Kabutops, one of the original fossil creatures, has classic rock/water typing, which is honestly not the best pairing; It is vulnerable to common fighting and ground attacks and suffers from quadruple weakness to grass.
From its types to its stats, Carracosta is very similar to Kabutops. However, he reduces the speed even further for the defense.
Rock and Grass is generally considered a poor defensive type, but they actually pair fine—no dual weaknesses, though watch out for Fighting and Ice.
Here's an incredibly tenacious tank that is excellent when you can avoid his Achilles heel. Bastiodon is pitifully short and weak, but his defense is through the roof.
Auroras gets a lot of things right, but it has one obvious flaw. Slow, like most fossils, she favors her particular stats on the physical and has an unusually high HP.
Armaldo has some of the best typing today with only three weaknesses, two of which (steel and water) aren't particularly common on offense.
Makes a good pairing for Flying Rock as it renders Archaeops immune to the ground, but he really stands out for his incredible 567 stat total.
For a low-risk version of Archaeops, the classic Aerodactyl has you covered. With a strong attack and excellent speed, he is the fastest Pokémon to date.
Compared to most fossils, Rampardos evolves from Cranidos to only level 30 earlier than usual, but his real threat comes from his ridiculously high attack of 165-35 points over Mega Charizard X!
The Tyrantrum offers a powerhouse with questionable stamina. Both physical attack and defense affect, and he is not as slow as most fossils.