Nikolay Zverkov currently works at the Geological Institute of RAS and at Borissiak Paleontological Institute of RAS. Nikolay does research in Paleontology with principal focus on Mesozoic marine reptiles.
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Research Items (37)
The Upper Jurassic ichthyosaurs, characterized by the intermedium/humeral contact are known from several localities in Europe and North America. However, they are often described either briefly, or based on fragmentary material, resulting in a taxonomic tangle in most overviews. Grendelius McGowan, 1976 was previously synonymized with Brachypterygius Huene, 1922. However, it possesses a number of distinct features: intermedium with wide distally faced facet for distal carpal 3 (faced anterodistally in Brachypterygius and equal in size with distal carpal 4 facet), posterodistal contact of metacarpal 5 with ulnare (distal in Brachypterygius), and absence of postaxial accessory digit (well developed in Brachypterygius). We apply a cladistic analysis to place Grendelius and Brachypterygiusin a phylogenetic context. Our analysis recovered Brachypterygius and Grendelius as distinct groups. The clade Grendelius + Otschevia gives us good reason to regard the genus Otschevia Efimov, 1998 as a subjective junior synonym of Grendelius
- Apr 2017
Zverkov, N.G., Averianov, A.O. & Popov E.V., April 2017. Basicranium of an elasmosaurid plesiosaur from the Campanian of European Russia. Alcheringa March. ISSN 0311-5518 The braincase of elasmosaurid plesiosaurs is poorly known. Here, we describe the exceptionally well-preserved elasmosaurid basicranium from the Rybushka Formation (lower Campanian) of Saratov Province, Russia. The material provides new anatomical information and peculiar features: single anterior foramen for the cerebral carotid arteries, anteroposteriorly elongated sella turcica and deep canal on the basioccipital process. This allow us to reconstruct a carotid circulation in plesiosaurs and propose new basicranial features (anteroposteriorly elongated sella turcica and single anterior foramen for the cerebral carotids), which could be potentially synapomorphic for a clade within the Elasmosauridae. Nikolay G. Zverkov* [email@example.com], Department of Palaeontology, Geological Faculty, Lomonosov Moscow State University, 1 Leninskie Gory, 119991 Moscow; Laboratory of Phanerozoic Stratigraphy, Department of Stratigraphy, Geological Institute of the Russian Academy of Sciences, Pyzhevsky lane 7, 119017 Moscow, Russia; Alexander O. Averianov [firstname.lastname@example.org], Zoological Institute of the Russian Academy of Sciences, Universitetskaya Emb. 1, Saint Petersburg 199034; Department of Sedimentary Geology, Geological Faculty, Saint Petersburg State University, 16 liniya VO 29, 199178 Saint Petersburg, Russia; Evgeny V. Popov [email@example.com], Department of Historical Geology and Paleontology, Geological Faculty, Saratov State University, 83 Astrakhanskaya Str., 410012 Saratov; Institute of Geology and Petroleum Technology, Kazan Federal University, Kremlevskaya Str. 4/5, 420008 Kazan, Russia.
- May 2017
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.
- Apr 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 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 have yielded a series of distinct tooth morphotypes, including the first reports of conical‐toothed pliosaurids from the latest Jurassic and 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.
- Jan 2019
Recent study of ophthalmosaurid ichthyosaurs has brought us a number of new taxa; however, the validity of several ophthalmosaurid taxa from the Volgian (Tithonian) of European Russia still remains unclear, complicating comparisons and in some cases affecting taxonomic decisions about new contributions. A revision of the type series of all three species of Undorosaurus, erected by Efimov in 1999, reveals the potential validity of two of them. This contradicts previous research, which concluded that only the type species, U. gorodischensis, is valid. Furthermore, examination of the holotype of Cryopterygius kristiansenae from coeval strata of Svalbard shows that it is synonymous with Undorosaurus gorodischensis, sharing all diagnostic features of the species, especially those related to forelimb morphology: humerus with extensive anteroposteriorly elongate proximal end, poorly pronounced trochanter dorsalis and reduced deltopectoral crest; and ulna proximodistally elongate and not involved in perichondral ossification on its whole posterior edge. This supports the idea of intensive exchange of ichthyosaurs between the Middle Russian Sea and other Boreal seas in the Late Jurassic. In order to resolve the phylogenetic position of Undorosaurus within Ophthalmosauridae as well as relationships of other ophthalmosaurids, a new data set including 33 taxa and 106 characters, 23 of which are new, was compiled. The results of this analysis challenge all previous phylogenetic hypotheses for Ophthalmosauridae in a number of aspects, including the fact that Undorosaurus spp. was recovered deeply nested within Platypterygiinae as a sister group to derived platypterygiines.
