Above are two pictures of a trace fossil, Conostichus, from the Ozark Plateaus region of Arkansas. Like other trace fossils, Conostichus are structures found in sedimentary rock that represent the spot where an animal lived, fed, or travelled. Despite their abundance, especially in rocks of the Carboniferous period (299 to359 million years ago), it’s not certain what kind of animal made Conostichus, because the animal’s body wasn’t preserved.
The upper picture is the top of the Conostichus and shows the hole through which the animal entered or exited the structure. The lower picture is the same Conostichus with the top facing down. As you can see, they taper and come to a rounded point at the base, vaguely resembling a badminton birdie.
At present, the most widely accepted theory for their origin is that Conostichus are burrow traces left by Sea Anemone.