Mosasaurus

Mosasaurus Temporal range: Campanian-Maastrichtian, 82.7–66.0 Ma[1][2][3][4] PreꞒ Ꞓ O S D C P T J K Pg N
Reconstructed skeleton of M. hoffmannii at the Maastricht Natural History Museum
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Clade:	†Mosasauria
Family:	†Mosasauridae
Tribe:	†Mosasaurini
Genus:	†Mosasaurus Conybeare, 1822
Type species
†Mosasaurus hoffmannii Mantell, 1829
Other species
†M. missouriensis (Harlan, 1834) †M. conodon (Cope, 1881) †M. lemonnieri Dollo, 1889 †M. beaugei Arambourg, 1952 Species pending reassessment †M. mokoroa Welles & Gregg, 1971 †M. hobetsuensis Suzuki, 1985 †M. flemingi Wiffen, 1990 †M. prismaticus Sakurai et al., 1999
Synonyms
List of synonyms Synonyms of genus[5][6] Batrachiosaurus Harlan, 1839 Batrachiotherium Harlan, 1839 Macrosaurus Owen, 1849 Drepanodon Leidy, 1856 Lesticodus Leidy, 1859 Baseodon Leidy, 1865 Nectoportheus Cope, 1868 Pterycollosaurus Dollo, 1882 Synonyms of M. hoffmannii[5][7]: 13–14, 213–214, 286–287 [8] Lacerta gigantea von Sömmerring, 1820 Mososaurus hoffmannii Mantell, 1829 Mosasaurus belgicus Holl, 1829 Mosasaurus camperi Meyer, 1832 Mosasaurus dekayi Bronn, 1838 Mosasaurus hoffmanni Owen, 1840 Mosasaurus major De Kay, 1842 Mosasaurus occidentalis Morton, 1844 Mosasaurus meirsii Marsh, 1869 Mosasaurus princeps Marsh, 1869 Mosasaurus maximus Cope, 1869 Mosasaurus giganteus Cope, 1869 Mosasaurus fulciatus Cope, 1869 Mosasaurus oarthus Cope, 1869 Synonyms of M. missouriensis[9][10] Ichthyosaurus missouriensis Harlan, 1834 Ictiosaurus missuriensis Harlan, 1834 Batrachiosaurus missouriensis Harlan, 1839 Batrachiotherium missouriensis Harlan, 1839 Mosasaurus maximiliani Goldfuss, 1845 Mosasaurus neovidii Meyer, 1845 Pterycollosaurus maximiliani Dollo, 1882 Mosasaurus horridus Williston, 1895 Synonyms of M. conodon[11] Clidastes conodon Cope, 1881

Mosasaurus (/ˌmoʊzəˈsɔːrəs/; "lizard of the Meuse River") is the type genus (defining example) of the mosasaurs, 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 around 1780 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. hoffmannii, is estimated to measure up to 12 meters (39 ft) in maximum length, making it one of the largest mosasaurs. 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. hoffmannii to the slender and serpentine M. lemonnieri—but an unclear diagnosis (description of distinguishing features) of the type species M. hoffmannii 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 five 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. In fighting likely took place in the form of snout grappling, as seen in modern crocodiles.