What did birds evolve from?

I don’t believe theres a straight answer to this question, but there have been many noted similarities between birds and dinosaurs so it is likely that modern day birds may have evolved from small tree-dwelling dinosaurs.

It probably depends to a certain extent on what kind of bird. In the long-run, they evolved from single-celled organisms.

I am pretty sure it is an uncontroversial fact within paleontology that birds evolved from dinosaurs. Actually, many paleontologists would correct me….saying that birds are dinosaurs.

Wabarr is entirely correct.

DINOSOURS.

Intentional misspelling. :)

In the spirit of presenting diverse viewpoints, I will say that there is substantial evidence that the genetic information within species does not vary except for rare, non-beneficial mutations, and some information may be “turned off” in dormant genes, and can be quickly activated to help a species adapt to a changing environment. This type of evolution is very different from the theory (remember, it is a theory) of evolution which says that all species evolved from a single ancestor. I believe that it is just as scientifically valid to believe that birds were always birds, varying within the limits of their original genetic information, or boundaries.

The third fingers of mortal men.

There is a marvellous BBC series by David Attenborough called The Life of Birds, it covers evolution. Highly recommended.