They’re birds, of course. But some scientists also see them as feathered dinosaurs.
True birds, complete with feathers, evolved during the Jurassic Period when the largest dinosaurs stalked the earth. The most famous prehistoric bird by far is Archaeopteryx, which left exquisite fossils that reveal its Jurassic feathers.
Besides feathers, birds had toothless beaks and hollow bones. After all, they had to stay light on their feet if they were to fly! Furthermore, birds resembled dinosaurs in that they walked on legs that held their bodies off the ground. Even today, most amphibians and reptiles crawl on their bellies.
We now know that at least some dinosaurs cared for their young. A few reptiles and fishes do, but not many. Of course, birds continue the dinosaur tradition of caring for their young. Although the term “bird-brain” is an insult, birds are generally more intelligent than reptiles, amphibians, and fishes.
Birds are also warm-blooded. Thus, they can live in far colder areas than reptiles and amphibians. (Some dinosaurs were likely warm-blooded, too.) Despite all their advances, birds remain, in a sense, primitive in at least one respect: All modern birds lay eggs. Even some fishes and reptiles evolved the ability to retain their eggs inside their bodies, where they hatch. Such animals—which are termed ovoviviparous—can travel around and protect their young at the same time, similar to mammals. But birds remain oviparous, just laying eggs.
On the other hand, being able to fly allows birds to lay eggs in places that are tough for predators to reach. There probably weren’t many dinosaurs adept at stealing bird eggs from trees or cliffs on remote islands!