Plesiosaur and Pliosaur Pictures and Profiles

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Meet the Vicious Marine Reptiles of the Later Mesozoic Era

plesiosaurus
Nobu Tamura

During a big chunk of the Mesozoic Era, long-necked, small-headed plesiosaurs and short-necked, big-headed pliosaurs were the apex marine reptiles of the world's oceans. On the following slides, you'll find pictures and detailed profiles of over 30 different plesiosaurs and pliosaurs, ranging from Aristonectes to Woolungasaurus.

 

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Aristonectes

aristonectes
Aristonectes. Nobu Tamura

Name:

Aristonectes (Greek for "best swimmer"); pronounced AH-riss-toe-NECK-tease

Habitat:

Shores of South America and Antarctica

Historical Period:

Late Cretaceous (70-65 million years ago)

Size and Weight:

About 25 feet long and 1-2 tons

Diet:

Plankton and krill

Distinguishing Characteristics:

Long neck; numerous, needle-shaped teeth

 

Aristonectes' fine, numerous, needle-shaped teeth are a dead giveaway that this plesiosaur subsisted on plankton and krill (small crustaceans) rather than larger fare. In this respect, paleontologists regard this late Cretaceous reptile as analogous with the modern crabeater seal, which has roughly the same diet and dental equipment. Perhaps because of its specialized diet, Aristonectes managed to survive in the southern hemisphere right up until the K/T Extinction 65 million years ago. Before then, many of the aquatic reptiles that fed on fish, including the fierce mosasaurs, had been rendered extinct by faster prey and more specialized undersea predators, such as prehistoric sharks.

 

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Attenborosaurus

attenborosaurus
Attenborosaurus. Nobu Tamura

Name:

Attenborosaurus (Greek for "Attenborough’s lizard"); pronounced AT-ten-buh-row-SORE-us

Habitat:

Shores of Western Europe

Historical Period:

Early Jurassic (195-190 million years ago)

Size and Weight:

About 16 feet long and 1,000-2,000 pounds

Diet:

Fish

Distinguishing Characteristics:

Extremely long neck; few (but big) teeth

 

As pliosaurs go, Attenborosaurus was an anomaly: most of these marine reptiles were characterized by their large heads and short necks, but Attenborosaurus, with its extremely long neck, looked more like a plesiosaur. This pliosaur also had a limited number of massive teeth, which it presumably used to chow down on fish during the early Jurassic period. When it was first discovered, Attenborosaurus was thought to be a species of Plesiosaurus. Long after the original fossil was destroyed in a bombing raid on England during World War II, a study of a plaster cast showed it to belong to its own genus, which was named after the British documentary filmmaker Sir David Attenborough in 1993.

 

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Augustasaurus

augustasaurus
Augustasaurus. Karen Carr

Name

Augustasaurus (after Nevada's Augusta Mountains); pronounced aw-GUS-tah-SORE-us

Habitat

Shallow seas of North America

Historical Period

Early Triassic (240 million years ago)

Size and Weight

Undisclosed

Diet

Fish and marine animals

Distinguishing Characteristics

Long neck; narrow flippers

 

Like its close relative, Pistosaurus, Augustasaurus was a transitional form between the nothosaurs of the early Triassic period (the classic example of which was Nothosaurus) and the plesiosaurs and pliosaurs of the later Mesozoic Era. In terms of its appearance, though, you'd have a hard time picking out its basal characteristics, since the long neck, narrow head and elongated flippers of Augustasaurus don't seem all that different from those of  later, "classic" plesiosaurs like Elasmosaurus. Like many marine reptiles, Augustasaurus plied the shallow seas that once covered western North America, which explains how its type fossil wound up being discovered in landlocked Nevada.

