Tylosaurus

Possible first finds The earliest Tylosaurus fossils were likely discovered by various Native American peoples and may have been the source of much of their folklore, with the earliest known ones dating back to well before the arrival of European settlers, around the 1500s. More recent accounts from peoples living in the Great Plains even speak of an ancient era ruled by massive aquatic creatures that were in constant combat with thunderbirds and were petrified by them. The considerable presence of fossils of large mosasaurs such as Tylosaurus and pterosaurs such as Pteranodon in this region may have been the origins of these myths. In 1804, the Lewis and Clark Expedition discovered a now-lost fossil skeleton alongside the Missouri River, which was identified as a long fish. In 2003, Richard Ellis speculated that the remains may have belonged to Mosasaurus missouriensis. Alternatively, a 2007 study led by Robert W. Meredith and colleagues suggested that the fossils would possibly come from a tylosaurine mosasaur based on the measurements cited by Clark and Gass and the evidence of Tylosaurus fossils that have been found in the Missouri River. However, the authors also mentioned the possibility that the remains would also come from an elasmosaurid plesiosaur, which are also known from the river, although being rarer. First formal discoveries Tylosaurus was the third new genus of mosasaur to be described from North America behind Clidastes and Platecarpus and the first in Kansas. The early history of the genus as a taxon was subject to complications spurred by the infamous rivalry between American paleontologists Edward Drinker Cope and Othniel Charles Marsh during the Bone Wars. The type specimen was described by Cope in 1869 based on a fragmentary skull measuring nearly in length and thirteen vertebrae lent to him by Louis Agassiz of the Harvard Museum of Comparative Zoology. The fossil, which remains in the same museum under the catalog number MCZ 4374, was recovered from a deposit of the Niobrara Formation located in the vicinity of Monument Rocks near the Union Pacific Railroad at Fort Hays, Kansas. Cope's first publication of the fossil was very brief and was named Macrosaurus proriger, the genus being a preexisting European mosasaur taxon. In 1870, Cope published a more thorough description of MCZ 4374. Without explanation, he moved the species into another European genus Liodon and declared his original Macrosaurus proriger a synonym. Cope responded by arguing that Rhinosaurus was already a preoccupied synonym of Liodon. He disagreed with Marsh's arguments but proposed that in case Marsh was indeed correct, the genus name Rhamphosaurus should be used. Marsh later discovered that the taxon Rhamphosaurus was preoccupied as a genus of lizard named in 1843. As a result, he suggested a move to a newly erected genus named Tylosaurus. This name means "knob lizard" in another reference to the elongated rostrum characteristic of the genus. It is derived from the Latin tylos (knob) and Ancient Greek . Despite coining the new genus, Marsh never formally transferred this Rhinosaurus species to Tylosaurus; this was first done in 1873 by Joseph Leidy. Tylosaurus subsequently became the almost universally accepted genus to include this species, the exception to this adoption being Cope, who refused to accept Marsh's new genus and continued to refer to its species as Liodon. Cope's persistence can be seen in his 1874 description of another species of Tylosaurus, which he named Liodon nepaeolicus. The type specimen of this species was discovered by geologist Benjamin Franklin Mudge near the Solomon River, and consists of several cranial fragments and a dorsal vertebra now catalogued as AMNH 1565. This species, whose specific epithet refers to Nepaholla, the Native American name for the Salomon River Later discoveries and other species In his major work published in 1967, Dale A. Russell recognized only two valid species in Tylosaurus, namely T. proriger and T. nepaeolicus. However, throughout the 19th and 20th centuries, many species of mosasaurs coming from around the world, originally described as being from separate genera, were now recognized as belonging to Tylosaurus. the specimen having since been catalogued as IRSNB R23. In 1896, Armand Thevenin described a new mosasaurid on the basis of a partial skull discovered at Éclusier-Vaux, in Somme, France. In his description, Thevenin thinks that this specimen, since catalogued as MNHN 1896–15, In 1967, Russell elevated the taxon to a separate species within the genus, and assigned to it fossils from the Niobrara Formation of Kansas, including a partial skull. When the taxon was significantly revised in a in 2002 study, being reassigned to Tylosaurus, Lindgren and Mikael Siverson referred additional fossils to this latter that had been