This page explains how to get through level 6 of the prehistoric world in The Lost Vikings.
Reach the Exit
Have Olaf go up the ladder so that the blue dinosaur is on the same side as the snail. Block the monsters, then have Baleog go up and kill them. Have Olaf go up the next ladder and block the two red dinosaurs. Then have Baleog go up and kill those, too. Then have one of them get the shield and the tomato.
Now have all three vikings go across the bubbles. It will be easier for Olaf and Erik, but Baleog will have to be careful since he can't jump or glide. If Baleog is in a bubble that is about to burst, and you can't see one below him, you will have to fall into a nearby bubble, because there is no guarantee that a bubble will appear below him after the one he's in pops.
Once you are all on the other side, have Olaf go up to the red keyhole and raise his shield, and have Erik jump on top of his shield and go up to the ledge. He will find a red key to the right. Have him go down to the keyhole, make sure Olaf lowers his shield to block the red dinosaur, and unlock the door. Have Baleog kill the red dinosaur. Go to the right and get the vegetable.
Have Olaf go up the ladders and carefully block the blue dinosaur, then have Baleog go up and kill that dinosaur.
There are more enemies up above, so have Olaf and Baleog deal with those. Then at the left side, have Olaf go up the ladder and block the red dinosaur. Baleog can go to the left and use arrows to kill the red dinosaur near the Omega Bomb, then he can go up the ladder and kill the red dinosaur that Olaf is blocking.
Now Erik should go to the other vikings and jump to get the Omega Bomb, the tomato, and the yellow key.
A red dinosaur is blocking your way to the next area, so deal with it however you want, then have Olaf stand next to the door and raise his shield. Have Erik jump onto the shield and go around to unlock the door.
Next, all you have to do is kill the snail and red dinosaurs to the right, then all three vikings can go to the right to reach the exit.