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Mosasaurus

Mosasaurus is the type genus of the Mosasauridae, an extinct group of aquatic squamate reptiles. It lived from about 82 to 66 million years ago during the Campanian and Maastrichtian stages of the Late Cretaceous. The genus was one of the first Mesozoic marine reptiles known to science—the first fossils of Mosasaurus were found as skulls in a chalk quarry near the Dutch city of Maastricht in the late 18th century, and were initially thought to be crocodiles or whales. One skull discovered around 1780 was famously nicknamed the "great animal of Maastricht". In 1808, naturalist Georges Cuvier concluded that it belonged to a giant marine lizard with similarities to monitor lizards but otherwise unlike any known living animal. This concept was revolutionary at the time and helped support the then-developing ideas of extinction. Cuvier did not designate a scientific name for the animal; this was done by William Daniel Conybeare in 1822 when he named it Mosasaurus in reference to its origin in fossil deposits near the Meuse River. The exact affinities of Mosasaurus as a squamate remain controversial, and scientists continue to debate whether its closest living relatives are monitor lizards or snakes.

Research history
Discovery and identification The first Mosasaurus fossil known to science was discovered in 1764 in a chalk quarry near Maastricht in the Netherlands in the form of a skull, which was initially identified as a whale. This specimen, cataloged as TM 7424, is now on display at the Teylers Museum in Haarlem. This caught the attention of French revolutionaries, who looted the fossil following the siege of Maastricht during the French Revolutionary Wars in 1794. After its seizure, the specimen was sent to the National Museum of Natural History, France in 1795 and later numbered as MNHN AC 9648. This story helped elevate the fossil into cultural fame, but historians agree that the narrative was exaggerated. By 1800, Camper's son Adriaan Gilles Camper concluded that the second skull, which by then was nicknamed the "great animal of Maastricht", belonged to a marine reptile sharing affinities to monitor lizards. This interpretation was confirmed by Georges Cuvier in a more detailed study published in 1808, in which he nevertheless established that it represented an extinct form not corresponding to any known living saurian. The skull became part of Cuvier's first speculations about the conception of extinction, which later led to his theory of catastrophism, a precursor to the theory of evolution. At the time, it was not believed that a species could go extinct, and fossils of animals were often interpreted as some form of an extant species. Cuvier's idea that there existed an animal unlike any today was revolutionary at the time, and in 1812 he proclaimed: In a 1822 book by James Parkinson, William Daniel Conybeare coined the genus Mosasaurus from the Latin Mosa "Meuse" and the Ancient Greek σαῦρος (saûros, "lizard"), in reference to the river near which the fossils were discovered. Later, the second skull is designated as the new species' holotype (defining example). Richard Ellis speculated in 2003 that this may have been the earliest discovery of the second species M. missouriensis, although competing speculations exist. In 1818, a fossil from Monmouth County, New Jersey became the first North American specimen to be correctly recognized as a Mosasaurus by scientists of the time. The type specimen of M. missouriensis was first described in 1834 by Richard Harlan based on a snout fragment found near the river's Big Bend, in South Dakota. but later as an amphibian named Batrachiosaurus. The rest of the skull had been discovered earlier by a fur-trapper, and it eventually came under the possession of prince Maximilian of Weid-Neuwied between 1832 and 1834. The fossil skull, now cataloged as RFWUIP 1327, The same year, Christian Erich Hermann von Meyer suspected that the skull and Harlan's snout were part of the same individual. Although the snout was noted as lost at the time, which has since entered common use. In 1966, Donald Baird and Gerard R. Case reidentified it as a species of Mosasaurus. Although Cope did not provide the etymology for the specific epithet conodon, it is suggested that it could be a portmanteau meaning "conical tooth", derived from the Ancient Greek κῶνος (kônos, "cone") and ὀδών (odṓn, "tooth"), probably in reference to conical surface teeth smooth of the species. {{multiple image M. lemonnieri was first described in 1889 by Louis Dollo on the basis of a relatively complete skull discovered