Tylosaurus

Tylosaurus (Greek τυλος/tylos "protuberance, knob" + Greek σαυρος/sauros "lizard") was a mosasaur, a large, predatory marine reptile closely related to modern monitor lizards and to snakes, from the Late Cretaceous.

Tylosaurus
Temporal range: Turonian-Maastrichtian, 86.5–75 Ma
Bunker Tylosaur
"Bunker" T. proriger (KUVP 5033) mounted skeleton in the Rocky Mountain Dinosaur Resource Center in Woodland Park, Colorado
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Superfamily: Mosasauroidea
Family: Mosasauridae
Subfamily: Tylosaurinae
Genus: Tylosaurus
Marsh, 1872
Species
  • T. proriger Cope, 1869 (type)
  • T. nepaeolicus Cope, 1874
  • T. pembinensis Russell, 1988
  • T. saskatchewanensis Jimenez-Huidobro et al., 2018[1]
  •  ?T. bernardi (Dollo, 1885)
  •  ?T. ivoensis(Persson 1963)
Synonyms
  • Elliptonodon Emmons, 1858
  • Rhamphosaurus Cope, 1872
  • Rhinosaurus Marsh, 1872
  •  ?Hainosaurus Dollo, 1885[2]

Description

Tylosaurus-proriger
Restoration of T. proriger

A distinguishing characteristic of Tylosaurus is its elongated, cylindrical premaxilla (snout) from which it takes its name. Unlike other mosasaurs, Tylosaurus did not have teeth all the way forward on its premaxilla, as the bony protuberance was free of teeth.[3] Tylosaurus also have 24 to 26 teeth in the upper jaw, 20 to 22 teeth on the palate, 26 teeth on the lower jaw, 29 to 30 vertebrate between the skull and hip, 6 to 7 vertebrae in the hip, 33 to 34 vertebrae in the tail with chevrons, and a further 56 to 58 vertebrae making up the tip of the tail.[2]

Early restorations showing Tylosaurus with a dorsal crest were based on misidentified tracheal cartilage, but when the error was discovered, depicting mosasaurs with such crests was already a trend.[4][5] Its skin had many small scales.

Size

Tylosaur Size
Size comparison of T. pembinensis

Along with plesiosaurs, sharks, fish, and other mosasaurs, Tylosaurus was a dominant predator of the Western Interior Seaway during the Late Cretaceous. The genus was among the largest of the mosasaurs (along with Mosasaurus hoffmannii), with the possibly conspecific[2] Hainosaurus bernardi reaching lengths up to 12.2 meters (40 ft), and T. pembinensis reaching comparable sizes.[6] T. proriger, the largest species of Tylosaurus, reached lengths of about 14 m (46 ft).[7]

Discovery and naming

Sharp osborn tylosaurus
Complete T. proriger skeleton, from H.F. Osborn's 1899 description

Like many other mosasaurs, the early history of this taxon is complex and involves the infamous rivalry between two early American paleontologists, Edward Drinker Cope and Othniel Charles Marsh. Originally, the name "Macrosaurus" proriger was proposed by Cope for a fragmentary skull and thirteen vertebrae collected from near Monument Rocks in western Kansas in 1868.[8] It was placed in the collections of the Harvard Museum of Comparative Zoology. Only a year later, Cope redescribed the same material in greater detail and referred it, instead, to the English mosasaur taxon Liodon. Then, in 1872, Marsh named a more complete specimen as a new genus, Rhinosaurus ("nose lizard"), but soon discovered that this name had already been used for a different animal. Cope suggested that Rhinosaurus be replaced by yet another new name, Rhamposaurus which also proved to be preoccupied. Marsh finally erected Tylosaurus later in 1872, to include the original Harvard material as well as additional, more complete specimens which had also been collected from Kansas.[9] A giant specimen of T. proriger, recovered in 1911 by C. D. Bunker near Wallace, Kansas is one of the largest skeletons of Tylosaurus ever found. It is currently on display at the University of Kansas Museum of Natural history.

