Cetaceans are basically mammals that have adapted to aquatic life.
The term Cetacea in biological terms means whale or (originally) large sea animal.
Although the term whale can be used to refer to all cetaceans it usually excludes dolphins and porpoises.
Toothed whales as the name suggest are born with teeth and are considered the active hunters of the two suborders.
Many toothed whales also use echolocation which helps them navigate the ocean and search for prey.
They are typically smaller than baleen whales.
Baleen whales are the larger suborder and have baleen plates instead of teeth.
These plates have many fine bristles which often resemble the bristles on a comb.
Since they aren’t able to attack their prey with teeth they hunt by swimming with their mouth open sucking up water, sediments and small prey such as krill, shrimp, fish and other small aquatic life forms, then expel the water with their tongue leaving their prey are trapped in their baleen bristles.
This method of hunting is also referred to as filter feeding.
Size does not determine what type of food a whale will eat.
For example the killer whale (actually a dolphin) has been known to hunt both sharks and whales while the blue whale (the largest living animal) survives on a diet primarily composed of krill.
Several characteristics are apparent among all cetacean species.
Unlike fish cetaceans must breathe air to survive and most species cannot stay submerged underwater more than an 90 minutes.
Depending in their suborder they either have one or two blowhole which they use to breathe.
All cetaceans are considered conscious breathers; meaning they never fall completely asleep due to their need to consciously come up for air.
The bones in their flippers indicate the previous existence of limbs which their ancestors used to walk and hunt on land before they evolved into completely aquatic animals.
Their spines also show previous signs of their land dwelling origins.
Instead of moving their bodies from left to right to move through the ocean as fish do, the curvature and function of the whales spine appear to be designed more for running and force them to move their tail and flukes up and down.
Most cetaceans are hairless (or nearly heirless) and have a thick layer of blubber which helps them insulate heat in cold/polar environments and keep them warm during feeding seasons which are typically in colder waters.
During mating season which usually occurs during the warmer months blubber is converted to energy as whales migrate toward the equator.