Fossil Puzzle 

A petrified earthworm?
Guess again!

Your local paleontologist will immediately recognize the "stack of coins" that breaks apart easily into individual disks called "columnals" that have earned the local nickname "Indian Money."

This is the stalk of a crinoid -- or "sea lilly" -- a filter-feeding animal that anchored itself to the sea floor and allowed the flower-like calyx to strain seawater for particles of food, including living plancton. That makes the crinoid an omnivore, related to the starfish and sand dollar, as noted previously.

However, if you look closely, you will see something peculiar about this specimen -- it includes a branch. Because crinoids are single animals, they do not typically branch out from a single stalk the way a plant would.

So what is going on?


The above crinoid arms have preserved pinnules -- feathery fronds that strained seawater for floating food. Particles were transferred it to a groove along the arms and eventually to the mouth. Its last meal was 440 million years ago. This sample was gathered near Nashville beside interstate 40. (Click to enlarge.)


Illustration courtesy Lindsay Davison

Crinoid BranchCrinoids arms branch from a common joint


One place where branches do appear is within the graceful lilly-like arms of the crown. Food sticks to mucus in the ambulacral groove on the inner side of the branching tentacles. Then the animal's nervous system can control the arms to bring food to the mouth, located in the cup of the armored Calyx, where it travels though a digestive tract until it is excreted from the nearby anis. Instead of muscles, the arms use a "hydrostatic skeleton" of fluid-filled tubes to control their motion.

However -- the branching fossil of the picture does not conform to the usual way in which crinoid arms branch from a common joint. Sometimes crinoids can feature side branches called Cirri, but these generally branch off the side of a single columnal.

The answer was suggested by Crinoid expert Joe Koniecki. That pattern of branching is more typically seen with the anchored holdfast, and our fossil above likely shows where the crinoid was rooted into the ocean floor. Thanks Joe for helping us solve our Puzzle fossil!

For more great photos of crinoids, be sure to visit Joe's crinoid website.