Tylosaurus Proriger
Tylosaurus may have ruled the Late Cretaceous seas because all other would-be competitors,
such as ichthyosaurs, were already extinct. Though they evolved from terrestrial lizards, the
paddle-like limbs of giant mosasaurs like Tylosaurus were useless on land.
Tylosaurus was the deadliest hunter of the ancient seas, ready to seize and kill just about any
smaller creature that crossed its path with true jaws of death—lined on each side with two rows
of pointy, cone-shaped teeth. Tylosaurus used its snout to locate prey, which, once inside the
mosasaur's menacing jaws, was swallowed whole. When the sea monster opened wide for the
final gulp, two extra rows of teeth on the roof of its mouth allowed crippled captives no escape.
Tylosaurus grew more than 45 feet (14 meters) long, making it the largest of the marine reptiles
called mosasaurs. Like all mosasaurs, a long and muscular, vertically flattened tail powered
Tylosaurus through the water, allowing it to ambush its prey with rapid bursts of acceleration.
Paddle-like limbs helped steer the slim body covered in lizard-like scales through the water.
Preserved stomach contents indicate a diet heavy on fish, but seabirds, sharks, plesiosaurs, and
other mosasaurs also failed to escape Tylosaurus's lethal grip. Though not a dinosaur, Tylosaurus
lived alongside them and went extinct at around the same time. Many Tylosaurus remains have
been found in Kansas, which was once covered by a large ocean called the Western Interior
Seaway.
Fast Facts
Type: Prehistoric
Diet: Carnivore
Size: Length, 45 ft (14 m)
Protection status: Extinct
Did you know? Mosasaurs gave birth to live young. A baby Tylosaurus was 3 to 6 ft (1 to 2 m)
long—small enough for predatory fish and sharks to eat.
Size relative to a bus:
Styxosaurus Snowii
Though artists often depict elasmosaurs with their heads held swanlike, high above the water, such a
position would have been physically impossible and unlikely for practical reasons since they wouldn't be
able to see beneath their chins.
Styxosaurus was an elasmosaur, a long-necked variety of the marine reptiles called plesiosaurs.
These sea monsters grew upwards of 40 feet (12 meters) long. About half that length was neck, a
feature that allowed Styxosaurus to sneak up on schools of fish as it slowly cruised the shallow
waters of the Late Cretaceous seas.
The long, pointed teeth of Styxosaurus were useful for seizing and holding prey, but they
couldn't cut or chew. Instead, the elasmosaur swallowed fish whole. Predators likely included
some of the fiercest monsters of the seas, such as the sharp-toothed shark Cretoxyrhina and the
giant mosasaur Tylosaurus.
Like all plesiosaurs, Styxosaurus's limbs were two pairs of flipper-like paddles, which it moved
in a figure eight motion to fly through the water much as seals and sea lions do today. In some
cases hundreds of stones, called gastroliths, have been found associated with the bellies of these
sea monsters, suggesting they swallowed the stones to help with digestion or perhaps provide
ballast as they swam.
Fast Facts
Type: Prehistoric
Size: Length, up to 40 ft (12 m)
Protection status: Extinct
Did you know? Like other plesiosaurs, Styxosaurus was restricted to prey no more than 2 feet
(0.6 meters) long.
Size relative to a bus:
Cretoxyrhina Mantelli
A keen sense of smell and quick speed helped Cretoxyrhina track prey.
Cretoxyrhina was one of the largest sharks and a formidable predator in the Late Cretaceous
seas. Nicknamed the Ginsu shark after the kitchen knife that slices and dices, Cretoxyrhina
ripped apart prey with a mouth full of razor-sharp, bone-shearing teeth. Evidence suggests
Cretoxyrhina fed on mosasaurs, plesiosaurs, and even the giant bony fish Xiphactinus, a fierce
predator itself.
Sharks are made of cartilage, which does not fossilize well. Much of what is known about them
comes from their abundant—and harder—teeth. Cretoxyrhina's were smooth, curved, and grew
more than two inches (five centimeters) long. Bite marks and teeth embedded in the bones of its
prey suggest Cretoxyrhina chomped with brutal force.
Estimates from a few calcified remains of cartilaginous Ginsu sharks suggest they grew upwards
of 24 feet (7 meters) long, similar in size to modern great white sharks. Though fierce and feared,
Cretoxyrhina was preyed upon by the giant mosasaur Tylosaurus, and Ginsu remains were
scavenged by the smaller shark of its time, Squalicorax.
Fast Facts
Type: Prehistoric
Diet: Carnivore
Size: Up to 24 ft (7 m)
Protection status: Extinct
Did you know? Fossil tooth marks suggest Cretoxyrhina and Squalicorax sharks went after the
same food, either hunting together or stealing from each other.
Size relative to a bus: