1) Boring fossil 
Petroxestes is a shallow, elongate boring (a type of trace fossil) originally found excavated in carbonate skeletons and hardgrounds of the Upper Ordovician of North America (Wilson and Palmer, 1988, 2006). These Ordovician borings were likely made by the mytilacean bivalve Corallidomus as it ground a shallow groove in the substrate to maintain it...