I agree with the too much terrain part, just because so much terrain will bring the fps down considerably. Te fossils pretty cool, and I do like the structure of the city, but it could use a bit of color to break up the monotony a bit.
Well, here's some tips: you have put too much terrain, terrain is useless, save space for the airplanes or spaceships, the city has always the same deco, it seems for the users that you spent more time doing the fossile than focusing on the buildings' tecture