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Revision of the plesiosaur Polycotylus sopozkoi from the Southern Urals (Russia) confirms the wide distribution of Polycotylus in the Late Cretaceous of the Northern Hemisphere
Abstract
Polycotylids are among the most common plesiosaurians of the Late Cretaceous, however, in Eurasia their findings are rare and fragmentary. In 2016, a partial polycotylid skeleton from the Upper Cretaceous of the Izhberda quarry in the Southern Urals region was described by Efimov et al. as a new species, Polycotylus sopozkoi. Here we revise this holotype specimen and show that many characters initially proposed to distinguish the species are the result of misinterpretations. However, P. sopozkoi is indeed referable to Polycotylus and is highly similar to its type species, P. latipinnis. Although only one distinctive trait of the species noted by Efimov et al., the protruding basioccipital tubera with deep carotid canals on their anterodorsal surface, is confirmed here, new observations revealed additional features that allow us to substantiate the validity of P. sopozkoi. The presence of Polycotylus in the Upper Cretaceous of North America and Eastern Europe highlights a wide distribution of some plesiosaurian genera and suggests caution in assumptions of ‘endemic’ plesiosaurian taxa in particular regions of the world.
... Efimov et al. (2016) described another species of Polycotylus, Polycotylus sopozkoi Efimov et al., 2016, from the upper Santonianlower Campanian of the Southern Urals (Izberda quarry, Gai District, Orenburg Region). The holotype of this species was one of the most complete polycotylid skeletons in Eurasia as of 2016 and its subsequent reassessment supported the validity of the species and its referral to Polycotylus and allowed to provide additional data on the axial skeleton of Polycotylus (Zverkov et al., 2024). The Izberda quarry has since yielded several more specimens of Polycotylus, including remains of small, osteologically immature, and large, mature individuals. ...
... OGMM 247, the holotype of Polycotylus sopozkoi, a partial skeleton, including basicranium, fragmentary right quadrate and pterygoid; posterior portions of the mandible; several isolated teeth; atlas-axis and eight cervical vertebrae, nine dorsal and one caudal centrum; fragments of neural arches and ribs; glenoid portions of right scapula and coracoid; two nearly complete forelimbs. This specimen is described in detail by Zverkov et al. (2024). ...
... Based on elasmobranch fauna the age of the bone bed is defined as late Santonian -early Campanian (Popov et al., 2021). For details on the geology of the Izhberda quarry and photographs of the outcrop, we direct the reader to Zverkov et al. (2024). ...
Since the discovery of the holotype of Polycotylus sopozkoi in the Southern Urals, several skeletons referable to Polycotylus were collected from the upper Santonian – lower Campanian bone bed at its type locality (Izhberda quarry, Orenburg Region, Russia). Here we describe these new specimens, which together with the holotype constitute an ontogenetic series from small juveniles with the propodial length of 27 cm to a large adult individual with the propodial length exceeding 47 cm and traces of senile pathologies of limb elements. The new specimens significantly expand the knowledge of the morphology and variation of the postcranial skeleton in Polycotylus. They also reveal additional diagnostic features of Polycotylus sopozkoi (28 cervical vertebrae, one of the highest counts for polycotylines, and strongly tapered anterodistal processes of cervical ribs), and shared traits with P. latipinnis (divergent anteromedial processes and pronounced anterior shelf of the coracoid), which were previously unnoticed in the known specimens and supplement the generic diagnosis. The observed individual variation in Polycotylus sopozkoi has implications for phylogenetic and ontogenetic studies of plesiosaurs, and for assessment of the taxonomic value of some characters in polycotylids.
... Однако это, по всей видимости, парафилетическая группа, от которой в разные моменты возникали формы с удлиненными и сильно укороченными позвонками [12,13]. Наконец, к последней группе относятся эласмозавриды с существенно укороченными телами шейных позвонков и уменьшенным числом позвонков в шее (40)(41)(42)(43)(44)(45). Это подсемейство Aristonectinae, характерное главным образом для маастрихтского века конца мела Южного полушария [12]. ...
... Одна из первых находок эласмозаврид в этом местонахождении -часть позвоночного столба эласмозаврида с относительно короткими шейными позвонками, как у Cimoliasaurus (рис. 8) -была сначала ошибочно отнесена к поликотилидам [41,42]. Находки последних лет из местонахождения Ижберда позволяют говорить о существовании в раннем кампане Русского моря не только гигантских длинношеих эласмозаврид, подобных Elasmosaurus и Albertonectes, но и не менее чем трех форм эласмозаврид средних размеров с шеей умеренной длины и даже укороченной. ...
Plesiosaurs of the family Elasmosauridae are widely known for their long necks with a record number of vertebrae. Currently, many genera and species of elasmosaurids are known: from small to gigantic, from super-long-necked to secondarily shortnecked. Elasmosaurid remains have been described from all regions of the world and are often found in Cretaceous deposits of Russia. Some historical finds from Russia were described as new species, but did not receive recognition in subsequent research. New finds of elasmosaurids from Russia shed light on the taxonomic diversity and evolutionary history of this family in Eurasia.
... Фото из архива М. С. Архангельского ГЕОЛОГИЯ находок -неполный посткраниальный скелет поликотилида -была обнаружена в 2014 г. и описана как новый вид -Polycotylus sopozkoi [34,35]. Позднее в данном местонахождении было найдено еще несколько неполных скелетов представителей данного вида, принадлежащих особям разных онтогенетических стадий (рис. ...
... ОШММ 507: д -после препаровки; е -фото передней части во время раскопок. Иллюстрация адаптирована из[35]. ...