 

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Brachauchenius

brachauchenius
Brachauchenius. Gary Staab

Name:

Brachauchenius (Greek for "short neck"); pronounced BRACK-ow-CANE-ee-us

Habitat:

Shallow waters of North America

Historical Period:

Late Cretaceous (95-90 million years ago)

Size and Weight:

About 30 feet long and 10 tons

Diet:

Fish and marine reptiles

Distinguishing Characteristics:

Large size; long, massive head with numerous teeth

 

As fearsome as they were, the giant marine reptiles known as pliosaurs were no match for the sleeker, faster mosasaurs that appeared on the scene toward the end of the Cretaceous period. The 90-million-year-old Brachauchenius may have been the last pliosaur indigenous to North America's Western Interior Sea; closely related to the much earlier (and much bigger) Liopleurodon, this aquatic predator was equipped with an unusually long, narrow, heavy head studded with numerous sharp teeth, an indication that it ate pretty much anything that happened across its path.

 

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Cryonectes

cryonectes
Cryonectes. Nobu Tamura

Name

Cryonectes (Greek for "cold swimmer"); pronounced CRY-oh-NECK-tease

Habitat

Shores of western Europe

Historical Period

Early Jurassic (185-180 million years ago)

Size and Weight

About 10 feet long and 500 pounds

Diet

Fish

Distinguishing Characteristics

Moderate size; narrow snout

 

Discovered in 2007 in Normandy, France, Cryonectes is considered to be a "basal" pliosaur--that is, it was a relatively small, undifferentiated runt compared to multi-ton genera like Pliosaurus that appeared on the scene millions of years later. This "cold swimmer" plied the shores of western Europe about 180 million years ago, not a particularly well-represented time in fossil history, during a time of plunging global temperatures, and it was characterized by its unusually long and narrow snout, doubtless an adaptation for catching and killing elusive fish.

 

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Cryptoclidus

cryptoclidus
Cryptoclidus. Wikimedia Commons

Name:

Cryptoclidus (Greek for "hidden collarbone"); pronounced CRIP-toe-CLIDE-us

Habitat:

Shallow oceans off Europe

Historical Period:

Late Jurassic (165-150 million years ago)

Size and Weight:

About 25 feet long and eight tons

Diet:

Fish and crustaceans

Distinguishing Features:

Long neck; flat head with numerous sharp teeth

 

Cryptoclidus sported the classic body plan of the family of marine reptiles known as plesiosaurs: a long neck, a small head, a relatively thick body and four powerful flippers. As with many of its dinosaur relatives, the name Cryptoclidus ("hidden collarbone") isn't particularly revealing to the non-scientist, referring to an obscure anatomical feature only paleontologists would find interesting (hard-to-find clavicles in the front limb girdle, if you must know).

As with many of its plesiosaur cousins, it's uncertain whether Cryptoclidus led a fully aquatic lifestyle or spent part of its time on land. Since it's often helpful to infer an ancient reptile's behavior from its resemblance to modern animals, Cryptoclidus' seal-like profile may be a good clue that it was amphibious in nature. (By the way, the first Cryptoclidus fossil was discovered way back in 1872--but it wasn't named until 1892, by the famous paleontologist Harry Seeley, because it had been misidentified as a species of Plesiosaurus.)

 

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Dolichorhynchops

dolichorhynchops
Dolichorhynchops. Wikimedia Commons

Name:

Dolichorhynchops (Greek for "long-snouted face"); pronounced DOE-lih-co-RIN-cops

Habitat:

Shores of North America

Historical Period:

Late Cretaceous (80-70 million years ago)

Size and Weight:

About 17 feet long and 1,000 pounds

Diet:

Probably squids

Distinguishing Characteristics:

Large head with long, narrow snout and small teeth

 

Called "Dolly" by some paleontologists (who don’t like pronouncing long, difficult Greek names any more than the average kid), Dolychorhynchops was an atypical plesiosaur that sported a long, narrow head and a short neck (most plesiosaurs, like Elasmosaurus, had tiny heads perched on the end of long necks). Based on an analysis of its skull, it seems that Dolichorhynchops wasn't the most robust biter and chewer of the late Cretaceous seas, and likely subsisted on soft-bodied squids rather than bony fish. By the way, this was one of the last plesiosaurs of the late Cretaceous period, existing at a time when these marine reptiles were quickly being supplanted by sleeker, faster, better-adapted mosasaurs.

