The Superfamily Delphinoidea contains all of the dolphins, along with the porpoises and a number of cetaceans that we commonly refer to as whales. The Family Delphinidae (AKA the Delphinids) is specifically the oceanic dolphins, although it includes a number of creatures that we do not commonly refer to as dolphins. Delphinidae includes orcas and pilot whales; some members of Delphinidae also have the blunter snout that is commonly associated with porpoises rather than dolphins.
Delphinids have a broad facial depression, which along with fatty deposits (called 'melons') located on their temples give them the appearance or bulging foreheads. They have expanded maxillae, although this is a subtle effect. The lower jaws are fused for less than 40% of their length, and the upper toothrows diverge posteriorly. They have peg-like teeth, with circular in cross sections. Their dental formula vary from 0/2 to 65/58. Most of them have protruding snouts, although this is not a hard and fast rule.
Generally speaking, members of Delphinidae prefer to stay close to shore and close to the surface, and so are a familiar sight to sailors and fishermen. They tend to be fast swimmers and quite agile, which is necessary due to their role as predators, feeding on fish and squid, and in the case of orcas, larger sea mammals.
The smallest Delphinids are less than two meters in length, with Haviside's dolphin measuring a mere 1.2 meters (3.9 ft) and weighing just 40 kilograms (88 lb). The largest is the orca whale, which can measure up to 9 metres (30 ft) and weigh up to 10 tonnes. There are 38 species in 17 genera.