Polycotylids are Cretaceous plesiosaurs with a relatively short neck and an elongated snout. For a long time, they were studied mainly based on the fossils from North America. Numerous finds of polycotylids from Russia shed light on their diversity in Late Cretaceous epicontinental seas of Europe. Russian finds demonstrate that some representatives of the family were widely distributed geographically and also shed light on unexpected features of the paleoecology of late representatives of the family.
... 2b; Burns et al. 2015;Matsumoto et al. 2019). Within Sauropterygia, the presence of a notochordal pit, accompanied or not by a single bulk [i.e., a central mammilla sensu Storrs (1999)], is exclusive of some Plesiosauria (Brown 1981;Storrs 1999;Kear 2002;Lazo and Cichowolski 2003; Bell et al. 2014;Cau and Fanti 2015;Miedema et al. 2019;Zverkov et al. 2024). None of the observed vertebral centra of MUPA-ATZ0101 or any other individual of P. multidentatus (including three other partial skeletons and isolated vertebral centra from the type locality) presents a notochordal pit, which is also absent in other basal sauropterygians (Rieppel 2000). ...
The record of paleopathologies in the marine reptile group Sauropterygia is relatively scarce in the literature. These pathologies generally correspond to avascular necrosis, vertebral lesions, or bite marks. Among the vertebral lesions, osteophytes and Schmorl nodes are the most commonly reported, interpreted as derived from degenerative pathologies. Other vertebral anomalies known in this lineage include vertebral fusions, hemivertebrae, blebs, and subchondral erosions and cysts. These have been proposed as being caused by congenital malformations (i.e., vertebral fusions, hemivertebrae), infections (i.e., vertebral fusions, blebs), bite marks (i.e., vertebral fusions), or osteoarthritis (i.e., subchondral erosions and cysts). Most of these pathologies have been reported in Jurassic and Cretaceous plesiosaurs. Conversely, the documented pathologies in Triassic sauropterygians are very limited. Simosauridae is a relatively poorly known lineage of Triassic eosauropterygians, considering both their relatively fragmentary fossil record and their limited diversity and paleobiogeographic distribution, only recorded from Europe and the Middle East (i.e., restricted to the western margin of the Tethys Sea). Most simosaurid remains come from Europe, from where the only two defined species of the group are known: Simosaurus gaillardoti, from the Ladinian of France and Germany, and Paludidraco multidentatus, from the Carnian of Spain. Despite the availability of relatively complete simosaur skeletons and additional, but mostly isolated remains, no pathologies have hitherto been reported for Simosauridae. In this study, we report on the first case of a pathology in Simosauridae, providing its detailed characterization. It corresponds to paired and symmetrical bulks located on the articular facets of several most posterior dorsal centra of the Paludidraco multidentatus holotype. This type of pathology has never been reported for any sauropterygian or other marine reptile. Additionally, the potential pathological origins for these structures are analyzed, with long-term biomechanical stress or a congenital disorder being discussed as the most probable causes.
... 2b; Burns et al. 2015;Matsumoto et al. 2019). Within Sauropterygia, the presence of a notochordal pit, accompanied or not by a single bulk [i.e., a central mammilla sensu Storrs (1999)], is exclusive of some Plesiosauria (Brown 1981;Storrs 1999;Kear 2002;Lazo and Cichowolski 2003; Bell et al. 2014;Cau and Fanti 2015;Miedema et al. 2019;Zverkov et al. 2024). None of the observed vertebral centra of MUPA-ATZ0101 or any other individual of P. multidentatus (including three other partial skeletons and isolated vertebral centra from the type locality) presents a notochordal pit, which is also absent in other basal sauropterygians (Rieppel 2000). ...
The record of paleopathologies in Mesozoic marine reptiles is relatively scarce in the literature compared to that on other lineages such as Dinosauria. In the case of Sauropterygia, these pathologies generally correspond to avascular necrosis, vertebral lesions or anomalies, or bite marks, mostly reported in Jurassic and Cretaceous plesiosaurs. The documented pathologies in Triassic sauropterygians are very limited. Among the Triassic eosauropterygians, Simosauridae is a relatively poorly known lineage, being restricted to the western margin of the Tethys Sea, recorded from Europe and the Middle East. To date, no pathologies have been reported for Simosauridae. In this study, we describe several abnormal vertebral centra corresponding to the most posterior dorsal region of the holotype of the Spanish simosaurid Paludidraco multidentatus. These centra exhibit paired and symmetrical bulks located on their articular facets. The bulks cannot be differentiated externally or internally from their surrounding healthy bone tissue, and there are no signs of reactive new bone formation, fractures, or remodeling. These pathologic structures have never been reported for any other Sauropterygia or marine reptiles, having only been rarely documented in some dinosaurs. A differential diagnosis rules out several possible pathological origins for these structures, suggesting that long-term biomechanical stress or a congenital disorder may be the potential causes.
... С тех пор участниками Орского клуба юных геологов на карьере регулярно ведутся мониторинг и полевые работы. Из данного местонахождения по неполному скелету был описан новый вид плезиозавра Polycotylus sopozkoi Efimov et al., 2016(Ефимов и др., 2016Zverkov et al., 2024), а также остатки костей динозавров (Аверьянов и др., 2021a; Скучас и др., 2022) и птерозавров (Аверьянов и др., 2021b, 2022). Помимо многочисленных остатков плезиозавров, хрящевых и костных рыб, за 10 лет была собрана коллекция и по мозазавридам. ...
