[Paleontology • 2025] The Osteology, Taxonomy, and Phylogenetic Placement of Seeleyosaurus guilelmiimperatoris (Plesiosauroidea: Microcleididae) from the Lower Jurassic Posidonia Shale of Germany

 

Seeleyosaurus guilelmiimperatoris (Dames, 1895) 

Sachs, Madzia, Marx, Roberts, Hampe et Kear, 2025. 

 DOI: doi.org/10.1002/ar.25620 

Researchgate.net/publication/389208223

Abstract

Seeleyosaurus guilelmiimperatoris is an early-diverging plesiosauroid from the lower Toarcian (Lower Jurassic) of the Posidonienschiefer Formation (Posidonia Shale) of Holzmaden, southwestern Germany. It is known from almost complete skeletons of two osteologically mature individuals, the holotype and a referred specimen that was largely destroyed during World War II. Although well-preserved and substantially complete, the anatomy of Seeleyosaurus and its taxonomic and phylogenetic significance remain insufficiently understood. Here, we provide a complete osteological description of the taxon. Seeleyosaurus guilelmiimperatoris can be diagnosed based on a unique combination of characters, including one autapomorphy: the tall and basally constricted neural spines of the posterior cervical, pectoral, and dorsal vertebrae which have a sinusoidal shape in lateral view. Our study supports the validity of the plesiosauroid taxon Plesiopterys wildi, which was considered a junior synonym of Seeleyosaurus in a previous joint assessment of the taxa. Our phylogenetic evaluation places S. guilelmiimperatoris among Microcleididae, in congruence with previous studies. However, in contrast to earlier phylogenetic reconstructions, our analyses, which take into account numerous changes to the character matrix, reconstruct S. guilelmiimperatoris as falling within the Microcleidus clade. While we admit that Seeleyosaurus might potentially be considered a species of Microcleidus, we refrain from promoting this nomenclatural change pending an osteological and taxonomic reassessment of Microcleidus spp. as well as other, potentially closely related forms, such as Lusonectes sauvagei.

Keywords: Plesiosauria, Microcleididae, Seeleyosaurus, Toarcian, Lower Jurassic, Germany

Skeleton of the referred specimen of Seeleyosaurus guilelmiimperatoris (SMNS 12039). (a) initial slab mount with original skull and unaltered paddles (from Fraas, 1910a, plate 6). (b) cast of the modified skeleton with modeled skull and arranged paddles (SMNS collection). Scale equals 50 cm.

Seeleyosaurus (left) and Thaumatosaurus, now Meyerasaurus (right)

as depicted in Water reptiles of the past and present (1914)

Sven Sachs, Daniel Madzia, Miguel Marx, Aubrey J. Roberts, Oliver Hampe and Benjamin P. Kear. 2025. The Osteology, Taxonomy, and Phylogenetic Placement of Seeleyosaurus guilelmiimperatoris (Plesiosauroidea, Microcleididae) from the Lower Jurassic Posidonia Shale of Germany. The Anatomical Record. DOI: doi.org/10.1002/ar.25620 [21 February 2025]

 Researchgate.net/publication/389208223_The_osteology_taxonomy_and_phylogenetic_placement_of_Seeleyosaurus_from_the_Lower_Jurassic_Posidonia_Shale_of_Germany

[Paleontology • 2025] Plesionectes longicollum • An unusual early-diverging plesiosauroid from the Lower Jurassic Posidonia Shale of Holzmaden, Germany

Plesionectes longicollum 

Sachs​ & Madzia, 2025 

DOI: doi.org/10.7717/peerj.19665 

life reconstruction by Peter Nickolaus.

 facebook.com/DanielMadzia

Abstract 

The lower Toarcian Posidonia Shale at Holzmaden, Southwest Germany, has yielded some of the most remarkable Lower Jurassic marine tetrapod specimens, including five plesiosaur taxa identified from nearly complete skeletons. This study provides a comprehensive description of an osteologically immature plesiosauroid skeleton found in a Holzmaden quarry in 1978. Despite that the specimen has been researched in the past, previous studies have been either brief or targeted some specific aspects of the specimen, such as its soft tissue preservation. The anatomy and taxonomy of the specimen have never been explored in detail. We reinterpret several of its osteological features and evaluate their taxonomic and phylogenetic significance. Our findings reveal that the specimen possesses an unusual combination of character states, which are not markedly affected by ontogenetic development, warranting the designation of a new taxon, Plesionectes longicollum gen. et sp. nov., thereby increasing the known plesiosaur diversity of both the Toarcian age and the Posidonia Shale.

