[4][5] Tylosaurines first appeared in the Coniacian[6] 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.

[7] Nevertheless, the subfamily survived to the end of the Cretaceous, covering a period lasting approximately twenty million years.

However, they are lightly built, having greatly reduced the weight of their bodies and possessing relatively small pectoral and pelvic girdles, fore- and hindlimbs.

Cranial nerves X, XI, and XII leave lateral wall of opisthotic through a single foramen.

Dorsal edge of surangular rounded and longitudinally horizontal...Twenty nine presacral vertebrae present.