discovered at Ivö Klack, including cranial and vertebral remains. In their study, the authors also found that Russell's attributions of the Kansas fossils to this species were erroneous, the remains coming from a distinct taxon. In 1992, Lingham-Soliar argued that the cranial features were not consistent with those of Mosasaurus and were more characteristic of Tylosaurus, the species being renamed as T. iembeensis. However, the author did not identify the holotype skull, which he considered to reside in the collections of the NOVA University Lisbon without a catalogue number, In 2005, Michael J. Everhart described the species T. kansasensis based on several specimens that had been discovered in Kansas, again in the fossil record of the Niobrara Formation. The holotype specimen consists of a well-preserved skull and six cervical vertebrae cataloged as FHSM VP-2295, which was discovered in 1968 in Ellis County. This specimen, nicknamed "Omācīw" (meaning "hunter" in Cree), was discovered in 1994 near Herbert Ferry, at the Lake Diefenbaker, Saskatchewan. Although originally described informally and via incompletely prepared fossils, the proposed taxon was nevertheless recognized as valid in some subsequent studies. The following year, Cope added more details to his visualization of the animal. For him, the head of Tylosaurus would be conical in shape, with eyes on top, and having a jaw connected to a throat similar to that of a pelican, thus facilitating the entry of its prey. Still according to Cope, the animal would have had only the flippers located at the front of the body, those at the back being absent. Thus, this reconstruction depicts the animal as very mobile marine predator with four flippers, a short neck and a much shorter tail than previous depictions, Williston also fixing a maximum body measurement close to those still cited today, i. e. long. ==Description==

Tylosaurus 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. A fragmentary skeleton of another T. proriger from the Sternberg Museum of Natural History (FHSM VP-2496) may be from an even larger individual; Everhart estimated the specimen to come from a individual compared to his estimate for Bunker. The genus exhibits Cope's rule, in which its body size has been observed to generally increase over geologic time. and Coniacian (90-86 mya), which included early T. nepaeolicus and its precursors, typically measured long During the Santonian (86-83 mya), T. nepaeolicus and newly-appearing T. proriger were long By the Early Campanian, T. proriger attained lengths of . Everhart speculated that because mosasaurs continuously grew throughout their lifetime, it would have been possible for some extremely old Tylosaurus individuals to reach in absolute maximum length. However, he stressed the lack of fossil evidence suggesting such sizes and the odds against any being preserved. Other Campanian-Maastrichtian species were similarly large. The most recent maximum estimate for T. bernardi is by Lindgren (2005); historically the species was erroneously estimated at even larger sizes of . A reconstruction of T. saskatchewanensis by the Royal Saskatchewan Museum estimated a total length of over . A mounted skeleton of T. pembinensis, nicknamed "Bruce," at the Canadian Fossil Discovery Centre measures at long and was awarded a Guinness World Records for "Largest mosasaur on display" in 2014. However, the skeleton was assembled for display prior to Bullard and Caldwell (2010)'s reassessment that found the species' number of vertebrae to be exaggerated. T. "borealis" is estimated at in total length. Skull The largest known skull of Tylosaurus is T. proriger KUVP 5033 (the "Bunker" specimen), estimated at long. Depending on age and individual variation, The head was strongly conical and the snout proportionally longer than most mosasaurs, with the exception of Ectenosaurus. Cranium The most recognizable characteristic of Tylosaurus is the elongated edentulous rostrum that protrudes from its snout, for which the genus is named. This is formed by the elongation of the front end of the premaxilla The external nares lead to the choanae (internal nares) in the palate, which provide passage from the nostrils to the throat. In Tylosaurus, they are shaped like a compressed teardrop and bordered by the vomers, palatines, and the maxilla. Anterior to the choanae, each vomer borders the fenestra for the Jacobson's organ, which is involved in the tongue-based sense of smell. It begins opposite of the fourth maxillary tooth in Tylosaurus, and also ends immediately past the fifth maxillary tooth in T. bernardi. The complex anatomy of the bone renders it extremely diagnostic, even to the species level. Tylosaurine dentaries were elongate; the dentary is between 56 and 60% of total length of the entire lower jaw in adult T. nepaeolicus and T. proriger, and 