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| 2. |
- Bremer, Oskar, 1985-, et al.
(författare)
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Exploring the three-dimensional vasculature of dermal hard tissues in thyestiid osteostracans using synchrotron radiation microtomography
- 2023
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Ingår i: Journal of Vertebrate Paleontology. - : Taylor & Francis. - 0272-4634 .- 1937-2809. ; 42:4
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Tidskriftsartikel (refereegranskat)abstract
- Osteostracans are stem-gnathostomes with bony tissues that represent an important link between living jawed and jawless vertebrates, the latter of which lack skeletal hard tissues. In this study, a number of skeletal microremains from a diverse group of osteostracans called thyestiids have been investigated using propagation phase-contrast X-ray synchrotron microtomography. This enabled detailed reconstructions of their three-dimensional vasculature. The dermal skeleton of thyestiids is divided into three layers that vary in proportion between taxa, similar to gnathostomes and other osteostracans. The basal layer is confirmed as an acellular bony tissue composed of fiber bundles that contains narrow, vertical canals and/or large cavities. Bundles bend around smaller canals but form jagged edges around larger cavities, which suggests delayed mineralization. The presumed vascular mesh canals of the deep middle layer are radially arranged in some taxa, but more irregular or even tree-like in others, suggesting a relation to how the elements developed and grew. A number of mesh canals ascend toward the superficial layer where they supply the subepidermal vascular plexus, or create pore fields that open to the surface in some taxa. These ascending mesh canals most likely expanded and formed a network of canals underneath more extensive pore fields. Aestiaspis viitaensis has a simple upper canal system above these fields, while Tremataspis mammillata and Tr. milleri scales have a polygonal network of upper mesh canals above extensive perforated septa. These systems are most likely homologous, but their relation to intra- and inter-areal canals described in other osteostracans remains ambiguous.
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| 3. |
- Bremer, Oskar, 1985-, et al.
(författare)
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The emergence of a complex pore-canal system in the dermal skeleton of Tremataspis (Osteostraci)
- 2021
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Ingår i: Journal of morphology. - : Wiley. - 0362-2525 .- 1097-4687. ; 282:8, s. 1141-1157
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Tidskriftsartikel (refereegranskat)abstract
- Thyestiids are a group of osteostracans (sister-group to jawed vertebrates) ranging in time from the early Silurian to Middle Devonian. Tremataspis is unique among thyestiids in having a continuous mesodentine and enameloid cover on its dermal elements, and an embedded pore-canal system divided into lower and upper parts by a perforated septum. The origin of this upper mesh canal system and its potential homology to similar canal systems of other osteostracans has remained a matter of debate. To investigate this, we use synchrotron radiation microtomography data of four species of Tremataspis and three other thyestiid genera. Procephalaspis oeselensis lacks an upper mesh canal system entirely, but Aestiaspis viitaensis has partially enclosed upper canals formed between slightly modified tubercles that generally only cover separate pore fields. Further modification of tubercles in Dartmuthia gemmifera forms a more extensive, semi-enclosed upper mesh canal system that overlies an extensive perforated septum, similar to that found in Tremataspis. Lower mesh canals in P. oeselensis are radially arranged and buried tubercles indicate a continuous growth and addition of dermal hard tissues. These features are lacking to varying degrees in the other investigated thyestiids, and Tremataspis probably had a determinate growth accompanied by a single mineralization phase of its dermal hard tissues. The previously proposed homology between the semi-enclosed upper canal system in Dartmuthia to the pore-canal system in Tremataspis is supported in this study, but the suggested homologies between these canals and other parts of the thyestiid vasculature to those in non-thyestiid osteostracans remain unclear. This study shows that three-dimensional modeling of high-resolution data can provide histological and structural details that can help clarify homology issues and elucidate the evolution of dermal hard tissues in osteostracans. In extension, this can give insights into how these tissues relate to those found among jawed vertebrates.
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| 4. |
- Jerve, Anna, et al.
