Resumen de Verwantschap van vogels met reptielen
In 1863, the British paleontologist Thomas Huxley presented a theory claiming that birds are descendants from Dinosaurs. He realized himself that some of the fossils revealed hollow bones to accommodate the air sacs, just as in birds. Both reptiles and birds breed on land. The shift from water to land required several adaptations. The principle changes were: 1) Production of an egg shell. 2) The development of an amnion. In combination these prevent desiccation of the embryo. 3) Exchange of oxygen and bicarbonate via pores in the shell. 4) A transition in the end products of the protein-metabolism away from the toxic ammonia and urea to uric acid. 5) Protection against invaders such as bacteria. Dinosaurs gave rise to birds and the present reptiles. The production of feathers is specific to birds. Fossilized feathers showed that they were colored by melanins. Both in reptiles and birds so-called structural colors developed. Vision of UV light enabled these to distinguish sexes