 

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Elasmosaurus

elasmosaurus
Elasmosaurus. Canadian Museum of Nature

Elasmosaurus had an enormously long neck consisting of 71 vertebrae. Some paleontologists believe this plesiosaur bent its head sideways around its body while hunting, while others say it held its head high above the water to scope out prey. See 10 Facts About Elasmosaurus

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Eoplesiosaurus

eoplesiosaurus
Eoplesiosaurus. Nobu Tamura

Name

Eoplesiosaurus (Greek for "dawn Plesiosaurus"); pronounced EE-oh-PLESS-ee-oh-SORE-us

Habitat

Shores of western Europe

Historical Period

Early Jurassic (200 million years ago)

Size and Weight

About 10 feet long and a few hundred pounds

Diet

Fish

Distinguishing Characteristics

Slender body; elongated neck

 

Pretty much everything you need to know about Eoplesiosaurus is contained in its name: this "dawn Plesiosaurus" preceded the more famous Plesiosaurus by tens of millions of years, and was correspondingly smaller and slimmer (only about 10 feet long and a few hundred pounds, compared to 15 feet long and half a ton for its late Jurassic descendant). What makes Eoplesiosaurus unusual is that its "type fossil" dates to the Triassic-Jurassic boundary, about 200 million years ago--a chunk of prehistoric history that has otherwise yielded scarce remains, not only of marine reptiles but of any kinds of creatures!

 

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Futabasaurus

futabasaurus
Futabasaurus. Wikimedia Commons

Name:

Futabasaurus (Greek for "Futaba lizard"); pronounced FOO-tah-bah-SORE-us

Habitat:

Oceans of eastern Asia

Historical Period:

Late Cretaceous (75-65 million years ago)

Size and Weight:

About 20 feet long and 2-3 tons

Diet:

Fish

Distinguishing Characteristics:

Slender body; narrow flippers; long neck

 

The first plesiosaur ever to be discovered in Japan, Futabasaurus was a typical member of the breed, albeit on the larger side (full-grown specimens weighed about 3 tons) and with an exceptionally long neck similar to that of Elasmosaurus. Intriguingly, fossil specimens of the late Cretaceous Futabasaurus bear evidence of predation by prehistoric sharks, a possible contributing factor to the global extinction of plesiosaurs and plesiosaurs 65 million years ago. (By the way, the plesiosaur Futabasaurus shouldn't be confused with the "unofficial" theropod dinosaur that sometimes goes by the same name.)

 

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Gallardosaurus

gallardosaurus
Gallardosaurus. Nobu Tamura

Name

Gallardosaurus (after paleontologist Juan Gallardo); pronounced gal-LARD-oh-SORE-us

Habitat

Waters of the Caribbean

Historical Period

Late Jurassic (160 million years ago)

Size and Weight

Undisclosed

Diet

Fish

Distinguishing Characteristics

Bulky torso; long snout and flippers

 

The Caribbean island nation of Cuba isn't exactly a hotbed of fossil activity, which is what makes Gallardosaurus so unusual: the partial skull and mandible of this marine reptile was discovered in the country's northwest in 1946. As is often the case for fragmentary remains, they were provisionally assigned to the genus Pliosaurus; a re-examination in 2006 resulted in their re-assignment to Peloneustes, and a re-re-examination in 2009 led to the erection of a brand-new genus, Gallardosaurus. Whatever name you choose to call it by, Gallardosaurus was a classic pliosaur of the late Jurassic period, a bulky, long-flippered, long-snouted predator that fed on pretty much anything swimming in its immediate vicinity.

 

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Hydrotherosaurus

hydrotherosaurus
Hydrotherosaurus. Procon

Name:

Hydrotherosaurus (Greek for "fisherman lizard"); pronounced HIGH-dro-THEE-roe-SORE-us

Habitat:

Shores of western North America

Historical Period:

Late Cretaceous (70-65 million years ago)

Size and Weight:

About 40 feet long and 10 tons

Diet:

Fish

Distinguishing Characteristics:

Small head; exceptionally long neck

 

In most ways, Hydrotherosaurus was a typical plesiosaur, a marine reptile with a long, flexible neck and a relatively small head. What made this genus stand out from the pack were the 60 vertebrae in its neck, which were shorter toward the head and longer toward the trunk, not to mention the fact that it lived at a time (the late Cretaceous period) when most other plesiosaurs had ceded their dominance to a family of even more vicious marine reptiles, the mosasaurs.