62% in T. saskatchwanensis. The dentary is robust, though not as strongly built as it is in Mosasaurus, Prognathodon, or Plesiotylosaurus. The ventral margin of the dentary ranges from straight A small dorsal ridge appears anterior to the first dentary tooth in mature individuals of T. proriger. while those in T. ivoensis and T. gaudryi appear more optimized for piercing or smashing prey, Carinae (cutting edges) are finely serrated with small denticles The group was originally defined as having slender teeth, Marginal teeth in T. gaudryi are virtually indistinguishable from those in T. ivoensis. The bases of the pterygoid teeth are nearly circular, and each tooth is divided into front and back-facing sides of near-equal surface area via a pair of faint buccal and lingual carinae, except in T. gaudryi, in which the teeth are mediolaterally compressed. Tylosaurus is also distinguished from other mosasaurs by a scapula that is significantly smaller than the coracoid and the absence of the anterior emargination of the coracoid, as well as the absence of a well-developed pubic tubercle. Tylosaurus limbs are primitive relative to other mosasaurs; their stylopodia (humeri and femora) lack both the complex muscle attachment sites and extreme proximodistal shortening present in other derived taxa. Both carpals and tarsals in tylosaurines are mostly unossified; while other mosasaurs typically have between three and five carpals and tarsals, adult Tylosaurus never possess more than two ossified carpal bones (usually only the ulnare, sometimes the ulnare and distal carpal four) and two ossified tarsal bones (usually only the astragalus, sometimes the astragalus and distal tarsal four). Hyperphalangy (increased number of phalanges relative to the ancestral condition) is present in both fore- and hindlimbs, and the phalanges are spindle-shaped, unlike the short, blocky hourglass-shaped phalanges possessed by mosasaurines. The pisiform appears to be either unossified or absent in tylosaurines. The functional consequences of differences in limb anatomy across different mosasaur clades is unclear. Tylosaurus had 29 to 30 presacral vertebrae, 6 to 7 pygal vertebrae, and 89 to 112 caudal vertebrae; due to the lack of a bony articulation between the ilium and vertebral column, it is unclear whether any mosasaurs possessed true sacral vertebrae. Soft tissue Skin and coloration Fossil evidence of the skin of Tylosaurus in the form of scales has been described since the late 1870s. These scales were small and diamond-shaped and were arranged in oblique rows, comparable to that found in modern rattlesnakes and other related reptiles. However, the scales in the mosasaur were much smaller in proportion to the whole body. An individual measuring in total body length had dermal scales measuring , and in each square inch (2.54 cm) of the mosasaur's underside an average of ninety scales were present. Microscopic analysis of scales in a T. nepaeolicus specimen by Lindgren et al. (2014) detected high traces of the pigment eumelanin indicative of a dark coloration similar to the leatherback sea turtle in life. This may have been complemented with countershading, present in many aquatic animals, though the distribution of dark and light pigments in the species remains unknown. A dark-colored form would have provided several evolutionary advantages. Dark coloration increases absorption of heat, allowing the animal to maintain elevated body temperatures in colder environments. Possession of this trait during infancy would in turn facilitate fast growth rates. Unreflective dark coloring and countershading would have provided the mosasaur with increased camouflage. Additional speculative functions includes increased tolerance to solar ultraviolet radiation, strengthened integuments. The study remarked that certain melanism-coding genes are pleiotropic for increased aggression. The pairing is suggestive of two functional lungs like modern limbed lizards but unlike snakes. Similar branching is also found in Platecarpus while in Mosasaurus the organ is dislocated. A bifurcation point's position ahead of the forelimbs would be unlike terrestrial lizards, whose point is within the chest region, but similar to the short trachea and parallel bronchi of whales. ==Classification==

