Mosasaur

Mosasaurs (from Latin Mosa meaning the 'Meuse river', and Greek sauros meaning 'lizard') are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. Mosasaurs are now considered to be the closest relatives of snakes, due to cladistic analyses that have taken into account similarities in jaw and skull anatomies. Mosasaurs were varanoids closely related to terrestrial monitor lizards. They probably evolved from semi-aquatic squamates known as aigialosaurs, which were more similar in appearance to modern-day monitor lizards, in the Early Cretaceous. 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.

Description

showing crescent-shaped tail fluke]] , 1899. This and images like it were based on misidentified tracheal cartilage, but when the error was discovered, depicting mosasaurs with such crests was already a trend]] Mosasaurs breathed air, were powerful swimmers, and 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. Tylosaurus 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. However, more recent evidence suggests that many advanced mosasaurs had large crescent-shaped flukes on the ends of their tails similar to those of sharks and ichthyosaurs. Rather than snake-like undulatory movement, the body probably remained stiff in these mosasaurs to improve hydrodynamic efficiency through the water while the end of the tail provided strong propulsion. 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 which 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.

Soft tissue

Despite the relatively high number of mosasaur remains collected worldwide, knowledge of the nature of their skin coverings remains in its early stages. An incredibly small amount of mosasaurid specimens collected from around the world retain fossilized scale imprints; this lack of knowledge is possibly due to the delicate nature of the scales, which nearly eliminates possibility of preservation, in addition to the preservation sediments types and the marine conditions under which the preservation occurred. Until the discovery of several mosasaur specimens along with their remarkably well preserved scale imprints from late Maastrichtian deposits of the Muwaqqar Chalk Marl Formation of Harrana in Jordan, knowledge of the nature of mosasaur integument was mainly based on very few accounts describing early mosasaur fossils dating back to the upper Santonian-lower Campanian such as the famous Tylosaurus specimen (KUVP-1075) from Cove County, Kansas. Material from Jordan has shown that the body of mosasaurs, as well as the membrane between the fingers and toes, was covered with small overlapping diamond-shaped scales resembling those of snakes. Much like modern reptiles, there existed regional variations in the type and size of the scales that covered the mosasaurs. In Harrana specimens, two types of scales were observed on a single specimen, it is suggested mosasaurs benefited greatly from the non-reflective keeled scales.

Environment

Sea 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, Denmark, Portugal, Sweden, the United Kingdom, Angola, Morocco, Australia, New Zealand, and on Vega Island off the coast of Antarctica. Mosasaurs have been found in Canada in Manitoba and Saskatchewan and in much of the contiguous United States. Complete or partial specimens have been found in Alabama, Mississippi, Tennessee, and Georgia -- as well as in states covered by the Cretaceous seaway: Texas, southwest Arkansas, New Mexico, Kansas, Colorado, Nebraska, South Dakota, Montana, and the Pierre Shale/Fox Hills formations of North Dakota. Lastly, mosasaur bones and teeth are also known from California, Mexico, and Peru.

Many of the so-called 'dinosaur' remains found on New Zealand are actually mosasaurs and plesiosaurs, both being Mesozoic predatory marine reptiles.

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.

Taxonomy

Classification

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Family Mosasauridae

*Subfamily Tylosaurinae

**Hainosaurus

**Tylosaurus

**Taniwhasaurus

*Subfamily Plioplatecarpinae

**Platecarpus

**Angolasaurus

**Ectenosaurus

**Selmasaurus

**Igdamanosaurus

**Yaguarasaurus

**Plioplatecarpus

*Subfamily Mosasaurinae

**Dallasaurus

**Clidastes

**Mosasaurus

**Moanasaurus

**Amphekepubis

**Plotosaurus

**Globidens

**Prognathodon

**Plesiotylosaurus

**Carinodens

*Subfamily Halisaurinae

**Eonatator

**Halisaurus

Incertae sedis

Liodon

Goronyosaurus

Pluridens

Kourisodon

Russellosaurus

Tethysaurus

Phylogeny

Cladogram of mosasaurs and related taxa modified from Bell and Polcyn, 2005:

|label2= Mosasauridae  |2= |2= |2= }} }} |2= |2= }} }} }} }} }} }} }} }} }} |2= |2= }} }} |label2= Russellosaurina  |2= |2= }} }} }} }} }} |2= }} }} |2= }} }} }} }} }} }} }}

Evolutionary antecedents

Based 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.

Distribution

The following is a list of geologic formations that have produced mosasaur fossils.

{| class="wikitable sortable" align="center" width="100%" |- ! Name ! Age ! Location ! Notes |- | Moreno Formation | | | |- | Niobrara Formation | | | |- |}

In popular culture

Mosasaurs appear in the BBC television series Sea Monsters.

Mosasaurs also feature heavily in the ITV television series Primeval. In this show, the mosasaurs are depicted incorrectly as having skin more like a crocodile's.

A highly evolved mosasaur appeared in an episode of . It was inhabiting Loch Ness as the legendary Loch Ness Monster.

The IMAX 3D film "Sea Monsters" features several mosasaurs (including Tylosaurus and Platecarpus) with detailed animated recreations of their movements and activities.

In Disney's Fantasia, there is a scene where a pod of mosasaurs are swimming by and one of them grabs a pteranodon.

References

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

Mosasaurus hoffmani"">Mike Everhart, "Mosasaurus hoffmani" until 1829.

Mosasaurus maximus mounted skeleton at University of Texas Memorial Museum

Canadian Fossil Discovery Centre

"The Mosasaur of Maastricht" by Hennie Reuvers in Crossroads web magazine

"Mosasaurs terrorized Cretaceous rivers" Planet Earth online

Georgia Southern University Museum Mosasaur Exhibit

Category:Mosasaurs Category:Cretaceous lizards M