Radius is thin and long and ulna is reduced to vestiges. 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. 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. For example, birds and bats both have wings, while mice and crocodiles do not. Feet (excluding toes) – Cats have metacarpals in their front legs and metatarsals in their hind legs. For example, all mammals have front limbs that look quite different and are used for different purposes. The hips and legs are slender, as they do not usually support any body weight. Each front foot has five metacarpal bones, and each hind foot has four metatarsal bones. Biogeography, the study of living things around the globe, helps solidify Darwin’s theory of biological evolution. The tailbone in human beings is so-named because it is a homologous structure to the beginning of many animals' tails, such as monkeys. The ancestor of tetrapods evolved four limbs, and its descendents have inherited that feature — so the presence of four limbs is a homology. The chest and shoulders are large and well-muscled to provide power to the wings. These similarities suggest that cats, dolphins, bats, and humans had a common ancestor. Eventually, the bones performed different functions in each type of animal. Each animal has a similar set of bones. Comparative Anatomy Shown below are images of the skeletal structure of the front limbs of 6 animals: human, crocodile, whale, cat, bird, and bat. 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. Bats use their front limbs to fly, whales use them to swim, and cats use them to run and climb. Bats, whales, and many other animals have very similar homologous structures, demonstrating that these creatures all had a common ancestor. Color code each of the bones according to this key: Humerus [] Carpals [] Ulna [] Metacarpals [] Radius [] Phalanges [] 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. The skeleton of a generalised bat is shown below. Wing shape, governed by the relative lengths of the forearm and the fingers, varies greatly, in adaptation to flight characteristics. AQUATIC ADAPTATION In aquatic animals such as dolphins and whales, limb is shortened to form a flipper. 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 animals manipulate these limbs in much the same way the cat does, able to flex and bend to suit its needs. Over millions of years, changes occurred in the limb bones. Color code each of the bones according to this key: For each animal, indicate what type of movement each limb is responsible for. Shown below are images of the skeletal structure of the front limbs of 6 animals: human, crocodile, whale, cat, bird, and bat. Bat - Bat - Form and function: Bats are mammals with front limbs modified for flight. Looking a little closer, we will find that some bats have developed an extra bone on the hind limbs near the ankle. Cat limbs help them move from place to place. Birds, bats, mice, and crocodiles all have four limbs. 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. Not all characters are homologies. The bat and whale have "fingers" that have extended into a wing and fin, respectively. Sharks and bony fish do not. 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