Tylosaurus

Credit: Gabriel Ugueto.

*Tylosaurus* is an extinct genus of mosasaur that lived in North America, and possibly Europe during the Late Cretaceous.

## Description

*Tylosaurus* is characterized by a long, cylindrical snout bearing a bony knob located along the ventral surface of the snout. Unlike most mosasaurs, *Tylosaurus* did not have full-forward-facing teeth on its premaxilla. *Tylosaurus* grew roughly 24-26 teeth on its upper jaw, 20-22 on its palate and 26 on its lower jaw. 29-33 vertebrae stretched between its skull and its hip, 6 or 7 at the hip, 33 or 34 on the tails chevrons and from 56-58 vertebrae from the rest of the body down to the tails tip. In early reconstructions, tracheal cartilage was misidentified for a dorsal crest, but was fixed once this organ became a paleoart meme. Its skin was covered in small, pebble-like scales, similar to monitor lizards that descended from it millions of years later. Based on melanosomes discovered in skin impressions from a mosasauroidea attributed to *Tylosaurus*, the animal was a dark brown with white counter-shading, and a dark black fades into its tail. *Tylosaurus proriger* and *Tylosaurus bernardi* were the largest species. In late 2014, Guinness World Records recorded the Largest Publicly Displayed Mosasaur to the Canadian Fossil Discovery Center, based on their specimen "Bruce". This was added to the 2016 Guinness World Records prints. *Tylosaurus* bore sclerotic rings.

## Species

* *T. proriger*
* *T. nepaeolicus*
* *T. saskatchewanensis*
* *T. bernardi (?)*
* *T. gaudryi*
* *T. ivoensis*
* *T. iembeensis*
* *T. pembinensis*
* *T. "kansasensis"*
* *T. "borealis"*

## Paleobiology

### Ontogeny

In 2018, Konishi et al. assigned FHSM VP-14845, a small juvenile mosasaur, to *Tylosaurus*. The specimen has a skull length of about 30 centimeters (12 inches) long. They studied the braincase proportions and the tooth arrangements on the snout and palate. However, the bony knob found in juveniles of *T. proriger* and *T. nepaeolicus* is absent, the other juveniles having skull lengths from 40 to 60 centimeters (16 to 24 inches) long. This means that *Tylosaurus* quickly acquired the bony protrusion in life, and it did not develop for sexual selection. Konishi et al. concluded that the bony knob was likely used to ram into prey, an exploitation used by killer whales.

### Diet

Stomach contents extracted from Tylosaurus remains suggest the animal had a wide diet, from fish and sharks, to plesiosaurs, flightless birds like *Hesperornis* and even smaller mosasaurs. A specimen known as the Talkeetna Mountains hadrosaur, a Hadrosauridae indet. collected from what was an outer shelf in the bathyalpelagic zone, now the Matanuska Formation. Any element of the skeleton not encased in concretions bore close-spaced ovular conical pits in them, ranging in diameter from 2.12-5.81 millimeters and 1.64-3.62 millimeters deep. They are likely bite marks. They are asymmetrical, meaning no gastropods could have burrowed into the bone and did not appear to be sponge borings. No fossil fish from the region fit the bites.

They do, however, match the teeth of *T. proriger*. They are unlikely to have happened before the carcass was washed to sea, which would have prevented fossilization. Some locations appear to have less damage, possibly where skin was still clung to the bones. Regions where skin was presumably devoid are considerably deeper. The carcass was likely attempted to fit into *Tylosaurus*' mouth, but when it could not, bones struck free were preserved in sandstone.

## Notable Specimens

* "Bruce": Added by Guinness World Records in 2014 as their Largest Publicly Displayed Mosasaur, and was added to their prints in 2016.
* KUVP 5033 "Bunker": A massive *Tylosaurus proriger* first assigned to *Macrosaurus* by Cope (1869). Bunker was found in 1911, and restored by Triebold Paleontology Inc. and the KU Natural History Museum in 3D in 1997. It is 14 meters (46 feet) long.
* "Mandy": A *Tylosaurus* specimen that preserves most of the body. Mandy was discovered by Anthony Maltese in June 2020, having 63 vertebrae, 55 chevrons, many shed shark teeth and an embedded *Pachyrhizodus* jaw. It was found when Maltese's wife uncovered the first caudal vertebrae.
* FFHM 1997-10: One of the most complete *T. proriger* crania.
* "Sophie": A *Tylosaurus* skull with both halves, including the mandible and braincase.
* "Alfred": A large *T. proriger* from the Mooreville Chalk.

## Gallery

### Fossils

The sclerotic ring of Tylosaurus.The bony knob of Tylosaurus located on its snout.(A) quadrate bones, (B) skull bones, and (C) teeth of (i) T. nepaeolicus, (ii) T. proriger, (iii) T. bernardi, (iv) T. pembinensis and (v) T. saskatchewanensisT. nepaeolicusT. prorigerT. bernardiT. pembinensisT. saskatchewanensisT. sp. (top) and Hsisosuchus (bottom).Tiny Tylosaurus remains.A Tylosaurus skull housed in a collection drawer in the Sternberg Museum.
**Credit: Let's Tour!: Sternberg Museum of Natural History on Youtube.**Front flipper from "Mandy" the Tylosaurus.A plaster jacket of specimen "Mandy's" tail.
**Credit: Triebold Paleontology Inc..**A suspected Tylosaurus fragment.
**Credit: Triebold Paleontology Inc..****Credit: Triebold Paleontology Inc..**Tylosaurus "Sophie"Sophie's braincaseTylosaurus snout with tip bitten off and Cretoxyrhina tooth embedded in the top. The right and left pterygoids of Tylosaurus at the Perot Museum."Alfred".
### Mounts

**Credit: Triebold Paleontology Inc..****Credit: Triebold Paleontology Inc..****Credit: Triebold Paleontology Inc..****Credit: Triebold Paleontology Inc..****Credit: Diana Staresinic-Deane.**Mounted 13.1 meter long *T. pembinensis*; "Bruce".A *Tylosaurus* specimen at The Smithsonian, preserved with a plesiosaur in its stomach.Oil Rig Mosasaur (ORM), a poached *Tylosaurus* specimen recovered.

## References

1. ↑ Russell (1967:16)
2. ↑ 2.0 2.1 2.2 https://en.wikipedia.org/wiki/Tylosaurus
3. ↑ E.D. Cope. 1869. [On some specimens of fossil reptiles of interest]. *Proceedings of the Academy of Natural Sciences of Philadelphia* **21**:123
4. ↑ https://twitter.com/TrieboldPaleo/status/1430538403360165896
5. ↑ https://twitter.com/ToddRockford/status/1500230443504967682
6. ↑ https://twitter.com/Mosasaurologist/status/1326195418347286533
7. ↑ https://twitter.com/Mosasaurologist/status/1288218681789632512
8. ↑ https://twitter.com/palaeotheoryum/status/1227493599689920512
9. ↑ https://twitter.com/auntbeast/status/1536727417804492802?t=NKJG2TuFYfDJzGk\_2iZCgg&s=19
10. ↑ https://www.researchgate.net/publication/27711025\_Tylosaurus\_kansasensis\_a\_new\_species\_of\_tylosaurine\_Squamata\_Mosasauridae\_from\_the\_Niobrara\_Chalk\_of\_western\_Kansas\_USA