Why do scientists think that birds evolved from dinosaurs?

Answer: birds and dinosaurs have more efficient hearts and lungs than mammals

Modern birds are descended from a group of two-legged dinosaurs. Based on these life-giving characteristics, scientists have concluded that theropods were ancestral birds. Perhaps the bird evolved from dinosaurs by accepting animal's pattern.

Explanation:

The respected scientific consensus is that the birds are Teherod dinosaur groups that continued living during the Mesozoic era. The velociraptor has a skull simmilar as the coyote and the brain of an pigeon.

Of course, these are just theories. It is not proven that birds evolved from dinosaurs, but many characteristics are leading to this theory, especially after the discovery of the primitive bird Archeopterik in Germany.