Изучение новых находок мозазаврид из Ижбердинского местонахождения (Южный Урал, Оренбург- ская обл.) позволило впервые установить для верхнего мела Оренбуржья присутствие мозазавров из подсемейств Mosasaurinae, Tylosaurinae и Plioplatecarpinae, в т.ч. представителей родов Mosasaurus, Prognathodon и Clidastes, известных из верхнего мела Северной Америки и Западной Европы. Интерес представляет обнаружение тилозаврина Taniwhasaurus, прежде известного из Новой Зеландии, Ан- тарктики, Южной Африки и Японии. Таким образом, кампанская фауна мозазаврид Южного Урала является смешанной и включает в свой состав североамериканско–европейские и азиатско–тихооке- анские таксоны. Однако все находки мозазавров из Ижбердинского местонахождения можно опре- делить лишь в открытой номенклатуре, что затрудняет подробные сравнения фаун. Ревизия типовой серии мозазавра Liodon rhipaeus Bogolubov, 1910 из Южного Урала показала, что в нее были также ошибочно включены кости плезиозавра. Liodon rhipaeus является nomen dubium. Типовой материал по этому виду определен как Tylosaurinae indet.
... Since then, members of the Orsk Club of Young Geologists have regularly carried out monitoring and field work at the quarry. A new plesiosaur species, Polycotylus sopozkoi Efimov et al., 2016(Efimov et al., 2016Zverkov et al., 2024), as well as remains of dinosaurs (Averianov et al., 2021a;Skutschas et al., 2022) and pterosaurs (Averianov et al., 2021b(Averianov et al., , 2022 were described from this locality. In addition to numerous remains of plesiosaurs and cartilaginous and bony fishes, a mosasaurid material was also collected over the ten years. ...
The study of new finds of mosasaurids from the Izhberda locality (Southern Urals, Orenburg Region) has made it possible to record for the first time the presence of mosasaurs from the subfamilies
Mosasaurinae, Tylosaurinae, and Plioplatecarpinae from the Upper Cretaceous of the Orenburg Region, including representatives of the genera Mosasaurus, Prognathodon, and Clidastes, which are known from the Upper Cretaceous of North America and Western Europe. Of interest is the discovery of the tylosaurine Taniwhasaurus, previously known from New Zealand, Antarctica, South Africa, and Japan. Therefore, the Campanian mosasaurid fauna of the Southern Urals is intermediate and includes North American–European and Asia–Pacific taxa. However, all the finds of mosasaurs from the Izhberda locality can only be identified in
open nomenclature, which makes detailed comparisons of the faunas difficult. Revision of the type series of mosasaur Liodon rhipaeus Bogolyubov, 1910 from the Southern Urals has allowed us to conclude that, in addition to the three mosasaurian vertebrae, it includes the ischium and posterior fragment of the mandible of a plesiosaur. Liodon rhipaeus is clearly a nomen dubium and the vertebrae of its type series cannot be iden-
tified more precisely than Tylosaurinae indet.
Most polycotylid plesiosaurians have isodont dentition with relatively small and slender conical teeth. However, large and robust caniniform teeth are known for some of their basal late Albian and early Cenomanian representatives, implying greater ecological diversity early in the evolutionary history of the clade. Here we report the first evidence of polycotylids with large teeth in the Campanian, thus c. 15 Myr younger than previous records. Several teeth with crowns exceeding 40 mm in height and some reaching 25 mm in basal diameter were collected from two Campanian localities in European Russia. These are the largest polycotylid teeth reported from the Cretaceous of Eurasia. Their large size and specific enamel ornamentation markedly differ from other known polycotylid teeth, suggesting that these teeth belong to an undescribed taxon. However, similar enamel ornamentation was previously reported for the now forgotten ‘Piratosaurus plicatus’ Leidy, 1865 from the Upper Cretaceous of Canada, which may indicate the wide distribution of polycotylids with such teeth in the latest Cretaceous. Unlike classical polycotylids, the new teeth have strong apical wear which implies consumption of abrasive prey, similar to modern killer whales that feed on sharks. Thus, our finding reveals higher ecological diversity of polycotylids in the latest Cretaceous, suggesting the coexistence of small- to medium-toothed and large-toothed (probably “latirostrine”) taxa at different times of the evolutionary history of the Polycotylidae.
Keywords
Upper Cretaceous coastal marine deposits are widespread in the Southern Urals with a number of marine vertebrates previously reported from this region. However, previous studies on the vertebrate faunas in this region often lack detailed taxonomic descriptions and illustrations, rendering comparisons to other faunal assemblages difficult. A new diverse vertebrate assemblage comprising cartilaginous and bony fishes, as well as marine reptiles, is described here from the Orenburg region near Akkermanovka (Southern Urals, Russia). Thirty five taxa are identified, including three holocephalans (Elasmodus sp., Ischyodus yanshini, Chimaeroid indet.), two hybodontiform sharks (Meristodonoides sp., cf. Polyacrodus sp.), 17 neoselachians (Paraorthacodus cf. andersoni, Paraorthacodus sp., Synechodus sp., Cederstroemia nilsi, Acrolamna acuminata, Archaeolamna ex gr. kopingensis, Cretalamna sarcoportheta, Cretoxyrhina mantelli, Eostriatolamia segedini, E. venusta, Hispidaspis horridus, Hispidaspis cf. gigas, Pseudocorax laevis, Pseudoscapanorhynchus compressidens, Scapanorhynchus rhaphiodon, Squalicorax kaupi, Ptychodus rugosus), a holostean (Lepisosteidae indet.), nine teleosts (Protosphyraena sp., Saurodontidae indet., cf. Pachyrhizodus sp., Pachyrhizodontidae indet., Enchodus petrosus, E. ferox, E. cf. gladiolus, E. spp., Alepisauroidei indet.), two plesiosaurs (Polycotylidae indet., Plesiosauria indet.), and one mosasaurid (Tylosaurinae indet.). Based on the faunal assemblage, a Santonian-?early Campanian age is proposed. Lamniform sharks are the best represented group in terms of taxic diversity and relative abundance, probably reflecting the peak in diversity this group experienced following the Cenomanian radiation in the Late Cretaceous. The faunal assemblage of Akkermanovka exhibits significant taxonomic overlaps with assemblages reported from Asia and North America, but not from Southern Hemisphere continents, indicating east-west dispersal of several marine taxa during the Late Cretaceous.
