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- El Albani, Abderrazak, et al.
(author)
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Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago
- 2010
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 466:7302, s. 100-104
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Journal article (peer-reviewed)abstract
- The evidence for macroscopic life during the Palaeoproterozoic era (2.5-1.6 Gyr ago) is controversial(1-5). Except for the nearly 2-Gyr-old coil-shaped fossil Grypania spiralis(6,7), which may have been eukaryotic, evidence for morphological and taxonomic bio-diversification of macroorganisms only occurs towards the beginning of the Mesoproterozoic era (1.6-1.0 Gyr)(8). Here we report the discovery of centimetre-sized structures from the 2.1-Gyr-old black shales of the Palaeoproterozoic Francevillian B Formation in Gabon, which we interpret as highly organized and spatially discrete populations of colonial organisms. The structures are up to 12 cm in size and have characteristic shapes, with a simple but distinct ground pattern of flexible sheets and, usually, a permeating radial fabric. Geochemical analyses suggest that the sediments were deposited under an oxygenated water column. Carbon and sulphur isotopic data indicate that the structures were distinct biogenic objects, fossilized by pyritization early in the formation of the rock. The growth patterns deduced from the fossil morphologies suggest that the organisms showed cell-to-cell signalling and coordinated responses, as is commonly associated with multicellular organization(9). The Gabon fossils, occurring after the 2.45-2.32-Gyr increase in atmospheric oxygen concentration(10), may be seen as ancient representatives of multicellular life, which expanded so rapidly 1.5 Gyr later, in the Cambrian explosion.
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| 4. |
- Botella, Hector, et al.
(author)
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Jaws and teeth of the earliest bony fishes
- 2007
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 448:7153, s. 583-586
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Journal article (peer-reviewed)abstract
- Extant jawed vertebrates, or gnathostomes, fall into two major monophyletic groups, namely chondrichthyans (cartilaginous fishes) and osteichthyans (bony fishes and tetrapods). Fossil representatives of the osteichthyan crown group are known from the latest Silurian period, 418 million years (Myr) ago, to the present. By contrast, stem chondrichthyans and stem osteichthyans are still largely unknown. Two extinct Palaeozoic groups, the acanthodians and placoderms, may fall into these stem groups or the common stem group of gnathostomes, but their relationships and monophyletic status are both debated. Here we report unambiguous evidence for osteichthyan characters in jaw bones referred to the late Silurian (423–416-Myr-old) fishes Andreolepis hedei and Lophosteus superbus, long known from isolated bone fragments, scales and teeth, and whose affinities to, or within, osteichthyans have been debated1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. The bones are a characteristic osteichthyan maxillary and dentary, but the organization of the tooth-like denticles they bear differs from the large, conical teeth of crown-group osteichthyans, indicating that they can be assigned to the stem group. Andreolepis and Lophosteus are thus not only the oldest but also the most phylogenetically basal securely identified osteichthyans known so far.
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| 5. |
- Chen, Donglei, 1985-, et al.
(author)
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Scale morphology and squamation of the Late Silurian osteichthyan Andreolepis from Gotland, Sweden
- 2012
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In: Historical Biology. - 0891-2963 .- 1029-2381. ; 24:4, s. 411-423
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Journal article (peer-reviewed)abstract
- The origin of osteichthyans (bony fishes and tetrapods) dates back to the Late Silurian, but the early evolution of the group is poorly understood. Andreolepis is one of the oldest known osteichthyans, but exclusively documented by detached and fragmentary dermal microremains. A large data-set of Andreolepis scales from the Silurian of Gotland has been used to explore the scale morphology on different parts of the body. Landmark-based geometric morphometrics together with comparative anatomy and functional morphology has allowed 10 morphotypes to be identified and incorporated into a squamation model, in which scales are allocated to anterior-mid lateral flank scales, posterior lateral flank scales, caudal peduncle scales, pectoral peduncle scales, dorsal flank scales, dorsal fulcral scales, caudal fulcral scales, ventral flank scales, medioventral scales and cranial scales. The scale morphology and squamation pattern ofAndreolepis may be primitive for the Osteichthyes and thus informative about the acquisition of the osteichthyan body plan.
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| 6. |
- Dupret, Vincent, 1977-, et al.
(author)
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The skull of Hagiangella goujeti Janvier, 2005, a high-crested acanthothoracid (Vertebrata, Placodermi) from the Lower Devonian of northern Vietnam
- 2011
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In: Journal of Vertebrate Paleontology. - : Informa UK Limited. - 0272-4634 .- 1937-2809. ; 31:3, s. 531-538
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Journal article (peer-reviewed)abstract
- The acanthothoracid Hagiangella goujeti Janvier, 2005, has been described exclusively on the basis of isolatedthoracic plates from the Lochkovian (Lower Devonian) Khao Loc Formation of Tung Vai, Ha Giang Province, northernVietnam. It is characterized by a very high, triangular median crest on the median dorsal plate, and has been referred to theAcanthothoraci on the basis of the morphology of its fused anterolateral, spinal and anterior ventrolateral plates, and thecharacteristic stellate ornamentation of the group. Isolated plates of H. goujeti are relatively abundant at Tung Vai and noother placoderm taxon from this locality seems to share the same type of ornamentation. However, the skull of this speciesremained elusive. Here we report two well-preserved skull roofs from Tung Vai, which we refer to H. goujeti. They display thesame stellate ornamentation and small size as the previously described plates of the thoracic armor of this species. This newmaterial shows that the head of H. goujeti is surprisingly short (i.e., possibly lacking dermal rostral and pineal elements), incontrast to the elongate and narrow skull of all other acanthothoracids. The combination of unique characters (e.g., presenceof two pairs of posterior pit lines, two pairs of central and paranuchal plates, etc.) suggests a possible sister group relationshipto the placoderm assemblage Petalichthyida + Ptyctodontida + Arthrodira.