Ichthyosaurus Smithsonian
T. proriger specimen which was found with a plesiosaur in its stomach
JVBA Mosasaur 6-09-2010
A 43 ft. (13 m) complete fossil specimen of T. proriger (with a human for scale) on display at the Academy of Natural Sciences in Philadelphia.

In 1918, Charles H. Sternberg found a Tylosaurus, with the remains of a plesiosaur in its stomach.[10] The specimen is currently mounted in the United States National Museum (Smithsonian) and the plesiosaur remains are stored in the collections. Although these important specimens were briefly reported by C. H. Sternberg (1922), the information was lost to science until 2001. This specimen was rediscovered and described by Everhart (2004a). It is the basis for the story line in the 2007 National Geographic IMAX movie Sea Monsters: A Prehistoric Adventure, and a book by the same name (Everhart, 2007).

A photograph of a Tylosaurus skull was taken by George F. Sternberg about 1926 after he collected and prepared the specimen. It was discovered in the Smoky Hill Chalk of Logan County, Kansas. Sternberg offered the specimen to the Smithsonian and included a photograph in his letter to Charles Gilmore. Copies of the original photos are in the archives of the Sternberg Museum of Natural History (FHSM). The specimen is FHSM VP-3, the exhibit specimen in the same museum.

A 34 feet (10 m) long Tylosaurus found in Kansas by Alan Komrosky in 2009 is now on display at the Museum of World Treasures in Wichita, Kansas.[11]

Tylosaurus has now been described from formations in Saskatchewan and South Dakota.[12]

Classification

Tylosaurus Bruce
Mounted 13.1 meter long specimen of T. pembinensis, nicknamed "Bruce"
Tylosaurus pembinensis 1DB
Restoration of T. pembinensis
Tylosaurus kansasensis Clean
Mounted skeleton of a juvenile T. nepaeolicus, Rocky Mountain Dinosaur Resource Center
Tylosaurus micromus - Naturmuseum Senckenberg - DSC02185
Specimen referred to T. micromus

Though many species of Tylosaurus have been named over the years, only a few are now recognized by scientists as taxonomically valid. They are as follows: Tylosaurus proriger (Cope, 1869[8]), from the Santonian and lower to middle Campanian of North America (Kansas, Alabama, Nebraska, etc.) and Tylosaurus nepaeolicus (Cope, 1874 [13]), from the Santonian of North America (Kansas). Tylosaurus kansasensis, named by Everhart in 2005[14] from the late Coniacian of Kansas, has been shown to be based on juvenile specimens of T. nepaeolicus.[15] It is likely that T. proriger evolved as a paedomorphic variety of T. nepaeolicus, retaining juvenile features into adulthood and attaining much larger adult size.[15]

A closely related genus, Hainosaurus, is known from the Cretaceous of North America and Europe. Both Tylosaurus and Hainosaurus are members of the group Tylosaurinae [16] and are referred to informally as "tylosaurines" or "tylosaurs." Research published in 2016, however, indicates that Hainosaurus is likely congeneric with Tylosaurus.[2] Bell [17] placed the tylosaurines together with the plioplatecarpine mosasaurs (Platecarpus, Plioplatecarpus, etc.) in an informal monophyletic grouping which he called the "Russellosaurinae."

The cladogram below follows the cladogram from a 2011 analysis by paleontologists Takuya Konishi and Michael W. Caldwell.[18]

Clidastes prophyton

Kourisodon puntledgensis

Russellosaurina

Yaguarasaurus columbianus

Russellosaurus coheni

Tethysaurus nopcsai

Tylosaurus nepaeolicus

Tylosaurus proriger

Plioplatecarpinae

Ectenosaurus clidastoides

Angolasaurus bocagei

Selmasaurus johnsoni

Selmasaurus russelli

Plesioplatecarpus planifrons

Platecarpus tympaniticus

Latoplatecarpus willistoni

Latoplatecarpus nichollsae

"Platecarpus somenensis"