Plesiosaurs are one of the longest-ranging tetrapod groups in the Mesozoic and underwent a major adaptive radiation in the Late Tri-assic/Early Jurassic, so they are an ideal clade to study the long-term implications and deep-time evolution of specific developmental patterns. We compiled a database of all published plesiosaur specimens and recorded their skeletal maturity status. We use statistical modelling to demonstrate that the abundance of allegedly 'juvenile' specimens increases through time, which contradicts the null hypothesis that the relative proportion of juvenile to adult specimens should remain constant throughout evolution. These results indicate that many 'juvenile' specimens are really adults exhibiting heterochronic traits, particularly paedomorphism. Heterochrony is a developmental pattern particularly widespread in secondarily adapted organisms such as plesiosaurs. However, heterochronic patterns are typically only studied in individual genera/species or restricted clades. We demonstrate that the pervasiveness of paedomor-phism in plesiosaurs increased gradually throughout the evolution of the clade, rather than being a specialization of specific clades.
Polycotylidae Cope, 1869 is a clade of short-necked plesiosaurians that achieved a cosmopolitan distribution by the Late Cretaceous. Here, the material previously referred to Polycotylidae/Pliosauridae from the Upper Cretaceous of New Zealand is reviewed, concluding that only 2.4% and 7.7% respectively of the total plesiosaurians specimens recovered in these formations (late Campanian-early Maastrichtian Tahora Formation and Campanian-Maastrichtian Conway Formation) belong to Polycotylidae. This proportion is similar to that recorded in upper Campanian-Maastrichtian levels of the Allen, Los Alamitos and La Colonia formations, northern Patagonia (Argentina) and southernmost Chile, but contrasts with the coeval absence of polycotylids in Campanian-Santonian levels of Antarctica and central Chile. These new results improve our knowledge about the representation of Weddellian polycotylids and underline the relative scarcity of Campanian-Maastrichtian records in the Weddellian Province.
Plesiosaurs are a group of Mesozoic marine diapsids. Most derived plesiosaurs fall into one of two typical body forms: those with proportionately small heads, short snouts, and elongated necks, and those with large heads, elongated snouts, and short necks. Serpentisuchops pfisterae is a polycotylid plesiosaur from the Upper Cretaceous Pierre Shale that presents the trait combination of both an elongate snout and elongate neck (consisting of 32 vertebrae). Phylogenetic analysis places Serpentisuchops within the Polycotylinae, indicating that its long snout is an ancestral trait, while its long neck is secondarily derived and convergent with that of ancestral plesiosaurs, contemporaneous elasmosaurids, and some more basal members of the Polycotylidae. The conical, recurved, and narrow teeth are consistent with a piscivorous diet. The tall and anteroposteriorly broad cervical neural spines indicate large epaxial muscles, suggesting that Serpentisuchops used both its neck and snout in fast lateral strikes aimed at proportionately small prey.
A diverse fish paleofauna occurs in the upper Campanian portion of the Rybushka Formation exposed near Saratov city in the Saratov Oblast, Russia. Twenty taxa have been identified, including two holocephalans (Ischyodus bifurcatus and Amylodon karamysh), twelve elasmobranchs (Synechodus sp., Cederstroemia sp., Cretalamna cf. C. borealis, C. cf. C. sarcoportheta, Archaeolamna kopingensis, Eostriatolamia segedini, E. venusta, Pseudocorax laevis, Squalicorax kaupi, Squalicorax Morphology 1, Squalidae indet., and Squatirhina sp.), and six teleosts (Pachyrhizodus sp., Saurocephalus lanciformis, Paralbula casei, Enchodus cf. E. dirus, E. cf. E. gladiolus, and E. petrosus). Many of these taxa are new to the Campanian fish record of Russia, and the assemblage demonstrates that there is significant taxonomic overlap between the Rybushka Formation paleofauna and that of North America.
Marine reptile occurrences are rare in the Lower Jurassic Series outside of Europe. Here we describe diverse marine reptile faunas from the Lower Jurassic Series (Pliensbachian and Toarcian stages, including the Toarcian–Aalenian boundary interval) of Eastern Siberia. The taxonomic composition of Toarcian marine reptile assemblages of Siberia highlight their cosmopolitan nature, with the presence of taxa previously known nearly exclusively from coeval strata of Europe, such as ichthyosaurians Temnodontosaurus and Stenopterygius, microcleidid plesiosaurians (including the genus Microcleidus), rhomaleosaurids and basal pliosaurids. The palaeogeographic reconstruction places these faunas to the palaeopolar region, north of the 80th northern parallel and up to the palaeo north pole (upper value within the 95% confidence interval for some of the localities). The materials include remains of both mature and juvenile (or even infant, judging by their very small size and poor ossification) animals, indicating a possibility that these polar seas may serve as a breeding area. The diversity and abundance of plesiosaurians and ichthyosaurians, along with a lack of thalattosuchian remains (considering their wide distribution elsewhere at low latitudes), is an additional argument that plesiosaurians and neoichthyosaurians were able to live and reproduce in a polar environment. There is no certainty whether these animals lived in polar seas permanently, or whether they were taking seasonal migrations. However, given the polar night conditions at high latitudes, the latter seems more plausible, and both these scenarios are further indirect evidence that these groups likely had a high metabolism.
