| 1. |
- Dupret, Vincent, et al.
(författare)
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A primitive placoderm sheds light on the origin of the jawed vertebrate face
- 2014
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 507:7493, s. 500-503
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Tidskriftsartikel (refereegranskat)abstract
- Extant vertebrates form two clades, the jawless Cyclostomata (lampreys and hagfishes) and the jawed Gnathostomata (all other vertebrates), with contrasting facial architectures(1,2). These arise during development from just a few key differences in the growth patterns of the cranial primordia: notably, the nasal sacs and hypophysis originate from a single placode in cyclostomes but from separate placodes in gnathostomes, and infraoptic ectomesenchyme migrates forward either side of the single placode in cyclostomes but between the placodes in gnathostomes(3-8). Fossil stem gnathostomes preserve cranial anatomies rich in landmarks that provide proxies for developmental processes and allow the transition from jawless to jawed vertebrates to be broken down into evolutionary steps(7,9-12). Here we use propagation phase contrast synchrotron microtomography to image the cranial anatomy of the primitive placoderm (jawed stem gnathostome) Romundina(13), and show that itcombines jawed vertebrate architecture with cranial and cerebral proportions resembling those of cyclostomes and the galeaspid (jawless stem gnathostome) Shuyu(11). This combination seems to be primitive for jawed vertebrates, and suggests a decoupling between ectomesenchymal growth trajectory, ectomesenchymal proliferation, and cerebral shape change during the origin of gnathostomes.
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| 2. |
- Dupret, Vincent, 1977-, et al.
(författare)
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Being Romundina stellina Ørvig, 1975 (Vertebrate, Placodermi, Acanthothoraci) : itracranial anatomy of one of the deepest gnathostomes revealed by synchrotron tomograpy in phase contrast protocole
- 2012
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Konferensbidrag (refereegranskat)abstract
- Dans la peau de Romundina stellina Ørvig, 1975 (Vertebrata, Placodermi, Acanthothoraci)Anatomie crânienne d'un des premiers gnathostomes révélée par tomographie synchrotron en contraste de phase Being Romundina stellina Ørvig, 1975 (Vertebrata, Placodermi, Acanthothoraci)Intracranial anatomy of one of the deepest gnathostomes revealed by synchrotron tomography in phase contrast protocole The acanthothoracid placoderms (armored fishes) are the most basal and primitive gnathostomes (jawed vertebrates; 1). However, their endocranial morphology is poorly understood, and only one genus (Brindabellaspis) has been described thoroughly (2).Here we present the 3D reconstruction of a subcomplete skull of Romundina stellina Ørvig, 3, from the Lochkovian of Prince of Wales Island, Canadian Arctic Archipelago. The specimen was imaged in 3D with propagation phase contrast microtomography (4) on the ID19 beamline of the ESRF, using a 7.45 µm isotropic voxel size.Most features are properly preserved and most of the missing structures can be virtually rebuilt by symmetry. Another advantage of this virtual approach is the possibility of connecting with certainty all the external foramina to the blood and nerve canals and the central/internal structures, and hence to identify accurate homologies without destroying the specimen. Ørvig’s original assumptions can now be checked with confidence.The vasculature of the dermal bones, rendered in detail, allowed a better understanding of plate growth. It permits the visualization of dermal bone establishment over perichondral bone (5).The high level of details of this model reveals that between the trigeminal and vagus nerve (and the inner ears), the perichondral bone wrapping the endocranial cavity shows a “lace” pattern, unknown so far in vertebrates (presumably because of the lack of data). The significance of this character is unclear, but it is definitely not an artifact of taphonomy or scanning. References1 Janvier, P. Early Vertebrates. Clarendon Press edn, Vol. 1 (Oxford Science Publications, 1996).2 Young, G. C. A new Early Devonian placoderm from New South Wales, Australia, with a discussion of placoderm phylogeny. Palaeontographica (A) 167, 10–76 (1980).3 Ørvig, T. Description, with special reference to the dermal skeleton, of a new Radotinid arthrodire from the Gedinnian of Arctic Canada. Extrait des Colloques internationaux du Centre National de la Recherche Scientifique - Problèmes actuels de Paléontologie - Evolution des Vertébrés 218, 41–71 (1975).4 Tafforeau, P. et al. Applications of X-ray synchrotron microtomography for non-destructive 3D studies of paleontological specimens. Applied Physics A - Materials Science & Processing 83, 195–202 (2006).5 Dupret, V., Sanchez, S., Goujet, D., Tafforeau, P. & Ahlberg, P. Bone vascularization and growth in placoderms (Vertebrata): the example of the premedian plate of Romundina stellina Ørvig, 1975 Comptes Rendus Palevol 9, 369–375 (2010).