Plioplatecarpus primaevus

Plioplatecarpus houzeaui

Plioplatecarpus marshi

Paleobiology

Growth

Konishi and colleagues in 2018 assigned specimen FHSM VP-14845, a small juvenile with an estimated skull length of 30 centimeters (12 in), to Tylosaurus based on the proportions of the braincase and the arrangement of the teeth in the snout and on the palate. However, the specimen lacks the characteristic snout projection of other Tylosaurus, which is present in juveniles of T. nepaeolicus and T. proriger with skull lengths of 40–60 cm (16–24 in). This suggests that Tylosaurus acquired the snout projection rapidly at an early stage in life, and also suggests that it did not develop due to sexual selection. Konishi and colleagues suggested a function in ramming prey, as employed by the modern orca.[3]

Diet

Tylosaurus skin
Scales of T. proriger (KUVP-1075)

Stomach contents associated with specimens of Tylosaurus proriger indicate that this mosasaur had a varied diet, including fish, sharks, smaller mosasaurs, plesiosaurs, and flightless diving birds such as Hesperornis.[19][20]

Knight Tylosaurus
T. proriger by Charles R. Knight, 1899

The Talkeetna Mountains Hadrosaur was a hadrosaurid of indeterminate classification whose carcass appeared to have been deposited in a bathyal or outer shelf environment that later became Alaska's Matanuska Formation. Every element of its skeleton not found in a concretion bore many closely spaced oval conical depressions ranging in diameter from 2.12–5.81 millimeters (0.083–0.229 in) and 1.64–3.62 mm (0.065–0.143 in) deep. These depressions are probably bite marks. The depressions are not symmetrical enough for gastropod drill marks and are not shaped like sponge borings. None of the preserved fish fossils of the Matanuska Formation fit the size or geometry of the borings. The size and spacing and shape by contrast, however, closely resembles the teeth of Tylosaurus proriger. The apparent tooth marks are unlikely to have occurred before the carcass was washed out to sea since that would have punctured the body, preventing the buildup of bloating gases that allowed the carcass to drift out to sea in the first place. The distribution of bite marks corresponds inversely to the presence of flesh in the animal. For instance, lower limb bones sustained the most damage because there was the least amount of flesh shielding the bones at those locations. The concretions formed as the flesh chemically reacted to the seafloor on the largest parts of the animal where the scavenging mosasaur would be unable to fully wrap its jaws around the carcass. Bones pulled free from the carcass were buried in the mud and preserved in mudstone.[21]