- Feb 2019
Recent study of ophthalmosaurid ichthyosaurs has brought us a number of new taxa, however, the validity of several ophthalmosaurid taxa from the Volgian (Tithonian) of European Russia still remains unclear, complicating the comparisons and in some cases affecting taxonomic decisions of new contributions. A revision of the type series of all three species of Undorosaurus, erected by Efimov in 1999, reveals the potential validity of two of them. This contradicts previous research, which concluded that only the type species, U. gorodischensis, is valid. Furthermore, examination of the holotype of Cryopterygius kristiansenae from the coeval strata of Svalbard show that it is synonymous with Undorosaurus gorodischensis sharing all diagnostic features of the species, especially those related to forelimb morphology: humerus with extensive anteroposteriorly elongate proximal end, poorly pronounced trochanter dorsalis and reduced deltopectoral crest; and ulna proximodistally elongate and not involved in perichondral ossification on its whole posterior edge. This supports the idea of intensive exchange of ichthyosaurs between the Middle Russian Sea and other Boreal seas in the Late Jurassic. In order to resolve the phylogenetic position of Undorosaurus within Ophthalmosauridae as well as relations of other ophthalmosaurids, a new dataset including 33 taxa and 106 characters, 23 of which are new, was compiled. The results of this analysis challenge all previous phylogenetic hypotheses for Ophthalmosauridae in a number of aspects including Undorosaurus spp. recovered deeply nested within Platypterygiinae as a sister group to derived platypterygiines.
A detailed description of the section of the Middle Jurassic terrigenous deposits exposed on the Yarenga River, Arkhangelsk Region, is provided. The section represents a new locality of fossil remains of Jurassic marine reptiles. Among them, the postcranial elements of the plesiosaur Muraenosaurus dominate. Pliosaur and ichthyosaur finds, each represented by a single bone, also occur in the assemblage. The palynological and micropaleontological data support the Early-Middle Bathonian age of the deposits. The lithological characters of the rocks and the presence of rare foraminifera indicate shallow marine environments. The significance of new discoveries for the fossil record of the Jurassic marine reptiles is briefly discussed.
Here we describe plesiosaur remains from Glebovo section, Yaroslavl Region. Although the specimens were found non in situ they are likely Early Cretaceous, Valanginian, in age. One cervical centrum is referable to Elasmosauridae – this is the first find of an elasmosaurid plesiosaur in the Valanginian of Russia.
Pliosaurid plesiosaurians played important roles in marine food chains from the Middle Jurassic to the mid Cretaceous, frequently as apex predators. All hitherto described pliosaurid species of the Kimmeridgian to the Hauterivian possess trihedral and subtrihedral teeth with a smooth labial surface, while Aptian–Turonian pliosaurids have exclusively conical crowns with apicobasal ridges typically arranged around the entire circumference, suggesting, for each of these time intervals, a restricted range of tooth morphologies, and thus, possibly, of ecological niches. However, current knowledge of pliosaurids comes mostly from several restricted time intervals and areas; the Jurassic-Cretaceous transition remains a persistent gap in our knowledge of pliosaurid evolution. Consequently, the effect of the Jurassic–Cretaceous boundary faunal turnover on pliosaurids is poorly understood. To tackle this issue, we describe a series of pliosaurid teeth ranging 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) and analyse the evolution of pliosaurid teeth through time. Unexpectedly, these teeth belong to widely distinct morphotypes, including the first report of conical-toothed pliosaurids from the latest Jurassic–earliest Cretaceous interval. This challenges the hypothesis that only one lineage of pliosaurids crossed the Jurassic–Cretaceous boundary. It appears that conical-toothed pliosaurids coexisted with their trihedral-toothed relatives for at least 25 million years over the Jurassic-Cretaceous transition. In fact, our quantitative analyses indicate that pliosaurids reached their maximal dental disparity (in both size and shape) during this interval, showing little evidence of a turnover associated with the Jurassic–Cretaceous boundary. Instead, disparity decreased later in the Early Cretaceous, with the disappearance of trihedral-toothed forms in the Barremian. Pliosaurids thus decreased their dental disparity (and thus, possibly, their ecological diversity) long before their extinction in the early Late Cretaceous.
