Mosasaurus

Before formal naming or identification, this organism was known as the following on this wiki:
**Pembina Gorge mosasaur**

## Statistics

### Diet

Carnivorous

*Mosasaurus*, *M. hoffmannii* sometimes called Hoffmann's Mosasaur[*citation needed*], is an extinct genus of mosasaurid mosasaur that lived in Africa, the Americas, Europe, Russia and Antarctica during the Late Cretaceous.

## History

—Georges Cuvier (1812)
The first *Mosasaurus* was a skull identified as a whale's in 1964 in a chalk quarry near Maastricht, Netherlands. Around 1780, another skull was found, attracting Johann Leonard Hoffmann, who identified it as a crocodile's. He then contacted Petrus Camper, gaining international attention, and was again identified as cetacean. During the capture of Maastricht, French revolutionaries looted the fossil in 1794. Barthélemy Faujas de Saint-Fond dramatically recalls the skull being retrieved by 12 grenadiers in exchange for 600 bottles of wine. This skull, at this point, was famous - but historians agree this narrative is dramatized The skull was sent to the National Museum of Natural History in 1795, catalogued later as MNHN AC 9648. Camper's son Adriaan Gilles Camper and Georges Cuvier (1808) concluded the remains (nicknamed the "great animal of Maastricht") belonged to a marine lizard affiliated with monitors and unlike any extant fauna. This skull was part of Cuvier's speculations about the concept of extinction, later leading to catastrophism, which was a precursor to evolution; at this time, extinction was seen as a myth, and Cuvier's hypothesis was revolutionary. William Daniel Conybeare (1822) named *Mosasaurus*, with Gideon Mantell (1829) adding *hoffmannii* as a specific epithet. Cuvier later assigned the second skull as the holotype.

The Lewis and Clark Expedition (1804) discovered a (now-lost) specimen from the Missouri River, then identified as a 45-foot (14-meter)-long fish. Richard Ellis (2003) speculates his may have been the first *M. missouriensis* discovered, but competing specimens have been recalled. In 1818, a specimen from Monmouth County, New Jersey became the first North American specimens to be referred to *Mosasaurus*. Richard Harlan (1834) described the type *M. missouriensis* from a rostral fragment discovered around the river's Big Bend, assigning it as *Ichthyosaurus*, and later, an amphibian. The remaining skull was found earlier by a fur trapper, with prince Maximilian of Weid-Neuwied (between 1832 and 1834) obtaining it. It was then delivered to Georg August Goldfuss, who published about it in 1845. The same year, Christain Erich Hermann von Meyer speculated that it and Harlan's skull were the same individual. This was confirmed in 2004. Edward Drinker Cope (1881) named *M. conodon* from fragments in New Jersey as a giant species of *Clidastes*, later reassigned to *Mosasaurus* in 1966. *M. lemonnieri* was found by Camper Jr. from fossils of his father's collections, discussed with Cuvier in a 1799 correspondence. However, Cuvier rejected the concept of *Mosasaurus* as non-monotypic. Louis Dollo (1889) reintroduced and named the species based on a skull from a Belgium phosphate quarry. Further excavation in said quarry recovered more well-preserved remains, including multiple partial postcrania, which represented a near-complete skeleton. Dollo described these later. Being the best anatomically-represented, *M. lemonnieri* was ignored in publications, for which Theagarten Lingham-Soliar suggested two reasons. First, it attracted little paleontologists, and second, it was overshadowed by the legendary type species.

*M. lemonnieri* is a controversial species, and it is debated if it is valid. Dale Russell (1967) argued it an *M. conodon* are the same, setting the former as a junior synonym of the latter. Lingham-Soliar (2000) refuted this based on comprehensive study of specimens, which is corroborated by an *M. conodon* cranial study by Ikejiri and Lucas (2014). Eric, Mulder, Dirk Cornelissen and Louis Verding (2004) suggested *M. lemonnieri* could be a juvenile *M. hoffmannii*, based on the argument that differences are age-based. However, more research is required. *M. beaugei* was named by Camille Arambourg (1952) based on isolated teeth from the phosphate deposits of the Oulad Abdoun Basin and Ganntour Basin.

