Dolphin

Lore & Background

Dolphins are descendants of land-dwelling mammals of the artiodactyl order (even-toed ungulates). They are related to the Indohyus, an extinct chevrotain-like ungulate, from which they split approximately 48 million years ago. The primitive cetaceans, or archaeocetes, first took to the sea approximately 49 million years ago and became fully aquatic by 5–10 million years later. Today, the closest living relatives of cetaceans are the hippopotamuses.

Reader's Guide

Dolphins range in size from the human-sized Maui's dolphin to the apex predator, the orca. They have streamlined, fish-like bodies with two forelimbs evolving into flippers, complete loss of hindlimbs (with only vestigial pelvic skeleton), and the tail forming a horizontal fluke. They use conical teeth to capture fast-moving prey such as forage fish, coleoids and shrimps. They have well-developed hearing adapted for both air and water.

Dolphins are widespread, mostly in pelagic marine environments but some thrive in brackish and freshwater bodies. Most species prefer warm waters of the tropic zones, but some, such as the right whale dolphin, prefer colder climates. Dolphins are carnivorous, feeding largely on fish and squid, but a few large-bodied dolphins, such as the orca, prey upon larger marine animals. Male dolphins typically mate with multiple females every year, but females only mate every two to three years.

Calves are typically born in spring and summer, and females bear all responsibility for raising them. Dolphins are highly social animals living in complex fission-fusion societies, forming fluid groups (pods) that constantly change in size and composition. They produce a variety of vocalizations, usually in the form of high-pitched clicks and whistles, and are very keen with echolocation.

Did You Know?

• A group of dolphins is called a school or a pod.
• Male dolphins are called bulls, females are called cows, and young dolphins are called calves.
• The name dolphin is originally from Greek delphís, meaning 'a fish with a womb'.
• The term mereswine ('sea pig') is also used for dolphins.