References

  1. ^ Paulina Jiménez-Huidobro; Michael W. Caldwell; Ilaria Paparella; Timon S. Bullard (2018). "A new species of tylosaurine mosasaur from the upper Campanian Bearpaw Formation of Saskatchewan, Canada". Journal of Systematic Palaeontology. Online edition. doi:10.1080/14772019.2018.1471744.
  2. ^ a b c d Paulina Jimenez-huidobro and Michael W. Caldwell (2016). "Reassessment and reassignment of the early Maastrichtian mosasaur Hainosaurus bernardi Dollo, 1885, to Tylosaurus Marsh, 1872". Journal of Vertebrate Paleontology. Online edition (3): e1096275. doi:10.1080/02724634.2016.1096275.
  3. ^ a b Konishi, Takuya; Jiménez-Huidobro, Paulina; Caldwell, Michael W. (2018). "The Smallest-Known Neonate Individual of Tylosaurus (Mosasauridae, Tylosaurinae) Sheds New Light on the Tylosaurine Rostrum and Heterochrony". Journal of Vertebrate Paleontology: 1–11. doi:10.1080/02724634.2018.1510835.
  4. ^ "H.F. Osborn 1899". Oceans of Kansas. April 18, 2008. Retrieved January 28, 2013.
  5. ^ "Mosasaur Fringe". Oceans of Kansas. January 13, 2013. Retrieved January 28, 2013.
  6. ^ Lindgren, J. (2005). "The first record of Hainosaurus (Reptilia, Mosasauridae) from Sweden". Journal of Paleontology. 79 (6): 1157–1165. doi:10.1666/0022-3360(2005)079[1157:TFROHR]2.0.CO;2.
  7. ^ "Fact File: Tylosaurus Proriger from National Geographic". Retrieved May 12, 2010.
  8. ^ a b Cope ED. 1869. [Remarks on Macrosaurus proriger.] Proceedings of the Academy of Natural Sciences of Philadelphia 11(81): 123.
  9. ^ Marsh OC. 1872. Note on Rhinosaurus. American Journal of Science 4 (20): 147.
  10. ^ "Tylosaur food". Oceansofkansas.com. Retrieved January 28, 2013.
  11. ^ "Museum Of World Treasures". Worldtreasures.org. Archived from the original on September 21, 2013. Retrieved January 28, 2013.
  12. ^ "[dinosaur] Tylosaurus saskatchewanensis (new species) + African araripemydid turtle Taquetochelys decorata". dml.cmnh.org. Retrieved February 4, 2019.
  13. ^ Cope ED. 1874. Review of the vertebrata of the Cretaceous period found west of the Mississippi River. U. S. Geological Survey of the Territories, Bulletin 1 (2): 3-48.
  14. ^ Everhart, M.J. (2005). "Tylosaurus kansasensis, a new species of tylosaurine (Squamata, Mosasauridae) from the Niobrara Chalk of western Kansas, USA". Netherlands Journal of Geosciences. 84 (3): 231–240. doi:10.1017/S0016774600021016.
  15. ^ a b Paulina Jiménez-Huidobro, Tiago R. Simões & Michael W. Caldwell. (2016). Re-characterization of Tylosaurus nepaeolicus (Cope, 1874) and Tylosaurus kansasensis Everhart, 2005: Ontogeny or sympatry? Cretaceous Research, doi:10.1016/j.cretres.2016.04.008
  16. ^ Williston SW. 1898. Mosasaurs. The University Geological Survey of Kansas, Part V. 4: 81-347 (pls. 10-72).
  17. ^ Bell GL. Jr. 1997. A phylogenetic revision of North American and Adriatic Mosasauroidea. pp. 293-332 In: Callaway J. M. and E. L Nicholls, (eds.), Ancient Marine Reptiles, Academic Press, 501 pages.
  18. ^ Konishi, Takuya; Michael W. Caldwell (2011). "Two new plioplatecarpine (Squamata, Mosasauridae) genera from the Upper Cretaceous of North America, and a global phylogenetic analysis of plioplatecarpines". Journal of Vertebrate Paleontology. 31 (4): 754–783. doi:10.1080/02724634.2011.579023.
  19. ^ "Mosasaurs ate plesiosaurs: New data on the gut contents of a Tylosaurus proriger (Squamata; Mosasauridae) from the Smoky Hill Chalk of western Kansas". Oceans Of Kansas.
  20. ^ Sea Monsters Creatures of the Deep. Mike Everhart.
  21. ^ Pasch, A. D.; May, K. C. (2001). "Taphonomy and paleoenvironment of a hadrosaur (Dinosauria) from the Matanuska Formation (Turonian) in South-Central Alaska". In Tanke, D.H.; Carpenter, K.; Skrepnick, M. W. (eds.). Mesozoic Vertebrate Life. Indiana University Press. pp. 219–236.
  • Bell GL. Jr. 1997. Part IV: Mosasauridae - Introduction. pp. 281–292 In: Callaway J. M. and E. L Nicholls, (eds.), Ancient Marine Reptiles, Academic Press, 501 pages.
  • Everhart MJ. 2001. Revisions to the biostratigraphy of the Mosasauridae (Squamata) in the Smoky Hill Chalk Member of the Niobrara Chalk (Late Cretaceous) of Kansas. Transactions of the Kansas Academy of Science 104 (1-2): 56-75.
  • Everhart MJ. 2005. Earliest record of the genus Tylosaurus (Squamata; Mosasauridae) from the Fort Hays Limestone (Lower Coniacian) of western Kansas. Transactions 108 (3/4): 149-155.
  • Everhart MJ. 2005. Oceans of Kansas - A Natural History of the Western Interior Sea. Indiana University Press, 322 pp.
  • Kiernan CR. 2002. Stratigraphic distribution and habitat segregation of mosasaurs in the Upper Cretaceous of western and central Alabama, with an historical review of Alabama mosasaur discoveries. Journal of Vertebrate Paleontology 22 (1): 91-103.
  • Russell DA. 1967. Systematics and morphology of American mosasaurs (Reptilia, Sauria). Yale Univ. Bull. 23: 241 pp.
  • Novas FE, Fernández M, Gasparini ZB, Lirio JM, Nuñez HJ, Puerta P. 2002. Lakumasaurus antarcticus, n. gen. et sp., a new mosasaur (Reptilia, Squamata) from the Upper Cretaceous of Antarctica. Ameghiniana 39 (2): 245-249.

