Short-necked Plesiosaurs Research Articles

Polycotylidae (Sauropterygia, Plesiosauria) from the La Colonia Formation, Patagonia, Argentina: Phylogenetic affinities of Sulcusuchus erraini and the Late Cretaceous circum-pacific polycotylid diversity

Polycotylids were a clade of short-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.

A Turonian Polycotylid Plesiosaur (Reptilia: Sauropterygia) from Obira Town, Hokkaido, and Its Biostratigraphic and Paleoecological Significance

Abstract. The Polycotylidae are short-necked plesiosaurs known from the Cretaceous in various parts of the world, but only a few occurrences have been documented in Japan, where elasmosaurid remains are much more common. An indeterminate polycotylid specimen from the Upper Cretaceous in Obira Town, Hokkaido, is described. Characteristics of the vertebrae and clavicular arch support its taxonomic affinity. The Turonian occurrence of the specimen indicates the continuous presence of the Polycotylidae across the Cenomanian-Turonian boundary in the northwestern Pacific. Macroscopic osteological features of the vertebrae and clavicular arch indicate an advanced stage of ossification, and there are histological characteristics suggesting slowed growth. The osteoporotic-like condition implies a high degree of aquatic adaption.

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 characterized as apex predators [2-5], whereas members of the distantly related clade Polycotylidae (middle to 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 convergencewith 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 EarlyCretaceous. 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.

Earliest North American occurrence of Polycotylidae (Sauropterygia: Plesiosauria) from the Lower Cretaceous (Albian) Clearwater Formation, Alberta, Canada

The polycotylidae is a family of short-necked (pliosauromorph) plesiosaurs, with examples known from epicontinental marine deposits of every major landmass except Antarctica. Our knowledge of its diversity and distribution has increased tremendously in the last decade, with new material described from North America (Sato, 2005; Albright et al., 2007; Schumacher, 2007; Schmeisser, 2008), South America (Gasparini and de la Fuente, 2000; Salgado et al., 2007), Africa (Bardet et al., 2003; Buchy et al., 2005), and Asia (Sato and Storrs, 2000; Arkhangel'skii et al., 2007). Polycotylid diversity is greatest in the Late Cretaceous, and particularly so in the Turonian; however, knowledge of the group's initial history in the Early Cretaceous is limited to a handful of specimens from North America (Storrs, 1981; Druckenmiller, 2002) and Australia (Kear 2003, 2005).

Unusual occurrence of gastroliths in a polycotylid plesiosaur from the Upper Cretaceous Tropic Shale, southern Utah

A polycotylid plesiosaur (Dolichorhynchops sp.), recently discovered in the Upper Cretaceous (Cenomanian-Turonian) Tropic Shale in Glen Canyon National Recreation Area, southern Utah, is associated with 289 gastroliths. This specimen is significant due to the general lack of gastroliths associated with most short-necked plesiosaur skeletons. The skeleton (MNA V10046) was excavated from a stratigraphic interval of marine shale that does not contain coarser-grained material. The stones were generally concentrated in one area of the skeleton, with the majority situated near the back of the skull. The stones are mainly composed of dark grey chert, are smooth and well rounded, and have varying degrees of polish. The majority of the stones are spherical in shape and are likely fluvial in origin. The gastroliths from this animal are similar in shape and number to those documented from elasmosaurid plesiosaurs. The gastroliths from MNA V10046, however, are much smaller and weigh considerably less than most elasmosaurid stomach stones. Given the lack of comparative material from other short-necked plesiosaurs, the size and mass differences are attributed to differences in function of gastroliths between long- and short-necked plesiosaurs.

Short-necked plesiosaurs of the family Polycotylidae from the Campanian of the Saratov Region

Fragments of the anterior part of a mandibular rostrum and a maxillary bone of the plesiosaur Polycotylidae indet. from the Karyakino and Beloe Ozero localities of the Saratov Region (Upper Cretaceous, Campanian) are described. The specimens belong to a relatively long-snouted polycotylid with a mandibular symphysis incorporating 13 pairs of teeth. A unique feature of this plesiosaur is the fact that, in the symphysis, the splenial extends to the very anterior end of the rostrum. The polycotylid from the Campanian of the Saratov Region is probably closely related or identical to Georgiasaurus from the Santonian of the Penza Region, in which structural details of the mandibular symphysis remain uncertain.

Plesiosaurs from the Upper Cretaceous (Cenomanian–Turonian) Tropic Shale of southern Utah, part 2: Polycotylidae

ABSTRACT Recent fieldwork in the Tropic Shale of southern Utah has resulted in the recovery of several specimens of short-necked plesiosaurs including both polycotylid plesiosauroids and pliosaurids. This report focuses on the former, whereas the latter are discussed in an accompanying paper. Although the Late Cretaceous Cenomanian/Turonian Stage boundary falls within the lower few meters of the Tropic Shale, all but one of the specimens were found in lower Turonian strata based on molluscan assemblages found in direct association with the skeletal material. The plesiosauroid family Polycotylidae is represented by at least three taxa: (1) the ‘typical’ late Cenomanian/early Turonian Trinacromerum; (2) Eopolycotylus rankini, gen. et sp. nov., a new genus and species that shares synapomorphies with the late Santonian/early Campanian Polycotylus latipinnus; and (3) Palmula quadratus, gen. et sp. nov., another new taxon that shares synapomorphies with unnamed taxa from the late Cenomanian of South Dakota and Japan. Cladistic analysis supports the division of the Polycotylidae into two new subfamilies, here designated the Polycotylinae and the Palmulainae. The Turonian plesiosaur fauna of the Tropic Shale, and consequently the large vertebrate fauna of the Cretaceous Western Interior Seaway, is considerably more diverse than previously realized, and there is no indication that this fauna suffered any negative consequences as a result of global scale oceanographic events, including marine extinctions, that transpired during late Cenomanian-early Turonian time.

