Pictured is the remains of an animal, called an Archimedes, that flourished in Arkansas about 350 million years ago. At that time, Arkansas was covered by a warm tropical sea, and invertebrate organisms such as Archimedes lived by straining tiny food particles from the sea water. Though similar filter-feeders exist today, this particular one is extinct.
In this photo, we see a cross section of the animal; the screw-like pillar supported it from the center and delicate, barely visible lattices whorled around the screw – in cross section they look like ribs of a fish bone (see picture). Those were the filters the animal used to trap food. Because the lattices were brittle, they were rarely preserved with the fossil, which makes this specimen exceptional.
The limestone pictured is from the Pitkin Formation in northern Arkansas.
For more views of Archimedes click here