Nails claws and hooves an amniote feature that begins

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Unformatted text preview: rmal bones under scutes are called osteoderms. Nails, Claws and Hooves An amniote feature that begins in the reptiles is the presence of hard keratin structures on the tips of the digits. These carry on in birds and mammals in various forms. They are made of keratin, and epidermal in origin. On the underside of the digit there may be some sort of friction pad, also composed of keratin. These pads in humans are uniquely sculptured “fingerprints”. KK 6.23 Bird Integument Aves have a thinly keratinized skin, otherwise generally similar that of reptiles. They have reptile-like keratin scales on their legs, and feathers are thought to be derived from keratin scales. They also have claws and friction pads on their feet. Avian innovations: in addition to feathers of various kinds, they have a keratin beak and a uropygial gland under the tail for grooming the feathers. KK 6.15, H&G 6.10, 6.11 Despite that feathers seem to come from deep in the integument, they are actually produced from the epidermis like all keratin structures. The epidermis penetrates the feather follicle and covers the dermal papilla around which a new feather develops. KK 6.16, H&G 6.12 Mammalian Integument Epidermal Glands - sebacious glands - sweat glands - mammary glands - scent glands Hair is also made of keratin, but is...
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