About Steno bredanensis (G.Cuvier, 1828)
The rough-toothed dolphin, Steno bredanensis, is a relatively large dolphin species. Adult length ranges from 2.09 to 2.83 metres (6.9 to 9.3 ft), and adult weight ranges between 90 and 155 kilograms (198 and 342 lb), with males growing larger than females. Its most prominent visible traits are a conical head and slender nose; other dolphin species typically have either a shorter snout, or a more noticeably bulging melon on the forehead. As the species' common name suggests, its teeth are also distinctive: they have a roughened surface formed by many narrow, irregular ridges. Individuals have between nineteen and twenty-eight teeth in each quarter of the jaw. The outer shape of the rough-toothed dolphin's jaw is very distinct, and the lower jaw is usually white, sometimes with a faint pink tint. The species' flippers are positioned further back along the body than those of other similar dolphins, though at sea rough-toothed dolphins may still be confused with spinner, spotted and bottlenose dolphins. The dorsal fin is prominent, with a height between 18 and 28 centimetres (7.1 to 11.0 in). The animal's flanks are light gray, while the back and dorsal fin are a much darker gray. Older individuals often develop distinct pinkish, yellow, or white markings around the mouth and along the underside. The distribution and total population of the rough-toothed dolphin are poorly understood. The species inhabits warm temperate to tropical waters of the Pacific, Atlantic, and Indian Oceans, as well as the Mediterranean Sea, with occasional reports of individuals in cooler environments. They are regularly sighted in areas stretching from the Windward Islands to Cape Verde, while only a small number of individuals have been recorded in the Azores and Madeira. Almost all live sightings occur far offshore, beyond the continental shelf, in water that is at least 1 kilometre (0.62 mi) deep. Most research on the species has focused on the eastern Pacific, where researchers produced a population estimate of 150,000 in the 1980s. Fossils belonging to the genus Steno, dated to the early to mid-Pliocene, have been found in Europe. In the Mediterranean Sea, the species was once thought to only visit from the North Atlantic, but recent findings confirm there is a small resident population in the eastern part of the sea. Rough-toothed dolphins give birth to a single calf, but the length of their gestation period is unknown, and it is also unclear whether they have a distinct breeding season. Newborn young are roughly 100 centimetres (39 in) long at birth, and grow rapidly for their first five years of life. Females reach sexual maturity between six and ten years of age, and males reach sexual maturity between five and ten years of age.