in a quarry owned by the Solvay S.A. company in the Ciply Basin of Belgium. This skull, since numbered as IRSNB R28, In 1967, Dale Russell argued that M. lemonnieri and M. conodon are the same species and designated the former as a junior synonym per the principle of priority. However, the need for more research to confirm any hypotheses of synonymy was expressed. M. beaugei was first described by Camille Arambourg in 1952 from isolated teeth originating from phosphate deposits in the Oulad Abdoun Basin and the Ganntour Basin in Morocco, the holotype tooth being cataloged as MNHN PMC 7. Early depictions Scientists during the early and mid-1800s initially imagined Mosasaurus as an amphibious marine reptile with webbed feet and limbs for walking. This was based on fossils like the M. missouriensis holotype, which indicated an elastic vertebral column that Goldfuss in 1845 saw as evidence of an ability to walk and interpretations of some phalanges as claws. One of the earliest depictions of Mosasaurus in paleoart is a life-size concrete sculpture created by Benjamin Waterhouse Hawkins between 1852 and 1854 as part of the collection of sculptures of prehistoric animals on display at the Crystal Palace Park in London. The restoration was primarily informed by Richard Owen's interpretation of the M. hoffmannii holotype and the anatomy of monitor lizards, so Hawkins depicted the animal as essentially a water-going monitor lizard. It was given a boxy head, nostrils at the side of the skull, large volumes of soft tissue around the eyes, lips reminiscent of monitor lizards, scales consistent with those in large monitors like the Komodo dragon, and a flipper. The model was deliberately sculpted incomplete, which Mark Witton believed was likely to save time and money. Many elements of the sculpture can be considered inaccurate, even for the time. It did not take into account Golduss' 1845 study of M. missouriensis which instead called for a narrower skull, nostrils at the top of the skull, and amphibious terrestrial limbs (the latter being incorrect in modern standards). ==Description==
Description
of M. hoffmannii Mosasaurus was a type of derived mosasaur, or a latecoming member with advanced evolutionary traits such as a fully aquatic lifestyle. As such, it had a streamlined body, an elongated tail ending with a downturn supporting a two-lobed fin, and two pairs of flippers. While in the past derived mosasaurs were depicted as akin to giant flippered sea snakes, it is now understood that they were more similar in build to other large marine vertebrates such as ichthyosaurs, marine crocodylomorphs, and archaeocete whales through convergent evolution. Based on this ratio, Grigoriev (2014) used the largest lower jaw attributed to M. hoffmannii (CCMGE 10/2469, also known as the Penza specimen; measuring in length) to estimate a maximum length of . Using a smaller partial jaw (NHMM 009002) measuring and "reliably estimated at" when complete, Lingham-Soliar (1995) estimated a larger maximum length of via the same ratio. No explicit justification for the 1:10 ratio was provided in Russell (1967), and it has been considered to be probably overestimated by Cleary et al. (2018). In 2014, Federico Fanti and colleagues alternatively argued that the total length of M. hoffmannii was more likely closer to seven times the length of the skull, which was based on a near-complete skeleton of the related species Prognathodon overtoni. The study estimated that an M. hoffmannii individual with a skull measuring more than would have been up to or more than in length and weighed in body mass. Using the same ratio, Gayford et al. (2024) calculated the total length for the Penza specimen to be . The skull of Mosasaurus is conical and tapers off to a short snout which extends a little beyond the frontmost teeth. The trachea likely stretched from the esophagus to below the back end of the lower jaw's coronoid process, where it split into smaller pairs of bronchi which extended parallel to each other. Mosasaurus teeth are large and robust except for those in M. conodon and M. lemonnieri, which instead have more slender teeth. while in M. conodon and M. lemonnieri serrations do not exist. The number of teeth in the maxillae, pterygoids, and dentaries vary between species and sometimes even individualsM. hoffmannii had fourteen to sixteen maxillary teeth, fourteen to fifteen dentary teeth, and eight pterygoid teeth; M. conodon had fourteen to fifteen maxillary teeth, sixteen to seventeen dentary teeth, and eight pterygoid teeth; Chemical studies conducted on a M. hoffmannii maxillary tooth measured an average rate of