Evolution of the Cretaceous short-necked plesiosaurians

Plesiosauria is the most diverse and probably the most disparate clade of secondarily aquatic tetrapods. The adaptive landscape of plesiosaurians has been often summarised to two global morphotypes: one for short-necked forms (pliosauromorphs) and one for long-necked forms (plesiosauromorphs). ‘Pliosauromorphs’ and especially 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 (Figure 1), 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 morphological data, we show that pliosaurids have repeatedly converged with another group of short-necked plesiosaurians, Polycotylidae, 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) and polycotylids at the KT boundary are both preceded by a marked contraction of their disparity, similar to the trajectory documented in ichthyosaurs, another successful marine reptile clade that disappeared during the Cretaceous

Laminar-turbulent transition structure on classic and wavy wing at low Reynolds number

This paper reviews results of researches of the boundary-layer structure and laminar-turbulent transition on the airfoil of unmanned air vehicles (UAVs). The researches have been performed in similar conditions at the Reynolds number for the airfoil chord Re=1.1-1.7•105 for wings with smooth and wavy surfaces. The authors have studied three types of airfoils. R-III-12 airfoil has been measured using a thermoanemometer, while Z-15 and Z-25 – by a PIV method. The method has allowed one to obtain a spatial pattern of perturbation distribution on the wing with wavy surface

Supplementary material

Associated bivalve remains, recoding of Anguanax zignoi, stratigraphic age data for OTUs, additional phylogeny and ancestral state reconstruction figures

Plasticity and convergence in the evolution of short-necked plesiosaurs

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

A new elasmosaurid plesiosaurian from the Early Cretaceous of Russia marks an early attempt at neck elongation

Plesiosaurian marine reptiles evolved a wide range of body shapes during the Jurassic and Cretaceous, including long-necked forms. Many Late Cretaceous members of the clade Elasmosauridae epitomized this part of the plesiosaurian morphological spectrum by evolving extremely long necks through somitogenesis (resulting in an increase in the number of cervical centra) and differential growth (resulting in the elongation of cervical centra). However, the early evolution of elasmosaurids remains poorly understood because of a generally poor Lower Cretaceous fossil record. We describe a new elasmosaurid, Jucha squalea gen. et sp. nov., from the upper Hauterivian (Lower Cretaceous) of Ulyanovsk (European Russia), in addition to other elasmosaurid remains from the same area. Jucha squalea is one of the oldest and basalmost elasmosaurids known and lacks a series of features that otherwise characterize the group, such as the heart-shaped intercoracoid fenestra and the median pectoral bar. However, Jucha squalea marks an early attempt at cervical elongation through differential growth. The data we gathered on the shape of cervical centra among elasmosaurids suggest multiple episodes of elongation and shortening. However, the precise patterns are obscured by an unstable phylogenetic signal

Unexpected diversification of pliosaurid marine reptiles after the Jurassic-Cretaceous boundary

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

Data from: Peculiar macrophagous adaptations in a new Cretaceous pliosaurid

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, but modified this feature in a unique way, 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

Anatomy and relationships of the bizarre Early Cretaceous pliosaurid Luskhan itilensis

peer reviewedPliosaurid plesiosaurians are iconic marine reptiles that regulated marine trophic chains from the Middle Jurassic to the early Late Cretaceous. However, their evolution during the Cretaceous remains poorly documented. Recent discoveries from the Hauterivian–Aptian interval suggest that the radiation of brachaucheniine pliosaurids produced a wide disparity of forms following the Pliosaurus-dominated assemblages of the Late Jurassic. Among the most bizarre of these early brachaucheniines is Luskhan itilensis, from the Hauterivian of Russia. We describe the osteology of this tusked, longirostrine pliosaurid and discuss its possible behaviour by drawing comparisons with other marine amniotes possessing forward-pointing teeth. We take this opportunity to make extensive anatomical comparisons among Cretaceous pliosaurids, including previously overlooked cranial features. Bayesian inference of phylogenetic relationships of plesiosaurians reveals that the internal branches in Late Jurassic–Late Cretaceous pliosaurids have generally low rates of morphological evolution, indicating that the recently described Early Cretaceous pliosaurids have effectively bisected the long branch leading to the ‘classical’ brachaucheniines of the middle Cretaceous (Brachauchenius, Kronosaurus and Megacephalosaurus). Pliosaurids exhibit low evolutionary rates and a dwindling disparity before their extinction, mirroring the events seen, roughly at the same time, for ichthyosaurians.SEASCAP

Supplementary Information

Associated bivalve, measurements, taxon-age data, R code, supplementary phylogeny figures

Nexus_full

Nexus full dataset with tree