Nipponites mirabilis

Nipponites mirabilis was an extremely abberant heteromorph ammonite, found in Upper Cretaceous oceans over what is now Japan and Western North America. These ammonites had a planktonic/swimming larval stage, where they developed a normal-looking shell. Eventually, they would settle to the bottom, and allow their shell to "unwind" into a "knot" of U-shaped loops. Some individuals, possibly elders, allowed their shells to unwravel completely, becoming a barely recognizable tangle.