Skeleton of Plesionectes longicollum gen. et sp. nov. (SMNS 51945).

Scale bar equals 30 cm.

Plesiosauria De Blainville, 1835

Plesiosauroidea Gray, 1825

Plesionectes gen. nov.

 

Etymology. The name Plesionectes derives from plēsíon (Greek), meaning “close”, “near”, referring to its plesiosaur affinities, and nēktēs (Greek), “swimmer”, common suffix in plesiosaur taxon names.

Plesionectes longicollum sp. nov.

Type locality and horizon. Holzmaden, Esslingen District, Baden-Württemberg, southwestern Germany; lower Toarcian (Lias ɛII1, ‘Koblenzer’, Dactylioceras tenuicostatum Zone, D. semicelatum Subzone; Hauff, 1921; Riegraf, Werner & Lörcher, 1984; Maisch, 2021), Lower Jurassic.

Diagnosis. Plesiosauroid plesiosaur bearing following unique combination of characters states: paraoccipital process being considerably longer as the height of the exoccipital body; neck comprising ≥43 cervical vertebrae; V-shaped neurocentral suture in the cervical and pectoral vertebrae (potential local autapomorphy sensu Beeston et al., 2024); conjoined parapophysis and diapophysis in the anterior, middle, and the majority of the posterior cervicals, one rib facet formed in the posteriormost cervical vertebrae; cervical rib processes strap-shaped and pronounced in anterior and mid-neck region; posterior cervical and pectoral neural spines not considerably taller than long (mostly < 1:2), lacking constriction at base; dorsal vertebral series comprising 20–21 vertebrae.

Etymology. The name longicollum derives from longus (Latin), meaning “long”, and collum (Latin), “neck”, in reference to its long neck, comprising at least 43 vertebrae.

Plesionectes longicollum 

life reconstruction by Peter Nickolaus.

Sven Sachs​ and Daniel Madzia. 2025. An unusual early-diverging plesiosauroid from the Lower Jurassic Posidonia Shale of Holzmaden, Germany. PeerJ. 13:e19665. DOI: doi.org/10.7717/peerj.19665 

 facebook.com/DanielMadzia/posts/10239111282586232

[Paleontology • 2024] Franconiasaurus brevispinus • Exquisite Skeletons of A New transitional Plesiosaur fill gap in the Evolutionary History of plesiosauroids

  Franconiasaurus brevispinus 

Sachs, Eggmaier & Madzia, 2024

DOI: 10.3389/feart.2024.1341470

  (artwork by Joschua Knüppe).

Plesiosaurs are Mesozoic reptiles fully adapted to an aquatic lifestyle. Throughout their evolutionary history exceeding 140 million years plesiosaurs dispersed globally, achieved substantial diversity, occupied a variety of ecological niches, and experienced multiple faunal turnovers. Of those, the Early/Middle Jurassic transition event (∼175–171 Mya) has recently became of increased interest because it apparently profoundly affected all three major lineages of plesiosaurs. Once dominant Rhomaleosauridae started to vanish, while Pliosauridae and Plesiosauroidea diversified and gave rise to several clades that flourished for tens of millions of years. Here, we report exquisite, three-dimensionally preserved skeletons of a new plesiosaur from the Lower Jurassic of Germany. Franconiasaurus brevispinus gen. et sp. nov. lived during the late Toarcian (∼175 Mya), near the onset of the Early–Middle Jurassic turnover. Franconiasaurus displays an intriguing mixture of features, combining characters almost uniformly distributed among early plesiosaurs with those typically observed in later-diverging members of the clade. Phylogenetic analyses firmly place Franconiasaurus as the sister taxon to Cryptoclidia, bridging an evolutionary gap between early plesiosauroids, such as Plesiosaurus-like forms and microcleidids, and later-diverging representatives of the clade, such as cryptoclidids, leptocleidians, and elasmosaurids.

