Oceanic dolphin

Oceanic dolphins, known scientifically as Delphinidae, are a diverse family of marine mammals. They live in oceans all over the world. There are close to forty different species recognized today.

This family is part of a larger group called Delphinoidea. This group also includes porpoises and the Monodontidae, which are beluga whales and narwhals. Some dolphins are so large that people often call them whales. These are sometimes called "blackfish." This group includes the orca, the pilot whale, and the false killer whale. Even though they have "whale" in their names, they are still part of the Delphinidae family.

The bodies of these animals are built for speed in the water. They have a streamlined, torpedo-shaped body that is very muscular. Their limbs are modified into flippers, which contain four digits. They also have a large tail fin to push them through the water. To help them swim straight, they have a dorsal fin on their backs. This prevents them from spinning involuntarily. Their neck vertebrae are fused together. This makes their necks inflexible, which helps them stay stable at high speeds. However, it also means they cannot turn their heads easily. Some species can swim at 29 km/h for short distances. The orca is even faster, reaching speeds of up to 40 km/h.

Dolphins use a sophisticated system called echolocation to navigate. They produce high-frequency broadband clicks between 80 and 220 kHz. They send these sounds out using a fatty organ in their forehead called a melon. These clicks bounce off objects and return to the dolphin. This process, known as biosonar, helps them understand the shape and size of objects.

Dolphins also communicate using low-frequency whistles. Their hearing is specially adapted for the ocean. Instead of an outer ear, they receive sound through their throat. The sound then passes through a fat-filled cavity to the inner ear. Air-filled sinus pockets isolate the ear from the skull. This allows them to have excellent directional hearing underwater.

Dolphins live in social groups called pods. These pods can be very large, sometimes containing one thousand individuals. Each pod may forage over areas spanning hundreds of square kilometers. Some pods have a loose social structure where members join or leave often. Other pods are more permanent. Some of these groups might be dominated by a single male and a harem of females. All oceanic dolphins are purely carnivorous. Most species eat fish and squid, or small crustaceans. However, some species are specialized. The orca is a notable example because it also eats marine mammals and birds.

The life cycle of a dolphin is quite specific. Gestation, or the time the baby grows inside the mother, lasts between 10 and 18 months. Each birth results in a single calf. Calves are typically born during the spring or summer. In many species, the mother bears all the responsibility for raising the young. Some mothers will fast, or go without eating, to nurse their young for long periods. To survive in cold water, dolphins have a thick layer of fat called blubber. This blubber provides insulation. It also acts as a layer of protection against predators. Calves are born with only a thin layer of blubber.

Scientists use many tools to study these animals. Recent molecular analyses, which look at DNA, show that some dolphin groups are not organized the way we once thought. This means the way we classify them, known as taxonomy, is likely to change. For example, in 2025, there was a significant revision of the genus Lagenorhynchus. Dolphins are also known for their ability to hybridize. This means different species can sometimes breed to create a hybrid, such as a "wholphin."

Dolphins have a deep connection to human culture. They appear in ancient art, such as frescoes from 1600 BC. They are also famous in modern movies, like the film Free Willy. Today, some dolphins are kept in captivity for shows. The bottlenose dolphin is the most common species found in these settings. In 2012, fewer than 50 orcas were found in oceanariums. Despite their fame, dolphins face many threats. They deal with habitat loss, marine pollution, and bycatch from fishing. In some places, such as Japan, they are also subject to dolphin drive hunting.