Plesiosauria Translation and Pronunciation Guide

Ben Creisler

al-ZAY-duh-SAWR-uhs (Alzada + Gr. sauros "lizard") (m) named for the town of Alzada in southeastern Montana, near where the holotype specimen (FMNH 12009) for Alzadasaurus riggsi was found, a partial skeleton without a skull. Carpenter (1999: Paludicola 2(2):148-173) synonymized the type species Alzadasaurus riggsi with Thalassomedon haningtoni, made the additional species Alzadasaurus kansasensis and A. pembertoni junior synonyms of Styxosaurus snowii, and erected the new genus Callawayasaurus for Alzadasaurus colombiensis. [= Thalassomedon] (revised 7/99)

Aphrosaurus Welles 1943 "sea-foam lizard"

AF-ro-SAWR-uhs (Gr. aphros "sea foam" + Gr. sauros "lizard")* (m) named to indicate a marine reptile; known from incomplete skeletons without skulls of an adult and a small juvenile, found in the coastal Moreno Formation, in Fresno County, California. A rather lightly built elasmosaurid with relatively short coracoids, described as a "less active but longer-necked form than Morenosaurus" (Welles 1943).

Vertebrae: 57 cervicals
Length: (estimated) ?10 m. (?33 ft.))

Type Species: Aphrosaurus furlongi [FUHR-long-ie] Welles 1943: for Eustace L. Furlong of the California Institute of Technology. (Holotype: CIT 2748). Plesiosauroidea Elasmosauridae Late Cretaceous (Maastrichtian) NA.

Apractocleidus Smellie 1915 "functionless clavicle"*

a-PRAK-to-KLIE-duhs (Gr. apraktos "functionless, incomplete" + Gr. kleid- (kleis) "key, clavicle" + -us) (m) named for the rigidity of the shoulder girdle, which rendered the clavicles "functionless." [= Cryptoclidus]

Aptychodon Reuss 1855 "unwrinkled tooth"

ap-TIK-o-don (Gr. aptykhos "unwrinkled" + Gr. odon "tooth") (m) named for the smooth appearance of the teeth; based on a number of eroded teeth found near Prague in the Czech Republic. Pleiosauria i.s. (Pliosauroidea?) Late Cretaceous Eur. [nomen dubium]

Archaeonectrus Novozhilov 1964 "ancient swimmer"

AHR-kee-o-NEK-truhs (Gr. arkhaios "ancient" + Gr. nektris "swimmer" + -us) (m) named to indicate a plesiosaur found in Early Jurassic deposits; proposed for "Plesiosaurus" rostratus Owen 1865, known from a complete skeleton with skull from the Lower Lias of Carmouth, England (Holotype: BMNH 38525). Notable for a relatively short neck (about 1.5 times the length of the skull) composed of short cervical vertebrae, and a large elongated head with a narrow snout and round orbits. The teeth are pointed, conical and recurved. The hindlimbs are larger than the forelimbs. Owen (1865) notes that some of the centra of the tail vertebrae were vertically compressed, suggesting to him the possible presence of a vertical tail fin. Novozhilov (1964) mentions undescribed remains from the Early Jurassic of Siberia that appear to belong to the genus.

Vertebrae: 20 cervicals / 4 pectorals / 23 dorsals / ?3 sacrals / 34 caudals
Length: (estimated) 3.5 m. (12.5 ft.); skull: 50 cm. (20 in.))

Type Species: Archaeonectrus rostratus [ros-TRAY-tus] (Owen 1865) "rostrate" ("having a rostrum"), for the elongated rostrum formed by its snout. Pliosauroidea Early Jurassic (Sinemurian) Eur.

Aristonectes Cabrera 1941 "best swimmer"

a-RIS-to-NEK-teez (Gr. aristos "superior, best" + Gr. nektes "swimmer") (m) named to indicate the best specimen of a plesiosaur found up to that time in Argentina--the first Argentine plesiosaur based on absolutely secure scientific evidence. Previous "plesiosaur" discoveries in Argentina consisted of a few isolated teeth (probably crocodilian) or absurd news reports about a supposed "living" plesiosaur sighted in Patagonia. The type specimen found in Canadon del Loro, northeast of Chubut, Patagonia, included parts of a long but fairly broad oval skull, a lower law with short symphysis, vertebrae from neck and tail, ribs, and a partial left fore paddle. Aristonectes is remarkable for the number of small tooth sockets in its jaws (around 45 upper, 58 lower per side), indicating a dense filter-trap arrangement of small, somewhat projecting, interlocking teeth, more developed than in Jurassic cryptoclidids. The neck is estimated to be about 2 meters long, probably consisting of at least 30 vertebrae. The cervicals are broader than long, with an elliptical cross-section in those toward the base of the neck. The articular surfaces of the centra are only slightly concave and the cervical ribs are single- headed.

The classification of Aristonectes remains controversial. Cabrera placed the genus among the elasmosaurids, based mainly on the single-headed ribs on the vertebrae (a feature common to many Cretaceous plesiosaurs). Persson (1963) classified Aristonectes along with Cimoliasaurus and Scanisaurus in the Cimoliasauridae, a poorly known group characterized by medium-length necks and rather long skulls with thin teeth. (See Cimoliasauridae.) Welles (1962) proposed that the genus was "an aberrant pliosaur." Brown (1981) included the genus in the family Cryptoclididae because of its dense arrangement of teeth, a feature in common with the Late Jurassic Cryptoclidus. Bardet (1995), however, considers Aristonectes and the apparently related but smaller Morturneria to be elasmosaurids, in line with Cabrera's original thinking.

Vertebrae: 30+ cervicals
Length: (estimated) ?7.5-8 m. (?25-27 ft.); skull: (estimated) 73 cm. (2.3 ft.); mandible: (estimated) 83 cm. (2.6 ft.)

Type Species: Aristonectes parvidens [PAHR-vi-denz] Cabrera 1941 "small-toothed," for the small size of the teeth, indicated by the size of the aveoli. The tooth sockets decrease in size from 8.5 mm in diameter in the front of the jaws to 6 mm at the back and show the teeth protruded at an angle. Though no actual teeth were found with the remains, it is likely the teeth were thin, pointed, and slightly recurved, forming a dense "trap" for schools or swarms of small prey. (Holotype: Museo de La Plata, Departamento de Paleozoologia, Vertebrados 40-XI-14-6). Plesiosauroidea ?Cryptoclididae (or ?Elasmosauridae) Late Cretaceous (Maastrichtian) SA.

Attenborosaurus Bakker 1993 "Attenborough's lizard"

AT-en-BOR-o-SAWR-uhs ((David) Attenboro(ugh) + Gr. sauros "lizard") (m) named "in honor of the naturalist and filmmaker David Attenborough, whose childhood fascination with Liassic plesiosaurs sparked a brilliant career in scientific journalism"; proposed for "Plesiosaurus" conybeari Sollas 1881. The original specimen was a nearly complete skeleton with skull, lacking most of the tail vertebrae. The fossil was found in Charmouth, England, and kept in the collection of the Bristol City Museum. The neck was about 4 times the length of the skull, and approximately half the length of the entire body, not counting the skull. Unusually the specimen preserved apparent patches of skin as a thin film over parts of the body. Sollas noted that the "thin brownish film...has nothing of the nature of scales and scutes, so far as we can see; it was a continuous membrane, not a collection of separate individual structures." However, small oblong bones were imbedded in the film in the pelvic region, and Sollas suggested "they may possibly be dermal plates." Tragically, this unusual and valuable fossil was destroyed during WWII by a German bombing raid in November, 1940; the British Museum has a cast. Bakker separated Attenborosaurus from Plesiosaurus because "it is the only plesiosaurian of any age that combines a very long neck with a long, massive, evenly tapered snout and very large, conical tooth crowns."

Vertebrae: 36 cervicals / 3 pectorals / 20 dorsals / ?4 sacrals / ?30 caudals
Length: (estimated) 5 m. (16.6 ft.); skull: 45 cm. (17 in.); mandible: 50 cm. (20 in.))

Type Species: Attenborosaurus conybeari [kon-i-BEER-ie] (Sollas 1881): for the Reverend William Conybeare (1787-1857), British paleontologist, "as a tribute to that classic authority who first made the existence and nature of Plesiosaurus known to us. This was sixty years ago; and it is singular that up to this date no one seems to have thought of calling some species of Plesiosaurus after the author of the genus." (Sollas 1881) Plesiosauroidea Early Jurassic (Sinemurian) Eur.

Bathyspondylus Delair 1982 "deep vertebra"

BATH-i-SPON-di-luhs (Gr. bathys "deep" + Gr. spondylos "vertebra") (m) referring to vertebrae with centra that are very deep in relation to their length, described as "very short antero-posteriorly" and "possess flat or incipiently concave terminal faces." An unusual, poorly known small form from Wiltshire England that appears to combine features found in both plesiosauroids and pliosauroids.

Vertebrae: ?21+ cervicals
Length: (estimated) 2 m.+ (7 ft.+)

Type Species: Bathyspondylus swindoniensis [swin-doh-nee-EN-sis] Delair 1982 "from Swindon (Wiltshire, England)" Holotype: 1774 Devizes Museum. ?Pliosauroidea Late Jurassic (Kimmeridgian) Eur. [?nomen dubium]

Bishanopliosaurus Dong 1980 "Wall Mountain (China) pliosaur"

BEE-SHAHN-o-PLIE-o-SAWR-uhs (Bishan (Chin. bi "wall" + Chin. shan "mountain") + Gr. pleion "more" + Gr. sauros "lizard") (m) named for Bishan ("Wall Mountain"), near where the fossils were found in Sichuan Province, China; an apparent freshwater form known from a post-cranial skeleton of the "rhomaleosaurid" type.

Length: (estimated) 4 m. (13.3 ft.)

Type Species: Bishanopliosaurus youngi [YUHNG-ie] Dong 1980: for Chung Chien Young [Yang Zhongjian] (1897-1979), a famous Chinese paleontologist. Pliosauroidea Early Jurassic (Toarcian) EAs. (China)

Brachaucheniidae Williston 1925 "Brachauchenius [short-neck] family"

BRAK-aw-kee-NIE-i-dee Pliosauroids in which the neck is very short (12-13 vertebrae, including atlas/axis), with single-headed ribs; Kronosaurus is currently under review and a revised description is due. Members: Brachauchenius (type), Kronosaurus

Brachauchenius Williston 1903 "short neck"

brak-aw-KEEN-ee-uhs (Gr. brakhys "short" + Gr. aukhen "neck" + -ius) (m) named to indicate "the shortest-neck plesiosaur known" at the time, with only 11 very short neck vertebrae in addition to the atlas/axis, in a neck only about 75% as long as the skull. The cervical vertebrae lack the ventral foramina (openings) found on most other plesiosaur vertebrae and support single-headed ribs (Pliosaurus had doubled-headed cervical ribs). The skull is distinctive for its broad, triangular, mosasaur-like shape, ending in a point, unlike other large pliosaurs such as Liopleurodon and Pliosaurus, which have skulls that taper abruptly in front of the nostrils into a narrow blunt snout. The large teeth have striations that branch toward the root, unlike the straight grooves on the teeth of Jurassic pliosaurs. Known from three nearly complete skulls with mandibles, and two partial skeletons (the holotype (USNM 4989) preserves 35 presacral vertebrae with ribs). Brachauchenius is a very large form (estimated to reach up to 11 m. (36.5 ft.) long based on a 1.53 m. skull (FHSM VP321)), and thus one of the last of the great mega-predator pliosaurs, dating from the Cenomanian-Turonian (early Late Cretaceous).

Vertebrae: 13 cervicals / ?2 pectorals / 20+ dorsals
Length: (estimated) up to 11 m. (36.5 ft.); skull: up to 1.53 m. (5 ft.)); mandible: up to 1.84 m (6.1 ft.)

Type Species: Brachauchenius lucasi [LOO-ka-sie] Williston 1903: for Frederick Augustus Lucas (1852-1929), at the U.S. National Museum (Smithsonian) "who has does much valuable work in American paleontology." Pliosauroidea Brachaucheniidae Late Cretaceous (Cenomanian- Turonian) NA.

Brancasaurus Wegner 1914 "Branca's lizard"

BRAHNG-kuh-SAWR-uhs ((W. v.) Branca + Gr. sauros "lizard") (m) named to honor Wilhelm von Branca (1844-1928), noted German paleontologist; for a small, primitive elasmosaur known from a fairly complete skeleton with skull found at Gronau, Westphalia, west-central Germany.

Vertebrae: 37 cervicals / 3 pectorals / 19 dorsals / 3 sacrals / 25+ caudals
Length: (estimated) 3.6 m. (12 ft.); skull: (estimated) 26 cm. (10.6 in.))

Type Species: Brancasaurus brancai [BRAHNG-ka-ie] Wegner 1914: for Wilhelm von Branca (1844-1928), German paleontologist. Plesiosauroidea Elasmosauridae Early Cretaceous (Berriasian) Eur.

