Sotalia fluviatilis and Sotalia guianensis are very similar in appearance and were once classified as a single species. However, phylogenetic evidence indicates that they diverged approximately 1.5 to 2 million years ago during the Pliocene or early Pleistocene. Despite their many similarities, three major differences help distinguish between these 2 species. First, S. fluviatilis largely prefers fresh water habitat, whereas S. guianensis prefers saline coastal habitat. Second S. fluviatilis is much smaller in size than S. guianensis. Finally, the haplotype and nucleotide sequences of S. fluviatilis are as diversified from S. guianensis as they are from other delphinids. In general, S. fluviatilis is smaller and has a shorter beak than most other members of the family Delphinidae. It ranges from blue to pearl-grey along the dorsal surface and from white to pale-pink along the ventral surface. Most individuals have a white tipped beak. The dorsal fin has a prominent triangular shape that sometimes hooks toward the caudal fin. Adults have between 28 and 35 teeth. Sotalia fluviatilis is not sexually dimorphic and ranges from 86 to 206 cm long and weighs 55 kg on average.
Average mass: 55 kg.
Range length: 86 to 206 cm.
Average length: 152 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: sexes alike
Average mass: 46666.7 g.
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