deposition of odontoblasts, the cells responsible for the formation of dentin, at per day. This was by observing the von Ebner lines, incremental marks in dentin that form daily. It was approximated that it took the odontoblasts 511 days and dentin 233 days to develop to the extent observed in the tooth. Postcranial skeleton in Lyon, France The tail structure of Mosasaurus is similar to relatives like Prognathodon, in which soft tissue evidence for a two-lobed tail is known. The tail vertebrae gradually shorten around the center of the tail and lengthen behind the center, suggesting rigidness around the tail center and excellent flexibility behind it. Like most advanced mosasaurs, the tail bends slightly downwards as it approached the center, but this bend is offset from the dorsal plane at a small degree. Mosasaurus also has large haemal arches located at the bottom of each caudal vertebra which bend near the middle of the tail, which contrasts with the reduction of haemal arches in other marine reptiles such as ichthyosaurs. These and other features support a large and powerful paddle-like fluke in Mosasaurus. The forelimbs of Mosasaurus are wide and robust. The scapula and humerus are fan-shaped and wider than tall. The radius and ulna are short, but the former is taller and larger than the latter. The ilium is rod-like and slender; in M. missouriensis, it is around 1.5 times longer than the femur. The femur itself is about twice as long as it is wide and ends at the distal side in a pair of distinct articular facets (of which one connects to the ilium and the other to the paddle bones) that meet at an angle of approximately 120°. Five sets of metacarpals and phalanges (finger bones) were encased in and supported the paddles, with the fifth set being shorter and offset from the rest. The overall structure of the paddle is compressed, similar to in Plotosaurus, and was well-suited for faster swimming. In the hindlimbs, the paddle is supported by four sets of digits. Image:Mosasaurus hoffmanni.png|center|700px poly 1828 572 1560 604 1392 688 1396 772 1408 824 1476 832 1500 864 1576 900 1800 840 1980 816 2056 780 2156 744 2236 704 2200 692 2208 664 2192 616 2152 604 2180 516 2140 500 1900 556 Cervical vertebrae poly 2328 464 2828 344 3100 308 3588 316 4368 384 5424 492 5980 520 5932 640 5964 676 5944 748 5576 736 4620 648 3620 536 3156 528 2580 624 2220 720 2200 700 2216 664 2184 608 2152 592 2188 512 2192 492 Dorsal vertebrae poly 84 920 80 836 396 732 736 648 1120 576 1332 572 1424 652 1416 720 1404 776 1408 828 1472 828 1492 852 1484 892 1104 1112 1024 1120 884 1088 628 1092 140 1036 64 1020 64 992 84 940 Skull poly 2568 1408 2596 1408 2604 1464 2656 1432 2688 1488 2676 1548 2648 1584 2516 1600 2504 1584 2532 1552 2504 1524 2460 1504 2500 1488 2524 1440 2532 1412 Humerus poly 2540 1640 2508 1604 2616 1588 2636 1584 2644 1612 2620 1648 2656 1668 2648 1700 2536 1744 2496 1716 2484 1668 Radius poly 2716 1510 2730 1508 2746 1574 2776 1592 2784 1618 2716 1662 2674 1670 2680 1628 2666 1608 2638 1602 2630 1584 2656 1566 2678 1546 2686 1514 2692 1504 Ulna poly 2808 1578 2772 1604 2780 1628 2714 1658 2652 1690 2644 1712 2534 1750 2558 1800 2598 1804 2656 1790 2670 1796 2754 1782 2832 1738 2842 1724 2812 1664 2804 1634 2830 1618 2838 1578 2808 1562 Carpal bones poly 2576 1828 2596 1886 2680 1862 2694 1876 2746 1848 2760 1874 2846 1826 2888 1788 2856 1764 2852 1732 2886 1732 2908 1684 2890 1656 2826 1680 2842 1728 2822 1742 2752 1782 2700 1790 2654 1802 2636 1792 2562 1810 Metacarpal bones poly 2594 1402 2594 1364 2794 1230 2826 1166 2784 1088 2680 984 2538 944 2416 966 2292 1070 2238 1218 2232 1386 2274 1432 2400 1404 2444 1402 2466 1440 2500 1424 2514 1442 2530 1406 Scapula poly 2612 1900 2682 2026 2816 2128 2970 2222 3096 2234 3186 2212 3248 2174 3212 2124 3020 1938 2914 1814 2912 1748 2968 1768 3024 1812 3046 1814 3034 1786 2956 1698 2906 1672 2900 1702 2890 1734 2852 1732 2856 1762 2894 1790 2848 1824 2758 1872 2746 1846 2696 1876 2682 1862 2598 1890 Phalanges poly 2054 1510 2060 1538 2164 1596 2394 1658 2478 1650 2528 1632 2502 1600 2516 1600 2500 1580 2522 1552 2496 1520 2448 1498 2506 1486 2518 1442 2492 1428 2424 1458 2266 1448 2148 1442 2070 1458 2040 1502 Coracoid poly 3540 1328 3428 1504 3300 1672 2940 1656 2884 1648 2812 1676 2804 1648 2844 1628 2844 1576 2808 1548 2768 1584 2736 1556 2724 1496 2684 1500 2648 1424 2624 1412 2632 1336 2796 1240 2816 1164 2776 1056 2692 976 2544 940 2408 964 2304 804 2212 712 2460 660 2776 584 3160 524 3356 520 3432 600 3560 996 Rib cage poly 3324 1682 3304 1712 2972 1720 2954 1688 2908 1670 3082 1662 3316 1660 Sternum poly 5976 816 5984 864 