  Diagnostic skeletal elements of the type specimen of Franconiasaurus brevispinus gen. et sp. nov. (BT 011224.00).
(A) main slab showing partly articulated skeleton in dorsal view. Posterior part of right mandibular ramus in (B) lateral and (C) dorsal aspect; anterior cervical vertebra (D) in articular and (E) lateral view; (F) posterior cervical vertebra in lateral view; (G) cervical rib in dorsolateral view; (H) dorsal vertebra in posterior view; (I) left scapula in medial view; (J) right coracoid in supposed dorsal view; (K) left humerus in dorsal view; (L) left femur with adjacent epipodials in dorsal view; and (M) left ilium in lateral view.

Systematic paleontology

Plesiosauria de Blainville, 1835 

Plesiosauroidea Gray, 1825 

Franconiasaurus gen. nov.

 

Etymology—After the region of Franconia (Franken in German), located in the northern part of Bavaria in southern Germany, where the specimens were found; and “σαῦρος” (sauros), Greek for “reptile”.

Franconiasaurus brevispinus sp. nov.

Diagnosis—A plesiosauroid diagnosed through the following unique combination of characters: surangular with transversely narrow dorsal side and convex lateral side, lacking a longitudinal lateral through; cervical centra amphicoelous, being wider than long/high; cervical zygapophyses narrower than centra, having planar facets and being not connected for most of their length; anterior cervical neural spines curve posterodorsally, posterior cervical neural spines inclined straight posterodorsally; posterior cervical and dorsal neural spines only moderately higher than long (height/length ratio approximately 1.6); cervical ribs with reduced anterior processes; dorsal process of scapula with slightly convex medial side, lacking a buttress like medial enforcement; long intercoracoid symphysis, coracoids being only slightly separated posteromedially; coracoid cornu does not extend to the level of the glenoid; ilium shaft straight, dorsal and ventral ends of ilium perpendicular to one another; femora and humeri subequal in length; propodials moderately elongate (length/width ratio 1.7); radius and tibia subquadratic with concave pre- and postaxial sides.

Type specimen—BT 011224.00, nearly complete, three-dimensionally preserved, and partly articulated skeleton.

 

Horizon and locality—The specimens were excavated in 2005 (BT 011241.00) and between 2014 and 2018 (BT 011224.00) by one of us (S.E.) in the lower section of the Jurensismergel Formation (Grammoceras thouarsense Zone), upper Toarcian, Lower Jurassic, in the Mistelgau fossil pit, Bayreuth District, Bavaria, Germany. For detailed information on the geological and stratigraphic settings see Electronic Supplementary Material S2.

Etymology—The name brevispinus refers to the low neural spines in the posterior cervical and dorsal vertebrae.

 Life reconstruction of Franconiasaurus brevispinus gen. et sp. nov. 

  (artwork by Joschua Knüppe).

Sven Sachs, Stefan Eggmaier and Daniel Madzia. 2024. Exquisite Skeletons of A New transitional Plesiosaur fill gap in the Evolutionary History of plesiosauroids. Front. Earth Sci. 12. DOI: 10.3389/feart.2024.1341470

[Paleontology • 2023] Lorrainosaurus keileni • The Rise of Macropredatory Pliosaurids near the Early-Middle Jurassic Transition

 Lorrainosaurus keileni   

 in Sachs, Madzia, Thuy & Kear, 2023.

