I've actually put alot of thought into this, if any new fossils apear, then these would be the ones I would like to see
Either;
Smiledon (Saber-Tooth) Pokemon
Mastiodon
(Mammoth) Pokemon (I know Mamoswine's a Mammoth, but meh) Both Ice/Ground Type.
And as a third,
Phorusrhacidae (TerrorBird) Pokemon. This is Fire/Flying Type, making it a perfect counter to them.
Mainly because they all lived in a simaliar and timeframe. TerrorBirds were once the most feared predator of N.America, and were for along time. Untill the land masses of North and South America combined, then the Sabertooth's entered the same range of the terrorbirds, which made the terrorbirds extinct (Irony, as the most powerful of the three would be the Bird). And all across America, Mammoths travelled. Any straggelers would most likely be killed by Sabertooth tigers.
Or...
Stegosaurus Pokemon,
Grass/Rock Type
Iguanadon Pokemon,
Poison/Rock Type
A third...
Tyranosaurus Pokemon
Dragon/Rock
Simple because Dinosaurs are awesome. Iguanadon is a poison-type because they are known to have large, clawed thumbs... If only they could inflict poison...
Hope you like my ideas.