Taxonomy of T. pembinensis Tylosaurus is classified within the family Mosasauridae in the superfamily Mosasauroidea. The genus is the type genus of its own subfamily, the Tylosaurinae. Other members of this group include Taniwhasaurus and possibly Kaikaifilu, and the subfamily is defined by a shared feature of an elongated premaxillary rostrum that does not bear teeth. -aged skull of T. sp. aff. kansasensis (SGM-M1) is one of the oldest known fossils of Tylosaurus. Tylosaurus was among the earliest derived mosasaurs. The oldest fossil attributable to the genus is a premaxilla (TMM 40092-27) recovered from Middle Turonian deposits of the Arcadia Park Shale in Texas, In the Western Interior Seaway, two species—T. nepaeolicus and T. proriger—may represent a chronospecies, in which they make up a single lineage that continuously evolves without branching in a process known as anagenesis. This is evident by how the two species do not stratigraphically overlap, are sister species, share minor and intermediate morphological differences such as a gradual change in the development of the quadrate bone, and lived in the same locations. The means by which this lineage evolved has been hypothesized to be through one of two evolutionary mechanisms related to changes in ontogeny. First, Jiménez-Huidobro, Simões, and Caldwell proposed in 2016 that T. proriger evolved as a paedomorph of T. nepaeolicus, in which the descendant arose as a result of morphological changes through the retention of juvenile features of the ancestor in adulthood. This was based on the presence of a frontal crest and convex borders of the parietal bone of the skull shared in both juvenile T. nepaeolicus and all T. proriger but lost in adult T. nepaeolicus. However, an ontogenetic study by Zietlow (2020) found that it was unclear whether this observation was a result of paedomorphosis, although this uncertainty may have been due that the sample size of mature T. nepaeolicus was too low to determine statistical significance. Second, the same study proposed an alternative hypothesis of peramorphosis, in which T. proriger evolved by developing traits found in mature T. nepaeolicus during immaturity. Based on results from a cladistical ontogram developed using data from 74 Tylosaurus specimens, the study identified a multitude of traits that were present in all T. proriger and mature T. nepaeolicus but absent in juvenile T. nepaeolicus: the skull size and depth are large, the length of the elongated rostrum exceeds 5% of the total skull length, the quadrate suprastapedial processes are thick, the overall quadrate shape converges, and the posteroventral process is fan-like. The following cladogram is modified from a phylogenetic analysis by Jiménez-Huidobro & Caldwell (2019) using Tylosaurus species with sufficiently known material to model accurate relationships; T. gaudryi, T. ivoensis, and T. iembeensis were excluded from the analysis due to extensive missing data (i.e., lack of material with scoreable phylogenetic characters). }} == Paleobiology ==

Function of edentulous rostrum s of a Taniwhasaurus skull, with the ophthalmic nerve (ramus ophthalmicus) in red Russell (1967) first speculated the elongated rostrum was used to "stun" prey or defend against sharks, though provided no further explanation. This combat hypothesis was further elaborated in Lingham-Soliar's (1992) review of Tylosaurus biomechanics. He observed that the internarial bar was unusually robust for a mosasaur, and sutured to the frontal with deep interdigitations such that there is a large interfacial shear area. This probably allowed for greater resistance to bending, shearing, and breaking forces though more effective shock absorption and stress transfer from a blunt force to the rostrum. and orcas to attack prey. Lingham-Soliar (1998) would later suggest possible evidence of a ram-attack in action in the skull of a subadult Mosasaurus whose braincase was fractured in life by a concentrated force, which he argued was rammed by a T. bernardi due to lack of damage elsewhere in the skull that would indicate other causes of injury. This pattern was later found in preliminary CT scans of a T. nepaeolicus skull by Paulina-Carabajal et al. (2023), which similarly observed profuse branching of the ophthalmic nerve inside the premaxilla exiting through many foramina on the dorsal tip of the rostrum. The high concentration of sensory nerves within the edentulous portion of the rostrum suggests that it housed a mechanosensory or electrosensory organ. Similar adaptations were previously found in plesiosaurs and ichthyosaurs. Several insights have been made nonetheless. Mosasaurs like Tylosaurus likely gave birth to live young. The youngest known Tylosaurus individual (FHSM VP-14845) is a newborn (neonate) estimated to have measured in skull length and in total length, about 17.2% the size of Bunker and 24.8–27.9% of the estimated maximum lengths for T. nepaeolicus. The premaxilla of this specimen lacked an edentulous elongation of the rostrum; this trait already appears in juvenile specimens only slightly larger than FHSM VP-14845, including T. nepaeolicus and T. proriger specimens with estimated skull lengths of and respectively. Metabolism Nearly all squamates are characterized by their cold-blooded ectothermic metabolism, but mosasaurs like Tylosaurus are unique in that they were likely endothermic, or warm-blooded. The