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

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 ULg; 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 ULg; Fischer, Valentin ULg

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 ▲]

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

Poster (2017, February)

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See detailPlasticity and convergence in the evolution of short-necked plesiosaurs
Fischer, Valentin ULg; 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 detailChangements globaux et diversité des grands prédateurs marins crétaces
Fischer, Valentin ULg

Conference (2016, December)

La diversité des grands prédateurs marins est souvent vue comme un indicateur de la santé des écosystèmes océaniques (Fröbisch et al.,  2013; Scheyer et al.,  2014; Kelley & Pyenson,  2015). Cependant ... [more ▼]

La diversité des grands prédateurs marins est souvent vue comme un indicateur de la santé des écosystèmes océaniques (Fröbisch et al.,  2013; Scheyer et al.,  2014; Kelley & Pyenson,  2015). Cependant, les moteurs, les causes des renouvellements fauniques sont souvent méconnus pour les animaux occupant les niveaux supérieurs des chaînes trophiques. Il est donc nécessaire d’identifier et de démêler les mécanismes qui dictent les fluctuations de la biodiversité fossile – y compris les multiples biais affectant ces données (ex. Benson et al.,  2010). Le Crétacé offre une occasion fantastique d’étudier cette relation, étant caractérisé par un climat globalement chaud mais variable et un assemblage diversifié de reptiles, ostéichtyens et néosélaciens qui régissaient les chaînes trophiques marines (Bardet et al.,  2014; Guinot & Cavin,  2015) et qui ont subi des perturbations majeures durant le Crétacé. L’approche choisie ici est résolument macroévolutive et exploratoire. Je combine révisions taxonomiques et analyses phylogénétiques avec des méthodes de reconstruction de la diversité (richesse taxonomique, disparité, diversité écologique) et la vitesse d’évolution dans le but de détecter et de quantifier les renouvellements majeurs des assemblages de reptiles pélagiques crétacés. Ensuite, ces variables sont confrontées aux données climatiques et une nouvelle approche pour rendre compte de la dynamique de ces fluctuations est proposée ici (voir également Fischer et al.,  2016). L’histoire des ichthyosaures et les pliosaures, les prédateurs dominants du Crétacé inférieur disparaissant « prématurément » (durant l’intervalle Cénomanien-Turonien), a été analysée au moyen de ces techniques quantitatives et montrent, contre toute attente, des trajectoires fort similaires avec un pic de diversité-disparité dans le Crétacé inférieur (de part et d’autre de l’Hauterivien) précédent des constrictions importantes de biodiversité vers l’Aptien et au Cénomanien. Les analyses indiquent que les taux d’extinctions chez les ichthyosaures se corrèlent avec l’importance des fluctuations climatiques, offrant une nouvelle perspective pour expliquer leur extinction abrupte durant le Cénomanien. [less ▲]

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See detailExtinction of fish-shaped marine reptiles associated with reduced evolutionary rates and global environmental volatility
Fischer, Valentin ULg; Bardet, Nathalie; Benson, Roger et al

in Nature Communications (2016), 7(10825), 1-11

Despite their profound adaptations to the aquatic realm and their apparent success throughout the Triassic and the Jurassic, ichthyosaurs became extinct roughly 30 million years before the end-Cretaceous ... [more ▼]

Despite their profound adaptations to the aquatic realm and their apparent success throughout the Triassic and the Jurassic, ichthyosaurs became extinct roughly 30 million years before the end-Cretaceous mass extinction. Current hypotheses for this early demise involve relatively minor biotic events, but are at odds with recent understanding of the ichthyosaur fossil record. Here, we show that ichthyosaurs maintained high but diminishing richness and disparity throughout the Early Cretaceous. The last ichthyosaurs are characterized by reduced rates of origination and phenotypic evolution and their elevated extinction rates correlate with increased environmental volatility. In addition, we find that ichthyosaurs suffered from a profound Early Cenomanian extinction that reduced their ecological diversity, likely contributing to their final extinction at the end of the Cenomanian. Our results support a growing body of evidence revealing that global environmental change resulted in a major, temporally staggered turnover event that profoundly reorganized marine ecosytems during the Cenomanian. [less ▲]

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See detailPeculiar macropredatory convergences in Cretaceous marine reptiles
Fischer, Valentin ULg; Benson, Roger; Arkhangelsky, Maxim et al

Conference (2016, January)

Colonization of ecological niches in the marine realm forced evolution of profound evolutionary convergences between several clades of tetrapods, with textbook examples regarding isodonty and body shape ... [more ▼]

