Back where you built part of the dino skeleton you should also have seen some dynamite. Throw some down the door beside it to blast part of it away. Go down and blow up the rest of it to get the pieces for the dino head, just set this beside the skeleton for now. Grab some more TNT and blast a part of the floor that highlights- this nets you the pieces for the tail. Once it is together you can walk up this and put the head in place.
The pillars Rob talks about is near the end of the Ancient City.