It is surprising that modern textbooks teach the ridiculous idea that birds are the descendents of dinosaurs! What a silly idea! There are many thousands of anatomical differences between reptiles and birds. Reptiles have four perfectly good legs that function just fine. Birds have two legs and two wings which also work fine as they are. If a reptile were to try to evolve into a bird, at some point it would have halfleg and half-wing. Now, it can no longer walk or run; yet, it cannot fly. This creature is doomed to extinction.