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Mosasaurs (from
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became ...

Latin
''Mosa'' meaning the '
Meuse The Meuse ( , , , ; wa, Moûze ) or Maas ( , ; li, Maos or ) is a major European river, rising in France and flowing through Belgium and the Netherlands before draining into the North Sea The North Sea is a sea The sea, connected ...

Meuse
', and
Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 million as of ...
' meaning 'lizard') comprise a group of extinct, large
marine reptile Marine reptiles are reptiles which have become secondarily adaptation, adapted for an aquatic animal, aquatic or List of semiaquatic tetrapods, semiaquatic life in a marine (ocean), marine Natural environment, environment. The earliest marine re ...
s from the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous The Cretaceous ( ) is a that lasted from about 145 to 66 (Mya). It is the third and final period of the , as well as the longest. At around 79 millio ...
. Their first fossil remains were discovered in a limestone quarry at
Maastricht Maastricht ( , , ; Limburgish language, Limburgish : ; french: Maestricht ; es, Mastrique ) is a city and a Municipalities of the Netherlands, municipality in the southeastern Netherlands. It is the capital city, capital and largest city of ...

Maastricht
on the Meuse in 1764. They belong to the order
Squamata Squamata (, Latin ''squamatus'' (“scaly, having scales”)) is the largest Order (biology), order of reptiles, comprising lizards, snakes, and amphisbaenians (worm lizards), which are collectively known as squamates or scaled reptiles. With o ...

Squamata
, which includes
lizard Lizards (suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. The well-known ranks in descending order are: lif ...

lizard
s and
snake Snakes are elongated, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Many species of snakes ...

snake
s. Mosasaurs probably evolved from an extinct group of aquatic
lizard Lizards (suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. The well-known ranks in descending order are: lif ...

lizard
s known as aigialosaurs in the Earliest Late Cretaceous and containing 41 genera in total. During the last 20 million years of the Cretaceous period (
Turonian The Turonian is, in the ICS ICS may refer to: Computing * Image Cytometry Standard, a digital multidimensional image file format used in life sciences microscopy * Industrial control system, computer systems and networks used to control industr ...
Maastrichtian The Maastrichtian () is, in the ICS ICS may refer to: Computing * Image Cytometry Standard, a digital multidimensional image file format used in life sciences microscopy * Industrial control system, computer systems and networks used to contr ...
ages), with the extinction of the
ichthyosaur Ichthyosaurs (Ancient Greek Ancient Greek includes the forms of the used in and the from around 1500 BC to 300 BC. It is often roughly divided into the following periods: (), Dark Ages (), the period (), and the period (). Ancient ...
s and pliosaurs, mosasaurs became the dominant marine predators. They became extinct as a result of the K-Pg event at the end of the Cretaceous period, about 66 million years ago.


Description

Mosasaurs breathed air, were powerful swimmers, and were well-adapted to living in the warm, shallow inland seas prevalent during the Late
Cretaceous The Cretaceous ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of division ...

Cretaceous
period. Mosasaurs were so well adapted to this environment that they most likely gave birth to live young, rather than returning to the shore to lay eggs as
sea turtle Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines Turtles are reptile Reptiles are tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constitut ...

sea turtle
s do. The smallest-known mosasaur was ''
Dallasaurus turneri
Dallasaurus turneri
'', which was less than long. Larger mosasaurs were more typical, with many species growing longer than . ''
Mosasaurus hoffmannii
Mosasaurus hoffmannii
'', the largest known species, may have reached up to in length. Currently, the largest publicly exhibited mosasaur skeleton in the world is on display at the
Canadian Fossil Discovery Centre The Canadian Fossil Discovery Centre, formerly known as the Morden and District Museum, is located in Morden, Manitoba in the lower level of the Access Events Centre. The museum currently houses the largest collection of marine reptile fossils in ...
in
Morden Morden is a district and town in south London, England, within the London Borough of Merton. It adjoins Merton Park and Wimbledon, London, Wimbledon to the north, Mitcham to the east, Sutton, London, Sutton to the south and Worcester Park to the ...
,
Manitoba Manitoba ( ) is a Provinces and territories of Canada, province of Canada at the Centre of Canada, longitudinal centre of the country. It is Canada's Population of Canada by province and territory, fifth-most populous province, with a population o ...

Manitoba
. The specimen, nicknamed "Bruce", is just over long. Mosasaurs had a body shape similar to that of modern-day
monitor lizard Monitor lizards are large lizard Lizards (suborder Lacertilia) are a widespread group of Squamata, squamate reptiles, with over 6,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group ...

monitor lizard
s (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 long finger and toe bones. Their tails were broad, and supplied their locomotive power. Until recently, mosasaurs were assumed to have swum in a method similar to the one used today by
conger eel ''Conger'' ( ) is a genus of marine congrid eels. It includes some of the largest types of eels, ranging up to 2 m (6 ft) or more in length, in the case of the European conger. Large congers have often been observed by divers during t ...

conger eel
s and
sea snake Sea snakes, or coral reef snakes, are a subfamily of Elapidae, elapid snakes, the Hydrophiinae, that inhabit Marine (ocean), marine environments for most or all of their lives. Most are venomous snake, venomous, except the genus ''Emydocephalus' ...

sea snake
s, undulating their entire bodies from side to side. However, new evidence suggests that many advanced mosasaurs had large, crescent-shaped flukes on the ends of their tails, similar to those of
shark Sharks are a group of elasmobranch fish characterized by a Chondrichthyes#Skeleton, cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified withi ...

shark
s and some
ichthyosaur Ichthyosaurs (Ancient Greek Ancient Greek includes the forms of the used in and the from around 1500 BC to 300 BC. It is often roughly divided into the following periods: (), Dark Ages (), the period (), and the period (). Ancient ...
s. Rather than use snake-like undulations, their bodies probably remained stiff to reduce drag through the water, while their tails provided strong propulsion. These animals may have lurked and pounced rapidly and powerfully on passing prey, rather than chasing after it. Early reconstructions showed mosasaurs with dorsal crests running the length of their bodies, which were based on misidentified remains of
trachea The trachea, also known as the windpipe, is a cartilaginous Cartilage (cartilaginous tissue) is a resilient and smooth elastic tissue, rubber-like padding that covers and protects the ends of long bone A bone is a Stiffness, rigid tissue ...

trachea
l cartilage. By the time this error was discovered, depicting mosasaurs with such crests in artwork had already become a trend.


Paleobiology

Mosasaurs had double-hinged jaws and flexible skulls (much like those of
snake Snakes are elongated, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Many species of snakes ...

snake
s), which enabled them to gulp down their prey almost whole. A skeleton of ''
Tylosaurus ''Tylosaurus'' (from the ancient Greek ''τυλος'' (') "protuberance, knob" + Greek (') "lizard") was a mosasaur, a large, predatory marine reptile closely related to modern monitor lizards and to snakes, from the Late Cretaceous. Descri ...

Tylosaurus
proriger'' from
South Dakota South Dakota () (Sioux The Sioux or Oceti Sakowin (; Dakota Dakota may refer to: * Dakota people, a sub-tribe of the Sioux ** Dakota language, their language From this origin, Dakota may also refer to: Places United States * Dako ...

South Dakota
included remains of the diving
seabird Seabirds (also known as marine birds) are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the ...

seabird
''
Hesperornis ''Hesperornis'' (meaning "western bird") is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circu ...

Hesperornis
'', a marine
bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse taxonomic Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may al ...
, a possible
shark Sharks are a group of elasmobranch fish characterized by a Chondrichthyes#Skeleton, cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified withi ...

shark
, and another, smaller mosasaur (''Clidastes''). Mosasaur bones have also been found with shark teeth embedded in them. One of the food items of mosasaurs were
ammonites Ammonoids are a group of Extinction, extinct marine mollusca, mollusc animals in the subclass Ammonoidea of the class (biology), class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids ( ...

ammonites
, molluscs with shells similar to those of ''
Nautilus The nautilus (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power ...

Nautilus
'', which were abundant in the Cretaceous seas. Holes have been found in fossil shells of some ammonites, mainly ''
Pachydiscus
Pachydiscus
'' and ''
Placenticeras
Placenticeras
''. These were once interpreted as a result of limpets attaching themselves to the ammonites, but the triangular shape of the holes, their size, and their presence on both sides of the shells, corresponding to upper and lower jaws, is evidence of the bite of medium-sized mosasaurs. Whether this behaviour was common across all size classes of mosasaurs is not clear. Virtually all forms were active predators of fish and ammonites; a few, such as ''
Globidens ''Globidens'' ("Globe teeth") is an extinct Extinction is the termination of a kind of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodi ...

Globidens
'', had blunt, spherical teeth, specialized for crushing mollusk shells. The smaller genera, such as ''
Platecarpus ''Platecarpus'' ("flat wrist") is an extinct genus of aquatic lizards belonging to the mosasaur family, living around 84–81 million years ago during the middle Santonian to early Campanian, of the Late Cretaceous Period (geology), period. Fossils ...
'' and ''
Dallasaurus ''Dallasaurus'' ("Dallas County, Texas, Dallas lizard") is a basal mosasauroid from the Upper Cretaceous of North America. Along with ''Russellosaurus'', ''Dallasaurus'' is one of the two oldest mosasauroid taxa currently known from North America ...

Dallasaurus
'', which were about long, probably fed on fish and other small prey. The smaller mosasaurs may have spent some time in fresh water, hunting for food. The larger mosasaurs, such as ''
Tylosaurus ''Tylosaurus'' (from the ancient Greek ''τυλος'' (') "protuberance, knob" + Greek (') "lizard") was a mosasaur, a large, predatory marine reptile closely related to modern monitor lizards and to snakes, from the Late Cretaceous. Descri ...

Tylosaurus
'', ''
Hainosaurus ''Hainosaurus'' (''Haino'' from the river Haine, where it was first discovered, and ''saurus'', from Greek sauros, meaning lizard) is an extinct genus of marine reptiles belonging to the mosasaur family. It is one of the largest mosasaurs, thoug ...
'' and ''
Mosasaurus ''Mosasaurus'' (; "lizard of the Meuse River The Meuse ( , , , ; wa, Moûze ) or Maas ( , ; li, Maos or ) is a major European river, rising in France and flowing through Belgium and the Netherlands before draining into the North Sea ...

Mosasaurus
'', reached sizes of long and were apex predators of the Late Cretaceous oceans, attacking other marine reptiles, as well as preying on large fish and ammonites.


Soft tissue

Despite the many mosasaur remains collected worldwide, knowledge of the nature of their skin coverings remains in its early stages. Few mosasaurid specimens collected from around the world retain fossilized scale imprints. This lack may be due to the delicate nature of the scales, which nearly eliminates the possibility of preservation, in addition to the preservation sediment types and the marine conditions under which the preservation occurred. Until the discovery of several mosasaur specimens with remarkably well-preserved scale imprints from late
Maastrichtian The Maastrichtian () is, in the ICS ICS may refer to: Computing * Image Cytometry Standard, a digital multidimensional image file format used in life sciences microscopy * Industrial control system, computer systems and networks used to contr ...
deposits of the Muwaqqar Chalk Marl Formation of
Harrana
Harrana
in
Jordan Jordan ( ar, الأردن; tr. ' ), officially the Hashemite Kingdom of Jordan,; tr. ') is a country in Western Asia Western Asia, West Asia, or Southwest Asia, is the westernmost subregion A subregion is a part of a larger region In ge ...

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 The Santonian is an age (geology), age in the geologic timescale or a chronostratigraphy, chronostratigraphic stage (stratigraphy), stage. It is a subdivision of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (stratigraphy), ...
–lower
Campanian The Campanian is the fifth of six age (geology), ages of the Late Cretaceous epoch (geology), epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stage (stratigraphy) ...
, such as the famous ''
Tylosaurus ''Tylosaurus'' (from the ancient Greek ''τυλος'' (') "protuberance, knob" + Greek (') "lizard") was a mosasaur, a large, predatory marine reptile closely related to modern monitor lizards and to snakes, from the Late Cretaceous. Descri ...

Tylosaurus
'' specimen (KUVP-1075) from Gove County, Kansas. Material from Jordan has shown that the bodies of mosasaurs, as well as the membranes between their fingers and toes, were covered with small, overlapping, diamond-shaped scales resembling those of snakes. Much like those of modern reptiles, mosasaur scales varied across the body in type and size. In Harrana specimens, two types of scales were observed on a single specimen: keeled scales covering the upper regions of the body and smooth scales covering the lower. As ambush predators, lurking and quickly capturing prey using stealth tactics, they may have benefited from the nonreflective, keeled scales. Additionally, mosasaurs had large pectoral girdles, and such genera as ''Plotosaurus'' may have used their front flippers in a breaststroke motion to gain added bursts of speed during an attack on prey. More recently, a fossil of ''
Platecarpus tympaniticus ''Platecarpus'' ("flat wrist") is an extinct genus of aquatic lizards belonging to the mosasaur family, living around 84–81 million years ago during the middle Santonian to early Campanian, of the Late Cretaceous Period (geology), period. Fossil ...
'' has been found that preserved not only skin impressions, but also internal organs. Several reddish areas in the fossil may represent the heart, lungs, and kidneys. The trachea is also preserved, along with part of what may be the
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well ...

retina
in the eye. The placement of the kidneys is farther forward in the abdomen than it is in monitor lizards, and is more similar to those of
cetacean Cetaceans (from la, cetus Cetus () is a constellation, sometimes called 'the whale' in English. The Cetus (mythology), Cetus was a sea monster in Greek mythology which both Perseus and Heracles needed to slay. Cetus is in the region of the ...
s. As in cetaceans, the
bronchi A bronchus is a passage or airway in the respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system A biological system is a complex network Network and networking may refer to: Arts, e ...
leading to the lungs run parallel to each other instead of splitting apart from one another as in monitors and other terrestrial reptiles. In mosasaurs, these features may be internal adaptations to fully marine lifestyles. In 2011,
collagen Collagen () is the main structural protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowder ...

collagen
protein was recovered from a ''
Prognathodon ''Prognathodon'' is an extinct genus of marine lizard belonging to the mosasaur family. It is classified as part of the Mosasaurinae subfamily, alongside genera like ''Mosasaurus'' and ''Clidastes''. ''Prognathodon'' has been recovered from deposi ...
'' humerus dated to the
Cretaceous The Cretaceous ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of division ...

Cretaceous
. In 2005, a
case study A case study involves an up-close, in-depth, and detailed examination of a particular case or cases, within a real-world context. For example, case studies in medicine may focus on an individual patient or ailment; case studies in business might co ...
by A.S. Schulp, E.W.A Mulder, and K. Schwenk outlined the fact that mosasaurs had paired
fenestra A fenestra (fenestration; plural fenestrae or fenestrations) is any small opening or pore, commonly used as a term in the biological sciences Biology is the natural science Natural science is a branch of science Science (from th ...
e in their palates. In monitor lizards and snakes, paired fenestrae are associated with a
forked tongue Forked tongue of a Carpet Python (''Morelia spilota mcdowelli'') A forked tongue is a tongue split into two distinct tines at the tip; this is a feature common to many species of reptiles. Reptiles olfaction, smell using the tip of their tongue, an ...
, which is flicked in and out to detect chemical traces and provide a directional sense of smell. They therefore proposed that mosasaurs probably also had a sensitive forked tongue.


Metabolism

A study published in 2016 by T. Lyn Harrell, Alberto Pérez-Huerta and Celina Suarez showed that mosasaurs were
endotherm An endotherm (from Ancient Greek, Greek ἔνδον ''endon'' "within" and θέρμη ''thermē'' "heat") is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat released by its internal bodily ...
ic. The study contradicted findings published in 2010 indicating mosasaurs were
ectotherm An ectotherm (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population i ...
ic. The 2010 study did not use warm-blooded animals for comparison but analogous groups of common marine animals. Based on comparisons with modern warm-blooded animals and fossils of known cold-blooded animals from the same time period, the 2016 study found mosasaurs likely had body temperatures similar to those of contemporary seabirds and were able to internally regulate their temperatures to remain warmer than the surrounding water.


Coloration

The coloration of mosasaurs was unknown until 2014, when the findings of Johan Lindgren of
Lund University Lund University ( sv, Lunds universitet) is a Public university, public research university in Sweden and one of northern Europe's oldest universities. The university is located in the city of Lund in the province of Scania, Sweden. It traces its r ...
and colleagues revealed the pigment
melanin Melanin (; from el, μέλας ''melas'', "black, dark") is a broad term for a group of natural pigments found in most organisms. Melanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the ami ...

melanin
in the fossilized scales of a mosasaur. Mosasaurs were likely countershaded, with dark backs and light underbellies, much like a
great white shark The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large mackerel shark The Lamniformes (, from Greek ''lamna'' "fish of prey") are an order of shark ...

great white shark
or
leatherback sea turtle The leatherback sea turtle (''Dermochelys coriacea''), sometimes called the lute turtle or leathery turtle or simply the luth, is the largest of all living turtle Turtles are an of s known as Testudines, characterized by a developed ma ...
, the latter of which had fossilized ancestors for which color was also determined. The findings were described in ''
Nature Nature, in the broadest sense, is the natural, physical, material world or universe The universe ( la, universus) is all of space and time and their contents, including planets, stars, galaxy, galaxies, and all other forms of matter an ...
''.


Teeth

Mosasaurs possessed a thecodont dentiton, meaning that the roots were cemented deeply into the jaw bone. Mosasaurs did not use permanent teeth but instead constantly shed them. Replacement teeth developed within a pit inside the roots of the original tooth called the resorption pit. This is done through a distinctively unique eight-stage process. The first stage was characterized by the mineralization of a small tooth crown developed elsewhere that descended into the resorption pit by the second stage. In the third stage, the developing crown firmly cemented itself within the resorption pit and grew in size; by the fourth stage, it would be of the same size as the crown in the original tooth. Stages five and six were characterized by the development of the replacement tooth's root: in stage five the root developed vertically, and in stage six the root expanded in all directions to the point that the replacement tooth became exposed and actively pushed on the original tooth. In the seventh stage, the original tooth was shed and the now-independent replacement tooth began to anchor itself into the vacancy. In the eighth and final stage, the replacement tooth has grown to firmly anchor itself.


Ontogeny and growth

Mosasaur growth is not well understood, as specimens of juveniles are rare, and many were mistaken for hesperornithine birds when discovered 100 years ago. However, the discovery of several specimens of juvenile and neonate-sized mosasaurs unearthed more than a century ago indicate that mosasaurs gave birth to live young, and that they spent their early years of life out in the open ocean, not in sheltered nurseries or areas such as shallow water as previously believed. Whether mosasaurs provided parental care, like other marine reptiles such as plesiosaurs, is currently unknown. The discovery of young mosasaurs was published in the journal ''Palaeontology''. In late 2014 Guinness World Records awarded the museum with a record for Largest Publicly Displayed Mosasaur – Bruce. The record was added to the 2016 print edition of ''Guinness World Records''.


Possible eggs

A 2020 study published in ''Nature'' described a large fossilized hatched egg from
Antarctica Antarctica ( or ) is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Oc ...

Antarctica
from the very end of the
Cretaceous The Cretaceous ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of division ...

Cretaceous
, about 68 million years ago. The egg is considered one of the largest
amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a clade A clade (), also known as a monophyletic ...
eggs ever known, rivalling that of the
elephant bird Elephant birds are members of the extinct Extinction is the termination of a kind of organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Bi ...

elephant bird
, and due to its soft, thin, folded texture, it likely belonged to a marine animal. While the organism that produced it remains unknown, the egg's pore structure is very similar to that of extant lepidosaurs such as lizards and snakes, and presence of mosasaur fossils nearby indicates that it may have been a mosasaur egg. It is unknown whether the egg was laid on land or in the water. The egg was assigned to the newly described
oospecies Egg fossils are the fossilized remains of eggs laid by Geologic time, ancient animals. As evidence of the Physiology, physiological processes of an animal, egg fossils are considered a type of trace fossil. Under rare circumstances a fossil egg may ...
'' Antarcticoolithus bradyi''.


Environment

Paleotologists compared the taxonomic diversity and patterns of morphological disparity in mosasaurs with sea level, sea surface temperature, and stable carbon isotope curves for the Upper Cretaceous to explore factors that may have influenced their evolution. No single factor unambiguously accounts for all radiations, diversification, and extinctions; however, the broader patterns of taxonomic diversification and morphological disparity point to niche differentiation in a "fishing up" scenario under the influence of "bottom-up" selective pressures. The most likely driving force in mosasaur evolution was high productivity in the Late Cretaceous, driven by tectonically controlled sea levels and climatically controlled ocean stratification and nutrient delivery. When productivity collapsed at the end of the Cretaceous, coincident with bolide impact, mosasaurs became extinct. 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
fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication used by humans, inc ...

fossil
s have been found in the
Netherlands ) , national_anthem = ( en, "William of Nassau") , image_map = EU-Netherlands.svg , map_caption = , image_map2 = BES islands location map.svg , map_caption2 = , image_map3 ...

Netherlands
,
Belgium Belgium ( nl, België ; french: Belgique ; german: Belgien ), officially the Kingdom of Belgium, is a country in Western Europe Western Europe is the western region of Europe. The region's countries and territories vary depending on cont ...

Belgium
,
Denmark Denmark ( da, Danmark, ) is a Nordic country The Nordic countries, or the Nordics, are a geographical and cultural region In geography, regions are areas that are broadly divided by physical characteristics ( physical geography), hu ...

Denmark
,
Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country A country is a distinct territorial body or political entity A polity is an identifiable political entity—any group of people who ...

Portugal
,
Sweden Sweden ( sv, Sverige ), officially the Kingdom of Sweden ( sv, links=no, Konungariket Sverige ), is a Nordic country The Nordic countries, or the Nordics, are a geographical and cultural region In geography, regions are areas that ...

Sweden
,
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. With over 60 million people, it is the world's 23rd-most populous nation and covers an area of . South Africa has three capital citie ...

South Africa
,
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = , national_anthem = , image_map = , map_caption = , image_map2 ...

Spain
,
France France (), officially the French Republic (french: link=no, République française), is a transcontinental country This is a list of countries located on more than one continent A continent is one of several large landmasses ...

