Plesiosaurs that used to be dinosaurs

Several marine reptiles have been confused for dinosaurs in the past, from sea lizard "Yezosaurus", to ichthyosaur Rachitrema, to sea turtle Pneumatoarthrus.  But what about plesiosaurs?  These are the specimens that I know of which have been previously assigned to saurischians.  If this has taught me anything, it's that there are a TON of century-old plesiosaur taxa that need to be reexamined.

unnamed thalassophonean (Hahnel, 1988)
Middle Kimmeridgian, Late Jurassic
La Caja Formation, Mexico
Material- (UANL-FCT-R2; The Monster of Aramberri) (~15 m) jaw fragment (lost), cranial fragments, nine cervical vertebrae, seven partial pectoral vertebrae (90-105 mm), rib fragments, gastralium?, axial material, incomplete scapula, incomplete coracoids, humerus, pelvis, femora (~1.2 m), epipodials

Jaw fragment of thalassophonean UANL-FCT-R2 which caused Hahnel to mistake it for a theropod (after Buchy, 2007).

Comments- Hahnel (1988) initially referred this specimen to Theropoda based on the large size and carnivorous teeth. Buchy et al. (2003) reidentified it as Pliosauridae indet. based on the pectoral section and lost snout. Frey et al. (2006) announced the recovery of much of the rest of the specimen, preliminary results which are given in Buchy's (2007) thesis. Buchy retained it as Pliosauridae indet., which can be narrowed to Thalassophonea indet. given its late age. Once more of the specimen is prepared, it may be possible to assign further.
References- Hahnel, 1988. Hallazgo de restos de dinosaurio en Aramberri, N.L., Mexico. Actas de la. Facultad de Ciencias de la Tierra, U.A.N.L. 3, 245-250.
Buchy, Frey, Stinnesbeck and Lopez-Oliva, 2003. First occurrence of a gigantic pliosaurid plesiosaur in the Late Jurassic (Kimmeridgian) of Mexico. Bulletin de la Societe Geologique de France. 174(3), 271-278.
Frey, Stinnesbeck and Buchy, 2006. The Monster of Aramberri. German Research. 27(3), 4-7.
Buchy, 2007. Mesozoic marine reptiles from north-east Mexico: Description, systematics, assemblages and palaeobiogeography. PhD thesis, Universitat Karlsruhe. 89 pp.

unnamed probable brachauchenine (Knoll, Collete, Dubus and Petit, 2000)
Early Albian, Early Cretaceous
Sables verts, France
Material- (Petit coll.) posterior dorsal centrum (107 mm)

Posterior dorsal centrum (Petit coll.) of a ?brachauchenine pliosaurid first published as a sauropod caudal by Knoll et al., in anterior (A), left lateral (B), posterior (C) and ventral (D) views (after Buffetaut et al., 2005).

Comments- Knoll et al. (2000) originally described this as a possibly brachiosaurid sauropod proximal caudal, but it was reidentified by Buffetaut et al. (2005) as a pliosaurid dorsal. Given its age, it is probably referrable to Brachaucheninae, but is likely to be indeterminate.
References- Knoll, Collete, Dubus and Petit, 2000. On the presence of a sauropod dinosaur (Saurischia) in the Albian of Aube (France). Geodiversitas. 22, 389-394.
Buffetaut, Collete, Dubus and Petit, 2005. The "sauropod" from the Albian of Mesnil-Saint-Père (Aube, France): A pliosaur, not a dinosaur. Carnets de Géologie. 2005/01, 1-5. 

Pliosaurus Owen, 1841 sensu Owen, 1842
?= Spondylosaurus Fischer de Waldheim, 1845
?= "Tapinosaurus" Lennier, 1887
= Stretosaurus Tarlo, 1959
= Strongylokrotaphus Novozhilov, 1964
Comments- This was originally erected as a subgenus of Plesiosaurus, spelled Pleiosaurus (Owen, 1841). As Benson et al. (2013) state, ICZN Article 33.3.1 indicates Pliosaurus is an incorrect subsequent spelling but should be retained as it has been "in prevailing usage and is attributed to the publication of the original spelling." Owen (1841) raised it to genus level. See Knutsen (2012) and Benson et al. (2013) for differing views on species validity.
References- Owen, 1841. Odontography; or a treatise on the comparative anatomy of the teeth, I Part 11. Dental system of reptiles. Hippolyte Bailliere, London. 179-295.
Owen, 1842. Report on British fossil reptiles. Part II. Report of the Eleventh Meeting of the British Association for the Advancement of Science. 60-204.
Fischer de Waldheim, 1845. Notice sur le Spondylosaurus genre de saurien fossile de l'oolithe de Moscow. Aus dem Bulletin de la Societe Imperiale des Naturalistes de Moscou. 18, 343-351.
Lennier, 1887. Études paléontologiques. Description des fossiles du Cap de la Hève. Bulletin de la Société Géologique de Normandie. 1886(12), 17-98.
Tarlo, 1959. Stretosaurus gen. nov., a giant pliosaur from the Kimmeridge Clay. Palaeontology. 2, 39-55.
Knutsen, 2012. A taxonomic revision of the genus Pliosaurus (Owen, 1841a) Owen, 1841b. Norwegian Journal of Geology. 92, 259-276.
Benson, Evans, Smith, Sassoon, Moore-Faye, Ketchum and Forrest, 2013. A giant pliosaurid skull from the Late Jurassic of England. PLoS ONE. 8(5), e65989.

