Sure! In particular, the ones I'm most familiar with are ones like Tirtouga and Carracosta, which were known as the "Prototurtle" Pokemon, and they once dominated the oceans of Unova. Then there's also Archen and it's evolved form Archeops, and they're known as the "First Bird" Pokemon, because it's believed that they are the ancestor of all the birds living in our world.

[Ash probably has data on other fossilized Pokemon from other regions that he's been to, but those are the ones that Cilan knows of from when Ash was traveling in Unova, and they actually got to see those Pokemon in person.]