 DOI: 10.1038/s41598-023-43015-y 

 facebook.com/DanielMadzia

artwork: Joschua Knüppe

Abstract

The emergence of gigantic pliosaurid plesiosaurs reshaped the trophic structure of Mesozoic marine ecosystems, and established an  ~ 80 million-year (Ma) dynasty of macropredatory marine reptiles. However, the timescale of their ‘defining’ trait evolution is incompletely understood because the fossil record of gigantic pliosaurids is scarce prior to the late-Middle Jurassic (Callovian),  ~ 165.3 Ma. Here, we pinpoint the appearance of large body size and robust dentitions to early-Middle Jurassic (Bajocian) pliosaurids from northeastern France and Switzerland. These specimens include a new genus that sheds light on the nascent diversification of macropredatory pliosaurids occurring shortly after the Early-Middle Jurassic transition, around  ~ 171 Ma. Furthermore, our multivariate assessment of dental character states shows that the first gigantic pliosaurids occupied different morphospace from coeval large-bodied rhomaleosaurid plesiosaurs, which were dominant in the Early Jurassic but declined during the mid-Jurassic, possibly facilitating the radiation and subsequent ecomorph acme of pliosaurids. Finally, we posit that while the emergence of macropredatory pliosaurids was apparently coordinated with regional faunal turnover in the epeiric basins of Europe, it paralleled a globally protracted extinction of other higher trophic-level marine reptiles that was not completed until after the earliest-Late Jurassic,  ~ 161.5 Ma.

Skeletal remains of the holotype (MNHNL BU159) of Lorrainosaurus keileni.
(a) Reconstruction in lateral view showing recovered elements. (b) Tooth crown with root. (c) Posterior section of mandible in lateral view. (d) Glenoid section of mandible in articular view. (e) Complete mandible in ventral view. (f) Enlargement of the mandibular symphysis. (g) Coracoid in dorsal view.

  

Plesiosauria de Blainville, 1835 

Pliosauridae Seeley, 1874 

Thalassophonea Benson & Druckenmiller, 2014 

Lorrainosaurus gen. nov.

Etymology: Derived from ‘Lorraine’, for the type locality; and ‘σαῦρος’ (sauros), Greek for ‘reptile’.

Type species: Lorrainosaurus keileni (Godefroit, 1994) 

Type locality and stage: A temporary road cutting between Montois-la-Montagne and Sainte-Marie-aux-Chênes ~ 18 km northeast of Metz in Lorraine, northeastern France. These deposits form part of the Marnes de Gravelotte regional lithostratigraphical unit correlated with the upper Bajocian (mid-Middle Jurassic) Parkinsonia parkinsoni Zone.

Diagnosis: Large-bodied thalassophonean pliosaurid autapomorphically distinguished by a transversely broad, ‘wedge-shaped’ splenial contact that extends anteriorly to the level of the fourth mandibular alveolus. Lorrainosaurus keileni also displays a unique character state combination: (1) laterally expanded and posteriorly constricted ‘spatulate’ symphyseal section of the mandible bearing five to six alveoli; (2) lateral trough on the mandible anterior to the glenoid fossa; (3) a retroarticular process that is shorter than the glenoid fossa; (4) retroarticular process with posteroventrally oriented dorsoventral long axis and slightly posteromedially inflected mediolateral long axis; (5) wide posteromedial seperation of the coracoids; (6) posterolateral edge of the coracoid (cornu) projecting beyond the level of the glenoid fossa (Fig. 1).

 

 Sven Sachs, Daniel Madzia, Ben Thuy and Benjamin P. Kear. 2023. The Rise of Macropredatory Pliosaurids near the Early-Middle Jurassic Transition. Scientific Reports. 13: 17558. DOI: 10.1038/s41598-023-43015-y

  facebook.com/DanielMadzia/posts/10232169972497818

 

[Paleontology • 2020] A Gigantic Pliosaurid (Pliosauridae: Brachaucheninae) from the Cenomanian (Upper Cretaceous) of the Volga Region, Russia

in Zverkov et Pervushov, 2020. 