France
,
Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin Berlin (; ) is the Capital city, capital and List of cities in Germany by population, largest city of Germany by both area and population. Its 3,769,495 inh ...

Germany
,
Poland Poland, officially the Republic of Poland, is a country located in Central Europe. It is divided into 16 Voivodeships of Poland, administrative provinces, covering an area of , and has a largely Temperate climate, temperate seasonal cli ...

Poland
, the
Czech Republic The Czech Republic, also known by its short-form name Czechia and formerly known as Bohemia, is a landlocked country in Central Europe. It is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to ...
,
Bulgaria Bulgaria (; bg, България, Bǎlgariya), officially the Republic of Bulgaria ( bg, Република България, links=no, Republika Bǎlgariya, ), is a country in Southeast Europe. It is bordered by Romania to the north, Serbia ...

Bulgaria
, the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use Britain as a synonym for the United Kingdom. Some prefer to use Britain as shorth ...

United Kingdom
,
Russia Russia ( rus, link=no, Россия, Rossiya, ), or the Russian Federation, is a country spanning Eastern Europe Eastern Europe is the eastern region of . There is no consistent definition of the precise area it covers, partly because th ...

Russia
,
Ukraine Ukraine ( uk, Україна, Ukraïna, ) is a country in . It is the in Europe after , which it borders to the east and north-east. Ukraine also shares borders with to the north; , , and to the west; and to the south; and has a coastli ...

Ukraine
,
Kazakhstan Kazakhstan ( kk, Қазақстан, Qazaqstan; russian: Казахстан, Kazakhstan), officially the Republic of Kazakhstan,; russian: Республика Казахстан, Respublika Kazakhstan, link=no) is a country located mainly in ...

Kazakhstan
,
Azerbaijan Azerbaijan (, ; az, Azərbaycan ), officially the Republic of Azerbaijan ( az, Azərbaycan Respublikası ), is a country in the Transcaucasia, Caucasus region of Eurasia. Located at the crossroads of Eastern Europe and Western Asia, it is boun ...

Azerbaijan
,
Japan Japan ( ja, 日本, or , and formally ) is an island country An island country or an island nation is a country A country is a distinct territory, territorial body or political entity. It is often referred to as the land of an in ...

Japan
,
Egypt Egypt ( ar, مِصر, Miṣr), officially the Arab Republic of Egypt, is a transcontinental country This is a list of countries located on more than one continent A continent is one of several large landmasses. Generally identi ...

Egypt
,
Israel Israel (; he, יִשְׂרָאֵל, translit=Yīsrāʾēl; ar, إِسْرَائِيل, translit=ʾIsrāʾīl), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a ...

Israel
,
Jordan Jordan ( ar, الأردن; tr. ' ), officially the Hashemite Kingdom of Jordan,; tr. ') is a country in Western Asia Western Asia, West Asia, or Southwest Asia, is the westernmost subregion A subregion is a part of a larger region In ge ...

Jordan
,
Syria Syria ( ar, سُورِيَا or ar, سُورِيَة, ''Sūriyā''), officially the Syrian Arab Republic ( ar, ٱلْجُمْهُورِيَّةُ ٱلْعَرَبِيَّةُ ٱلسُّورِيَّةُ, al-Jumhūrīyah al-ʻArabīyah as-S ...

Syria
,
Turkey Turkey ( tr, Türkiye ), officially the Republic of Turkey, is a country located mainly on Anatolia Anatolia,, tr, Anadolu Yarımadası), and the Anatolian plateau. also known as Asia Minor, is a large peninsula in Western Asia an ...

Turkey
,
Niger ) , official_languages = French , languages_type = National language A national language is a language A language is a structured system of communication used by humans, including speech (spoken language), gestures (Signed languag ...

Niger
,
Angola , national_anthem = "Angola Avante "Angola Avante" (, ) is the national anthem A national anthem is a song that officially symbolizes a country A country is a distinct territory, territorial body or political entity. It is often r ...

Angola
,
Morocco ) , image_map = Morocco (orthographic projection, WS claimed).svg , map_caption = Location of Morocco in northwest Africa.Dark green: Undisputed territory of Morocco.Lighter green: Western Sahara, a United Nations lis ...

Morocco
,
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Australia
,
New Zealand New Zealand ( mi, Aotearoa ''Aotearoa'' (; commonly pronounced by English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon Engl ...

New Zealand
, and on
Vega Island Vega Island is a small island to the northwest of James Ross Island, on the Antarctic Peninsula. It is separated from James Ross Island by Herbert Sound. The island was named by Otto Nordenskjold, leader of the Swedish Antarctic Expedition (1901 ...
off the coast of
Antarctica Antarctica ( or ) is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Oc ...

Antarctica
. Tooth taxon ''Globidens timorensis'' is known from the island of
Timor Timor is an island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atoll An atoll (), sometimes k ...

Timor
; however, the phylogenetic placement of this species is uncertain and it might not even be a mosasaur. Mosasaurs have been found in
Canada Canada is a country in the northern part of North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, ...

Canada
in
Manitoba Manitoba ( ) is a Provinces and territories of Canada, province of Canada at the Centre of Canada, longitudinal centre of the country. It is Canada's Population of Canada by province and territory, fifth-most populous province, with a population o ...

Manitoba
and
Saskatchewan ("From Many Peoples Strength") , image_map = Saskatchewan in Canada 2.svg , Label_map = yes , coordinates = , official_lang = English language, English , capital = Regina, S ...
and in much of the contiguous United States. Complete or partial specimens have been found in
Alabama (We dare defend our rights) , anthem = "Alabama (We dare defend our rights) , anthem = "Alabama (state song), Alabama" , image_map = Alabama in United States.svg , seat ...