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| 3. |
- Dupret, Vincent, 1977-, et al.
(författare)
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Bone vascularization and growth in placoderms (Vertebrata) : The example of the premedian plate of Romundina stellina Ørvig, 1975
- 2010
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Ingår i: Comptes rendus. Palevol. - : Elsevier BV. - 1631-0683 .- 1777-571X. ; 9:6-7, s. 369-375
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Tidskriftsartikel (refereegranskat)abstract
- The Placodermi (armored jawed fishes), which appeared during the Lower Silurian and disappeared without leading any descendants at the end of the Famennian (Latest Devonian), have the highest diversity of known Devonian vertebrate groups. As phylogenetically basal gnathostomes (jawed vertebrates), they are potentially informative about primitive jawed vertebrate anatomy and origins. Until recently, the study of their internal or histological structures has required destructive methods such as sectioning or serial grinding. Recent advances in tomography and imaging technologies, especially through the increasing use of synchrotron phase contrast imaging for the study of fossils, allow us to reveal the inner structures of the fossil nondestructively and with unprecedented three-dimensional level of detail. Here, we present for the first time the prerostral anatomy of the small acanthothoracid Romundina stellina, one of the earliest and most basal placoderms. Phase contrast imaging allows us to reconstruct the vascularization and nerve canals of the premedian plate and adjacent parts of the skeleton three-dimensionally in great detail, providing important clues to the growth modes and biology of the animal.
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| 4. |
- Dupret, Vincent, 1977-, et al.
(författare)
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Fossil early vertebrates shed lights on the origin of the gnathostome face
- 2013
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Ingår i: Program and Abstracts of the 10th International Congress of Vertebrate Morphology. - Barcelona, Spain. ; , s. 245-245
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Konferensbidrag (refereegranskat)abstract
- Jawless cyclostomes and jawed gnathostomes show very different face patterns. Cyclostomes have a single median nasohypophysial duct, an anterior hypophysis and a short telencephalon, while gnathostomes have a pair of nasal sacs opening externally, a more posterior separate hypophysis open in the palate and a longer telencephalon.Embryonic processes differ as well. In cyclostomes, premandibular crest cells migrate forwards either side of the nasohypophysial placode to form the upper lip; in gnathostomes they migrate between the hypophysial and nasal placodes to form the trabecular region. Supraoptic neural crest remains posterior to the nasohypophysial duct in cyclostomes; it moves forward to create the nasal capsules in gnathostomes.Some fossil forms illustrate a transition between these two patterns.The jawless galeaspid Shuyu (-430 Ma) has a nasohypophysial duct, short telencephalon, and anteriorly oriented hypophysis, but the paired nasal sacs and hypophysis are separated by a rudimentary trabecula.The jawed primitive placoderm Romundina (-415 Ma) shows a cranial cavity reminiscent of that of Shuyu (anteriorly directed hypophysis, very short telencephalon). The trabecular region is long and wide, the nasal capsule is small and located far behind the tip of the snout but just in front of the orbits. We interpret these features as uniquely primitive among gnathostomes. The premandibular crest of Romundina formed a trabecular region extending as anteriorly as the tip of the snout (like in extant cyclostome and the fossil Shuyu). The position of the nasal capsule suggests that the supraoptic crest had not migrated forwards.We suggest that the evolutionary sequence for the creation of the extant gnathostome face from a cyclostome pattern involved 1) separation of the nasal and hypophysial placodes (galeaspids), 2) loss of the nasohypophysial duct (placoderms), and 3) lengthening of the telencephalon and the migration of the nasal capsules to the snout tip.
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| 5. |
- Dupret, Vincent, 1977-, et al.
