Features are iffy here and there on some of these, and that makes sense since I haven't done extensive studies of features yet. But I have noticed the planar head studies paying off big time, I've become incredibly mindful of proportion and placement, and even some quirks that help out with fleshing out a head. I'll have to make a post about that soon.
I think I may be preemptive and work on some eye structure studies soon, because I've noticed myself really trying to grok how that assembles, but I'm defaulting to gut instincts on it instead of how it really looks and comes together. Looking at modern and classical sculptures' approach to eyes made me switch out my eyes three times - you'll notice that there's three varieties of eyes amongst this group, with the last being the most recent/accurate to what I want.
Something I have noticed in regards to sculpting these heads and dinosaurs, and when I think about it in regards to my 2D stuff it's the same thing - progress on a piece works a steep curve. When you first start on a project you make GREAT progress, that's why it's always exciting to block out gestures or thumbnails or rough in shapes in clay. But about midway in the curve you move from block-in to refinement and iteration, and from there on it's a finishing game.