What are the functions of the supraorbital crests?
Protection of the eyeballs from physical attack, I would hypothesize. The skull is in essence a protective capsule for the brain and surrounding apparatus. If you strike out at somebody, cahnces are you will swing your arm in a lateral to medial direction, i.e. your arm starts out wide and comes towards the centre. This would mean that you srtike your target from the side. Alternatively, if you go for an overarm attack (such as with a club or similar primitive weapon), you have a down swing, in which case the target is struck from above. The supraorbital crests protect your eyes from attacks above and (to a slightly lesser degree) from the side. This is because they overhang and border the lateral side of your eyes, with the nose providing some protection from the median. There is less protection from below, perhaps because you are less likely to be hit from below (an uppercut is not really a natural attack) and because you need to see the ground more than you need to see above.
