Prehistoric pokemon always have the hiccup of there not being a lot of material to study. Case in point, my archen studies were mostly just looking at what avialae we've have found so far and the paleoart of them, I took down some notes that I #lost oops, and drew a few things before I understood the basic concept of what I wanted to go for here.

After that I took reference images of modern birds and paleoart avialae and concepted a design body type for these two. I like archeops, but my main beef with it is that it looks too much like a Big archen, and that the rock type doesn't really appear much beyond the fact that its a fossil(tm) so it has to have it. I decided to play with mixing it up with other ancient fliers of the era, such as tapejara and gannets for the wing style and a different crest. The idea is that it'd be filling the gaps of a missing fossil.

After that it was just a matter of posing! I wanted them to be flying together, and i tried to make it so the crest texture felt like crystals to justify the rock type beyond them being fossils.

Also I drew this on the same canvas.