(författare)
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Fossils of early vertebrates and the evolution of the gnathostome face revealed by Synchrotron imaging
- 2013
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Ingår i: Programme and Abstracts. - Edinburgh, U.K.. ; , s. 21-21
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Konferensbidrag (refereegranskat)abstract
- Cyclostomes and gnathostomes have distinct face patterns. Cyclostomes possess a median nasohypophysial duct, an anterior hypophysis and a short telencephalon, contra gnathostomes possessing a pair of nasal sacs opening externally, a separate posterior hypophysis opening onto the palate and a long telencephalon. Embryonic development also differs. In cyclostomes, premandibular crest cells migrate forwards either side of the nasohypophysial placode, forming an upper lip; in gnathostomes they migrate between the hypophysial and nasal placodes forming the trabecular region. Supraoptic neural crest remains posterior to the nasohypophysial duct in cyclostomes but moves forward to create the nasal capsules in gnathostomes. Fossil stem gnathostomes illustrate a transitional sequence between these two patterns: 1) The galeaspid Shuyu (jawless stem gnathostome): nasohypophysial duct, short telencephalon, and anteriorly oriented hypophysis as in a cyclostome, but paired nasal sacs and hypophysis separated by a rudimentary trabecula. 2) The primitive placoderm Romundina (jawed stem gnathostome): short telencephalon, anteriorly directed hypophysis, trabecular region long and wide, nasal capsule located far behind the tip of the snout but just in front of the orbits. These features are interpreted as uniquely primitive among gnathostomes. The trabeculae of Romundina form an extensive precerebral region resembling the upper lip of extant cyclostomes and Shuyu. The position of the nasal capsule suggests that the supraoptic crest had not migrated forwards. 3) The arthrodire Kujdanowiapsis (a more derived placoderm): short telencephalon and vertically oriented hypophysis. The trabecula has been shortened anteriorly, making the nasal capsule terminal. These positional relationships are maintained in crown gnathostomes.
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| 6. |
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| 7. |
- Dupret, Vincent, 1977-, et al.
(författare)
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Intracranial anatomy of Romundina stellina Ørvig 1975 (Vertebrata, Placodermi, Acanthothoraci) revealed by phase contrast synchrotron imaging
- 2011
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Ingår i: Abstracts. ; , s. 6-6
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Acanthothoracid placoderms are considered amongst the most basal of primitive gnathostomes. However, their endocranial morphology is poorly understood, and only one genus (Brindabellaspis) has been described in detail. Here we present a synchrotrongenerated 3D reconstruction of a nearly complete skull of Romundina stellina, a taxon established in 1975 by the Norwegian-born Swedish palaeontologist Tor Ørvig based on remains from the Lochkovian (Lower Devonian) of Prince of Wales Island, Canadian Arctic Archipelago. The specimen was imaged with propagation phase contrast microtomography on the ID19 beamline of the ESRF, using a 7.45 µm isotropic voxel size. Most structural features of the fossil are very well preserved, allowing missing elements to be virtually rebuilt by symmetry. This permitted reconnection of the external foramina and blood vessel/nerve canals, and alignment of the central/internal structures. Expanding on Ørvig’s original interpretations, our virtual models show the vasculature of the skull bones, and indicate establishment of successive dermal over perichondral bone layers. The perichondral bone wrapping the endocranial cavity, in between the trigeminal and vagus nerve (and the inner ears), shows a “lace” pattern, which is otherwise unknown in vertebrates (presumably because of the lack of data). The significance of this trait is unclear but it is not an artifact of taphonomy or scanning.
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| 8. |
- Dupret, Vincent, 1977-, et al.