Brimosaurus Leidy 1854 "strong lizard"

BRIEM-o-SAWR-uhs (Gr. brime "strength" + Gr. sauros "lizard") (m) alluding to very large size of two apparent neck vertebrae that indicate a plesiosaur with a relatively short neck. Welles (1952) suggested Brimosaurus is a synonym of Cimoliasaurus. Plesiosauria i.s. Late Cretaceous NA. [nomen dubium]

Callawayasaurus Carpenter 1999 "Callaway's lizard"

KAL-uh-way-uh-SAWR-uhs (Callaway + Gr. sauros) (m) named to honor Jack M. Callaway (1930-1997), "who in his brief career as a vertebrate paleontologist, did much to improve our understanding of marine reptiles"; for "Alzadasaurus" colombiensis Welles 1962, known from a nearly complete skeleton with crushed skull (Holotype: UCMP 38349), found in the Paja Formation (Upper Aptian), near Villa de Leiva, Provincia Boyaca, Colombia; a second referred specimen found nearby is less robust than the holotype, but also is an adult, possibly indicating a sexual difference. External nares elongate in shape, positioned over maxillary teeth 3-5. A rather primitive elasmosaurid with 56 relatively short neck vertebrae. Holotype found with about 100 gastroliths.

Vertebrae: 56 cervicals / 2 pectorals / 23 dorsals / ?4 sacrals / ?28 caudals
Length: (estimated) 7.4-8 m. (25-26 ft.); skull: 34 cm. (1.3 ft.)

Type Species: Callawayasaurus colombiensis [ko-lom-bee-EN-sis] (Welles 1962): "from Colombia" in South America, where the specimens were found near the village of Leiva, Boyaca Province. Plesiosauroidea Elasmosauridae Early Cretaceous (Aptian) SA. (added 7/99)

Ceraunosaurus Thurmond 1968 "thunderbolt lizard"

se-RAWN-o-SAWR-uhs (Gr. keraunos "thunderbolt" + Gr. sauros "lizard")* (m) alluding to the long, narrow shape of the skull; known from a nearly complete skeleton with a damaged skull, found in the Lake Waco Formation (Cenomanian) of Texas. According to Carpenter (1996), Ceraunosaurus brownorum, is a junior synonym of Trinacromerum bentonianum. [= Trinacromerum]

Cimoliasauridae Delair 1959 "Cimoliasaurus [Cretaceous-lizard] family"

si-MOH-lee-uh-SAWR-i-dee (masc. plural) A few researchers have recognized a distinct group of plesiosaurs (Mesodira) with necks intermediate in length between typical plesiosauroids and pliosauroids, though the evidence remains scrappy and difficult to interpret. Persson (1960) defined the Cimoliasauridae as: "A family in the Plesiosauroidea with neck relatively shorter than in the Plesiosauridae and the Elasmosauridae. Teeth of the general Plesiosaurian type (crowns high and slender). The height of at least the middle and posterior cervical centra approximately equal to the length, but the breadth of these centra considerably greater than the length; the end faces of the centra flat or slightly concave. Ribs single-headed." He initially included the poorly documented genera Cimoliasaurus and Scanisaurus in the family, but later revised the definition to accommodate Aristonectes as well. Currently, most scholars reserve judgment concerning "cimoliasaurs," pending discovery and description of better and more complete material.

Cimoliasaurus Leidy 1851 "Cretaceous lizard"

si-MOH-lee-uh-SAWR-uhs (Gr. kimolia "white chalky earth" [Cretaceous] + Gr. sauros "lizard") (m) named for the Late Cretaceous age of the Green Sand deposits in Burlington County, New Jersey in which the 13 type vertebrae (ANSP 9235) were found. Cimoliasaurus remains a poorly known form. No skull has been found, though various researchers have considered its neck vertebrae diagnostic: the centra are broader than long, much shorter than the corresponding centra of typical long-necked plesiosauroids but also distinct from the neck bones of pliosauroids, being somewhat longer with cervical ribs fused to the neck vertebrae and with end-faces that are nearly flat. Attributed teeth are described as high, slender and recurved.

Lydekker (1889) redefined the genus and assigned many species of Late Jurassic and Cretaceous plesiosaurs from around the world to Cimoliasaurus (which he respelled "Cimoliosaurus"), based on such general similarities as neck vertebrae with single-headed ribs and a number of features in the front limb-girdles. His redefinition of the taxon and wholesale usage of the generic name were eventually rejected by other authors. Those who still recognized Cimoliasaurus as a definable taxon saw it as much more restricted genus. (See additional comments under Crymocetus.) Despite the scrappy nature of Leidy's type specimen, Welles (1952) and Persson (1960) concluded that Cimoliasaurus belonged to a third type of Cretaceous plesiosaur (Mesodira), with necks intermediate between elasmosaurs and pliosaurs at about two to three times the length of the skull. Welles considered Cimoliasaurus a probable polycotylid. Persson, however, supported use of the separate family Cimoliasauridae (1960), classified as a branch of the Plesiosauroidea, and later included the genera Scanisaurus and Aristonectes.

Because specimens now identified as Cimoliasaurus all lack a skull or any well preserved limb girdles, most modern researchers prefer to treat the genus as a nomen dubium that cannot be defined in a scientifically useful way. It was evidently a rather large plesiosaur, though exactly how many neck vertebrae it had is not known. Welles (1952) suggested the animal was about twice as large as Polycotylus based on North American material. A smaller species has been proposed based on material from Australia (Cimoliasaurus maccoyi Etheridge 1904), including some neck vertebrae that lack longitudinal ridges, and a few paddle bones.

Length: (estimated) ?8 m. (?29 ft.)).

Type Species: Cimoliasaurus magnus [MAG-nuhs] Leidy 1851 "large": to indicate a "giant saurian." Plesiosauroidea Late Cretaceous (Santonian) NA., ?Aus., ?Eur. [? nomen dubium]

Colymbosaurus Seeley 1874 "diving lizard"

ko-LIM-bo-SAWR-uhs (Gr. kolymbo "dive" + Gr. sauros "lizard") (m) named to indicate a swimming reptile; for "Plesiosaurus" trochanterius Owen 1840. Colymbosaurus is based on a five incomplete skeletons and some isolated limb bones (propodials) from the Kimmeridge Clay in Oxfordshire. It is the longest and most massive of all English plesiosauroids, with vertebrae similar in shape and proportions to those of Cryptoclidus. The neck (proportionately about a third longer than in Cryptoclidus) is lengthened only by an increased number of vertebrae, not by the additional lengthening of the individual neck vertebrae themselves as in Muraenosaurus or Microcleidus. Colymbosaurus has been classified as an elasmosaurid because of its long neck, but the skull is poorly known. Brown, Milner and Taylor (1986. Bulletin of the British Museum of Natural History (Geology) 40(5):225-234) suggest Kimmerosaurus (known only from a few vertebrae, and a lightly built, delicate skull rather similar to Cryptoclidus with a dense arrangement of thin teeth to trap soft- bodied prey) may be a junior synonym based on the form of the neck vertebrae and its occurrence in the same Kimmeridgian deposits. If this synonymy is confirmed, Colymbosaurus would be a long-necked cryptoclidid rather than an elasmosaurid.

Vertebrae: 42 cervicals / 3 pectorals / 25 dorsals / 4 sacrals / ?26 caudals
Length: (estimated) 5-6.6 m. (16.5-22 ft.); skull (Kimmerosaurus): (estimated) 45 cm. (18 in.))

Type Species: Colymbosaurus trochanterius [troh-kan-TEER-ee-us] (Owen 1840): for "a strongly developed trochanterian ridge projecting from the outer side of the head" of the humerus and femur (Owen 1840)). (Holotype: BMNH 31787) Plesiosauroidea Cryptoclididae Late Jurassic (Kimmeridgian- Tithonian) Eur.

Crymocetus Cope 1869 "dreadful sea monster"

krim-o-SEE-tus (Gr. krymos "chill, dread" + Gr. ketos "sea monster") (n) name proposed for "Plesiosaurus" bernardi Owen 1850, which Owen based on the centrum of a large posterior neck vertebra from Sussex, England, notable for the its deeply concave ends and very large rib facets. The centrum is somewhat higher than it is long. Cope (1869) identified his new genus Crymocetus as a supposed streptosaurian "reversed lizard" (See "Streptosauria"), but misspelled the species name as "Crymocetus barnardi."

Various researchers have used the species "Plesiosaurus" bernardi or "Cimoliasaurus" bernardi for incomplete remains of European Cretaceous plesiosaurs that have similar deeply concave vertebrae, though none of these authors accepted Cope's new generic name. Lydekker (1889) transferred the species to his revised "Cimoliosaurus," with "Plesiosaurus" ichthyspondylus, and possibly "Plesiosaurus" balticus as synonyms. Riabinin (1909) attributed a large forelimb and paddle found in the Char'kov region of the Ukraine to Cimoliasaurus bernardi (depicted in Bakker 1993). Persson (1963) suggested Lydekker's (1889) Cimoliosaurus cantabrigiensis was another probable synonym. According to Welles (1962), Owen's type vertebra comes from an indeterminate pliosaur; Persson (1963) suggested the species was a "rhomaleosaurid."

NOTE: Romer (Vertebrate Paleontology (1966)) misspelled the name "Gymocetus," the garbled version of the name cited in some later books. ?Pliosauroidea Late Cretaceous (Senonian) Eur. [nomen dubium]

Cryptoclididae Williston 1925 "Cryptoclidus [hidden-clavicle] family"

KRIP-to-KLIE-di-dee (masc. plural) Plesiosauroids with broad, short skulls specialized for filter- trap feeding on small, soft-bodied prey (crustaceans, small fish); jaws have a dense arrangement of thin, interlocking somewhat curved teeth. The neck is relatively long (29-42 vertebrae); individual cervical vertebrae are moderate in length and not elongated as in elasmosaurids, with single-headed ribs. The relationship between elasmosaurids and cryptoclidids needs more study. Cryptoclidids are best known from the Late Jurassic. A number of Late Cretaceous plesiosaurs (Aristonectes, Morturneria, Shag Point plesiosaur) have broad jaws and filter- trap teeth, and have been classified as cryptoclidids, but not all researchers agree. Bardet suggests Aristonectes and Morturneria are elasmosaurids while Persson has classified Aristonectes as a "cimoliasaurid."

Members: Cryptoclidus (type), Tricleidus, Kimmerosaurus, Colymbosaurus, ?Morturneria, ?Aristonectes Undescribed Members: "Tatenektes" (a small Late Jurassic "tricleidid" from Wyoming, NA); Shag Point plesiosaur, a 7 meter- long highly derived cryptoclidid from the Late Cretaceous (Maastrichtian) of New Zealand, with a much longer neck (more vertebrae) than Jurassic forms (to be described by Fordyce and Cruickshank).

Cryptoclidus Seeley 1892 "hidden clavicle"

KRIP-to-KLIE-duhs (Gr. kryptos "hidden" + Gr. kleid- (kleis) "key, clavicle" + -us) (m) named for the small clavicle bones that rest in "shallow depressions" on the inner surface of the scapular symphysis of the front limb girdle, and are thus "entirely hidden from view" from below (Seeley 1892, Proceedings of the Royal Society of London 51: 139). Proposed for "Plesiosaurus" eurymerus Phillips 1871, a taxon originally based on a forelimb notable for a humerus that widens at the bottom-- the limb was mistaken at first for a hindlimb, thus the misleading species name eurymerus "wide femur." Seeley's type specimen is now lost. Brown (1981) designated a neotype (BMNH R.2860) for Cryptoclidus eurymerus in the British Museum of Natural History--one of the most complete adult skeletons of a plesiosaur ever found, described by Andrews in 1910. Brown (1981) also declared the name Cryptoclidus oxoniensis (used by many authors as the type species) a nomen dubium based on a non- diagnostic vertebra ("Plesiosaurus" oxoniensis Phillips 1871).

Cryptoclidus is among the best documented of all plesiosaurs, known from many specimens, including adults and juveniles. The skull is relatively broad, rather lightly built, and notable for the dense arrangement of thin, sharply inclined outward pointing teeth that intermeshed when the jaws met. There were 24-27 teeth on each ramus of the mandible for approximately a hundred total in the entire mouth. Cryptoclidus probably fed on schools of soft-bodied cephalopods and small fish, using its many teeth as a filter or trap--its lightly built skull and jaws were not designed to resist strong twisting forces generated by biting or tearing prey. The small size of its external nasal openings and the forward position of the internal nares on the roof of its mouth have suggested to some researchers (Brown & Cruickshank 1994) that its nostrils were not used for breathing, but for "smelling" underwater--Cryptoclidus would have passed water through the internal nares on the roof of its mouth, then up and out its nose to detect chemical traces of prey.

Vertebrae: 29-32 cervicals / 3 pectorals / 20-23 dorsals / 4 sacrals / 25 caudals
Length: 3-4 m. (10-13 ft.); skull: 22 cm. (9.4 in.); mandible: 25.4 cm. (10.25 in.)

Type Species: Cryptoclidus eurymerus [yoor-i-MEER-uhs] (Phillips 1871) "wide femur": for a humerus that widens at the bottom--the namesake limb bone was originally mistaken for a hindlimb, thus the misleading species name eurymerus "wide femur."

Additional species: Cryptoclidus richardsoni [RICH-ahrd-SOH-nie] (Lydekker 1889) for Nelson M. Richardson of Dorset, who collected the specimen (nearly complete skeleton without skull); differs in shape of humerus, which is not expanded at the front bottom end.

