9 Extinct Exotic Sea Creatures

The Tylosaurus was a large, water-bound lizard that evolved from its land-based ancestors by developing a long, powerful tail and sturdy limbs that looked and functioned like paddles. The prehistoric carnivore relied on an imposing and effective double set of cone-shaped chompers. Its muscular jaw allowed the creature to often swallow prey whole, while two rows of sharp teeth ensured that anything trapped inside a Tylosaurus' mouth wasn't getting out alive [source: National Geographic].

At about 45 feet (14 meters) long, the Tylosaurus was one of the largest members of the mosasaur family of marine reptiles. These beasts roamed the seas roughly 65 million years ago, but their remains have been discovered in some decidedly dry places. That includes parts of Texas and Kansas, which are believed to have once been covered by the Western Interior Seaway and where researchers have located Tylosaurus and other mosasuar fossils [sources: National Geographic, Fossil Guy]. If you didn't get to catch these sea monsters in real life, you can still see Hollywood's version on the big screen. The Tylosaurus is among the prehistoric beasts featured in the 2015 movie "Jurassic World."

From what paleontologists can decipher of this reptile's remains, the Tanystropheus appears to have been a prehistoric reptile version of a giraffe with shorter legs, a long neck that juts out rather than up and a massive tail. The largest of these animals stretched up to 20 feet (6 meters) long, with the Tanystropheus' 12-vertebrae neck comprising more than half of that [sources: University of California Museum of Paleontology, Prehistoric Wildlife].

That made this shorefaring specimen a natural fisher, able to pluck a variety of seafood fresh out of the water without even getting his collar wet. Adding to this theory of the Tanystropheus feeding habits are fossils indicating that the creature's front legs were shorter than the back pair. That suggests that the Tanystropheus did his hunting from dry land, pitching his neck in the water at chow time. Just how much time the animal spent on terra firma as opposed to in the waters off Europe, the Middle East and China remains a subject of debate. It's disputed whether the Tanystropheus' feet were actually were made for swimming and how much it was able to move that long neck with such a relatively small body [source: Prehistoric Wildlife].

This extinct shark was the big daddy of them all. More than three times the size of a great white, the megalodon was a ferocious behemoth that used its massive jaw and a set of 7-inch (12 centimeters) teeth to feast on whales and other gigantic prey. In fact, researchers estimate that this species went extinct around the same time that primitive baleen whales – a group that today includes the humongous blue whale – began growing to their modern, larger size. That's because marine scientists believe that the removal of the 59-foot (18-meter), 55-ton (50-metric ton) predators from sea life allowed the whales to flourish and grow larger. Fossils from the gigantic sharks have been found around the world, from waters off Africa to Europe and the Americas [source: Rincon].

Just what caused the megalodon's demise remains a mystery. What we do know is that this fearsome creature hasn't patrolled Earth's waters in roughly 2.6 million years, despite rumors that the beasts are still lurking [sources: Rincon, Prigg]. Whale watchers can breathe easy.

File this one under "almost extinct." With a face that only a mother could love, the frilled shark (named for its six pairs of frill-like gills) is quite possibly the ugliest, strangest and most frightening monster on this list [sources: SETFIA, Chappell]. This bizarre and menacing creature is not, in other words, the type of shark one might find dancing behind Katy Perry during a Super Bowl halftime show.

The frilled shark kind of looks like an ugly version of an electric eel. Its 5-foot (1.5-meter) frame slithers around with the help of a few small fins and strikes a bowel movement-inducing fear in the heart of any human who crosses its path, with a set of 300 razor-sharp teeth laid out in 25 rows. The shark has been called a "living fossil" thanks to those primitive features and an origin that traces back roughly 80 million years [sources: SETFIA, Chappell].

Until recently, it may have been safe to believe that this beast had gone the way of the megalodon. That's until a couple of Australian fishermen happened to inadvertently scoop one up in their net in January 2015 [source: Chappell]. It's one of a few known modern encounters with the beast, at least by anyone who's lived to tell about it.

Ex-professional basketball player Shaquille O'Neal is a humongous man. At 7 feet 1 inch (2.2 meters) and 325 pounds (147 kilograms), he's the type of guy who has to duck into doorways, has trouble getting into European cars and should probably buy two seats if his private jet is in the shop and he has to fly coach [source: ESPN]. Consider the Stupendemys the Shaq of the turtle world.