(författare)
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Structures intra-crâniennes de Romundina stellina Ørvig 1975 (Vertebrata, Placodermi, Acanthothoraci) révélé par tomographie synchrotron en contraste de phase
- 2012
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Konferensbidrag (refereegranskat)abstract
- Les placodermes acanthothoracides sont parmi les vertébrés gnathostomes les plus basaux phylogénetiquement et morphologiquement. Néanmoins, une bonne connaissance anatomie crânienne fait défaut, et à ce jour un seul genre (Brindabellaspis) a été décrit en détails. Nous présentons le modèle en 3 dimensions d’un crâne presque complet de Romundina stellina, un petit acanthothoracide du Dévonien inférieur de l’Archipel Arctique Canadien, décrit originellement par Ørvig (1975). Le spécimen a été microtomographié sur la ligne de faisceau ID 19 de l’ESRF de Grenoble (European Synchrotron Radiation Facility), en protocole de contraste de phase, avec un voxel isotrope de 7,45 micromètres.Malgré une cassure oblique, la plupart des structures peuvent être reconstruites par symétrie. Chaque nerf crânien peut être suivi entre la cavité encéphalique et les murs du neurocrâne composés d’os périchondral. Il en est de même pour les vaisseaux sanguins. La détermination des homologies en est donc facilitée, tout en assurant la non destruction du spécimen. Les hypothèses d’homologies formulées par Ørvig peuvent être traitées en toute confidence.La couche d’os périchondrale entourant la cavité encéphalique n’est pas homogène mais présente un aspect en dentelle entre les nerfs trijumeaux (V) et vague (X) ; il en est de même pour les oreilles internes, dont les canaux semi-circulaires ne sont pas ossifiés du tout latéralement et dorsalement. Cet aspect en dentelle n’est ni un artefact de fossilisation, de préservation ou de modélisation, et n’a jamais été retrouvé sur aucun autre vertébré (mais l’échantillonnage à cette résolution fait encore cruellement défaut).Les canalicules nerveux reliés aux neuromastes de la ligne latérale permettent de retracer leur origine à une branche du nerf facial (VII). Les deux oreilles internes ont été reconstruites avec précision et montrent une morphologie primitive.Le réseau vasculaire de l’os dermique a été reconstruit en détails, et permet de mettre en évidence les limites de plaques du toit crânien, invisibles autrement. Ce réseau vasculaire est relié à des veines drainant la bordure de la boîte crânienne ou à une branche de la veine jugulaire. La courbure de ces vaisseaux autour de l’oreille interne pourrait démarquer la limite entre la capsule otique et l’arc hyoïdien qui s’y attachait.D’un point de vue général, la morphologie de la boîte crânienne et de ses structures associées paraît moins primitive (et moins extrême) que celle de Brindabellaspis, mais rappelle au contraire plus les structures observées chez le placoderme arthrodire Kujdanowiaspis, plus dérivé.Ces différences mettent en lumière les premiers stades de l’évolution du crâne des placodermes, donc des gnathostomes.
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| 9. |
- Dupret, Vincent, 1977-, et al.
(författare)
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The cranial anatomy of Romundina stellina Ørvig, 1975 (Vertebrata, Placodermi, Acanthothoraci) revealed by phase contrast synchrotron scanning
- 2010
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Konferensbidrag (populärvet., debatt m.m.)abstract
- The acanthothoracid placoderms are among the most phylogenetically basal and morphologically primitive gnathostomes. However, their endocranial anatomy is not well understood; only one genus, Brindabellaspis, has been described in detail. Here we present a near-complete three-dimensional skull of Romundina stellina, a small Early Devonian acanthothoracid from the Canadian Arctic Archipelago, scanned at the European Synchrotron Radiation Facility, Grenoble, France, at a 7.45 µm resolution using propagation phase contrast. Despite some loss of material along an oblique crack, most of the internal structures are remarkably preserved. Each postethmoid cranial and craniospinal nerve can be followed between the well-preserved endocranial cavity and the walls of the perichondrally ossified neurocranium. The minute nerve canals that supplied the neuromast organs of the sensory line system are preserved and can in the postorbital area be traced directly to a branch of the facial nerve. Both inner ears are present. The vascular mesh of the dermal bones has been reconstructed in detail, rendering visible the dermal plate boundaries of the skull roof, and is shown to connect to larger internal veins that drain to the edge of the braincase or into the jugular vein canal. The curvature of the latter vessels parallels the outer surface of the inner ear and may demarcate the boundary between otic capsule proper and applied hyoid arch material. Overall, the braincase morphology appears less extreme (and less primitive?) than that of Brindabellaspis, in some respects more reminiscent of a primitive arthrodire such as Kujdanowiaspis. These differences may illuminate the earliest stages of placoderm cranial evolution.
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| 10. |
- Dupret, Vincent, et al.