NOTE: Cryptoclidus oxoniensis [ok-soh-nee-EN-sis] (Phillips 1871) "from Oxford, England," often cited as the type species, was declared a nomen dubium by Brown (1981), who made redefined Cryptoclidus eurymerus the type species based on a neotype specimen (BMNH R.2860). Plesiosauroidea Cryptoclididae Late Jurassic (Callovian) Eur.

Discosaurus Leidy 1852 "disk (vertebra) lizard"

DIS-ko-SAWR-uhs (Gr. diskos "discus" + Gr. sauros "lizard") (m) named for the round shape of an isolated tail vertebra. Welles (1962) suggested it was pliosaurian. Plesiosauria i.s. Late Cretaceous NA. [nomen dubium]

Dolichorhynchops Williston 1902 "long snout face"

DOL-i-ko-RING-kops (Gr. dolikhos "long" + Gr. rhygkhos "snout, beak" + ops "face") (m) named for the "remarkably elongate and slender form" of the skull, with "the facial region much attenuated," resulting in a narrow, elongated snout, reminiscent of ichthyosaurs; known from a number of complete adult skeletons with skulls, as well as partial skeletons and skulls of juveniles.

Studies by Ken Carpenter (1996: Neues Jahrbuch fuer Geologie und Palaeontologie. Abhandlungen. 201 (2): 259-287) indicate Dolichorhynchops is a definable genus distinct from the geologically earlier Trinacromerum, often considered a synonym. Carpenter differentiated the two genera based in part on the form of their teeth (slender and finely ridged in Dolichorhynchops; robust and coarsely ridged in Trinacromerum), and the shape of the temporal openings in the skull (short and wide in Dolichorhynchops; long and narrow in Trinacromerum). The two genera also occur in different stratigraphic ranges in the interior of western North America: Trinacromerum for 3.3 million years to upper Cenomanian; Dolichorhynchops for 4 million years during lower Campanian.

Vertebrae: 19 cervicals / 3 pectorals / 23-24 dorsals / 3 sacrals / ?23-25 caudals
Length: 3-5 m. (10-17 ft.); skull: 52-98 cm. (17-39 in.); mandible: 56-102 cm. (20-41 in.).

Type Species: Dolichorhynchops osborni Williston 1902 "in honor of Prof. H[enry] F[airfield] Osborn of Columbia University" (Holotype: KUVP 1300); Synonyms: Trinacromerum osborni; Trinacromerum bonneri.

NOTE: "Trinacromerum bonneri" Adams 1997, was described in a paper written, but not published, before Ken Carpenter's 1996 revision of Trinacromerum and Dolichorhynchops. Carpenter attributes the skull in the Kansas Museum of Natural History (KUMNH 40001) that Adams used as part of the type specimen of T. bonneri to Dolichorhynchops osborni--Trinacromerum bonneri Adams appears to be a junior synonym of Dolichorhynchops osborni Williston as defined by Carpenter (1996). Plesiosauroidea Polycotylidae Late Cretaceous (Campanian) NA.

Dravidosaurus Yadagiri & Ayyasami 1979 "Dravidian lizard"

dra-VID-o-SAWR-uhs (from Dravidandu + Gr. sauros "lizard") (m) named for Dravidandu, the region of the southern Indian peninsula, where the fossil was found. The fragmentary specimen consisted of bones originally misidentified as armor plates supposedly belonging a very small stegosaurian dinosaur. Chatterjee and Rudra (1996: Memoirs of the Queensland Museum 39(3): 489-532) reidentified the remains as highly weathered limb and girdle elements that probably belong to plesiosaurs. Plesiosauria Late Cretaceous India [nomen dubium]

Edgarosaurus Druckenmiller 2002 "Edgar (Montana) lizard"

ED-guhr-o-SAWR-us (Edgar + Gr. sauros "lizard") (m) named to indicate a plesiosaur found near the community of Edgar, in Carbon County, Montana. Edgarosaurus is a moderate size (around 3.5 m (11.7 ft) long) short-necked plesiosaur, known from a complete skull, 34 vertebrae (26 neck/3 pectoral/5 dorsal), and a nearly complete forelimb (Holotype: MOR 751 (Museum of the Rockies, Bozeman, Montana)), found in the Early Cretaceous (upper Albian), upper Thermopolis Shale, near Edgar, Carbon County, Montana. Recent research has questioned the traditional idea that all short-necked plesiosaurs are related; instead, polycotylids are thought to represent a group of specialized plesiosauroids that developed shortened necks independently of pliosauroids. Edgarosaurus differs from known polycotylids in having a relatively robust and only moderately elongated rostrum, in retaining a pineal opening in the skull roof, in lacking a vomeronasal fenestra and in possessing large caniniform teeth; its neck is also relatively long (26 vertebrae). However, Edgarosaurus has derived features on its palate similar to those of polycotylids, and also has single-headed ribs, and wide and short epipodials on its fins, unlike pliosauroids. For now, Edgarosaurus appears to be a possible primitive polycotylid or close relative of polycotylids.

Type Species: Edgarosaurus muddi [MUH-die] Druckenmiller 2002: in memory of Kevin Mudd of Bridger, Montana. Plesiosauroidea Polycotylidae(?) Early Cretaceous (upper Albian) NA [added 6-2002]

Elasmosauridae Cope 1869 "Elasmosaurus [plate-lizard] family"

e-LAS-mo-SAWR-i-dee (masc. plural) Plesiosauroids with very long necks (32-72 vertebrae); individual cervical vertebrae are typically more elongated than in other plesiosaurs, particularly in the anterior region of the neck. Late Jurassic and Cretaceous forms have single-headed cervicals ribs. Traditionally, most authors have used this family for all forms with very long necks, but new research has begun to complicate the picture. The family may date back to the Early Jurassic (Eretmosaurus) (Bardet 1995). Colymbosaurus and Tricleidus, once considered elasmosaurs (Brown 1981), now appear to be a long-necked cryptoclidids (Brown 1993). Bakker (1993) has argued that Cretaceous elasmosaurs (from Brancasaurus on), evolved separately from pliosaurs similar to Leptocleidus and are not closely related to long-necked Late Jurassic forms such as Muraenosaurus, making the traditional version of Elasmosauridae an unnatural group. Carpenter (1996, 1997), by contrast, has retained the traditional Elasmosauridae (including Jurassic forms) and revised the short-necked polycotylids as a family of plesiosauroids closely related to elasmosaurids (see Polycotylidae below). The incompletely known Late Cretaceous Artistonectes and Morturneria have skulls with filter-trap jaws similar to cryptoclidids, but have been placed in the Elasmosauridae by Bardet (1995).

Jurassic elasmosaurids differ from Cretaceous elasmosaurids in a range of features, but most notably the construction of the front limb girdle. Jurassic forms, like all other types of plesiosaurs, have scapulae that are proportionately much smaller than the coracoids. In contrast, many Late Cretaceous elasmosaurids have well-developed scapulae, indicating muscles that could power a strong backing stroke, making the animals highly maneuverable. In Cretaceous elasmosaurs the right and left coracoids meet along the animal's midline then separate toward the back to form a scooped-out, roughly heart-shaped opening--Jurassic elasmosaurids and other types of plesiosaurs lack this rounded separation in the front limb girdle.

Members: Elasmosaurus (type), ?Eretmosaurus, Microcleidus, Muraenosaurus, Brancasaurus, Woolungasaurus, Alzadasaurus, Aphrosaurus, Fresnosaurus, Hydralmosaurus, Hydrotherosaurus, Leurospondylus, Libonectes, Mauisaurus, Morenosaurus, Styxosaurus, Thalassomedon, Tuarangisaurus, (?Aristonectes, ?Morturneria) Undescribed members: Courtenay Museum elasmosaurid, a very large elasmosaurid (est. 10 m. (34 ft.)) discovered on the Puntledge River west of Courtenay on eastern Vancouver Island, British Columbia; probably a new genus, although study of the specimen has not been completed. Its lower jaw is large for an elasmosaur (about half a meter in length). "Elasmosaurus" amalitskii Pravoslavlev 1914, from the Turonian of the Liski River, Don Province, Russia, is based on a large series of vertebrae, including greatly elongated cervicals; Welles (1962) considered the material undiagnostic, but restudy of the specimen could permit a modern rediagnosis, possibly as a new genus.

Elasmosaurus Cope 1868 "plate (bone) lizard"

e-LAS-mo-SAWR-uhs (Gr. elasma "metal plate" + Gr. sauros "lizard") (m) "called Elasmosaurus...from the...great plate bones of the sternal and pelvic regions" (Cope 1868: Proceedings of the Academy of Natural Sciences Philadelphia (v. 20)). (Contrary to some sources, the name Elasmosaurus does NOT mean "ribbon lizard" or "swan lizard.") The "plate bones" on the underside of the animal consisted of flattened scapulae and coracoids that braced the front limbs, and wide flattened pubes and ischia that braced the hind limbs. Cope originally misinterpreted the scapula bones as "pubes" (Transactions of the American Philosophical Society 1869 (withdrawn and republished)), but later "corrected" his analysis (TAPS 1870 corrected version), and re(mis)identifed the scapula bones as "clavicles." Regrettably, the original fossil "plate bones" that inspired the name Elasmosaurus are now lost from the type material remaining in the Academy of Natural Sciences in Philadelphia (ANSP 10081).

According to the original 1868 description, Cope's creature's "propulsion was more largely accomplished by its tail than by its paddles"--but the "tail" referred to was really Elasmosaurus' spectacular long neck! In a notorious scientific blunder, Cope had mistakenly attached the animal's head to the end of the true tail. He then erected a new reptilian order, Streptosauria "reversed lizards," to accommodate his odd creature --"streptosaurs" resembled plesiosaurs except that all their vertebral articulations were backward! (See additional comments at "Streptosauria.") The type species name Elasmosaurus platyurus "flat-tailed" immortalizes Cope's error--the "enormous and flattened tail" that he characterized in the species name was based on NECK bones with high neural arches along the top. O. C. Marsh "gently" pointed out Cope's anatomical juggling when he saw the specimen during a visit to Philadelphia in early 1870. According to Marsh, the incident so wounded Cope's vanity that it brought on the infamous feud between the two paleontologists. Joseph Leidy also rebutted Cope's reconstruction at a meeting of the Academy of Natural Sciences in March of the same year, though Cope continued to trace his own error to Leidy's 1865 description of Cimoliasaurus, which depicted that plesiosaur's vertebrae upsidedown. Forced to face facts, Cope had to recall, revise, and reillustrate copies of his official description of Elasmosaurus in the Transactions of the American Philosophical Society (1870) at personal expense. Resorting to a devious bit of scientific face-saving, though, he back-dated the corrected version to 1869. (Storrs, 1984. "Elasmosaurus platyurus and A Page from the Cope- Marsh War" Discovery 17(2) 25-27)).

The extraordinary long neck had around 72 cervical vertebrae, a record for vertebrates, and is the longest neck in both relative and absolute terms for any plesiosaur. (The sauropod dinosaur Mamenchisaurus had the longest neck of any known animal at an estimated 13.1 m. (46 ft.) for the largest species (Mamenchisaurus sinocanadorum), but its neck was composed of "only" 19 cervical vertebrae. Some supergiant sauropods from the Late Jurassic of North America (Seismosaurus, Supersaurus, Amphicoelias) may have had even longer necks on proportionately much larger bodies, but adequate skeletons to directly confirm this fact are lacking.)

Elasmosaurus's long neck anchored a surprisingly small head. The type skull was incomplete, consisting of part of a snout with thin teeth and a small occipital condyle; the somewhat more robust head shown in many modern restorations is based on a different specimen now identified as Styxosaurus snowii. Remains of the pelagic predatory ctenoid fish Enchodus were found under the dorsal ribs of the type specimen, leading Cope to conclude that, "The most ravenous fish--the Enchodi, or great barracudas of the Cretaceous, were his food." It thus appears, that despite its small head, Elasmosaurus could catch and swallow fast swimming prey thanks to a wide gape and sharp spike-like teeth.

Ken Carpenter (1997) has restricted the genus Elasmosaurus to its type species Elasmosaurus platyurus, known from the single, incomplete specimen in the Philadelphia Academy of Natural Sciences (ANSP 10081). Other named species of Elasmosaurus either have been redescribed as new genera (E. morgani = Libonectes, E. serpentinus = Hydralmosaurus, E. snowii = Styxosaurus) or need to be revised ("Elasmosaurus" amalitskii).

Vertebrae: 72 cervicals / 5 pectorals / ?18 dorsals / 6 sacrals / ?21 caudals
Length: (estimated) 11-12 m. (37-42 ft.); skull: (estimated) ?40 cm. (16 in.)

Type Species: Elasmosaurus platyurus [plat-ee-YOOR-uhs] Cope 1868 "flat-tailed": referring to the "enormous and flattened tail"-- Cope mistakenly put the animal's head on the tip of its real tail, and the supposed tail cited in the species name actually the animal's neck! Plesiosauroidea Elasmosauridae Late Cretaceous (Campanian) NA.