Not ever thought to be a dinosaur, but how often do you get to see the holotype of Spondylosaurus frearsi?  This probable Pliosaurus specimen from the Late Jurassic of Russia hasn't been redescribed in 170 years, and according to Storrs et al. (2000) is of unknown whereabouts.  Posterior cervical centrum in (left to right) ventral, left lateral, anteroventral and oblique anterodorsolateral views (after Fischer de Waldheim, 1845).

P. rigauxi (Sauvage, 1874) new comb.
= Cetiosaurus rigauxi Sauvage, 1874
Middle Tithonian, Late Jurassic
Portel, France
Holotype- (MHNL coll.; = MHNB 233) posterior cervical centrum (85 mm)

Comments- Sauvage (1874) initially described this as a posterior cervical centrum of a new Cetiosaurus species, notable for its short proportions. In 1895 he referred it to Pliosaurus sp. in a brief note, which would technically make it Pliosaurus rigauxi. That combination has never been used to my knowledge, however. Sauvage (1902) later referred the specimen to Pliosaurus grandis without stated justification. P? grandis is based on a scapula and three unassociated propodials from the Kimmeridgian of England which were poorly described and lost, so there's no reason to connect them to rigauxi. No more recent studies have been published, and the specimen has never been illustrated. The specimen number is taken from Fossilworks' website, though the Museum d'Histoire naturelle de Boulogne-sur-Mer (MHNB) closed in 2003 and transferred its collections to the Musée d'Histoire naturelle de Lille. Thus rigauxi presumedly has a MHNL number now instead.

Holotype of Pliosaurus suprajurensis, incomplete anterior cervical pectoral (thanks Sven Sachs) vertebra (MHNL coll.) in (left to right) ventral, left lateral, and anterior views (after Sauvage, 1879).  This may be the same species as "Cetiosaurus" rigauxi, though the latter has never been figured.

Based on the original description, rigauxi differs from sauropods such as Cetiosaurus in the short centrum (52% of height, compared to no less than 154% in Cetiosaurus), with even the short-necked Brachytrachelopan having subequal proportions at best. Furthermore, all gravisaurs have strongly opisthocoelous cervicals, whereas rigauxi's is weakly amphicoelous. The parapophyses are 55% of centrum height, while they are much smaller in sauropods (e.g. 34% in cervical 12 of Cetiosaurus). All of these features are seen in pliosaur posterior cervicals however (e.g. length/width ratio of 51-58% and parapophysis/centrum height ratio 70% in P. brachydeirus' holotype). The undivided parapophysis located on the centrum indicates Sauvage had its position in the vertebral column correct despite assigning it to the wrong group. Notably, Sauvage states the ventral surface is "cut into a peak", which suggests a median keel like that which characterizes P. brachydeirus. The latter species' holotype is from the Early Kimmeridgian, but at least one other keeled pliosaur centrum is known from the Tithonian of France- Pliosaurus suprajurensis. It's possible both rigauxi and suprajurensis are members of a long-lived P. brachydeirus, or that the French species are synonymous but distinct from P. brachydeirus. In the latter case, rigauxi would have priority over suprajurensis, but they cannot be directly compared as they're from different sections of the neck (though rigauxi is from a much larger individual, with length x height x width 85x165x185 mm vs. 50x68x75 mm in suprajurensis), and its likely neither can be anatomically distinguished from P. brachydeirus. rigauxi is not officially synonymized here though, pending verification of the keeled morphology and modern description of the specimen.