6028 930 6054 956 6060 1000 6082 1006 6086 982 6144 974 6128 946 6074 910 5998 804 5974 798 Ilium poly 6002 1032 6022 1014 6058 986 6086 1010 6094 1060 6076 1122 6072 1172 6060 1202 6024 1182 6032 1096 6010 1072 5984 1064 5976 1046 Pubis poly 6172 1006 6198 1026 6192 1076 6234 1132 6220 1136 6192 1098 6182 1078 6148 1070 6138 1046 6156 1018 6156 996 Ischium poly 6116 1140 6080 1138 6076 1116 6082 1076 6092 1058 6084 1010 6082 992 6110 974 6152 982 6158 1002 6154 1022 6138 1050 6150 1072 6186 1082 6190 1104 6168 1116 6172 1138 Femur poly 6128 1268 6072 1262 6058 1228 6070 1206 6072 1176 6090 1134 6162 1138 6166 1160 6166 1194 6202 1218 6164 1270 6150 1262 Tibia poly 6260 1186 6272 1154 6256 1140 6228 1148 6200 1106 6180 1108 6162 1128 6166 1148 6198 1164 6210 1202 6240 1200 Fibula poly 6286 1154 6312 1168 6308 1214 6336 1250 6286 1272 6252 1254 6220 1288 6166 1288 6154 1272 6198 1224 6248 1192 6276 1160 Tarsals poly 6088 1308 6112 1362 6194 1352 6190 1392 6252 1374 6260 1356 6316 1334 6366 1300 6332 1242 6368 1222 6388 1172 6348 1158 6310 1170 6310 1208 6330 1242 6290 1266 6258 1258 6226 1280 6174 1280 6154 1262 6094 1264 6074 1286 Metatarsal bones poly 6512 1260 6436 1210 6362 1214 6328 1248 6364 1300 6320 1332 6262 1348 6250 1368 6182 1398 6186 1348 6102 1370 6102 1398 6162 1488 6236 1560 6336 1636 6476 1676 6582 1684 6660 1664 6716 1628 6686 1562 6542 1480 6434 1386 6378 1324 6370 1238 6452 1260 6512 1282 Phalanges poly 7360 564 8488 568 9036 548 9448 612 9948 804 10480 1000 11016 1148 11292 1188 11288 1260 11052 1268 10672 1220 10152 1124 9620 968 9016 788 8856 772 8540 816 7616 840 7056 816 7060 748 7080 660 7100 556 Caudal vertebrae poly 11116 1296 10764 1336 10260 1336 9888 1284 9404 1112 9100 956 9052 928 8968 808 8888 772 9024 784 9480 924 10176 1128 10744 1236 11076 1268 11240 1264 Haemal arches poly 6308 536 7092 552 7080 684 7076 752 7056 808 6652 808 5940 800 5936 740 5964 684 5932 632 5980 520 6112 524 Pygal vertebrae Interactive skeletal reconstruction of M. hoffmannii (hover over or click on each skeletal component to identify the structure) ==Classification==
Classification
History of taxonomy Because nomenclatural rules were not well-defined at the time, 19th century scientists did not give Mosasaurus a proper diagnosis during its initial descriptions, which led to ambiguity in how the genus is defined. This led Mosasaurus to become a wastebasket taxon containing as many as fifty different species. A 2017 study by Hallie Street and Michael Caldwell performed the first proper diagnosis and description of the M. hoffmannii holotype, which allowed a major taxonomic cleanup confirming five species as likely validM. hoffmannii, M. missouriensis, M. conodon, M. lemonnieri, and M. beaugei. The study also held four additional species from Pacific depositsM. mokoroa, M. hobetsuensis, M. flemingi, and M. prismaticusto be possibly valid, pending a future formal reassessment. Systematics and evolution As the type genus of the family Mosasauridae and the subfamily Mosasaurinae, Mosasaurus is a member of the order Squamata (which comprises lizards and snakes). Relationships between mosasaurs and living squamates remain controversial as scientists still fiercely debate on whether the closest living relatives of mosasaurs are monitor lizards or snakes. Mosasaurus, along with mosasaur genera Eremiasaurus, Plotosaurus, and Moanasaurus traditionally form a tribe within the Mosasaurinae variously called Mosasaurini or Plotosaurini. He proposed that Mosasaurus evolved from a Clidastes-like mosasaur, and diverged into two lineages, one giving rise to M. conodon and another siring a chronospecies sequence which contained in order of succession M. ivoensis, M. missouriensis, and M. maximus-hoffmanni. with at least one study also recovering M. missouriensis to be the most basal species of the genus instead of M. conodon. In 2014, Konishi and colleagues expressed a number of concerns with the reliance on Bell's study. First, the genus was severely underrepresented by incorporating only the three North American species M. hoffmannii/M. maximus, M. missouriensis, and M. conodon; by doing so, others like M. lemonnieri, which is one of the most completely known species in the genus, were neglected, which affected phylogenetic results. Second, the studies relied on an unclean and shaky taxonomy of the Mosasaurus genus due to the lack of a clear holotype diagnosis, which may have been behind the genus's paraphyletic status. However, the study used a method unorthodox to traditional phylogenetic studies on mosasaur species because its focus was on the relationships of entire squamate groups