Sea Monsters

Mosasaurs Designed for Life at Sea

Who doesn’t love a good monster story? Real-life monsters, called mosasaurs, once terrorized the seas. In all the excitement about their size and ferocity, however, we shouldn’t lose sight of their many other amazing designs for life at sea.

Afraid to swim in the ocean because of sharks? The fictional 25-foot (7.6 m) great white shark in the movie Jaws made quite a sensation. But it would barely make a mid-morning snack for the real-life monsters that stalked the seas in Noah’s day.

The Bible explains that the earth and everything in it was once “very good” (Genesis 1:31), but the earth became corrupt and violent as a result of Adam’s sin (Genesis 6:11). Even some sea creatures turned into dangerous hunters, as we can see from their fossil remains. The Flood preserved many specimens of these sea creatures.

Seagoing Reptiles

Many natural history museums display skeletons of enormous sea monsters, the mosasaurs. Their features are unmistakable. They look a lot like oversized lizards designed for life in the sea. Imagine a komodo dragon with flippers instead of arms and legs. Then make it really, really big—the biggest of them (like the Mosasaurus and Tylosaurus) were 50 feet (15 m) or more in length! They make the shark in Jaws look puny by comparison.


Tylosaurus, one of the largest mosasaurs, could reach 50 feet or more in length. Its body was long and streamlined, with four paddle-like limbs and a long, powerful tail.

Some mosasaurs had a torpedo snout for ramming and a long row of deadly teeth for tearing and crushing. Like modern snakes, they could flex their lower jaw to swallow extra-large prey. Such designs speak of a Creator, who supplied sea creatures with tools to survive in a fallen world after Adam’s sin.1

But in our childlike fascination with scary monsters, we often overlook other more benign marvels.

Mosasaurs possessed stunning designs for life in the ocean. Mosasaur bodies were long and streamlined, with four paddle-like limbs and a long, powerful tail that pumped from side to side, like a crocodile’s. When they were about to attack, their tails gave mosasaurs a burst of speed, allowing them to ambush unsuspecting prey. The front flippers would steer, while the rear paddles were likely stabilizers.

As reptiles, mosasaurs had to surface to breathe air. So they had nostrils near the top of their heads. But life in water presented another challenge.

Did You Know?

  • First discovered in the Netherlands, remains of mosasaurs are found on every continent, including Antarctica.
  • Globidens was a medium-sized mosasaur that had rounded, onion-shaped teeth capable of crushing clam shells.
  • Mosasaurs had scales much like snakes, which helped them glide through the water.
  • The largest number of mosasaur remains have been found in Kansas.
  • Most mosasaurs used a fast, ambush-style attack to capture prey.
  • All mosasaur fossils are from rock layers of the upper Cretaceous, likely deposited mid- to late-Flood.
  • The word mosasaur means “Meuse lizard,” after the Meuse River (in Latin, Mosa), on the border between Belgium and the Netherlands, where the first mosasaur fossils were discovered.
  • Be careful not to say a female reptile is “pregnant.” She’s not. The technical term is gravid.

Class: Reptilia (reptiles)
Order: Squamata (scaled reptiles)
Family: Mosasauridae
Genus: There are 26 described genera of mosasaurs.
Size: The smallest mosasaur (Dallasaurus) was only 3 feet (1 m) long; the largest (Mosasaurus) was more than 50 feet (17 m) and weighed up to 20 tons.
Diet: Fish, clams, ammonites (an extinct creature that looks like a squid in a shell), and other marine life
Habitat: Most lived in the open ocean, while a few lived closer to or in streams.

Live Birth—Underwater

While most reptiles lay eggs in nests, some give birth to live young. Mosasaurs did, but under extreme conditions. Without special designs and instincts, a baby born underwater would drown.

Like whales, mosasaurs gave birth in the open ocean, but the way their young developed in the mother was very, very different: mother mosasaurs didn’t have a separate womb. Instead, the eggs developed inside the body cavity, where the young began to grow within a shell. The shell dissolved, but the young remained inside with a yolk sac that provided food; they were not fed by the mother.

Once developed enough to survive outside, the young mosasaurs passed through an opening called a cloaca (which also served in waste removal) and swam up to the surface for their first breath. But from then on, as far as we know, they were on their own.2

How do we know about live births? In 1996, a skeleton of the mosasaur Plioplatecarpus was discovered in ocean-deposited rocks in South Dakota, evidence that Flood waters once covered what is now North America.3 The skeleton had even been scavenged by sharks before burial. (Paleontologists found scrape marks, and teeth stuck in the bones.) But in the area near the rear flippers, were several tiny mosasaurs, which were identified as Plioplatecarpus, the same genus as the adult.

The researchers ruled out cannibalism because the bones showed no evidence of passing through the big mosasaur’s stomach (which would have left acid marks on them). All of the tiny skeletal parts were still in the process of developing when fossilized, indicating that these were, in fact, unborn mosasaurs. No eggshells were found, and it was determined that any egg large enough to encase these unborn mosasaurs would have had a shell too thick for them to break. So mosasaurs must have given live births.

This was a beautiful discovery, and it shows another way God provides for His creations. Through the evidence of the natural world, including the fossils of these stunning creatures, all creation proclaims the Lord’s handiwork.

Answers Magazine

January – March 2010

Fossils are filled with mystery. They are commonly used to attack the biblical worldview, but in reality the Bible gives us the keys to help us solve these mysteries. How could recently discovered dinosaur tissue have survived until today? Why is the first fossil layer filled with such an astonishing variety of life (“the Cambrian Explosion”)? Read this issue to understand these and other mysteries of our world!

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  1. For a fuller explanation of how “designs to kill” could still point to God as the designer, see Rick Oliver’s Designed to Kill in a Fallen World in Answers (July–September, 2009), pp. 36–39.
  2. Since similar reptiles do not display any care for their young, it is likely that mosasaurs did not do so, either.
  3. The information on the Plioplatecarpus embryos comes from an excellent presentation by paleontologist Gorden Bell at the First Mosasaur Meeting in 2004. The specimen is awaiting a full scientific description. Bell does not endorse the young-earth creationist perspective of this article.


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