References- Sauvage, 1874. Mémoire sur les dinosauriens et les crocodiliens des terrains jurassiques de Boulogne-sur-Mer. Mémoires de la Société Géologique de France, série 2. 10(2), 1-57.
Sauvage, 1895. Les dinosauriens du terrain jurassique supérieur du Boulonnais. Bulletin de la Société Géologique de France, 3e série. 22, 465-470.
Sauvage, 1902. Note sur quelques Reptiles du Jurassique supérieur du Boulonnais. Bulletin de la Societe Academique de l‘Arrondissement de Boulogne-sur-Mer. 6, 380-398.
Fossilworks http://fossilworks.org/cgi-bin/bridge.pl?a=taxonInfo&taxon_no=65160 

P? sp. (Lennier, 1887)
= "Tapinosaurus" Lennier, 1887
Late Kimmeridgian, Late Jurassic
lower Argiles d'Ecqueville Member of the Argiles d'Octeville Formation, France
Material- (Muséum d’Histoire naturelle du Havre; destroyed) anterior cervical centrum (70 mm) (Lennier, 1887)
(Muséum d’Histoire naturelle du Havre; destroyed) three cervical centra (80, 78, 65 mm), two cervical ribs, two partial cervical or anterior dorsal neural arches, four incomplete dorsal neural arches, six dorsal ribs (four partial, one fragmentary; 1 m) (Rabeck, 1925)
?...(Lepage coll. 15.8.31.E1) posterior cervical centrum (91 mm) (Lepage et al., 2009)
?...(Muséum du Havre IIFD358) incomplete dorsal rib (Lepage et al., 2009)
Early Kimmeridgian, Late Jurassic
Marnes de Bleville, France
(Muséum d’Histoire naturelle du Havre; destroyed) proximal dorsal rib (Lennier, 1887)

?Pliosaurus anterior cervical centrum (Muséum d’Histoire naturelle du Havre coll.) in anterior or posterior view first figured as Tapinosaurus sp., a misspelling of Tapinocephalus (after Lennier, 1887).

Comments- Lennier (1887) referred an unassociated cervical centrum and dorsal rib (both originally in the Muséum d’Histoire naturelle du Havre, but destroyed in 1944) to Tapinocephalus, then thought to be dinosaurian but now known to be a dinocephalian synapsid. This was seemingly due to their large size. The figure caption of Lennier's plate illustrating the centrum mistakenly said "Tapinosaurus sp?", clearly a misspelling of Tapinocephalus and not previously suggested to be a valid genus.
Rabeck (1925) described a specimen found in 1923 as the dinosaur "Tapinosaurus sp?", based on resemblence to Lennier's specimens, unaware that "Tapinosaurus" was not an accepted genus. This specimen (consisting of partial vertebrae and ribs) was also held at the Muséum d’Histoire naturelle du Havre and similarly destroyed in WWII. Stiegelmann (1925) provided measurements of the specimen.

Only existing photo of Rabeck's "Tapinosaurus sp." material (Muséum d’Histoire naturelle du Havre coll.), consisting of three cervical centra (left center), two cervical ribs (around the bottom centrum), neural arches and dorsal ribs (after Lepage et al., 2009).

After this, "Tapinosaurus" was seldomly mentioned. Kuhn (1939) includes Rabeck's material questionably under Omosaurus, which is treated as Saurischia indet. by Kuhn despite being stegosaurid (a replacement name for Dacentrurus). Steel (1970) realized Lennier's article was supposed to reference Tapinocephalus, but stated Rabeck's material "seemingly pertains to a large dinosaur, but is indeterminable", placing "Tapinosaurus" in Sauropoda incertae sedis.  Rabeck's specimen is not a sauropod, as it has short amphicoelous cervical centra without pleurocoels, short laterally oriented cervical ribs, dorsal neural arches lacking laminae, and single-headed dorsal ribs.  Buffetaut et al. (1991) first noticed the discrepency between the article and plate caption in Lennier's work, and identified both this centrum and Rebeck's "Tapinosaurus" as sauropterygians. Similarly, Molnar (pers comm. in Olshevsky, 1991) stated these specimens were probably plesiosaurian. Finally, Lepage et al. (2009) published detailed overview of "Tapinosaurus"' history (forming the basis of most of this entry), and redescribed the specimens as Pliosaurus sp. for Lennier's and Pliosaurus cf. macromerus for Rabeck's. They also described three new specimens from the lower Argiles d'Ecqueville, two of which might be referrable to the same individual as Rabeck's specimen as they are from the same layer and of similar size.

Holotype of Pliosaurus archiaci (MNHN 24.1), dentaries in dorsal and lateral views (after Lennier, 1870).  This may be conspecific with the "Tapinosaurus" specimens.

"Tapinosaurus" is Pliosaurus?- Unfortunately, the alpha level taxonomy of Pliosaurus is currently controversial, and most proposed distinguishing characters are cranial. The only axial character currently used to distinguish Pliosaurus species is the median ventral keel on cervical centra of P. brachydeirus. Rabeck's specimen lacks this, as do P. brachyspondylus (both current and proposed neotypes), P. funkei (paratype), P. macromerus (lectotype), P. rossicus (holotype) and P. westburyensis. Yet this morphology is plesiomorphic, also being found in e.g. Brachauchenius, Simolestes and "P." andrewsi. Pliosaurus archiaci is based on a mandible (MNHN 24.1) also discovered in the Kimmeridgian deposits of Le Havre, but cannot be compared to "Tapinosaurus". Another method would be to correlate the "Tapinosaurus" specimens stratigraphically with known Pliosaurus species. According to Lepage et al., at least Rabeck's specimen derives from the Aulacostephanus mutabilis zone of the Late Kimmeridgian. This corresponds to CAMSM J35990, a partial skeleton initially referred to a broad concept of P. macromerus (Pliosaurus without ventral cervical keels) but more recently found to be closest to P. kevani (in an analysis that did not include the P. macromerus lectotype or proposed neotype). CAMSM J35990 is similar Rabeck's specimen in being larger than most and lacking ventral cervical keels, so there may be a real large A. mutabilis zone species of Pliosaurus that is currently undiagnosed. This may correspond to the large P. portentificus, although that has been considered a nomen dubium and may belong to the more recent A. euxodus zone. Perhaps notable is that P. portentificus has the same number of symphyseal alveoli (8) as P. archiaci, whereas other species have more (>11 in P. brachydeirus, 9 in P. carpenteri, ~14-15 in P. kevani) or less (6 in P. rossicus and P. patagonicus). In any case, both P. macromerus' lectotype and proposed neotype are from more recently deposited sediments, so Lepage et al.'s assignment seems unlikely. Pending further studies, the "Tapinosaurus" material is best retained as Pliosaurus sp.. Lennier's dorsal rib is from a different locality, whose age corresponds to P. brachydeirus and P. kevani, though it is near certainly indeterminate.

References- Lennier, 1887. Études paléontologiques. Description des fossiles du Cap de la Hève. Bulletin de la Société Géologique de Normandie. 1886(12), 17-98.
Rabeck, 1925. Notes sur la découverte d'ossements de dinosaurien dans les Argiles supérieures Kimméridgiennes du Cap de la Hève (Octeville-sur-Mer). Bulletin de la Société Géologique de Normandie. 1916/1923(34), 72-74
Stiegelmann, 1925. Note additionnelle [à Notes sur la découverte d'ossements de dinosaurien dans les Argiles supérieures Kimméridgiennes du Cap de la Hève (Octeville-sur-Mer) de G. Rabeck]. Bulletin de la Société Géologique de Normandie.1916/1923(34), 75.
Kuhn, 1939. Saurischia. In Fossilium Catalogus I. Animalia. 87. 124 pp.
Steel, 1970. Part 14. Saurischia. Handbuch der Paläoherpetologie/Encyclopedia of Paleoherpetology. Gustav Fischer Verlag, Stuttgart. 87 pp.
Buffetaut, Cuny and Le Loeuff, 1991. French dinosaurs: The best record in Europe? Modern Geology. 16, 17-42.
Olshevsky, 1991. A Revision of the Parainfraclass Archosauria Cope, 1869, Excluding the Advanced Crocodylia. Mesozoic Meanderings. 2, 196 pp.
Lepage, Buffetaut and Lepage, 2009. Qu'est-ce que Tapinosaurus? Lennier, Rabeck et les grands Sauroptérygiens du Kimméridgien supérieur de la région havraise (Normandie, France). Bulletin de la Société géologique de Normandie et des amis du Muséum du Havre. 96(1), 27-59.

Blog entry specific references- Lennier, 1870. Etudes géologiques et paléontologiques sur l'embouchure de la Seine et les Falaises de la Haute-Normandie. Imprimerie Eugène Costey, Havre. 245 pp.

Sauvage, 1879. Prodrome des Plesiosauriens et des Elasmosauriens des formations Jurassiques superieures de Boulogne-sur-Mer. Annales des Sciences Naturelles, 6 Serie. 8(13), 1-38.

Storrs, Arkhangelskii and Efimov, 2000. Mesozoic marine reptiles of Russia and other former Soviet Republics. In Benton, Shishkin, Unwin and Kurochkin (eds.). The Age of Dinosaurs in Russia and Mongolia. Cambridge University Press. 187-210.