Alabama
,
Mississippi Mississippi () is a U.S. state, state in the Southeastern United States, Southeastern region of the United States, bordered to the north by Tennessee; to the east by Alabama; to the south by the Gulf of Mexico; to the southwest by Louisiana; a ...
,
New Jersey New Jersey is a U.S. state, state in the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. It is bordered on the north and east by the state of New York (state), New York; on the ea ...
,
Tennessee Tennessee (, ), officially the State of Tennessee, is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The S ...

Tennessee
, and
Georgia Georgia usually refers to: * Georgia (country) Georgia (, ; ) is a country located at the intersection of Eastern Europe and Western Asia. It is a part of the Caucasus region, bounded to the west by the Black Sea, to the north and east by ...
, as well as in states covered by the Cretaceous seaway:
Texas Texas (, ; Spanish Spanish may refer to: * Items from or related to Spain: **Spaniards, a nation and ethnic group indigenous to Spain **Spanish language **Spanish cuisine Other places * Spanish, Ontario, Canada * Spanish River (disambigu ...

Texas
, southwest
Arkansas Arkansas () is a U.S. state, state in the South Central United States, South Central region of the United States, home to more than three million people as of 2018. Its name is from the Osage language, a Dhegihan languages, Dhegiha Siouan la ...

Arkansas
,
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Greater Albuquerque , OfficialLang = None , Languages = English English usually refer ...

New Mexico
,
Kansas Kansas () is a U.S. state, state in the Midwestern United States, Midwestern United States. Its Capital city, capital is Topeka and its largest city is Wichita, Kansas, Wichita. Kansas is a landlocked state bordered by Nebraska to the north; ...

Kansas
,
Colorado Colorado (, other variants) is a state in the Mountain West The Mountain West Conference (MW) is one of the collegiate athletic conferences affiliated with the National Collegiate Athletic Association The National Collegiate Athletic ...

Colorado
,
Nebraska Nebraska () is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper ...

Nebraska
,
South Dakota South Dakota () (Sioux The Sioux or Oceti Sakowin (; Dakota Dakota may refer to: * Dakota people, a sub-tribe of the Sioux ** Dakota language, their language From this origin, Dakota may also refer to: Places United States * Dako ...

South Dakota
,
Montana Montana () is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper ...

Montana
,
Wyoming Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. The List of U.S. states and territories by area, 10th largest state by area, it is also the List of U.S. states and territories b ...
, and the
Pierre Shale The Pierre Shale is a geologic formation A geological formation, or formation, is a body of rock having a consistent set of physical characteristics (lithology as seen in southeastern Utah The lithology of a Rock (geology), rock unit is a desc ...
/ Fox Hills formations of
North Dakota North Dakota () is a U.S. state In the , a state is a , of which there are currently 50. Bound together in a , each state holds al jurisdiction over a separate and defined geographic territory where it shares its with the . Due to th ...
. Lastly, mosasaur bones and teeth are also known from
California California is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper i ...

California
,
Mexico Mexico, officially the United Mexican States, is a country A country is a distinct territorial body or political entity A polity is an identifiable political entity—any group of people who have a collective identity, who are organi ...

Mexico
,
Colombia Colombia ( , ; ), officially the Republic of Colombia, is a transcontinental country This is a list of countries located on more than one continent A continent is one of several large landmasses. Generally identified by conv ...

Colombia
,
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At 8.5 million square kilometers (3.2 million square miles) and with over 211 mill ...

Brazil
,
Peru , , image_flag = Flag_of_Peru.svg , image_coat = Escudo_nacional_del_Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = Seal (device), National seal , national_mott ...

Peru
, and
Chile Chile, officially the Republic of Chile, is a country in the western part of South America South America is a entirely in the and mostly in the , with a relatively small portion in the . It can also be described as the southern ...

Chile
. Many of the so-called 'dinosaur' remains found on
New Zealand New Zealand ( mi, Aotearoa ''Aotearoa'' (; commonly pronounced by English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon Engl ...

New Zealand
are actually mosasaurs and
plesiosaur The Plesiosauria (; Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is ap ...

plesiosaur
s, 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 in
Mount Saint Peter Mount Saint Peter (French: ''Montagne Saint-Pierre''; Dutch Dutch commonly refers to: * Something of, from, or related to the Netherlands * Dutch people () * Dutch language () *Dutch language , spoken in Belgium (also referred as ''flemish'') D ...
, near the Dutch city of
Maastricht Maastricht ( , , ; Limburgish language, Limburgish : ; french: Maestricht ; es, Mastrique ) is a city and a Municipalities of the Netherlands, municipality in the southeastern Netherlands. It is the capital city, capital and largest 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 The Age of Enlightenment (also known as the Age of Reason or simply the Enlightenment); ger, Aufklärung, "Enlightenment"; it, L'Illuminismo, "Enlightenment"; pl, Oświecenie , "Enlightenment"; pt, Iluminismo, "Enlightenment"; es, link= ...
'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 Johann Leonard Hoffmann (1710–1782) was a Maastricht army surgeon and amateur geologist who collected fossils from the local Mount Saint Peter. He is known for fossils named after him, and was one of the three people contacted on the discovery o ...
, 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 600 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 Adriaan Gilles Camper (March 31, 1759 – February 5, 1820) was a 19th-century Dutch mathematics and physics professor at the University of Franeker who took to politics and became a statesman in his later years. He was the son of Petrus Camper is ...
in 1799. In 1808,
Georges Cuvier Jean Léopold Nicolas Frédéric, Baron Cuvier (; 23 August 1769 – 13 May 1832), known as Georges Cuvier, was a French naturalist Natural history is a domain of inquiry involving organism In biology, an organism () is any orga ...