Although it may have lived elsewhere, Hydrotherosaurus is known mostly from a single complete fossil found in California, which contains the remnants of this creature's last meal. Paleontologists also discovered a set of fossilized gastroliths ("stomach stones"), which likely helped anchor Hydrotherosaurus to the sea bottom, where it liked to feed.

 

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Kaiwhekea

kaiwhekea
Kaiwhekea. Dmitri Bogdanov

Name:

Kaiwhekea (Maori for "squid eater"); pronounced KY-wheh-KAY-ah

Habitat:

Coasts of New Zealand

Historical Period:

Late Cretaceous (70 million years ago)

Size and Weight:

About 20 feet long and 500-1,000 pounds

Diet:

Fish and squids

Distinguishing Characteristics:

Long neck; short head with needle-like teeth

 

If there was any justice in the world, Kaiwhekea would be much better-known than its fellow New Zealand marine reptile, Mauisaurus: the latter has been reconstructed from a single paddle, whereas Kaiwhekea is represented by a near-complete skeleton (to be fair, though, Mauisaurus was the much bigger beast, tipping the scales at 10 to 15 tons compared to half a ton, max, for its relatively shrimpy competitor). As plesiosaurs go, Kaiwhekea appears to have been most closely related to Aristonectes; its short head and numerous, needle-like teeth point to a diet of fish and squids, hence its name (Maori for "squid eater").

 

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Kronosaurus

kronosaurus
Kronosaurus. American Museum of Natural History

With its 10-foot-long skull studded with 10-inch-long teeth, the giant pliosaur Kronosaurus clearly wouldn't have contented itself with just fish and squids, feasting occasionally on the other marine reptiles of the Cretaceous period. See 10 Facts About Kronosaurus

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Leptocleidus

leptocleidus
Leptocleidus. Dmitry Bogdanov

Name:

Leptocleidus (Greek for "slender clavicle"); pronounced LEP-toe-CLYDE-us

Habitat:

Shallow lakes of Western Europe

Historical Period:

Early Cretaceous (130-125 million years ago)

Size and Weight:

About 10 feet long and 500 pounds

Diet:

Fish

Distinguishing Characteristics:

Large head and collarbone; short neck

 

Although it wasn't very big by the standards of later marine reptiles like Kronosaurus and Liopleurodon, Leptocleidus is valued by paleontologists because it's one of the few pliosaurs to date from the early Cretaceous period, thus helping to plug a yawning gap in the fossil record. Based on where it was found (modern England's Isle of Wight), it's theorized that Leptocleidus confined itself to small, freshwater ponds and lakes, rather than venturing out into the wider seas where it would have to compete against (or be eaten by) its much bigger relatives.

 

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Libonectes

libonectes
Libonectes. Wikimedia Commons

Name:

Libonectes; pronounced LIH-bow-NECK-tease

Habitat:

Shallow waters of North America

Historical Period:

Late Cretaceous (95-90 million years ago)

Size and Weight:

About 35 feet long and 1-2 tons

Diet:

Fish

Distinguishing Characteristics:

Long neck; short tail; large front flippers

 

With its long neck, strong flippers, and relatively streamlined body, Libonectes was a classic example of the family of marine reptiles known as the plesiosaurs. The "type fossil" of Libonectes was discovered in Texas, which was submerged under a shallow body of water during much of the late Cretaceous period; reconstructions point to a creature uncannily similar to the later Elasmosaurus, though not nearly as well known by the general public.

