I stole some time to get back to this painting this morning. I drew a bunch more dinosaurs and tried them in the hole made by erasing the previous T-rex. So far I've just "colourized" the pencil drawings and smudged and erased a bit to get them in the direction of matching the rest of the piece. It's kind of obvious they're both sitting on different layers and I haven't done any painting to them yet.
Gonna let these sit a bit before I decide on which one to go with and exact placement. Right now the left one looks too centered in the opening and the right one could be rotated counter-clockwise a bit to feel more like it's moving.
I've also decided I have to place a few more bit of ruin here and there so the giant stone head makes a bit more sense