As with the rest of the modelling process, detailing is best approached by starting out with the larger details first and working in ever-increasing resolution as the finer details are added. There are decisions to be made at this stage too, deciding how much to actually model with geometry and how much to add using displacement maps and texturing. For the time being, I'm going to continue adding to the geometry as we're still dealing with larger details rather than the tiny stuff.
As you can see I've started to refine some areas that were difficult to model by pulling polygons and points, such as much of the skull detailing including the rostral and orbit areas, the epioccipitals and general refinements around the skull. I'm also adding wrinkles to the skin, especially in limb areas. I'm also attempting to keep the animal looking quite fleshy as I'm anxious too avoid an overly skinny look with bones poking through everywhere. Most of this work is done using standard zBrush brushes and alphas; the need for custom alphas will be when the finer detailing such as skin texture is being applied.
Many of the decisions on how the muscles look are based on our earlier reconstruction of the musculature of Triceratops, but at this stage it's worth considering how the integument of the animal affects the way the skin might fold and fall across the skin and muscles. Keep referring to any reference you have gathered and be mindful of the analogues you choose; elephant skin is probably very different to ceratopsian skin, so do the research. More on this in the next post.