(författare)
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The internal cranial anatomy of Romundina stellina Orvig, 1975 (Vertebrata, Placodermi, Acanthothoraci) and the origin of jawed vertebrates : Anatomical atlas of a primitive gnathostome
- 2017
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- Placoderms are considered as the first jawed vertebrates and constitute a paraphyletic group in the stem-gnathostome grade. The acanthothoracid placoderms are among the phylogenetically most basal and morphologically primitive gnathostomes, but their neurocranial anatomy is poorly understood. Here we present a near-complete three-dimensional skull of Romundina stellina, a small Early Devonian acanthothoracid from the Canadian Arctic Archipelago, scanned with propagation phase contrast microtomography at a 7.46 mu m isotropic voxel size at the European Synchrotron Radiation Facility, Grenoble, France. This is the first model of an early gnathostome skull produced using this technique, and as such represents a major advance in objectivity compared to past descriptions of placoderm neurocrania on the basis of grinding series. Despite some loss of material along an oblique crack, most of the internal structures are remarkably preserved, and most of the missing structures can be reconstructed by symmetry. This virtual approach offers the possibility to connect with certainty all the external foramina to the blood and nerve canals and the central structures, and thus identify accurate homologies without destroying the specimen. The high level of detail enables description of the main arterial, venous and nerve canals of the skull, and other perichondrally ossified endocranial structures such as the palatoquadrate articulations, the endocranial cavity and the inner ear cavities. The braincase morphology appears less extreme than that of Brindabellaspis, and is in some respects more reminiscent of a basal arthrodire such as Kujdanowiaspis.
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| 11. |
- Dupret, Vincent, 1977-, et al.
(författare)
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The origin of the jawed vertebrate face : new insights from a synchrotron scanned skull of the primituve placoderm Romundina
- 2013
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Ingår i: Program and abstracts. - Los Angeles, U.S.A.. ; , s. 118-118
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Jawless cyclostomes and jawed gnathostomes show very different face patterns.Cyclostomes have a single median nasohypophysial duct, an anterior hypophysis and ashort telencephalon, while gnathostomes have a pair of nasal sacs opening externally, amore posterior separate hypophysis opening in the palate and a longer telencephalon.Embryonic processes differ as well. In cyclostomes, infraorbital premandibular crest cellsmigrate forwards either side of the nasohypophysial placode to form the upper lip; ingnathostomes they migrate between the hypophysial and nasal placodes to form thetrabecular-ethmoid region. Supraoptic neural crest remains posterior to thenasohypophysial duct in cyclostomes; it moves forward to create the nasal capsules ingnathostomes. Some fossil forms illustrate a sequenced transition between these twopatterns. The Silurian galeaspid (jawless stem gnathostome) Shuyu has a nasohypophysialduct, a short telencephalon, and an anteriorly oriented hypophysis, but the paired nasalsacs and hypophysis are separated by a rudimentary trabecula. A synchrotron scannedskull of the primitive Early Devonian placoderm (jawed stem gnathostome) Romundinashows a cranial cavity reminiscent of that of Shuyu (anteriorly directed hypophysis, veryshort telencephalon). The trabecular-ethmoid region is long and wide, extending anteriorto the small nasal capsule which is located just in front of the orbits. We interpret thesefeatures as uniquely primitive among gnathostomes. In size and position the trabecularethmoidregion of Romundina resembles the upper lip of cyclostomes and Shuyu,suggesting a cyclostome-like pattern of proliferation coupled with a gnathostome-likemigration path for the premandibular crest. The position of the nasal capsule suggests thatthe supraoptic crest had not migrated forwards. A new phylogenetic analysis suggeststhat the evolutionary sequence for the creation of the extant gnathostome face from acyclostome ancestral pattern involved 1) separation of the nasal and hypophysialplacodes (galeaspids: Shuyu), 2) loss of the nasohypophysial duct (basal placoderms:antiarchs, Brindabellaspis, Romundina), 3) shortening and narrowing of the trabecularethmoidregion, the nasal capsule becoming anterior (derived placoderms such asarthrodires); 4) lengthening of the telencephalon (crown gnathostomes). Galeaspid facialanatomy appears closer to gnathostomes than that of osteostracans, but it is unclearwhether osteostracans are primitive or autapomorphic in this respect.
