Archaeopteryx was a bird-like reptile that had a toothed beak. Modern birds have no teeth in their beaks. Even though modern birds are not thought to have evolved directly from Archaeopteryx, presumably teeth were present in the ancestors of birds. Give an evolutionary explanation for the elimination of teeth in a bird's beak.
While amphibians have rudimentary lungs, skin is the primary respiratory organ. Because of this, they are much more sensitive to air pollution, especially particulate matter, than higher vertebrates. Why would skin be more sensitive to pollution than lungs?