only other known lizard with such a trait is the Argentine black and white tegu, though only partially. Endothermy in Tylosaurus was demonstrated in a 2016 study by Harrell, Pérez‐Huerta, and Suarez by examining δ18O isotopes in Tylosaurus bones. δ18O levels can be used to calculate the internal body temperature of animals, and by comparing such calculated temperatures between coexisting cold-blooded and warm-blooded animals, the type of metabolism can be inferred. The study used the body temperatures of the cold-blooded fish Enchodus and sea turtle Toxochelys (correlated with ocean temperatures) and warm-blooded seabird Ichthyornis from the Mooreville Chalk as a proxy. Analyzing the isotope levels of eleven Tylosaurus specimens an average internal body temperature of was calculated. This was much higher than the body temperature of Enchodus and Toxochelys ( and respectively) and similar to that of Ichthyornis (). Harrell, Pérez‐Huerta, and Suarez also calculated the body temperatures of Platecarpus and Clidastes with similar numbers, and respectively. The fact that the other mosasaurs were much smaller in size than Tylosaurus and yet maintained similar body temperatures made it unlikely that Tylosauruss body temperature was the result of another metabolic type like gigantothermy. Endothermy would have provided several advantages to Tylosaurus such as increased stamina for foraging larger areas and pursuing prey, the ability to access colder waters, and better adaptation to withstand the gradual cooling of global temperatures during the Late Cretaceous. This is corroborated by a statistical reconstruction of the tail fin by Song and Lindgren (2025), which predicted an outline resembling those in carangiform sharks. A BS thesis by Jesse Carpenter published in 2017 examined the vertebral mobility of T. proriger spinal columns and found that the dorsal vertebrae were relatively rigid but the cervical, pygal, and caudal vertebrae were more liberal in movement, indicating flexibility in the neck, hip, and tail regions. This contrasted with more derived mosasaurs like Plotosaurus, whose vertebral column was stiff up to the hip. Interestingly, an examination of a juvenile T. proriger found that its cervical and dorsal vertebrae were much stiffer than those in adult specimens. This may have been an evolutionary adaptation among young individuals; a more rigid tail-based locomotion is associated with faster speed, and this would allow vulnerable juveniles to better escape predators or catch prey. Older individuals would see their spine grow in flexibility as predator evasion becomes less important for survival. Feeding One of the largest marine carnivores of its time, Tylosaurus was an apex predator that exploited the wide variety of species in the marine fauna of its ecosystem. Stomach contents are well documented in the genus, which includes other mosasaurs, plesiosaurs, turtles, birds, bony fish, and sharks. Additional evidence from bite marks suggests the animal also preyed on giant squid and ammonites. The enormous and varied appetite of Tylosaurus can be demonstrated in a 1987 find that identified fossils of a mosasaur measuring or longer, the diving bird Hesperornis, a Bananogmius fish, and possibly a shark all within the stomach of a single T. proriger skeleton (SDSM 10439) recovered from the Pierre Shale of South Dakota. Other records of stomach contents include a sea turtle in a T. bernardi-like species, Puncture marks on fossils of ammonites, Garvey (2020) criticized the lack of conclusive evidence to support this hypothesis and ruled out T. proriger as a possible culprit, given that the species did not appear until the Santonian and is exclusive to the Western Interior Seaway. Social behavior The behavior of Tylosaurus towards each other may have been mostly aggressive, evidenced by fossils with injuries inflicted by another of their own kind. Such remains were frequently reported by fossil hunters during the late 19th and early 20th centuries, but few examples reside as specimens in scientific collections. Many of these fossils consist of healed bite marks and wounds that are concentrated around or near the head region, implying that there were the result of non-lethal interaction, but the motives of such contact remain speculative. In 1993, Bruce M. Rothschild and Larry D. Martin noted that some modern lizards affectionately bite their mate's head during courtship, which can sometimes result in injuries. Alternatively, they also observed that some males lizards also employ head-biting as territorial behavior against rivals in a show of dominance by grappling the head to turn over the other on its back. It is possible that Tylosaurus behaved in similar ways. Carlsen (2017) posited that Tylosaurus gained avascular necrosis because it lacked the necessary adaptations for deep or repetitive