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See detailComparative histology of dwarf titanosaurians from the Late Cretaceous of France
Jentgen, Benjamin ULiege; Stein, Koen ULiege; Díez Díaz, Verónica et al

Conference (2018, December)

The derived sauropod clade Titanosaurs encompasses the largest land animals that ever roamed the Earth as well as dwarfed species that evolved in restricted, insular habitats. Here, we report on the long ... [more ▼]

The derived sauropod clade Titanosaurs encompasses the largest land animals that ever roamed the Earth as well as dwarfed species that evolved in restricted, insular habitats. Here, we report on the long bone histology (humeri and femora) of several mature individuals belonging to a new, small-sized titanosaur from the Upper Cretaceous of Velaux – La Bastide Neuve (Provence, France). The main osteohistological feature of the new titanosaur is the heavy remodelling of the cortex, from the outermost cortex retaining some primary vascular canals with traces of External Fundamental System onsets (F to G bone tissue types) to the complete remodelling of the cortex (H bone tissue type). Histological Ontogenetic Stages (HOS) of the samples range from HOS 12 to 14, meaning these bones belong to mature close to or at final body size. Overall long bone histology of the new taxon is strikingly similar to that Atsinganosaurus velauciensis, another titanosaur from the same site and time period. A mature osteohistology combined with femora and humeri that are markedly reduced in size compared to more basal macronarians indicates an earlier onset of the remodelling process during ontogeny at a rate that surpassed the apposition one. Insular dwarfism is a consistent hypothesis for this combination of features, raising the number of dwarfed titanosaurs lineages in the European archipelago. [less ▲]

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See detailDiversification of axial body plan and its underlying developmental mechanisms in a clade of extinct marine reptiles
Soul, Laura; Benson, Roger B.J; Fischer, Valentin ULiege

Conference (2018, August)

Understanding how developmental processes change on macroevolutionary timescales to generate body plan diversity is fundamental to the study of vertebrate evolution. In this study we highlight that the ... [more ▼]

Understanding how developmental processes change on macroevolutionary timescales to generate body plan diversity is fundamental to the study of vertebrate evolution. In this study we highlight that the application of phylogenetic comparative methods to extinct clades can complement results from living groups, to shed light on the macroevolutionary dynamics of morphology, and its underlying developmental mechanisms, particularly on very long timescales. Sauropterygian marine reptiles (nothosaurs, plesiosaurs, pliosaurs and kin) have long been the focus of qualitative hypotheses about the evolution of body plan, and its relationship with ecological niche occupation. Early taxonomy of the Jurassic-Cretaceous members of this clade classified taxa into two groups corresponding to their gross axial body plan morphologies: ‘plesiosaurs’ characterised by long necks, small skulls and short trunks, and ‘pliosaurs’ characterised by short necks, large skulls and long trunks; these have since been shown not to represent clades. Recently developed phylogenetic comparative methods, applied to trees of fossil taxa, offer an opportunity to quantitatively assess long-standing qualitative hypotheses. Here we use two heterogeneous phylogenetic modelling approaches – AUTEUR and the general FPK model - applied to a comprehensive phylogeny of Sauropterygia. We show that change in relative neck length was primarily enabled by homeotic shifts, with a lesser but important contribution from post-patterning growth, and is best modelled by constant rate Brownian motion. This is in contrast to relative skull size, which is best modelled by a two-peak adaptive landscape. Both of these contradict the traditional hypothesis of long-term divergent trends, beginning in the Middle Triassic. In combination with our other recent work this demonstrates that the apparent Sauropterygian body plan dichotomy resulted from ancestrally high evolutionary plasticity, which was subsequently maintained, and a complex evolutionary history and pattern of ecological diversification. [less ▲]

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See detailCases of pathological bone growth in Isanosaurus and Spinophorosaurus (Sauropoda)
Jentgen, Benjamin ULiege; Stein, Koen ULiege; Fischer, Valentin ULiege

Poster (2018, July)

The histology of the long bone of sauropods appears uniform and conservative along the Sauropoda evolutionary tree. One of the main aspects of their bone histology is to exhibit a Fibrolamellar Complex ... [more ▼]

