previously established for the site mainly based on isolated scales. The high-resolution scans also enable investigations of the composition and growth of acanthodian fin spines when compared to similar studies of extinct and extant gnathostomes. In total, seven fin spine morphotypes that have affinities to both Climatiidae Berg 1940 and Ischnacanthiformes Berg 1940 are described. The majority are interpreted as median fin spines, but three possible paired spines are also identified. The spines display differences in their compositions, but generally agree with that presented for climatiids and ischnacanthiforms in previous studies. Their inferred growth modes appear to be more similar to those of fossil and extant chondrichthyan fin spines than to those described from placoderms and stem-osteichthyans, which is congruent with the emerging view of acanthodians as stem-chondrichthyans.

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