A great tract of land on the southern and southwestern shore of the North American continent consists of deltas, swamps and backwaters. Since Cretaceous times it has gradually been rising above sea level, and it is now covered in marshy vegetation, comprising vast areas of reed beds and mangroves with stands of conifers, evergreen oaks and magnolias on the drier banks. The available moisture and warm climate mean that several varieties of plants and animals live here. Bird and pterosaur life is particularly abundant, as the birds have adapted well to this pleasant environment. Anseriforms graze the waterweed, gaviiforms plunge into the waters after ray-finned fish, and charadriiforms peck after smaller creatures in the mud and shallows. However, the pterosaurs live side by side with the various species of birds and reveal similar adaptations to the same conditions.The sift is built to the general pterosaur design, with a small lightweight body stiffened for flight, wings of membrane supported by the arms and extended fourth finger, and a very flexible neck. However, in appearance the sift is more like a wading bird, with its long-shanked legs and its tapering beaked jaws. The sift congregates in flocks out in the shallows. The folded wings, larger in proportion than those of birds, catch the sun and provide an ever-changing pattern of light as the flock moves about filtering the tiny insects and crustaceans from the muddy water. The long, thin jaws are armed with a multitude of tiny, comb-like teeth which are used to trap the waterborne food.