 

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Liopleurodon

liopleurodon
Liopleurodon. Andrey Atuchin

As big and bulky as Liopleurodon was, it was able to propel itself quickly and smoothly through the water with its four powerful flippers, holding its mouth open to catch unfortunate fish and squids (and perhaps other marine reptiles). See 10 Facts About Liopleurodon

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Macroplata

macroplata
Macroplata (Wikimedia Commons).

Name:

Macroplata (Greek for "giant plate"); pronounced MACK-roe-PLAT-ah

Habitat:

Shores of Western Europe

Historical Period:

Early-Middle Jurassic (200-175 million years ago)

Size and Weight:

About 15 feet long and 1,000 pounds

Diet:

Fish

Distinguishing Characteristics:

Long, thin head and medium-length neck; powerful shoulder muscles

 

As marine reptiles go, Macroplata stands out for three reasons. First, the two known species of this genus span over 15 million years of the early Jurassic period--an unusually long time span for a single animal (which has led some paleontologists to speculate that the two species actually belong to separate genera). Second, although it's technically classified as a pliosaur, Macroplata had some distinctively plesiosaur-like characteristics, most notably its long neck. Third (and by no means least), an analysis of Macroplata's remains demonstrates that this reptile had unusually powerful front flippers, and must have been an unusually fast swimmer by the standards of the early to middle Jurassic.

 

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Mauisaurus

mauisaurus
Mauisaurus. Nobu Tamura

Name:

Mauisaurus (Greek for "Maui lizard"); pronounced MAO-ee-SORE-us

Habitat:

Shores of Australasia

Historical Period:

Late Cretaceous (65 million years ago)

Size and Weight:

About 55 feet long and 10-15 tons

Diet:

Fish

Distinguishing Characteristics:

Large size; extremely long neck and slender body

 

The name Mauisaurus is misleading in two ways: first, this marine reptile should not be confused with Maiasaura (a land-dwelling, duck-billed dinosaur known for its excellent parenting skills), and second, the "Maui" in its name refers not to the lush Hawaiian island, but to a deity of the Maori people of New Zealand, thousands of miles away. Now that we've gotten those details out of the way, Mauisaurus was one of the biggest plesiosaurs still alive at the end of the Cretaceous period, attaining lengths of close to 60 feet from head to tail (though a fair proportion of this was taken up by its long, slender neck, which comprised no less than 68 separate vertebrae).

Because it's one of the few dinosaur-era fossils ever to be discovered in New Zealand, Mauisaurus was honored there in 1993 with an official postage stamp.

 

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Megalneusaurus

megalneusaurus
Megalneusaurus. Wikimedia Commons

Name:

Megalneusaurus (Greek for "great swimming lizard"); pronounced MEG-al-noy-SORE-us

Habitat:

Shores of North America

Historical Period:

Late Jurassic (155-150 million years ago)

Size and Weight:

About 40 feet long and 20 or 30 tons

Diet:

Fish, squids and aquatic reptiles

Distinguishing Characteristics:

Large size; large head with numerous teeth

 

Paleontologists don't know a whole lot about Megalneusaurus; this impressively named pliosaur (its moniker means "great swimming lizard") has been reconstructed from scattered fossils discovered in Wyoming. How did a giant marine reptile wind up in the American midwest, you ask? Well, 150 million years ago, during the late Jurassic period, a good part of the North American continent was covered with a shallow body of water called the "Sundance Sea." Judging from the size of Megalneusaurus' bones, it appears that this pliosaur may have given Liopleurodon a run for its money, attaining lengths of 40 feet or so and weights in the neighborhood of 20 or 30 tons.

 

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Muraenosaurus

muraenosaurus
Muraenosaurus (Dmitry Bogdanov).

Name:

Muraenosaurus (Greek for "eel lizard"); pronounced more-RAIN-oh-SORE-us

Habitat:

Oceans worldwide

Historical Period:

Late Jurassic (160-150 million years ago)

Size and Weight:

About 20 feet long and 1,000 pounds

Diet:

Fish

Distinguishing Characteristics:

Exceptionally long, thin neck; small head

 

Muraenosaurus took the basic plesiosaur body plan to its logical extreme: this marine reptile possessed an almost comically long, thin neck, topped by an unusually small, narrow head (containing, of course, a correspondingly small brain)--a mix of features reminiscent of earlier, long-necked land reptiles like Tanystropheus. Although the remains of Muraenosaurus have only been found in western Europe, its similarity to other fossils hints at a worldwide distribution during the late Jurassic period.

