You shot yourself in the foot, I think, with your comment --"Hey, let's carve a big lion." If that is indeed what happened, or anything similar, you have implied a rather advanced culture exists; for anyone to have time to do such a thing, ( my own carving included), you have to have a surplus of time--liesure time, essentially, and resources. The Sphinx is a massive undertaking calling for surveying skills, skilled and unskilled labor (stone masons, rubble removal, etc), crew supervision, feeding, housing, as well as a system of either recruiting, or forcing labor to be expended on the building of such a monument. These workers are not working the crops, catching the fish, hunting the game; someone ELSE has to do that, i.e., a division/specialisation of labor, something usually associated with 'civilisations'.

You imply that it takes no skill to produce a carving; I have seen the unskilled try to pull it off, and, I'm afraid, it doesn't work. Skill is proven by the fact that we can view this huge statue of a 'lion', and know that's what it is-we can recognize the subject of the carving; if it had been done by unskilled labor just 'hacking away' at the rock, we would be viewing it and reacting like 'O.K., yeah, um, what the hell is it?"