The histology of the long bone of sauropods appears uniform and conservative along the Sauropoda evolutionary tree. One of the main aspects of their bone histology is to exhibit a Fibrolamellar Complex (FLC) in the cortex of their long bones. However, we report Radial Fibrolamellar bone (RFB) in the outer cortex of the humeri of a young adult Isanosaurus (Histological Ontogenetic Stage – HOS – 8) and an adult Spinophorosaurus (HOS 12). RFB is regarded as a fast-growing bone tissue and has been documented in a few dinosaurian taxa, but never among Sauropoda. Its outermost position within the cortex raises questions, because such a rapidly apposited bone tissue would rather be expected in the inner cortex (corresponding to an early juvenile ontogenetic stage). Our thorough histological analysis of these specimens reveals some highly vascularized RFB yielding densely packed plump osteocyte lacunae that can even obscure the surrounding bone in both transverse and longitudinal sections. This osteocyte pattern is restricted to the RFB. Bone remodelling is more expressed in this cortical layer with more dense secondary osteons deposited in the RFB than more internally or externally. This contrasts with the other dinosaurian taxa affected by RFB which contains no secondary osteon in this bone tissue. The individual of Spinophorosaurus represents the first occurrence of RFB in Sauropoda buried in the outer cortex followed by a recovery of a ‘normal’ FLC after this event meaning this individual survived for some time after its phase of accelerated growth. This sequence of widely distinct modes of bone apposition suggests that these specimens are pathological. [less ▲]

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See detailLightning and the thunder: insular dwarfism inferred from long bone histology of the titanosaurian Atsinganosaurus velauciensis
Jentgen, Benjamin ULiege; Stein, Koen ULiege; Díez Díaz, Verónica et al

Poster (2018, June)

Titanosaurian sauropods include the largest land animals that ever walked on Earth. However, some of them evolved into dwarfed species, linked to their insular habitats. Here, we report on the long bone ... [more ▼]

Titanosaurian sauropods include the largest land animals that ever walked on Earth. However, some of them evolved into dwarfed species, linked to their insular habitats. Here, we report on the long bone histology of several mature individuals of the small-sized titanosaur Atsinganosaurus velauciensis from the Upper Cretaceous of Velaux – La Bastide Neuve (Provence, South-Eastern France). The completely remodelled H bone tissue type in all specimens characterizes mature and fully grown individuals. Together with the extensive bone remodelling, the samples range from HOS (Histological Ontogenetic Stages) 14 and from RS (Remodeling Stages) 13 to 14. Considering the reduced size of the sampled femur and humeri, the remodelling process would have begun early in the ontogeny of this titanosaur compared to non-titanosaurian sauropods, at a rate that surpassed the apposition rate. Thus, size reduction of A. velauciensis has to be taken into account to explain the advanced state of its long bone histology. Insular dwarfism is a consistent hypothesis for this combination of features and has been proposed for a series of other titanosaurs from the European archipelago (e.g. the Romanian Magyarosaurus dacus and the Spanish Lirainosaurus astibiae) that show comparable long bone histology and inferred body size. [less ▲]

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See detailLes bacheliers du bloc 1 Géologie de l'ULiège. Journées de terrain, travaux pratiques: Évolution des environnements et de la tectonique de la région de Boulogne-sur-Mer, Wimereux et Wissant, sous la conduite du Prof. Valentin Fischer et de ses collaborateurs. Séquence video et photos
Marion, Jean-Marc ULiege; Fischer, Valentin ULiege; Denayer, Julien ULiege et al

Learning material (2018)

Field days are essential in learning and understanding geology. From April 16 to 18, 2018, graduates from block 1 Geology of the University of Liège (Belgium) studied the evolution of environments and ... [more ▼]

Field days are essential in learning and understanding geology. From April 16 to 18, 2018, graduates from block 1 Geology of the University of Liège (Belgium) studied the evolution of environments and tectonics in the region of Boulogne-sur-Mer, Wimereux and Wissant (France). [less ▲]

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See detailCARNAGES – Une analyse critique du succès des Canivores (Mammalia)
Solé, Floréal; Le Verger, Kévin; Mennecart, Bastien et al

Conference (2018, April)

Pourquoi sommes-nous aujourd'hui entourés par un seul groupe de mammifères carnassiers (les Carnivora), alors qu'au moins trois autres groupes de mammifères placentaires (Hyaenodonta, Mesonychia ... [more ▼]