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| 12. |
- Dupret, Vincent, 1977-, et al.
(författare)
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The Placoderm Romundina and the Origin of the Gnathostome Face
- 2013
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Ingår i: The Making of a Vertebrate. - Kobe, Japan. ; , s. 110-111
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Konferensbidrag (refereegranskat)abstract
- Facial anatomy differs fundamentally between extant jawless and jawed vertebrates (cyclostomes and gnathostomes). Cyclostomes have a median nasohypophysial duct; gnathostomes have separate nasal sacs opening externally, and a palatal hypophysis. Premandibular crest cells migrate forwards either side of the nasohypophysial placode to form the upper lip in cyclostomes, but between the hypophysial and nasal placodes to form the trabecular region in gnathostomes1,2. Supraoptic neural crest remains posterior to the nasohypophysial duct in cyclostomes but moves forward to create the nasal capsules of gnathostomes1,2. In cyclostomes the telencephalon is much shorter than in gnathostomes and the hypophysis is relatively anterior. The galeaspid Shuyu, a 430 million year old jawless vertebrate, partly bridges the gap between these facial architectures3. Shuyu has a nasohypophysial duct, short telencephalon, and anteriorly oriented hypophysis, but the nasal sacs and hypophysis are separated by a rudimentary trabecula. Here we present the placoderm Romundina, a 415 million year old jawed vertebrate that represents a further transitional step. Its cranial cavity is similar to that of Shuyu, with an anteriorly directed hypophysis and very short telencephalon. The trabecular region is exceptionally long and wide whereas the nasal capsule (demarcated by a fissure) is small and located far behind the tip of the snout. The upper jaw articulates with the side of the trabecular region to its anterior end, without contacting the nasal capsule. We interpret these features as uniquely primitive among gnathostomes. The premandibular crest of Romundina formed a trabecular region, but like the upper lip of cyclostomes and Shuyu it was a large structure reaching the tip of the snout. The position of the nasal capsule suggests that the supraoptic crest had not migrated forwards. We suggest that during the creation of the gnathostome face, separation of the nasal and hypophysial placodes was followed by loss of the nasohypophysial duct, with lengthening of the telencephalon and migration of the nasal capsules to the snout tip as the final step.
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| 13. |
- Roy, Jean-Claude, et al.
(författare)
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The ORS Vertebrates of Spitsbergen (Svalbard)
- 2010
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Ingår i: Résumés. ; , s. 223-223
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In the Arctic, Spitsbergen (Svalbard archipelago) comprises a Caledonian metamorphic basement structured around 420 Ma, cut by faults that demarcate a sedimentary, NS graben, filled up by siliclastic detrital series of Old Red Sandstone facies (ca. 418 - ca. 326 Ma), with a lateral cumulative thickness of 6300 to more than 10,800 meters. The latter yields a particularly abundant fauna of early fishes, which are the main guide fossils for stratigraphic purposes (Agnatha, Placodermi and Crossopterygii). These sediments are faulted and folded, and disconformably overlapped by the unfolded, marine Carboniferous - Permian carbonate platform. The Old Red Sandstone of Spitsbergen is a reference for all the contemporaneous series of the ORS Continent. However, since the outcrops were hitherto discontinuous in the Polar zone, the stratigraphic correlations were difficult to establish, and the definition of the lithostratigraphic units are still discussed. This region is one of the least studied as for paleontology and stratigraphy, even if several fossil collections and partial field mappings have been made, notably in 1939 with the Anglo-Norwegian-Swedish palaeontological expedition, and in 1969 with the French CNRS-MNHN expedition, later completed by the Russian and German works (Murasov and Mokin 1976, 1979; Schweitzer, 1999). Since the acceleration of the melting of the glaciers and of the ice-cap, the gradual continental rise by glacioisostasy and the erosion by torrents and the tide cause incisions in the moraines, and new outcrops appear. In the framework of a collaboration with the Norsk Polarinstitutt, our field teams could visit some of them, such as LGGST - Chorowicz 1986 to 1994, Roy 1999, CAST 401 IFRTP - ipev 2002 and 2003, Roy 2008, and SPITZ P3 1005 ipev 2010, and the stratigraphical correlation of the nunataks is in