Mosasaurine remains excavated from Breien Member, Hell Creek Formation in 2016 were found to belong to an indeterminate mosasaurine by Clint Boyd and Nathan Van Vranken (2021), which is either assignable to *M. hoffmannii* or *Prognathodon*. This proves that large mosasaurs lived with Hell Creek fauna. These remains represent an individual 15 meters long. This was a coastal taxon, who may have ventured into more brackish water. The specimen was collected from the property of a landowner, who had found loose at the base of a hill, and a vertebrae was sent to Clint Boyd to analyze. Shrimp burrows nearby indicates the remains were possibly scattered as they pushed tissue out of their way, with small shark teeth also found nearby. More remains were found emerging from prairie grass, whose roots had extended so deep it was difficult to prepare them. They were brought back to a lab to further prepare.

One specimen, postcrania, were collected from 2012 through 2014 and the second specimen, a skull and neck, were collected from Pembina Gorge in 2015-2016. These specimens were discovered 2 meters apart, directly atop each other. The hillside quarry they were recovered from slopes down toward a passing road, and it is thought that the postcrania were separated from the crania were dislodged from one another and were sent in different directions, rather than two individuals. This is further evidenced by how no overlapping material is present, the parts are "almost perfectly complimentary" and how the material has consistent size. Clint Boyd is working on describing it. It may be part of the Pierre Shale. It is similar to *M. conodon* and may represent variation in this species or something novel.

### Paleoart

Mid-1800s depictions of *Mosasaurus* typically consists of an amphibious marine reptile that has webbed feet for walking. This was based on the M. missouriensis holotype, which had an elastic vertebral column that Goldfuss (1845) saw as evidence for walking, alongside analyses of phalanges. Hermann Schlegel (1854) saw *Mosasaurus* had fully aquatic flippers by showing the "claws" were erroneous and the phalanges showed no signs of muscle/tendon attachment. They were also flat, broad and formed a paddle-like shape. This was largely ignored by scientists at the time, but was accepted in the 1870s when Othniel Charles Marsh and Cope found more complete remains in North America. Some of the earliest paleoart is a life-sized concrete sculpture made by Benjamin Water house Hawkins (between 1852 and 1854) as part of the Crystal Palace statues. It was partially-informed by Richard Owen's interpretation of the holotype and monitor lizards, depicting it as an aquatic version of the latter with a boxy head, nostrils oriented to the side, large amounts of tissues around the eyes, lips, flippers and monitor-esque scales. It was deliberately sculpted incomplete, stated by Mark Witton later, to likely save time and money. Even back then, many elements could be considered inaccurate, as it neglected Goldfuss (1845)'s research, which called for a narrower skull, nostrils oriented at the top of the skull and terrestrial limbs (now seen as inaccurate).

## Description

In 2022, the presence of *M. hoffmannii* in the Moroccan Maastrichtian Phosphates from a marginal tooth crown was published. A Mosasaurus sp. tooth was recovered from the Peedee Formation on a grand stand beach.

*M. hoffmannii* has a blunt snout and *M. lemmonieri* has a pointed snout. The foramina in the jaws are similar in pattern to *Clidastes*. All species except *M. conodon* have skulls that are robust, broad and deep. *M. hoffmannii* and the largest specimens of *M. lemmonieri* have a slightly upturned dentary. However, more typical skulls of the former are straighter. In *M. hoffmannii* and *M. lemmonieri*, the premaxillary bar constricts near the midpoint, typical of mosasaurs, but *M. missouriensis* has a robust bar that does not constrict. In *M. hoffmannii*, the external nares are 21-24% of the skull length, and placed farther back than any other mosasaur except *Goronyosaurus*, beginning above the 4th and 5th maxillary teeth. Thus, the posterior of the maxilla lack a dorsal concavity, which would fit the typical mosasaur nostril. The palate is compacted for stability, the brain was more slender and smaller than other mosasaurs, the occipital lobe and cerebral hemisphere are narrow and shallow, suggesting they were small, the parietal foramen is the smallest in any mosasaurid and the quadrate is tall and somewhat rectangular.

