Biology Reference
In-Depth Information
Physical Description of the Ganges Dolphin
The Ganges River dolphins have long, pointed snout characteristic of all river dolphins.
Both the upper and lower jaw sets of long sharp teeth are visible even when the mouth is
closed. The snout is long and widens at the tip. In females, the snout is generally longer and
may curve upwards and to one side. The eyes are extremely small resembling pinhole
openings slightly above the mouth. The species does not have crystalline eye lenses,
rendering it effectively blind, although it may still be able to detect the intensity and direction
of light. The river water where they live is so murky that good eyesight would most-likely not
be advantageous. Navigation and hunting are carried out using echo-location. The body is
subtle and robust, attenuating posteriorly from the dorsal fin to a narrow tail stalk. The body
is deep and has a brownish color and is stocky at the middle. They have round bellies. The
dorsal fin is very low triangular hump located two-thirds body length from the anterior end.
The broad flippers have a crenellated margin, with visible hand and arm bones. Its flukes are
broad and these along with their flippers are thin and large in relation to body size, which
normally ranges from 2-2.2 m in adult males and 2.4-2.6 m in adult females. At the time of
birth they measure 70-90 cm and weigh 4 - 7.5 kg. Adults (2 - 2.6 meter) weigh between 70
and 90 kg, however, an adult pregnant female (2.5 m) caught at Araria in Northeastern Bihar,
near Indo-Nepal border, weighed 114 kg (caught in February 1993 and brought to Patna Zoo).
We also recorded a 70 cm male fetus weighing 4 kg, 77.5 cm male 6.6 kg and a 91 cm female
weighing 11 kg, all collected from the Ganges in and around Patna.
Primitive Characters
Platanista g. gangetica bears some of the very primitive characters not known in other
cetaceans, videlicet the presence of the ceacum at the junction of the small and large
intestines, a testis position that is much more dorsal compared to other marine cetaceans
(testes are extra-peritoneal in terrestrial mammals), and subcutaneous muscle between two
layers of blubber. The following informations were recorded while working on a carcass of a
male dolphin at Patna:
Body Length: 171cm, Body Weight: 55 kg, Blubber thickness (cm): Dorsal Skin (0.1) +
Blubber (2.5), Lateral Skin (0.1) + Outer blubber (1.3) + Panniculus (0.2) + Inner blubber
(2.7), Ventral Skin (0.1) + Outer blubber (1.9) + Panniculus (0.2) + Inner blubber (0.7),
Intestine length (cm): Small intestine (620) + Caecum (8) + Large intestine (80).
Morphological Characters of Interest
1.
Texture of subcutaneous tissue: Cetacean fatty tissues are accumulated in blubber,
whereas in terrestrial mammals fatty tissues can be found here and there in the
subcutaneous connective tissues. In Platanista , they have certain thickness of blubber,
but at the same time texture of the deeper connective tissues is somewhat more
similar to those of the terrestrial mammals. We are not sure if this has anything to do
with
primitiveness
or
similarity
to
ancestral
terrestrial
mammals
(Personal
communication Tadasu Yamada).
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