yeah the foreground could use some darker shadows and those mountains should be a little lighter. I checked those pictures and I agree he is playing with the digitally before posting them, but still the darkest spot in the background isn't as dark as the darkest spot up front. Might be worth checking with the colordropper and put those two next to each other.
This last one looks awsome and the textures are great! However I think it could do with a more dramatic background its such a dramatic beast and the background is so soft and cuddly (maybe I have a weird taste in backgrounds) But it should be more dark and creapy or maybe bloody and messy. Other than that I find it most inspiering!
hey davi, last creature is one of your bests. about the ref sites maybe deviantart.com its always a great source, PBase.com and national geographic. ( at least those are what i use.. ) keep up with the studies they look great ^^