Cutting structures, prismatic surfaces and two opposite cutting edges diagnose the genus. *M. conodon* and *M. lemmonieri* are the only species whose teeth are not large and robust. *M. hoffmanni* and *M. missouriensis* have finely serrated edges while *M. conodon* and *M. lemmonieri* do not have serrations and *M. beaugei* has edges that are nor serrated nor smoothed, with small crenulations. The number of prisms in the teeth vary between tooth types and between species; *M. hoffmannii* has 2-3 on the labial side and none on the lingual, *M. missouriensis* has 4-6 on the labial and 8 on the lingual, *M. lemonnieri* has 8-10 on the labial and *M. beaugei* has 3-5 on the labial and 8-9 on the lingual. *Mosasaurus* has 2 premaxillary, 12-16 maxillary, 8-16 pterygoid and 17 dentary teeth, which were homodont, minus the smaller pterygoid teeth, This makes 20-34 teeth on the upper jaw and 17 on the lower, on average, since the number of teeth on each region varies between species and individuals. *M. hoffmannii* has 14-16 maxillary, 14-15 dentary and 8 pterygoid teeth. *M. missouriensis* has 14-15 maxillary, 14-15 dentary and 8-9 pterygoid teeth. *M. conodon* has 14-15 maxillary, 16-17 dentary and 8 pterygoid teeth. *M. lemmonieri* has 15 maxillary, 14-17 dentary and 11-12 pterygoid teeth. M. beaugei has 12-13 maxillary, 14-16 dentary and 6 (or more) pterygoid teeth. An indeterminate specimen of Mosasaurus and similar to *M. conodon* from Pembina Gorge State Recreation Area, North Dakota has 16 pterygoid teeth, which is much larger than any species. The dentition was thecodont and constantly replacing, finding 10.9 micrometers of odontoblasts per day in *M. hoffmannii*. This was found through the von Ebner lines, which further finds it took 511 days for the odontoblasts and 233 days for the dentin to develop the teeth.

*M. sp.* SDSM 452 is one of the most complete specimen in terms of vertebrae, having, 7 cervicals, 38 dorsals, 8 pygal and 68 caudals. All species have 7 caudals, but other counts vary; Partial skeletons of *M. conodon*, *M. hoffmannii* and *M. missouriensis* suggest that *M. conodon* probably had up to 36 dorsals and 9 pygals. *M. hoffmannii* has up to 32 dorsals and 10 pygals, *M. lemmonieri* with ~40 dorsals, 22 pygals and 90 caudals (the most vertebrae-rich of the genus) and *M. missouriensis* with ~33 dorsals, 11 pygals and at least 79 caudals. The ribs were very deep and makes an almost perfect semicircle in cross-section, which makes the chest barrel-shaped. Cartilage attached the ribs rather than bone fusion, which aided with breathing in deep water. Bone texture is nearly identical to cetaceans, which suggests neutral buoyancy and aquatic adaptation. The tail is similar to *Proganthodon* and evidence for two lobes is present. The caudals gradually shorten at the center of the tail and lengthen behind the center, which made the tail rigid around the center and flexible behind that point. The dorsal plane slightly offsets the tail bend that starts at the midpoint. The large haemal arches bend at the tail's midpoint. All of these suggest the fluke at the end of the tail was a power locomotion device. The fins were wide anf robust, the scapula and humerus are fan-shaped and wider than the tail, the radius and ulna were short (the former taller than the latter), the ilium is slender and rod-like (being ~1.5x longer than the femur in *M. missouriensis*), the femur is 2x as long than its width and ends at the distal side in a pair of articular facets that meet at an angle of ~120°, the 5th set of metacarpals and phalanges shorter and offset, compressed paddle structure similar to *Plotosaurus* (suggesting fast swimming) and hindlimbs that have 4 digits.

## Classification

Russell (1967) was one of the earliest evolutionary attempts at defining *Mosasaurus*, finding a *Clidastes*-like ancestor that diverged into two lineages, one leading to *M. conodon* and the other having several chronospecies (*M. ivoensis*, *M. missouriensis* and *M. maximus*-*hoffmannii* (in that order)). However, he used an early version of phylogenetics rather than cladistics. Bell (1997) published a cladistic analysis of North American mosasaurs, finding *M. missouriensis*, *M. conodon*, *M. maximus* and USM 77040, an indeterminate specimen, finding some agreements with Russell (such as ancestry related to *Clidastes* and *M. conodon* being the most basal). Contrary, he found a sister relationship with *Globidens* and *Prognathodon*, with *M. maximus* sister to *Plotosaurus*. This made the genus paraphyletic, but *Plotosaurus* was still determined valid by Bell. This study formed a precedent for later works, although some later studies replace the sister clade of *Mosasaurus*/*Plotosaurus* to consist of *Eremiasaurus* and *Plesiotylosaurus* depending on the methodology, and at least one study finding *M. missouriensis* to be the most basal of the genus. Konishi et al. (2014) expressed concerns with Bell, finding that the sample severely underrepresented the genus, leaving a wealth of material unaccounted for and thus distorting phylogeny. They also find that the holotype data was unclear and made the taxonomy shaky and that there was a lack of comparative anatomical studies. Street (2016) used this to update their results. Conrad (2008) used only *M. hoffmannii* and *M. lemmonieri*, finding the former to be basal to many descendants, from most to least basal, *Globidens*, *M. lemmonieri*, *Goronyosaurus* and *Plotosaurus*. This suggests that they are not the same genus, but this was unorthodox because he focused on squamates and not mosasaurs specifically. This had led to many disregarding this result based on technical issues.