Embaphias Cope 1894 "saucer (vertebrae)"

em-BAF-ee-as (Gr. embaphion "saucer" + -ias "in character") (m) named for the saucer-like shape of its concave vertebrae; for three vertebrae from the Pierre Shale of South Dakota. Pliosauroidea Late Cretaceous NA. [nomen dubium]

Eretmosaurus Seeley 1874 "oar lizard"

e-RET-mo-SAWR-uhs (Gr. eretmos "oar" + Gr. sauros "lizard") (m) referring to the powerful limb paddles found in plesiosaurs. Scientists in Seeley's day assumed that plesiosaurs "rowed" with their large paddle-like limbs; modern research indicates plesiosaurs swam more like sea lions, using a modified form of underwater "flight." Proposed for "Plesiosaurus" rugosus ("rugose") Owen 1840, a form originally based on isolated vertebrae with rugged surfaces on the centra except on the concave ends, which were smooth. Although this "rugose" appearance is found on the vertebrae of some other types of plesiosaurs and is not diagnostic, Owen used the same species name for a nearly complete, but headless, long-necked plesiosaur skeleton in the British Museum that he illustrated and described in his 1865 "Monograph of the Fossil Reptilia of the Liassic Formations." Seeley (1874) based his new genus Eretmosaurus on the British Museum skeleton. Because of confusion over the type material, Brown and Bardet filed a formal petition with the International Commission on Zoological Nomenclature in 1994. ICZN Opinion 1831 (March 1996) made the headless skeleton (BMNH 14435) described by Owen in 1865 the official holotype specimen for "Plesiosaurus" [Eretmosaurus] rugosus. (M. Benton and P. Spencer, in Fossil Reptiles of Great Britain (1995)(pg. 115), mistakenly indicate that Watson made Plesiosaurus macropterus the neotype of Eretmosaurus in 1911. Watson (1911) transferred Plesiosaurus macropterus to the genus Microcleidus, not to Eretmosaurus.)

Based on its long neck, Bardet (1995) suggests that Eretmosaurus is the earliest known elasmosaurid, although the individual neck vertebrae are not elongated as in later elasmosaurids. Other classifications have listed Eretmosaurus as a plesiosaurid or as a pliosauroid (Brown 1981).

Vertebrae: 35+ cervicals
Length: (estimated) 4-5 m. (14-17 ft.)) (skull not known)

Type Species: Eretmosaurus rugosus [ruh-GOH-suhs] (Owen 1840) "rugose": "distinguishable from all other vertebrae by the peculiarly rugous character of the free or non-articular surfaces of the body." (Owen 1840)) Plesiosauroidea ?Elasmosauridae Early Jurassic (Sinemurian) Eur.

Eurycleidus Andrews 1922 "wide clavicle"

YOOR-i-KLIE-duhs (Gr. eurys "wide" + Gr. kleid- (kleis) "key, clavicle" + -us) (m) alluding to a large clavicular arch similar in form to that of Leptocleidus "but the interclavicle is wider"; for "Plesiosaurus" arcuatus Owen 1840. Based on an incomplete skeleton, and parts of a skull and a lower jaw (the part made the holotype: BMNH 2030). Total tooth count not known, but on each side of the lower jaw at least five large, procumbent teeth in the front, with at least 22 much smaller teeth behind. The neck vertebrae have long centra (a plesiosauroid characteristic), but the skull is large and broad, and the front limb girdle has long coracoids (pliosauroid characteristics). Some authors (Storrs & Taylor 1996) have considered Eurycleidus arcuatus a probable synonym of Rhomaleosaurus megacephalus. However, Cruickshank (1994. Zoological Journal of the Linnaen Society 112:151-178) has identified a juvenile specimen of Eurycleidus that supplies additional information about the taxon. If the identification is correct, Eurycleidus had a mosaic of cranial features found in plesiosauroids (arrangement and shape of bones at the back of the skull and back of the lower jaw) and pliosauroids (large teeth in the front of the jaw and a long symphysis with at least 4 tooth positions), making it a distinct genus that shows a mixture of features traditionally used to separate the Plesiosauria into two superfamilies Plesiosauroidea and Pliosauroidea. Its "intermediate" appearance in turn raises questions about the current system for classifying early plesiosaurs. Eurycleidus was probably a generalist feeder that preyed on soft-bodied animals such as belemnites, small fish and ammonites.

Length: (estimated) 4 m. (13-14 ft.); skull: (estimated) 25.5 cm (10 in.); mandible: 35 cm. (13 in.))

Type Species: Eurycleidus arcuatus [ahr-koo-AY-tuhs] (Owen 1848) "curved," for Plesiosaurus arcuatus Owen 1840, in apparent reference to the "nearly circular" contour of the articular surface on the body of the vertebrae, contrasting with the "triangular form" of the centra of the vertebrae in "Plesiosaurus" subtrigonus Owen 1840.

NOTE: The species Eurycleidus megacephalus proposed by Andrews in 1922 for "Plesiosaurus" megacephalus Stutchbury 1846, and still recognized by some authors, was classified as Rhomaleosaurus megacephalus by Cruickshank (1994). (See Rhomaleosaurus)). ?Pliosauroidea Early Jurassic (Hettangian) Eur.

Eurysaurus Gaudry 1878 "broad lizard"

YOOR-i-SAWR-uhs (Gr. eurys "wide, broad" + Gr. sauros "lizard")* (m) so-named "because the animal must have had a very broad head and body," based on the large proportions of preserved parts of its skull; type material (cranium, teeth and 5 vertebrae) from Echenoz-la-Meline, France, is now lost. Pliosauroidea Early Jurassic Eur. [nomen dubium]

Fresnosaurus Welles 1943 "Fresno (County) lizard"

FREZ-no-SAWR-uhs (Fresno + Gr. sauros "lizard") (m) named for Fresno County, California, where the fragmentary type skeleton was found in the Moreno Formation; a juvenile specimen "of more massive proportions" than Aphrosaurus, with an unusual coracoid and humerus.

Length: Adult size unknown but estimated by Welles (1943) to be "very large" (35+ ft.) from the massive proportions of the juvenile.

Type Species: Fresnosaurus drescheri [DRESH-uhr-ie] Welles 1943 : for Arthur Drescher, "who was in charge of collecting the Pasaena plesiosaurs." (Holotype: CIT 346) Plesiosauroidea Elasmosauridae Late Cretaceous (Maastrichtian) NA.

Georgia Ochev 1976 "for Georgy (Ochev)"

gay-OR-gee-uh (Georgii + -ia) (f) named to honor V. A. Ochev's father, Georgy Ochev, a geodesist, whose death coincided with his son's work on describing the specimen from Penza Province, in the Volga Region of Russia. (V.A. Ochev, personal communication). NOTE: In principle, the "g" would be pronounced hard in a Russian-derived name. (Preoccupied by Georgia Baird & Girrard 1853; see Georgiasaurus) [= Georgiasaurus]

Georgiasaurus Ochev 1977 "Georgy's lizard"

gay-OR-gee-uh-SAWR-uhs (Georgii + -ia + Gr. sauros "lizard") (m) named to honor V. A. Ochev's late father, Georgy Ochev (replacement for preoccupied Georgia Ochev). Originally a complete skeleton, the specimen was damaged in preparation of the quarry stone. Poorly preserved bones left impressions and cavities in the matrix that indicate a plesiosaur with clear resemblances to the narrow-skulled Trinacromerum, but with a relatively shorter skull.

Length: (estimated) 4-5 m. (13-16 ft.); skull: (estimated) 70 cm. (28 in.))

Type Species: Georgiasaurus penzensis [pen-ZEN-sis] Ochev, 1977 "from Penza Province" in the Volga Region of central Russia, where the type material was found. (Holotype: Penza Province, Regional Studies Museum 11658).

NOTE: The generic name Georgiasaurus has NO connection with the country (and former Soviet Republic) in southwest Asia called Georgia in English, Gruziya in Russian. Plesiosauroidea Polycotylidae Late Cretaceous (Santonian) EEur.

Halidracon Wagler 1830 "sea dragon"

ha-LID-ra-kon (Gr. halis "sea" + Gr. drakon "dragon") (m) for an animal belonging to the Gryphi, erected by Wagler for marine animals supposedly between mammals and birds. [= Plesiosaurus]

Hauffiosaurus O'Keefe 2001 "Hauff (Museum) lizard"

HOW-fee-oh-SAWR-uhs (Hauffius + Gr. sauros "lizard") (m) named for the Hauff Museum (Urwelt-Museum Hauff) in Holzmaden, Baden-Wuerttemberg, Germany, where the type specimen is housed; the private Hauff Museum was established by Dr. Bernhard Hauff (1866-1950), who prepared fossils found in the famous Holzmaden slate quarries of southern Germany. Hauffiosaurus is a relatively small (2.5 m (8.3 ft) long) pliosaurid known from a complete skeleton (Holotype: uncatalogued specimen in Hauff Museum) found in the Early Jurassic (Toarcian) Posidonien-Schiefer, in Holzmaden, Germany. The narrow, extended snout has a long symphysis, with 7 teeth in the premaxilla; the palate shows a mixture of primitive and derived features, intermediate between Macroplata and Peloneustes. The propodials (humerus and femur) are proportionately extremely long-- longer than any of the bones in the associated limb girdles, a situation not found in any other known plesiosaurs. Hauffiosaurus has relatively small limb girdles, high aspect-ratio fins and a relatively long neck (somewhat less than 1/3 length of entire body) for a pliosauroid.

Skull: 43 cm (17.2 in) long
Vertebrae: 28-30 cervicals/(probably around ?5 pectorals/ ?20 dorsals /?4 sacrals / ?30 caudals)
Length: 2.5 m (8.3 ft).

Type Species: Hauffiosaurus zanoni [ZAN-o-nie] O'Keefe 2001: for the American paleontologist Robert Thomas Zanon (1957-1990) "who first realized this specimen represented a new genus." Pliosauroidea Pliosauridae Early Jurassic (Toarcian) Eur. [added 6-2002]

Hexatarsostinus Hawkins 1840 "six-tarsal boned"

HEK-sa-tar-SOS-tin-uhs (Gr. hexa "six" + Gr. tarsos "tarsus" + Gr. ostinos "bony") (m) named for the construction of its paddles, with extra bones. Plesiosauria i.s. Early Jurassic Eur. [nomen dubium]

Hydralmosaurus Welles 1943 "salt water lizard"

hie-DRAL-mo-SAWR-uhs (Gr. hydralme "salt water" + Gr. sauros "lizard")* (m) named to indicate a sea-going elasmosaurid; proposed for "Elasmosaurus" serpentinus Cope, 1877, based on a nearly complete skeleton (lacking skull) from Nebraska (Holotype: AMNH 1495); notable for a massive humerus, indicating a powerful swimmer. Carpenter (1999: Paludicola 2(2)) includes Styxosaurus browni Welles 1952 (partial skeleton with skull: AMNH 5835) as a junior synonym of the type species, based on the distinctive posterior expansion on the distal end of the humerus not found in other types of elasmosaurids. The skull has external nares that are elongate in shape.

Vertebrae: 63 cervicals / 3 pectorals / 19 dorsals / 4 sacrals / ?25-30 caudals
Length: (estimated) 11 m. (38 ft.); skull: 37 cm. (15 in.)

Type Species: Hydralmosaurus serpentinus [ser-pen-TIEN-uhs] (Cope 1877) ("serpentine" for its long neck). (Synonyms: Styxosaurus browni Welles 1952.) Plesiosauroidea Elasmosauridae Late Cretaceous (Santonian-Campanian) NA. (revised 7/99)

Hydrotherosaurus Welles 1943 "fisher lizard"

hie-dro-THEER-o-SAWR-uhs (Gr. hydrotheras "fisherman" + Gr. sauros "lizard")* (m) named to indicate "an active piscivore with long, flexible neck"; fish vertebrae were found among its gastroliths, confirming its diet. Hydrotherosaurus was a coast- dweller, known from a complete skeleton with skull (Holotype: UCMP 33912) from the Maastrichtian Moreno Formation, Panoche Hills, Fresno County, California, and notable for vertebrae that are relatively lower and narrower at the anterior end, but broader and higher toward the base compared with other elasmosaurs. In restoring Hydrotherosaurus, Welles gave the ribs a raking angle, slanted backward as in crocodiles, resulting in a narrower, more streamlined body. Welles argued that the traditional broad, turtle-like reconstruction of the plesiosaur trunk with ribs projecting nearly straight out is incorrect and a misinterpretation based on post-mortem crushing of the skeletons.

Vertebrae: 60 cervicals / 2 pectorals / 17 dorsals / 3 sacrals / ?30 caudals
Length: (estimated) 12.75 m. (42 ft.); skull: 33 cm. (13 in.)

Type Species: Hydrotherosaurus alexandrae [al-eg-ZAN-dree] Welles 1943: for Annie Montague Alexander (1867-1950), a fossil collector and science patron who "contributed so much to the work of the vertebrates of the West" through her work with and support for the University of California, Berkeley. Plesiosauroidea Elasmosauridae Late Cretaceous (Maastrichtian) NA.