rather than mosasaur classification. As a result, some paleontologists caution that lower-order classification results from Conrad's 2008 study such as the specific placement of Mosasaurus may contain technical problems, making them inaccurate. The following cladogram on the left (Topology A) is modified from a maximum clade credibility tree inferred by a Bayesian analysis in the most recent major phylogenetic analysis of the Mosasaurinae subfamily by Madzia & Cau (2017), which was self-described as a refinement of a larger study by Simões et al. (2017). The cladogram on the right (Topology B) is modified from Street's 2016 doctoral thesis proposing a revision to the Mosasaurinae, with proposed new taxa and renamings in single quotations. Positions of groups Positions of individual taxa }} }} ==Paleobiology==
Paleobiology
Head musculature and mechanics In 1995, Lingham-Soliar studied the head musculature of M. hoffmannii. Because soft tissue like muscles do not easily fossilize, reconstruction of the musculature was largely based on the structure of the skull, muscle scarring on the skull, and the musculature in extant monitor lizards. Rather, M. hoffmannii likely employed inertial feeding (in which the animal thrusts its head and neck backward to release a held prey item and immediately thrust the head and neck forward to close the jaws around the item) and used jaw adduction to assist in biting during prey seizure. The magnus adductor muscles, which attach to the lower jaws to the cranium and have a major role in biting function, are massive, indicating M. hoffmannii was capable of enormous bite forces. The long, narrow, and heavy nature of the lower jaws and attachment of tendons at the coronoid process would have allowed quick opening and closing of the mouth with little energy input underwater, which also contributed to the powerful bite force of M. hoffmannii and suggests it would not have needed the strong magnus depressor muscles (jaw-opening muscles) seen in some plesiosaurs. Its elongated paddle-like limbs functioned as hydrofoils for maneuvering the animal. The paddles' steering function was enabled by large muscle attachments from the outwards-facing side of the humerus to the radius and ulna and modified joints allowed an enhanced ability of rotating the flippers. The powerful forces resulting from use of the paddles may have sometimes resulted in bone damage, as evidenced by a M. hoffmannii ilium with significant separation of the bone's head from the rest of the bone likely caused by frequent shearing forces at the articulation joint. Mosasaurus was likely endothermic and maintained a constant body temperature independent of the external environment. Although there is no direct evidence specific to the genus, studies on the biochemistry of related mosasaur genera such as Clidastes suggests that endothermy was likely present in all mosasaurs. Such a trait is unique among squamates, the only known exception being the Argentine black and white tegu, which can maintain partial endothermy. This adaptation would have given several advantages to Mosasaurus, including increased stamina when foraging across larger areas and pursuing prey. It may have also been a factor that allowed Mosasaurus to thrive in the colder climates of locations such as Antarctica. Sensory functions of Mosasaurus Mosasaurus had relatively large eye sockets but alternatively allowed excellent processing of a two-dimensional environment, such as the near-surface waters inhabited by Mosasaurus. Chemical and structural data in the fossils of M. lemonnieri and M. conodon suggests they may have also hunted in deeper waters. Carbon isotope studies on fossils of multiple M. hoffmannii individuals have found extremely low values of δ13C, the lowest in all mosasaurs for the largest individuals. Mosasaurs with lower δ13C values tended to occupy higher trophic levels, and one factor for this was dietary: a diet of prey rich in lipids such as sea turtles and other large marine reptiles can lower δ13C values. M. hoffmannii's low δ13C levels reinforces its likely position as an apex predator. which also appears to be the case with M. missouriensis. Currently, there are only two known examples of a Mosasaurus preserved with stomach contents. The first is a well-preserved partial skeleton of a small M. missouriensis dated about 75 million years old with dismembered and punctured remains of a long fish in its gut. This fish was much longer than the length of the mosasaur's skull, which measured in length, confirming that M. missouriensis consumed prey larger than its head by dismembering and consuming bits at a time. Due