Mosasaur facts for kids
Quick facts for kids Mosasaurs |
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| Mounted skeleton of a russellosaurine (Plesioplatecarpus planifrons) | |
Scientific classification  |
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Squamata |
| Superfamily: | †Mosasauroidea |
| Family: | †Mosasauridae Gervais, 1853 |
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Mosasaurs were a group of huge, ancient marine reptiles. Their name comes from the Latin word Mosa, for the Meuse River, and the Greek word sauros, meaning 'lizard'. These amazing creatures lived in the oceans during the Late Cretaceous period. This was a long time ago, between 98 and 66 million years ago.
The first mosasaur fossil was found in 1764. It was discovered in a limestone quarry near the Meuse River in Maastricht. Mosasaurs are part of a group called Squamata. This group also includes modern-day lizards and snakes.
For the last 20 million years of the Cretaceous period, mosasaurs ruled the seas. They became the top predators after other large marine reptiles, like ichthyosaurs and pliosaurs, died out. But then, about 66 million years ago, mosasaurs also disappeared. This happened during a major event called the K-Pg event. This event caused many animals, including the dinosaurs, to go extinct.
Contents
What Mosasaurs Looked Like
Mosasaurs were air-breathing reptiles. They were amazing swimmers. They lived in the warm, shallow inland seas of the Late Cretaceous period. They were so well-suited to ocean life that they likely gave birth to live young. This is different from sea turtles, which lay eggs on land.
The smallest mosasaur known was Dallasaurus turneri. It was less than 1 meter (3 feet) long. But most mosasaurs were much bigger. Many species grew longer than 4 meters (13 feet). The largest known species, Mosasaurus hoffmannii, might have reached up to 17 meters (56 feet).
Mosasaurs looked a bit like modern monitor lizards. However, their bodies were longer and smoother for swimming fast. Their limb bones were short. Their flippers were formed by webbing between their long finger and toe bones. Their tails were wide and flat, ending in a powerful fluke. This fluke helped them push through the water.
Scientists once thought mosasaurs swam like conger eels or sea snakes. This means they would wiggle their whole bodies. But new evidence shows that many advanced mosasaurs had large, crescent-shaped tail flukes. These were similar to those of sharks and some ichthyosaurs. Instead of wiggling, their bodies likely stayed stiff. This helped them cut through the water with less drag. Their strong tails gave them powerful pushes. They probably waited quietly and then quickly attacked their prey. Some species could even flap their flippers like sea lions to move through the water.
Some old drawings of mosasaurs showed them with crests along their backs. These crests were based on mistaken ideas about their bones. By the time scientists realized this error, the image of crested mosasaurs was already popular in art.
How Mosasaurs Lived and Hunted
Mosasaurs had special jaws that could open very wide. Their skulls were flexible, much like a snake's. This allowed them to swallow their prey almost whole. Scientists found a skeleton of a Tylosaurus mosasaur in South Dakota. Inside it were the remains of a diving seabird called Hesperornis. There were also bones from a bony fish, a possible shark, and even a smaller mosasaur. This shows they ate many different animals. Sometimes, shark teeth have been found stuck in mosasaur bones.
One common food for mosasaurs was ammonites. These were ancient sea creatures with spiral shells, similar to a modern Nautilus. Ammonites were very common in the Cretaceous seas. Scientists have found holes in fossil ammonite shells. These holes are triangular and appear on both sides of the shell. This suggests they were made by the bite of a mosasaur. Some mosasaurs, like Globidens, had blunt, round teeth. These teeth were perfect for crushing the shells of mollusks.
Most mosasaurs were active hunters. They ate fish and ammonites. Smaller mosasaurs, like Platecarpus and Dallasaurus, were about 1 to 6 meters (3 to 20 feet) long. They probably hunted fish and other small creatures. Some smaller mosasaurs might have even hunted in fresh water. The huge Mosasaurus hoffmannii was the apex predator, or top hunter, of its time. It could grow to 11 meters (36 feet) long and weigh 3.8 metric tons (4.2 short tons).