External links

Dallasaurus

Dallasaurus ("Dallas lizard") is a basal mosasauroid from the Upper Cretaceous of North America. Along with Russellosaurus, Dallasaurus is one of the two oldest mosasauroid taxa currently known from North America. This small semi-aquatic lizard measured less than a meter in length, compared to such gigantic derived mosasaurs as Tylosaurus and Mosasaurus, each exceeding 14 meters.

Goronyosaurus

Goronyosaurus is an extinct genus of marine lizard belonging to the mosasaur family. Fossils of Goronyosaurus are exclusively known from the Dukamaje Formation of Niger and Nigeria and are Maastrichtian in age. Its fossils were first described in the 1930s as Mosasaurus nigeriensis, but subsequent remains revealed a highly unique set of adaptations that prompted the species to be reclassified as the only species of the new genus Goronyosaurus in 1972. These unique adaptations have made Goronyosaurus notoriously difficult to classify within the Mosasauridae and it is often left out of phylogenetic analyses.

Goronyosaurus possesses unique teeth, which are unlike the teeth of any other mosasaur. Instead of the cutting teeth common among mosasaurs, Goronyosaurus has straight teeth with rounded apices adapted for smashing food.

Hainosaurus

Hainosaurus (Haino from the river Haine, where it was first discovered, and saurus, from Greek sauros, meaning lizard) is an extinct genus of marine reptiles belonging to the mosasaur family. It is one of the largest mosasaurs, though its size has been revised more than once. At first it was estimated to be 17 metres (56 ft), and the largest mosasaurid. During the 1990s, its size was revised to 15 metres (49 ft) long; more recently, Johan Lindgren estimated that it reached lengths of up to 12.2 metres (40 ft). It was one of the top marine predators of the Late Cretaceous. Like other giant mosasaurs, this giant predator preyed on turtles, plesiosaurs, pterosaurs, cephalopods, sharks, fish, and smaller mosasaurs.

The fossils of H. pembinensis were found in the Upper Cretaceous Pierre Shale in Manitoba, Canada in 1988. It was distinguished from Tylosaurus by having a greater number of vertebrae before the tail, a larger femur to humerus ratio, and larger nostrils. However, a 2008 study found that conclusion to be problematic, and thus reclassified into the genus Tylosaurus as T. pembinensis. Likewise, Hainosaurus neumilleri Martin, 2007 is a nomen dubium within Tylosaurus.

Hainosaurus is a member of the subfamily Tylosaurinae, and it is related to the wholly North American Tylosaurus. However, it has more vertebrae from the neck to the part of the tail with chevrons (53) than Tylosaurus (35). Both genera are large marine superpredators. Hainosaurus' tail has less chevron-bearing vertebrae, making it shorter than that of Tylosaurus. The type species of Hainosaurus is H. bernardi, named after the Belgian Léopold Bernard, owner of the phosphate chalk exploitation where the fossil was unearthed. In a paper published in 2016, Hainosaurus was considered congeneric with Tylosaurus.

Halisaurus

Halisaurus is an extinct genus of marine reptile belonging to the mosasaur family. The holotype, consisting of an angular and a basicranium fragment discovered near Hornerstown, New Jersey, already revealed a relatively unique combination of features and prompted a new genus to be described. It was named by Othniel Charles Marsh in 1869 and means "ocean lizard". It was renamed by Marsh to Baptosaurus in 1870, since he believed the name to already be preoccupied by the fish Halosaurus. According to modern rules, a difference of a letter is enough and the substitute name is unneeded, making "Baptosaurus" a junior synonym.

