Tyrantrum is better than Aurorus most of the time. This is because of better bulk, a higher Attack stat, and a more diverse movepool. Aurorus functions, as does everything in-game, but the 4x weaknesses to Fighting and Steel really hinder it. I've personally used both Fossil Pokemon in Kalos Nuzlockes, and Tyrantrum performed much better than Aurorus.
Tyrantrum @ Hard Stone
Ability: Strong Jaw
- Dragon Claw
- Earthquake
- Rock Tomb / Rock Slide
- Crunch