Mosasaurs' Skin and Organs
We are still learning about mosasaur skin. Not many fossils show clear scale patterns. This is because scales are delicate and hard to preserve. But some amazing fossils from Jordan have shown us more. These fossils show that mosasaurs had small, overlapping, diamond-shaped scales. They looked a lot like snake scales.
Just like modern reptiles, mosasaur scales varied. Some parts of their bodies had keeled scales. These scales had a ridge, making them less shiny. This might have helped them hide as ambush predators. Other parts had smooth scales. Some mosasaurs, like Plotosaurus, might have used their front flippers. They could have flapped them like a breaststroke for quick bursts of speed.
Recently, a Platecarpus tympaniticus fossil was found. It preserved not only skin but also internal organs. Reddish areas might be the heart, lungs, and kidneys. The windpipe (trachea) was also preserved. Even part of the eye's retina might be there. The kidneys were placed further forward than in monitor lizards. This is similar to cetaceans (whales and dolphins). Their lung tubes (bronchi) also ran parallel, like in cetaceans. These features suggest mosasaurs were fully adapted to life in the ocean.
In 2011, scientists even found collagen protein in a Prognathodon bone. This bone was from the Cretaceous period. This was an exciting discovery.
Scientists also think mosasaurs had a forked tongue, like snakes. This is because they had special openings in the roof of their mouths. Snakes use their forked tongues to "smell" their surroundings. This helps them find prey. So, mosasaurs likely had a very sensitive sense of smell too.
Mosasaurs' Body Temperature
A study in 2016 showed that mosasaurs were endothermic. This means they could keep their bodies warm from the inside. They were warm-blooded, like birds and mammals. This was different from an earlier study in 2010. That study suggested mosasaurs were cold-blooded. The 2016 study compared mosasaurs to modern warm-blooded animals. It found mosasaurs likely had body temperatures similar to seabirds. They could keep themselves warmer than the surrounding ocean water.
Mosasaurs' Colors
For a long time, we didn't know what color mosasaurs were. But in 2014, scientists found the pigment melanin in the fossilized scales of a Tylosaurus nepaeolicus. Melanin is the same pigment that gives color to our skin and hair. This discovery suggests mosasaurs were likely countershaded. This means they had dark backs and light bellies. This coloring helps animals blend in with the ocean. It's like how a great white shark or a leatherback sea turtle is colored today. These findings were published in the scientific journal Nature.
Mosasaurs' Teeth and Replacement
Mosasaurs had teeth that were deeply set into their jawbones. They didn't keep the same teeth their whole lives. Instead, they constantly shed and replaced them. New teeth grew in a special pit inside the roots of the old teeth. This process happened in eight unique steps. A new tooth crown would first form. Then it would move into the pit and grow larger. As it grew, it would push the old tooth out. Finally, the old tooth would fall out, and the new tooth would firmly anchor itself.
Mosasaurs' Reproduction and Growth
We don't know much about how mosasaurs grew. Young mosasaur fossils are rare. Many were mistaken for ancient birds when first found. However, discoveries of baby mosasaur fossils show that they gave birth to live young. They also spent their early lives in the open ocean. They did not stay in shallow, protected areas as once thought. We still don't know if mosasaurs cared for their young, like some other marine reptiles. The discovery of these young mosasaurs was published in the journal Palaeontology.
Possible Mosasaur Eggs
In 2020, a study in Nature described a huge fossilized egg from Antarctica. This egg was from about 68 million years ago, near the end of the Cretaceous. It is one of the largest amniote eggs ever found, similar in size to an elephant bird egg. The egg was soft, thin, and folded. This suggests it belonged to a marine animal. We don't know for sure what animal laid it. However, the egg's structure is like that of modern lizards and snakes. Also, mosasaur fossils were found nearby. This makes scientists think it might have been a mosasaur egg. It's unclear if the egg was laid on land or in the water. This egg was given the new name Antarcticoolithus bradyi. Some scientists have also suggested it might have belonged to a dinosaur.