Georges Cuvier
confirmed this conclusion, although ''le Grand Animal fossile de Maëstricht'' was not actually named ''Mosasaurus'' ('
Meuse The Meuse ( , , , ; wa, Moûze ) or Maas ( , ; li, Maos or ) is a major European river, rising in France and flowing through Belgium and the Netherlands before draining into the North Sea The North Sea is a sea The sea, connected ...

Meuse
reptile') until 1822 and not given its full species name, ''Mosasaurus hoffmannii,'' until 1829. Several sets of mosasaur remains, which had been discovered earlier at Maastricht but were not identified as mosasaurs until the 19th century, have been on display in the
Teylers Museum Teylers Museum () is an art Art is a diverse range of (products of) human activities Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and ...
,
Haarlem Haarlem (; predecessor of ''Harlem'' in ) is a and in the . It is the of the of . Haarlem is situated at the northern edge of the , one of the s in Europe; it is also part of the . Haarlem had a population of in . Haarlem was granted cit ...

Haarlem
, procured from 1790. The Maastricht
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
beds were rendered so famous by the mosasaur discovery, they have given their name to the final six-million-year epoch of the Cretaceous, the
Maastrichtian The Maastrichtian () is, in the ICS ICS may refer to: Computing * Image Cytometry Standard, a digital multidimensional image file format used in life sciences microscopy * Industrial control system, computer systems and networks used to contr ...
.


Classification


Relation with snakes or monitor lizards

The specific placement of mosasaurs within the Squamata has been controversial since its inception. Cuvier was the first scientist to deeply analyze their possible taxonomic placement through ''Mosasaurus''. While his original 1808 hypothesis that the genus was a lizard with affinities to monitor lizards remained the most popular, Cuvier was uncertain, even at the time, about the accuracy of this placement. He simultaneously proposed a number of alternative hypotheses, with one such alternative suggesting that ''Mosasaurus'' instead had closer affinities with
iguana ''Iguana'' (, ) is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), c ...

iguana
s due to their shared presence of pterygoid teeth. With the absence of sufficient fossil evidence, researchers during the early and mid-19th century had little to work with. Instead, they primarily relied on stratigraphic associations and Cuvier's 1808 research on the holotype skull. Thus, in-depth research on the placement of ''Mosasaurus'' was not undertaken until the discovery of more complete mosasaur fossils during the late 19th century, which reignited research on the placement of mosasaurs among squamates. In a span of about 30 to 40 years during the late 19th to early 20th centuries, paleontologists fiercely debated the issue, which created two major schools of thought: one that supported a monitor lizard relationship and one that supported a closer relationship with snakes. The proposition of a snake relationship was spearheaded by Cope, who first published such a hypothesis in 1869 by proposing that mosasaurs, which he classified under a group called the
Pythonomorpha Pythonomorpha was originally proposed by paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene The Holocene ...
, was the sister group of snakes. Some scientists went as far as to interpret mosasaurs as direct ancestors of snakes. Opponents supporting a relationship with monitor lizards argued that mosasaurs should be placed within the
infraorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions ...
Anguimorpha Anguimorphs of the infraorder Anguimorpha include the anguids (alligator lizard An alligator lizard is any one of various species of lizards in the Family (biology), family Anguidae that have some shared characteristics. The term may specifically ...
, with lower classifications varying from placing mosasaurs within
Varanoidea Varanoidea is a superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamili ...
or its sister taxa, or as true monitor lizards within
Varanidae The Varanidae are a family (biology), family of lizards in the superfamily (zoology), superfamily Varanoidea within the Anguimorpha group. The family, a group of carnivore, carnivorous and frugivore, frugivorous lizards, includes the living genus ...
. These debates spawned higher taxonomic groups that were erected in attempts to classify the placement of mosasaurs (although not all are compatible). One of these was the Mosasauria, a loosely-defined group erected by Marsh in 1880 but is still used by some researchers today that includes all descendants of the last common ancestor of ''Mosasaurus'' and some of its ancestral relatives, including the dolichosaurs '''' and '''' and the marine squamate ''''. In 1923,
Charles Lewis Camp Charles Lewis Camp (March 12, 1893 Jamestown, North Dakota – August 14, 1975 San Jose, California) was a Palaeontology, palaeontologist and Zoology, zoologist, working from the University of California, Berkeley. He took part in excavations at th ...
published ''Classification of the Lizards'', in which he proposed through the review and rebuttal of previous arguments using his own anatomical observations that all taxa more closely related to ''Mosasaurus'' than ''Dolichosaurus'' should be classified into a superfamily called the , which would be a sister superfamily to the Varanoidea. Camp's take on the subject virtually ended the snake-monitor lizard debate for approximately 70 years, with nearly all subsequent studies supporting a relationship with monitor lizards. However, many studies continued to support going further than Camp in the monitor lizard relationship, placing mosasaurs within the Varanoidea. The debate was reignited with the publication of a 1997 cladistical study by Michael S. Y. Lee, which recovered the Mosasauroidea as a sister taxon to the snake suborder Serpentes and resurrected the argument for a snake relationship. Prior, there had never been a modern phylogenetic study specifically testing the relationships between mosasaurs or snakes. Lee also resurrected the defunct Pythonomorpha and redefined it to unify the Mosasauroidea and Serpentes under one clade. Multiple subsequent studies conducted by scientists such as Lee, Caldwell, and Alessandro Palci refined this hypothesis. In some studies, the Mosasauria clade was used to represent mosasaurs. However, there still remained little consensus. For example, a large-scale 2008 phylogenetic study by paleontologist Jack Conrad of the American Museum of Natural History recovered the Mosasauria clade in a
polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...
, or a clade with unresolved relationships, with monitor lizards and ; and a 2012 study by
Gauthier Gauthier () is a French name of Germanic origin, corresponding to the English given name Walter (name), Walter. People with the given name *Gauthier de Costes, seigneur de la Calprenède *Gauthier de Brienne, Counts Walter III of Brienne, Walter IV ...
''et al.'' recovered Mosasauria as a clade
basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is neces ...
to both monitor lizards and snakes. With the advent of
molecular genetics Molecular genetics is a sub-field of biology that addresses how differences in the structures or expression of DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image ...
during the 2010s, some scientists argued for the combining of
molecular A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon ...
and morphological data to examine relationships between mosasaurs and living squamates. An early study was Lee (2009), which based on nuclear and
mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five car ...

