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The Rough-Toothed Dolphin
The only species in the genus Steno is the rough-toothed dolphin,
Steno bredanensis. Although first described in 1828, virtually nothing
about this species was known before 1964, when the first specimen was taken
into captivity. The rough-toothed dolphin has long been considered an enigma
to cetologists. It is approximately 2.5 meters in length, with a somewhat
elevated dorsal fin near the middle of the body. On the dorsal side, it
is described as sooty black or purplish, while the ventral side has an
almost rosy color and has numerous black patches. The demarcation between
the two main areas of color is very irregular. On the dark area, there
are many white or pinkish blotches, leading to one of the most unusual
colorations of any species of cetacean: "pink with purple polka dots."
Another characteristically unusual feature is that there is no crease between
the forehead and the beak. In this respect the species looks almost like an
icthyosaur. The flippers are proportionally large, and the lips are white
with crisscrossed scars, possibly resulting from encounters with squid. Older
specimens are fat and heavily scarred. Because of these irregularities, some
consider this species to be the ugliest dolphin.
The rough-toothed dolphin prefers deeper waters where the temperature is
more than 25° C. It is found is nearly all tropical and subtropical waters
around the world, although its distribution in the Atlantic is limited to
regions north of the equator. In the past it was believed that its appearance
in the Mediterranean Sea was rare, but recent sightings near Sicily suggest
that there may be a permanent population there.
A somewhat rare animal, very few individuals are actually seen in the
wild. It likes remaining under water and will dive for long periods of around
15 minutes when approached. The rough-toothed dolphin is one of the more
skillful of the dolphins at diving. In one experiment, an individual named
Pono was able to dive to a depth of 30.5 meters without actually nearing its
maximum abilities. It was also able to perform 51 dives in 105 minutes
without exerting much effort. Although a quick learner, rough-toothed
dolphins are known to have hot tempers, and trainer errors such as
contradiction and confusion may elicit strong emotional responses. It is not
a bow-rider, but it has been known to travel in the stern wake of a vessel.
Echolocating abilities have been demonstrated in this species, and the
echolocating clicks are remarkably directional.
Baker, Mary L. Whales, Dolphins, and Porpoises of the World. New York: Doubleday & Company, Inc., 1987.
Carwardine, Mark. Eyewitness Handbooks: Whales, Dolphins, and Porpoises. New York: Dorling Kindersley Ltd., 1995.
Ellis, Richard. Dolphins and Porpoises. New York: Alfred & Knopf, Inc., 1982.
Klinowska, Margaret. Dolphins, Porpoises, and Whales of the World: The IUCN Red Data Book. Gland, Switzerland: World Conservation Union, 1991.