Mosasaurus
| Mosasaurus | |
|---|---|
 | |
| Reconstructed skeleton of M. hoffmanni at the Maastricht Natural History Museum | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Squamata |
| Clade: | †Mosasauria |
| Family: | †Mosasauridae |
| Tribe: | †Mosasaurini |
| Genus: | †Mosasaurus Conybeare, 1822 |
| Type species | |
| †Mosasaurus hoffmanni Mantell, 1829 | |
| Other species | |
Species pending reassessment
| |
| Synonyms | |
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List of synonyms
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Mosasaurus (/ˌmoʊzəˈsɔːrəs/; "lizard of the Meuse River") is the type genus (defining example) of the Mosasauridae, an extinct group of aquatic squamate reptiles. It lived from about 82 to 66 million years ago during the Campanian and Maastrichtian stages of the Late Cretaceous. The genus was one of the first Mesozoic marine reptiles known to science—the first fossils of Mosasaurus were found as skulls in a chalk quarry near the Dutch city of Maastricht in the late 18th century, and were initially thought to be crocodiles or whales. One skull discovered in 1778 was famously nicknamed the "great animal of Maastricht". In 1808, naturalist Georges Cuvier concluded that it belonged to a giant marine lizard with similarities to monitor lizards but otherwise unlike any known living animal. This concept was revolutionary at the time and helped support the then-developing ideas of extinction. Cuvier did not designate a scientific name for the animal; this was done by William Daniel Conybeare in 1822 when he named it Mosasaurus in reference to its origin in fossil deposits near the Meuse River. The exact affinities of Mosasaurus as a squamate remain controversial, and scientists continue to debate whether its closest living relatives are monitor lizards or snakes.
The largest species, M. hoffmanni, is estimated to measure up to 12 meters (39 ft) in maximum length. The skull of Mosasaurus had robust jaws and strong muscles capable of powerful bites using dozens of large teeth adapted for cutting prey. Its four limbs were shaped into paddles to steer the animal underwater. Its tail was long and ended in a downward bend and a paddle-like fluke. Mosasaurus possessed excellent vision to compensate for its poor sense of smell, and a high metabolic rate suggesting it was endothermic ("warm-blooded"), an adaptation in squamates only found in mosasaurs. There is considerable morphological variability across the currently-recognized species in Mosasaurus—from the robustly-built M. hoffmanni to the slender and serpentine M. lemonnieri—but an unclear diagnosis (description of distinguishing features) of the type species M. hoffmanni led to a historically problematic classification. As a result, more than fifty species have been attributed to the genus in the past. A redescription of the type specimen in 2017 helped resolve the taxonomy issue and confirmed at least four other species to be within the genus. Another five species still nominally classified within Mosasaurus are planned to be reassessed.
Fossil evidence suggests Mosasaurus inhabited much of the Atlantic Ocean and the adjacent seaways. Mosasaurus fossils have been found in North and South America, Europe, Africa, Western Asia, and Antarctica. This distribution encompassed a wide range of oceanic climates including tropical, subtropical, temperate, and subpolar. Mosasaurus was a common large predator in these oceans and was positioned at the top of the food chain. Paleontologists believe its diet would have included virtually any animal; it likely preyed on bony fish, sharks, cephalopods, birds, and other marine reptiles including sea turtles and other mosasaurs. It likely preferred to hunt in open water near the surface. From an ecological standpoint, Mosasaurus probably had a profound impact on the structuring of marine ecosystems; its arrival in some locations such as the Western Interior Seaway in North America coincides with a complete turnover of faunal assemblages and diversity. Mosasaurus faced competition with other large predatory mosasaurs such as Prognathodon and Tylosaurus—which were known to feed on similar prey—though they were able to coexist in the same ecosystems through niche partitioning. There were still conflicts among them, as an instance of Tylosaurus attacking a Mosasaurus has been documented. Several fossils document deliberate attacks on Mosasaurus individuals by members of the same species. Fighting likely took place in the form of snout grappling, as seen in modern crocodiles.
Research history
[edit]Discovery and identification
[edit]
The first Mosasaurus fossil known to science was discovered in 1764 in a chalk quarry near Maastricht in the Netherlands in the form of a skull, which was initially identified as a whale.[11] This specimen, cataloged as TM 7424, is now on display at the Teylers Museum in Haarlem.[12][13][14] Later, in 1778,[a] the quarry produced a second skull that caught the attention of Johann Leonard Hoffmann, who thought it was a crocodile. He then contacted Petrus Camper, and the skull gained international attention after Camper published a study identifying it as a whale in 1786.[13][16][17] This caught the attention of French revolutionaries, who looted the fossil following the siege of Maastricht during the French Revolutionary Wars in 1794. After its seizure, the specimen was sent to the National Museum of Natural History, France in 1795 and later numbered as MNHN AC 9648.[17][14] In a 1799 narrative of this event by Barthélemy Faujas de Saint-Fond, the skull was allegedly retrieved by twelve grenadiers in exchange for an offer of 600 bottles of wine.[18] This story helped elevate the fossil into cultural fame, but historians agree that the narrative was exaggerated.[17][14]
By 1800, Camper's son Adriaan Gilles Camper concluded that the second skull, which by then was nicknamed the "great animal of Maastricht", belonged to a marine reptile sharing affinities to monitor lizards.[19] This interpretation was confirmed by Georges Cuvier in a more detailed study published in 1808, in which he nevertheless established that it represented an extinct form not corresponding to any known living saurian.[20][12][13] The skull became part of Cuvier's first speculations about the conception of extinction, which later led to his theory of catastrophism, a precursor to the theory of evolution. At the time, it was not believed that a species could go extinct, and fossils of animals were often interpreted as some form of an extant species.[21] Cuvier's idea that there existed an animal unlike any today was revolutionary at the time, and in 1812 he proclaimed:
Above all, the precise determination of the famous animal from Maastricht seems to us as important for the theory of zoological laws, as for the history of the globe.
In a 1822 book by James Parkinson, William Daniel Conybeare coined the genus Mosasaurus from the Latin Mosa "Meuse" and the Ancient Greek σαῦρος (saûros, "lizard"), in reference to the river near which the fossils were discovered.[22][12][23] In 1829, Gideon Mantell added the specific epithet hoffmanni, in honor to Hoffmann.[24][b] Later, the second skull is designated as the new species' holotype (defining example).[25][5]
Later discoveries and other species
[edit]
In 1804, the Lewis and Clark Expedition discovered a now-lost fossil skeleton alongside the Missouri River, which was identified as a 49-foot (15 m) long fish.[26][27] Richard Ellis speculated in 2003 that this may have been the earliest discovery of the second species M. missouriensis,[28] although competing speculations exist.[29] In 1818, a fossil from Monmouth County, New Jersey became the first North American specimen to be correctly recognized as a Mosasaurus by scientists of the time.