Pictures and Profiles of Mosasaurs

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Meet the Apex Marine Reptiles of the Cretaceous Period

Mosasaurs--sleek, speedy, and above all else extremely dangerous marine reptiles--dominated the world's oceans during the middle to late Cretaceous period. On the following slides, you'll find pictures and detailed profiles of over a dozen mosasaurs, ranging from Aigialosaurus to Tylosaurus.

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Aigialosaurus

Name

Aigialosaurus; pronounced EYE-gee-AH-low-SORE-us

Habitat

Lakes and rivers of western Europe

Historical Period

Middle Cretaceous (100-95 million years ago)

Size and Weight

About 4-5 feet long and 20 pounds

Diet

Marine organisms

Distinguishing Characteristics

Long, slender body; sharp teeth

Also known as Opetiosaurus, Aigialosaurus represents an important link in the chain of the evolution of mosasaurs--the slender, vicious marine reptiles that dominated the oceans of the late Cretaceous period. As far as paleontologists can tell, Aigialosaurus was an intermediate form between the land-dwelling monitor lizards of the early Cretaceous period and the first true mosasaurs that appeared tens of millions of years later. Befitting its semi-aquatic lifestyle, this prehistoric reptile was equipped with relatively large (but hydrodynamic) hands and feet, and its slender, tooth-studded jaws were well-suited to snagging marine organisms.

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Clidastes

Name:

Clidastes; pronounced klie-DASS-tease

Habitat:

Oceans of North America

Historical Period:

Late Cretaceous (75-65 million years ago)

Size and Weight:

About 10 feet long and 100 pounds

Diet:

Fish and marine reptiles

Distinguishing Characteristics:

Small, sleek body; fast swimming speed

Like many other mosasaurs (the sharp-toothed marine reptiles that dominated the end of the Cretaceous period), fossils of Clidastes have been found in areas of North America (such as Kansas) that were once covered by the Western Interior Sea. Other than that, there's not much to say about this sleek predator, except that it was on the smaller end of the mosasaur spectrum (other genera like Mosasaurus and Hainosaurus weighed as much as a ton) and that it probably made up for its lack of heft by being an unusually fast and accurate swimmer.

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Dallasaurus

Name:

Dallasaurus (Greek for "Dallas lizard"); pronounced DAH-lah-SORE-us

Habitat:

Oceans of North America

Historical Period:

Middle Cretaceous (90 million years ago)

Size and Weight:

About three feet long and 25 pounds

Diet:

Probably fish

Distinguishing Characteristics:

Small size; ability to walk on land

You might think a prehistoric reptile named after Dallas would be big and land-bound, like a buffalo, rather than small, sleek and semi-aquatic, like a seal. However, one of the ironies of the marine reptiles that lived alongside the dinosaurs during the Mesozoic Era is that their fossils are very common in the now-arid American west and midwest, which used to be covered with shallow seas during the Cretaceous period.

What makes Dallasaurus important is that it's the most "basal" mosasaur yet known, the distant ancestor of a fierce, sleek family of marine reptiles that preyed relentlessly on fish and other ocean life. In fact, Dallasaurus shows evidence of movable, limb-like flippers, a clue that this reptile occupied an intermediate niche between a terrestrial and an aquatic existence. In this way, Dallasaurus is the mirror image of the earliest tetrapods, which climbed from water onto land rather than vice-versa!

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Ectenosaurus

Until the discovery of Ectenosaurus, paleontologists assumed that mosasaurs swam by undulating their entire bodies, much like snakes (in fact, it was once believed that snakes evolved from mosasaurs, though this now seems unlikely). See an in-depth profile of Ectenosaurus

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Eonatator

Name:

Eonatator (Greek for "dawn swimmer"); pronounced EE-oh-nah-tay-tore

Habitat:

Oceans of North America

Historical Period:

Middle-Late Cretaceous (90-75 million years ago)

Size and Weight:

About 10 feet long and a few hundred pounds

Diet:

Probably fish

Distinguishing Characteristics:

Small size; slender body

As is the case with many mosasaurs--the marine reptiles that succeeded plesiosaurs and pliosaurs as the scourges of the world's oceans during the late Cretaceous period--the exact taxonomy of Eonatator is still being puzzled out by experts. Once thought to be a species of Clidastes, and then of Halisaurus, Eonatator is now believed to have been one of the earliest mosasaurs, and suitably small (10 feet long and a few hundred pounds, max) for the progenitor of such a fearful race.

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Globidens

Name:

Globidens (Greek for "globular teeth"); pronounced GLOW-bih-denz

Habitat:

Oceans worldwide

Historical Period:

Late Cretaceous (75-65 million years ago)

Size and Weight:

About 20 feet long and 1,000 pounds

Diet:

Turtles, ammonites and bivalves

Distinguishing Characteristics:

Sleek profile; round teeth

You can tell a lot about the diet of a marine reptile by the shape and arrangement of its teeth--and the round, pebbly teeth of Globidens demonstrate that this mosasaur was specially adapted to feeding on hard-shelled turtles, ammonites and shellfish. As with many mosasaurs, the sleek, vicious predators of the late Cretaceous seas, the fossils of Globidens have turned up in some unexpected places, such as modern-day Alabama and Colorado, which used to be covered with shallow water tens of millions of years ago.

