Aquatic mammals have adapted to live fully or partially in water. Some mammals, like whales and dolphins, live their entire lives in water. Others, like seals and otters, spend most of their time in water but need to return to land for activities like mating. Adaptations for aquatic life include streamlined bodies, webbed limbs or flippers, large lungs and nostrils placed high on the head. Examples of fully aquatic mammals are whales, dolphins and manatees. Semi-aquatic mammals include seals, otters and hippopotamuses.

1. Shri Shankaracharya Mahavidyalaya, Junwani , Bhilai
Dr. Sonia Bajaj
(Head of Department)
Aquatic mammals & their adaptation

2. Aquatic Mammals
All living beings on the planet have their origin in the aquatic environment .Throughout
evolutionary history, mammals have been changing and adapting to conditions on the
surface of the earth until, several million years ago, some submerged themselves in the
oceans and rivers, adapting to life under these conditions. Mammals are primarily
terrestrial animals, but some of them have wonderfully adapted their secondary aquatic
life.
• mammals are classified in to two group:
•They either live in fresh water or salt water.
1. Entirely/Completely aquatic mammals
2. Semi-aquatic or amphibious mammals
1.Entirely/Completely aquatic mammals: Aquatic mammals include species that live their
entire live in the water and depend on it for survival, such as whales, dolphins or manatees
etc. They never come to land and are completely reside in water.
2. Semi-aquatic or amphibious mammals: •There are some mammals reside their live in
both terrestrial and aquatic environments called semi-aquatic animals/Amphibious
mammals, like seals, otters, and hippopotamuses etc.
•The semi-aquatic mammals spend the majority of their time in the water (for food and
shelter), but need to return to the land for important activities such as mating, breeding
and molting.

3. Aquatic Adaptations
The body of aquatic animals is streamlined i.e. trapped at both ends. Head is blunt and tail is long.
The body is provided with air sacs or air bladder so that they do not sink when they stop swimming. They
have paired and unpaired fins, flippers and paddles and webbed legs for swimming.
A. Morphology Structures
Body Shape: The external fishlike form, elongated head, indistinct neck.
Large Size and Weight: In aquatic mammals, the large size and body weight help the aquatic mammals.
Flippers: In aquatic mammals, the forelimbs are transformed into skin-covered, un-jointed paddles or
flippers, having no separate indication of fingers. The broad and flattened paddles or flippers serve as
balancers and provide stability during swimming.
Hyperdactyly and Hyperphalangy: extra digits (hyperdactyly) and extra phalanges (hyperphalangy) up to
14 or more .
High and Valvular Nostrils: the nostrils are placed far back on the top of head so that animal can breathe
air without raising head much out of water. The nostrils can also be closed by valves during diving under
water.
Mammary Ducts: This arrangement facilitates suckling of young under water.
Oblique Diaphragm: oblique diaphragm makes the thoracic cavity larger dorsal and barrel-shaped for
providing more space to lungs for expansion.
Large Lungs:large unlobulated and highly elastic lungs ensure taking down maximum air Lore
submergence.

4. B. Loss of Structures
There is a loss of hairs.
Pinnae are also absent.
Fingernails are absent.
C. Development of New Structures:
Tail Flukes
Dorsal Fin
Blubber
Foam
Melon
Harderian Glands

5. Primary Feather of Aquatic Mammals
The characteristics of aquatic animals are as follows:
1. Most of their Species live in water and some of them live on the land.
2. They have paired and unpaired fins which help them to swim.
3. They have either webbed limbs or limbs are modified to paddles for swimming.
4. Their body shape is streamlined and their bones are light and spongy.
5. The skull undergoes modification to form a slender snout.
6. The neck is reduced and external ears are disappeared.
7. Gills or ability to hold breath underwater for long periods.
8. Fins or limbs adapted for swimming, including webbed feet, for animals that don't spend
all their time in the water, like otters and beavers.
9. Tails that act as paddles. Fish tend to have tails that are vertical, necessitating a side-to-
side movement, while aquatic mammals have flukes, which are horizontal; they propel
themselves with an up-down motion. Even semi-aquatic mammals, like otters and beavers,
have tails that are sort of horizontally flat.

6. Group Example
Cetaceaa (Marine,Whale like mammals) Whales , dolphins , porpoises
Sirenia (aquatic herbivorous mammals) Dugongs , manatees
Completely aquatic mammals
Aquatic mammals divided into the following categories:
1. Amphibious Mammals:
These mammals do not live permanently in water. They live on land but go into water for
food and shelter.
(i) Small external ears,
(ii) Webbed feet,
(iii) Flattened nails,
(iv) Subcutaneous fat.
The mammals of this category include the beaver (Castor), musk rat (Ondatra), nutria
(Myocaster), otter (Lutra), mink (Mustela) and many others.
2. Aquatic Mammals:
The mammals under this category spend most of the time in water and usually come to
land for reproduction. The typical examples are seals and hippopotamus.
3. Marine Mammals:
These mammals never come to land and are perfectly at home in water. The typical
examples are whales.

7. References-
Modern text book – R.L.Kotpal
Jantu Vigyan- S.M. sexsena
Jantu Vigyan- Dr.H.N. Baijal
Jordan, E.L. and Verma , P.S.,
Chordate Zoology, S. Chand