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Dolphins: Life Cycle, Anatomy & Habitat

Instructor: Jennifer Pettigrew

Jennifer has a master's degree in nursing and been a clinical instructor for BSN students.

Dolphins make up an informal grouping of animals within the order Cetartiodactyla. In this lesson we'll explore where dolphins live, what they look like and the major events of a dolphin's life cycle.

Dolphin Icons

What do Flipper, Dan Marino and Willy (of Free Willy fame) all have in common?

The bottlenose dolphin from the 1960s TV series Flipper
Flipper resized

They're all dolphins! Okay, so Dan Marino is a football player, but he played for the Miami Dolphins. And yes, Free Willy the killer whale, or orca, is part of a species of dolphin, not whales! There are even species of dolphins that live in rivers around the world.

Dolphins come in many shapes and sizes, but they are well known for their intelligence and curiosity. They have many unique adaptations that make them able to thrive as mammals living in the water in a variety of water types, depths and temperatures.

Habitat

There are 39 species of ocean-dwelling dolphins and five species of river-dwelling dolphins.

The Amazon river dolphin is the largest species of river dolphin. As an adult, it develops a pinkish hue to its skin.
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Dolphins can be found in every major ocean on Earth, plus a few rivers, so it's safe to say they can live in diverse habitats. Some prefer colder water, some warmer; some stay close to the coastline and some prefer the open seas.

Some dolphins migrate, other dolphins stay in one body of water their entire lives. There are species that live in freshwater only, saltwater only and some that can live in brackish water.

Anatomy

Dolphin's bodies are well adapted to life in the water, and many have anatomical adaptations to the specific habitat in which they live. For example, dolphins raised from infancy in colder water develop more blubber (fat) than dolphins raised in warmer water.

Generally, though, their bodies are streamlined and their skin is very smooth to avoid resistance as they propel themselves through the water. They have:

  • a dorsal fin (on their backs) to stabilize them in the water
  • flukes, the two parts that make up the tail
  • two pectoral fins, also known as flippers, which help them change directions

There are a handful of species that do not have a dorsal fin, the most well-known of which are the Northern- and Southern Right Whale Dolphins.

A pair of northern right whale dolphins, which do not have dorsal fins
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Despite the power of the tail, it does not have any bones. Dolphins use their powerful muscles to move it up and down to propel them through the water (unlike fish, which move their tales side to side- picture a shark).

The pectoral fins, by contrast, do have bones. Interestingly, the bones in the pectoral fins look like hands with five fingers, although you can't see that from the outside. They are analogous to our own hand structures.

Dolphins have a blowhole on their heads, which is an adapted set of nasal openings used for breathing at the surface without interrupting swimming. Dolphins cannot breathe through their mouths and they do not have vocal cords, so they can't vocalize with their mouths either. Sounds are generated by the blowhole.

They have a network of air sacks and fat in their large foreheads that assist in echolocation, a type of sonar system that dolphins use to detect objects in the water. They emit clicking sounds that echo back to them and give them an idea of the identity and location of the objects around them.

Dolphins' eyes are small and not well adapted to seeing underwater.

Life Cycle

Birth

A dolphin is born after the mother has been pregnant for 9-17 months, depending on the species. The birth takes place in the open ocean when the mother separates herself from the rest of the pod (family group).

Dolphins are born tail first and pushed the rest of the way to surface by the mother or another member of the pod so that the calf (baby dolphin) can breathe air. Dolphins usually give birth to only one calf at a time and rarely bare twins.

Within minutes after birth the calf is able to swim on its own. The calf ingests milk produced by the mother for the first year or two of life (depending on the species), and some continue to nurse after they start eating fish. Dolphin calves have specialized, straw-like tongues that allow them to nurse without ingesting seawater.

A mother dolphin and calf swimming close together
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