An incomplete skeleton of the ichthyosaur Ophthalmosaurus icenicus Seeley, 1874 excavated in the Oxfordian-Kimmeridgian beds south of the town of Syzran (Samara Region) is described. Members of the genus Ophthalmosaurus are characterized by a unique combination of characters, most of which are well-pronounced in the specimen described here: the extracondylar area of the basioccipital is reduced, but still visible beyond the occipital condyle and has a well-pronounced ventral notch; the scapular shaft is mediolaterelly flattened; the humerus has three distal facets: the anterior facet is the smallest; the facet for the accessory preaxial element has a sharpened anterior margin; the facet for the radius faces distally; the facet for the ulna faces posterodistally; the posterior margin of the ulna is concave and sharpened, involved in the perichondral ossification; the intermedium is rhomboid, with two distal facets equal in size for the second and third distal carpals; the epipodial and autopodial elements are round and thickened, loosely arranged in the fin. This specimen is the first reliable evidence of the presence of Ophthalmosaurus in the Oxfordian-Kimmeridgian of Russia. The previously described remains of a Kimmeridgian ichthyosaur referred to as O. undorensis Efimov, 1991 should be identified as Ophthalmosauridae indet.
Описан неполный скелет ихтиозавра Ophthalmosaurus icenicus Seeley, 1874, обнаруженный в оксфордско-кимериджских отложениях южнее г. Сызрани (Самарская область). Представители рода Ophthalmosaurus характеризуются уникальной комбинацией признаков скелета, бóльшая часть из которых выражена у описываемого экземпляра: basioccipitale с редуцированной, но выступающей за пределы затылочного мыщелка и обладающей ярко выраженной вентральной вырезкой замыщелковой областью; уплощенное сечение осевой части лопатки; плечевая кость с тремя дистальными фасетками, передняя из которых наименьшая, фасетка для дополнительного преаксиального элемента имеет заостренный передний край, фасетка для лучевой кости обращенная дистально, фасетка для локтевой кости – постеродистально; задний край лучевой кости вогнутый и заостренный, вовлеченный в перихондральное окостенение; интермедиум ромбовидной формы с двумя соразмерными дистальными фасетками для второй и третьей дистальных карпалий; элементы эпиподия и автоподия округлые и утолщенные, свободно располагавшиеся в ласте. Данная находка – первое достоверное свидетельство присутствия офтальмозавров в оксфорде–кимеридже России. Остатки кимериджского ихтиозавра, описанные ранее как O. undorensis Efimov, 1991, следует рассматривать как Ophthalmosauridae indet.
Here we describe incomplete plesiosaur skeleton from the Upper Santonian of Saratov Region (Russia), referable to Polycotylidae Williston, 1908. Hitherto remains of polycotylids from Saratov Region were known only from the Cenomanian, Campanian and Maastrichtian deposits. Polycotylid skeleton was found earlier in the Santonian deposits of Penza region and described by Vitaly Georgievich Ochev as Georgiasaurus penzensis Otschev, 1977. Until recently, it was the only definable remains of the Santonian polycotylid plesiosaur, found in our country.