DOI: 10.1016/j.cretres.2020.104419 

  elementy.ru

Illustration: Andrey Atuchin   twitter.com/AndreyAtuchin

Abstract

Pliosaurid plesiosaurs were among the largest predators of Mesozoic marine ecosystems attaining giant sizes up to 10–11 m in length, near a quarter of which could be constituted by a massive head. The known Late Cretaceous pliosaurids are comparatively smaller than the stratigraphically older taxa and lack a suite of macropredaceous features, demonstrating a somewhat decline of the group members towards their extinction in the Turonian. However, the early Late Cretaceous (Cenomanian) record of pliosaurids is scarce and mostly represented by isolated teeth, thus hampering the recognition of diversity and disparity of pliosaurids in this time interval. Here we describe a very large isolated cervical centrum (19 cm in maximum diameter) belonging to a brachauchenine pliosaurid. The comparison with other pliosaurids indicates that the centrum belonged to one of the largest known pliosaurids, comparable in size to Kronosaurus queenslandicus, ‘Kronosaurus’ boyacensis and Sachicasaurus vitae from the Aptian–Albian of Australia and Barremian–Aptian of Colombia. This finding indicates that gigantic pliosaurids were also present in the Cenomanian. Thus, the previously inferred decrease in size of pliosaurids in the Late Cretaceous is likely a result of sampling bias, and, if present, it happened not earlier than in the late Cenomanian–Turonian, right before the extinction of the group.

 

Keywords: Pliosauridae, Brachaucheninae, Gigantic pliosaurids, Late Cretaceous, Cenomanian

 

 Nikolay G. Zverkov and Evgeny M. Pervushov. 2020. A Gigantic Pliosaurid from the Cenomanian (Upper Cretaceous) of the Volga Region, Russia. Cretaceous Research. 110, 104419. DOI: 10.1016/j.cretres.2020.104419 

Найденный на берегу Волги позвонок удлинил время существования гигантских плиозавров

 elementy.ru/novosti_nauki/433620/Naydennyy_na_beregu_Volgi_pozvonok_udlinil_vremya_sushchestvovaniya_gigantskikh_pliozavrov

 twitter.com/undorymuseum/status/1239488190857261056

 twitter.com/AndreyAtuchin/status/1239431892073660417

[Paleontology • 2017] Arminisaurus schuberti • A Rare New Pliensbachian Plesiosaurian from the Amaltheenton Formation of Bielefeld in northwestern Germany

Arminisaurus schuberti  Sachs & Kear, 2017

DOI: 10.1080/03115518.2017.1367419

 Artwork by Joschua Knüppe  hyrotrioskjan.deviantart.com 

Abstract

We describe a new plesiosaurian from the upper Pliensbachian Amaltheenton Formation of Bielefeld in northwestern Germany. The taxon is based upon an incomplete associated skeleton comprising part of the right mandibular ramus, several teeth, a series of cervical, pectoral, dorsal and caudal vertebrae, as well as ribs, limb girdle elements including a nearly complete right scapula, and various distal limb bones. A unique character state combination serves to distinguish the Amaltheenton Formation remains from other previously documented Early Jurassic plesiosaurians. The most important features are the presence of a longitudinal notch incising the posterior rim of the glenoid fossa and retroarticular process, and a pronounced ventrolateral shelf on the scapula, both of which constitute derived states otherwise shared with Early Cretaceous leptocleidians. However, phylogenetic analysis using a ‘total group’ Plesiosauria data-set that specifically accommodates for Pliensbachian taxa unanimously placed the Amaltheenton Formation plesiosaurian among Early–Middle Jurassic pliosaurids. This discovery is significant because it reveals unexpected homoplasy, but also because it establishes what is only the third formally named plesiosaurian taxon thus far documented from Pliensbachian strata worldwide.

Key words: Plesiosauria, Early Jurassic, pliosaurid, ‘Pliensbachian gap’. 

Systematic palaeontology

SAUROPTERYGIA Owen, 1860

PLESIOSAURIA de Blainville, 1835

PLIOSAURIDAE Seeley, 1874

Arminisaurus gen. nov. 

Etymology. Armini-, referring to Arminius (Armin), chieftain of the Germanic Cherusci tribe who defeated a Roman army in the Battle of the Teutoburg Forest; and -saurus Latinized Greek for ‘lizard’. 

Arminisaurus schuberti sp. nov.

