Each gradualistic change would have to have a survival benefit that would allow it to take over the population. The animal would not be able to hunt as well as his other fellow dinosaurs, nor would he be able to fly. It would seem that such changes would have a zero to nil chance of taking over a population let alone progressing further to become birds. Evolutionists propose that mutations serve as the vehicle capable of producing these dramatic changes. The problem with this explanation is that mutations involve the loss of information, not the gain of information.
Mutations also create what is called a genetic load which only tends to weaken a species.
In order to illustrate this point consider a computer program analogy. If DNA code is the computer code, then a mutation would be a corrupted file. The answer is they don't. Mutations are found to be either neutral or destructive to organisms. They do not produce greater complexity.