Since its description, more complete remains have been uncovered from fossil deposits throughout the world with particularly complete remains found in Morocco and the United States. The genus remains a key taxon in mosasaur systematics due to its unique set of features and as the most complete representative of its subfamily, the Halisaurinae.

With a length of 3–4 m (9.8–13.1 ft), Halisaurus was comparatively small by mosasaur standards. Though bigger than earlier and more basal mosasaurs, such as Dallasaurus, the sleek Halisaurus would have been dwarfed by many of its contemporaries, such as Tylosaurus and larger species of Clidastes.

Kaikaifilu

Kaikaifilu is a genus of tylosaurine mosasaur from the Late Cretaceous part of the Lopez de Bertodano Formation of Antarctica, just before the Cretaceous–Paleogene extinction event. It is among the largest members of the tylosaurines, a group of marine lizards that lived during the Cretaceous, and the only really large Antarctic tylosaurine.

List of mosasaur-bearing stratigraphic units

This is a list of stratigraphic units from which mosasaur body fossils have been recovered. Units listed are all either formation rank or higher (e.g. group). Formations are listed by continent, and alphabetically within the individual lists.

List of mosasaur genera

This list of mosasaurs is a comprehensive listing of all genera that have ever been included in the family Mosasauridae or the parent clade Mosasauroidea, excluding purely vernacular terms. The list includes all commonly accepted genera, but also genera that are now considered invalid, doubtful (nomen dubium), or were not formally published (nomen nudum), as well as junior synonyms of more established names, and genera that are no longer considered mosasauroid. Non-mosasaurid mosasauroids shall be noted as such. The list currently includes 78 genera.

List of the Mesozoic life of Kansas

This list of the Mesozoic life of Kansas contains the various prehistoric life-forms whose fossilized remains have been reported from within the US state of Kansas and are between 252.17 and 66 million years of age.

Mosasaur

Mosasaurs (from Latin Mosa meaning the 'Meuse river', and Greek σαύρος sauros meaning 'lizard') comprise a group of extinct, large marine reptiles containing 38 genera in total. Their first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. Mosasaurs probably evolved from an extinct group of aquatic lizards known as aigialosaurs in the Earliest Late Cretaceous. During the last 20 million years of the Cretaceous period (Turonian-Maastrichtian ages), with the extinction of the ichthyosaurs and pliosaurs, mosasaurs became the dominant marine predators. They became extinct as a result of the K-Pg event at the end of the Cretaceous period, about 66 million years ago.

Museum of World Treasures

The Museum of World Treasures is a world history museum in Wichita, Kansas, United States. Among the many items on display are Tyrannosaurus, Daspletosaurus, and Tylosaurus specimens (Including "Ivan the T. rex"), Egyptian mummies, signatures of all the American presidents, a section of the Berlin Wall, and a genuine shrunken head. The Museum of World Treasures is not limited to a particular era of history, but has opted to display an extremely diverse collection representing many different fields of interest and a wide range of subjects. This museum is a member of the American Alliance of Museums, but is not accredited by the organization.

Natantia

Natantia (Boas, 1880) is an obsolete taxon of decapod crustaceans, comprising those families that move predominantly by swimming – the shrimp (comprising Caridea and Procarididea), prawns (Dendrobranchiata) and boxer shrimp. The remaining Decapoda were placed in the Reptantia, and consisted of crabs, lobsters and other large animals that move chiefly by walking along the bottom. The division between Natantia and Reptantia was replaced in 1963, when Martin Burkenroad erected the suborder Pleocyemata for those animals that brood their eggs on the pleopods, leaving Dendrobranchiata for the prawns. Under this system, Natantia is a paraphyletic group. Burkenroad's primary division of Decapoda into Dendrobranchiata and Pleocyemata has since been corroborated by molecular analyses.