Ischyrodon von Meyer 1838 "strong tooth"

is-KIE-ro-don (Gr. iskhyros "strong" + Gr. odon "tooth") (m) for a very large tooth from Argau Canton, Switzerland, round in cross-section, with striations on the enamal. [= ?Liopleurodon]

Kaiwhekea Cruickshank & Fordyce 2002 "squid-eater"

kie-FEK-ay-uh (Maori kai "eat" + Maori wheke "squid, octopus" + -a) (f) named to indicate a squid-eating plesiosaur from New Zealand, homeland of the Maori. Kaiwhekea is a large (6.5+ m (22 ft)) long-necked plesiosaur known from an articulated skeleton with skull (Holotype: OU 12649 (Geology Museum, University of Otago, Dunedin, New Zealand)) from the Late Cretaceous (Maastrichtian) Katiki Formation, at Shag Point, North Otago, South Island, New Zealand; commonly referred to as the "Shag Point plesiosaur." The skull is 62 cm (24.8 in) long, triangular in profile, very high with a short snout; the orbits are quite large and face outwardly and forwardly, suggesting a degree of stereoscopic vision. The teeth are relatively small, uniform in shape, thin, pointed and slightly recurved, with 43+ on each side of the upper jaw and 42+ on each side of the lower jaw. The neck is very long for a cryptoclidid (43 vertebrae), with bilobate (binocular) shaped centra that are much wider than long or high (similar to the neck vertebrae of Aristonectes and Morturneria). Its long neck was relatively inflexible, with limited vertical and lateral movement, although its head could pivot. Kaiwhekea likely fed on fast-moving medium to large-sized prey, probably shoals of unarmored cephalopods and small fish--its jaws seemed designed for fast snapping attacks with a wide gape. Its large, forward-facing eyes suggest it hunted in low light levels, further down in the water column than elasmosaurs (which have relatively small, upward-facing eyes and probably hunted prey silhouetted against light from the surface). Cruickshank and Fordyce classify Kaiwhekea as a cryptoclidid, related to Aristonectes and Morturneria. However, O'Keefe (Acta Zoologica Fennica 213 (2001)) has recently classified Morturneria (and Aristonectes) in the Cimoliasauridae; although some key details of its palate and skull are not well preserved and its neck is longer, Kaiwhekea may belong in the Cimoliasauridae sensu O'Keefe.

Skull: 62 cm (24.8 in) long
Vertebrae: 43 cervicals/ 3 pectorals /19-20 dorsals / 3-4?sacrals/ (probably around 25-30 caudals)
Length: 6.5+ m (22 ft)

Type Species: Kaiwhekea katiki [KUH-ti-kee] Cruickshank & Fordyce 2002: for Katiki Beach, "which lies immediately to the north of Shag Point." Plesiosauroidea Cryptoclididae (or Cimoliasauridae) Late Cretaceous (Maastrichtian) New Zealand [added 6-2002]

Kimmerosaurus Brown 1981 "Kimmeridge lizard"

KIM-uhr-o-SAWR-uhs (Kimmer(idge) + Gr. sauros "lizard") (m) named for the stratigraphical horizon of the type specimen (a partial skull): Kimmeridgian Stage, Kimmeridge Clay, at Dorset, England; known from three partial skulls with mandibles, and a few neck vertebrae, including the atlas/axis. The skull is broad, but very lightly built, and more elongated than in Cryptoclidus. The teeth are highly recurved, thin, sharply pointed, with 36 in each side of the lower jaw, indicating a trap-feeder on relatively small, soft prey. The axis/atlas and neck vertebrae are similar to Colymbosaurus, a genus found in the same deposits. Colymbosaurus is only known from skeletons without a skull, and the skull of Kimmerosaurus could very well belong to Colymbosaurus, making Kimmerosaurus a junior synonym (Brown, Milner & Taylor, 1986). See additional comments at Colymbosaurus.

Length: skull: (estimated) 22 cm. (17 in.); mandible (estimated) 30 cm. (12 in.)

Type Species: Kimmerosaurus langhami [LANG-uhm-ie] Brown 1981 for "R. A. Langham, Esq., of Reading, Berkshire, who found the holotype skull [BMNH R. 8431] in 1967 and presented it to the British Museum (Natural History) the following year." Plesiosauroidea Cryptoclididae Late Jurassic (Kimmeridgian) Eur. [= ?Colymbosaurus]

Kronosaurus Longman 1924 "Kronos lizard"

KRON-o-SAWR-uhs (Kronos, a Titan in Greek mythology + Gr. sauros "lizard") (m) named for Kronos, a mythical giant Titan who ruled the universe before his son Zeus overthrew him; alluding to the animal's huge size and fierce appetite--Kronos swallowed his own children shortly after each was born to prevent any of them from deposing him. His efforts failed when his wife Rhea hid the infant Zeus and substituted a rock wrapped in swaddling to deceive her cannibalistic husband.

Although widely illustrated and discussed in popular books, the genus Kronosaurus remains problematical. The name Kronosaurus queenslandicus was originally proposed by Heber Longman in 1924 for poorly preserved but very large lower jaw fragments found near Hughendend, Queensland, Australia in 1899 (Holotype: QM F1609). Gigantic but fragmentary limb elements discovered in 1929 were described in 1932, with part of a humerus indicating an animal larger than Megalneusaurus. A Harvard expedition in 1931- 1932 recovered two specimens of large plesiosaurs in another region of Queensland: a giant incomplete skeleton, removed in part by dynamiting, from Army Downs, 35 miles north of Richmond, Queensland; and the rostrum (with upper and lower jaws) of a smaller individual from Grampian Valley, 30 miles north of Richmond. More recent finds may help clear up many questions about the status of the genus. A nearly complete skull about 6 feet long that was found near the same region as the type specimen jaw fragments, as well as various parts of skeletons and limbs, and a partial skull from the Toolebuc Formation. So far all the material appears to be consistent with a single genus (though perhaps more than one species)--Colin McHenry of the Queensland Museum is studying the new material but his new formal description has not been published yet.

Complicating the picture is the precise identity of the well- known gigantic specimen (MCZ No. 1285) in the Harvard University Museum of Comparative Zoology (originally restored at 12.8 m. (42 ft.); revised estimated total length: 9 m. (30 ft.); skull: originally estimated 2.9 m. (9 ft. 8. in) (likely too long)). The Harvard kronosaur came from the older Wallumbilla Formation. Although identified as Kronosaurus queenslandicus by White in 1935 and Romer in 1959, the famous Harvard kronosaur might be taxonomically distinct from the Hughendend Toolebuc Formation material, at least on the species level. Settling the issue will be difficult. Despite the spectacular appearance of the mounted skeleton at the Museum of Comparative Zoology, much of the Harvard fossil was badly eroded when found. About a third of the displayed specimen was restored in plaster, including large parts of the skull. White (1935) published a description of the Harvard skull material from near Richmond, and what remains of the giant specimen's head and the isolated rostrum suggests the skull was deeper and different in some details from the skull material from Hughendend. Recent examination of the mounted skeleton at Harvard (Colin McHenry, personal communication) indicates that the reconstructed body is too long by about 10 trunk vertebrae. Subtracting the extra vertebrae brings the total length down from around 13 meters (45 feet) to the 9-meter (30-foot) range, thus making the Harvard specimen similar in size and proportions to the recently described Kronosaurus boyacensis Hampe 1992, from Colombia, South America (see below).

The rather speculative nature of the heavily restored Harvard giant seems an irony in view of the mount's history--funding for the preparation of the specimen came from the wealthy Cabot family of Boston, who were involved in reports of the great Boston sea serpent in the 19th century. That notorious incident had clouded the family's reputation, and they wanted to support display of any "sea monster" that might be available at Harvard! R. Zallinger's famous 1955 painting of Kronosaurus for Life Magazine incorrectly depicted the creature swimming at the surface with an overlong, arched, flexible neck (not possible for large pliosaurs) and a head with a rather broad-tipped snout (Kronosaurus had a fairly narrow-tipped snout).

Vertebrae: 12 cervicals / 3 pectorals / 19-20 dorsals / 4-5 sacrals / ?31 caudals [NOTE: Romer and Price (1959) indicated that the Harvard specimen had "probably 30 dorsals"; however, Colin McHenry (personal communication) has revised the estimate down to around 20, consistent with the 19 dorsals indicated for the better preserved Kronosaurus boyacensis (Hampe 1992).]

Type Species: Kronosaurus queenslandicus [kweenz-LAN-di-kuhs] Longman 1924 "from Queensland (Australia)" where the type material was found.

Additional Species: Kronosaurus boyacensis [boy-ah-SEN-sis] Hampe 1992: "from Boyaca Province, Colombia." Known from a fairly complete skeleton with skull (total est. length: 9 m. (30 ft.); skull: 2.36 m. (7.8 ft.); mandible: est. 2.62 m. (8.7 ft.)) found near the village of Leiva, Boyaca Province, in Colombia, South America; notable for thick ribs not found in the Harvard specimen, though whether the ribs are truly pachyostosed (composed of dense bone) can only be determined by cross- sectioning. The Colombian form possibly may be revised as a new genus after more study. Pliosauroidea Brachaucheniidae Early Cretaceous (Aptian-Albian) Aus., SA.

Leptocleidus Andrews 1922 "thin clavicle"

LEP-to-KLIE-duhs (Gr. leptos "slender, thin" + Gr. kleid- (kleis) "key, clavicle" + -us) (m) named for the vertically "thin clavicular arch" along the edge of the front limb girdle, composed of two "rather large" clavicles and a "transversely elongated" interclavicle. Andrews (1922) thought this Early Cretaceous form retained primitive features in the well-developed clavicular arch of its shoulder-girdle, similar to Early Jurassic Liassic plesiosaurs such as Eurycleidus--an idea expressed in the Latin species name superstes "surviving, long-lived". Andrews concluded that "the retention of the primitive condition in Leptocleidus...may be a consequence of the freshwater, probably fluviatile, habitat of this Plesiosaur, which resulted in its leading a life sheltered from the great competition among the marine Plesiosaurs." Other authors (Cruickshank 1997) have found primitive features in the skull as well.

Leptocleidus somewhat resembles the Early Jurassic Rhomaleosaurus, with large clavicles and interclavicle, and small, widely separated scapulae. There are only 21 teeth on each side in the upper jaws (probably 35 teeth in each lower jaw), and indicate a generalist type predator, capable of capturing active prey, or using twist-feeding to tear flesh from a large carcass. The triangular skull has a distinctive crest along the top, running from a forward-pointing "cockscomb" at the very back to a ridge over the nasal region. Unlike early pliosauroids, Leptocleidus has single-headed cervical ribs and a deep central depression in the centra of the neck vertebrae.

Leptocleidus is similar to a modern seal in size and may have had a similar diet and lifestyle. The genus occurs in lagoonal or shallow, close inshore marine facies (Cruickshank 1997), though it may have frequented freshwater environments such as lakes and rivers as well. Despite an apparently restricted habitat, species have been identified from England, South Africa and Australia, suggesting Leptocleidus could move freely along coastlines.

Vertebrae: 13-24 cervicals / ?20 dorsals
Length: (estimated) 2-3 m. (7-10 ft.); skull: 31 cm.(12.5 in.)

Type Species: Leptocleidus superstes [suh-PER-steez] Andrews 1922 "long-lived," alluding to its retention of primitive features found in much earlier plesiosaurs. (Holotype: BMNH R4824)

Additional species: Leptocleidus capensis [kay-PEN-sis] (Andrews 1911) "from Cape Province"; for "Plesiosaurus" capensis Andrews 1911, based on a partial skeleton with incomplete skull found in Cape Province, South Africa. Stromer (1935) created a separate genus named Peyerus for this African form, but most researchers now accept Andrew's assignment of the species to the genus Leptocleidus. (Holotype: SAM-K5822) (See additional comments at Peyerus.)

Leptocleidus clemai [KLEM-uh-ie] Cruickshank & Long 1997; named for John Clema, who helped sponsor the expedition that excavated the fossils. The largest known species (3 m. (10 ft.) long), based on three partial skeletons from the Birdsong Sandstone, north of Kalbarri in Western Australia. Notable for more robust femur and humerus.

NOTE: An opalized specimen about 85% complete recently found in Coober Pedy, South Australia, is still under study. Nicknamed "Eric" (for Eric Idle of Monty Python fame), it appears to be another new species of Leptocleidus, but slightly less than 2 meters long. Teleost fish vertebrae and gastroliths were found in the gut region. Pliosauroidea Early Cretaceous (Hauterivian-Berremian) Eur., SAfr., Aus.

Leurospondylus Brown 1913 "flat vertebra"

LOOR-o-SPON-di-luhs (Gr. leuros "smooth, even, flat" + Gr. spondylos "vertebra") (m) named "in reference to the flat vertebrae," contrasting with the concave-ended centra found in most other plesiosaurs. Based on a partial skeleton (without a skull) (Holotype: AMNH 5261) of a juvenile "plesiosaur associated with dinosaur remains high up in the brackish water Edmonton beds" of the Red Deer River, Alberta, Canada (Horseshoe Formation). Only 12 neck vertebrae were found, but Barnum Brown estimated from the relative sizes that "twice the number preserved, if not more, were present in life," and that the immature animal would have been "about seven feet in length exclusive of the head." Welles (1962) noted that "The cervical vertebrae are very short, suggesting pliosaurian relationships, whereas the scapulae and coracoids seem to be elasmosaurian, as do the short pubes." The specimen appears to represent a distinct taxon, but it might possibly be the juvenile of another known species. The discovery of a juvenile plesiosaur in a non-marine setting lends support to the idea that some plesiosaurs spent the early part of life in estuarine or freshwater environments, then migrated to the open sea. Some species remained non-marine as adults, though whether this was the case with Leurospondylus has not been determined.

