Those look a hell of a lot like sling shot to me.

Wikipedia says: "The sling is an ancient weapon known to Neolithic peoples around the Mediterranean, but is likely to be much older. It is possible that the sling was invented during the Upper Palaeolithic at a time when new technologies such as the spear-thrower and the bow and arrow were beginning to emerge."

Seems unlikely, though - 1.4m years vs 50k years.