I always thought the term fossil fuel came from Latin fossa, or ditch, trench. Coal being an exemplar. This probably ended up with its cognate fossil, an item

I always thought the term fossil fuel came from Latin fossa, or ditch, trench. Coal being an exemplar. This probably ended up with its cognate fossil, an item, usually of historical value, dug up from a ditch. Since dinosaurs are represented by fossils, people put the two together.