Common Name: River Dolphins
Class: Mammalia
Order: Cetacea
Family:
Platanistidae
Genus: Four
genera
Species: Four
species |

Yangtze River
dolphin, Lipotes vexillifer |
River Dolphins: Family
Platanistidae
The family Platanistidae
includes four species of dolphins, collectively called “river
dolphins”, although only three species inhabit river systems.
Platanistidae belongs to the Mammalian Order Cetacea, in the
suborder Odontoceti. All toothed whales belong to the suborder
Odontoceti, which is Latin for "toothed whales". Platanistidae is
derived from the Greek word platus, meaning "flat". A Latin
derivation of the word, platanista, was used by the Roman
historian Pliny to describe a fish he observed in the Ganges River.
The beaks the dolphins in this family are generally broader than
those of the cetaceans in Delphinidae and Ziphiidae. The species of
this family are the La Plata dolphin or Fanciscana, Pontoporia
blainvillei, the Ganges and Indus River dolphins, Platanista
gangetica, the Amazon River dolphin or Boto, Inia geoffrensis,
and the Yangtze River dolphin or white fin dolphin, Lipotes
vexillifer. Some researchers place each genus in a separate
family, Iniidae includes Inia, Platanistidae includes
Platanista, Pontoporiidae includes Pontoporia, and
Lipotidae includes Lipotes. In fact, so little is known
about the evolution of these species, that some researchers question
the monophyly, or common ancestry, of the group.

Yangtze River dolphin,
Lipotes vexillifer
Generally, Platanistids
are recognized from other dolphins by a long, slender rostrum and
tiny eyes. Their neck vertebra are unfused, which allows these
dolphins to rotate their heads in a manner not associated with most
cetaceans. There is evidence that all species use echolocation to
navigate and find prey, but the use of their long snouts to probe
riverbeds and ocean bottoms to find prey is also common. Fish,
squid and shrimp are the common components of their diet.
Genus: Pontoporia
The generic name
Pontoporia, is derived from the Greek words pontos,
meaning "sea", and poreuo, meaning "to carry". This probably
refers to the dolphin's coastal, ocean habitat.
La Plata dolphin
or Franciscana Pontoporia blainvillei
The specific name,
blainvillei, is named for Henri Marie Ducrotay de Blainville
(1777-1850), a French zoologist and anatomist. Blainville became
the chair of anatomy and zoology in the Faculty of Sciences at
Paris. The common name, La Plata, means "silver" in Spanish and
Portuguese. This probably refers to the dolphin's gray coloration.
The only member of Platanistidae to prefer saltwater, the La Plata
dolphin resides in the coastal waters and estuarine habitats of
southeastern South America. Adults reach 4-6ft in length and
45-130lbs in weight. Females are generally larger than males. La
Plata dolphins are gray dorsally and light yellow ventrally.
Gestation lasts 10-11 months. Calves are 35 inches in length and
15lbs in weight at birth. They are weaned at nine months, reaching
sexual maturity at 2-3 years. La Plata dolphins, along with members
of Phocoenidae, are the only Odontocetes with symmetrical skulls.
Genus: Inia
The generic name Inia,
is a Bolivian word for dolphin.
Amazon River
dolphin or Boto Inia geoffrensis
The specific name,
geoffrensis, is named for the French zoologist Etienne Geoffroy
Saint-Hilaire (1772-1844). The common name, boto, is the Portuguese
name for this animal. Portuguese is the principal language of
Brazil, the region in which this animal is found. This species
prefers freshwater, inhabiting slow moving streams and waterways of
the Amazon and Orinoco River systems . Adults reach 5-9ft in length
and 110-195lbs in weight. Males are generally larger than females.
Amazon River dolphins range from pink to dark blue in coloration.
Dolphins found in cloudy waters are more pinkish, while those in
clearer waters have more dark blue coloration. Unlike all other
members of Platanistidae, Amazon River dolphins have bristly hair on
their snouts. This hair may be used to locate prey. Gestation
lasts 10-11 months. Calves are two feet at birth. They are weaned
at one year. Groups of 12-15 individuals have been observed,
although solitary animals and mother with calf pairs are more
common.

Amazon River
dolphin, Inia geoffrensis
Genus: Lipotes
The generic name
Lipotes, is Latin, derived from the Greek words leipo,
meaning "left behind". This refers to the morphological
similarities of this species with fossilized remains of prehistoric
dolphin species, as though this animal was "left behind" as a relic
of the past.
Yangtze River
dolphin or whitefin dolphin Lipotes
vexillifer
The specific name,
vexillifer, is derived from the Greek words vexillum,
meaning "flag", and feros, meaning "to bear". This may refer
to the dorsal fin of the species, which is observed at the surface
of the water. This species prefers freshwater, inhabiting the
Yangtze River system of China. Males of this species reach 4.5-6ft
in length and 100-275lbs in weight. Females grow 5-8ft in length
and 140-350lbs in weight. Yangtze River dolphins are pale gray
dorsally and white ventrally. Gestation lasts 10-11 months. Calves
are about four feet at birth. Group size ranges from 3-10
individuals.

Yangtze River dolphin,
Lipotes vexillifer
Genus: Platanista
The generic name
Platanista, is derived from the Greek word platus,
meaning "flat". A Latin derivation of the word, platanista,
was used by the Roman historian Pliny to describe a fish he observed
in the Ganges River. This refers to the broad beaks of the animals
in this genus.
Ganges River Dolphin
Platanista gangetica
The specific name,
gangetica, is Latin for "belonging to the Ganges", one of the
Indian rivers in which it is found. This species prefers
freshwater, inhabiting the Brahmaputra-Meghna River system and the
Karnaphuli River of India, Bangladesh and Nepal. Some scientists
classify the population of Platanista gangetica living in the
Indus River system as a separate species, Plantanista minor,
commonly called the Indus River dolphin. Adults reach 6-9ft in
length and 110-195lbs in weight. Females are generally larger than
males. Ganges River dolphins are dark gray dorsally and lighter
gray ventrally. The Ganges River dolphin's eye lacks a lens. Light
can only be received at a certain angle, resulting in sideways
swimming. Gestation lasts 11-12 months. Calves are 30 inches at
birth. They are weaned at one year, reaching sexual maturity at ten
years. Groups of 3-10 individuals have been observed.

Amazon River
dolphin, Inia geoffrensis
Conservation
All species of river
dolphins are endangered. The Yangtze River dolphin is critically
endangered, numbering about 20 individuals. Ganges River dolphins
arguably number 4000-5000, with the population of Indus River
dolphins estimated at 500 individuals. Local peoples in all regions
may hunt river dolphins for food, bait, or fat. Fisherman may
accidentally drown dolphins with their nets. The construction of
damns on the river systems in which some species are found may
negatively impact river dolphin populations by altering their
ecosystem. Pollution from urban development and boat traffic have
adverse effects on river dolphins as well.

Amazon River
dolphin, Inia geoffrensis