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Birds are vertebrates adapted for flight. Important adaptations include
feathers, wings, warm-blooded metabolism, hollow bones, and loss of teeth
and tail bones. Class Aves (birds): Warm-blooded, feathered vertebrates. Flight adaptations: Birds have adaptations for flying, including wings, feathers (modified scales), and good vision. Modern flying birds also have strong ribs and a rigid sternum (breastbone) with a keel. Metabolism: A high rate of metabolism is needed for flight. Birds are warm-blooded, meaning that their metabolic rates and body temperatures are always rather high, regardless of external temperature. Downy feathers are part of an insulating layer that makes a high internal body temperature possible. The complete separation of oxygen-poor and oxygen-rich blood in the heart also increases metabolic efficiency. Weight reduction: Modern birds have many adaptations that reduce weight, including reduction of the tail bones, loss of the teeth and lightening of the jaws, development of hollow air spaces in the arm bones, and loss of one ovary in female birds. Archaeopteryx and the origin of birds: Archaeopteryx, the oldest bird, was preserved in a fine-grained Jurassic limestone. It had many reptile characteristics, including a long tail, slender ribs, weak sternum, small braincase, and jaws with teeth. However, it also had feathers and was probably capable of flight, and is, therefore, classified as a bird. Scientists now think that birds evolved from carnivorous dinosaurs. Modern birds:
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