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Goronyosaurus

Name

Goronyosaurus (Greek for "Goronyo lizard"); pronounced go-ROAN-yo-SORE-us

Habitat

Rivers of western Africa

Historical Period

Late Cretaceous (70-65 million years ago)

Size and Weight

About 20-25 feet long and 1-2 tons

Diet

Marine and terrestrial animals

Distinguishing Characteristics

Slender build; extremely long, narrow snout

Although it's technically classified as a mosasaur--the family of sleek, vicious marine reptiles that dominated the late Cretaceous period--Goronyosaurus also had a lot in common with the marine crocodiles of its day, most notably its presumed habit of lurking in rivers and ambushing any aquatic or terrestrial prey that came within reach. We can infer this behavior from the distinctive shape of Goronyosaurus' jaws, which were unusually long and tapered, even by mosasaur standards, and clearly adapted for delivering quick, lethal chomps.

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Hainosaurus

Name:

Hainosaurus (Greek for "Haino lizard"); pronounced HIGH-no-SORE-us

Habitat:

Oceans of Asia

Historical Period:

Late Cretaceous (80-65 million years ago)

Size and Weight:

About 50 feet long and 15 tons

Diet:

Fish, turtles and marine reptiles

Distinguishing Characteristics:

Large size; narrow skull with sharp teeth

As mosasaurs go, Hainosaurus was on the giant end of the evolutionary spectrum, measuring almost 50 feet from snout to tail and weighing as much as 15 tons. This marine reptile, fossils of which have been discovered in Asia, was closely related to the North American Tylosaurus (although mosasaur fossils have been dug up in various locations, these creatures had a global distribution, making it a chancy proposition to assign a specific genus to a specific continent). Wherever it lived, Hainosaurus was clearly the apex predator of the late Cretaceous seas, a position later filled by equally huge predators such as the giant prehistoric shark Megalodon.

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Halisaurus

Name:

Halisaurus (Greek for "ocean lizard"); pronounced HAY-lih-SORE-us

Habitat:

Oceans of North America and western Europe

Historical Period:

Late Cretaceous (85-75 million years ago)

Size and Weight:

About 12 feet long and a few hundred pounds

Diet:

Probably fish

Distinguishing Characteristics:

Relatively small size; sleek body

A relatively obscure mosasaur--one of the fierce, predatory marine reptiles that succeeded the plesiosaurs and pliosaurs of the preceding Jurassic period--Halisaurus had its moment in the pop-culture spotlight when the BBC nature show Sea Monsters portrayed it as hiding beneath shallow ledges and feeding on unsuspecting prehistoric birds like Hesperornis. Unfortunately, this is sheer speculation; this early, sleek mosasaur (just like its closest relative, Eonatator) more likely fed on fish and smaller marine reptiles.

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Latoplatecarpus

Name

Latoplatecarpus (Greek for "wide flat wrist"); pronounced LAT-oh-PLAT-er-CAR-pus

Habitat

Shores of North America

Historical Period

Late Cretaceous (80 million years ago)

Size and Weight

Undisclosed

Diet

Fish and squids

Distinguishing Characteristics

Wide front flippers; short snout

As you may not be surprised to learn, Latoplatecarpus ("wide flat wrist") was named in reference to Platecarpus ("flat wrist")--and this mosasaur was also a close relative of Plioplatecarpus ("Pliocene flat wrist," even though this marine reptile lived tens of millions of years before the Pliocene epoch). To make a long story short, Latoplatecarpus was "diagnosed" on the basis of a partial fossil discovered in Canada, and a species of Plioplatecarpus was later assigned to its taxon (and there are rumblings that a Platecarpus species may experience this fate as well). However things turn out, Latoplatecarpus was a typical mosasaur of the late Cretaceous period, a sleek, vicious predator that had much in common with modern sharks (which eventually supplanted mosasaurs from the world's oceans).

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Mosasaurus

Mosasaurus was the eponymous genus of the mosasaurs, which, as a rule, were characterized by their large heads, powerful jaws, streamlined bodies and front and rear paddles, not to mention their voracious appetites. See an in-depth profile of Mosasaurus

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Pannoniasaurus

Name

Pannoniasaurus (Greek for "Hungarian lizard"); pronounced pah-NO-nee-ah-SORE-us

Habitat

Rivers of central Europe

Historical Period

Late Cretaceous (80 million years ago)

Size and Weight

About 20 feet long and 1,000 pounds

Diet

Fish and small animals

Distinguishing Characteristics

Long, narrow snout; freshwater habitat

Starting about 100 million years ago, during the late Cretaceous period, mosasaurs became the apex predators of the world's oceans, displacing less well-adapted marine reptiles like plesiosaurs and pliosaurs. Naturalists have been excavating mosasaur fossils since the late 17th century, but it wasn't until 1999 that researchers discovered bones in an unexpected location: a freshwater river basin in Hungary. Finally announced to the world in 2012, Pannoniasaurus is the world's first identified freshwater mosasaur, and it indicates that mosasaurs were even more widespread than previously believed--and may well have terrorized terrestrial mammals in addition to their usual deep-sea prey.

