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Mosasaurs (from Latin Mosa meaning the 'Meuse river', and Greek sauros meaning 'lizard') were serpentine marine reptiles. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. These ferocious marine predators are now considered to be the closest relatives of snakes, due to cladistic analysis of symptomatic similarities in jaw and skull anatomies.[1] Mosasaurs were not dinosaurs but lepidosaurs, reptiles with overlapping scales. These predators evolved from semi-aquatic squamates[2] known as the aigialosaurs, close relatives of modern-day monitor lizards, in the Early Cretaceous Period. During the last 20 million years of the Cretaceous Period (Turonian-Maastrichtian), with the extinction of the ichthyosaurs and pliosaurs, mosasaurs became the dominant marine predators.
[edit] Description Mosasaurs breathed air and were powerful swimmers that were well-adapted to living in the warm, shallow epicontinental seas prevalent during the Late Cretaceous Period. Mosasaurs were so well adapted to this environment that they gave birth to live young, rather than return to the shore to lay eggs, as sea turtles do. The smallest-known mosasaur was Carinodens belgicus, which was about 3.0 to 3.5 m long and probably lived in shallow waters near shore, cracking mollusks and sea urchins with its bulbous teeth. Larger mosasaurs were more typical: mosasaurs ranged in size up to 17 m. Hainosaurus holds the record for longest mosasaur, at 17.5 m. Mosasaurs had a body shape similar to that of modern-day monitor lizards (varanids), but were more elongated and streamlined for swimming. Their limb bones were reduced in length and their paddles were formed by webbing between their elongated digit-bones. Their tails were broad and supplied the locomotive power. This method of locomotion may have been similar to that used by the conger eel or sea snakes today. The animal may have lurked and pounced rapidly and powerfully on passing prey, rather than hunting for it.  Mosasaurs had a double-hinged jaw and flexible skull (much like that of a snake), which enabled them to gulp down their prey almost whole, a snakelike habit that has helped identify the unmasticated gut contents fossilized within mosasaur skeletons. A skeleton of Tylosaurus proriger from South Dakota included remains of the diving seabird Hesperornis, a marine bony fish, a possible shark and another, smaller mosasaur (Clidastes). Mosasaur bones have also been found with shark teeth embedded in them. Based on features such as the double row of pterygoid ("flanged") teeth on the palate, the double-hinged jaw, modified/reduced limbs and probable methods of locomotion, many researchers believe that snakes and mosasaurs may have had a common ancestor. This theory was first suggested in 1869, by Edward Drinker Cope, who coined the term "Pythonomorpha" to include them. The idea lay dormant for more than a century, before being revived in the 1990s.[3][4] [edit] EnvironmentSea levels were high during the Cretaceous Period, causing marine transgressions in many parts of the world and a great inland seaway in what is now North America. Mosasaur fossils have been found in the Netherlands, in Sweden, in Africa, in Australia, in New Zealand and on Vega Island, off the coast of Antarctica. In Canada and the United States, complete or partial specimens have been found in Alabama, Mississippi, Tennessee, and Georgia and in almost all the states covered by the seaway: Texas, southwest Arkansas, New Mexico, Kansas,[5] Colorado, Nebraska, the Dakotas, Montana, Manitoba,[6] and the Pierre Shale and Fox Hills formations of North Dakota.[7] Mosasaurs are also known from California, Mexico, Peru and Denmark. Many of the 'dinosaur' remains found on New Zealand are actually mosasaurs and plesiosaurs, another group of Mesozoic predatory marine reptiles. [edit] Discovery The first publicized discovery of a partial fossil mosasaur skull in 1764 by quarry-workers in a subterranean gallery of a limestone quarry near the Dutch city of Maastricht, preceded any major dinosaur fossil discoveries but remained little known. However, a second find of a partial skull drew the Age of Enlightenment's attention to the existence of fossilized animals that were different from any known living creatures. When the specimen was discovered between 1770 and 1774, Johann Leonard Hoffmann, a surgeon and fossil-collector, corresponded about it with the most influential scientists of his day, making the fossil famous. The original owner though was Godding, a canon of Maastricht cathedral. When the French Revolutionary forces occupied Maastricht in 1794, the carefully-hidden fossil was uncovered, after a reward, it is said, of six hundred bottles of wine, and transported to Paris. After it had been earlier interpreted as a fish, a crocodile and a sperm whale, the first to understand its lizard affinities was the Dutch scientist Adriaan Gilles Camper in 1799. In 1808 Georges Cuvier confirmed this conclusion, although le Grand Animal fossile de Maëstricht was not actually named Mosasaurus ('Meuse reptile') until 1822 and not given its full species name, Mosasaurus hoffmannii, until 1829. Several sets of mosasaur remains, that had been discovered earlier at Maastricht but were not identified as mosasaurs until the nineteenth century, have been on display in the Teylers Museum, Haarlem, procured from 1790. The Maastricht limestone beds were rendered so famous by the Mosasaur discovery that they have given their name to the final six-million-year epoch of the Cretaceous, the Maastrichtian. [edit] Evolutionary antecedentsBased on features such as the loosely-hinged jaw, modified/reduced limbs and probable locomotion, many researchers believe that snakes share a common marine ancestry with mosasaurs, a suggestion advanced in 1869, by Edward Drinker Cope, who coined the term "Pythonomorpha" to unite them. The idea lay dormant for more than a century, to be revived in the 1990s.[3] Recently, the discovery of Najash rionegrina, a fossorial snake from South America cast doubt on the marine origin theory. On 2005-11-16, research reported in Netherlands Journal of Geosciences, confirmed that the recently uncovered Dallasaurus turneri is an early link between land-based monitor lizards (such as the Komodo dragon) and the aquatic mosasaurs.[8] [edit] In popular culture
[edit] Taxonomy[edit] Classification
Incertae sedis [edit] PhylogenyCladogram of mosasaurs and related taxa modified from Bell and Polcyn, 2005:[9]
[edit] References
[edit] External links
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