The Tyrannozor is a powerful primal zerg lifeform.
It appears in the Heart of the Swarm mission The Crucible. Killing it gives additional levels to Kerrigan.
Notes
The ravasaur uses a modified tyrannozor model.
References
Blizzard Entertainment. StarCraft II: Heart of the Swarm. (Activision Blizzard). PC. Mission: Heart of the Swarm, The Crucible (in English). 2013-05-16.