Colonization of ecological niches in the marine realm forced evolution of profound evolutionary convergences between several clades of tetrapods, with textbook examples regarding isodonty and body shape. Craniodental details have, however, received less attention. As a result, both the depth of diet-related convergences and niche partitioning mechanisms among contemporaneous clades are poorly understood, particularly during the Early Cretaceous. Here, we analyse the craniodental morphology of new ophthalmosaurid ichthyosaurs and pliosaurid plesiosaurs that exhibit unique macropredatory adaptations. A new brachauchenine pliosaur from the Hauterivian of Russia is the first plesiosaur exhibiting complex serrations of its carinae. This taxon appears convergent with some metriorhynchid crocodyliforms and occurs just after an important diversity drop in these taxa. Contrary to common belief, cluster analyses of diet-related craniodental measurements indicate several ichthyosaur clades colonized a macropredatory niche during the Early Cretaceous, with one extreme example in the latest Aptian of France. Inference of ecological niches or ecological parameters in updated phylogenetic datasets for ichthyosaurs and pliosaurs suggest their ecological diversity was high in the Early Cretaceous and low to very low in the Late Cretaceous, where both clades disappeared prematurely. [less ▲]

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See detailTaxonomy of Platypterygius campylodon and the diversity of the last ichthyosaurs
Fischer, Valentin ULg

in PeerJ (2016), 4(e2604), 1--21

A complex and confusing taxonomy has concealed the diversity dynamics of Cretaceous ichthyosaurs (Reptilia) for decades. The near totality of Albian-Cenomanian remains from Eurasia has been assigned, by ... [more ▼]

A complex and confusing taxonomy has concealed the diversity dynamics of Cretaceous ichthyosaurs (Reptilia) for decades. The near totality of Albian-Cenomanian remains from Eurasia has been assigned, by default, to the loosely defined entity Platypterygius campylodon, whose holotype was supposed to be lost. By thoroughly examining the Cenomanian ichthyosaur collections from the UK, I redescribe the syntypic series of Platypterygius campylodon. This material, along with a handful of other coeval remains, is diagnostic and seemingly differs from the vast majority of Cretaceous remains previously assigned to this taxon. A lectotype for Platypterygius campylodon is designated and I reassign this species to Pervushovisaurus campylodon nov. comb. The feeding ecology of this species is assessed and conforms to the scenario of an early Cenomanian diversity drop prior to the latest Cenomanian final extinction. [less ▲]

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See detailEdouard Poty: a bio- and bibliography
Denayer, Julien ULg; Aretz, Markus ULg; Barchy, Laurent et al

in Geologica Belgica (2016), 19(1-2), 3-6

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See detailLarge predatory marine reptiles from the Albian–Cenomanian of Annopol, Poland
Bardet, Nathalie; Fischer, Valentin ULg; Machalski, Marcin

in Geological Magazine (2016)

During the Early–Late Cretaceous transition, marine ecosystems in Eurasia hosted a diverse set of large predatory reptiles that occupied various niches. However, most of our current knowledge of these ... [more ▼]

During the Early–Late Cretaceous transition, marine ecosystems in Eurasia hosted a diverse set of large predatory reptiles that occupied various niches. However, most of our current knowledge of these animals is restricted to a small number of bonebed-like deposits. Little is known of the geographical and temporal extent of such associations. The middle Albian – middle Cenomanian phosphorite-bearing succession exposed at Annopol, Poland produces numerous ichthyosaurian and plesiosaurian fossils. These are mostly isolated skeletal elements (e.g. teeth, vertebrae), but disarticulated partial skeletons and an articulated, sub vertically embedded ichthyosaur skull are also available. The following taxa are identified: ‘Platypterygius’ sp., cf. Ophthalmosaurinae, Ichthyosauria indet., Polyptychodon interruptus, Pliosauridae indet., Elasmosauridae<indet. and Plesiosauria indet. The large-sized ichthyosaur ‘Platypterygius’ and the pliosaurid Polyptychodon interruptus predominate within the upper Albian – middle Cenomanian deposits. The Annopol record, combined with data from England, France and western Russia, suggests that ‘Platypterygius’ and Polyptychodon interruptus formed a long-term, stable ecological sympatry in marine ecosystems of the European archipelago, at least during the Albian – middle Cenomanian. In addition, the marine reptile assemblage from Annopol is distinct from other Eurasian ecosystems in containing also elasmosaurids in its Albian portion. [less ▲]