Etymology: The species name honours Mr. Siegfried Schubert, who recovered the holotype NAMU ES/jl 36052 for science and has contributed to palaeontological research in the Bielefeld region for the last decade.

Type locality and unit. Beukenhorst-II claypit in the Jöllenbeck district of Bielefeld, North Rhine-Westphalia, northwestern Germany. Type stratum is the upper Pliensbachian (Lower Jurassic) middle Amaltheus subnodosus Subzone (Amaltheus margaritatus Zone) of the Amaltheenton Formation.

Sven Sachs and Benjamin P. Kear. 2017. A Rare New Pliensbachian Plesiosaurian from the Amaltheenton Formation of Bielefeld in northwestern Germany. Alcheringa.  DOI: 10.1080/03115518.2017.1367419

 Ancestor of sea reptile super-predators found in Germany http://phy.so/424681896  via @physorg_com

https://www.uu.se/en/research/news/article/?id=9324&typ=artikel

[Paleontology • 2016] Stenorhynchosaurus munozi • A New Pliosaurid from the Upper Barremian (Lower Cretaceous) of Villa de Leiva, Colombia

Stenorhynchosaurus munozi 

Páramo-Fonseca, Gómez-Pérez, Noé & Etayo-Serna, 2016

  DOI: 10.18257/raccefyn.239 

Abstract 

From one of the most complete Lower Cretaceous rock sequences in the world (in Villa de Leiva region, central Colombia), we describe a new genus and species of pliosaurid plesiosaur Stenorhynchosaurus munozi. Stenorhynchosaurus displays a series of features which differentiate it from all the other Cretaceous pliosaurid genera: the anterior of the vomer, in ventral view, posterior of the palatal premaxilla-maxilla suture, contacting the posterior palatal process of the premaxilla level with the third maxillary alveolus; rostrum narrow and elongated with straight sides in dorsal view; lacrimal forming the anterior border and greater part of the ventral border of the orbit and broadly borders the maxilla anteriorly; anterior interpterygoid vacuity present; internal nares located between vomer and maxilla at the level of 13th-15th maxillary alveoli; anterior of rostrum and mandible without lateral expansion or marked increase in size of the functional alveoli; penultimate premaxillary alveolus slightly larger than adjacent premaxillary alveoli; homodont maxillary functional alveoli, with fourth tooth positions very slightly enlarged with respect to the neighboring alveoli; homodont dentary dentition; and epipodials extremely short. Based on morphological analysis of phylogenetic characters, Stenorhynchosaurus most likely nests within the increasingly inclusive Pliosauridae and Pliosauroidea, however, as currently defined, firm inference for referral of Stenorhynchosaurus to Thalassophonea is much more problematic, but ultimately seems likely based on characters shared with Pliosaurus and Brachaucheninae. However, this uncertainty indicates Thalassophonea requires rigorous redefinition. As to whether Stenorhynchosaurus is a member of the currently exclusively Jurassic genus Pliosaurus, or the Cretaceous sub-family Brachaucheninae, remains equivocal.

Keywords: Pliosauridae; Barremian; Lower Cretaceous; Colombia

Figure 1. VL17052004-1, holotype specimen of Stenorhynchosaurus munozi gen. and sp. nov. General view of the specimen in dorsal view. Photography in the field and interpretation of the skeleton.

María Eurídice Páramo-Fonseca, Marcela Gómez-Pérez, Leslie F. Noé and Fernando Etayo-Serna. 2016. Stenorhynchosaurus munozi, gen. et sp. nov. A New Pliosaurid from the Upper Barremian (Lower Cretaceous) of Villa de Leiva, Colombia, South America. Rev. Acad. Colomb. Cienc. Ex. Fis. Nat. 40(154); 84-103. DOI: 10.18257/raccefyn.239

[Paleontology • 2013] A Giant Pliosaurid Skull from the Late Jurassic of England; Pliosaurus kevani, P. carpenteri & P. westburyensis