Type Species: Leurospondylus ultimus [UHL-ti-muhs] Brown 1913 "last," because it was thought to be the last occurrence of a plesiosaur: "so far as known marks the termination of this group of Mesozoic reptiles." (Brown 1913) However, revised dating of the Horseshoe Canyon Formation (Gibson 1977) means that some California elasmosaurids (Morenosaurus) were younger in age. Plesiosauroidea Elasmosauridae Late Cretaceous (Maastrichtian) NA.

Libonectes Carpenter 1997 "Southwest swimmer"

LIE-bo-NEK-teez (Gr. libo- (lips) "southwest wind" + Gr. nektes "swimmer") (m) named for the American Southwest, the region in which the holotype was found (Britton Formation, Eagle Ford Group, Dallas County, Texas); proposed for "Elasmosaurus" morgani Welles 1949. The holotype material (SMUSMP 69120) now consists only of a skull (with braincase preserved), lower jaw and 62 neck vertebrae (est. length: 18.5 ft.); a large front-limb girdle (scapulae and coracoids) and part of a humerus described and illustrated by Welles were later discarded(!) by museum staff, but appear to indicate an animal with trunk and limb proportions similar to Elasmosaurus, though with a shorter neck. Libonectes differs from Elasmosaurus in the short and deep shape of the atlas/axis centrum (long and low in Elasmosaurus). The external nares are elongate in shape and located over maxillary teeth 3-4. The new generic name Libonectes was suggested by Ben Creisler.

Vertebrae: 62 cervicals
Length: (estimated) ?10 m. (?34 ft.); skull: 42.5 cm. (17 in.); mandible: (estimated) 55 cm. (22 in.)

Type Species: Libonectes morgani [MOR-ga-nie] (Welles 1949): for Charles Gill Morgan, who obtained and prepared the specimen. Plesiosauroidea Elasmosauridae Late Cretaceous (Turonian) NA. (revised 7/99)

Liopleurodon Sauvage 1873 "smooth-sided tooth"

LIE-o-PLOOR-o-don (Gr. leios "smooth" + Gr. pleuron "side" + Gr. odon "tooth") (m) named for a very large tooth with contrasting sides: "one side is nearly smooth, while the other has strong striations that run its length, the two edges being marked by a rather prominent ridge." (Sauvage 1873) The type material consisted of an isolated tooth found in the Oxford Clay of Wast near Boulogne-sur-Mer in northern France.

The original tooth is considered diagnostic and appears identical to teeth found with an associated skeleton (BMNH R. 3536) in the Oxford Clay at Peterborough, England. Based on the skeleton now in the British Museum, Tarlo (1960: Bulletin of the British Museum (Natural History) (Geology) 4(5)) recognized Liopleurodon as a genus distinct from Pliosaurus, with a lower jaw that has a short symphysis with 5-7 pairs of large canine-like teeth, and a total of 25-28 teeth in each ramus of the jaws; the teeth are circular in cross-section. (Pliosaurus has a longer symphysis with up to 10-11 pairs of large teeth, with a total of 30-38 teeth in each ramus of the jaws; the teeth are trihedral in cross-section.) The propodials and epipodials are long and robust, indicating a powerful swimmer. Liopleurodon was a giant form with a skull nearly a quarter of the animal's entire length- -isolated vertebrae and jaw parts indicate Liopleurodon could reach 15 m. (50 ft.) with a jaw over 3 m. (10 ft.) long, exceeding the heavily restored Harvard Kronosaurus in size.

Vertebrae: 17-20 cervicals
Length: (estimated) 12-15 m. (39-50 ft.); skull: up to 2.2-3 m. (8-10 ft.)

Type Species: Liopleurodon ferox [FER-oks] Sauvage 1873 "fierce"; for the large size of its teeth; the largest known species, possibly reaching 15 meters (50 ft.). (Callovian)

Additional Species: Liopleurodon pachydeirus [pak-ee-DIE-ruhs] (Seeley 1869) "stout-necked": differs from Liopleurodon ferox in the form of the neck vertebrae, which are longer, with a faint keel on the underside; the longitudinal ridges on the tooth enamel are finer and more closely packed than in Liopleurodon ferox. (Callovian)

Liopleurodon rossicus [ROS-i-kuhs] (Novozhilov 1964) "Russian"; for Pliosaurus rossicus Novozhilov 1964, a large pliosaur from the Lower Volgian of the Moscow Basin, Russia, based on a skull; teeth trihedral in cross-section. (Tithonian)

Liopleurodon macromerus [mak-ro-MEER-uhs] "long femur" (Phillips 1871). Tarlo (1959) created a new genus Stretosaurus for Pliosaurus macromerus Phillips 1871, based on the supposedly unusual form of the scapula. Halstead [= Tarlo] (1989) reidentified the "scapula" as an ilium after a more complete specimen was found, and transferred the species to Liopleurodon. However, Tarlo's 1960 definition mentions teeth that are trihedral in cross-section, considered a characteristic of Pliosaurus. Hampe (1992) disputed Halstead's (1989) placement of this species in the genus Liopleurodon, and restored it to Pliosaurus. The species is also identified from Argentina, South America. (Kimmeridgian-Tithonian) Pliosauroidea Pliosauridae Late Jurassic (Callovian-Tithonian) Eur., EEur., SA., ?NA.

Luetkesaurus Kiprijanoff 1883 "Luetken's lizard"

LOOT-kuh-SAWR-uhs (Luetken + Gr. sauros "lizard") (m) to honor Christian Frederich Luetken (1827--1901), Danish zoologist and paleontologist; proposed for teeth that are finely striated, and vertebrae, found in the Sewerisch Osteolite of the Kursk region of western Russia. No type species designated. Pliosauroidea Late Cretaceous EEur. [nomen dubium]

Macroplata Swinton 1930 "long blades"

ma-KROP-la-tuh or MAK-ro-PLAY-tuh (Gr. makros "long, large" + Gr. plate "a blade, and, especially in the plural, the shoulder-blades")* (f) referring to the frontlimb girdle, with "very long and comparatively narrow coracoids which have considerable preglenoidal extension"; the shoulder blades (scapulae and coracoids) were modified to form large bony plates on the underside of the body to brace the front paddles. Like other short-necked plesiosaurs, Macroplata had coracoids that were proportionately much larger than the scapulae, indicating a powerful forward stroke for fast swimming. Macroplata is a relatively primitive short-necked form, with a needle-nosed snout and a tapering, rather rigid neck a little over twice the length of the skull, made of short flattened, vertebrae.

Vertebrae: 27 cervicals / 5 pectorals / 19 dorsals / 4 sacrals / 30-32 caudals
Length: 4.5 m. (15.4 ft.); skull: 58 cm. (1.9 ft.))

Type Species: Macroplata tenuiceps [te-NOO-i-seps] Swinton 1930 "narrow headed" for the narrow, elongated, subtriangular form of its skull. (Holotype: BMNH R.5488) (Hettangian)

Additional species: Macroplata longirostris [lon-ji-ROS-tris] (Blake 1876) "long-snouted"; for "Plesiosaurus" longirostris Blake 1876, transferred to Macroplata by White in 1940; with a very long thin snout, about half the length of the entire skull and a jaw symphysis 13 tooth positions long. Some authors have included the species "Plesiosaurus" longirostris in Rhomaleosaurus; it may be revised as a new genus. (Holotype: MCZ 1033) (5 m. long; skull 70 cm. long) (Toarcian) Pliosauroidea Early Jurassic (Hettangian(-Toarcian)) Eur.

Maresaurus Gasparini 1997 "sea lizard"

MAR-ee-SAWR-uhs (Lat. mare "sea" + Greek sauros "lizard")* (m) named to indicate a marine pliosauroid found in the Neuquen Basin, central-western Argentina. Known only from a skull and mandible (Holotype: MOZ 4386 V (Museal Prof. Olsacher, Zapala, Neuquen)), and a few neck vertebrae; the form has a medium-length spatulate snout similar to Simolestes, which it may otherwise have resembled. In some features, Maresaurus appears to be intermediate between the primitive Rhomaleosaurus and the derived Simolestes, but determining its true phylogenetic position would require a revision of all Jurassic pliosauroids. The shortenend spoon-shaped snout in the three animals could be an example of convergence based on similar diets or life style rather than evidence of close evolutionary kinship.

Length: (estimated) 5-6 m. (16-20 ft.); skull: .8 m. (2.5 ft.))

Type Species: Maresaurus coccai [KOH-kah-ie] Gasparini 1997: for "the brothers Sergio and Rafael Cocca, members of the Museo Prof. Olsacher of Zapala, and valuable collaborators in all the fieldwork related to the search for marine reptiles in the Neuquen Basin." Pliosauroidea Middle Jurassic (Bajocian) SA.

Mauisaurus Hector 1874 "Maui's lizard"

MOW-ee-SAWR-uhs (Maui (Maori demi-god) + Gr. sauros "lizard") (m) named for Maui, a Maori demi-god and hero; to indicate a plesiosaur found in New Zealand, home of the Maori people. Mauisaurus remains a poorly known form, originally based on material from several localities; Welles (1962) designated the pubes and pelvic paddle as the lectotype, indicating "a unique plesiosaur" characterized by a narrow pubis and what Welles called a "long narrow femur" with a shape and form "quite different from other plesiosaurs." However, Hector had figured the femur in edge-on view, rather than face on, misleading Welles. Welles, along with D.R. Gregg, redescribed the material after personal examination in 1971 (Records of the Canterbury Museum), noting that the femur was in fact "distinctive in being short and massive with a hemispherical capitulum and extremely rough muscle scars on the medial surface of the shaft." The adult animal's size is difficult to estimate from currently available material (a few vertebrae, limb elements), but it may have been up to 12 m. (40 ft.) long.

Type Species: Mauisaurus haasti [HAHS-tie] Hector 1874 : for Julius Haast (Sir Julius von Haast), who found the first specimens, and was also the founder and first director of the Canterbury Museum in Christchurch, Canterbury Province, New Zealand. (Holotype (Lectotype Welles 1962): DM R1529 (Dominion Museum)) Plesiosauroidea Elasmosauridae Late Cretaceous (Maastrichtian) NZ.

Megalneusaurus Knight 1898 "great swimming lizard"

MEG-al-nyoo-SAWR-uhs (from Gr. megal- (megas) "great" + Gr. neus- (neusis) "swimming" + Gr. sauros "lizard") (m) named to indicate "the largest known animals of the order Sauropterygia," with a forelimb and paddle originally (over)estimated at 2.209 meters in length (1.5 meters may be more realistic); the largest known plesiosaur prior to the discovery of Kronosaurus, and apparently similar in size to giant specimens of Liopleurodon. Williston (1903) states that "A large portion of the type species is known; the parts so far described are the vertebrae and limbs." However, some of the original remains (ribs, vertebrae) mentioned by Knight and Williston now would appear to be lost, since the surviving specimen consists only of a fore-paddle, some vertebrae and fragments of a pectoral girdle--material many researchers (but not all) have considered inadequate to diagnose a genus and species. The relatively long and slender humerus appears distinct in some details from the forelimbs of other Jurassic pliosaurs. Recently Weems and Blodgett (U.S. Geological Survey Bulletin 2152: 169-175 (1996)) have identified parts of a plesiosaur humerus from the Late Jurassic Naknek Formation of southern Alaska as Megalneusaurus, though the animal would have been about half as large as the type specimen individual. Robert Bakker is restudying the type material.

Length: (estimated) ?10-14 m. (?34-46 ft.))

Type Species: Megalneusaurus rex [reks] (Knight 1895) "king," for its large size; for Cimoliosaurus rex Knight 1895. Pliosauroidea Late Jurassic (Kimmeridgian-Portlandian) NA.

Microcleidus Watson 1909 "small clavicle"

MIEK-ro-KLIE-duhs (Gr. mikros "small" + Gr. kleid- (kleis) "key, clavicle" + -us) (m) named for the small size of the clavicles: "The clavicular arch is reduced to thin sheets of bone adherent to the dorsal surface of the anterior rami of the scapulae. The interclavicle seems to have vanished completely" (Watson 1909); proposed for "Plesiosaurus" homalospondylus Owen 1865, founded on a nearly complete skeleton with a long neck (missing limb girdles) in the British Museum (BMNH 36184); Watson's description (1909) is based on a specimen in Manchester Museum (L. 7077, Manchester Museum), which included the limb girdles. The centra of the anterior neck vertebrae are relatively elongated; considered the earliest elasmosaurid by some researchers (Brown 1981).

Vertebrae: 39-40 cervicals / 5 pectorals / 17 dorsals / 3 sacrals / ?28 caudals
Length: 6 m. (20 ft.); skull: .25 m. (10 in.)

Type Species: Microcleidus homalospondylus [HOM-a-lo-SPON-di- luhs] (Owen 1865) "even vertebrae": "for the even or level character of the terminal articular surfaces of the cervical vertebrae" (Owen 1865). (Holotype: BMNH 36184) Additional Species: Microcleidus macropterus [ma-KROP-ter-uhs] "large fin" (Seeley 1865); for "Plesiosaurus" macropterus Seeley 1865 ("the limbs are very large, and the hinder ones being slightly longer"). Watson (1911) transferred the species to Microcleidus because of similarities in the vertebrae and limb girdles, but considered the species distinct from M. homalospondylus based on differences in the limb structure.