## Paleobiology

Lingham-Soliar (1995) studied the head musculature of *M. hoffmannii*, which was mostly reconstructed based on the skull structure, muscle scarring and the structure of monitor lizards. The frontals and parietals of mosasaurs overlap with monitor lizards, forming a flexible pivot point that allows flexion int he jaws to prevent prey escape. This forms a rigid three-pivot geometric structure that is united by strong interlocking sutures to resist the compression and shear force produced during a downward or upward thrust of the jaw muscles. This makes the cranium rigid but shock resistent, making a powerful bite. The mandible could swing forwards and backwards like all mosasaur. Including *Prognathodon* and *M. lemmonieri*, this fuctioned to allow ratchet feeding (where the pterygoids move prey like a conveyor belt. Compared to the latter, the pterygoid teeth in *M. hoffmannii* are small, which suggests that this was unimportant, likely choosing inertial feeding with the jaw adduction to bite in seizure instead. The magnus adductor muscles are massive in *M. hoffmannii*, suggesting an enormous bite force. The jaws would have been quickly opened and closed by the tendons of the coronoid process using little energy, which would have also contributed to the bite. It would not have to have a strong magnus depressor, contrary to some plesiosaurs.

*M. hoffmannii* from the K-Pg boundary in southeast Missouri between the Paleocene Clayton Formation and the Cretaceous Owl Creek Formation preserve fractures in the vertebrae that may have been deposited by a tsunamite. This was nicknamed the "Cretaceous cocktail deposit", forming through catastrophic seismic and geologic disturbances, mega-hurricanes and giant tsunamis following the Chicxulub impactor. Any *Mosasaurus* who seeked refuge from ecosystem collapse and blocked sunlight in greater depths would have suffered starvation. Other specimens are found less than 15 meters beneath the boundry of the Maastricht, Davutlar, Jagüel and Stevns Klint Formations. One *M.* sp. from Hornerstown Formation, typically of the Paleocene Danian period, was found associated with *Squalicorax*, *Enchodus* and ammonites. One theory states that they were worked from older Cretaceous deposits during early deposition, which is evidenced by abraded and eroded remains. However, the same assemblage preserves more pristine *Mosasaurus* fossils. Another theory posits that it is a Maastrichtian time-averaged remanié deposit. One last hypothesis suggests that it is a lag deposit brought out by a tsunami impact, and the remainder was refilled by Cenozoic sediment.

### Life History

*Mosasaurus* used sub-carangiform tail-based swimming, using their flippers as hydrofoils. Large muscles attached to the o name="1:"utwards-facing surface of the humerus to the radius, ulna and then modified joints that enhanced flipper rotatation. The powerful force generated by using these may have sometimes caused boen damage, based on an *M. hoffmannii* ilium with the head significantly separated from the body caused by shearing forces in the articulation joint. The tissue structure in the bones suggests a metabolic rate that is much higher than modern squamates and a resting metabolism between a leatherback turtle and ichthyosaurs/plesiosaurs. It was likely endothermic and had a constant, distinct body temperature. *Clidastes* indicates that endothermy was present in all mosasaurs. This is unique to squamaes, except for several species, which would have allowed *Mosasaurus* to have increased stamina when foraging in larger areas and pursuing prey (among other things). It may have allowed some species of this genus to live in colder climates such as Antarctica. It was likely viviparous, but there is no direct evidence of live birth in *Mosasaurus* though it is inferred from other taxa. Microanatomical research on juvenile elements suggest that juveniles had bone structures comparable to adults, unlike older mosasauroids who bear different structure to support buoyancy in shallower water. This implies that they were percocial, being fully functional in open water at very young age and did not require nurseries. However, some European and South Dakotan assemblages of concentrated juvenile *M. hoffmannii*, *M. missouriensis* and *M. lemmonieri* suggest that some juveniles lived in shallow waters.

