Quoted By:
Head north to the Mirage Tower and choose between one of two fossils giving rise to Anorith or Lileep:
Anorith evolves into Armaldo at level 40 and it a very solid Pokemon stat and even move wise. Sadly it does not get access to a neat ability in Swift Swim until the fifth generation which doubles speed in rain.
Lileep similarly evolves into Cradily at level 40 and is a bulky grass/rock type. Unfortunately it does not learn Leech Seed in this generation, but it still has access to solid attacking and supporting moves alike.
Both of these can be revived at Devon Corp. back at Rustboro, but the one you don't choose sinks into the sand. It can be retrieved in the postgame thankfully!