The Nautilus is still standing as the sole survivor of Nautilaceae and is considered a living fossil. The nautilus has remained unchanged for the hundreds of million years they've been around. The fossil record first shows them appearing in the late Triassic and they've looked pretty much the same ever since. Chambered nautiluses have a hard external shell that it is able to completely withdraw into to hide from predators. The chambers help maintain the buoyancy of the nautilus, and they are able to swim around the ocean by jetting out seawater from the chambers.