Yes dolphins are mammals or rather marine mammals.
Dolphins are warm-blooded animals that require air for survival.
While these marine mammals have been sharing the ocean with fish for millions of years they are very different from one another and posses unique characteristics that make them unique among the many different ocean bearing animals.
Dolphins get their oxygen from the surface of the water, which they obtain by inhaling air through their blowhole when they rise to the surface.
Fish on the other hand are cold-blooded creatures that pull oxygen directly out of the water through their gills.
In fact while dolphins can breathe above the surface of the water they would drown if they tried to breathe underwater.
In comparison many species of fish would suffocate above the surface of the water because they do not possess lungs and their gills are not designed for breathing above the surface.
One of the most different characteristics amongst marine mammals like dolphins and whales is the fact that their breathing passage and food passage are completely separate.
Unlike humans and most land animals dolphins do not breathe through their mouth, they breathe through their blowhole.
This is very important because as dolphins hunt for food such as fish, squid and crustaceans they need to ensure that they do not accidentally inhale water into their lungs while swallowing their prey underwater.
By having a separate breathing passage dolphins can hunt for food without worry about drowning or engulfing water.
In addition to being warm-blooded and breathing air dolphins also possess a vertebrae (which not all fish species possess) and have mammary glands which produce milk to feed their young.
The earliest dolphins can be traced back to as far as 10 million years and dolphins are considered close relatives to the whale species.
The earliest whales (or rather their relatives) existed 40 million years ago and lived on land before they slowly evolved into marine mammals.
By understanding their past we can gain a better understanding of why dolphins and whales are warm-blooded creatures that require air despite being oceanic animals.
Further evidence of their mammalian past can be identified by look at their bone structure.
Close examination of the bones that exist in a dolphins flippers indicate the previous existence of limbs which were likely used for walking, maneuvering and hunting on land.
As stated earlier dolphins possess a spine, however unlike fish dolphins propel themselves through the water by moving their vertebrae in a vertical manner.
This vertical movement of the spine is a common feature among most mammals, including humans.
Dolphins show a number of common characteristics found amongst most mammals including:
- Dolphins give birth to their young instead of producing eggs as fish, platypus & echidna do
- Dolphins have lungs and must rise above the surface to breathe oxygen
- Dolphins are warm-blooded mammals
- Female dolphins have mammary glands which produce milk to feed their young calves