Pliosaurus kevani

Abstract

Pliosaurids were a long-lived and cosmopolitan group of marine predators that spanned 110 million years and occupied the upper tiers of marine ecosystems from the Middle Jurassic until the early Late Cretaceous. A well-preserved giant pliosaurid skull from the Late Jurassic Kimmeridge Clay Formation of Dorset, United Kingdom, represents a new species, Pliosaurus kevani. This specimen is described in detail, and the taxonomy and systematics of Late Jurassic pliosaurids is revised. We name two additional new species, Pliosaurus carpenteri and Pliosaurus westburyensis, based on previously described relatively complete, well-preserved remains. Most or all Late Jurassic pliosaurids represent a globally distributed monophyletic group (the genus Pliosaurus, excluding ‘Pliosaurus’ andrewsi). Despite its high species diversity, and geographically widespread, temporally extensive occurrence, Pliosaurus shows relatively less morphological and ecological variation than is seen in earlier, multi-genus pliosaurid assemblages such as that of the Middle Jurassic Oxford Clay Formation. It also shows less ecological variation than the pliosaurid-like Cretaceous clade Polycotylidae. Species of Pliosaurus had robust skulls, large body sizes (with skull lengths of 1.7–2.1 metres), and trihedral or subtrihedral teeth suggesting macropredaceous habits. Our data support a trend of decreasing length of the mandibular symphysis through Late Jurassic time, as previously suggested. This may be correlated with increasing adaptation to feeding on large prey. Maximum body size of pliosaurids increased from their first appearance in the Early Jurassic until the Early Cretaceous (skull lengths up to 2360 mm). However, some reduction occurred before their final extinction in the early Late Cretaceous (skull lengths up to 1750 mm).

Benson RBJ, Evans M, Smith AS, Sassoon J, Moore-Faye S, et al. 2013. A Giant Pliosaurid Skull from the Late Jurassic of England. PLoS ONE. 8(5): e65989. doi: dx.doi.org/10.1371/journal.pone.0065989

Pliosaurus kevani – the Weymouth Bay Pliosaur

http://www.plesiosauria.com/news/index.php/pliosaurus-kevani-the-weymouth-bay-pliosaur/

[Paleontology • 2012] Pliosaurus funkei | 'Predator X' • A new species of Pliosaurus (Sauropterygia: Plesiosauria) from the Middle Volgian of central Spitsbergen, Norway

Scene From Ancient Seas 

A pliosaur Pliosaurus funkei attacks a plesiosaur. 

Painting by Raul Martin (National Geographic Magazine Dec. 2008)

Sea Monsters of the North: Day 11-Skull Discovered at Last! http://on.natgeo.com/P3Es3l  

Enormous "Sea Monster"; Fossil Found in Norway

http://www.redorbit.com/

Predator X - Pliosaurus funkei 

http://theropoda.blogspot.com 

Eight seasons of fieldwork in the Upper Jurassic black shales of the Slottsmøya Member of the Agardhfjellet Formation (Upper Jurassic; Middle Volgian) in the Arctic archipelago of Svalbard have yielded numerous skeletal remains of plesiosaurs and ichthyosaurs. Among the new discoveries from the Slottsmøya Member are two very large specimens of short-necked plesiosaurians. Dental and postcranial morphology suggest that they represent a new species of the genus Pliosaurus, a taxon known from several specimens of Kimmeridgian and Tithonian-aged strata in England, France and Russia. Skeletal dimensions of this new taxon suggest that it was one of the largest members of the Pliosauridae and that it possessed comparatively longer front limbs than other known pliosaurids. A morphometric analysis of pliosaurids indicates they had a wide range of interspecific variability in relative paddle lengths compared to body size.

