2. INTRODUCTION
• Mammals are primarily terrestrial animals.
• Some of them have wonderfully adapted for a
secondary aquatic life.
• Based on the relation to water and the degree of
aquatic adaptations aquatic mammals are grouped
into :
1. Completely aquatic mammals
2. Semi aquatic or amphibious mammals
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3. AQUATIC ADAPTATIONS
1. Modification of body contour
2. Integumentary modifications
3. Locomotor adaptations
4. Skeletal modifications
5. Modification in the digestive system
6. Respiratory modifications
7. Modifications of sense organ
8. Reproductive modifications
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4. Modifications Of Body Contour
• Most aquatic mammals have a tapering
and streamlined body.
• Elongation of skull
• Reduction of zygomatic arches
• Development of cylindrical chest
• Reduction of projecting structures – hind
limbs, pinnae, scrotum, etc.
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5. Integumentary Modifications
• The modifications mainly loss of hair & skin glands & the
formation of blubber(fatty layer of adipose tissue).
• Blubber serve as a heat insulator and there by prevents
the loss of body heat & maintains a constant body
temperature.
• Reduce specific gravity of the body in the water.
• Acts as shock absorber to absorb the hydraulic pressure
during deep diving.
• Skin surface has become smooth by the loss of hair.
• Hair represents by a few bristles around the mouth
(exception in white whales) present in whales & sea
cows.
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6. Locomotory Adaptations
•Elongation of the body.
•Reduction or loss of hind limbs.
•Formation of dorsal fin, tail
flukes & flippers or swimming
paddles.
•Hyperdactylity (formation of
extra fingers) & hyperphalangy
(formation of extra phalanges).
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7. Modification, Reduction And Loss Of Hind Limbs
• In cetaceans & sirenians hind limb
altogether absent since tail, fore
limb & dorsal fin are mainly
involved in locomotion.
• In Platypus– forelimbs and
hindlimbs have webbed digits.
• In pinnipidians, hindlimbs are
enclosed by skin, forming oar like
structures.
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8. Formation Of Dorsal fin &Tail Flukes
• Tail of aquatic mammals, in general is
horizontally flattened, forming a sort of
caudal fin.
• In cetaceans, the flattened tail is provide
with lateral expansion of the skin called
tail flukes.
• The movement of tail & tail flukes help to
forward & vertical movement of an
organism.
• Dorsal fin & dorsal fluke, which act as a
rudder or keel in swimming.
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DORSAL FIN
9. Formation Of Flippers
• In completely aquatic mammals fore
limbs are modified into swimming
paddles of flippers.
• A flipper consists of an internal
support of fused bones, covered by
skin.
• In semi aquatic mammals fingers are
webbed.
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10. Hyperdactyly and hyperphalangy
•Flippers are characterised by
Hyperdactyl and
hyperphalangy (development
of extra finger & extra
phalanges).
•This gives them sufficient
strength and support and
increases their surface area.
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Hyperphalangy in whales
11. Skeletal Modification
• Endoskeleton is lighter by presence of oil
inside bone.
• Dorso ventrally flattened cranial nerve.
• Elongated facial region for catching prey.
• Vertebrae are simple with well developed
neural spines and transverse process for
the attachment of muscle .
• Cervical vertebrae are fused to form a
small solid bone and neck region reduced.
• Ribs are movable & dorsally attached this
enhance the lung capacity and also
increases the thoracic cavity backward for
flotation.
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12. Modification InThe Digestive System
• In fully aquatic jaws are used only for catching the prey and not for
mastication.
• Mastication is practically absent in oral cavity.
• Salivary glands are very much reduced
• Stomach of mostly aquatic mammals has chambered & specialised for
crushing and digesting the food.
• Teeth are simple and dentition is homodont and arranged on upper jaw into
transverse rows.
• In toothed whales are quite numerous (more than 250).
• Baleen plates act as strainers for filtering planktonic food.
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13. Respiratory Modifications
• Respiratory system of fully aquatic mammals
is highly modified for a life in water.
• External nostrils are valvular and located far
back on the top of the head.
• Dorsal position of the nostrils enables the
animal to inhale atmospheric air, without
raising head.
• Nostrils are valvular, they can be closed during
under water stay.
• Epiglottis has become tubular & elongated.
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14. Storage Of Large Quantity Of Air
• Modification of lungs.
• Lungs are large, highly elastic & non
lobular with high storage capacity.
• High concentration of myoglobin in
muscles.
• Storage of large volume of oxygen in
rete mirabile.
• Diaphragm is oblique & this makes the
thoracic cavity sufficiently large for
maximum expansion of lungs.
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15. Modification of sense organs
• EYES :
1. Relatively smaller in size.
2. Cornea is flat and lens is reduced.
3. Nictating membrane, lacrimal
gland, lacrimal ducts are absent.
4. During under water eyes are
protected by a fatty secretion
from Harderian gland.
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16. EAR :
1. External auditory
opening is small.
2. Acoustic system is
reduced.
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17. Reproductive Modifications
• Testes are intra abdominal in
position and scrotal sacs are
absent.
• The period of gestation is
considerably long (more than
one year) so that young ones will
much grow and nearly one third
of the mother’s size when born.
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18. Development OfYoung Ones
• It can be divided into 3 categories:-
• Neoformations : development of tail flukes, dorsal
fin, baleen plates, Harderian gland.
• Degenerations : loss of ancestral structures, loss of
hair, hind limbs, finger nails, pinnae, cutaneous
glands, lacrimal glands, Nictating membrane,
scrotum.
• Modifications: streamlined body, dorsal valvular
nostrils, blubber rete mirabile, highly oblique
diaphragm, flippers, simple bilobed liver, non
lobular lungs, tubular & elongated epiglottis,
chambered stomach, elongation of skull,
Hyperdactylity, hyperphalangy, reduced sternum,
shortening & fusion of cervical vertebrae, etc.
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HUMPBACKWHALEWITH NEW BORN