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Peloneustes

peloneustes
Peloneustes. Wikimedia Commons

Name:

Peloneustes (Greek for "mud swimmer"); pronounced PEH-low-NOY-steez

Habitat:

Shores of western Europe

Historical Period:

Late Jurassic (165-160 million years ago)

Size and Weight:

About 10 feet long and 500 pounds

Diet:

Squids and mollusks

Distinguishing Characteristics:

Relatively small size; long head with few teeth

 

Unlike contemporary marine predators like Liopleurodon--which pretty much ate anything that moved--Peloneustes pursued a specialized diet of squids and mollusks, as evidenced by its long, crushing jaws studded with relatively few teeth (it also doesn't hurt that paleontologists have found the remnants of cephalopod tentacles among the fossilized contents of Peloneustes fossils!) Aside from its unique diet, this pliosaur was distinguished by its relatively long neck, about the same length as its head, as well as its short, stocky, stubby-tailed body, which nonetheless was streamlined enough to enable it to chase down speedy prey.

 

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Plesiosaurus

plesiosaurus
Plesiosaurus. Nobu Tamura

Plesiosaurus is the eponymous genus of the plesiosaurs, characterized by their sleek bodies, wide flippers, and small heads set at the end of long necks. This marine reptile was once famously described as "a snake threaded through the shell of a turtle." See an in-depth profile of Plesiosaurus

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Pliosaurus

pliosaurus
Pliosaurus. Wikimedia Commons

Pliosaurus is what paleontologists call a "wastebasket taxon":  for example, after the recent discovery of an intact pliosaur in Norway, paleontologists described it as a species of Pliosaurus, even though its genus designation will eventually change. See an in-depth profile of Pliosaurus

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Rhomaleosaurus

rhomaleosaurus
Rhomaleosaurus. Nobu Tamura

Rhomaleosaurus is one of those marine reptiles that was discovered before its time: a complete skeleton was unearthed by a group of miners in Yorkshire, England in 1848, and must have given them quite a fright! See an in-depth profile of Rhomaleosaurus

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Styxosaurus

styxosaurus
Styxosaurus. Wikimedia Commons

Name:

Styxosaurus (Greek for "Styx lizard"); pronounced STICKS-oh-SORE-us

Habitat:

Shores of North America

Historical Period:

Late Cretaceous (85-70 million years ago)

Size and Weight:

About 35 feet long and 3-4 tons

Diet:

Fish

Distinguishing Characteristics:

Extremely long neck; large trunk

 

During the latter part of the Mesozoic Era, plesiosaurs and pliosaurs (a populous family of marine reptiles) roamed the Sundance Sea, a shallow body of water that covered much of central and western North America. That explains the discovery of a huge, 35-foot-long Styxosaurus skeleton in South Dakota in 1945, which was given the name Alzadosaurus until it was realized to which genus it actually belonged.

Interestingly, this South Dakotan Styxosaurus specimen came complete with over 200 gastroliths--small stones this marine reptile deliberately swallowed. Why? The gastroliths of terrestrial, herbivorous dinosaurs aided in digestion (by helping to mash up tough vegetation in these creatures' stomachs), but Styxosaurus probably swallowed these stones as a means of ballast--that is, to enable it to float near the sea bottom, where the tastiest food was.

 

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Terminonatator

terminonatator
The skull of Terminonatator (Flickr).

