Placodus: Aquatic animals adopt several methods of dealing with buoyancy. The placodonts used what is known as pachystasis: the development of particularly thick and heavy bones to keep the body submerged. Voluminous lungs allowed them to adjust their buoyancy. Thistechnique is often used by animals that feed whilewalking along the sea bed, such as modern dugongs and sca-ottcrs.(animatronic dinosaur)
Features: Like Paraplacodus. Placodus has protruding teeth at the front. However they are shorter, thicker and more spoorvshaped. The crushing teeth are not confined to the edges of the mouth but form a broad pavement across the palate, and the skull is particularly strong to withstand the stresses of crushing seashells. A row of bony scutes forms a jagged ridge along the back. A gap at the top of the skull may have held a light-sensitive organ.
The laws of Paraplacodus are uniquely adapted to picking up shellfish, with three pairs of protruding teeth in the top and two in the bottom. The teeth project from the front of the mouth. They have a senes of rounded crushing teeth in the upper and lower jaws. The thick ribs produce a distinctly box-like body with an almost square cross-section, a strong set of belly ribs forming the flat floor of the body – a heavy design that kept it close to the seabed.