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See detailPeculiar macrophagous adaptations in a new Cretaceous pliosaurid
Fischer, Valentin ULg; Arkhangelsky, Maxim; Stenshin, Ilya et al

in Royal Society Open Science (2015), 2(150552.), 112

During the Middle and Late Jurassic, pliosaurid plesiosaurs evolved gigantic body size and a series of craniodental adaptations that have been linked to the occupation of an apex predator niche ... [more ▼]

During the Middle and Late Jurassic, pliosaurid plesiosaurs evolved gigantic body size and a series of craniodental adaptations that have been linked to the occupation of an apex predator niche. Cretaceous pliosaurids (i.e. Brachaucheninae) depart from this morphology, being slightly smaller and lacking the macrophagous adaptations seen in earlier forms. However, the fossil record of Early Cretaceous pliosaurids is poor, concealing the evolution and ecological diversity of the group. Here, we report a new pliosaurid from the Late Hauterivian (Early Cretaceous) of Russia. Phylogenetic analyses using reduced consensus methods recover it as the basalmost brachauchenine. This pliosaurid is smaller than other derived pliosaurids, has tooth alveoli clustered in pairs and possesses trihedral teeth with complex serrated carinae. Maximum-likelihood ancestral state reconstruction suggests early brachauchenines retained trihedral teeth from their ancestors, butmodified this feature in a uniqueway, convergent with macrophagous archosaurs or sphenacodontoids. Our findings indicate that Early Cretaceous marine reptile teeth with serrated carinae cannot be unequivocally assigned to metriorhynchoid crocodylomorphs. Furthermore, they extend the known diversity of dental adaptations seen in Sauropterygia, the longest lived clade of marine tetrapods. [less ▲]

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See detailA mysterious giant ichthyosaur from the lowermost Jurassic of Wales
Martin, Jeremy E; Vincent, Peggy; Suan, Guillaume et al

in Acta Palaeontologica Polonica (2015), 60(4), 837-842

Ichthyosaurs rapidly diversified and colonised a wide range of ecological niches during the Early and Middle Triassic period, but experienced a major decline in diversity near the end of the Triassic ... [more ▼]

Ichthyosaurs rapidly diversified and colonised a wide range of ecological niches during the Early and Middle Triassic period, but experienced a major decline in diversity near the end of the Triassic. Timing and causes of this demise and the subsequent rapid radiation of the diverse, but less disparate, parvipelvian ichthyosaurs are still unknown, notably because of inadequate sampling in strata of latest Triassic age. Here, we describe an exceptionally large radius from Lower Jurassic deposits at Penarth near Cardiff, South Wales (UK) the morphology of which places it within the giant Triassic shastasaurids. A tentative total body size estimate, based on a regression analysis of various complete ichthyosaur skeletons, yields a value of 12-15 m. The specimen is substantially younger than any previously reported last known occurrences of shastasaurids and implies a Lazarus range in the lowermost Jurassic for this ichthyosaur morphotype. [less ▲]

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See detailEvolution et extinctions des ichthyosaures
Fischer, Valentin ULg

in L'écho des falaises (2015), 19

lchthyosaurs are marine reptiles that colonized numerous ecological niches during the Mesozoic. ln addition to their morphology similar to that of fast swimming sharks and teleosts, ichthyosaurs have the ... [more ▼]

lchthyosaurs are marine reptiles that colonized numerous ecological niches during the Mesozoic. ln addition to their morphology similar to that of fast swimming sharks and teleosts, ichthyosaurs have the particularity to go extinct before the CretaceousPalaeogene boundary, during the Cenomanian (early Late Cretaceous). Although many ichthyosaur-rich localities have been known for a long ti me, the extinction phases that marked the ir history were analysed and quantified in detail only recently. This article summarizes the evolutionary history of ichthyosaurs, with a focus on these extinctions phases. [less ▲]

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See detailIchthyosaurs from the Jurassic of Skye, Scotland
Brusatte, S. L.; Young, M. T.; Challands, T. J. et al

in Scottish Journal of Geology (2015), 51(1), 4355

Fossils of Mesozoic vertebrates are rare in Scotland, particularly specimens of marine reptiles such as plesiosaurs and ichthyosaurs. We describe a suite of ichthyosaur fossils from the Early to Middle ... [more ▼]