Pourquoi sommes-nous aujourd'hui entourés par un seul groupe de mammifères carnassiers (les Carnivora), alors qu'au moins trois autres groupes de mammifères placentaires (Hyaenodonta, Mesonychia, Oxyaenidae) étaient en compétition avec les carnivores il y a 50 millions d'années ? Ces quatre groupes de mammifères partagent une caractéristique importante: la présence de dents spécialisées dédiées à la « découpe » de la viande, les dents carnassières. Traditionnellement, leur présence/absence ainsi que leur position dans la mâchoire ont été considérées comme des caractéristiques cruciales pour discriminer les différents groupes de mammifères carnassiers. Depuis les années 1990, les paléontologues ont étudié en détail le succès des carnivores ainsi que leurs adaptations clés. Il est ainsi apparu que les Carnivora ont surpassé, en Amérique du Nord, les Hyaenodonta, les Mesonychia et les Oxyaenidae durant l'Éocène, en particulier aux alentours de 50 millions d'années, lorsque les carnivores ont augmenté en nombre et se sont diversifiés. Des études portant sur l'écomorphologie des mammifères carnassiers ont révélé que les carnivores ont vraisemblablement réussi grâce à la position antérieure des dents carnassières par rapport aux autres mammifères carnassiers. Il a en effet été suggéré que le succès de l'évolution des carnivores pouvait résulter de la vaste gamme d'adaptations dentaires (c'est-à-dire une grande variété de régimes) conférée par cette position particulière de leurs dents carnassières. Afin de tester cette hypothèse, nous avons analysé la richesse spécifique des mammifères carnassiers européens ainsi que l’évolution de leur masse corporelle durant le Paléogène. Étonnamment, notre enquête suggère que les résultats de cette compétition sont diamétralement opposés en Amérique du Nord et en Europe : les carnivores ne se sont pas « imposés » en Europe dès l'Éocène inférieur. Il ressort, en outre, que la « Grande Coupure de Stehlin » marque, en Europe, le début de la domination des carnivores sur les autres mammifères carnassiers. [less ▲]

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See detailUnexpected diversity of Cretaceous plesiosaurians
Fischer, Valentin ULiege

Speech/Talk (2018)

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See detailIncreased pliosaurid dental disparity across the Jurassic-Cretaceous transition
Zverkov, Nikolay G.; Fischer, Valentin ULiege; Madzia, Daniel et al

in Palaeontology (2018)

Pliosaurid marine reptiles played important roles in marine food chains from the Middle Jurassic to the 'middle' Cretaceous, frequently as apex predators. The evolution of pliosaurids during the later ... [more ▼]

Pliosaurid marine reptiles played important roles in marine food chains from the Middle Jurassic to the 'middle' Cretaceous, frequently as apex predators. The evolution of pliosaurids during the later parts of the Early Cretaceous has recently been illuminated by discoveries from Russia (Hauterivian) and Colombia (Barremian). However, knowledge of pliosaurids representing the Jurassic-Cretaceous transition (late Tithonian-Valanginian), is still largely incomplete, especially during the earliest Cretaceous. As such, the effect on pliosaurids of hypothesized faunal turnover during the Jurassic-Cretaceous boundary interval is poorly understood. We report pliosaurid teeth from the upper Volgian (Tithonian, Upper Jurassic) of the Kheta river basin (Eastern Siberia, Russia), to the Berriasian and Valanginian (Lower Cretaceous) of the Volga region (European Russia). These assemblages yielded a series of distinct tooth morphotypes, including the first reports of conical-toothed pliosaurids from the latest Jurassic-earliest Cretaceous. This challenges the hypothesis that only one lineage of pliosaurids crossed the Jurassic-Cretaceous boundary. It appears that conical-toothed pliosaurids co-existed with their trihedral-toothed relatives for at least 25 million years during the latest Jurassic and earliest Cretaceous. In fact, our quantitative analyses indicate that pliosaurids reached their maximal dental disparity during this interval, showing little evidence of turnover associated with the Jurassic-Cretaceous transition. Instead, disparity decreased later in the Early Cretaceous, with the disappearance of trihedral-toothed forms in the Barremian. [less ▲]

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See detailThe evolutionary history of polycotylid plesiosaurians
Fischer, Valentin ULiege; Benson, Roger B.J.; Druckenmiller, Patrick et al

in Royal Society Open Science (2018), 5(172177), 1-26

Polycotylidae is a clade of plesiosaurians that appeared during the Early Cretaceous and became speciose and abundant early in the Late Cretaceous. However, this radiation is poorly understood. Thililua ... [more ▼]

