Step 4: Imprint the dough

Picture of Imprint the dough
For just a little extra authenticity you can use a (cleaned, washed) fossil to make impressions in the dough.  (This is a pyritised Ammonite I collected at Charmouth in Dorset)

If you can't find a suitable fossil for this, you might be able to find a rubber stamp in a craft store, or make a model out of air-drying clay to use.