Mosasaurs' Ancient Environment
Scientists have studied mosasaurs' evolution. They looked at how many different types of mosasaurs existed. They also studied how different their body shapes were. They compared this to sea levels, ocean temperatures, and carbon levels in the Late Cretaceous. Many things likely affected their evolution. But it seems that a lot of food in the Late Cretaceous seas was a big factor. This food supply was affected by sea levels and ocean conditions. When the food supply crashed at the end of the Cretaceous, mosasaurs died out. This happened at the same time as a giant asteroid impact.
Sea levels were high during the Cretaceous period. This caused large parts of the land to be covered by shallow seas. For example, a great inland seaway covered much of what is now North America. Mosasaur fossils have been found all over the world. This includes places like the Netherlands, Belgium, Denmark, Portugal, Sweden, South Africa, Spain, France, Germany, Poland, the Czech Republic, Italy, Bulgaria, the United Kingdom, Russia, Ukraine, Kazakhstan, Azerbaijan, Japan, Egypt, Israel, Jordan, Syria, Turkey, Niger, Angola, Morocco, Australia, New Zealand, and Vega Island near Antarctica.
In Canada, mosasaur fossils have been found in Manitoba and Saskatchewan. In the United States, they have been found in many states. This includes Alabama, Mississippi, New Jersey, Tennessee, and Georgia. They are also found in states once covered by the ancient seaway. These include Texas, Arkansas, New Mexico, Kansas, Colorado, Nebraska, South Dakota, Montana, Wyoming, and North Dakota. Mosasaur bones and teeth have also been found in Colombia, Brazil, and Chile.
Many fossils once thought to be dinosaurs in New Zealand are actually mosasaurs and plesiosaurs. Both were large marine reptiles from the Mesozoic Era.
The largest mosasaur on public display today is named Bruce. It is a 13.05 meter (42 feet 9.75 inches) long Tylosaurus pembinensis. This fossil is about 80 million years old. Bruce was found in 1974 in Manitoba, Canada. It is now at the Canadian Fossil Discovery Centre in Morden, Manitoba. In 2014, Bruce earned a Guinness Record for being the largest mosasaur on public display.
How Mosasaurs Were Discovered
The first discovery of a mosasaur fossil was in 1764. Quarry workers found part of a skull in a limestone quarry near Maastricht, Netherlands. This happened before any major dinosaur fossils were found. But this first find wasn't widely known.
However, a second skull discovery between 1770 and 1774 changed everything. This fossil caught the attention of scientists during the Age of Enlightenment. This was a time when people were very interested in new knowledge. A surgeon and fossil collector named Johann Leonard Hoffmann wrote to important scientists about it. This made the fossil very famous. The original owner was a church official named Godding.
In 1794, French soldiers occupied Maastricht. They found the hidden fossil. It is said they were offered 600 bottles of wine as a reward. The fossil was then taken to Paris. At first, people thought it was a fish, a crocodile, or even a sperm whale. But in 1799, a Dutch scientist, Adriaan Gilles Camper, realized it was a type of lizard. In 1808, Georges Cuvier agreed. The large fossil animal from Maastricht was finally named Mosasaurus ('Meuse reptile') in 1822. Its full species name, Mosasaurus hoffmannii, was given in 1829. Other mosasaur remains found earlier in Maastricht are now displayed in the Teylers Museum in Haarlem.
The discovery of the mosasaur made the Maastricht limestone beds famous. So famous, in fact, that the last six million years of the Cretaceous period are now called the Maastrichtian age.
Mosasaurs and Modern Lizards
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Scientists are still debating which modern animals are the closest relatives to mosasaurs. They are trying to figure out if mosasaurs are more closely related to monitor lizards or snakes. Both groups belong to the same larger group, Squamata, as mosasaurs.
Images for kids
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Restoration of Opetiosaurus bucchichi, an early mosasaur relative.
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Life restoration of a mosasaurine, Globidens alabamaensis.
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Life restoration of a mosasaurine, Plotosaurus bennisoni.
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Restoration of a tylosaurine, Tylosaurus pembinensis.
See also
In Spanish: Mosasaurios para niños
