Complete fossilized skeletons are rare. In fact...it can be a challenge to even find a complete fossilized bone. Many of the skeletons you see in museums include some real fossils (or casts) with sculpted bones & filler to either complete the individual bone or to complete the skeleton. Sometimes the the filler is left white to clearly differentiate the fossil from the filler. Other times, the filler is painted to blend in with the fossil for a more realistic appearance. In this activity I work with the kiddos to finish off one of the partial fossils they found.

What you'll need

• Hardening clay. (Self hardening, or oven hardening - see sidebar)
• A partial/broken fossil
• A photo of what the completed bone looks like (thank you Internet)
• Sculpting tools or found dyi sculpting tools (tooth picks, plastic spoon, etc.) 

What to do

• Prepare the clay per instructions. This usually involves kneading the clay until it is soft and plyable.
• Roll the clay and shape it until it is about the right size for your fossil filler.
• Press clay onto broken edge of fossil.
• Shape and sculpt the clay to complete the bone. Discard clay that has bee pulled or scraped off
• Use sculpting tools to texture the clay
• Let harden according to instructions
• Optionally - paint the filler after hardening.

About the clay

Polymer clay. Recommended for older children 9+. Hardens in the oven in about 10-30 minutes depending on the clay and size of object. Clay is stiff and harder for young ones work. Clay will still be soft after baking but will become very hard as it cools. Took me a while to figure that out. Easily painted after hardening.

Air hardening clay. Recommended for children 8 and under. Air dries but takes at least 24 hours to harden. Soft and easy to work with while still stiff enough to retain shape and sculpt. Dried clay is hard but not as hard as polymer clay. Can be painted after hardening.

Salt dough. Make it at home in the kitchen! Does not hold shape quite as well as clay but can be made at home and is very easy to work with. Hardens in oven, but plan on several hours of baking time. Instructions for making salt dough.

Sculpting filler made from salt dough to complete a magalodon tooth.

The filled in megaladon tooth as sculpted by my 10 year old.

The tip of a spinosaurus tooth (left), a full spinosaurus tooth (right) used as a model. Sculpting tools (top) and a ball of polymer clay (bottom).

Clay sculpted into a bone fragment to complete the tooth.

Filler material painted to make a completed model of a spinosaurus tooth. Real fossil on the left, sculpted filler on the right.

Orthoceras repair. Top photo are the original fossil pieces from an orthoceras. Second photo are the cleaned fossils. Third is the repair filler. Fourth is the filler painted and entire fossil polished.