I agree with both answers. You'd have to have something like, "Fossils of Man" which would be many different types or specimens of fossil, and their category would be human beings (male and female, under the heading of "Man").
If it was one man, like the king whose bones were found recently in a car park, you'd write, "Fossils of a Man", or "A Man's Fossils".
Because the fossils (preserved remains) belong to one person.
So by this example, the only way you could use "Fossils of Dinosaur" would be if people categorised dinosaurs with one word, and they don't. "Fossils of Creation", "Fossils of Nature". But not "Fossils of Dinosaur". Unless that's something else I didn't know about. That's possible :) being an ignoramus hehehe