Fossils of Mesozoic vertebrates are rare in Scotland, particularly specimens of marine reptiles such as plesiosaurs and ichthyosaurs. We describe a suite of ichthyosaur fossils from the Early to Middle Jurassic of Skye, which to our knowledge are the first ichthyosaurs from Scotland to be described and figured in detail. These fossils span approximately 30 million years, from the Sinemurian to the Bathonian, and indicate that ichthyosaurs were a major component of Scottish marine faunas during this time. The specimens include isolated teeth that could represent the most northerly known occurrences of the widespread Sinemurian species Ichthyosaurus communis, a characteristic component of the famous Lyme Regis faunas of England, suggesting that such faunas were also present in Scotland during the Early Jurassic. An associated humerus and vertebrae from Toarcian–Bajocian-aged deposits are named as a new genus and species of basal neoichthyosaurian, Dearcmhara shawcrossi. The taxonomic affinities of this taxon, which comes from a critical but poorly sampled interval in the fossil record, suggest that non-ophthalmosaurid neoichthyosaurians dominated European assemblages around the Early–Middle Jurassic boundary, and were later replaced by ophthalmosaurids, whose radiation likely took place outside Europe. Many of these specimens were collected by amateurs and donated to museum collections, a co-operative relationship essential to the preservation of Scotland’s fossil heritage. [less ▲]

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See detailMesozoic marine crises and ichthyosaur history: a non-direct relationship
Fischer, Valentin ULg

Conference (2014, October)

Marine ecosystems underwent several profound crises throughout the Mesozoic; many of them are correlated with supra-regional to worldwide anoxic events. The impact of these crises is relatively well ... [more ▼]

Marine ecosystems underwent several profound crises throughout the Mesozoic; many of them are correlated with supra-regional to worldwide anoxic events. The impact of these crises is relatively well understood among animals occupying lower trophic levels but their influence on top predators of that time, fishes and marine reptiles, remains unclear. The fossil record of marine reptiles is of fluctuating quality but thoroughly revised taxonomic and phylogenetic frameworks now allow assessment of the influence of past climatic and oceanic changes on these top predators, by quantifying their cladogenesis and extinction rates across selected intervals. Here, I focus on ichthyosaurs, a successful clade of marine reptiles that colonized marine ecosystems during most of the Mesozoic. The ichthyosaur record indicates relatively few severe turnovers and a non direct relationship with environmental drivers, notably anoxic events. New fossils from France reveal the middle-late Norian extinctions did not eradicate the clade of whale-sized shastasaurid ichthyosaurs; similarly, the severe early Toarcian anoxic event, the end-Jurassic climate changes and several Cretaceous anoxic events did not impacted ichthyosaurs significantly, at least at the suprageneric level. On the other hand, severe turnovers or extinctions occurred during the latest Triassic and the Cenomanian and are coincident with a number of profound environmental and biotic changes. This indicates that unique drivers fail to explain the turnover patterns in ichthyosaur evolutionary history. Notably, oceanic anoxic events only impacted ichthyosaurs during the end-Cenomanian and did so during a period of intense climatic and biological upheavals. These major crises in ichthyosaur history are seemingly protracted over several million years and are probably best explained by a conjunction of causes. This is part of a wider project that will incorporate data from other contemporaneous groups to shed a new light on the general turnover patterns among marine top predators of the Mesozoic and the influence of ancient environmental changes in shaping their biodiversity. [less ▲]

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See detailIchthyosaurs from the French Rhaetian indicate a severe turnover across the Triassic–Jurassic boundary
Fischer, Valentin ULg; Cappetta, Henri; Vincent, Peggy et al

in Naturwissenschaften (Die) (2014), 101

Mesozoic marine reptiles went through a severe turnover near the end of the Triassic. Notably, an important extinction event affected ichthyosaurs, sweeping a large part of the group. This crisis is ... [more ▼]

Mesozoic marine reptiles went through a severe turnover near the end of the Triassic. Notably, an important extinction event affected ichthyosaurs, sweeping a large part of the group. This crisis is, however, obscured by an extremely poor fossil record and is regarded as protracted over the entire Norian–earliest Jurassic interval, for the lack of a more precise scenario. The iconic whale-sized shastasaurid ichthyosaurs are regarded as early victims of this turnover, disappearing by the middle Norian. Here we evaluate the pattern of this turnover among ichthyosaurs by analysing the faunal record of two Rhaetian localities. One locality is Autun, eastern France; we rediscovered in this material the holotypes or partial ‘type’ series of Rachitrema pellati, Actiosaurus gaudryi, Ichthyosaurus rheticus, Ichthyosaurus carinatus and Plesiosaurus bibractensis; a revised taxonomic scheme is proposed. The second assemblage comes from a new locality: Cuers, southeastern France. Both these assemblages provide several lines of evidence for the presence of shastasaurid-like ichthyosaurs in the Rhaetian of Europe. These occurrences suggest that both the demise of shastasaurids and the sudden radiation of neoichthyosaurians occurred within a short time window; this turnover appears not only more abrupt but also more complex than previously postulated and adds a new facet of the end-Triassic mass extinction [less ▲]

