Dolphins: Photo by lowjumpingfrog on Flickr.
‘Dolphins’ comprise the largest family of the cetaceans, with over forty species within some 17 genera varying in size from 1.2 m (4 ft) and 40 kg (90 lb) for the Maui’s dolphin – Cephalorhynchus hectori maui (a big name for a small animal), up to 9.5 m (30 ft) and 10 tonnes – the orca or orca orcinus (a small name for a big animal).
All dolphins are pack animals that hunt and play cooperatively. They also are representative of the major division of the cetaceans between the Mysticetes (‘mustache’ or baleen whales) and Odontocetes (toothed whales).
The difference between these divisions is akin to the terrestrial division between cows and wolves; the large Mysticetes graze on massive gullet-full quantities of small organisms, the Odontocetes pack-hunt prey which they pick off individually.
The Dolphin’s vocalization repertoire reflects their high-speed social and tactical adaptations. They use mid frequency vocalizations for social interaction (within our human auditory band), and high frequency bio-sonar to perceive their surroundings and “see” their prey.
The other most familiar members of the sub-order “odontoceti” are the porpoises (Phocenidae) with a similar behavioral repertoire to the dolphins. One simple distinguishing difference is that the dolphins have round teeth, and the porpoises have flat teeth – a distinction that hopefully remains only academic to the reader.
The dentition of other odontocetes (from narwhals to beaked whales) is for too varied, and a bit too tangential to outline here.
Wikipedia: Common Dolphin
Discovery of Sound in the Sea: Common Dolphin
Discovery of Sound in the Sea: Spinner Dolphin
Discovery of Sound in the Sea: Bottlenose Dolphin