Vertebrate Body Form and Function - Most fish are fusiform, which permits the body to pass through the dense medium of water with minimal resistance. The tapered head grades into the trunk with no constriction or neck, and the trunk narrows gradually into the caudal (tail) region. The greatest diameter is near the middle of the body. Various modifications on this plan include the dorsoventrally flattened bodies of skates and rays; the laterally compressed bodies of angelfish; and the greatly elongated (anguilliform) bodies of eels. Many larval amphibians also possess a fusiform body; however, adult salamanders may be fusiform or anguilliform. Aquatic mammals, such as whales, whose ancestral forms reinvaded water, also tend to be fusiform.
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| Body Form (Sourcw: http://www.mun.ca/biology) |
As vertebrates evolved, changes to terrestrial and aerial locomotion brought major changes in body form. The head became readily movable on the constricted and more or less elongated neck. The caudal region became progressively constricted in diameter, but usually remained as a balancing organ. The evolution of bipedal locomotion in ancestral reptiles and in some lines of mammals brought additional changes in body form. Saltatorial (jumping) locomotion iswell developed in modern anuran amphibians (frogs and toads), and it brought additional shortening of the body, increased development of the posterior appendages, and loss of the tail. In saltatorial mammals such as kangaroos and kangaroo rats, the tail has been retained to provide balance. Elongation of the body and reduction or loss of limbs occurred in some lineages (caecilians, legless lizards, snakes) as adaptations for burrowing.
Aerial locomotion occurred in flying reptiles (pterosaurs), and it is currently a method of locomotion in birds and some mammals. Although pterosaurs became extinct, flying has become the principal method of locomotion in birds and bats. The bodies of gliding and flying vertebrates tend to be shortened and relatively rigid, although the neck is quite long in many birds
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