Mosasaur: Wikis

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Mosasaurs
Fossil range: Late Cretaceous, 85–65 Ma
Mosasaurus.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Lepidosauria
Order: Squamata
Suborder: Scleroglossa
Infraorder: Anguimorpha
Superfamily: Mosasauroidea
Family: Mosasauridae
Gervais, 1853
Subfamilies

Halisaurinae
Mosasaurinae
Plioplatecarpinae
Tylosaurinae

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 archosaurs 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.

Contents

Description

Plioplatecarpus primaevus skull Oxford University Museum of Natural History.

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. 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. The animal may have lurked and pounced rapidly and powerfully on passing prey, rather than hunting for it.

Skeletal drawings of three types of mosasaur

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]

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 probably due to the delicate nature of the scales which make it harder for them to preserve in addition to the type of sediments that preserved the remains and the marine conditions under which the preservation occurred. Up 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[5] 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.[6] 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,[5] Keeled scales covering the upper regions of the body and smooth scales covering the lower regions. As ambush predators lurking and quickly capturing prey,[7] mosasaurs benifited greatly from the non-reflective keeled scales which may suggest they had a more success rate ambushing, approaching, and attacking prey from beneath unnoticed.[5]

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, in Denmark, in Sweden, in Africa (e.g., Morocco), in Australia, in New Zealand, and on Vega Island off the coast of Antarctica. Mosasaurs have been found in Canada in Manitoba [8] 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,[9] Colorado, Nebraska, South Dakota, Montana, and the Pierre Shale/Fox Hills formations of North Dakota. [10] 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 Mosasaurus discovered in a Maastricht limestone quarry, 1770 (contemporary engraving)

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 Mosasaur skull found in Masstricht in 1764 AD

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

Incertae sedis

Phylogeny

Cladogram of mosasaurs and related taxa modified from Bell and Polcyn, 2005:[11]

Mosasauroidea 
 Aigialosauridae 

Aigialosaurus dalmaticus



 Mosasauridae 
 Mosasaurinae

Dallasaurus turneri





Clidastes KU-liodontus



Clidastes YP-liodontus





Clidastes moorevillensis




Clidastes novum sp.




Clidastes propython






Globidens alabamaensis



Globidens dakotensis





Prognathodon overtoni




Plesiotylosaurus crassidens



Prognathodon rapax







Mosasasaurus conodon




Mosasaurus missouriensis





Mosasaurus indet.



Mosasaurus maximus





Plotosaurus bensoni



Plotosaurus tuckeri














Haasiasaurus gittelmani



 Halisauromorpha 

Trieste aigialosaur





Halisaurus novum sp.



Halisaurus platyspondylus





Halisaurus sternbergi



Halosaurus cf. sternbergi





 Russellosaurina 




Ectenosaurus clidastoides



Ectenosaurus YPcomposit





Platecarpus planifrons




Angolasaurus bocagei




Platecarpus 600tympaniticus




Platecarpus 8769tympaniticus




Plioplatecarpus AMNH sp.



Plioplatecarpus RMM sp.










Tylosaurus novum sp.




Tylosaurus nepaeolicus



Tylosaurus proriger







Tethysaurus nopcsai




Yaguarasaurus columbianus



Russellosaurus coheni









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.[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.[12]

Distribution

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

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[citation needed] as having skin more like a crocodile's.
  • A highly evolved mosasaur appeared in an episode of Godzilla: The Series. It was inhabiting Loch Ness as the legendary Loch Ness Monster.
  • The IMAX 3D film "Sea Monsters" features mosasaurs (including Tylosaurus) with detailed animated recreations of their movements and activities.