diving, although noted that the genus had well-developed eardrums that could protect themselves from rapid changes in pressure. Unnatural fusion of some vertebrae in the tail has been reported in some Tylosaurus skeletons. A variation of these fusions may concentrate near the end of the tail to form a single mass of multiple fused vertebrae called a "club tail." Rothschild and Everhart (2015) surveyed 23 North American Tylosaurus skeletons and one T. bernardi skeleton and found that five of the North American skeletons exhibited fused tail vertebrae. The condition was not found in T. bernardi, but this does not rule out its presence due to the low sample size. Vertebral fusion occurs when the bones remodel themselves after damage from trauma or disease. However, the cause of such events can vary between individuals and/or remain hypothetical. One juvenile specimen with the club tail condition was found with a shark tooth embedded in the fusion, which confirms that at least some cases were caused by infections inflicted by predator attacks. The majority of vertebral fusion cases in Tylosaurus were caused by bone infections, but some cases may have alternatively been caused by any type of joint disease such as arthritis. However, evidence of joint disease was rare in Tylosaurus when compared to mosasaurs such as Plioplatecarpus and Clidastes. Similar amassing of remodeled bone is also documented in bone fractures in other body parts. One T. kansasensis specimen possesses two fractured ribs that fully healed. Another T. proriger skull shows a fractured snout, probably caused by ramming into a hard object such as a rock. Presence of some healing indicates that the individual survived for some extended time before death, albeit under extreme pain. ==Paleoecology==

to North Atlantic waters above 30°N. Throughout its ~20 million-year history, Tylosaurus was endemic to the North Atlantic Circle Basin, a geographic region comprising the North Atlantic and neighboring waters including the Western Interior Seaway in North America and Mediterranean Tethys in Europe above 30°N. There are a few exceptions of occurrences in warmer low-latitude zones in scientific literature. This includes T. iembeensis from the Coniacian of Angola, an isolated tooth from Maastrichtian deposits in the Democratic Republic of the Congo suggested as a possible Hainosaurus, Habitat preference Stratigraphic evidence in the WIS is inconsistent on whether Tylosaurus preferred a specific habitat. Russell (1967) suggested that Tylosaurus in the Niobrara Formation frequented open waters far offshore, potentially up to from the nearest coastline in the WIS. This is supported by evidence in bone structure indicative of adaptation towards deeper waters. This includes osteoporosis, which naturally occurs in modern deep-diving or fast-swimming tetrapods due to bone growth in low-gravity environments both lifestyles create, and high fat deposition within bony microstructures, which together with osteoporosis would have allowed Tylosaurus to achieve neutral buoyancy in deep water. However, later work found that Tylosaurus is found throughout both shallow and open water deposits of the Niobrara Formation. On the other hand, Kiernan (2002) found that Tylosaurus comprised 57.7% of all mosasaurs found in Santonian to early Campanian deposits in Alabama that correspond to shallow continental shelves, and only 8.2% of mosasaurs in offshore deposits of similar ages. This implied that, at least in this region, Tylosaurus preferred nearshore waters. Carbon-13 isotope analysis (δ13C) of tooth enamel by Robbins (2010) and Polcyn et al. (2025) also support a generalized habitat distribution. Unlike REEs, δ13C is correlated with the habitat the animal fed or foraged in, with lower values associated with more offshore foraging habitats. Both studies together found a δ13C range of -8.2‰ to -13.3‰ for Campanian T. proriger-like teeth from Texas (T. sp. aff. T. proriger) and -7.6‰ to 12.6‰ (all but one within -7.6‰ to -10.6‰) for T. ivoensis from Sweden. Isotope analyses of modern marine mammal teeth previously found that δ13C ratios between roughly -8‰ to -12.5‰ correspond to nearshore marine habitats and 11.5‰ to 15‰ to offshore marine habitats. Based on this, Polcyn et al. (2025) inferred that the T. proriger affiliates foraged in both nearshore and offshore marine habitats, while T. ivoensis foraged primarily nearshore with occasional offshore excursions. Both studies also examined a yet-undescribed Turonian specimen belonging to a long individual and found a δ13C ratio of -7.0‰. This corresponded to shallow waters analogous to modern kelp beds. Polcyn et al. (2025) suggested that early representatives of Tylosaurus were restricted to shallower habitats but expanded to more offshore zones over time as it evolved into larger sizes. == See also ==