The rough-toothed dolphin (Steno bredanensis) is a species of dolphin that lives in deep warm and tropical waters around the world. It was first described by Georges Cuvier in 1823. The genus name Steno, of which it is the only member, comes from the Greek for 'narrow', referring to the animal's beak, which is a diagnostic characteristic of this dolphin. Its specific name honours van Breda, who studied Cuvier's writings. There are no recognised subspecies.
Taxonomy
This species was formerly classified in the now-defunct subfamily Stenoninae, but more recent evidence has found that, despite its prominent bill, it in fact belongs with the blunt-nosed dolphins in the subfamily Globicephalinae.
Description
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The rough-toothed dolphin is a relatively large species, with adults ranging from in length, and weighing between ; males are larger than females. Its most visible characteristic feature is its conical head and slender nose; other dolphins either have a shorter snout or a more visibly bulging melon on the forehead. As the common name for the species implies, the teeth are also distinctive, having a roughened surface formed by numerous narrow irregular ridges. They have been reported to have between nineteen and twenty-eight teeth in each quarter of the jaw. The rough-toothed dolphins jaw on the outside is very distinct. The color of the lower jaw is usually white, but can have a hint of pink mixed in.
The flippers are set back further along the body than in other similar dolphins, although, at sea this dolphin may be confused with spinner, spotted and bottlenose dolphins. The dorsal fin is pronounced, being from in height. The animal's flanks are a light gray, while the back and dorsal fin are a much darker gray. Older individuals often have distinctive pinkish, yellow, or white markings around the mouth and along the underside.
Most of the research activity concerning the dolphin has been directed in the eastern Pacific, where a population estimate of 150,000 was obtained by researchers in the 1980s. Fossils belonging to the genus Steno are known from Europe and date to the early to mid-Pliocene.
Behaviour and diet
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Rough-toothed dolphins are typically social animals, although solitary individuals are also sighted. Such groups are thought to be temporary assemblages, composed of smaller, more permanent groups of two to eight closely related individuals that occasionally join with others. They have also been reported to school together with other species of dolphin, and with pilot whales, false killer whales, and humpback whales.
Rough-toothed dolphins have been reported to bow-ride on a number of occasions, and be able to stay underwater for at least fifteen minutes.
Reproduction
Rough-toothed dolphins give birth to a single young, after an unknown period of gestation; it is also unknown whether or not they have a distinct breeding season. The young are about long at birth, and grow rapidly for the first five years of life. Females reach sexual maturity somewhere between six and ten The facility is one of two that houses the species in North America.
See also
- List of cetaceans