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Platecarpus

Name:

Platecarpus (Greek for "flat wrist"); pronounced PLAH-teh-CAR-pus

Habitat:

Oceans of North America

Historical Period:

Late Cretaceous (85-80 million years ago)

Size and Weight:

About 14 feet long and a few hundred pounds

Diet:

Probably shellfish

Distinguishing Characteristics:

Long, sleek body; short skull with few teeth

During the late Cretaceous period, 75 to 65 million years ago, much of the western and central United States was covered with a shallow ocean--and no mosasaur was more common in this "Western Interior Ocean" than Platecarpus, numerous fossils of which have been unearthed in Kansas. As mosasaurs go, Platecarpus was unusually short and slender, and its short skull and minimal number of teeth indicate that it pursued a specialized diet (probably soft-shelled mollusks). Because it was discovered relatively early in paleontological history--in the late 19th century--there has been some confusion about the exact taxonomy of Platecarpus, with some species being reassigned to other genera or downgraded completely.

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Plioplatecarpus

Name:

Plioplatecarpus (Greek for "flat wrist of the Pliocene"); pronounced PLY-oh-PLATT-ee-CAR-pus

Habitat:

Oceans of North America and Western Europe

Historical Period:

Late Cretaceous (80-75 million years ago)

Size and Weight:

About 18 feet long and 1,000 pounds

Diet:

Probably fish

Distinguishing Characteristics:

Large size; relatively short skull with few teeth

As you may have guessed from its name, the marine reptile Plioplatecarpus was very similar to Platecarpus, the most common mosasaur of Cretaceous North America. Plioplatecarpus lived a few million years after its more famous ancestor; other than that, the exact evolutionary relationships between Plioplatecarpus and Platecarpus (and between these two marine reptiles and others of their kind) are still being worked out. (By the way, the "plio" in this creature's name refers to the Pliocene epoch, to which it was mistakenly assigned until paleontologists realized it actually lived during the late Cretaceous period.)

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Plotosaurus

Name:

Plotosaurus (Greek for "floating lizard"); pronounced PLOE-toe-SORE-us

Habitat:

Oceans worldwide

Historical Period:

Late Cretaceous (70-65 million years ago)

Size and Weight:

About 40 feet long and five tons

Diet:

Fish

Distinguishing Characteristics:

Long, slender head; streamlined body

Paleontologists consider the fast, sleek Plotosaurus to be the pinnacle of the evolution of mosasaurs--the streamlined, predatory marine reptiles that largely displaced the plesiosaurs and pliosaurs of the preceding Jurassic period, and were themselves closely related to modern snakes. The five-ton Plotosaurus was about as hydrodynamic as this breed ever got, with a relatively, sleek narrow body and flexible tail; its unusually large eyes were also well-adapted for homing in on fish (and possibly other aquatic reptiles as well).

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Prognathodon

Name:

Prognathodon (Greek for "forejaw tooth"); pronounced prog-NATH-oh-don

Habitat:

Oceans worldwide

Historical Period:

Late Cretaceous (75-65 million years ago)

Size and Weight:

About 30 feet long and one ton

Diet:

Turtles, ammonites and shellfish

Distinguishing Characteristics:

Long, heavy skull with crushing teeth

Prognathodon was one of the more specialized of the mosasaurs (sleek, predatory marine reptiles) that dominated the world's oceans toward the end of the Cretaceous period, equipped with a broad, heavy, powerful skull and big (but not especially sharp) teeth. As with a related mosasaur, Globidens, it's believed that Prognathodon used its dental equipment to crush and eat shelled marine life, ranging from turtles to ammonites to bivalves.

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Taniwhasaurus

Name

Taniwhasaurus (Maori for "water monster lizard"); pronounced TAN-ee-wah-SORE-us

Habitat

Shores of New Zealand

Historical Period

Late Cretaceous (75-70 million years ago)

Size and Weight

About 20 feet long and 1-2 tons

Diet

Marine organisms

Distinguishing Characteristics

Long, slender body; pointed snout

Mosasaurs were among the first prehistoric reptiles to be identified by modern naturalists, not only in western Europe but in the rest of the world as well. A good example is Taniwhasaurus, a sleek, 20-foot-long marine predator that was discovered in New Zealand way back in 1874. As deadly as it was, Taniwhasaurus was extremely similar to two other, more famous mosasaurs, Tylosaurus and Hainosaurus, and one extant species has been "synonymized" with the former genus. (On the other hand, two other mosasaur genera, Lakumasaurus and Yezosaurus, have since been synonymized with Taniwhasaurus, so everything turned out OK in the end!)

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Tylosaurus

Tylosaurus was as well-adapted to terrorizing marine life as any mosasaur could be, equipped with a narrow, hydrodynamic body, a blunt, powerful head suited to ramming prey, agile flippers, and a maneuverable fin on the end of its long tail. See an in-depth profile of Tylosaurus