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- Jerve, Anna
(author)
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Development and three-dimensional histology of vertebrate dermal fin spines
- 2016
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Doctoral thesis (other academic/artistic)abstract
- Jawed vertebrates (gnathostomes) consist of two clades with living representatives, the chondricthyans (cartilaginous fish including sharks, rays, and chimaeras) and the osteichthyans (bony fish and tetrapods), and two fossil groups, the "placoderms" and "acanthodians". These extinct forms were thought to be monophyletic, but are now considered to be paraphyletic partly due to the discovery of early chondrichthyans and osteichthyans with characters that had been previously used to define them. Among these are fin spines, large dermal structures that, when present, sit anterior to both median and/or paired fins in many extant and fossil jawed vertebrates. Making comparisons among early gnathostomes is difficult since the early chondrichthyans and "acanthodians", which have less mineralized skeleton, do not have large dermal bones on their skulls. As a result, fossil fin spines are potential sources for phylogenetic characters that could help in the study of the gnathostome evolutionary history. This thesis examines the development and internal structure of fin spines in jawed vertebrates using two-dimensional (2D) thin sections and three-dimensional (3D) synchrotron datasets. The development of the dorsal fin spine of the holocephalan, Callorhinchus milii, was described from embryos and compared to that of the neoselachian, Squalus acanthias, whose spine has been the model for studying fossil shark spines. It was found that the development of the C. milii fin presents differences from S. acanthias that suggest it might be a better candidate for studying "acanthodian" fin spines. The 3D histology of fossil fin spines was studied in Romundina stellina, a "placoderm"; Lophosteus superbus, a probable stem-osteichthyan; and several "acanthodians". The 3D vascularization reconstructed from synchrotron radiation microtomographic data reveal that "acanthodian" and Lophosteus spines grew similarly to what is observed in chondrichthyans, which differs slightly from the growth of the Romundina spine. Chondrichthyans and "acanthodians" also share similarities in their internal organization. Overall, Lophosteus and Romundina spines are more similar in terms of morphology and histology compared to chondrichthyans and "acanthodians". These results support the current hypothesis of gnathostome phylogeny, which places "acanthodians" on the chondrichthyan stem. They also emphasize the need for further study of vertebrate fin spines using 3D approaches.
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| 9. |
- Muscarella, Robert, et al.
(author)
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The global abundance of tree palms
- 2020
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In: Global Ecology and Biogeography. - : Wiley. - 1466-822X .- 1466-8238. ; 29:9, s. 1495-1514
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Journal article (peer-reviewed)abstract
- AimPalms are an iconic, diverse and often abundant component of tropical ecosystems that provide many ecosystem services. Being monocots, tree palms are evolutionarily, morphologically and physiologically distinct from other trees, and these differences have important consequences for ecosystem services (e.g., carbon sequestration and storage) and in terms of responses to climate change. We quantified global patterns of tree palm relative abundance to help improve understanding of tropical forests and reduce uncertainty about these ecosystems under climate change.LocationTropical and subtropical moist forests.Time periodCurrent.Major taxa studiedPalms (Arecaceae).MethodsWe assembled a pantropical dataset of 2,548 forest plots (covering 1,191 ha) and quantified tree palm (i.e., ≥10 cm diameter at breast height) abundance relative to co‐occurring non‐palm trees. We compared the relative abundance of tree palms across biogeographical realms and tested for associations with palaeoclimate stability, current climate, edaphic conditions and metrics of forest structure.ResultsOn average, the relative abundance of tree palms was more than five times larger between Neotropical locations and other biogeographical realms. Tree palms were absent in most locations outside the Neotropics but present in >80% of Neotropical locations. The relative abundance of tree palms was more strongly associated with local conditions (e.g., higher mean annual precipitation, lower soil fertility, shallower water table and lower plot mean wood density) than metrics of long‐term climate stability. Life‐form diversity also influenced the patterns; palm assemblages outside the Neotropics comprise many non‐tree (e.g., climbing) palms. Finally, we show that tree palms can influence estimates of above‐ground biomass, but the magnitude and direction of the effect require additional work.ConclusionsTree palms are not only quintessentially tropical, but they are also overwhelmingly Neotropical. Future work to understand the contributions of tree palms to biomass estimates and carbon cycling will be particularly crucial in Neotropical forests.
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| 10. |
- Roy, Jean-Claude, et al.
(author)
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The ORS Vertebrates of Spitsbergen (Svalbard)
- 2010
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In: Résumés. ; , s. 223-223
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Conference paper (other academic/artistic)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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