Polycotylidae is a clade of plesiosaurians that appeared during the Early Cretaceous and became speciose and abundant early in the Late Cretaceous. However, this radiation is poorly understood. Thililua longicollis from the Middle Turonian of Morocco is an enigmatic taxon possessing an atypically long-neck and, as originally reported, a series of unusual cranial features that cause unstable phylogenetic relationships for polycotylids. We reinterpret the holotype specimen of Thililua longicollis and clarify its cranial anatomy. Thililua longicollis possesses an extensive, foramina-bearing jugal, a premaxilla-parietal contact, and carinated teeth. Phylogenetic analyses of a new cladistic dataset based on first hand observation of most polycotylids, recovers Thililua and Mauriciosaurus as successive lineages at the base of the earliest Late Cretaceous polycotyline radiation. A new dataset summarizing the Bauplan of polycotylids reveal that their radiation produced an early burst of disparity during the Cenomanian-Turonian interval, with marked plasticity in relative neck length, but this did not arise as an ecological release following the extinction of ichthyosaurs and pliosaurids. This disparity vanished during and after the Turonian, which is consistent with a model of 'early experimentation/late constraint'. Two polycotylid clades, Occultonectia clade nov. and Polycotylinae, survived up to the Maastrichtian, but with low diversity. [less ▲]

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See detailRhinochelys amaberti (Moret 1935), a protostegid turtle from the Early Cretaceous of France
Scavezzoni, Isaure ULiege; Fischer, Valentin ULiege

in PeerJ (2018), 6(e4594),

Modern marine turtles (chelonioids) are the remnants of an ancient radiation that roots in the Cretaceous. The oldest members of that radiation are first recorded from the Early Cretaceous and a series of ... [more ▼]

Modern marine turtles (chelonioids) are the remnants of an ancient radiation that roots in the Cretaceous. The oldest members of that radiation are first recorded from the Early Cretaceous and a series of species are known from the Albian-Cenomanian interval, many of which have been allocated to the widespread but poorly defined genus Rhinochelys, possibly concealing the diversity and the evolution of early marine turtles. In order to better understand the radiation of chelonioids, we redescribe the holotype and assess the taxonomy of Rhinochelys amaberti Moret 1935 (UJF-ID.11167) from the Late Albian (Stoliczkaia dispar Zone) of the Vallon de la Fauge (Isère, France). We also make preliminary assessments of the phylogenetic relationships of Chelonioidea using two updated datasets that widely sample Cretaceous taxa, especially Rhinochelys. Rhinochelys amaberti is a valid taxon that is supported by eight autapomorphies; an emended diagnosis is proposed. Our phylogenetic analyses suggest that Rhinochelys could be polyphyletic, but constraining it as a monophyletic entity does not produce trees that are significantly less parsimonious. Moreover, support values and stratigraphic congruence indexes are fairly low for the recovered typologies, suggesting that missing data still strongly affect our understanding of the Cretaceous diversification of sea turtles [less ▲]

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See detailLe mystère de la disparition des dinosaures
Fischer, Valentin ULiege

Conference given outside the academic context (2017)

Les dinosaures captent l'imaginaire populaire par leurs tailles et leurs morphologies parfois démesurées. Ils véhiculent ainsi, assez logiquement, une image d'un groupe animal résistant et innovant ... [more ▼]

Les dinosaures captent l'imaginaire populaire par leurs tailles et leurs morphologies parfois démesurées. Ils véhiculent ainsi, assez logiquement, une image d'un groupe animal résistant et innovant, capable de résister aux changements de la Terre. Or, à l'heure actuelle, il ne subsiste des dinosaures qu'un seul groupe de théropodes, les oiseaux. Ceci est résultat d'une extinction dite "de masse" qui s'est déroulée il y a 66 millions d'années, à la fin du Crétacé. Nous analyserons le détail et le contexte de cette disparition afin de comprendre les raisons biologiques, géologiques voire spatiales pouvant amener des groupes diversifiés peuvent être amenés à l'extinction. [less ▲]

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See detailA fresh look at ancient extinctions
Fischer, Valentin ULiege

Speech/Talk (2017)

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See detailMegaloolithid dinosaur eggs: scrambled parataxonomy and nesting strategies
Jentgen, Benjamin ULiege; Fischer, Valentin ULiege; Stein, Koen ULiege

Poster (2017, June 02)

The detailed study of fossil dinosaur eggshells from Upper Cretaceous continental deposits from the Hateg Basin (Romania), the Arc Basin and Argentina and from the Thanetian of the Rians Basin (France ... [more ▼]

