Mosasaur

Mosasaurs (from Latin Mosa, the Meuse river where the fossils were first discovered, and Greek sauros, lizard) were serpentine marine lizards, more closely related to snakes than to monitor lizards (Lee 1997). Mosasaurs were not dinosaurs, but lepidosaurs. These predators evolved from semi-aquatic squamates, the aigialosaurs, in the early Cretaceous and were the dominate marine predators during the Upper Cretaceous Period (Turonian-Maastrichtian).

Known genera include Clidastes, Mosasaurus, Prognathodon, Globidens, Plotosaurus, Plesiotylosaurus, Carinodens, Dallasaurus, Igdamanosaurus, Halisaurus, Tylosaurus, Platecarpus, Selmasaurus, Plioplatecarpus, Amphekepubis, Goronyosaurus, Liodon, Moanasaurus, Pluridens, Lakumasaurus, Yaguarasaurus, Eonatator, Tethysaurus, Angolasaurus, Kourisodon, and Russellosaurus.

Description

Mosasaurs breathed air and were powerful swimmers, well-adapted to living in the warm shallow epicontinental seas prevalent during the late Creatceous. They also gave birth to live young rather than returning to the shore to lay eggs, as do sea turtles.

The smallest-known Mosasaur is Carinodens belgicus, which was about 3 to 3.5 m long and probably lived on the sea floor, 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 more elongated and streamlined for swimming. Their front leg bones were reduced in length, and their fin-like paddles were formed by long finger-bones. Their rear limbs were atrophied. Their tails were believed to have been equipped with a dorsal fin and it is believed the tail supplied the locomotor power. This method of locomotion may have been similar to that used by the conger eel, today. The animal may have lurked and pounced rapidly and powerfully on passing prey, rather than hunting for it.

Mosasaurs had a loosely-hinged jaw which enabled them to swallow their prey almost whole. This snake-like feature helped identify the stomach contents fossilized within a mosasaur skeleton (Tylosaurus proriger), which included the diving seabird Hesperornis, a marine bony fish, a shark, and part of another, smaller mosasaur. Mosasaur bones have also been found with shark teeth embedded in them.

Based on features such as the double row of pterygoid teeth in the maxilla, loosely-hinged jaw, modified/reduced limbs, and probable locomotion, many researchers believe that snakes and mosasaurs may have a common ancestor; 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 ^*,^*.

Environment

Sea-levels were high during the Cretaceous, causing marine ingressions in many parts of the world, and a great inland seaway in North America. Mosasaur fossils have been found in the Netherlands and Sweden, in Africa, in Australia, New Zealand, and 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, Colorado, the Dakotas and Montana. Mosasaurs are also known from California, Mexico, and Peru.

The "dinosaurs" of New Zealand, a volcanic island arc that has never been part of a continent, are a unique series of mosasaurs and plesiosaurs, another group of predatory marine reptiles of the Mesozoic era.

Discovery

The first publicized discovery of a fossil mosasaur preceded any dinosaur fossil discoveries, and drew the Enlightenment's attention to the existence of fossilized animals; the specimen was discovered in 1780 by quarry-workers in a subterranean gallery who quickly alerted Doctor C. K. Hoffman, a surgeon and fossil-hunter in the Dutch city of Maastricht, though rights of ownership lay with a canon of Maastricht, as owner of the overlying land.

Dr. Hoffman's correspondence among men of science made the find famous. When the Revolutionary forces occupied Maastricht, the carefully-hidden fossil was uncovered, betrayed, it is said, by a case of wine, and transported to Paris, where Georges Cuvier was able to describe it for science, though le grand animal fossile de Maastricht was not described as a Mosasaur ("Meuse reptile") until 1822, and not given its official name, Mosasaurus hoffmani, until 1829. A Mosasaur skull that had actually been discovered at Maastricht earlier, has recently been reidentified in the Teylers Museum, Haarlem.

The Maastricht limestone beds were rendered so famous they have given their name to the ultimate 6-million-year epoch of the Cretaceous: the Maastrichtian.

On 2005-11-16, research in Netherlands Journal of Geosciences confirmed that the recently uncovered Dallasaurus turneri is an early link between land-based, komodo dragon-like varanid lizards and the aquatic mosasaurs ^*

Purported modern sightings

Although paleontologists have determined that all mosasaurs went extinct around the same time as the dinosaurs, and there's no fossil evidence of them beyond the end of the Cretaceous (Maastrichtian), some cryptozoologists feel that sporadic reports of crocodile-like sea serpents may be suggest surviving mosasaurs. The Taniwha of Māori lore has also been connected to mosasaurs by journalists.

External links

Palaeos: Vertebrates: Mosasaurs
BBC Science and Nature: Mosasaurs
Mike Everhart and David Lewis, "Mesozoic marine monsters of the Mangahouanga": New Zealand fossil fauna
Mike Everhart, "A day in the life of a Mosasaur": life in the Sea of Kansas, illus. by Carl Buell
Mike Everhart, "Mosasaurus hoffmani" until 1829.
Mosasaurus maximus mounted skeleton at University of Texas Memorial Museum

References

Lee, 1997, "The phylogeny of varanoid lizards and the affinities of snakes," in Phil. Trans. R. Soc. Lond. B 352: 53-91.

Everhart, M.J. 2005. "Enter the Mosasaurs," Chapter 9 in "Oceans of Kansas: A Natural History of the Western Interior Sea." Indiana University Press, Bloomington, 322 p.