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Mosasaurs are a third type of marine reptiles. There has always been a special place in my heart for mosasaurs. When I was growing up in Austin, Texas, my Mom would take my brother and I to Texas Memorial Museum, where a mosasaur specimen called the Onion Creek Mosasaur was on prominent display. This mosasaur skeleton was one of the animals that got me interested in paleontology and animals in general. The Onion Creek Mosasaur is still on display at Texas Memorial Museum, but it has been remounted into a more dynamic mount, and moved to the museum's natural history and paleontology exhibit.
Mosasaurs are members of the Superfamily Varanoidea, a group of lizards that also contains the monitor lizards, Komodo dragons, and Gila monsters. The mosasaurs originated from small, semi-aquatic lizards called aigialosaurs whose remains are found in rocks from the Lower Cretaceous Period. Mosasaurs had long heads with short necks, and long, slender bodies and tails. Mosasaurs reached lengths of 5 to 10 meters (16 to 33 feet). Their tails were flattened from side to side, and were used to propel the animal through the water. They used their flippers to steer. Like the lizards they are related to, the mosasaurs had diapsid skulls (see my article "Reptile Skulls" for more information). Mosasaur remains are found only in rocks from the Upper Cretaceous Period. They probably primarily ate fish, at the time when they lived there was an abundance of primitive teleost fish (see my article "The Fish, Part IV" for more information about teleosts and other ray-finned fish). The ichthyosaurs were on the decline during this period, so there was little competition with them for prey, but they would have competed with the Plesiosaurs for food. Mosasaurs also fed on ammonites, ammonite shells have been found with what appear to be mosasaur tooth marks (see my article "Ammonites"). The mosasaurs were widely distributed, their remains have been found on every continent except Antactica and Australia (but they have been found in New Zealand!). Their fossils are particularly abundant in Kansas (which was covered by the Western Interior Seaway) and in Northwest Europe. The first recorded specimen of a mosasaur was a set of jaws that were found in 1770 in a chalk cavern in Maastricht (southeast Holland). The fossil was so famous that when a French Republican army approached Maastricht in 1795, the commander deliberately refrained from attacking the chateau where it was kept. When Maastricht had fallen, the general ordered his troops to seize it for the French Republic, and it was taken to Paris, where Georges Cuvier later studied it. The fossil was finally named Mosasaurus in 1829 by William Conybeare; the name means "Meuse lizard", after the Meuse River near which it was found. The original specimen is still in Paris, but efforts are underway to have it moved to the Natural History Museum of Maastricht.
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The copyright of the article Marine Reptiles III: Mosasaurs in Paleontology is owned by . Permission to republish Marine Reptiles III: Mosasaurs in print or online must be granted by the author in writing.
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