 Enormous "Sea Monster"; Fossil Found in Norway

http://www.redorbit.com/news/

 ''T. Rex of the Ocean'' Found in Arctic

http://news.nationalgeographic.com/

Knutsen, E.M., Druckenmiller, P.S. & Hurum, J.H. 2012. A new species of Pliosaurus (Sauropterygia: Plesiosauria) from the Middle Volgian of central Spitsbergen, Norway. Norwegian Journal of Geology. 92 (2-3): 235-258.

 http://www.geologi.no/data/f/0/21/02/6_2401_0/NJG_2_3_2012_13_Knutsen_etal_Scr.pdf

http://theropoda.blogspot.it/2012/10/predator-x-pliosaurus-funkei.html

http://en.wikipedia.org/wiki/Pliosaurus_funkei

Real sea monsters: The hunt for predator X

http://www.newscientist.com/article/dn18047-real-sea-monsters-the-hunt-for-predator-x.html

Sea Monsters of the North: Day 11-Skull Discovered at Last! http://on.natgeo.com/P3Es3l via @NatGeoNewsWatch

Enormous "Sea Monster"; Fossil Found in Norway http://www.redorbit.com/news/science/1271275/enormous_sea_monster_fossil_found_in_norway/

[Paleontology • 2009] Predator X | Hunt for the ultimate Killer

EACH summer, a team from the University of Oslo in Norway go hunting for monsters on the island of Spitsbergen. They carry guns in case they get menaced by the world's largest living land carnivore, the polar bear. But it is not bears they are after. They are searching for much bigger quarry, the most formidable predators that ever lived.

Step back 150 million years and Spitsbergen was covered by a cool, shallow sea swarming with marine reptiles. The creatures died out and their fossils became part of an island stuffed full of bones. Nowhere else in the world are so many marine reptiles found in one place.

For a few short weeks the sun never sets and temperatures soar to just above freezing. Knowing that before long the ground will be frozen solid, the researchers dig like crazy. "It's like a gold rush, there are so many fossils waiting to be found," says team leader Jørn Hurum. "The site is densely packed with skeletons. As we speak there are probably more than 1000 skeletons weathering out."

Monsters of the deep 

(Nigel Hawtin/New Scientist)

..............

Real sea monsters: The hunt for predator X

http://www.newscientist.com/article/dn18047-real-sea-monsters-the-hunt-for-predator-x.html

Espen M. Knutsen, Patrick S. Druckenmiller & Jørn H. Hurum (2012) A new species of Pliosaurus (Sauropterygia: Plesiosauria) from the Middle Volgian of central Spitsbergen, Norway. Norwegian Journal of Geology. 92 (2-3): 235-258.

http://www.geologi.no/data/f/0/21/02/6_2401_0/NJG_2_3_2012_13_Knutsen_etal_Scr.pdf

http://theropoda.blogspot.it/2012/10/predator-x-pliosaurus-funkei.html

http://en.wikipedia.org/wiki/Pliosaurus_funkei

[Paleontology • 2008] Enormous ‘Sea Monster’ Fossil Found in the Arctic island chain of Svalbard, Norway

Artist's interpretation of the monster catching a pterosaur.

Scientists from the University of Oslo announced their discovery of a fossilized, 150 million-year-old “sea monster” on Spitspergen, in the Arctic island chain of Svalbard. 

The 50 ft. sea reptile, nicknamed “The Monster”, is the biggest on record, and is one of 40 such fossils discovered on the island. prior field expedition in the area revealed remains of another large pliosaur that is thought to be among the same species as “The Monster” 

The Monster's flipper alone measures 3m in length

Scene From Ancient Seas 

A pliosaur Pliosaurus funkei attacks a plesiosaur. 

Painting by Raul Martin (National Geographic Magazine Dec. 2008)

Sea Monsters of the North: Day 11-Skull Discovered at Last! http://on.natgeo.com/P3Es3l  

Pliosaurus funkei | 'Predator X'

• A new species of Pliosaurus (Sauropterygia: Plesiosauria)

from the Middle Volgian of central Spitsbergen, Norway

http://novataxa.blogspot.com/2012/10/2012-predator-x-pliosaurus-funkei.html

Enormous "Sea Monster"; Fossil Found in Norway http://www.redorbit.com/news/science/1271275/enormous_sea_monster_fossil_found_in_norway/

''T. Rex of the Ocean'' Found in Arctic

http://news.nationalgeographic.com/news/2008/02/photogalleries/seamonster-pictures/photo4.html

Sea reptile is biggest on record

http://news.bbc.co.uk/2/hi/science/nature/7264856.stm