The ancestor of tetrapods evolved four limbs, and its descendents have inherited that feature — so the presence of four limbs is a homology. Over millions of years, changes occurred in the limb bones. Cats are limber and gymnasts they can hope, jump, and stretch to get about anywhere. Birds, bats, mice, and crocodiles all have four limbs. The bat and whale have "fingers" that have extended into a wing and fin, respectively. Biogeography, the study of living things around the globe, helps solidify Darwin’s theory of biological evolution. Wing shape, governed by the relative lengths of the forearm and the fingers, varies greatly, in adaptation to flight characteristics. Shown below are images of the skeletal structure of the front limbs of 6 animals: human, crocodile, whale, cat, bird, and bat. Bats, whales, and many other animals have very similar homologous structures, demonstrating that these creatures all had a common ancestor. Bat - Bat - Form and function: Bats are mammals with front limbs modified for flight. The animals manipulate these limbs in much the same way the cat does, able to flex and bend to suit its needs. If you were to look at an x-ray or skeleton-only of the three, you would see very similar structures on each forelimb. The tailbone in human beings is so-named because it is a homologous structure to the beginning of many animals' tails, such as monkeys. Not all characters are homologies. The structure and order of bones of a human arm are similar to those of the front limbs of a cat, a dolphin, and a bat. Color code each of the bones according to this key: Humerus  Carpals  Ulna  Metacarpals  Radius  Phalanges  Color code each of the bones according to this key: For each animal, indicate what type of movement each limb is responsible for. The skeleton of a generalised bat is shown below. Comparative anatomy of the bones in the front limbs of humans, cats, whales, and bats. The chest and shoulders are large and well-muscled to provide power to the wings. In bats four of the digits are thin and exceedingly long to support the modified skin called patagium, while the first digit bears a large curved claw for clinging on to the branches. However, the front limbs of all three animals—as well as humans—have the same basic underlying bone structure. Each front foot has five metacarpal bones, and each hind foot has four metatarsal bones. Radius is thin and long and ulna is reduced to vestiges. For example, birds and bats both have wings, while mice and crocodiles do not. A common example of morphological homology is evident in the skeletal structure of the front limbs of vertebrates like humans, cats, whales, bats, porpoises, horses, frogs, etc. These similarities suggest that cats, dolphins, bats, and humans had a common ancestor. Toes – Cats have five toes (phalanges) on the front (foreleg), one of these toes is the dewclaw which sits higher up on the foot and does not come into contact with the ground. Comparative Anatomy Shown below are images of the skeletal structure of the front limbs of 6 animals: human, crocodile, whale, cat, bird, and bat. The hips and legs are slender, as they do not usually support any body weight. Looking a little closer, we will find that some bats have developed an extra bone on the hind limbs near the ankle. The most obvious changes are of course in the greatly elongated bones of the fore limbs, particualrly the metacarpals and phalanges. Each animal has a similar set of bones. Sharks and bony fish do not. Bats use their front limbs to fly, whales use them to swim, and cats use them to run and climb. Each animal has a similar set of bones. AQUATIC ADAPTATION In aquatic animals such as dolphins and whales, limb is shortened to form a flipper. For example, all mammals have front limbs that look quite different and are used for different purposes. Cat limbs help them move from place to place. Feet (excluding toes) – Cats have metacarpals in their front legs and metatarsals in their hind legs. Eventually, the bones performed different functions in each type of animal.
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