progress. Palaeontology, geology, geophysical and geochimical geochronology show that, in Spitsbergen, the deposition of the ORS began in Late Silurian (?Pridoli) times and continued in the Devonian and Carboniferous until the beginning of the late Mississipian. The new information we now have, thanks to studies led in the framework of the International Geologic Correlation Programme 328 (Blieck and Turner 2000) and IGCP 406 Programme, 'Circum Arctic Lower - Middle Paleozoic Vertebrate Palaeontology and Biostratigraphy', with H. Blom (Uppsala) and V. Talimaa (Vilnius), lead us to consider the sedimentation of the graben and its tectonic behaviour as an essential source of data for understanding the natural history of the Arctic: the consequences of the closure of the Iapetus ocean and the dismantling of the Caledonian chain. The bio- and litho- stratigraphy begins to be accurately known, notably thanks to the vertebrate-based biozones (Agnatha, Placodermi and Crossopterygii); a work that was been initiated by Daniel Goujet (1984) and continued by the research team on vertebrate fossils of Spitsbergen (Blieck, 1982, 1984; Goujet, 1984; Janvier 1985; Blieck et al., 1987; Clément, 2001; Pernegre, 2004). If some of these vertebrates seem endemic to Spitsbergen and to the Arctic, they are closely connected to marine species of global distribution, notably with Australian species.
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| 14. |
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| 15. |
- Zigaite, Zivile, et al.
(författare)
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New observations on the squamation patterns of articulated specimens of Loganellia scotica (Traquair, 1898) (Vertebrata : Thelodonti) from the Lower Silurian of Scotland
- 2012
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Ingår i: Geodiversitas. - : Museum National d'Histoire Naturelle, Paris, France. - 1280-9659 .- 1638-9395. ; 34:2, s. 253-270
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Tidskriftsartikel (refereegranskat)abstract
- Articulated squamations of Loganellia scotica (Traquair, 1898) from the Lower Silurian Lesmahagow inliers of southern Scotland have been studied. They include seven articulated specimens, three of them representing complete thelodont fossils, and four partially preserved postpectoral, precaudal and caudal parrs of the exoskeleton. All the five main types of thelodont scales that is rostral, cephalo-pectoral, postpectoral, precaudal and pinnal sacles, as well as respective squamation patterns have been observed on articulated specimens. The specific orbital, branchial, and bucco-pharyngeal scales, characteristic of L. scotica, have not been found due to the poor or non-preservation of these particular areas within the specimens studied. Tail morphology and squamation pattern of the caudal fin have been studied with particular attention, and the constitution of the caudal fin rays has been analyzed. The rostral squamation pattern is argued to be characteristic to L. scotico.
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| 16. |
- Žigaitė, Živilė, et al.
(författare)
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New vertebrate assemblages from the Andrée Land Group, Spitsbergen, and their biostratigraphic significance
- 2010
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Ingår i: Programme and Abstracts. ; , s. 80-81
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Lower and Middle Devonian successions of Spitsbergen provide excellent examples of vertebrate biostratigraphy applied to sedimentary basin analysis. A number of previous works on the Red Bay Group (Lochkovian, Lower Devonian) made a notable study of the earliest Devonian vertebrate record, and their use in biostratigraphy. Our current study concerns the Lower to Middle Devonian of the Andrée Land Group, which comprises the Wood Bay Formation, spanning from Pragian to Emsian in age, and the Grey Hoek Formation, representing the Eifelian. It consists of thick layers of terrigenous sediments, the stratigraphy is largely based on the lithofacies.Two new thelodont assemblages are considered to represent different depostional phases of the late Lower - early Middle Devonian of the Andrée Land Group. The first, older assemblage comprises turiinid, talivaliid, and furcacaudid thelodonts, and identifies the lower Wood Bay Formation. The second, younger assemblage is prevailed by the talivaliid thelodont Amaltheolepis winsnesi, and is characteristic for the upper Wood Bay Fm., as well as the lower Grey Hoek Fm. The recognition of these two new thelodont assemblages allows us to precise the relative age of the Lower – Middle Devonian strata.
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| 17. |
- Zigaite, Zivile, et al.
