User blog comment:Nethrim/A Dino a Day/@comment-5109847-20120605182844/@comment-5142786-20120606055359

I copied this from the tips & tricks on the Dino page,

"When you hatch using Random Dino method, check the Hurry Cost to hatch the dino instantly. By looking the cost, you can GUESS that the random dino will give you a rare dino or not. All Common Dino have 72 hurry cost, but remember that Homalocephale, Pterodactyl and Triceratops also have  72 hurry cost. (thanks to Vincijuggers in comment). See Dino Den to view all Hurry Cost to Hatch. NOTE : This is only for guessing the outcome of Rare Dino from Random Dino, you still get Rare Dino randomly."