Is a bird a mammal or reptile?

Answer 1

Dinosaurs evolved from an earlier group of reptiles, and birds evolved from a group of dinosaurs.

One of the earliest birds, Archaeopteryx, dates back to the Jurassic. It has many features of dinosaurs, and indeed, several fossils of Archaopteryx were initially mistaken for dinosaur fossils. It is fairly clear from the fossil evidence that birds evolved from dinosaurs.

Dinosaurs themselves date back to the middle to late Triassic. You may wish to look up Eoraptor. Dinosaurs appear to have evolved from socket-toothed archosaurs common in the mid Triassic, which were an early reptile.

The skeletal structure of dinosaurs bears many similarities to that of birds. Birds are classified as dinosaurs, while all "non avian" dinosaurs went extinct at the end of the Cretaceous.

Answer:That may depend on the dinosaur. All dinosaurs are likely to have ultimately evolved from reptiles, but the theropods (bipedal carnivorous dinosaurs) may have evolved from ancient birds. Birds have many features in common with theropods which suggests that they had a common ancestor. It is generally believed that this common ancestor was a dinosaur but it may well have been a bird (see related links).

Looking back in time through the theropod fossil record, these dinosaurs appear to be more bird-like the further back in time you look. Raptors are known to have had feathers and were fairly bird-like, but Archaeopteryx was much more bird-like and lived much earlier and may have been an ancestor of the raptors. There is also a controversial fossil called Protoavis that was dated even earlier and was more bird-like still, with hollow bones like modern birds.

So birds may have been around throughout the mesozoic era and pre-date the dinosaurs. We have little record of them though because their more fragile, hollow bones reduce the chances of any fossils surviving to the present day.

Answer 2

The short answer: Yes, they wer. The long answer depends on understanding that the term "reptile" is a paraphyletic grade rather than a natural clade. Dinosaurs were members of the clade Sauropsida, alongside every other animal that you would call a reptile (snakes, turtles, lizards etc.).

Answer 3

Dinosaurs are currently classified as reptiles while birds are classified as one branch of the dinosaurs. Some claim, however, that dinosaurs should be given their own group.

Answer 4

Neither. Birds are in their own class.