Dolphins are marine mammals. They belong to the Odontoceti order, a suborder of the Cetacean family. There are about 40 different dolphin species. Dolphins spend their entire lives in water, but they breathe air. They have a single nostril on the top of their heads called a blowhole. Powerful lungs allow dolphins to stay underwater for up to 15 minutes. Their kidneys filter salt water so they do not get dehydrated. A dorsal fin provides stability, keeping the animal upright. Dolphins are social animals. They live in schools ranging from two to 1,000 members, organized by a strict hierarchy. Dolphin groups leap from water in unison, responding to a signal from the dominant animal. Dolphins have a vocabulary of whistles, squeaks, and clicks. They can emit up to 50 signals a minute. Dolphin noises have a sequential order, much like human language. Dolphins hunt for fish, their main prey, in groups. They use natural sonar, called echolocation, to detect objects in water. It helps dolphins locate fish on the seafloor, in muddy water or in the dark.

Dolphins stay in close contact by rubbing each other with their fins. Doing so helps them to maintain bonds and procreate. Dolphins are among the rare animals that have sex for more than simple reproductive purposes. The male dolphin’s genital organ is slightly hooked and located inside the animal. Female dolphins give birth to a single calf after about a year of gestation.
Immediately after birth, the mother pushes her baby to the surface so the little one can breathe. The first breastfeeding is a critical moment for the infant dolphin. The female dolphin has two mammary glands, or breasts, located next to the vagina. The mother must forcibly expel her milk so the newborn can drink it. Dolphins do not have lips, and therefore cannot suck a nipple. Dolphins have always fascinated people, which accounts for theme parks around the world featuring dolphins as their main attraction. Dolphins have also been used in the military. The United States Navy, for example, trained dolphins to find mines on the seafloor.
Human fascination with dolphins goes back a long way. There are many tales of dolphins in ancient mythology. A dolphin was said to have saved the Greek god Poseidon’s son after sailors robbed him and cast him into the sea.