(författare)
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Three-dimensional paleohistology of the scale and median fin spine of Lophosteus superbus (Pander 1856)
- 2016
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Ingår i: PeerJ. - : PeerJ. - 2167-8359. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- Lophosteus superbus is one of only a handful of probable stem-group osteichthyans known from the fossil record. First collected and described in the late 19th century from the upper Silurian Saaremaa Cliff locality in Estonia, it is known from a wealth of disarticulated scales, fin spines, and bone fragments. In this study we provide the first description of the morphology and paleohistology of a fin spine and scale from Lophosteus using virtual thin sections and 3D reconstructions that were segmented using phase-contrast synchrotron X-ray microtomography. These data reveal that both structures have fully or partially buried odontodes, which retain fine morphological details in older generations, including sharp nodes and serrated ridgelets. The vascular architecture of the fin spine tip, which is composed of several layers of longitudinally directed bone vascular canals, is much more complex compared to the bulbous horizontal canals within the scale, but they both have distinctive networks of ascending canals within each individual odontode. Other histological characteristics that can be observed from the data are cell spaces and Sharpey's fibers that, when combined with the vascularization, could help to provide insights into the growth of the structure. The 3D data of the scales from Lophosteus superbus is similar to comparable data from other fossil osteichthyans, and the morphology of the reconstructed buried odontodes from this species is identical to scale material of Lophosteus ohesaarensis, casting doubt on the validity of that species. The 3D data presented in this paper is the first for fossil fin spines and so comparable data is not yet available. However, the overall morphology and histology seems to be similar to the structure of placoderm dermal plates. The 3D datasets presented here provide show that microtomography is a powerful tool for investigating the three-dimensional microstructure of fossils, which is difficult to study using traditional histological methods. These results also increase the utility of fin spines and scales suggest that these data are a potentially rich source of morphological data that could be used for studying questions relating to early vertebrate growth and evolution.
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| 6. |
- Qu, Qingming, 1985-
(författare)
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3D Histological Architecture And Ontogeny In Two Early Osteichthyan Scales : the Origin Of Cosmine And A Reconsideration Of The Phylogenetic Application Of Paleohistology Data
- 2013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The histology of early osteichthyan scales have been extensively studied using thin sections and acid-etched ground surfaces, and it is known that these rhombic scales are composed of multiple odontodes (tooth-like denticles) in the crown and bony tissues in the base. However, the 2D nature of the ground sections does not allow us to know the 3D morphology and distribution of the odontodes, which contain the ontogenetic history of the scales. To compensate the traditional study based on ground sections, we used Propagation phase contrast X-ray Synchrotron microtomography (PPC-SRµCT) to examine body scales of two early osteichthyans Andreolepis and Psarolepis, both of which are important taxa to understand the origin of osteichthyan crown group. The reconstructed 3D models of the histological architecture provide novel data of the ontogenetic history of the scales. The crown of Andreolepis scale is constructed two distinct type of growth patterns: a linear polarized pattern in the initial stage and a gap-filling pattern in the later stage. In the crown of Psarolepis scale the second odontode is most peculiar, with a the enamel covering penetrated by several pores, while the primordia odontode is almost morphologically identical with that of Andreolepis scale. A developmental shift following the formation of the primordia odontode may be the key step of the evolution of cosmoid scales, and Psarolepis scale is explained as a transitional form between the Andreolepis-type scale and the typical cosmoid scales in more derived sarcopterygians such as Osteolepis. Comparison of the entire canal system among Andreolepis, Psarolepis and more derived sarcopterygians show that the pore-canal system and cosmine-like construction are already present in Psarolepis scales, although the construction is different from typical cosmine as in Osteolepis. A stepwise scenario of the origin of pore-canal system and cosmine is proposed according to the new data. New characters are composed based on the in situ 3D data and could be incorporated into phylogenetic analysis in the future when more taxa have been studied using similar imaging method and 3D histology obtained. The 3D histology study of skeletal fossils using PPC-SRµCT could provide more informative and reliable phylogenetic data.