### Senses

It had large orbits and large sclerotic rings that occupied much of the orbit's diameter, with corresponds with a large eye size and good vision. The binocular field was small, ~28.5°, based on the placement of the eyes at the sides of the skull. This would have allowed for excellent processing of 2D environments, such as the near-surfce environments they lived in. Brain casts made from *Mosasaurus* suggest that the olfactory bulb and vomeronasal organ, both controlling smell, were poorly developed and lack some structures in *M. hoffmannii*. This suggests a poor sense of smell. In *M. lemmonieri*, these are still small but are better developed and have the parts lacking in derived forms. This suggests that olfaction was not very important in *Mosasaurus*, exploiting other senses.

### Diet

*Mosasaurus* was likely an active predator that fed on bony fish, sharks, cephalopods, birds and marine reptiles, including other mosasaurs and turtles. It is unlikely to be a scavenger based on the poor sense of smell. It's great size, heavy bite and robust teeth would have allowed it to challenge any animal. Lingham-Soliar (1995) suggested a "savage" feeding method based on large tooth marks on the scutes of *Allopleuron hofmanni* and rehealed jaw fractures in *M. hoffmannii*. It likely hunted near the surface, as its eyes were better suited to this environment, ad an ambush predator. *M. lemonnieri* and *M. conodon* may have hunted in deeper water based on chemical and structural data. Carbon isotope of *M. hoffmannii* suggests that they had the lowest value of δ13C of the largest mosasaur individuals. Mosasaurs with a higher value occupied higher trophic levels and those with lower were caused by a prey diet rich in sea turtles, large marine reptiles and other lipids. This suggests that *M. hoffmannii* was an apex predator. A small *M. missouriensis* of 75 million years old is one of the few examples of stomach contents preserved in mosasaurs. It is a partial skeleton with dismembered and punctured remains of a 1-meter-long fish in its gut. Though it is much longer than its entire skull, it dismembered prey and consumed parts. It lived with *Prognathodon*, who focused on robust prey, so by niche partitioning it preyed on animals that were best consumed via cutting-adapted teeth. *Mosasaurus* may have taught children how to hunt, as seen in a specimen of *Argonautilus catarinae* that preserves bite marks from 2 conspecific mosasaurs, one a juvenile and the other an adult. Kauffman (2014) suggests that they were made either by *Mosasaurus* or *Platecarpus*, with the nautiloid either sick or dead upon attack given the direction of the marks. This is either the parent teaching of alternate food sources, or a juvenile weakly biting once and then strongly biting. However, the spacing suggests different jaw sizes.

### Conflict

Intraspecific combat was aggressive and lethal. One partial *M. conodon* bears multiple cuts, breaks and punctures across the skeleton, particularly on the rear skull and neck, and a tooth of the same species penetrating the quadrate. None of these show evidence of healing, suggesting that a fatal blow to the skull killed it. An *M. missouriensis* skeleton has a tooth from another individual lodged in the lower jaw under the eye, where healing was detected and implying survival. Konishi ssuggests that this head biting may have occurred in courtship. Some injuries attributed to intraspecific combat may actually be due to attempting to crush turtle shells. Lingham-Soliar (2004) suggests that if they were intraspecific, then a pattern of head-specific injury would be observed. Modern crocodiles attack other individuals by grappling their heads with their jaws, with Lingham-Soliar suggesting that *Mosasaurus* did this. Many of these specimens with injuries are juveniles or subadults, so it may have been common to attack them due to being smaller or weaker. However, the attackers in *M. conodon* and *M. missouriensis* were likely of similar size to their victims. Schulp et al. (2006) speculated that these encounters may have occasionally led to cannibalism.