Throughout their evolution, tetrapods have repeatedly colonised a series of ecological niches in marine ecosystems, producing textbook examples of convergent evolution. However, this evolutionary phenomenon has typically been assessed qualitatively and in broad-brush frameworks that imply simplistic macroevolutionary landscapes. We establish a protocol to visualize the density of trait space occupancy and thoroughly test for the existence of macroevolutionary landscapes. We apply this protocol to a new phenotypic dataset describing the morphology of short-necked plesiosaurians, a major component of the Mesozoic marine food webs (ca. 201 to 66 Mya). Plesiosaurians evolved this body plan multiple times during their 135-million-year history, making them an ideal test case for the existence of macroevolutionary landscapes. We find ample evidence for a bimodal craniodental macroevolutionary landscape separating latirostrines from longirostrine taxa, providing the first phylogenetically-explicit quantitative assessment of trophic diversity in extinct marine reptiles. This bimodal pattern was established as early as the Middle Jurassic and was maintained in evolutionary patterns of short-necked plesiosaurians until a Late Cretaceous (Turonian) collapse to a unimodal landscape comprising longirostrine forms with novel morphologies. This study highlights the potential of severe environmental perturbations to profoundly alter the macroevolutionary dynamics of animals occupying the top of food chains.
Plesiosauria is an extinct clade of diapsid marine reptiles that evolved in the Late Triassic and radiated globally for the remainder of the Mesozoic. The recent description of a pregnant specimen of Polycotylus latipinnis demonstrates that some plesiosaurs were viviparous. To establish a baseline of histological data on plesiosaur ontogeny, we sampled the mother and fetus of the gravid plesiosaur specimen. To widen the base of data concerning ontogeny and life history of plesiosaurs, we gathered additional morphologic and histologic data from a securely identified growth series of polycotylids from the Pierre Shale of South Dakota. Paleohistological thin sections were prepared from the three humeri. Both adults show a dense, heavily remodeled cortex consisting entirely of longitudinally oriented secondary osteons, except for a thin rind of superficial primary bone. The mother exhibits an external fundamental system, indicating it was fully mature; the other adult does not. In both adults the cortex grades into a spongy medulla, comprising large vascular canals and erosion rooms surrounded by secondary lamellar trabecular bone, and lacking a marrow cavity. The fetal humerus possesses a medullary region similar to that of the Dolichorhynchops bonneri adult, although its lamellar bone is primary and deposited around calcified cartilage. The medulla is demarcated from the cortex by a prominent Kastschenko’s line. The cortex of the fetus is a relatively thin layer of periosteal woven bone, longitudinally to radially vascularized, and interfingered with columns of osteoblasts surrounded by rapidly-deposited extracellular matrix. The neonate humerus resembles the fetus, with its trabeculae identical in both size and histology, although it lacks calcified cartilage. The cortex is also similar but much thicker, consisting entirely of rapidly deposited, radially vascularized, woven to fibrolamellar bone. The cortex carries a line near its surface. This feature is not a line of arrested growth, but a sudden change in vascular angle and increase in bone density. We argue this feature is a birth line indicating a change in growth regime, possibly in response to increased hydrodynamic forces after birth. The birth line indicates that the neonate was about 40% of maternal length when born. Our histological data demonstrate that polycotylids had very high fetal growth rates, and that birth size was large. Comparison with the geologically oldest plesiosaur confirms that rapid growth evolved in the Triassic, although histological details differ, and the degree to which the polycotylid ontogenetic pattern is generalizable to other plesiosaurs is currently unknown. Further histological research utilizing full growth series is needed, particularly for Jurassic taxa.
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 recover Thililua and Mauriciosaurus as successive lineages at the base of the earliest Late Cretaceous polycotyline radiation. A new dataset summarizing the Bauplan of polycotylids reveals 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.
A nearly complete skeleton of a polycotylid
plesiosaur is described from
the early Late Cretaceous laminated
limestones at Vallecillo, northeast
Mexico. It shows extensive soft tissue
preservation. In some exceedingly
well preserved areas there are transversely
elongate rectangular to trapezoid
millimetric scale-like structures
arranged in longitudinal rows. The
trailing edge skin flap preserves fibers
and scale rows perpendicular to the
trailing edge. A thick layer of subdermal
tissue is present, especially along
the tail base. It was responsible for
the hydrodynamic drop-shaped body
contour, with the body and tail forming
a single unit. The body shape
determined from the preserved soft
tissues suggests a swimming speed
similar to extant leatherback turtles.
Based on the unique osteology of the
palate, which is intermediate between
Dolichorhynchops and Trinacromerum,
and according to the unique morphology
of the girdles and propodials
as well as the medially converging
gastralia, the new specimen is placed
in a new genus and species of Polycotylidae,
Mauriciosaurus fernandezi
gen. et sp. nov.
Isolated skeletal remains of elasmosaurid plesiosaurs are described from the upper Upper Maastrichtian of the type area of that stage and compared with material from the Maastrichtian of southern Belgium (Mons Basin) and Morocco. An overview of Maastrichtian elasmosaurids worldwide is presented. The rarity of elasmosaurids in the latest Cretaceous marginal seas of the type Maastrichtian as compared with their common occurrence in the oceanic waters near California and Morocco of that age may be related to food abundance in upwelling areas along the margins of continental plates.
This chapter presents comparative cranial anatomy of two North American cretaceous Plesiosaurs. The skulls of Elasmosaurus morgani and Dolichorhynchops osborni are compared as representatives of the Cretaceous plesiosaur families Elasmosauridae and Polycotylidae, respectively. Cranial features and the atlas-axis complex appear to be more stable evolutionarily than postcranial features. Similarities indicate that the short-necked Cretaceous polycotylids are the sister group to long-necked elasmosaurids. This implies that the short-necked polycotylids of the Cretaceous are not descended from the short-necked pliosaurs of the Jurassic. The chapter further elaborated the significance of similarities between Libonectes and Dolichorhynchops. The short neck has appeared independently at least twice in the Plesiosauria, and the term "pliosaur" to refer any short-necked plesiosaur should be abandoned to avoid any phyletic implications. Differences between Elasmosaurus morgani and Elasmosaurus platyurus demonstrate that the two species belong to a different genera and a new name is proposed for E. morgani.