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See detailLost and found: Rediscovery of de Ryckholt's collection of Cretaceous Mollusca (Belgium and N. France)
Fischer, Valentin ULg; Denayer, Julien ULg; Mottequin, Bernard ULg

in 4th International Palaeontological Congress, Mendoza, Abstracts volume (2014)

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See detailSimbirskiasaurus and Pervushovisaurus reassessed: implications for the taxonomy and cranial osteology of Cretaceous platypterygiine ichthyosaurs
Fischer, Valentin ULg; Arkhangelsky, Maxim; Stenshin, Ilya et al

in Zoological Journal of the Linnean Society (2014), 171(4), 822841

The ichthyosaur fossil record is interspersed by several hiatuses, notably during the Cretaceous. This hampers our understanding of the evolution and extinction of this group of marine reptiles during the ... [more ▼]

The ichthyosaur fossil record is interspersed by several hiatuses, notably during the Cretaceous. This hampers our understanding of the evolution and extinction of this group of marine reptiles during the last 50 million years of its history. Several Cretaceous ichthyosaur taxa named in the past have subsequently been dismissed and referred to the highly inclusive taxon Platypterygius, a trend that has created the impression of low Cretaceous ichthyosaur diversity. Here, we describe the cranial osteology, reassess the stratigraphic age, and evaluate the taxonomy and phylogenetic relationships of two Cretaceous ichthyosaurs from western Russia: Simbirskiasaurus birjukovi from the early Barremian and Pervushovisaurus bannovkensis from the middle Cenomanian, both formerly regarded as nomina dubia, and allocated to Platypterygius sp. and Platypterygius campylodon, respectively. We show that Simbirskiasaurus birjukovi and Pervushovisaurus bannovkensis are valid platypterygiine ophthalmosaurids, notably characterized by a peculiar narial aperture. The cranial anatomy and phylogenetic relationships of these taxa illuminate the evolution of narial aperture anatomy in Cretaceous ichthyosaurs, clarify the phylogenetic relationships among platypterygiines, and provide further arguments for a thorough revision of Platypterygius. [less ▲]

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See detailMesozoic marine reptile palaeobiogeography in response to drifting plates
Bardet, Nathalie; Falconnet, Jocelyn; Fischer, Valentin ULg et al

in Gondwana Research (2014)

During the Mesozoic, various groups of reptiles underwent a spectacular return to an aquatic life, colonizing most marine environments. They were highly diversified both systematically and ecologically ... [more ▼]

During the Mesozoic, various groups of reptiles underwent a spectacular return to an aquatic life, colonizing most marine environments. They were highly diversified both systematically and ecologically, and most were the largest top-predators of the marine ecosystems of their time. The main groups were Ichthyosauria, Sauropterygia, Thalattosauria, and several lineages of Testudinata, Crocodyliformes, Rhynchocephalia and Squamata. Here we show that the palaeobiogeographical distribution of these marine reptiles closely followed the break-up of the supercontinent Pangaea and that they globally used the main marine corridors created by this break-up to disperse. Most Mesozoic marine reptile clades exhibit a cosmopolitan, or at least pandemic, distribution very early in their evolutionary history. The acquisition of morphological adaptations to a fully aquatic life, combined to special thermophysiological characteristics, are probably responsible for these animals to become efficient long-distance open-marine cruisers. Generally, Early Triassic taxa were near-shore animals mainly linked to the Tethys or Panthalassa coastlines. By the end of the Triassic and during the Jurassic, the break-up of Pangaea resulted in the formation of large marine corridors connecting the Tethys to the North Atlantic and Pacific realms, a trend increasing on during the Cretaceous with the expansion of the Atlantic Ocean and the break-up of the southern Gondwana, allowing open-sea marine reptiles to spread out over large distances. However, if large faunal interchanges were possible at a global scale following a dispersal model, some provinces, such as the Mediterranean Tethys, were characterized by a peculiar faunal identity, illustrating an absence of migration with time despite the apparent lack of barriers. So, if Continental Drift enabled global circulations and faunal interchanges via dispersals among Mesozoic marine reptiles, others parameters, such as ecological and biological constraints, probably also played a role in the local endemic distribution of some of these marine groups, as they do today. [less ▲]

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