Genetically manipulated for amphibious qualities that would allow survival on both land and water, Miaplacidus is an aggressive creature with a sharp dorsal fin. Miaplacidus is also capable of spitting high-pressure jets of water as a long-range attack.
The Miaplacidus was created from the DNA of a Spinosaurus by M.T.H.R. supercomputer, in hopes of creating a better lifeform than Australis. Miaplacidus shared some physical attributes to the Spinosaurus, such as long jaws filled with sharp teeth, long grasping arms and tall spine. The creature also sports large fins covering its head, akin to a frilled lizard. It is, by far, the tallest creature in Dino Crisis 3.
Miaplacidus was created by the M.T.H.R. as part of a pre-record order by Captain Satoko Evans to create a new lifeform to inhabit and colonize planet a2.
It is later encountered by S.O.A.R. member Patrick Tyler as he attempted to shut down the Energy Core overloaded by M.T.H.R. Patrick fought the creature and when he reached higher ground, the Miaplacidus retreated. It was encountered later in the M.T.H.R.'s control room when Patrick tried to sabotage M.T.H.R. from taking the genetically-engineered dinosaurs back to Earth. M.T.H.R. released some sort of green liquid which created a pool around her chamber and immediately after released Miaplacidus to attack Patrick.
Miaplacidus serves as a boss enemy fought in the M.T.H.R. chamber, and should not be confronted directly. Its primary attacks are biting and using water blast, while at some points it may also use its tail to whip. WASPs is very useful in this fight since Miaplacidus' constant movement means that the player needs to constantly dodging its attacks.
Oftentimes, the creature will swim in the water surrounding the battle area. The creature will sometimes show itself and spray a powerful water blast, dealing high damage to the player.
- The Miaplacidus' water blast attack and its aquatic behavior is comparable to the Plesioth from Capcom's Monster Hunter series.
- The large fins covering the head of Miaplacidus, are shown to fan out and somewhat vibrate when the creature is on the attack. This is mostly based on the Dilophosaurus from Jurassic Park franchise, akin to how the Oviraptors spit poison in previous game.