I scanned an ammonite fossil that I had laying around in my room since I thought it would be cool. I have not printed it yet , but I imagine that doing so vertically would allow for a good amount of detail (if anyone prints it and finds out if a particular way works well post it to the comments so I can edit the description).
The actual fossil (what is imaged) is about 7cm x 6cm x 3cm (give or take a few mm) and is whole and you can actually see the little squid face a little (poor guy). The model should be the same dimensions as the actual fossil.
The author marked this model as their own original creation.