Name:

Terminonatator (Greek for "last swimmer"); pronounced TER-mih-no-nah-TAY-tore

Habitat:

Shores of North America

Historical Period:

Late Cretaceous (80-70 million years ago)

Size and Weight:

About 23 feet long and 1,000-2,000 pounds

Diet:

Fish

Distinguishing Characteristics:

Long, sleek body and neck with narrow head

 

For a marine reptile whose name sounds an awful lot like "Terminator," Terminonatator ("last swimmer" in Greek) was a bit of a lightweight. This plesiosaur only reached a medium length of about 23 feet (shorter than other famous plesiosaurs like Elasmosaurus and Plesiosaurus), and judging by the structure of its teeth and jaws, it seems to have subsisted mainly on fish. Notably, Terminonatator is one of the last plesiosaurs known to have swum the shallow seas covering much of North America during the late Cretaceous period, before the K/T Extinction 65 million years ago rendered all the dinosaurs and marine reptiles extinct. In this respect, it may have shared some qualities with Arnold Schwarzenegger after all!

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Thalassiodracon

thalassiodracon
Thalassiodracon. Wikimedia Commons

Other pliosaurs are more deserving of it name (Greek for "sea dragon"), but paleontology operates by a strict set of rules, with the result that Thalassiodracon was a relatively small, unassuming, and not very bright marine reptile. See an in-depth profile of Thalassiodracon

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Thililua

thililua
Thililua. Wikimedia Commons

Name:

Thililua (after an ancient Berber deity); pronounced THIH-lih-LOO-ah

Habitat:

Shores of northern Africa

Historical Period:

Middle Cretaceous (95-90 million years ago)

Size and Weight:

About 18 feet long and 1,000-2,000 pounds

Diet:

Fish

Distinguishing Characteristics:

Slender trunk with long neck and small head

 

If you want to get noticed in paleontological journals, it helps to come up with a striking name--and Thililua certainly fits the bill. It's borrowed from a god of the ancient Berbers of north Africa, where the only fossil of this marine reptile was discovered. In every way except for its name, Thililua appears to have been a typical plesiosaur of the middle Cretaceous period: a fast, sleek aquatic swimmer with a small head perched at the end of a long, flexible neck, much like its more famous cousins Plesiosaurus and Elasmosaurus. Based on a comparison with its presumed close relative, Dolichorhynchops, paleontologists believe Thililua reached only a modest length of about 18 feet.

 

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Trinacromerum

trinacromerum
Trinacromerum. Royal Ontario Museum

Name:

Trinacromerum (Greek for "three-tipped femur"); pronounced TRY-nack-roe-MARE-um

Habitat:

Shallow waters of North America

Historical Period:

Late Cretaceous (90 million years ago)

Size and Weight:

About 15 feet long and 1,000 pounds

Diet:

Fish

Distinguishing Characteristics:

Narrow head; short neck; streamlined body

 

Trinacromerum dates from the stage of the late Cretaceous period, about 90 million years ago, when the last plesiosaurs and pliosaurs were trying to hold their own against the better-adapted marine reptiles known as mosasaurs. As you might expect, given its fierce competition, Trinacromerum was sleeker and faster than most plesiosaurs, with long, powerful flippers and a narrow snout suited to snapping up fish at high speeds. In its overall appearance and behavior, Trinacromerum was very similar to the later Dolichorhynchops, and was once thought to be a species of this better-known plesiosaur.

 

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Woolungasaurus

woolungasaurus
Woolungasaurus being attacked by Kronosaurus. Dmitry Bogdanov

Name:

Woolungasaurus (Greek for "Woolung lizard"); pronounced WOO-lung-ah-SORE-us

Habitat:

Shores of Australasia

Historical Period:

Middle Cretaceous (110 million years ago)

Size and Weight:

About 30 feet long and 5-10 tons

Diet:

Fish

Distinguishing Characteristics:

Slender trunk with long neck and small head

 

Just as every country lays claim to its own terrestrial dinosaur, it helps to be able to brag about a marine reptile or two. Woolungasaurus is Australia's native plesiosaur (a family of aquatic reptiles characterized by their slender bodies, long necks and small heads), though this creature pales in comparison to Mauisaurus, a plesiosaur discovered within the environs of Australia's neighbor New Zealand that was about twice as big. (To give Australia its due, though, Mauisaurus lived tens of million years after Woolungosaurus, during the late rather than middle Cretaceous period, and so had sufficient time to evolve to larger sizes.)