Marine reptile remains from the Jurassic of Moscow area were at first described in the year 1845, since then considerable materials from the Callovian, Oxfordian and Volgian (Tithonian) strata were accumulated. Here we review all available Jurassic marine reptile materials from Moscow area stored in museums and private collections. Callovian marine reptiles are quite rare, being represented by isolated bones and teeth of Plesiosaurs fam. Cryptoclididae, pliosaurs Liopleurodon and Simolestes, ichthyosaurs, and thatattosuchians. Several teeth in matrix belonging to Liopleurodon and a thalattosuchian crown are likely from the Late Oxfordian to Early Kimmeridgian deposits. Volgian marine reptiles are common and diverse. In Panderi ammonite zone plesiosaur Colymbosaurus, pliosaurids Pliosaurus, and indeterminate ophthalmosaurid ichthyosaurs were found. In layers of Virgatus – Fulgens ammonite zones numerous teeth, isolated bones and incomplete skeletons were collected, representing the following taxa: pliosaurids Pliosaurus spp., small and moderate-sized plesiosaurs of the subfamily Colymbosaurinae and ophthalmosaurid ichthyosaurs, among which small-sized Paraophthalmosaurus and large Undorosaurus are unambiguously identified.
Here we report the first find of marine reptile tooth crown from the Upper Jurassic (Middle to Upper Oxfordian) of Crimean Mountains near Yalta. The crow is slender and circular in cross section; it is ornamented by fine longitudinal ridges by its entire circumference. This crown likely belongs to a plesiosaur, however, it also shows similarities to teleosaurid thatattosuchians
The limbs of marine reptiles lack some function and characteristics essential for most amniotes: they do no more support body weight in terrestrial conditions but are modified into fins to steer or stabilize underwater motion, and into flippers , primary propulsive organs. Thereby their structure was partially reorganized in order to serve new functions. ln some cases, this leads to ambiguous identifications of certain elements and makes their homologization problematic. The main controversy is the identification of mesopodial elements related to the emerge of 'neomorphic' ossicles in advanced ichthyosaurs and plesiosaurs. According to some researchers, the element located distal to the zeugopodia and between them is the astragalus , whereas anterior to it the enlarged centrale emerges (e.g. Caldwe ll 1997a, b), or even the distal tarsal, shifted proximally to the tibia, fills the empty space anterior to the astragalus (e.g. McGowan and Motani 2003 : p. 53). Others prefer to interpret the mesopodial elements using amphibian-like pattern, thereby identifying a separated intermedium and tibiale (e.g. Andrews 1910; McGowan and Motani 2003: p. 44). Recently published data on 're-evolution' of mesopodial elements in chameleons due to 'missing structures' (Diaz & Trainor 2015) could be successively applied for marine reptile tarsus. Thereby lacking of an astragalus and evolving of an 'ancestral' structure convergent with amphibians seems to be preferable. This adaptation could be explained by strengthening of a leading edge of a limb in order to resist a hydrodynamic loading, which is essential for basal aquatic reptiles retaining the terrestrial hindlimb structure and lacking ossifications in the anterior part of the mesopodium.
The braincase of elasmosaurid plesiosaurs is poorly known despite numerous relatively complete and well-studied skeletons. Thereby a new find of an elasmosaurid basicranium from the Rybushka Formation (mid-Campanian) of Saratov Region, Russia, is of great interest. The specimen, attributed to an elasmosaurid plesiosaur, possess an elongated plate-like median keel of the parasphenoid and the condyle demarcated from the rest of the basioccipital by a deep groove. The studied basicranium is characterized by a number of peculiar features: extremely anteroposteriorly elongated pituitary fossa, single anterior foramen for the internal carotid arteries, reduced clinoid process, and deep channel on the basioccipital process. These features indicate profound morphological changes of the brain and head vessels compared with the other known plesiosaurs. Because of its hidden position, the pituitary fossa is rarely described in amniotes. However, the foramen for the anterior exit of the internal (cerebral) carotid artery is paired in most described amniotes. In all hitherto known sauropterygians these foramina are widely spaced (e.g. Rieppel, 1994; Druckenmiller, 2002; Sato et al., 2011). The single anterior foramen for the internal (cerebral) carotid was recently described in a new aristonectine elasmosaurid Alexandronectes zealandiensis (Otero et al., 2016). This feature is a potential synapomorphy for derived elasmosaurids.