mitochondrial DNA
in living squamates and morphological data recovered mosasaurs as a
stem group In phylogenetics In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, p ...
to snakes, which some later authors interpreted as placement of snakes within the Mosasauria clade itself. However, a 2010 study by Weins ''et al.'' attempted to replicate Lee (2009) using a larger dataset but instead yielded results that recovered the Mosasauria as a sister clade to the monitor lizards. The frequent discrepancies are due to the high prevalence of convergent evolution in squamates, which creates much room for interpreting molecular and morphological data; many of these studies had results that often contradicted each other, for example in completely different phylogenetic results by simply adding more datasets or varying which taxa are represented, which resulted in various conflicts creating even more uncertainty. Due to this, some scientists argued that a molecular perspective should be abandoned entirely. Nevertheless, other scientists have attempted to resolve these problems. One approach was utilized by a 2015 study by Reeder ''et al.'': it closely integrated morphological, molecular, and paleontological data in a large dataset to overcome previous conflicts, which revealed new morphological support for molecular results that recovered Mosasauria as a sister clade to Serpentes. Another approach was developed by R. Alexander Pyron in a 2016 study, which also recovered Mosasauria as a sister clade to the Serpentes.


Lower classifications

The traditional view of mosasaur evolution held that all paddle-limbed (hydropedal) mosasaurs originated from a single common ancestor with functional legs (plesiopedal). However, this was shaken with the discovery of ''
Dallasaurus ''Dallasaurus'' ("Dallas County, Texas, Dallas lizard") is a basal mosasauroid from the Upper Cretaceous of North America. Along with ''Russellosaurus'', ''Dallasaurus'' is one of the two oldest mosasauroid taxa currently known from North America ...

Dallasaurus
'', a plesiopedal mosasauroid that was found by multiple phylogenetic analyses to be an ancestor of the Mosasaurinae but unrelated to other mosasaurs. Bell and Polycn (2005) grouped these outside mosasaurs into two clades: the Russellosaurina, whose basal members include plesiopedal genera (Tethysaurinae) of their own and derived members consisting of the Plioplatecarpinae and Tylosaurinae; and the Halisauromorpha, containing the Halisaurinae. The placement of ''Dallasaurus'' suggested that the Russellosaurina and Halisauromorpha may have evolved a hydropedal form independently, the former through the tethysaurines, meaning that their placement within the Mosasauridae creates an unnatural
polyphyly A polyphyletic group or assemblage is a set of organisms, or other evolving elements, that have been grouped together based on characteristics that do not imply that they share a common ancestor that is not also the common ancestor of many othe ...
and thus potentially invalid. Caldwell informally proposed in a 2012 publication that the definition of a mosasaur must thus be redefined into one that does not consider russellosaurines and halisauromorphs as true mosasaurs, but as an independent group of marine lizards. However, phylogenetic studies of mosasaurs can be fickle, especially when wild card taxa like ''Dallasaurus'' remain poorly understood. For example, some studies such as a 2009 analysis by Dutchak and Caldwell instead found that ''Dallasaurus'' was ancestral to both russellosaurines and mosasaurines, although results were inconsistent in later studies. A 2017 study by Simoes ''et al.'' noted that utilization of different methods of phylogenetic analyses can yield different findings and ultimately found a consistent indication that tethysaurines were a case of hydropedal mosasaurs reversing back to a plesiopedal condition rather than an independent ancestral feature.


Phylogeny

Cladogram A cladogram (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appr ...

Cladogram
of the Mosasauroidea from Madzia and Cau (2017):


Distribution

Though no individual genus or subfamily is found worldwide, the Mosasauridae as a whole achieved global distribution during the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous The Cretaceous ( ) is a that lasted from about 145 to 66 (Mya). It is the third and final period of the , as well as the longest. At around 79 millio ...
with many locations typically having complex mosasaur faunas with multiple different genera and species in different
ecological niche In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms ...

ecological niche
s. Two African countries are particularly rich in mosasaurs: Morocco and Angola.


References


External links


Palaeos: Vertebrates: Mosasaurs

BBC Science and Nature: Mosasaurs


New Zealand fossil fauna

life in the Sea of Kansas, illus. by Carl Buell

until 1829.
''Mosasaurus maximus'' mounted skeleton at University of Texas Memorial Museum

Canadian Fossil Discovery Centre

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

"Mosasaurs terrorized Cretaceous rivers" Planet Earth online

Georgia Southern University Museum Mosasaur Exhibit

Kansas Geological Survey Vol IV (1899)
containing the famous summary of American mosasaurs by Samuel Williston. * William R. Wahl
MOSASAUR BITE MARKS ON AN AMMONITE. PRESERVATION OF AN ABORTED ATTACK?


{{Taxonbar, from=Q729456 01 Cretaceous lizards Turonian first appearances Maastrichtian extinctions Taxa named by Paul Gervais