This gigantic sea turtle called the rivers and lakes of South America home as recently as about 5 or 6 million years ago. Its name means "astonishing turtle" for good reason: The Stupendemys shell often stretched more than 7 feet (1.8 meters) in length and another 7 feet in width. That's good enough to probably make it the world's largest turtle, perhaps even bigger than the mammoth Archelon from the late Cretaceous period 65 million years ago. The Stupendemys' neck was so long, it had to fold it to one side to fit it in the shell. It's believed that the turtle grew in size over time in response to the gargantuan beasts with whom the Stupendemys shared living spaces, including various types of large crocodile [sources: Prehistoric Wildlife, McCormick].

This prehistoric shark (270 million years old) is best-known for its circular, toothy saw, a natural defense tool that was probably pretty effective in warding off underwater enemies. What paleontologists haven't been able to agree about is just where the whorl of teeth was located on the Helicoprion's body. Many assumed that it protruded from the animal's upper or lower jaw, while others surmised that it was connected to the creature's tail [source: Crew].

In 1950, a specimen of the saw was located in a bay in Idaho. The 117-tooth whorl included some cranial cartridge, according to researchers, indicating that it probably sat inside the Helicoprion's mouth. Still, there's little agreement about just where the saw would have been located. Some say it served as a tongue, and others maintain that it probably extended from the animal's lower lip and curled under the chin. Most recently, Idaho paleontologists have used new technology to create a 3-D animated model of what they believe was the shark's skull. It shows the saw connected to the Helicoprion's lower jaw [source: Crew].

Call the Dunkleosteus a nasty brute. Call it ugly. Even call it old-fashioned. Just don't call it a picky eater or late to dinner.

This powerful placoderm fish subsisted on just about anything it could get its mitts on: Sharks, fish and even other members of his or her own clan. Without actual teeth, the hungry fish used two long blades to snap and crush its prey. The Dunkleosteus apparently had no problem tracking down its meals, thanks to an enormous frame, speedy swimming and mighty jaw. However it seemed to suffer often from indigestion, not surprisingly [source: BBC].

It's almost as if the Dunkleosteus was designed for destruction. Checking in at more than 33 feet (10 meters) and 4,000 tons (3,600 metric tons), the beast was bigger than a killer whale and at least as fierce. It also featured a series of hard, bony plates around its head that are believed to have served as armor for the battering ram. But the fearsome creature also appears to have been both a lover and a fighter. One of the first species to exist in male and female forms, the Dunkleosteus would have been one of the earliest to mate physically in order to reproduce [sources: BBC, Animal Planet].

This marine lizard might be the coolest animal on the list, a kind of hybrid that looks like a crocodile mated with a dolphin. It's also one that experts didn't know existed until recently. By piecing together fossil remains first discovered in 1959, Scottish researchers determined that the Dearcmhara – Scottish-Gaelic for "marine lizard" – likely made its home in the then-warm waters off Scotland's west coast some 170 million years ago. The scientists announced their discovery of this new genus of ichthyosaur (sea-going reptile) in January 2015 [source: Moss].

Stretching roughly 14 feet (4.3 meters), the Dearcmhara Shawcrossi was believed to be near the top of the food chain in its day, likely dining on smaller fish and reptiles. Still, the animal is a smaller and more primitive version of the beasts that would come later in the Jurassic period (150 to 200 million years ago). By dating the Dearcmhara back to the same time frame, some researchers now believe that the shift to larger aquatic life may have been more subtle than the sudden shift in temperature of volcanic eruption some folks have theorized might have preceded the change [sources: Moss, Bittel].

Speaking of Jurassic, the pliosaur was the most fearsome beast the waters saw in those days. Described by one news outlet as a "crocodile on steroids," this creature ran up to 59 feet (18 meters) in length. The roughly 155 million-year-old mammoth featured a human-sized jaw and large teeth that may have been able to take down a Dearcmhara in one bite, as well as huge, melon-sized eyes that gave the animal impressive binocular vision. In the early 2000s, fossils of the beast have been located in England and Norway [source: Morelle].

A short-necked marine reptile, the pliosaur resembles a large croc with longer, paddle-shaped limbs. That made it faster than many of its counterparts, traveling at speeds of up to 6 mph (10 kph). The creature fed mostly on fish, mollusks and other marine reptiles, but paleontologists have also found something else in pliosaur stomachs: dinosaur remains. They don't believe that these beasts actually hunted dinosaurs, but instead probably feasted on discarded remains [source: BBC].