A frontal of the mosasaur Clidastes propython from the Beloe Ozero locality in the Saratov Region (Rybushka Formation, Campanian Stage, Upper Cretaceous) is described. The investigated specimen differs from the frontals of other members of the genus Clidastes in the relatively straight lateral flanks. Reliable records of Clidastes outside America have previously been reported only from Great Britain, Sweden, and Germany. The new record from the Beloe Ozero locality expands the known geographical range of the species C. propython and genus Clidastes.
We report here a large mosasaur skull, preserved three-dimensionally in a concretion recovered from Ziebach County, South Dakota, USA. This fossil represents the first articulated mosasaur skull from the Trail City Member of the Fox Hills Formation and the first definitive occurrence of Mosasaurus hoffmanni Mantell, 1829 from that area and the northernmost occurrence in the Western Interior Seaway, greatly extending the paleobiogeographic range of this taxon. The age of this specimen is determined to be between 68.3 and 67.6 Ma based on the associated invertebrate fauna. Although previous authors have suggested synonomy of the North American Mosasaurus maximus Cope, 1869 and the European M. hoffmanni, this is the most comprehensive analysis to date and is based on comparisons with Mosasaurus specimens recovered across the Northern Hemisphere, allowing an emended diagnosis of the species M. hoffmanni. Minor differences are considered individual variation or to reflect ontogenetic stage, including slender dentaries in some individuals, range of development of the C-shaped notch of the coronoid and differences in the shape of the supratemporal fenestra.
The study of new finds of mosasaurids from the Izhberda locality (Southern Urals, Orenburg Region) has made it possible to record for the first time the presence of mosasaurs from the subfamilies
Mosasaurinae, Tylosaurinae, and Plioplatecarpinae from the Upper Cretaceous of the Orenburg Region, including representatives of the genera Mosasaurus, Prognathodon, and Clidastes, which are known from the Upper Cretaceous of North America and Western Europe. Of interest is the discovery of the tylosaurine Taniwhasaurus, previously known from New Zealand, Antarctica, South Africa, and Japan. Therefore, the Campanian mosasaurid fauna of the Southern Urals is intermediate and includes North American–European and Asia–Pacific taxa. However, all the finds of mosasaurs from the Izhberda locality can only be identified in
open nomenclature, which makes detailed comparisons of the faunas difficult. Revision of the type series of mosasaur Liodon rhipaeus Bogolyubov, 1910 from the Southern Urals has allowed us to conclude that, in addition to the three mosasaurian vertebrae, it includes the ischium and posterior fragment of the mandible of a plesiosaur. Liodon rhipaeus is clearly a nomen dubium and the vertebrae of its type series cannot be iden-
tified more precisely than Tylosaurinae indet.
Here we describe the first findings of reptile remains in the Upper Cretaceous marine strata of Siberia, which represent the northernmost occurrences of plesiosaurians, ?mosasaurids and turtles in the Cretaceous of Eurasia (66-72° N palaeolatitudes). The specimens come from the upper Cenomanian, Turonian and Coniacian of the Pyasina River basin, Santonian and Maastrichtian of the Tanama River and upper Santonian–lower Campanian of the Kheta River. They include remains of polycotylid and elasmosaurid plesiosaurians, as well as indeterminate small and osteologically immature plesiosaurians, indicating a somewhat typical Late Cretaceous plesiosaurian assemblage at the Arctic Polar Circle and implying that these shallow-water regions possibly used by plesiosaurians as a birth and nursery areas during the polar summer. In addition to plesiosaurian remains, a partial carinate ?mosasaurid tooth, and two turtle shell fragments, assigned to either non-marine Macrobaenidae or to marine Chelonioidea, and to non-marine Testudinoidea, are discovered, providing first direct evidence for the presence of these reptile groups in the Late Cretaceous of Northern Siberia. The findings of turtles are the northern most records of this group in the Cenomanian and Coniacian of Eurasia, which parallels previous records from the upper Cenomanian of Arctic Canada, and further supports warm climate conditions during the Cretaceous Greenhouse at high latitudes. Therefore, the Cenomanian–Turonian Boundary Event associated to the climate warming and to the beginning of the Cretaceous thermal maximum is well-recognized in Northern Siberia showing an expression of this “global” event over the Arctic region.
A partial elasmosaurid plesiosaur skeleton (DMNH V.90000) recovered from the Juana Lopez Member, Carlile Shale of southeastern Colorado is stratigraphically unique. The contextual occurrence of the Juana Lopez elasmosaur is rare both in terms of geologic age (late Middle Turonian) and paleoecology (littoral shore deposit). The skeletal anatomy contains diagnostic characters of an intermediate grade of derivation although the paucity of material prevents formal naming of a new taxon. Another partial elasmosaurid skeleton (UNSM 50134, also known as the Holyrood elasmosaur) from the Lincoln Limestone (Middle Cenomanian), Greenhorn Limestone of central Kansas is similarly unique in terms of context. The Holyrood elasmosaur also occurs in littoral shore deposits and possesses a unique suite of plesiomorphic characters previously undocumented within Elasmosauridae of the Western Interior Seaway. Dimensional data for vertebrae and appendicular elements leads to a refined generalization that there are minimally three lineages of elasmosaurids present in the Western Interior Seaway; a plesiomorphic group (equidimensional mid-cervical centra, elongate podials), a group intermediate in morphology (elongate mid-cervicals, equidimensional podials), and a derived group (highly elongate mid-cervicals, foreshortened podials). The plesiomorphic group is represented by UNSM 50134 (Holyrood elasmosaur), a new genus and species described herein (Plesioelasmosaurus walkeri, gen. et sp. nov.). Gastroliths are present with both specimens, reinforcing the prevalence of silicic stones routinely occurring within elasmosaurid partial skeletons, and the link of elasmosaurid ecology to nearshore environments. Shared plesiomorphic limb traits among early (Cenomanian) representatives of both elasmosaurid and polycotylid lineages may serve as an indicator of shared heritage (Xenopsaria) and subsequent convergent evolution of foreshortened limb elements.