to coexistence with other large mosasaurs like Prognathodon, which specialized in robust prey, M. missouriensis likely specialized more on prey best consumed using cutting-adapted teeth in an example of niche partitioning. Mosasaurus may have taught their offspring how to hunt, as supported by a fossil nautiloid Argonautilus catarinae with bite marks from two conspecific mosasaurs, one being from a juvenile and the other being from an adult. Analysis of the tooth marks by a 2004 study by Kauffman concluded that the mosasaurs were either Mosasaurus or Platecarpus. The positioning of both bite marks are at the direction the nautiloid's head would have been facing, indicating it was incapable of escaping and was thus already sick or dead during the attacks; it is possible this phenomenon was from a parent mosasaur teaching its offspring about cephalopods as an alternate source of prey and how to hunt one. An alternate explanation postulates the bite marks as from one individual mosasaur that lightly bit the nautiloid at first, then proceeded to bite again with greater force. However, there are differences in tooth spacing between both bites which indicate different jaw sizes. Behavior and paleopathology Intraspecific combat There is fossil evidence that Mosasaurus engaged in aggressive and lethal combat with others of its kind. One partial skeleton of M. conodon bears multiple cuts, breaks, and punctures on various bones, particularly in the rear portions of the skull and neck, and a tooth from another M. conodon piercing through the quadrate bone. No injuries on the fossil show signs of healing, suggesting that the mosasaur was killed by its attacker by a fatal blow in the skull. Likewise, an M. missouriensis skeleton has a tooth from another M. missouriensis embedded in the lower jaw underneath the eye. In this case, there were signs of healing around the wound, implying survival of the incident. Takuya Konishi suggested an alternative cause of this example being head-biting behavior during courtship as seen in modern lizards. Attacks by another Mosasaurus are a possible cause of physical pathologies in other skulls, but they could have instead arisen from other incidents like attempted biting on hard turtle shells. In 2004, Lingham-Soliar observed that if these injuries were indeed the result of an intraspecific attack, then there is a pattern of them concentrating in the skull region. Modern crocodiles commonly attack each other by grappling an opponent's head using their jaws, and Lingham-Soliar hypothesized that Mosasaurus employed similar head-grappling behavior during intraspecific combat. Many of the fossils with injuries possibly attributable to intraspecific combat are of juvenile or sub-adult Mosasaurus, leading to the possibility that attacks on smaller, weaker individuals may have been more common. However, the attacking mosasaurs of the M. conodon and M. missouriensis specimens were likely similar in size to the victims. Diseases There are some M. hoffmannii jaws with evidence of infectious diseases as a result of physical injuries. Two examples include IRSNB R25 and IRSNB R27, both having fractures and other pathologies in their dentaries. IRSNB R25 preserves a complete fracture near the sixth tooth socket. Extensive amounts of bony callus almost overgrowing the tooth socket are present around the fracture along with various osteolytic cavities, abscess canals, damages to the trigeminal nerve, and inflamed erosions signifying severe bacterial infection. There are two finely ulcerated scratches on the bone callus, which may have developed as part of the healing process. IRSNB R27 has two fractures: one had almost fully healed and the other is an open fracture with nearby teeth broken off as a result. The fracture is covered with a nonunion formation of bony callus with shallow scratch marks and a large pit connected to an abscess canal. Lingham-Soliar described this pit as resembling a tooth mark from a possible attacking mosasaur. Both specimens show signs of deep bacterial infection alongside the fractures; some bacteria may have spread to nearby damaged teeth and caused tooth decay, which may have entered deeper tissue from prior post-traumatic or secondary infections. The dentaries ahead of the fractures in both specimens are in good condition, suggesting that the arteries and trigeminal nerves had not been damaged; if they were, those areas would have necrotized due to lack of blood. The dentaries' condition suggests that the species may have had an efficient process of immobilizing the fracture during healing, which helped prevent damage to vital blood vessels