One of the more fascinating things about dolphins and their larger whale relatives is that they are not fish. They’re marine mammals.
This means, among other things, that they breathe air.
They also reproduce like other mammals, and the females give birth to live young and nurse them with milk.
Yet, they live all the time in the water, so how did this come to be?
How Dolphins Adapted Over Time
The ancestors of dolphins were animals that once lived on land.
No one is quite sure why they turned to the sea, but they did so about 50 million years ago and never returned to land.
When this happened, the dolphin’s ancestor slowly adapted to its new environment.
Its front legs became flippers, and its tail became flukes.
Its back legs diminished till they were absorbed into the body.
Even now, vestigial, floating pelvic bones can still be seen if a person looks at a dolphin’s skeleton.
Now and then, a baby dolphin or whale is born with tiny hind legs, but this is rare.
Mammals also have fur or hair, and dolphins are sometimes born with hair around their beaks, but they lose this hair not long after birth.
Nature wants the dolphin to be as hydrodynamic as possible, so the animal sacrificed its hair, though it still retains hair follicles.
What dolphins have to keep them warm is a layer of blubber beneath their skin.
The dolphin’s body became streamlined to move more efficiently through the water.
The nostrils moved from the front of its snout to the top of the head, which is very convenient.
This means that the dolphin only needs to break the water’s surface to breathe.
This is probably a reason why dolphin babies are born tail first.
When they’re entirely out of the womb, the mother, sometimes with the help of a sister or a friend, helps the baby to the surface so it can have its first lungful of air.
Even though this evolution, dolphins have lungs and not gills as fish do.
A dolphin must hold its breath when swimming underwater and can do this for a long time.
But it can’t hold its breath forever and needs to surface.
Some biologists believe that only one-half of its brain is asleep when a dolphin sleeps, and the other half is awake or at least sharp enough to make it swim up to the surface of the water to take a breath.
Though it doesn’t seem that way to a human swimmer, sounds travel much better underwater than through air and can travel hundreds of miles underwater.
Though their outer ears have also been reduced to holes on either side of their heads, dolphins can hear much better than humans.
When they’re underwater, dolphins pick up sounds through their lower mandible.
Dolphins have developed high-pitched clicks and whistles to communicate with each other.
Biologists believe that this may be an actual language and not just the series of sounds other animals make that indicate the presence of food or danger or to declare the animal’s territory.
Dolphins also use echolocation through an organ in their head called the melon.
Echolocation is so accurate that the dolphin knows precisely where the object is, how big it is, and what shape it is.
The dolphin, the descendant of a dog-sized land animal, has adapted beautifully to its aquatic life.