The detailed study of fossil dinosaur eggshells from Upper Cretaceous continental deposits from the Hateg Basin (Romania), the Arc Basin and Argentina and from the Thanetian of the Rians Basin (France) was made in order to test the robustness of fossil eggs' parataxonomy and to reveal novel data on dinosaur palaeobiology. µXRF, XRD and cathodoluminescence analyses attest a limited diagenesis on these fossils, which allow interpreting observed traits from a palaeobiological point of view. According to their microstructure, analysed eggs mainly belong to the titanosaur-related Megaloolithidae oofamily. Measured histological variables analysed through PCA - clustering unveil a weak megaloolithid parataxonomy scheme which needs to include whole shell units morphology forming the eggshell in addition to descriptions. XRD analyses point to an almost pure calcite eggshell composition (LMC) as well as a preferential orientation of this calcite along the shell unit growth axis, the latter involving biomechanical properties of the egg. Water vapour conductance (GH2O) estimation of some fossil eggshells together with the corresponding porosity - modelled mass pairs suggest that Hat eg and Arc Basins titanosaurs burrowed their nest in humid conditions. The vegetation-mount hypothesis is rejected whereas a hydrothermal environment is proposed for the Argentinian sample. [less ▲]

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See detailNew data on the Mesozoic radiation of chelonioids
Scavezzoni, Isaure ULiege; Fischer, Valentin ULiege

Poster (2017, June)

"Turtles" (Testudines) form a successful group of reptiles with several terrestrial, marine and fresh-water species. Their peculiar and somewhat constrained morphology (i. e. : carapace incorporating ribs ... [more ▼]

"Turtles" (Testudines) form a successful group of reptiles with several terrestrial, marine and fresh-water species. Their peculiar and somewhat constrained morphology (i. e. : carapace incorporating ribs, curved limbs, anapsid skull exempt of temporal fenestrae) and ecology has often obscured their relationships and, hence, their evolutionary history, notably in marine turtles (chelonioids). Modern chelonioids are divided in two clades (i. e. : shoft-shelled turtles and hard-shelled turtles) supported by distinct morphological and embryological characters. Their origin is traced back up to the Cretaceous, along with a series of extinct forms, many of which being collectively known as Protostegidae. Fossil evidence show that at least five clades of marine turtles were roaming the seas at the end of the Cretaceous. In fact, chelonioids appeared during the first stages of the Early Cretaceous and quickly exploded to reach a high level of disparity at the lowermost part of the late Cretaceous. Therefore, the Mesozoic radiation of chelonioids must have happened during the "middle" Cretaceous (especially the Aptian-Albian interval). However this radiation is poorly understood as the phylogenetic relationships of marine turtles are not resolved yet. Bringing new data may help resolve these issues, and it is the exact reason why the genus Rhinochelys is being investigated. [less ▲]

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See detailUnexpected diversification of pliosaurid marine reptiles after the Jurassic-Cretaceous boundary
Fischer, Valentin ULiege; Benson, Roger; Zverkov, Nikolay et al

Conference (2017, April)

Pliosaurids are iconic marine reptiles that dominated marine ecosystems during the Jurassic and the Cretaceous. These giant predators met their demise during the early Late Cretaceous but the final ... [more ▼]

Pliosaurids are iconic marine reptiles that dominated marine ecosystems during the Jurassic and the Cretaceous. These giant predators met their demise during the early Late Cretaceous but the final chapter of their long evolutionary history remains barely documented. Prompted by the discovery of a peculiar and very well preserved new taxon from Russia, we compute the evolution of pliosaurid disparity from their Early Jurassic radiation to their Late Cretaceous extinction. Despite a patchy Early Cretaceous fossil record, we show pliosaurids reached their maximal disparity during the Hauterivian-Barremian interval, suggesting a strong Early Cretaceous recovery from the apparently low phenotypic disparity of Late Jurassic pliosaurids. By using cladistic and ecomorphological data, we show that pliosaurids have repeatedly evolved slender-snouted polycotylid-like morphologies in each of their temporal radiations (Early Jurassic, Middle Jurassic and Early Cretaceous), demonstrating a more complex evolutionary history than their traditional representation as gigantic apex predators of Mesozoic marine ecosystems suggests. The extinction of pliosaurids during the Turonian (early Late Cretaceous) appears preceded by a late Early Cretaceous contraction of their disparity, the trajectory documented in ichthyosaurs, another successful marine reptile clade that disappeared during the Cenomanian-Turonian interval. [less ▲]

