Jaw and Sail Fossil

In every Pokemon game you get a chance to pick one of two fossil pokemon. Pokemon X and Y are no different. Between playing the first and second gym, you will get a chance to choose between jaw fossil, or sail fossil. You only get one per game.
pokemon x y sail jaw fossil
If you choose the jaw fossil you will get Tyrunt, if you choose the sail fossil you will get amaura. Also females only have a 12% rate of coming from fossils, so you may want to save and retry the fossil if planning on breeding.

Amaura is a rock/ice pokemon, who is only obtainable by a sail fossil or breeding.
Amaura evolves into Aurorus.

Tyrunt is a dragon/rock pokemon, who is only obtainable by jaw fossil or breeding.
Tyrunt evolves into Tyrantum.