Until recently, Tholodus, a rare ichthyosaur with spherical tooth crowns of the pressing–crushing type, has only been known from the Middle Triassic (Anisian) beds of Western Europe. A record of Tholodus remains in the Karazin Formation (Middle Anisian) of southern Primorye (Russian Far East) significantly expands the range of these reptiles.
Tholodus – редкий ихтиозавр со сферическими коронками зубов давяще-дробящего типа, известный до недавнего времени лишь из среднетриасовых (анизийских) отложений Западной Европы. Находка остатков толодуса в отложениях каразинской свиты (средний анизий) Южного Приморья значительно расширяет известный ареал этих рептилий.
- Dec 2015
During the Middle and Late Jurassic, pliosaurid plesiosaursevolved 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.
Supplementary material. Includes: pictures of a bivalve associated with YKM 68249/1-10, stratigraphic age data for all taxon incorporated in the phylogeny, revised phylogenetic coding for Anguanax zignoi, additional figures of strict consensus topologies, detailed results from the ancestral state reconstruction and R scripts. -Nexus files. With character-taxon matrices and most parsimonious trees.
A jaw fragment of the rare ichthyosaur Tholodus is found for the first time in the Middle Triassic deposits of the Karazin Formation (South Primorye, Russian Far East). An analysis of the cephalopod systematics (Acrochordiceras kiparisovae Zharnikova, A. korobkovi Zharnikova, Acrochordiceras pacificum (Zharnikova), Stenopopanoceras? russkiense sp. nov., Parasturia primorica sp. nov., and Atractites sp. indet.) from the Tholodus-bearing unit of the Karazin Formation shows that they correspond to the complex of the middle Anisian (Acrochordiceras kiparisovae zone). New ammonoid species from the families Parapopanoceratidae and Sturiidae are described.
Here we describe a specimen from the Lower Callovian of Kostroma region, referable to the short‐snouted pliosaurian genus Simolestes Andrews, 1909. This finding expands geographic distribution of the genus Simolestes, and deepens our understanding of the Callovian herpetofauna of the Russian Sea, which was apparently similar to that of Western Europe, with typical ichthyosaurs (Arkhangelsky, 1999) and long‐snouted pliosaurs Liopleurodon (Trautschold, 1860; Shmakov, 2014), as well as specific short‐snouted pliosaurs such as Simolestes.
For the first time a specimen referred to Pliosaurus is described from the Lower Cretaceous (Lower Valanginian), represented by a single tooth from Mount Sheludivaya in Crimea. This specimen demonstrates that two pliosaurian lineages crossed the Jurassic – Cretaceous boundary: the typically Cretaceous subfamily Brachaucheninae Benson et Druckenmiller, 2013 and typically Late Jurassic genus Pliosaurus Owen, 1841.
Here we gave a brief description of an ichthyosaurian remains from the Lower Valanginian of the European Russia (Kirov region) referable to the family Ophthalmosauridae Baur, 1887. The record of ichthyosaurs from the Berriasian–Barremian interval is extremely limited so even fragmental remains are of great interest. This finding confirms the assumption that the Jurassic–Cretaceous boundary extinction event had a negligible effect on ichthyosaurs .