The name Natantia Owen, 1851 was utilized in a phylogenetic context by Madzia and Cau (2017) as the most exclusive mosasaurid clade including Mosasaurus and Tylosaurus but not Halisaurus.

Plesiotylosaurus

Plesiotylosaurus, meaning "near Tylosaurus", is an extinct genus of marine lizard belonging to the mosasaur family. It is classified as part of the Mosasaurinae subfamily, alongside genera like Mosasaurus and Prognathodon. The genus contains one species, Plesiotylosaurus crassidens, recovered from deposits of Middle Maastrichtian age in the Moreno Formation in California.Though it is classified as a mosasaurine mosasaur, and not closely related to Tylosaurus, the name is not entirely misplaced as a number of cranial features found in the relatively intact holotype skull suggest some degree of convergent evolution with tylosaurine mosasaurs.

Pythonomorpha

Pythonomorpha was originally proposed by paleontologist Edward Drinker Cope (1869) as a reptilian order comprising mosasaurs, which he believed to be close relatives of Ophidia (snakes). The etymology of the term Pythonomorpha comes from the Greek Python (a monstrous snake from Greek mythology) and morphe ("form"), and refers to the generally serpentine body plan of members of the group. Cope wrote, "In the mosasauroids, we almost realize the fictions of snake-like dragons and sea-serpents, in which men have been ever prone to indulge. On account of the ophidian part of their affinities, I have called this order Pythonomorpha." Cope incorporated two families, the Clidastidae (now defunct but including only Clidastes) and the Mosasauridae (including Macrosaurus [?=Tylosaurus], Mosasaurus, and Platecarpus).

However, a close relationship between mosasaurs and snakes was rejected by most 20th-century herpetologists and paleontologists, who sought, instead, to demonstrate a close relationship between mosasaurs and varanid (monitor) lizards and who generally considered snakes to have evolved from terrestrial, burrowing lizards (see, for example, Russell, 1967). Cope's Pythonomorpha was later resurrected by a number of paleontologists (Lee, 1997; Caldwell et Lee, 1997) who had conducted cladistic analyses that seemed to show that snakes and mosasaurs may have been more closely related to one another than either were to the varanid lizards, and that snakes more likely arose from aquatic ancestors. As redefined by Lee (1997), the monophyletic Pythonomorpha consists of "The most recent common ancestor of mosasauroids and snakes, and all its descendants." This would include the aigialosaurs, dolichosaurs, coniasaurs, mosasaurs, and all snakes. Lee (1997) was able to show no less than 38 synapomorphies supporting Pythonomorpha.

If Pythonomorpha is valid, it contains not only mosauroids but the Ophidiomorpha, which was defined as a node-based clade containing the most recent common ancestor of dolichosaurs, adriosaurs, Aphanizocnemus, and fossil and extant Ophidia and all of its descendants.However, the validity of Pythonomorpha is still debated; indeed, there is no consensus about the relationships of snakes or mosasaurs to each other, or to the rest of the lizards. An analysis by Conrad (2008) placed mosasaurs with varanoid lizards, and snakes with skinks, while an analysis by Gauthier et al. (2012) suggested that mosasaurs are more primitive than either snakes or varanoids. However, a combined morphological and molecular analysis by Reeder et al. (2015) recovered Mosasauria and Serpentes as sisters, consistent with Pythonomorpha.

Santonian

The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous epoch or Upper Cretaceous series. It spans the time between 86.3 ± 0.7 mya (million years ago) and 83.6 ± 0.7 mya. The Santonian is preceded by the Coniacian and is followed by the Campanian.

Taniwhasaurus

Taniwhasaurus (from the Māori taniwha, a supernatural, aquatic creature, and the Greek σαυρος/sauros, meaning lizard) is an extinct genus of mosasaur (carnivorous marine lizards) which inhabited New Zealand, Japan and Antarctica. The genus was a close relative of the genera Tylosaurus and Hainosaurus.