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See detailNew data on the Mesozoic radiation of chelonioids
Scavezzoni, Isaure ULiege; Fischer, Valentin ULiege

Poster (2017, February)

"Turtles" (Testudines) form a successful group of reptiles with several terrestrial, marine and fresh-water species. Their peculiar and somewhat constrained morphology (i. e. : carapace incorporating ribs ... [more ▼]

"Turtles" (Testudines) form a successful group of reptiles with several terrestrial, marine and fresh-water species. Their peculiar and somewhat constrained morphology (i. e. : carapace incorporating ribs, curved limbs, anapsid skull exempt of temporal fenestrae) and ecology has often obscured their relationships and, hence, their evolutionary history, notably in marine turtles (chelonioids). Modern chelonioids are divided in two clades (i. e. : shoft-shelled turtles and hard-shelled turtles) supported by distinct morphological and embryological characters. Their origin is traced back up to the Cretaceous, along with a series of extinct forms, many of which being collectively known as Protostegidae. Fossil evidence show that at least five clades of marine turtles were roaming the seas at the end of the Cretaceous. In fact, chelonioids appeared during the first stages of the Early Cretaceous and quickly exploded to reach a high level of disparity at the lowermost part of the late Cretaceous. Therefore, the Mesozoic radiation of chelonioids must have happened during the "middle" Cretaceous (especially the Aptian-Albian interval). However this radiation is poorly understood as the phylogenetic relationships of marine turtles are not resolved yet. Bringing new data may help resolve these issues, and it is the exact reason why the genus Rhinochelys is being investigated. [less ▲]

Detailed reference viewed: 42 (7 ULiège)
See detailMegaloolithid dinosaur eggs: scrambled parataxonomy and nesting strategies
Jentgen, Benjamin ULiege; Stein, Koen; Fischer, Valentin ULiege

Poster (2017, February)

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See detailPlasticity and convergence in the evolution of short-necked plesiosaurs
Fischer, Valentin ULiege; Benson, Roger B. J.; Zverkov, Nikolai G. et al

in Current Biology (2017), 27

Plesiosaurs were the longest-surviving group of secondarily marine tetrapods, comparable in diversity to today’s cetaceans. During their long evolutionary history, which spanned the Jurassic and the ... [more ▼]

Plesiosaurs were the longest-surviving group of secondarily marine tetrapods, comparable in diversity to today’s cetaceans. During their long evolutionary history, which spanned the Jurassic and the Cretaceous (201 to 66 Ma), plesiosaurs repeatedly evolved long- and short-necked body plans [1,2]. Despite this postcranial plasticity, short-necked plesiosaur clades have traditionally been regarded as being highly constrained to persistent and clearly distinct ecological niches: advanced members of Pliosauridae (ranging from the Middle Jurassic to the early Late Cretaceous) have been characterised as apex predators [2–5], whereas members of the distantly related clade Polycotylidae (middle–Late Cretaceous) were thought to have been fast-swimming piscivores [1,5–7]. We report a new, highly unusual pliosaurid from the Early Cretaceous of Russia that shows close convergence with the cranial structure of polycotylids: Luskhan itilensis gen. et sp. nov. Using novel cladistic and ecomorphological data, we show that pliosaurids iteratively evolved polycotylid-like cranial morphologies from the Early Jurassic until the Early Cretaceous. This underscores the ecological diversity of derived pliosaurids and reveals a more complex evolutionary history than their iconic representation as gigantic apex predators of Mesozoic marine ecosystems suggests. Collectively, these data demonstrate an even higher degree of morphological plasticity and convergence in the evolution of plesiosaurs than previously thought, and suggest the existence of an optimal ecomorphology for short-necked piscivorous plesiosaurs through time and across phylogeny. [less ▲]

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See detailFeeding and ecological diversity of Tournaisian holocephalans: insights from dental microwear
Demoulin, Catherine ULiege; Derycke, Claire; Michel, Christian ULiege et al

Conference (2017)

At the end of the Devonian, several profound extinctions affected a large number of marine groups. However, some of them, such as holocephalan chondrichtyans, showed a great diversification during the ... [more ▼]