Polycotylids were a clade of shorth-necked plesiosaur that achieved a worldwide distribution and a peak of diversity during the Albian-Turonian, reaching the K/Pg mass extinction with a relative low diversity. One of the youngest polycotylids worldwide recorded is Sulcusuchus erraini, from Los Alamitos and La Colonia formations (Patagonia). Here, a new polycotylid specimen, also from Maastrichtian levels of the La Colonia Formation, is described; and the affinities of the new material and Sulcusuchus erraini are evaluated. Additionally, the phylogenetic position of Sulcusuchus erraini is reevaluated recovering Sulcusuchus erraini outside the Occultonectia, the latter comprising only Cenomanian-Turonian polycotylids. However, additional analysis indicate that the position of S. erraini is far from being well resolved.
Community zonation of the Late Cretaceous Western Interior Seaway (WIS) has been suggested for bivalves, cephalopods, foraminifera, gastropods, and tetrapods. Most proposed WIS community zones consist of a northern and southern subprovince with a gradational boundary across central or south-central North America. Since it has been over three decades since the WIS community zonation hypothesis has been investigated for vertebrates, recent radiometric age determinations, taxonomic revisions, additional specimen discoveries, and recently available online museum specimen catalogues allow for an updated description of Manitoba (MB) escarpment faunal assemblages and testing of the community zonation hypothesis. Nine time bins were used to represent nine Upper Cretaceous lithostratigraphic units of the MB escarpment to test the zonation hypothesis consistency for nearly the entire Late Cretaceous (~71–95 Ma). Relatively high genus-level community similarity values (25–50%) of south-central WIS localities and low values (<20%) of localities furthest north and south support the existence of a central subprovince during late Cenomanian to early Turonian and late Coniacian to early Campanian times, when the gradational subprovincial boundary would have been furthest south between Kansas and Texas localities. Comparatively low genus-level community similarity values (<25%) of all localities south of MB during mid-Cenomanian and early to mid-Campanian times indicate the southern subprovincial boundary was farthest north between MB and South Dakota localities during these time intervals and had migrated throughout the Late Cretaceous. This work highlights significant fluctuations in vertebrate community zonation throughout the WIS through time and space and offers insight into the magnitude of compositional and palaeoecological changes that can occur in shallow marine vertebrate communities over an approximately 25 million year interval.
The Campanian Beloe Ozero locality within the Rybushka Formation in Saratov Province, Russia, produces numerous isolated bones of sea turtles (clade Pan-Chelonioidea) identified as belonging to Protostega gigas, a giant protostegid, previously reliably known only from the Coniacian – Campanian of North America, and Pan-Chelonioidea indet. The Protostega gigas specimens described in this paper include bones of the skull (maxillae, jugal, ?quadratojugal, and squamosal), shell (neural, peripherals, and hypoplastron), and appendicular skeleton (scapula and humeri). The material of Pan-Chelonioidea indet. demonstrates similarity with representatives of non-Protostega protostegids, Toxochelys spp., ctenochelyids, dermochelyids, and pan-cheloniids. The estimated size of the Protostega gigas specimens from the Beloe Ozero locality well corresponds to those of the largest specimens of this species from North America. Protostega gigas from the Beloe Ozero locality represents the first finding of this species outside North America and the first reliable evidence of its cosmopolitanism.
Plesiosaur specimens from the Upper Jurassic of European Russia are mainly referable to the genus Colymbosaurus Seeley, 1874, based on elongated propodials with extensive posterodistal expansion, and relatively short mid-cervical vertebrae. However, a historical specimen described by Bogolubov (1911) and subsequently revised as Plesiosauria indet. (Storrs et al. 2000) was hitherto the only and ambiguous evidence for the presence of Colymbosaurus in the Upper Jurassic of European Russia. Here, we provide descriptions of several specimens from the Volgian of European Russia referable to Colymbosaurus sp. and Colymbosaurinae indet. The presence of Colymbosaurus in the Late Jurassic (Volgian/Tithonian) of the Middle Russian Sea makes it possible to formulate hypotheses on herpetophauna exchange between NW Europe, Svalbard and European Russia. Found only in these basins, Colymbosaurus is a unifying element of marine herpetofauna in the Panboreal palaeobiogeographic superrealm.
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.
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* [zverkovnik@mail.ru], 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 [dzharakuduk@mail.ru], 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 [elasmodus74@gmail.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.