NOTE: Bakker (1993) included the species Plesiosaurus brachypterygius Huene 1923 in the genus Microcleidus as Microcleidus brachypterygius (Heune 1923). However, Storrs (1997) has studied the original specimens and classifies the species Plesiosaurus brachypterygius as a junior synonym of Plesiosaurus guilelmiimperatoris Dames 1895. Plesiosaurus is very different from Microcleidus. Plesiosauroidea Elasmosauridae Early Jurassic (Toarcian) Eur.

Morenosaurus Welles 1943 "Moreno (Formation) lizard"

moh-REEN-o-SAWR-uhs (Moreno (anglicized Spanish moreno "brown") + Gr. sauros "lizard") (m) named for the Moreno Formation (Maastrichtian) of the Panoche Hills, Fresno County, California, where the nearly complete type skeleton (Holotype: CIT 2802), lacking a head, was found. A relatively short-necked elasmosaur, notable for the unusual construction of its limb girdle, with an interclavicle. The well developed propodials (humerus and femur) appear to indicate an active animal. One of the latest known (upper Maastrichtian) plesiosaurs.

Vertebrae: 47 cervicals / 2 pectorals / 17 dorsals / 3 sacrals / 30 caudals
Length: (estimated) 8.3 m. (28 ft.))

Type Species: Morenosaurus stocki [STOK-ie] Welles 1943 (for Dr. Chester Stock, who collected the fossils). Plesiosauroidea Elasmosauridae Late Cretaceous (Maastrichtian) NA.

Morturneria Chatterjee & Creisler 1994 "for Mort Turner"

mor-tuhr-NEER-ee-uh (Mor(timer) + Turner + -ia) (f) named to honor Dr. Mort D. Turner, noted American geologist, for his support of the Seymour Island project in Antarctica, which recovered the type specimen (skull, vertebrae) (Holotype: TTU P 9219 (Texas Tech University)). (To replace preoccupied Turneria Chatterjee & Small 1989). Morturneria was a "trap" feeder with a broad skull, and upper and lower jaws lined with densely arranged small sharp teeth (38+ maxillary; 46+ dentary; 15 premaxillary), similar to Jurassic cryptoclidids and Aristonectes. The preserved cervical vertebrae are very unusual: the centra are short in length front-to-back (as in "pliosaurs"), broader than long or high (as in "cimoliasaurs"), with a strongly "binocular" shape, unlike the simple cylindrical shape of cervical vertebrae found in other known plesiosaurs (though Aristonectes has ovoid vertebrae toward the base of the neck). The articular ends are flattened: "platycoelous with distinctive lateral ridges." The classification is debated. N. Bardet (1995) has identified Morturneria and the apparently related (and larger) Aristonectes as elasmosaurids rather than cryptoclidids.

Length: skull: (estimated) 40 cm. (16 in.); mandible: 44 cm. (17.5 in.)

Type Species: Morturneria seymourensis [see-moh-REN-sis] (Chatterjee & Small 1989) "from Seymour Island," Antarctica. Plesiosauroidea ?Cryptoclididae (or ?Elasmosauridae) Late Cretaceous (Maastrichtian) Ant.

Muraenosaurus Seeley 1874 "moray eel lizard"

myoo-REEN-o-SAWR-uhs (Muraena genus name for the moray eel (from Lat. muraena (Gr. myraina) "sea eel")) + Gr. sauros "lizard") (m) alluding to the reptile's long neck, suggesting a moray. Muraenosaurus is known from complete skeletons and skulls from the lowest deposits of the Oxford Clay, England, and additional material from the Calvados region of France. In addition to a neck about half the length of the entire body, it had a broad trunk section but proportionately small paddles, and a short tail. Brown (1981) noted many similarities between Muraenosaurus and Cryptoclidus; however, in Muraenosaurus the neck is twice as long, with more vertebrae and longer individual vertebrae; the skull has a proportionately shorter snout and a tooth pattern closely resembling that of a Cretaceous elasmosaurid, with fewer and larger, longitudinally ridged teeth; the front-limb (pectoral) girdle differs in the shape of the coracoids and in having a well-developed interclavicle. The scapulae are relatively small compared to the coracoids (unlike some Cretaceous elasmosaurids, which had scapulae and coracoids about equal in size, indicating a powerful backing stroke), and along with the proportionately small size of the paddles, suggest a maneuverable but rather slow-swimming ambush predator.

Vertebrae: 43-44 cervicals / 3 pectorals / 19-20 dorsals / 4 sacral / 24 caudals
Length: 4.5-5.2 m. (15-21 ft.); skull: 40 cm. (16 in.)

Type Species: Muraenosaurus leedsii [LEED-zee-ie] Seeley 1874: for Charles E. Leeds, a British fossil collector, along with his brother Alfred Leeds. C.E. Leeds showed Seeley the type specimen when Seeley visited Exeter College, Oxford, England. He also wrote up the description published in the Quarterly Journal of the Geological Society from Seeley's dictation. (Holotype: BMNH R.2421)

Additional Species: Muraenosaurus beloclis [BEL-o-klis] Seeley 1892 "arrow clavicle," for the pointed shape of the small interclavicle. A small species, with an estimated adult size of about 2.5 m. (8.4 ft.) long; made a separate genus (Picrocleidus) by Andrews in 1909. Plesiosauroidea Elasmosauridae Late Jurassic (Callovian) Eur. (?West Indies ?SA.)

Occitanosaurus Bardet, Godefroit & Sciau 1999 "Occitanian lizard"

ok-si-TAYN-o-SAWR-us (Occitania + Gr. sauros "lizard") (m) named for Occitania, the area in which the Occitan Romance language is spoken (currently most of southern France, Val d'Aran of Spain and some Piedmont valleys of Italy), to indicate a fossil plesiosaur ("Plesiosaurus" tournemirensis Sciau, Crochet & Mattei 1990) found in southern France. Occitanosaurus is a small (about 4 m (13.3 ft) long) elasmosaurid known from an almost complete, partially articulated skeleton including the skull (Holotype: MMM J.T. 86-100 (Musee Municipal de Millau)), from the Early Jurassic (Upper Toarcian) Alalensis Zone at Tournemire, Aveyron Department, southern France. The skull has spatulate premaxillae containing long curved teeth that are round in cross-section with striations on the crowns. The cervical vertebrae are longer than high, but not "dumb-bell" shaped as in more advanced elasmosaurids, and have double-headed ribs. Occitanosaurus is similar to Microcleidus but has a proportionatley longer skull, a longer neck and a very different pectoral girdle (the interclavicle is well developed; the interclavicle is absent in Microcleidus).

Vertebrae: 43 cervicals / 3 pectorals / 16 dorsals / 4 sacrals / (?25 caudals)
Length: estimated 4 m. (13.3 ft); skull: 25 cm (10 in.)

Type Species: Occitanosaurus tournemirensis [toor-nuh-meer-EN-sis] (Sciau, Crochet & Mattei 1990: "from Tournemire," the town near where the fossil was found in the Aveyron Department, southern France; originally Plesiosaurus tournemirensis Sciau, Crochet & Mattei 1990. Plesiosauroidea Elasmosauridae Early Jurassic (Toarcian) Eur. [added 11/99]

Ogmodirus Williston & Moodie 1913 "straight-line neck"

og-mo-DIE-ruhs (Gr. ogmos "straight line, furrow" + Gr. deire "neck" + -us) (m) named for the "short, uniform centra of the cervical vertebrae." Welles (1943: 193) suggested the specimen could be a juvenile Thalassomedon. Plesiosauroidea Elasmosauridae Late Cretaceous NA. [nomen dubium (?Thalassomedon)]

Oligosimus Leidy 1872 "small shortened (vertebra)"

OL-i-go-SIE-mus (Gr. oligos "little, few" + Gr. simos "depressed, concave, snub-nosed") (m) named for the shape of a small caudal vertebra: "The vertebra is from the base of the tail and is much shorter in relation to its other dimensions than in Plesiosaurus or Discosaurus." Plesiosauria i.s. Late Cretaceous NA. [nomen dubium]

Orophosaurus Cope 1887 "roofed lizard"

OR-o-fo-SAWR-uhs (Gr. orophe "roof" + Gr. sauros "lizard") (m) probably alluding to the coossified neural arches on the neck vertebrae, in contrast to Piptomerus, which had loose, unfused neural arches. Based on three vertebrae (caudals according to Welles). Plesiosauria i.s. Late Cretaceous NA [nomen dubium]

Pachycostasaurus Cruickshank, Martill & Noe 1996 "thick rib lizard"

PAK-ee-KOS-ta-SAWR-uhs (Gr. pakhys "thick" + Lat. costa "rib" + Gr. sauros "lizard") (m) named to indicate a marine reptile with thickened dorsal ribs and heavily ossified gastralia, in constrast to the lightly built bone stucture found in most other known pliosaurids, which pursued prey near the surface. Pachycostasaurus probably fed near the bottom on slower moving prey such as anthropods, and may have been an estuarine or possibly a freshwater form (similar bones have been identified in Australia from a fragmentary freshwater plesiosaur). Heavy bone structure appears to be a feature of juvenile plesiosaurs, associated with a near-shore life-style. The type specimen of Pachycostasaurus seems to have some juvenile features, but whether it represents an immature individual of a previously known species, or whether the thick bone structure would have changed in the fully adult form is unclear at present. The unusual light construction of the skull along with distinctive teeth and the massive and pachyostotic nature of the ribs and lumber vertebrae support status as a distinct genus.

Vertebrae: 13+ cervicals
Length: (estimated) 3.1 m. (10.3 ft.); skull (estimated): 63 cm. (25 in.))

Type Species: Pachycostasaurus dawni [DAW-nie] Cruickshank, Martill & Noe 1996: "after Alan Dawn, discoverer of this new animal" from the Peterborough Member, Oxford Clay Formation, Cambridgeshire, England. (Holotype: PETMG R338 (Peterborough City Museum and Art Gallery)) Pliosauroidea Middle Jurassic (Callovian) Eur.

Pantosaurus Marsh 1893 "all lizard"

PAN-to-SAWR-uhs (Gr. pant- (pan) "all" + Gr. sauros "lizard") (m) replacement name for preoccupied Parasaurus Marsh; "The neck was long and slender. The vertebrae resemble most nearly in form and size those of Plesiosaurus plicatus Phillips." Plesiosauria i.s. Late Jurassic NA. [nomen dubium]

Parasaurus Marsh 1893 "near lizard"

PAYR-a-SAWR-uhs (Gr. para- "near" + Gr. sauros "lizard") (m) probably patterned after the name Plesiosaurus "near lizard"; for a fragmentary specimen of a small plesiosaur "the first Jurassic form observed in this country," consisting of a few strongly grooved vertebrae. (Preoccupied by Parasaurus Meyer. See Pantosaurus)

Peloneustes Lydekker 1889 "clay swimmer" ("Oxford Clay swimmer")

PEEL-o-NYOOS-teez (Gr. pelos "clay, mud" + Gr. neustes "swimmer") (m) alluding to the Oxford Clay in south central England, where the fossils were found; for "Plesiosaurus" philarchus Seeley 1869. Peloneustes is a relatively small short- necked form, known from a number of nearly complete skeletons and skulls. It resembles the much larger Pliosaurus in many details, but is separated as a distinct genus primarily because its mandibular symphysis, which is longer than in any other pliosaurid, containing 13-14 pairs of teeth, with the first 6-7 pairs canine in form. There are about 40 teeth in each ramus of the jaws. The teeth are circular in cross-section, with distinctive vertical ridges that reach only half-way to the tip. The neck vertebrae have a keel on the underside.

Vertebrae: 21-22 cervicals / 5 pectorals / 20 dorsals / 3 sacrals / ?25 caudals
Length: 3.1-4 m. (11-14 ft.); skull: 58 cm. (23.2 in.); mandible: 80 cm. (32 in.) )

Type Species: Peloneustes philarchus [fi-LAHR-kuhs] (Seeley 1869) "power-loving," probably alluding to its proportionately big head and jaws, represented in the type specimen by part of the cranial rostrum and a very long, nearly complete mandible. (Holotype: J.46913, Sedgwick Museum, Cambridge) Pliosauroidea Pliosauridae Late Jurassic (Callovian) Eur.

Pentatarsostinus Hawkins 1840 "five tarsal boned"

PEN-ta-tar-SOS-tin-uhs (Gr. penta "five" + Gr. tarsos "tarsus" + Gr. ostinos "bony") (m) referring to the construction of the paddle [= Plesiosaurus]

Peyerus Stromer 1935 "for Peyer"

PIE-e-rus (Peyer + -us) (m) named to honor Bernhard Peyer (1885--1963), noted Swiss paleontologist, professor at Zurich, and friend of Stromer; for a specimen found in the Sunday River marine or estuary beds at Uintenhage (Cape Province) South Africa ("Plesiosaurus" capensis Andrews 1911). The form appears to be quite similar to, if not congeneric with, the small freshwater or estuarine Wealden pliosaurid Leptocleidus from England, and is treated as a junior synonym of Leptocleidus by most current authors (Cruickshank 1997).

