Tiers

Fossil Fighters
The Fossil Fighters metagame has been optimized at the highest level, but no work has been done beyond the top vivosaurs/top team, leaving this tier list massively incomplete.

Fossil Fighters: Champions
The top part of the tier list is perfectly organized, while B, C, and D are completely lumped together. There likely will not be optimizations of the lower tiers, meaning there will not be a true, true tier list.

Older tier list in case you wanted to know what the lower tiers actually looked like. Note that Tiers 1-2 are legitimately wrong, and Tiers 3-14 are quite likely to shift if there were to be actual optimization of the lower metagame. The shifts would not be that significant, however, as the fundamental structure of the tier list isn't actually that faulty.

Also note that the vivosaur writeups linked in this tier list are also very outdated, citing things like Saichan being the best in the game.

Fossil Fighters: Frontier
Still a major work in progress, as minimal testing has been done and theory has by far been the biggest component in shaping this metagame.

Vivosaurs:

Paleo Pals:

Still a work in progress.