### Paleopathology

IRSNB R25 and IRSNB R27, *M. hoffmannii*, both bear fractures and other pathological elements on their dentaries; the former has a full fracture near the 6th tooth, with extensive bony callus overgrowing the socket and along various osteolytic cavities, abscess canals, trigeminal nerve damage and inflamed erosions that suggest severe bactarial infection are seen. Two finely ulcerated marks on the bone callus may have developed during healing. In the latter, one fracture with full healing and an open one with broken teeth as a result. It it is covered by a nonunion formation of callus with shallow scratching and a large pit that connects to the abscess canal. Lingham-Soliar thought this pit resembled tooth marks from an attacking mosasaur. Both specimens had deep bacterial infection and fracturing, which suggests that bacteria may have travelled to damaged teeth nearby and caused tooth decay, which in turn may have penetrated to deeper tissue from prior post traumatic or secondary infections. The dentaries ahead from the fractures are of good condition, which suggests effective fracture immobilization during healing, preventing further damage to vital blood vessels and nerves, which suggests that they were not fatal. Schulp et al. (2006) describe a quadrate of the same species with multiple openings with an estimated 0.5 liters (0.13 US gallons) of tissue lost, likely a severe bone infection initiated by septic arthritis and spread to a large area of the quadrate and reduced said part to abscess. Much reparative bone tissue suggests the infection and healing may have spanned several months of painful recovery. This would have hampered its biting ability and possibly even breathing. They speculated that it may have had to forage on soft-bodied prey such as squid that could be consumed whole based on this. One of the marks may have been a tooth puncture that became infected if this is intraspecific, though it is unknown. Avascular necrosis have been found in every specimen of *M. lemmonieri* and *M. conodon* in Alabama/New Jersey and Belgium, respectively. Rothschild and Martin (2005) found it affected 3-17% of mosasaur vertebrae. This is often caused by decompression sickness, which suggests that these animals were habitual deep divers or repetitive divers. Carlsen considered the simplest explanation was that they were inadequately adapted. However, mosasaurs who suffered decompression sickness still show substantial adaptation in the eardrum (against rapid pressure shifts). Unnatural caudal fusion is found in this genus, which occurs during remodeling after trauma or disease. Rothschild and Everhart (2015) compiled 15 specimens from North America and Belgium and found fused caudals in 3. 2 of such had irregular surface deformities around the fusion site that was caused by vertebral sinus drainage and thus bone infection. The cause of this infection is uncertain, but fused vertebrae in other mosasaurs is typically indicative of shark attacks and other predation attempts. The third case was caused by a form of arthritis based on how the bridging bone tissue is smooth.

## Paleoecology

It was a transatlantic species found on both sides of the Atlantic, including the Midwest and East Coast of the United States, Canada, Europe, Turkey, Russia, the Levant, Morocco to South Africa, Brazil, Argentina and possibly Antarctica. These comprise the Atlantic Ocean, Western Interior Seaway and Mediterranean Tethys during the Cretaceous, spanning tropical, subtropical, temperate and subpolar climates. The Mediterranean Tethys was located in Eurasia and Africa during the Maastrichtian, with most of today's landmass being submerged. *M. hoffmannii* and *Prognathodon sectorius* were dominant in the north. In Belgium, *M. lemmonieri* was far more dominant. Other mosasaurs in the European sector include *Halisaurus*, *Plioplatecarpus*, *Platecarpus*, *Carinodens*, *Tylosaurus bernardi* and *Prognathodon* sensu lato. Other taxa include *Allopleurodon*, *Glyptochelone* and elasmosaurs. In New Jersey, the fauna is similar but lacks *M. lemmonieri*, *Carinodens*. *Tylosaurus* and certain *Halisaurus* and *Prognathodon* species. *M. conodon*, *Halisaurus platyspondylus* and *Prognathodon rapax* are here exclusive. Fish fauna in the northern Tethyan margin include *Squalicorax*, *Cretalamna*, sand sharks, *Cimolichthys* and other bony fish, *Enchodus* and *Protosphyraena*. The southern margin, along the equator and thus more tropical, extended through Africa, Arabia, the Levant and Brazil providing many shallow environments. Here, *Globidens phosphaticus* is characteristic, with the African and Arabian sector dominated by *Halisaurus arambourgi* and *Gavialimimus* and were contemporaneous with *Globidens*. *M. beaugei* distribution here is restricted to Morocco and Brazil, with *M. lemmonieri* possibly in Syria and *M. hoffmannii* having some presence. Other mosasaurs include *Goronyosaurus*, *Igdamanosaurus*, *Eremiasaurus*, *Prognathodon*, *Halisaurus* and *Carinodens*. Other fauna are *Pachyvaranus*. *Palaeophis*, *Zarafasaura*, plesiosaurs, *Enchodus*, *Stratodus* and sharks.