References

  1. ^ Lee MSY (1997-01-29). "The phylogeny of varanoid lizards and the affinities of snakes". Philos Trans R Soc Lond B Biol Sci. 352 (1349): 53–91. doi:10.1098/rstb.1997.0005. 
  2. ^ Squamates consist of the living varanoid lizards, snakes and their fossil relatives the mosasaurs.
  3. ^ a b Palaeos Vertebrates 260.100 Pythonomorpha: Pythonomorpha
  4. ^ Mosasaurs: Last of the Great Marine Reptiles
  5. ^ a b c Kaddumi, H.F. (2009). "On the latest scale coverings of mosasaurs (Squamata: Mosasauridae) from the Harrana Fauna in addition to the description of s new species of Mosasaurus". Fossils of the Harrana Fauna and the Adjacent Areas. Amman: Eternal River Museum of Natural History. pp. 80–94. 
  6. ^ Snow, F. H. (1878). "On the dermal covering of a mosasauroid reptile". Transactions of the Kansas Academy of Science 6: 54–58. 
  7. ^ Massare, J. A. (1987). "Tooth morphology and prey preference of Mesozoic marine reptiles". Journal of Vertebrate Paleontology 7 (2): 121–137. 
  8. ^ http://www.discoverfossils.com
  9. ^ Michael J. Everhart (2005). "Chapter 9: Enter the Mosasaurs". Oceans of Kansas: a natural history of the western interior sea. Bloomington: Indiana University Press. ISBN 0-253-34547-2. 
  10. ^ Getman, Myron RC (1994). Occurrences of Mosasaur and other reptilian fossil remains from the Fox Hills Formation (Maastrichtian: late Cretaceous) of North Dakota. St. Lawrence University Dept. of Geology theses. 
  11. ^ Bell, G. L. Jr.; and Polcyn, M. J.. "Dallasaurus turneri, a new primitive mosasauroid from the Middle Turonian of Texas and comments on the phylogeny of Mosasauridae (Squamata)". Netherlands Journal of Geosciences — Geologie en Mijnbouw 84 (3): 177–194. 
  12. ^ Dallasaurus / Ancient Mosasaur - Dallasaurus - SMU

External links


Simple English

Mosasaurs
Fossil range: Upper Cretaceous
File:Mosasaurus
Scientific classification
Phylum: Chordata
Class: Reptilia
Superorder: Lepidosauria
Order: Squamata
Suborder: Scleroglossa
Family: Mosasauridae
Genus: Mosasaurus
Conybeare 1822

Mosasaurs were large, predatory marine lizards of the Upper Cretaceous. The first fossil Mosasaur, Mosasaurus hoffmanni, was found in the Netherlands in 1776.[1]p7 It was named in 1822 by W.D. Conybeare.

Contents

Discovery and interpretation

The type specimen was found in a chalk quarry in Maastricht, Holland. It was found by a German Army surgeon, Johann Hoffmann, who collected fossils for the Haarlem Museum. In the course of a struggle for ownership, the skeletal parts went to the museum, whilst the skull stayed with the owner of the land, who refused to let anyone see it.

The true identity of the monster was decided correctly by the French anatomist Georges Cuvier. In 1795 French troops were outside Maastricht, and Cuvier aranged for the large skull to be saved when they stormed the town. The skull duly went to Cuvier in Paris, fortunately, because he was the leading comparative anatomist of the day. He recognised the skull as that of a giant lizard, from its teeth and skull bones,[1]p10 though not until 1808, and by then the son of a Dutch professor, Adriaan Camper, had already had the same idea. The discovery of the specimen was important in another way, because it helped to convince Cuvier that extinction of some species was a fact. Cuvier later came up with a catastrophism-type theory.

Size

The type species was estimated to be 33' (10m) long. Mosasaurus had four paddle-like limbs on a long, streamlined body and a long, powerful tail. The large head had huge jaws, up to 4 ft (1.2 m long) with many teeth. The jaws could open about 3 feet (1 m). The lower jaw is loosely hinged to the skull with a moveable joint on each side (behind the teeth). This loose joint let it swallow huge prey. They would have hunted fish, turtles, molluscs, and shellfish. Ammonites have been found bearing mosasaur teeth marks.

An interesting fact is that Ichthyosaurs had died out by the middle of the Upper Cretaceous, and also crocodiles and plesiosaurs were in decline. It is this large marine predator niche which mosasaurs apparently occupied. They gave birth to live young, just as the Ichthyosaurs had done. They flourished in the latest Cretaceous, only to become extinct at the K/T extinction event.

Other species

Many other species of mosasaur have since been found, some even larger than Mosasaurus, for example, Mosasaurus maximus found in Onion Creek, Texas. All have the same general body style and pattern of life, though some, like Prognathodon, had crushing teeth for dealing with shellfish. Present thought is that their closest living relatives are the monitor lizards.[2]

References

Look up Mosasaurus in Wikispecies, a directory of species
  1. 1.0 1.1 Benton M. 1990. The reign of the reptiles. Crescent, N.Y.
  2. Bell G.L. Jr and Polcyn M.J. Dallasaurus turneri, a new primitive mosasauroid from the Middle Turonian of Texas and comments on the phylogeny of Mosasauridae (Squamata). Netherlands Journal of Geosciences — Geologie en Mijnbouw 84: 177-194.


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