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| 7. |
- Qu, Qingming, 1985-, et al.
(författare)
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New genomic and fossil data illuminate the origin of enamel
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 526:7571, s. 108-120
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Tidskriftsartikel (refereegranskat)abstract
- Enamel, the hardest vertebrate tissue, covers the teeth of almost all sarcopterygians (lobe-finned bony fishes and tetrapods) as well as the scales and dermal bones of many fossil lobe-fins(1-5). Enamel deposition requires an organic matrix containing the unique enamel matrix proteins (EMPs) amelogenin (AMEL), enamelin (ENAM) and ameloblastin (AMBN)(6). Chondrichthyans (cartilaginous fishes) lack both enamel and EMP genes(7,8). Many fossil and a few living non-teleost actinopterygians (ray-finned bony fishes) such as the gar, Lepisosteus, have scales and dermal bones covered with a proposed enamel homologue called ganoine(1,9). However, no gene or transcript data for EMPs have been described from actinopterygians(10,11). Here we show that Psarolepis romeri, a bony fish from the the Early Devonian period, combines enamel-covered dermal odontodes on scales and skull bones with teeth of naked dentine, and that Lepisosteus oculatus (the spotted gar) has enam andambn genes that are expressed in the skin, probably associated with ganoine formation. The genetic evidence strengthens the hypothesis that ganoine is homologous with enamel. The fossil evidence, further supported by the Silurian bony fish Andreolepis, which has enamel-covered scales but teeth and odontodes on its dermal bones made of naked dentine(12-16), indicates that this tissue originated on the dermal skeleton, probably on the scales. It subsequently underwent heterotopic expansion across two highly conserved patterning boundaries (scales/head-shoulder and dermal/oral) within the odontode skeleton.
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| 8. |
- Qu, Qingming, et al.
(författare)
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Scales and Dermal Skeletal Histology of an Early Bony Fish Psarolepis romeri and Their Bearing on the Evolution of Rhombic Scales and Hard Tissues
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:4, s. e61485-
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Tidskriftsartikel (refereegranskat)abstract
- Recent discoveries of early bony fishes from the Silurian and earliest Devonian of South China (e. g. Psarolepis, Achoania, Meemannia, Styloichthys and Guiyu) have been crucial in understanding the origin and early diversification of the osteichthyans (bony fishes and tetrapods). All these early fishes, except Guiyu, have their dermal skeletal surface punctured by relatively large pore openings. However, among these early fishes little is known about scale morphology and dermal skeletal histology. Here we report new data about the scales and dermal skeletal histology of Psarolepis romeri, a taxon with important implications for studying the phylogeny of early gnathostomes and early osteichthyans. Seven subtypes of rhombic scales with similar histological composition and surface sculpture are referred to Psarolepis romeri. They are generally thick and show a faint antero-dorsal process and a broad peg-and-socket structure. In contrast to previously reported rhombic scales of osteichthyans, these scales bear a neck between crown and base as in acanthodian scales. Histologically, the crown is composed of several generations of odontodes and an irregular canal system connecting cylindrical pore cavities. Younger odontodes are deposited on older ones both superpositionally and areally. The bony tissues forming the keel of the scale are shown to be lamellar bone with plywood-like structure, whereas the other parts of the base are composed of pseudo-lamellar bone with parallel collagen fibers. The unique tissue combination in the keel (i.e., extrinsic Sharpey's fibers orthogonal to the intrinsic orthogonal sets of collagen fibers) has rarely been reported in the keel of other rhombic scales. The new data provide insights into the early evolution of rhombic (ganoid and cosmoid) scales in osteichthyans, and add to our knowledge of hard tissues of early vertebrates.
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| 9. |
- Qu, Qingming, et al.
