Guiana dolphins are found in Lake Maracaibo, in the rivers of Guyana, and in the nearshore coastal waters of the northeastern portion of the Guianas.
In their very limited range, stranded Guiana dolphins can be readily identified by their extremely small size (to 5.6 feet [1.7 m]) and nearly triangular dorsal fin. Furthermore, in addition to the characteristics listed above distinguishing living Guiana dolphins from Atlantic bottlenosed dolphins, the species can be distinguished by differences in the numbers of teeth:
ATLANTIC BOTTLENOSED GUIANA DOLPHINS DOLPHINS
20-26 in each upper jaw; 26-35 in each jaw; often 18-26 in each lower jaw. ragged in arrangement.
[Illustration: Figure 147.--A Guiana dolphin from Kartabo, British Guiana. In the coastal portion of its range along the northeastern South American coast, this species is most likely to be confused with the Atlantic bottlenosed dolphin. Guiana dolphins are much smaller, rarely exceeding 5.6 feet (1.7 m), have a more triangular dorsal fin, and tend to be found more frequently in estuaries and rivers. (_Photo by A. B. Van Beneden from Zoologica VII(4), by permission of the New York Zoological Society._)]
[Illustration: Figure 148.--Guiana dolphins harpooned in Kartabo, British Guiana. Guiana dolphins have from 26 to 35 teeth in each jaw. Atlantic bottlenosed dolphins, which are larger but somewhat similar in appearance, have from 20 to 26 teeth in each upper jaw and from 18 to 26 in each lower jaw. (_Photo by A. B. Van Beneden from Zoologica VII (4), by permission of the New York Zoological Society._)]
_Steno bredanensis_ (G. Cuvier in Lesson 1828)
Rough-toothed porpoise, goggle-eyed porpoise.
Rough-toothed dolphins reach a length of at least 8 feet (2.4 m). The coloration of the rough-toothed dolphins is quite variable. Individuals are often dark gray to dark purplish gray on the back with pinkish-white blotches on the sides and belly. The flippers and flukes are dark and the belly is white. Individuals are frequently scarred with numerous white streaks.
The most distinctive characteristic of the rough-toothed dolphin is its beak, which is quite long and slender, may be white or pinkish white along both sides, including one or both lips and the tip of the snout, and is not separated from the forehead by the transverse groove present in other long-snouted dolphins. Because the forehead and the sides of the head slope smoothly into the rostrum, when this animal is seen from above or from the side, its entire head appears very long and nearly conical.