The holotype of Libonectes atlasense is an almost complete skeleton from Upper Cretaceous (mid-Turonian)
rocks of the Goulmima area in eastern Morocco. Initial assessment of this specimen in 2005
proposed generic referral based on stratigraphical contemporaneity with Libonectes morgani from the
CenomanianeTuronian of Texas, U.S.A. Nevertheless, relative differences in the profile of the
premaxillary-maxillary tooth row, position of the external bony nasal opening, number of teeth and
rostrad inclination of the mandibular symphysis, proportions of the axial neural arch, and number of
cervical and pectoral vertebrae were used to distinguish between these species. As part of an on-going
comparative appraisal of elasmosaurid plesiosaurian osteo-anatomy, we re-examined the type and
formally referred material of both L. atlasense and L. morgani in order to establish species validity, as well
as compile a comparative atlas for use in future works. Our inspections revealed that these reportedly
distinct species-level fossils are in fact virtually indistinguishable in gross morphology. Indeed, the only
substantial difference occurs in relative prominence of the midline keel along the mandibular symphysis,
which might be explained by intraspecific variation. Furthermore, our observations permit an amendment
to the published generic diagnosis of Libonectes with the confirmation of important states such as
the likely presence of a pectoral bar, distocaudad expansion of the humerus, and an epipodial foramen. In
addition, novel features include a prominent ‘prong-like’ ventral midline process on the coracoids, and
the development of a median pelvic bar that encloses a central fenestration. The composite remains of
L. morgani thus constitute one of the most complete elasmosaurid skeletal hypodigms documented
worldwide, and evidence a trans-Atlantic distribution for this apparently dispersive species during the
earlyeLate Cretaceous.
The most complete specimen of the plesiosaur genus Polycotylus from the Upper Cretaceous of the southern Urals is described. This specimen has much in common with the species P. latipinnis described from North America, but differs in the limb structure and cranial bones, so that it is assigned to a separate species, Polycotylus sopozkoi sp. nov.
The holotype of Plesiosaurus houzeaui Dollo, 1909 consists of plesiosaurian bones, discovered in the Spiennes Chalk (Upper Campanian) of the Ciply area (Mons Basin, Belgium). The description of the type material shows that Plesiosaurus houzeaui is an invalid species based on heterogeneous elasmosaurid and also probably non-elasmosaurid plesiosaurian material. A review of plesiosaurian material previously described from the Upper Cretaceous of Europe indicates that Elasmosauridae and Pliosauridae are represented. Polyptychodon is the only valid genus of pleiosaur from the Upper Cretaceous of Europe. -Authors
A new polycotylid plesiosaur from the early Turonian (Upper Cretaceous) of the region of Goulmima, Morocco, is described. The holotype of Manemergus anguirostris n. gen. et sp. comprises the subcomplete axial skeleton and partial appendicular skeleton of an articulated juvenile individual. Owing to the young age of the specimen, the nature of anatomical variation during ontogeny in plesiosaurs is discussed. The new taxon is characterised by its skull architecture combining a narrow, relatively short rostrum and a box-like post-orbital segment, and slender, smooth teeth. The state of preservation of the specimen hints at a relative in vivo stiffness of the neck due to strong ligamentous intervertebral connections.
A nearly complete skeleton of Polycotylus latipinnis (SDSM 23020) from the upper Niobrara Formation (early Campanian) of South Dakota (U.S.A) greatly improves information for this formerly poorly known taxon. Specimens SDSM 23020 and YPM 1125 (paratype P. latipinnis) exhibit numerous postcranial characters that distinguish Polycotylus, in particular presacral vertebral count, nature of chevron facets, unique ilia, and highly derived paddles including five epipodial ossifications and increased hyperphalangy. Greater vertebral and phalangeal counts of Polycotylus are accompanied by exceptional foreshortening; thus, the relative body and limb proportions are likely similar to less derived polycotylids, with fewer, more elongate vertebrae and phalanges. The complete skull, derived among polycotylids, has short temporal fenestrae, elongate frontals, exceptionally slender parasphenoid with prominent cultriform process, and exceptionally long extensions of the angulars and splenials within the mandibular symphysis. Cladistic analysis indicates that Polycotylus nests firmly within derived Polycotylidae as a potential sister taxon to Dolichorhynchops osborni and Trinacromerum, despite a ‘primitive’ presacral vertebral count. Future improvements in available data, in particular better information regarding basal polycotylids, and refinement of character selection to nullify homoplasy could significantly alter the tree structure to show distinct subgroups within Polycotylidae. North American polycotylids with elongate temporal fenestrae, elongate podials, and relatively long vertebrae are confined to occurrences of late Cenomanian and earliest Turonian age, whereas polycotylids distinctly foreshortened in these respects are restricted to post-Turonian occurrences. Ilium morphology is highly variable among polycotylids and, in addition to taxonomic utility, may be in part attributable to sexual dimorphism. Citation for this article: Schumacher, B. A., and J. E. Martin. 2015. Polycotylus latipinnis Cope (Plesiosauria, Polycotylidae), a nearly complete skeleton from the Niobrara Formation (early Campanian) of southwestern South Dakota. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2015.1031341. 2015
A plesiosaur skeleton from the base of the Greenhorn Limestone (lower upper Cenomanian), western South Dakota, represents a new taxon tentatively referred to the Polycotylidae. The specimen possesses a number of features in common with the Polycotylidae, including an exceptionally elongate muzzle and mandibular symphysis, lack of a parietal foramen, homodont dentition, and faint striae only on the medial side of teeth. However, the palate and limb morphologies differ with respect to Polycotylidae as currently known. The pterygoids are united along their midline anterior to the parasphenoid, lacking an anterior interpterygoid vacuity. The preserved parasphenoid is relatively robust, possesses a strong ventral keel, and is sutured to the dorsal surface of the pterygoids. The paddles possess many plesiomorphic features, including only relatively minor postero-distal expansion of the propodials, epipodials that are longer than wide, a distinct antebrachial foramen, and relatively elongate phalanges. Derived features make it a plausible representative sister taxon to Polycotylidae, a prospect that is complemented by its stratigraphic position. This hypothesis is hampered by the palate morphology, which suggests a separate lineage of short-necked plesiosaurs far removed from genera classically assigned to Polycotylidae (Dolichorhynchops, Polycotylus, Trinacromerum). Nevertheless, the specimen represents the persistence of plesiomorphic limb traits and possession of a closed palate within an early polycotylid lineage until at least the early late Cenomanian in the Midcontinent of North America.