Editing Mosasaur (section)

==Paleobiology==
[[File:Placenticeratidae - Placenticeras whitfieldi.jpg|thumb|Fossil shell of ammonite ''[[Placenticeras whitfieldi]]'' showing punctures caused by the bite of a mosasaur, [[Peabody Museum of Natural History]], Yale]]
[[File:Mosasaur tooth.jpg|thumb|A tooth from a mosasaur]]
Mosasaurs had double-hinged jaws and flexible skulls (much like those of [[snake]]s), which enabled them to gulp down their prey almost whole. 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.

One of the food items of mosasaurs were [[ammonites]], molluscs with shells similar to those of ''[[Nautilus]]'', which were abundant in the Cretaceous seas. Holes have been found in fossil shells of some ammonites, mainly ''[[Pachydiscus]]'' and ''[[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]]'', had blunt, spherical teeth, specialized for crushing mollusk shells. The smaller genera, such as ''[[Platecarpus]]'' and ''[[Dallasaurus]]'', which were about {{convert|1|–|6|m|ft|abbr=on}} long, probably fed on fish and other small prey. The smaller mosasaurs may have spent some time in fresh water, hunting for food. The largest mosasaur ''Mosasaurus hoffmannii'' was the [[apex predator]] of the Late Cretaceous oceans, reaching more than {{convert|11|m|ft}} in length and weighing up to {{convert|10|MT|ST}} in body mass.<ref>{{cite journal|author1=Fedrico Fanti|author2=Andrea Cau|author3=Alessandra Negri|title=A giant mosasaur (Reptilia, Squamata) with an unusually twisted dentition from the Argille Scagliose Complex (late Campanian) of Northern Italy|year=2014|journal=Cretaceous Research|volume=49|issue=2014|pages=91–104|doi=10.1016/j.cretres.2014.01.003|bibcode=2014CrRes..49...91F |url=https://www.disva.univpm.it/sites/www.disva.univpm.it/files/disva/news_dipartimento/cretaceus%20research.pdf}}</ref>

===Soft tissue===
[[Image:Tylosaurus skin.jpg|thumb|left|Scales of ''Tylosaurus proriger'' (KUVP-1075)]]
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]] deposits of the Muwaqqar Chalk Marl Formation of [[Harrana]]<ref name=Kaddumi>{{cite book |last=Kaddumi |first=H.F. |year=2009 |chapter=On the latest scale coverings of mosasaurs (Squamata: ''Mosasauridae'') from the Harrana Fauna in addition to the description of s new species of Mosasaurus |title=Fossils of the Harrana Fauna and the Adjacent Areas |publisher=Eternal River Museum of Natural History |location=[[Amman]] |pages=80–94}}</ref> 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 Gove County, Kansas.<ref name=Snow>{{cite journal |last=Snow |first=F. H. |year=1878 |title=On the dermal covering of a mosasauroid reptile |journal=Transactions of the Kansas Academy of Science |volume=6 |pages=54–58 |doi=10.2307/3623557 |jstor=3623557 }}</ref>

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.<ref name=Kaddumi/> As ambush predators, lurking and quickly capturing prey using stealth tactics,<ref name=Massare>{{cite journal |doi=10.1080/02724634.1987.10011647 |last=Massare |first=J. A. |year=1987 |title=Tooth morphology and prey preference of Mesozoic marine reptiles |journal=Journal of Vertebrate Paleontology |volume=7 |issue=2 |pages=121–137|bibcode=1987JVPal...7..121M }}</ref> they may have benefited from the nonreflective, keeled scales.<ref name=Kaddumi/> 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.<ref>{{Cite web | url=https://www.sciencedaily.com/releases/2019/09/190923140812.htm |title = Did mosasaurs do the breast stroke?}}</ref> 
[[Image:Soft tissue structures in Platecarpus.png|thumb|Soft tissues in the head and neck of ''Platecarpus tympaniticus'' specimen LACM 128319: Tracheal rings are shown in the bottom three photographs.]]
More recently, a fossil of ''[[Platecarpus|Platecarpus tympaniticus]]'' 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]] 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]]s. As in cetaceans, the [[bronchi]] 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.<ref name=LCKC10/>
[[File:Prognathodon tissue.jpg|thumb|left|Fibrous tissues and microstructures recovered from ''Prognathodon'' specimen IRSNB 1624]]

In 2011, [[collagen]] protein was recovered from a ''[[Prognathodon]]'' humerus dated to the [[Cretaceous]].<ref>{{Cite journal |last1=Lindgren |first1=Johan |last2=Uvdal |first2=Per |last3=Engdahl |first3=Anders |last4=Lee |first4=Andrew H. |last5=Alwmark |first5=Carl |last6=Bergquist |first6=Karl-Erik |last7=Nilsson |first7=Einar |last8=Ekström |first8=Peter |last9=Rasmussen |first9=Magnus |date=29 April 2011 |title=Microspectroscopic Evidence of Cretaceous Bone Proteins |journal=[[PLoS ONE]] |language=en |volume=6 |issue=4 |pages=e19445 |doi=10.1371/journal.pone.0019445 |issn=1932-6203 |pmc=3084868 |pmid=21559386 |first10=Desirée A. |last10=Douglas |first11=Michael J. |last11=Polcyn |first12=Louis L. |last12=Jacobs|bibcode=2011PLoSO...619445L |doi-access=free }}</ref>

