Pliosaurus

 is one of the organisms in Birthdays the Beginning.

Ancestor: Diplocaulus

Needed for Birth: Ceratoglanis Descendant: Pliosaurmimus, Tarbosaurus, R. schlegelii

Trivia

 * For some reason, this massive, jurassic predator (~ 15 metres (49 ft) long) is depicted as a tiny cute frog. Pliosaurus.