While waiting at the San Francisco International Airport, in Terminal 3, I viewed a rotating exhibit from the California Academy of Science "Captured in Stone - Fossils from the Ancient World"


inset (left) examples  Nautilus pompilius (modern)   about

Cephalopods above - many from the Cretaceous (71-144 Ma)  - have internal chambers that they can inject with water or air controlling buoyancy, allowing them to hover or move up or down.




Ammonite (spiny, model) from the end of the Cretaceous







Above - two 110 M year old Brazilian fossils






Trilobites (Paleozoic - 520 - 245 Ma) are arthropods with exoskeletons, yet could still roll up into a ball when threatened. They had compound eyes with lenses of single calcite crystals.  They plowed the sea bottom or across mud.