In 2005, a [[case study]] by A.S. Schulp, E.W.A Mulder, and K. Schwenk outlined the fact that mosasaurs had paired [[fenestra]]e in their palates. In monitor lizards and snakes, paired fenestrae are associated with a [[forked tongue]], which is flicked in and out to detect chemical traces and provide a directional sense of [[Olfaction|smell]]. They therefore proposed that mosasaurs probably also had a sensitive forked tongue.<ref>{{Cite journal |last1=Schulp |first1=A. S. |last2=Mulder |first2=E. W. A. |last3=Schwenk |first3=K. |date=2005-09-01 |title=Did mosasaurs have forked tongues? |journal=Netherlands Journal of Geosciences |volume=84 |issue=3 |pages=359–371 |doi=10.1017/S0016774600021144 |doi-access=free |bibcode=2005NJGeo..84..359S }}</ref>

===Metabolism===
A study published in 2016 by T. Lyn Harrell, Alberto Pérez-Huerta and [[Celina A. Suarez|Celina Suarez]] showed that mosasaurs were [[endotherm]]ic. The study contradicted findings published in 2010 indicating mosasaurs were [[ectotherm]]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.<ref>{{cite journal |last1=Harrell |first1=T. Lynn |last2=Pérez-Huerta |first2=Alberto |last3=Suarez |first3=Celina A. |last4=Benson |first4=Roger |title=Endothermic mosasaurs? Possible thermoregulation of Late Cretaceous mosasaurs (Reptilia, Squamata) indicated by stable oxygen isotopes in fossil bioapatite in comparison with coeval marine fish and pelagic seabirds |journal=Palaeontology |date=May 2016 |volume=59 |issue=3 |pages=351–363 |doi=10.1111/pala.12240|s2cid=130190966 |doi-access=free |bibcode=2016Palgy..59..351H }}
*{{cite press release |date=May 6, 2016 |title=Scientists cite evidence that mosasaurs were warm-blooded |website=ScienceDaily |url=https://www.sciencedaily.com/releases/2016/05/160506160429.htm}}</ref>

===Coloration===
The coloration of mosasaurs was unknown until 2014, when the findings of Johan Lindgren of [[Lund University]] and colleagues revealed the pigment [[melanin]] in the fossilized scales of a mosasaur. Mosasaurs were likely [[countershaded]], with dark backs and light underbellies, much like a [[great white shark]] or [[leatherback sea turtle]], the latter of which had fossilized ancestors for which color was also determined. The findings were described in ''[[Nature (journal)|Nature]]''.<ref>{{Cite journal |last1=Lindgren |first1=J. |last2=Sjövall |first2=P. |last3=Carney |first3=R. M. |last4=Uvdal |first4=P. |last5=Gren |first5=J. A. |last6=Dyke |first6=G. |last7=Schultz |first7=B. P. |last8=Shawkey |first8=M. D. |last9=Barnes |first9=K. R. |year=2014 |title=Skin pigmentation provides evidence of convergent melanism in extinct marine reptiles |journal=Nature |volume=506 |issue=7489 |pages=484–8 |doi=10.1038/nature12899 |pmid=24402224 |last10=Polcyn |first10=M. J.|bibcode=2014Natur.506..484L |s2cid=4468035 }}</ref>

===Teeth===
Mosasaurs possessed a [[Thecodont dentition|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.<ref name=CaldwellDentition>{{cite journal|author1=Michael W. Caldwell|title=Ontogeny, anatomy and attachment of the dentition in mosasaurs (Mosasauridae: Squamata)|year=2007|journal=Zoological Journal of the Linnean Society|volume=149|issue=4|pages=687–700|doi=10.1111/j.1096-3642.2007.00280.x|doi-access=free}}</ref>

===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''.<ref>{{Cite news|url=https://www.sciencedaily.com/releases/2015/04/150410113408.htm|title=What life was like for newborn giant sea lizards during the age of the dinosaur|work=ScienceDaily|access-date=2017-08-01|language=en}}</ref>

=== Possible eggs ===
A 2020 study published in [[Nature (journal)|''Nature'']] described a large fossilized hatched egg from [[Antarctica]] from the very end of the [[Cretaceous]], about 68 million years ago. The egg is considered one of the largest [[amniote]] eggs ever known, rivalling that of the [[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 [[Lepidosauria|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 [[Egg fossil|oospecies]] ''[[Antarcticoolithus bradyi]]''.<ref>{{Cite news|date=2020-06-17|title=Mystery egg likely 'belonged to giant sea reptile'|language=en-GB|work=BBC News|url=https://www.bbc.com/news/science-environment-53085318|access-date=2020-06-18}}</ref><ref>{{Cite news|last=Joel|first=Lucas|date=2020-06-17|title=Life Hatched From Soft Eggs, Some a Foot Long, in Dinosaur Era|language=en-US|work=The New York Times|url=https://www.nytimes.com/2020/06/17/science/dinosaurs-soft-eggs.html|access-date=2020-06-18|issn=0362-4331}}</ref><ref>{{Cite journal|last1=Legendre|first1=Lucas J.|last2=Rubilar-Rogers|first2=David|last3=Musser|first3=Grace M.|last4=Davis|first4=Sarah N.|last5=Otero|first5=Rodrigo A.|last6=Vargas|first6=Alexander O.|last7=Clarke|first7=Julia A.|date=2020-06-17|title=A giant soft-shelled egg from the Late Cretaceous of Antarctica|journal=Nature|volume=583|issue=7816|language=en|pages=411–414|doi=10.1038/s41586-020-2377-7|pmid=32555453|bibcode=2020Natur.583..411L|issn=1476-4687|doi-access=free}}</ref> However, it has been proposed that this egg belonged to a dinosaur.<ref>{{Cite journal |last=Lindgren |first=Johan |last2=Kear |first2=Benjamin P. |date=July 2020 |title=Hard evidence from soft fossil eggs |url=https://www.nature.com/articles/d41586-020-01732-8 |journal=Nature |language=en |volume=583 |issue=7816 |pages=365–366 |doi=10.1038/d41586-020-01732-8|url-access=subscription }}</ref>