(författare)
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Scales and Tooth Whorls of Ancient Fishes Challenge Distinction between External and Oral 'Teeth'
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:8, s. e71890-
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Tidskriftsartikel (refereegranskat)abstract
- The debate about the origin of the vertebrate dentition has been given fresh fuel by new fossil discoveries and developmental studies of extant animals. Odontodes (teeth or tooth-like structures) can be found in two distinct regions, the 'internal' oropharyngeal cavity and the 'external' skin. A recent hypothesis argues that regularly patterned odontodes is a specific oropharyngeal feature, whereas odontodes in the external skeleton lack this organization. However, this argument relies on the skeletal system of modern chondrichthyans (sharks and their relatives), which differ from other gnathostome (jawed vertebrate) groups in not having dermal bones associated with the odontodes. Their external skeleton is also composed of monoodontode 'placoid scales', whereas the scales of most early fossil gnathostomes are polyodontode, i.e. constructed from several odontodes on a shared bony base. Propagation phase contrast X-ray Synchrotron microtomography (PPC-SRmCT) is used to study the polyodontode scales of the early bony fish Andreolepis hedei. The odontodes constructing a single scale are reconstructed in 3D, and a linear and regular growth mechanism similar to that in a gnathostome dentition is confirmed, together with a second, gap-filling growth mechanism. Acanthodian tooth whorls are described, which show that ossification of the whorl base preceded and probably patterned the development of the dental lamina, in contrast to the condition in sharks where the dental lamina develops early and patterns the dentition. The new findings reveal, for the first time, how polyodontode scales grow in 3D in an extinct bony fish. They show that dentition-like odontode patterning occurs on scales and that the primary patterning unit of a tooth whorl may be the bony base rather than the odontodes it carries. These results contradict the hypothesis that oropharyngeal and external odontode skeletons are fundamentally separate and suggest that the importance of dermal bone interactions to odontode patterning has been underestimated.
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| 10. |
- Qu, Qingming, et al.
(författare)
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The origin of novel features by changes in developmental mechanisms : ontogeny and three-dimensional microanatomy of polyodontode scales of two early osteichthyans
- 2017
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Ingår i: Biological Reviews. - : Wiley. - 1464-7931 .- 1469-185X. ; 92:2, s. 1189-1212
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Tidskriftsartikel (refereegranskat)abstract
- Recent advances in synchrotron imaging allow us to study the three-dimensional (3D) histology of vertebrate fossils, including microfossils (e.g. teeth and scales) of early jawed vertebrates. These microfossils can often be scanned at submicron resolution (<1 µm) because of their small size. The resulting voxel (3D pixel) stacks can be processed into virtual thin sections revealing almost every internal detail of the samples, comparable to traditional thin sections. In addition, 3D models of the internal microanatomical structures, such as embedded odontodes and vasculature, can be assembled and examined in situ. Scales of two early osteichthyans, Psarolepis romeri from the Early Devonian of China and Andreolepis hedei from the Late Silurian of Sweden, were scanned using propagation phase-contrast synchrotron X-ray microtomography (PPC-SRµCT), and 3D models of internal canal systems and buried odontodes were created from the scans. Based on these new data, we review the evolutionary origin of cosmine and its associated pore-canal system, which has been long recognized as a synapomorphy of sarcopterygians. The first odontode that appeared during growth shows almost identical morphology in the two scales, but the second odontode of the Psarolepis scale shows a distinctive morphology with several pores on the surface. It is suggested that a shift from ridge-like odontode to pore-bearing odontode was the key step in the origin of cosmine, which was then elaborated further in more-derived sarcopterygians. We perform a detailed comparison between the two scales and propose a primary homology framework to generate microanatomical characters, which can be used in the phylogenetic analysis of early osteichthyans when more 3D data become available. Our results highlight the importance of 3D data for the study of histology and ontogeny of the dermal skeleton of early jawed vertebrates, especially scales of the polyodontode type. The traditional microvertebrate collection is not only useful for biostratigraphic studies, but also preserves invaluable biological information about the growth of vertebrate hard tissues. Today, we are only beginning to understand the biological meaning of the new 3D data. The increasing availability of such data will enable, and indeed require, a complete revision of traditional palaeohistological studies on early vertebrates.
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