9 Main Physiological Adaptation to Marine Life
Physiological Adaptation to Marine Life
1. Stream-lined Body – The body shape is stream-lined like primarily adapted forms: neck construction disappears and tail enlarges, e.g- Ichthyosauria (extinct fish-lizard), Cetacea (whales, dolphins, porpoises), Sirenia (manatees and dugongs), Pinnipedia (walrushes and seals). Frog also contains stream-lined body.
2. Enlargement of Size – Aquatic vertebrates tend to be larger in size because in these creatures energy, which in terrestrial from is exhausted in gravitational forces, is turned into growth. For example, largest sulphur- bottom whale (balaenoptera musculus) is several times bigger than the largest elephant. Other example include giant sharks and squids.
3. Shortening of Neck- These occurs reduction of length and mobility of neck. In whales cervical vertebrae (which are seven in number like other mammals) are fused to form a solid and compressed mass of bone.
4. Mouth Armament – Since jaws are not used for mastication in whales they lost the power of movement. Teeth become simplified (homodont in dolphins) and greater in number. In sperm whole, teeth are present only on one jaw or entirely absent from both the jaws (baleen whale).
5. Skull Modification – In certain aquatic mammals (dolphins, propoises) the cranium is shortened and front part of the skull becomes elongated to acquire the shape of a rostrum. In the skull of the cetacea, the zygomatic arch is reduced to a vestige.
6. Simplification of Vertebrae – In secondary aquatic forms the vertebrae tend to be simple. In Ichthyosaurs, Vertebrae are simple with biconcave centra like the fishes. Various secondary articulations or zygapophysis become reduced, as body weight is supported by water. The chest too become cylindrical. The rib articulations are modified and are central, i.e. they are articulated to the centrum and are not articulated to the transverse processes.
Sacrum in cetaceans and sirenians is more or less reduced, since it does not with stand and transmit the supporting impact of the hindlimbs, as does in terrestrial forms.
7. Lightness of Bones – The bones in aquatic forms are light and spongy. In wholes, their interstices are filled with oil.
8. Disappearance of Hairs, Skin Glands – In whales and sirenians, the skin becomes makes due to loss of hairs. The hair loss is compensated by the formation of a fatty layer below the skin (blubber) for the retention of the bodily heat. The blubber also has a hydrostatic advantage.
9. Occurrence of Locomotory Paddles (Fins) – There occure fleshy and fin-like expansions of the body wall in whales and ichthyosaurs which help in propulsion. These fins may be dorsal or caudal. Dorsal fin is present in killer whale, while absent in Delphinopterus and Balaena. Caudal fin (also called caudal or tail fluke) of marine mammals in horizontal and the bone divides the tail into two equal parts rather than running into one lobe. In tulles oar propulsion occurs by fin-like limbs, but in whales, sirenians etc. tail propulsion takes places as their hind limbs become disappeared.
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