During the Late Jurassic, important palaeogeographic events occurred in Eurasia, North America and Gondwana. Continental rift, subduction and orogeny produced different levels of marine inundation of terrestrial systems, with rising sea level. Shallow epicontinental seaways started to separate North America from Eurasia, Gondwana, and also between segments of Gondwana itself. Tethys, the east-west seaway, expanded and at times covered large parts of the continental interior of Eurasia. The aperture of new seaways such as the Greenland-Norwegian seaway and the Mezen-Pechora strait system in the northern hemisphere; the Hispanic Corridor, between North and South America; and the Trans-Erythrean seaway (or South Africa/Rocas Verdes seaway) in the southern hemisphere allowed for intermittent interchange of invertebrate and marine vertebrate faunas. During the past five years, the ichthyosaur fossil record has provided a way to describe new species so as to complement diagnoses of species that for a long time had been either synonymised or considered invalid. These taxonomic studies allow us now to understand the paleo-distribution of the ichthyosaurs around the world better as the relationships between the realms of the northern-southern hemisphere and boreal regions. The present report is a generic-level analysis of the dispersal routes of ichthyosaurs during the Late Jurassic compared with one of its top predators, Pliosaurus, and the palaeogeographic significance of high-latitude species such as Arthropterygius spp., Undorosaurs spp., Cryopterygius spp, Janusaurus and non-ubiquitous ichthyosaurs.
Rhomaleosaurid plesiosaurians were a common and ecologically significant component of Early Jurassic marine faunas, primarily as large-bodied predators. They declined in abundance and made their last fossil appearance in the Middle Jurassic. However, the geographic pattern of rhomaleosaurid extinction has thus far been obscured by spatial bias in the Middle Jurassic marine reptile fossil record, which is strongly focussed on low-latitude European assemblages. We report two rhomaleosaurid specimens from the Callovian (late Middle Jurassic) of the UK and Russia. Along with Borealonectes from Arctic Canada, these are the youngest-known occurrences of rhomaleosaurids. The UK specimen is the first identified from the Callovian of Europe, despite intensive fossil sampling over almost 200 years and the recovery of hundreds of other plesiosaurian specimens. Its discovery indicates that rhomaleosaurids were present, but extremely rare, at low palaeolatitudes of the Callovian. The Russian specimen is one of relatively few marine reptile specimens from its mid-palaeolatitude assemblage, as with the high latitude taxon Borealonectes. Furthermore, we suggest that a mid latitude southern hemisphere occurrence from the Callovian of Argentina, previously referred to Pliosauridae, in fact represents a rhomaleosaurid. These findings suggest that rhomaleosaurids were actually common elements of mid-high palaeolatitude marine faunas, indicating a geographically staggered pattern of declining rhomaleosaurid abundance, and demonstrating the apparent persistence of an archaic marine reptile group in cool, mid–high latitude environments of the Middle Jurassic. It is therefore possible that sustained Middle–Late Jurassic global warming accelerated the ultimate extinction of rhomaleosaurids. Our findings suggest that widening the geographical breadth of fossil exploration could considerably enhance current knowledge of Jurassic marine reptile evolution.
An ichthyosaurian skeletal remains assigned to the genera Arthropterygius and Ophthalmosaurus are described from the Volgian deposits of the Komi Republic and Nenets Autonomous Region (Okrug) (Russia). These specimens along with findings from Svalbard provide an opportunity to draw some preliminary conclusions on the distribution of ichthyosaurs during the Late Jurassic and Early Cretaceous epoch.
A new species of ichthyosaur genus Undorosaurus from the Volgian stage of Moscow is described based on an incomplete forelimb. It differs from congeners basically in the form and position of pisiforme. With the application of cladistic method the phylogenetic position of two genera Undorosaurus and Paraophthalmosaurus in the system of Ichthyosauridae is defined. Both taxa are referred to the clade Ophthalmosaurinae.
Tholodus is rare ichthyosaur with durophagous dentition, until recently known only from the Anisian deposits of Western Europe. Finding of Tholodus remains in the Anisian deposits (Karazinskaya suite formation) of Primorsky Kray significantly expands our understanding of the area of distribution of these reptiles and confirms previously suggested assumption of their wide geographical distribution during the Anisian time.
Дан краткий обзор истории изучения, систематики и образа жизни ихтиозавров — необычных морских рептилий мезозоя. // The brief review of history of studying, systematics and habitats of ichthyosaurs, uncommon marine reptiles of Mesozoic is given.