Who created the Dinosaurs and other animals?

So if the Engineers created us, who created the dinosaurs, them, and other animals? Easy, god. Well here is the thing. Our fossil records shows that Man has been on this planet for thousands of years. The cave painting in the film pre-dated the others by 35,000 years. So, we know man was here then and that the Engineers visited to influence the painting of the caves. Now, since the earth was a gas laden, hot mess, when life first formed in our seas, which took millions of years to become land dwelling life, here is my theory. The Engineers did not create life here, they simply helped it along. They took what was here, refinded it, and let nature take its course. Why in water? Easy, that feeds into the entire ecosystem. For the opening scene to be the creation of life on earth it would have to have been millions of years prior, and Earth would not be the scenic locale depicted. It was not very pleasant at that time according to all scientific research.