Re: Where did birds come from in their evolutional process?

> The oter day, I learned,in paleontology class,that birds have evolved
> form
> Saurischia.And our professor said,"once the carnivorous animal have evolved
> into the animal which don't eat meat, they don't evolve into the carnivorous
> animal again. So bird has never come from Ornithischia."But I heard that a
> fossil of Ornithischia which has traces of feathers (parrot-dinosaur ?) was
> found in China. Could this discovery be a counterargument against an
> established theory or argue the theory like "some of Ornithischias ate
> meat"? (* I don't know about the theories, sorry.)

First of all, I know of no basis for a theory stating that carnivorous animals cannot evolve from herbivorous ones. I can't think of any conflicting examples, but I don't see a reason why this would be true. Secondly, many ornithischians were probably omnivorous, including lesothosaurs, basal thyreophorans, hypsilophodonts, heterodontosaurs and pachycephalosaurs. The Psittacosaurus specimen you are referring to is unpublished, but I don't see any reason the structures on it are closer to feathers than they are to scales. Certainly the almost fully developed retrices and remiges of maniraptoran coelurosaurs are much more similar to feathers. This brings up the last point, that even if feathered ornithischians are found (and I suspect them to have filaments if anything), maniraptorans also had feathers and share many more characters with birds than they do. Thus, the maniraptoran ancestry for birds would not be challenged and is by far the best supported theory of bird origins at this time.