(författare)
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Palaeoenvironments revealed by rare-earth element systematics in vertebrate bioapatite from the Lower Devonian of Svalbard
- 2016
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Ingår i: Canadian journal of earth sciences (Print). - : Canadian Science Publishing. - 0008-4077 .- 1480-3313. ; 53:8, s. 788-794
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Tidskriftsartikel (refereegranskat)abstract
- In situ rare-earth element (REE) compositions have been measured in early vertebrate microremains from the Lower Devonian basin of Andree Land (Svalbard), with the aim of obtaining information about their early depositional environment and potential reworking. Vertebrate microremains with different histology were used for the analyses, sourced from two different localities of marginal marine to freshwater sediments from geographically distant parts of the Grey Hoek Formation (Skamdalen and Tavlefjellet members). We selected thelodont and undescribed ? chondrichthyan scales, which allowed us to define potential taxonomic, histological, and taphonomic variables of the REE uptake. Results showed REE concentrations to be relatively uniform within the scales of each taxon, but apparent discrepancies were visible between the studied localities and separate taxa. The compilation of REE abundance patterns as well as REE ratios have revealed that thelodont and ? chondrichthyan originating from the same locality must have had different burial and early diagenetic histories. The shapes of the REE profiles, together with the presence and absence of the Eu and Ce anomalies, equally suggested different depositional and diagenetic environments for these two sympatric taxa resulting from either stratigraphical or long-distance reworking. The REE concentrations appear to have visible differences between separate dental tissues, particularly between enameloid and dentine of thelodonts, emphasizing the importance of in situ measurements in microfossil biomineral geochemistry.
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| 18. |
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| 19. |
- Zigaite, Zivile, et al.
(författare)
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Thelodont scales from the Lower and Middle Devonian Andree Land Group, Spitsbergen
- 2013
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 135:1, s. 57-73
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Tidskriftsartikel (refereegranskat)abstract
- Scales of six thelodont taxa are described from the Devonian of Spitsbergen. Numerous samples from localities widely dispersed on Spitsbergen yield several assemblages considered to represent different depositional phases of the late Lower lower Middle Devonian of the Andrée Land Group, but also support the view that certain lithostratigraphic units of the Andrée Land Group should be regarded as contemporaneous lithofacies subjected to different sedimentary environments, rather than as separate stratigraphic members. The description of Woodfjordia collisa gen. et sp. nov., Talivalia svalbardia sp. nov., Canonia cf. C. grossi, Amaltheolepis montiwatsonia sp. nov., Amaltheolepis winsnesi and Amaltheolepis austfjordia sp. nov. also allows for a comparison with similar faunas from other regions of the Northern Hemisphere and motivates further elaboration of Early-Middle Devonian thelodont biostratigraphy.
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| 20. |
- Zigaite, Zivile, 1979-, et al.
(författare)
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Vertebrate Microfossils as Tools in Stratigraphy: A Study of the LowerDevonian Andrée Land Group Spitsbergen
- 2014
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Ingår i: Springer Geology. - Cham : Springer International Publishing. ; , s. 1167-1171, s. 1167-1171
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Tidskriftsartikel (refereegranskat)abstract
- We have studied vertebrate microremains from the Lower to Middle Devonian of the Andrée Land Group, comprising the Wood Bay and Grey Hoek formations. We have defined two new thelodont assemblages, which represent different depositional phases during the late Early to early Middle Devonian formation of the Andrée Land Group. The definition of these two new thelodont assemblages allows us to precisely establish the relative ages of the Lower–Middle Devonian strata. Rare earth element (REE) abundances were measured in a number of thelodont and chondrichthyan microfossil dental tissue biominerals, using laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS). The evaluation of fossil preservation level was performed using semiquantitative spot-geochemistry analyses on finely polished thelodont scale thin-sections using Energy Dispersive X-ray Spectroscopy (EDS), and Electron Backscattering Diffractometry (EBSD) was applied to detect recrystallization. Stable oxygen isotope measurements (δ18O) of bulk biominerals were conducted in parallel, and showed lower heavy oxygen values in the fossil tissues with stronger visible alteration, such as those from the Grey Hoek Formation. Our results suggest that certain lithostratigraphic units of the Andrée Land Group must be regarded as contemporaneous lithofacies subjected to different sedimentary environments, rather than as separate stratigraphic members.
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