Many of the earliest *Mosasaurus* discoveries were from the Western Interior Seaway, which once flowed through central United States and Canada, connecting the Arctic Ocean to the Gulf of Mexico, being shallow for a seaway. A full faunal turnover when *M. missouriensis* and *M. conodon* appear 79.5 million years ago suggests that this genus has a lasting effect in this area. This faunal assemblage is generally more diverse than other bodies of water before *Mosasaurus* appears during the Niobraran Age. The assemblage includes *Clidastes*, *Tylosaurus*, *Globidens*, *Halisaurus* and *Platecarpus* as key species that vanished upon *Mosasaurus* colonization. However, taxa such as *Tylosaurus*, *Cretoxyrhina* (another key species), hesperornithids, *Terminotator* and *Dolichorhynchops* persist until the uppermost Campanoan, which the seaway began to recede northwards. Other taxa include *Protostega*. *Archelon*, *Baptornis*, *Ichthyornis*, *Halimornis*, *Cretalamna*, *Squalicorax*, *Pseudocorax*, *Serratolamna*, *Scapanorhynchus*, *Odontaspis* *Ischyrhiza*. *Enchodus*, *Protosphyraena*, *Stratodus*, *Xiphactinus* and *Saurodon*. It was one of the most dominant faunal elements in the Western Interior Seaway until the rear of the Navesinkan Age near the terminal Cretaceous.

It was a large apex predator that was a contemporary of tylosaurines and *Prognathodon* sensu lato, and all survived on similar prey items. Schulp et al. (2013) tested *P. saturator* and *M. hoffmannii* using δ13C analysis to find the degree of contemporeity. Though similar, the results show that their levels differed in the Maastricht Formation and there was some convergence and niche partitioning through different foraging areas and diets. The teeth of *M. hoffmannii* are somewhat adapted for turtles, but better towards a wide range of prey; whereas the other was specialized to robust prey like turtles. Konishi et al. (2014) report similar niche partitioning through dietary divide in the Bearpaw Formation, *M. hoffmannii* and *"P." overtoni*, in preserved stomach contents. The latter preserves turtles and ammonites, robust prey, and the former with fish, softer prey. However, evidence of interspecific combat amongst species suggests that competition did take place. One subadult *M. hoffmannii* with fractures caused by one large blow to the neurocranium was argued by Lingham-Soliar (1998) to have been from a ramming attack by *Tylosaurus bernardi*; the pathology bears traits similar to concentrated blows and such lines up with its robust yet angular, elongate snout. This is seen in bottlenose dolphins when warding away/killing lemon sharks: therefore, this *Tylosaurus* may have ambushed the *M. hoffmannii*.

## Species

* *M. hoffmannii*
* *M. beaugei*
* *M. conodon*
* *M. lemonnieri*
* *M. missouriensis*
* *M.* sp. nov. Pembina Gorge?

Pending assessment:

* *M. glycys*?
* *M. hobetsuensis*?
* *M. mokoroa*?
* *M. prismaticus*?

### Reassigned Species

* *"M." flemingi*
* *"M." gigantea*
* *"M." johnsoni*?
* *"M." nigeriensis*
* *"M." gaudryi*
* *M. poultneyi* (=dubious)
* *M. iguanavus* (=dubious)
* *M. neovidii* (=*M. missouriensis*)
* *"M." copeanus*

## Synonyms

* *Batrachiosaurus*
* *Batrachotherium*
* *Drepanodon*
* *Baseodon*
* *Nectoportheus*
* *Pterycollosaurus*
* *Capelliniosuchus*

## Gallery

**Credit: Mark Witton.***M. sp.* skull restored by Triebold Paleontology Inc..
## References

1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 https://en.wikipedia.org/wiki/Mosasaurus

	* https://escholarship.org/uc/item/8v08w2d6
	* https://twitter.com/boydpaleo/status/1428506685920907265
	* https://www.aaps-journal.org/pdf/JPS.C.22.0001.pdf
3. ↑ https://twitter.com/boydpaleo/status/1486500763190927363
4. ↑ https://twitter.com/boydpaleo/status/1488217764951212035
5. ↑ https://www.dmr.nd.gov/dmr/paleontology/fossil-digs/2022-public-fossil-dig-pembina-gorge
6. ↑ https://www.dmr.nd.gov/ndgs/documents/newsletter/2017Winter/A%20New%20Addition%20to%20the%20Cretaceous%20Seaway%20of%20North%20Dakota.pdf
7. ↑ https://twitter.com/CofCNatHistory/status/1531298747690500096
8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 8.6 8.7 Cope CD. 1869. On the reptilian orders, Pythonomorpha and Streptosauria. Proceedings of the Boston Society of Natural History 12: 250–266.