Timeline of mosasaur research

This timeline of mosasaur research is a chronologically ordered list of important fossil discoveries, controversies of interpretation, and taxonomic revisions of mosasaurs, a group of giant marine lizards that lived during the Late Cretaceous Epoch. Although mosasaurs went extinct millions of years before humans evolved, humans have coexisted with mosasaur fossils for millennia. Before the development of paleontology as a formal science, these remains would have been interpreted through a mythological lens. Myths about warfare between serpentine water monsters and aerial thunderbirds told by the Native Americans of the modern western United States may have been influenced by observations of mosasaur fossils and their co-occurrence with creatures like Pteranodon and Hesperornis.The scientific study of mosasaurs began in the late 18th century with the serendipitous discovery of a large fossilized skeleton in a limestone mine near Maastricht in the Netherlands. The fossils were studied by local scholar Adriaan Gilles Camper, who noted a resemblance to modern monitor lizards in correspondence with renowned French anatomist Georges Cuvier. Nevertheless, the animal was not scientifically described until the English Reverend William Daniel Conybeare named it Mosasaurus, after the river Meuse located near the site of its discovery.By this time the first mosasaur fossils from the United States were discovered by the Lewis and Clark expedition, and the first remains in the country to be scientifically described were reported slightly later from New Jersey. This was followed by an avalanche of discoveries by the feuding Bone War paleontologists Edward Drinker Cope and Othniel Charles Marsh in the Smoky Hill Chalk of Kansas. By the end of the century a specimen of Tylosaurus would be found that preserved its scaley skin. Later Samuel Wendell Williston mistook fossilized tracheal rings for the remains of a fringe of skin running down the animal’s back, which subsequently became a common inaccuracy in artistic restorations.The 20th century soon saw the discovery in Alabama of a strange mosasaur called Globidens, with rounded teeth suited to crushing shells. Mosasaur remains were also discovered in Africa and California. In 1967 Dale Russell published a scientific monograph dedicated to mosasaurs. Embryonic remains in the 1990s confirmed that mosasaurs gave live birth like in ichthyosaurs. The 1990s also saw a revival and escalation of a debate regarding whether or not some supposed mosasaur toothmarks in ammonoid shells were actually made by limpets. By the end of the century, the evolutionary relationship between mosasaurs and snakes as well as the possible involvement of mosasaurs in the extinction of the aforementioned ichthyosaurs became hot button controversies.The debates regarding snakes, toothmarks, and ichthyosaurs spilled over into the early 21st century. These discussions were also accompanied by the discovery of many new taxa, including new species of Globidens, Mosasaurus, and Tylosaurus as well as entirely new genera like Yaguarasaurus and Tethysaurus. In 2013, Lindgren, Kaddumi, and Polcyn reported the discovery of a Prognathodon specimen from Jordan that preserved the soft tissues of its scaley skin, flippers and tail. Significantly, the tail resembled those of modern carcharinid sharks, although the bottom lobe of the tail fin was longest in the mosasaur whereas shark tails have longer upper lobes.

Tylosaurinae

The Tylosaurinae are a subfamily of mosasaurs, a diverse group of Late Cretaceous marine squamates. Members of the subfamily are informally and collectively known as "tylosaurines" and have been recovered from every continent except for South America. The subfamily includes the genera Tylosaurus, Taniwhasaurus, Hainosaurus and Kaikaifilu.

Tylosaurines first appeared in the Coniacian and gave rise to some of the largest mosasaurs within the genera Tylosaurus and Hainosaurus which came to dominate as apex predators in marine ecosystems throughout the Santonian and Campanian, but appear to have been largely replaced by large mosasaurines, such as Mosasaurus, by the end of the Maastrichtian. Nevertheless, the subfamily survived to the end of the Cretaceous, covering a period lasting approximately twenty million years.

The etymology of this group derives from the genus Tylosaurus (Greek tylos = "knob" + Greek sauros = "lizard").

Tylosurus

Not to be confused with Tylosaurus.

Tylosurus is a genus of needlefish, one of ten in the family Belonidae. They are found worldwide in tropical and warmer temperate seas and two species have been recorded as Lessepsian migrants in the eastern Mediterranean Sea.

Undetermined
Mosasaurinae
Halisaurinae
Russellosaurina
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