Osteology of a new plesiosaur from the lower Cretaceous (Albian) Thermopolis Shale of Montana

ABSTRACT A new taxon of Cretaceous short-necked plesiosaur, Edgarosaurus muddi, gen. et sp. nov., is described. The specimen consists of a complete skull, 34 vertebrae including the entire series of 26 cervicale, and a nearly complete forelimb. The new taxon occurs in marine sediments of the Thermopolis Shale (late Albian), deposited during an early transgression of the Western Interior Seaway. The skull of Edgarosaurus is the oldest, and one of the best preserved plesiosaur specimens from the Cretaceous Western Interior of North America described to date. Edgarosarus differs from the morphologically and stratigraphically close short-necked taxon Plesiopleurodon wellesi in a number of cranial characters. In the absence of an established phylogenetic framework, the new plesiosaur is placed in the Polycotylidae, as recently defined by Carpenter in 1996. It is plesiomorphic with respect to other polycotylids in that it possesses a relatively robust and moderately elongated rostrum, a pineal foramen, caniniform teeth, a shorter mandibular symphysis, and a relatively high number of cervical vertebrae.

AN EARLY POLYCOTYLID PLESIOSAUR (REPTILIA: SAUROPTERYGIA) FROM THE CRETACEOUS OF HOKKAIDO, JAPAN

A partial skeleton of a short-necked plesiosaur excavated from the Upper Cenomanian of the Middle Yezo Group of Hokkaido, Japan, includes disarticulated vertebrae, the right half of the pectoral girdle, fragments of the pelvic girdle, ribs, gastralia, and gastroliths. Gastroliths are unusual in short-necked plesiosaurs. Skeletal characters indicate that the specimen belongs to the Family Polycotylidae, well known from North America, the former Soviet Republics, and possibly from New Zealand. They are rare in East Asia and hitherto unknown from Japan. Extensive ossification indicates that this specimen is an adult individual, yet it is smaller than the adult specimens of other known polycotylids. The elongated epipodial bones are a unique character of the specimen but are probably plesiomorphic. The fossil is evidence of biogeographical diversification of the family at the beginning of the Late Cretaceous.

An early polycotylid plesiosaur (Reptilia: Sauropterygia) from the Cretaceous of Hokkaido, Japan

A partial skeleton of a short-necked plesiosaur excavated from the Upper Cenomanian of the Middle Yezo Group of Hokkaido, Japan, includes disarticulated vertebrae, the right half of the pectoral girdle, fragments of the pelvic girdle, ribs, gastralia, and gastroliths. Gastroliths are unusual in short-necked plesiosaurs. Skeletal characters indicate that the specimen belongs to the Family Polycotylidae, well known from North America, the former Soviet Republics, and possibly from New Zealand. They are rare in East Asia and hitherto unknown from Japan. Extensive ossification indicates that this specimen is an adult individual, yet it is smaller than the adult specimens of other known polycotylids. The elongated epipodial bones are a unique character of the specimen but are probably plesiomorphic. The fossil is evidence of biogeographical diversification of the family at the beginning of the Late Cretaceous.

Cretaceous plesiosaurs ate ammonites

The Plesiosauria, large Mesozoic marine reptiles, have been regarded as dominant predators in Mesozoic seas, although there is only a little (including some doubtful) direct evidence of their stomach contents1,2,3,. Here we report the occurrence in Hokkaido, northern Japan, of a partial skeleton of a Cretaceous short-necked plesiosaur together with a large number of isolated ammonoid jaws. This is, to our knowledge, the first description of the stomach contents of a polycotylid plesiosaur, and the first firm evidence of prey-predator relationships between plesiosaurs and ammonites.

A review of short-necked plesiosaurs from the Cretaceous of the Western Interior, North America

A review of short-necked plesiosaurs from the Cretaceous of the Western Interior, North America

Taxonomy and taphonomy of Rhomaleosaurus zetlandicus (Plesiosauria, Reptilia) from the Toarcian (Lower Jurassic) of the Yorkshire coast

SUMMARY The holotype skeleton of the large-headed, short-necked plesiosaur Plesiosaurus zetlandicus Phillips, in Anon., 1854 comes from the Toarcian of the Yorkshire coast and has been housed in the Yorkshire Museum since 1852. It is a pliosauroid of the genus Rhomaleosaurus. Rhomaleosaurus zetlandicus (Phillips, in Anon., 1854) is the earliest named valid species of any Toarcian pliosauroid. The skeleton is preserved in a pyritous nodule requiring mechanical preparation using tungsten carbide percussion tools, including electric engravers holding specially fabricated tungsten carbide needles. This technique is useful for similar material. The animal probably floated at the surface of the sea after death until rupture of the body cavity by decay or scavenging released the gases of putrefaction and the corpse sank upside down to the sea floor.

CRETACEOUS VERTEBRATES FROM THE ANDERSON RIVER N.W.T.

Vertebrate remains have been recovered from two horizons in late Cretaceous strata along the east bank of the Anderson River at latitude 69 °N. The lower horizon has produced a fauna very similar to that of the Niobrara Chalk in western Kansas, including mosasaurs, plesiosaurs, and abundant toothed birds. The upper horizon has yielded a moderately short-necked plesiosaur of cimoliasaurian affinities. These vertebrates lived in or near a strait linking the Arctic Ocean with the interior sea in very late Cretaceous time.