Vertebrae: 21-22 cervicals
Length: (estimated) 2.4 m. (9 ft.); skull: 27.7 cm. (11 in.))

Type species: Peyerus capensis [kay-PEN-sis] (Andrews 1911) "from Cape Province". Pliosauroidea Early Cretaceous SAfr. [= Leptocleidus]

Picrocleidus Andrews 1909 "sharp-pointed clavicle"

PIK-ro-KLIE-dus (Gr. pikros "sharp-pointed" + Gr. kleid- (kleis) "key, clavicle" + -us) (m) named for the small arrow-shaped interclavicle and rudimentary clavicles in the front limb girdle; proposed for Seeley's Muraenosaurus beloclis ("arrow clavicle"); a rare small species. (estimated total length: 2.5 m. (8.3 ft.)). [= Muraenosaurus]

Piptomerus Cope 1887 "fall-out part (vertebrae)"

pip-TOM-e-ruhs (Gr. pipto "fall out" + Gr. meros "part, portion") (m) probably so-named because the various vertebrae have "neurapophyses and other processes articulating freely with the centra," an indication the specimens belonged to juveniles with unfused bones; based on various vertebrae that are not diagnostic. Plesiosauria i.s. Late Cretaceous NA. [nomen dubium]

Piratosaurus Leidy 1865 "pirate lizard"

pie-RAY-to-SAWR-uhs (Gr. peirates "pirate, robber" + Gr. sauros "lizard") (m) based on a single sharp-pointed tooth, originally attributed to a crocodilian. Plesiosauria i.s. Late Cretaceous NA. [nomen dubium]

Plesiopleurodon Carpenter 1996 "near-Liopleurodon"

PLEE-see-o-PLOOR-o-don (Gr. plesios "near" + (Lio)pleurodon (Gr. leios "smooth" + Gr. pleuron "side" + Gr. odon "tooth")) (m) named for its close resemblance to the Late Jurassic pliosaurid Liopleurodon; for a small pliosaur from the early Late Cretaceous (lowest Cenomanian) of North America (Belle Fourche Shale, Wyoming), known from a complete skull and lower jaw, plus some cervical vertebrae that are a little wider than long, and a coracoid. The mandible has a moderately long symphysis containing 8 pairs of large procumbent canine-shaped teeth; teeth circular in cross-section, with outer surface smooth except near the base, which is striated. The cervical vertebrae have single-headed ribs, as in other Cretaceous pliosauroids; the Late Jurassic Liopleurodon has double-headed cervical ribs.

Length: (estimated) 2.9 m. (9.2 ft.); skull: 71.2 cm. (2.3 ft.))

Type Species: Plesiopleurodon wellesi [WEL-zie] Carpenter 1996: for Samuel P. Welles (1909-1997), noted vertebrate paleontologist, for his lifelong work on plesiosaurs. (Holotype: CM 2815) Pliosauroidea Pliosauridae Late Cretaceous (Cenomanian) NA.

Plesiosauridae Gray 1825 "Plesiosaurus [near-lizard] family"

PLEE-see-o-SAWR-i-dee (masc. plural) Currently containing the single genus Plesiosaurus. On-going studies of early plesiosaurs could revise or expand the family with new genera.

Plesiosauroidea Welles 1943 "Plesiosaurus [near-lizard] super- family"

PLEE-see-o-saw-ROY-dee-uh (neuter plural) The group including plesiosaurs with relatively long necks (28-72 cervical vertebrae) and proportionately small skulls. The individual neck vertebrae are typically moderate to elongated in length, contrasting with the shorter, more compressed shape typical of "pliosaur" cervical vertebrae. Brown (1981) divided the Plesiosauroidea into the families Plesiosauridae, Elasmosauridae and Cryptoclididae. Ken Carpenter (1996) has included the Late Cretaceous Polycotylidae as a group of modified plesiosauroids related to elasmosaurids, but with short necks and relatively large, elongated skulls. (Currently, a range of other authors still classify the Polycotylidae as pliosauroids.) Some early forms such as Attenborosaurus combine long necks with relatively elongated pliosaur-like skulls, and may represent another distinct type of plesiosauroid, though as pointed out in Brown and Cruickshank (1994), on-going research into Early Jurassic plesiosaurs "is almost certain to overthrow the present superfamily and family divisions in the Plesiosauria." Persson (1960) recognized the family Cimoliasauridae for robust plesiosauroids that have necks intermediate in length with cervical vertebrae that are broader than long; until better material for the enigmatic and poorly known "cimoliasaurs" comes to light, however, most other researchers consider the group inadequately defined when based on such scrappy material. The Late Cretaceous plesiosauroids Aristonectes and Morturneria have a dense arrangement of small, thin teeth in their jaws and thus resemble cryptoclidids, though some authors have classified them as elasmosaurs, or even "cimoliasaurs."

Members: Plesiosauridae, Elasmosauridae, Cryptoclididae, Polycotylidae; Attenborosaurus, Thalassiodracon, Sthenarosaurus, "Plesiosaurus" macrocephalus (to be redescribed by Brown and Storrs); Aristonectes, Morturneria

Plesiosaurus De la Beche & Conybeare 1821 "near lizard" ("approximate to the Saurians"*)

PLEE-see-o-SAWR-uhs (Gr. plesios "near to, approaching" + Gr. sauros "lizard" + -us)* (m) a name "expressing its near approach to the order Lacerta." As explained by Taylor (1994. Zoological Journal of the Linnean Society 112: 183), "De la Beche & Conybeare accepted Charles Koenig's name Ichthyosaurus to suit its role as a link between fishes and reptiles, and coined Plesiosaurus from the Greek words for 'nearer to the reptiles', 'The newly discovered animal, named on that account Plesiosaurus, approaches much more nearly to the crocodile, forming in its whole structure a link between it and the Ichthyosaurus'." De la Beche and Conybeare, along with many other early 19th century British researchers, accepted the Great Chain of Being, a hierarchical, static and non-evolutionary view of nature that dated back to Plato and Aristotle: All living things were individual creations, arranged by divine agency as a sequence of links, from simple to complex, to fill out all possible designs and habits. According to this scheme, fishes-Ichthyosaurus- Plesiosaurus-crocodiles formed part of an anatomical series that linked fishes and reptiles. Although advocates of the Great Chain of Being originally rejected the idea that species of animals could go extinct, Conybeare saw paleontology as a way to fill in additional missing links on the Great Chain--extinct creatures from the distant past could fill gaps that might exist in the modern order of nature.

Plesiosaurus is distinguished from other genera by the small size of its head, as well as by the relative shortness of its skull in front of the orbit and in the temporal region. The snout is fairly broad and has a pointed tip. The pineal opening is large. The teeth are uniform in shape: long, slender, pointed, round in cross-section, with vertical striations but no carinae. The internal nostrils on the palate are placed almost directly under the external nostrils, and so do not appear to be designed for underwater olfaction, unlike in plesiosaurs such as Cryptoclidus and Rhomalaeosaurus that have the internal nares shifted forward, apparently to allow water to pass through the roof of the mouth and up and out the animal's nose as it swam.

The genus Plesiosaurus has a long and complex taxonomic history, complicated by use of the name as a "wastebasket" genus for various scrappy finds--most proposed species of Plesiosaurus from outside Europe or dating from the Cretaceous are based on such fragmentary material that they cannot be defined in a scientifically useful way.

In the most recent review of Plesiosaurus, Glenn Storrs (1997, in Ancient Marine Reptiles:145-190) only recognizes two currently definable species: (1) the type species Plesiosaurus dolichodeirus from the Sinemurian (Lower Lias) of Britain; and (2) Plesiosaurus guilelmiimperatoris from the later Toarcian (Upper Lias) of Southern Germany, distinguished by "a more delicate skull and a more robust, straighter humerus" than in P. dolichodeirus. Storrs included two other forms as junior synonyms of P. guilelmiimperatoris: Plesiosaurus brachypterygius ("short fin") Heune 1923 (classified by Bakker (1993) as Microcleidus brachyptergius), and the proposed distinct genus Seeleyosaurus holzmadensis White 1940. Another proposed species, Plesiosaurus tournemirensis Sciau, Crochet & Mattieu 1990 from the Toarcian of France, needs more study: it may be a distinct and definable species of Plesiosaurus, or a junior synonym of P. guilelmiimperatoris, or it may merit placement in a new genus as an early elasmosaurid, as indicated in Bardet (1995).

A number of Jurassic species originally classified in Plesiosaurus and based on good type material have been redescribed as new genera: Archaeonectrus, Attenborosaurus, Eretmosaurus, Eurycleidus, Microcleidus, Peloneustes, Rhomaleosaurus, Thalassiodracon. "Plesiosaurus" propinquus (sometimes classified as a species of Rhomaleosaurus) and "Plesiosaurus" longirostris (currently classified as a species of Macroplata) may also be revised as new genera. Dave Brown and Glenn Storrs are currently revising the species "Plesiosaurus" macrocephalus "large-headed" Conybeare in Buckland 1836 (Type: BMNH R1336) (synonym: "Plesiosaurus" brachycephalus Owen 1840) from the Lias (Sinemurian) of England; known from nearly complete skeletons (up to 3.2 m. (10.5 ft.) long) that combine a neck consisting of 29-30 relatively long, plesiosaurid-type vertebrae with a comparatively large, broad triangular skull ending in an elongated blunt snout, the neck being about twice as long as the head. A specimen of "Plesiosaurus" macrocephalus in the Manchester Museum preserves "the apparent remains of the skin indicating the former existence of a posterior extension of the fin unsupported by bone" (Watson 1911); this soft-tissue outline appears less extensive than the controversial impression around the right forefin of the type specimen of Plesiosaurus guilelmiimperatoris (see comments below).

The derivation of the name Plesiosaurus continues to cause confusion. Some recent books indicate incorrectly that Plesiosaurus means "ribbon lizard," supposedly for the ribbon- like appearance of the neural spines along its backbone. There is NO basis in Greek or Latin for such a reading--nor in Conybeare's own comments! Conybeare originally proposed the name based on incomplete material (vertebrae, paddles, ribs) that permitted only an imperfect notion of what the entire animal looked like. Mary Anning's discovery in 1823 of a nearly complete specimen (BMNH 22656, now the holotype) prompted Conybeare to revise his thinking about his choice of name. He stated in 1824 that: "The name I have originally given to this animal, Plesiosaurus (approximate to the Saurians), may appear rather vague in this stage of our knowledge, and an appellation derived from its peculiar length of neck might be preferred; but for the present I shall retain the old generic name, adding for specific distinction the well-known Homeric epithet Dolichodeirus ["long- necked"], as characterizing the most striking peculiarity of its osteology." The derivation of Plesiosaurus is now typically simplified to "near lizard" (a noun), though Conybeare (1824) explained that he formed the name as a substantivized adjective by analogy with classical Greek adjectives such as isodendros (isos "equal to" + dendron "tree" + -os) "tree-like"--some of Conybeare's Greek-savvy colleagues originally objected to the proposed name Plesiosaurus on philological grounds.

Vertebrae: 37-42 cervicals / 4-5 pectorals / 21 dorsals / 3 sacrals / ?28-32 caudals
Length: up to 3.5 m. (12 ft.); skull: 16-19 cm. (6.3-7.8 in.); mandible: 21-24 cm. (9-10.5 in.)

Type Species: Plesiosaurus dolichodeirus [DOL-ik-o-DIE-ruhs] Conybeare 1824 "long-necked" Holotype: BMNH 22656. Known from a number of complete specimens. (Synonyms: Plesiosaurus macromus Owen 1840.)

Additional Species: Plesiosaurus guilelmiimperatoris [gwi-LEL- mie-IM-per-ay-TOH-ris] Dames 1895: "of Emperor Wilhelm"--to honor Kaiser Wilhelm II, Emperor of Germany, (1859-1941), who authorized funds for the purchase of the specimen for the Royal Natural History Museum (now Humboldt Museum fuer Naturkunde) in Berlin. The holotype specimen (MB.1893/94.1961) is a nearly complete skeleton from the Holzmaden slates, the most complete remains of a Plesiosaurus found in Germany up to that time. The specimen is especially notable for traces of carbonized organic material on the right front paddle and on the tail. Dames and later Tarlo (1959) interpreted these impressions as the original outlines of fleshy portions of the paddle and the tail, indicating that a large area of soft-tissue must have surrounded the paddles and that the tail ended in a vertical, probably rhomboid-shaped fin. However, not all researchers have accepted these interpretations, and the preserved impressions may simply be fluids from the decaying corpse rather than an accurate outline of the living animal's soft tissue (Glenn Storrs, personal communication). Storrs (1997) lists Plesiosaurus brachypterygius Huene 1923 and Seeleyosaurus holzmadensis White 1940, and possibly Plesiosaurus tournemirensis Sciau, Crochet & Mattieu 1990, as junior synonyms of Plesiosaurus guilelmiimperatoris. A famous second specimen in the Stuttgart Museum was destroyed during WWII. Vertebrae: 37 cervicals / 4 pectorals / 16 dorsals / 3 sacrals / ?37-40 caudals Plesiosauroidea Plesiosauridae Early Jurassic (Sinemurian- Toarcian) Eur.

Pliosauridae Seeley 1874 "Pliosaurus [near-saurian] family"

PLIE-o-SAWR-i-dee (masc. plu