At the end of the Devonian, several profound extinctions affected a large number of marine groups. However, some of them, such as holocephalan chondrichtyans, showed a great diversification during the recovery of the ecosystems, during the Tournaisian. Despite the fact that a large taxic diversity has been documented for these holocephalans; their ecological diversity is however poorly known, because the shape of isolated teeth can be a poor predictor of the ecology of these animals. Microwear analysis has the potential to reveal distinct diets and actual use of teeth in these extinct animals during the Tournaisian. We analysed the microwear of Tournaisian holocephalans from the Tournai and Ourthe formations of Belgium. Dental microwears were observed qualitatively on 20 teeth with a scanning electron microscope and mapped and analysed in detail for 7 of them with ArcMap software. While pits are almost totally absent in our sample, our microwear dataset revealed two populations of scratches with distinct length distributions. We suggest that these populations were produced by two different mechanisms. The first population contains mainly long scratches (>0.2 mm, up to 2.0 mm) that are often oriented 40° to 70° compared to the anteroposterior axis of the tooth. We propose that these scratches would have been produced by trituration. The second population comprises almost exclusively of short scratches (<0.2 mm) especially abundant on the mesial face of the teeth and preferentially oriented subparallel to the anteroposterior axis. They would have been produced when the holocephalans dug into sea bottom sediments while searching for food. To identify materials that might have caused the observed microwear, we compared the hardness of the holocephalan orthodentine, making the bulk of the crown of holocephalan teeth, and materials present in their environment. The skeleton of a wide series of marine organisms (crinoids, brachiopods, molluscs) is composed of calcite or aragonite, which appears to be slightly harder than holocephalan orthodentine. These materials may thus scratch holocephalan teeth but are hardly able to produce pits because of the small difference in hardness. Tournaisian holocephalans were thus probably feeding on benthic faunae and they likely dug in the sediment at the search of food. If correct, this might rule out prey items located clearly above the sea floor, such as ammonioids or high-stalked crinoids. However, most of our specimens showed similar microwear features, which prevents us to highlight ecological differences between the taxa we sampled. [less ▲]

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See detailFeeding and ecological diversity of Tournaisian holocephalans: approach through the study of dental microwear
Demoulin, Catherine ULiege; Derycke, Claire; Michel, Christian ULiege et al

Scientific conference (2017)

At the end of the Devonian, several profound extinctions affected a large number of marine groups. However, some of them, such as holocephalan chondrichtyans, showed a great diversification during the ... [more ▼]

At the end of the Devonian, several profound extinctions affected a large number of marine groups. However, some of them, such as holocephalan chondrichtyans, showed a great diversification during the recovery of the ecosystems, during the Tournaisian. Despite the fact that a large taxic diversity has been documented for these holocephalans; their ecological diversity is however poorly known, because the shape of isolated teeth can be a poor predictor of the ecology of these animals. Microwear analysis has the potential to reveal distinct diets and actual use of teeth in these extinct animals during the Tournaisian. We analysed the microwear of Tournaisian holocephalans from the Tournai and Ourthe formations of Belgium. Dental microwears were observed qualitatively on 20 teeth with a scanning electron microscope and mapped and analysed in detail for 7 of them with ArcMap software. While pits are almost totally absent in our sample, our microwear dataset revealed two populations of scratches with distinct length distributions. We suggest that these populations were produced by two different mechanisms. The first population contains mainly long scratches (>0.2 mm, up to 2.0 mm) that are often oriented 40° to 70° compared to the anteroposterior axis of the tooth. We propose that these scratches would have been produced by trituration. The second population comprises almost exclusively of short scratches (<0.2 mm) especially abundant on the mesial face of the teeth and preferentially oriented subparallel to the anteroposterior axis. They would have been produced when the holocephalans dug into sea bottom sediments while searching for food. To identify materials that might have caused the observed microwear, we compared the hardness of the holocephalan orthodentine, making the bulk of the crown of holocephalan teeth, and materials present in their environment. The skeleton of a wide series of marine organisms (crinoids, brachiopods, molluscs) is composed of calcite or aragonite, which appears to be slightly harder than holocephalan orthodentine. These materials may thus scratch holocephalan teeth but are hardly able to produce pits because of the small difference in hardness. Tournaisian holocephalans were thus probably feeding on benthic faunae and they likely dug in the sediment at the search of food. If correct, this might rule out prey items located clearly above the sea floor, such as ammonioids or high-stalked crinoids. However, most of our specimens showed similar microwear features, which prevents us to highlight ecological differences between the taxa we sampled. [less ▲]

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