Birds include any warm-blooded vertebrate of the class Aves, having a body covered with feathers, forelimbs modified into wings, scaly legs, a beak, and no teeth, and bearing young in a hard-shelled egg. Birds have a beak, which is a hard bill covering the jaw, and a four-chambered heart. It is generally believed that birds are descended from dinosaurs and probably evolved from them during the Jurassic Period. While most paleontologists believe that birds evolved from a small dinosaur called the theropod, which in turn evolved from the thecodont, a reptile from the Triassic Period, other paleontologists believe that birds and dinosaurs both evolved from the thecodont. There are some who even consider the bird to be an actual dinosaur. According to this view, the bird is an avian dinosaur, and the older dinosaur a nonavian dinosaur. Although there are variations of thought on the exact evolution of birds, the similarities between birds and dinosaurs are striking and undeniable. Small meat-eating dinosaurs and primitive birds share about twenty characteristics that neither group shares with any other kind of animal; these include tubular bones, the position of the pelvis, the shape of the shoulder blades, a wishbone-shaped collarbone, and the structure of the eggs. Dinosaurs had scales, and birds have modified scales—their feathers—and scaly feet. Some dinosaurs also may have had feathers; a recently discovered fossil of a small dinosaur indicates that it had a featherlike covering.

'Monster' bird reveals dark side

Shoebill chick is filmed attacking its younger sibling

Aggressive bullying between bizarre-looking shoebill chicks has been filmed for the first time. The encounter was captured at Bangweulu wetlands, near Kasanka, in northern Zambia for the BBC One series Africa. Wildlife filmmakers were surprised to witness an older chick attacking its younger sibling while their mother was foraging away from the nest. The birds are rare subjects for study because their swamp breeding grounds are very difficult to access. The team's aim was to shed light on the species by documenting intimate behaviour of shoebill parents and young at the nest. Siblicide, the phenomenon of offspring killing their siblings, is common among many larger birds.