Found a free Triceratops at CGtraders.com Obj format w/o textures.
This one I selected some random areas,(main body, face mask, horns and hood) applied more materials, now have 3powerfractal textures for hide.
I think you should make the skin more subtle in color (grey tones with some mud or so, and apply a tiny voronoi bump to it, and a bit of reflection. Procedurally you can get quite far.
Agree with Dune, I'd go with a green-grey base with the voronoi bump/displace for starters....
Thanks guys. That is actually what is on there, but scale is not small enough and displace is giving me black spots...reworking. :) My grown son's favorite dino, lol