Taniwhasaurus was an extinct genus of mosasaur, a carnivorous, marine reptile which inhabited New Zealand, Japan and Antarctica. The genus was a close relative of the genera Tylosaurus and Hainosaurus.
Caldwell et al. (2008) found that Lakumasaurus is a junior synonym of Taniwhasaurus.
Taniwhasaurus oweni, the type species for Taniwhasaurus, was named by Hector in 1874 from a fossil specimen found in the late Campanian Conway Formation outcrops at Haumuri Bluff, New Zealand. Known from an individual that may have measured at least 20+ feet in length, based on the estimations of the remains found. It is synonymous with Tylosaurus haumuriensis, which was named more recently, from the front parts of the jaws.
The genus Lakumasaurus was described in 2002 by Novas et al. from a fossil specimen found in the Santa Marta Formation of James Ross Island, Antarctica. When the type material was reexamined in 2007, James E. Martin and Marta Fernández determined Lakumasaurus to be a junior synonym of Taniwhasaurus and recombined the species Lakumasaurus antarcticus as T. antarcticus.
"Yezosaurus" was the name given to an undescribed genus of prehistoric marine reptile. Originally thought to be a theropod dinosaur, it was later identified as a mosasaur or ichthyosaur which lived in what is now Japan. The "type species", "Yezosaurus mikasaensis", was coined by Obata and Muramoto in 1977, but was not formally described until 2008, when the species T. mikasaensis was described by M.W. Caldwell et al.