and nerves. This, along with signs of healing, indicates that the fractures were not imminently fatal. In examinations of M. conodon fossils from Alabama and New Jersey and M. lemonnieri fossils from Belgium, Rothschild and Martin in 2005 observed that the condition affected between 3-17% of the vertebrae in the mosasaurs' spines. Life history , Netherlands It is likely that Mosasaurus was viviparous (giving live birth) like most modern mammals today. There is no evidence for live birth in Mosasaurus itself, but it is known in a number of other mosasaurs; examples include a skeleton of a pregnant Carsosaurus, and fossils of newborn Clidastes from pelagic (open ocean) deposits. ==Paleoecology==
Paleoecology
Distribution, ecosystem, and ecological impact |Mosasaurus inhabited the Western Interior Seaway of North America and Mediterranean Tethys of Europe and Africa. Mosasaurus had a transatlantic distribution, with its fossils having been found in marine deposits on both sides of the Atlantic Ocean. These localities include the Midwest and East Coast of the United States, Canada, Europe, Turkey, Russia, the Levant, the African coastline from Morocco to South Africa, Brazil, Argentina, and Antarctica. Multiple oceanic climate zones encompassed the seaways, including tropical, subtropical, temperate, and subpolar climates. The wide range of oceanic climates yielded a large diversity of fauna that coexisted with Mosasaurus. Mediterranean Tethys The Mediterranean Tethys during the Maastrichtian stage was located in what is now Europe, Africa, and the Middle East. In recent studies, the confirmation of paleogeographical affinities extended this range to areas across the Atlantic including Brazil and the East Coast state of New Jersey. It is geographically subdivided into two biogeographic provinces that respectively include the northern and southern Tethyan margins. The two mosasaurs Mosasaurus and Prognathodon appear to have been the dominant taxa, being widespread and ecologically diversified throughout the seaway. as well as bony fish such as Cimolichthys, the saber-toothed herring Enchodus, and the swordfish-like Protosphyraena are represented in the northern Tethyan margin. The southern Tethyan margin was located along the equator between 20°N and 20°S, resulting in warmer tropical climates. Seabeds bordering the cratons in Africa and Arabia and extending to the Levant and Brazil provided vast shallow marine environments. These environments were dominated by mosasaurs and marine side-necked turtles. Of the mosasaurs, Globidens phosphaticus is the characteristic species of the southern province; in the African and Arabian domain, Halisaurus arambourgi and Platecarpus ptychodon Extensive drainage from the neighboring continents, Appalachia and Laramidia, brought in vast amounts of sediment. Together with the formation of a nutrient-rich deepwater mass from the mixing of continental freshwater, Arctic waters from the north, and warmer saline Tethyan waters from the south, this created a warm and productive seaway that supported a rich diversity of marine life. The biogeography of the region has been subdivided into two Interior Subprovinces characterized by different climates and faunal structures, and their borders are separated in modern-day Kansas. The oceanic climate of the Northern Interior Subprovince was likely a cool temperate one, while the Southern Interior Subprovince had warm temperate to subtropical climates. The faunal structure of both provinces was generally much more diverse prior to the appearance of Mosasaurus, during a faunal stage known as the Niobraran Age, than it was during the following Navesinkan Age. In what is now Alabama within the Southern Interior Subprovince, most of the key genera including sharks like Cretoxyrhina and the mosasaurs Clidastes, Tylosaurus, Globidens, Halisaurus, and Platecarpus disappeared and were replaced by Mosasaurus. During the Navesinkan Age, Mosasaurus dominated the whole region, accounting for around two-thirds of all mosasaur diversity with Plioplatecarpus and Prognathodon sharing the remaining third. The Northern Interior Subprovince also saw a restructuring of mosasaur assemblages, characterized by the disappearance of mosasaurs like Platecarpus and their replacement by Mosasaurus and Plioplatecarpus. Cretoxyrhina, hesperornithids, and plesiosaurs including elasmosaurs such as Terminonatator and polycotylids like Dolichorhynchops maintained their presence until around the end of the Campanian, during which the entire Western Interior Seaway started receding from the north. many species of sea birds including Baptornis, Antarctica |Mosasaurus fossils were found in the Seymour Island of Antarctica, which once provided cool temperate waters. Mosasaurus is known from late Maastrichtian deposits in the Antarctic Peninsula, specifically the López de Bertodano Formation in Seymour Island. Mosasaurus appears to be the most diverse mosasaur in the Maastrichtian Antarctica. At least two species of Mosasaurus have been described, but the true number of species is unknown as remains are often fragmentary and specimens are described in open nomenclature. These species include one comparable with M. lemonnieri, and another that appears to be closely related to M. hoffmannii. Prognathodon and Globidens are also expected to be present based on distribution trends of both genera, although conclusive fossils have yet to be found. The fish assemblage of the López de Bertodano Formation was dominated by Enchodus and ichthyodectiformes. Habitat preference Known fossils of Mosasaurus have typically been recovered from deposits representing nearshore habitats during the Cretaceous period, with some fossils coming from deeper-water deposits. Lingham-Soliar (1995) elaborated on this, finding that Maastrichtian deposits in the Netherlands with M. hoffmannii occurrences represented nearshore waters around deep. Changing temperatures and an abundance in marine life were characteristic of these localities. The morphological build of M. hoffmannii, nevertheless, was best adapted for a pelagic surface lifestyle. while the largest coexisting species of Prognathodon like P. saturator exceeded . ==Extinction==
Extinction
|Mosasaurus went extinct as a result of the K-Pg extinction event; its last fossils were found at or close to the boundary, which is represented by the thick dark band separating the lighter and darker layers of this cliff. By the end of the Cretaceous, mosasaurs were at the height of their evolutionary radiation, and their extinction was a sudden event. The last fossils of Mosasaurus, which include those of M. hoffmannii and indeterminate species, occur up to the Cretaceous-Paleogene boundary (K-Pg boundary). The demise of the genus was likely a result of the Cretaceous-Paleogene extinction event which also wiped out the non-avian dinosaurs. Mosasaurus fossils have been found less than below the boundary in the Maastricht Formation, the Davutlar Formation in Turkey, the Jagüel Formation in Argentina, Stevns Klint in Denmark, Seymour Island, and Missouri. M. hoffmannii fossils have been found within the K-Pg boundary itself in southeastern Missouri between the Paleocene Clayton Formation and Cretaceous Owl Creek Formation. Fossil vertebrae from the layer were found with fractures formed after death. The layer was likely deposited as a tsunamite, alternatively nicknamed the "Cretaceous cocktail deposit". This formed through a combination of catastrophic seismic and geological disturbances, mega-hurricanes, and giant tsunamis caused by the impact of the Chicxulub asteroid that catalyzed the K-Pg extinction event. leading to a collapse of marine food webs. Any Mosasaurus surviving the immediate cataclysms by taking refuge in deeper waters would have died out due to starvation from a loss of prey. One enigmatic occurrence of Mosasaurus sp. fossils is in the Hornerstown Formation, a deposit typically dated to be from the Paleocene Danian age, which was immediately after the Maastrichtian age. The fossils were found in association with fossils of Squalicorax, Enchodus, and various ammonites within a uniquely fossil-rich bed at the base of the Hornerstown Formation known as the Main Fossiliferous Layer. This does not mean Mosasaurus and its associated fauna survived the K-Pg extinction. According to one hypothesis, the fossils may have originated from an earlier Cretaceous deposit and were reworked into the Paleocene formation during its early deposition. Evidence of reworking typically comes from fossils worn down due to further erosion during their exposure at the time of redeposition. Many of the Mosasaurus fossils from the Main Fossiliferous Layer consist of isolated bones commonly abraded and worn, but the layer also yielded better-preserved Mosasaurus remains. Another explanation suggests the Main Fossiliferous Layer is a Maastrichtian time-averaged remanié deposit, which means it originated from a Cretaceous deposit with winnowed low-sediment conditions. A third hypothesis proposes that the layer is a lag deposit of Cretaceous sediments forced out by a strong impact by a tsunami, and what remained was subsequently refilled with Cenozoic fossils. == See also ==
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