Strolling through downtown Columbia, towering buildings of steel, stone and glass surround you. You pause at one point along the Avenue of the Columns, as something catches your eye. It's a building stone. Much like many you see in the area, it shows the interaction man has had upon it. Looking closer, you come face to face with the humble crinoid...or what's left of it.
WHAT ARE CRINOIDS?
Crinoids are marine animals that make up the class Crinoidea of the echinoderms (phylum Echinodermata). The name comes from the Greek word krinon, "a lily", and eidos, "form". They live both in shallow water and in depths as great as 30,000 feet. Those crinoids which, in their adult form, are attached to the sea bottom by a stalk are commonly called sea lilies, while the non-stalked forms are called feather stars or comatulids.
Crinoids are characterized by a mouth on the top surface that is surrounded by feeding arms. They have a U-shaped gut, and their anus is located next to the mouth. Although the basic echinoderm pattern of five-fold symmetry can be recognized, most crinoids have many more than five arms, but they are always a multiple of five. Crinoids usually have a stem used to attach themselves to a substrate, but many live attached only as juveniles and become free-swimming as adults.
Based on the fossil record of crinoids, especially the details of the plates that made up the arms and aboral cup, experts have identified hundreds of different fossil crinoid species. There are about 600 extant crinoid species alive today.
CRINOID ORIGINS
Crinoids have lived in the world's oceans since at least the beginning of the Ordovician Period, approximately 490 million years ago. Some paleontologists, however, say they are older still. It is thought by some that a fossil called Echmatocrinus, from the famous Burgess Shale fossil site in British Columbia, may be the earliest crinoid. The Burgess Shale fossils date to the Middle Cambrian, well over 500 million years ago. No matter what, crinoids have had a long and successful history on earth, and continue that success.
Crinoids flourished during the Paleozoic Era, carpeting the ocean floor with strange arrays of swaying, flower-like colonies. They peaked during the Mississippian Period, when the shallow, marine environments they preferred were widespread. Massive limestones in North America, such as the Burlington Limestone here in Missouri, are often made up almost entirely of crinoid fragments. This attests to the abundance of these creatures during the this time in history.
Crinoids nearly faced extinction towards the end of the Permian Period, about 250 million years ago. The end of the Permian was marked by the largest mass extinction event in the history of Earth itself. The fossil record shows that nearly all the crinoid species died out at this time, and the one or two surviving species eventually gave rise to the crinoids populating our oceans and seas today.
CRINOIDS IN MISSOURI
Missouri is a fertile hunting ground for fossil collectors. Fossils of almost every size have been found in Missouri, from the bones of the gigantic Woolly Mammoth of the Ice Age to the microscopic remains of primitive, one-celled animals that once lived in warm, ancient sea waters. Most of the fossils represent species of marine life because the sedimentary layers of rock common to Missouri, such as sandstone, chert, shale, dolomite and limestone, were formed millions of years ago by deposits laid down when shallow inland seas covered most of the state.
It is in limestone beds that crinoids are generally found. The Burlington Limestone is most renowned for its abundant crinoid fossils. It contains more species of crinoids than any other formation. About 260 species have been identified, some of which may be descriptions studied only casually.
Crinoids often appear as tiny discs of stone that may have a hole (often star-shaped) in their center. Loose pieces of stem can often be strung like beads, much like what Native Americans did in the past. In addition to individual discs, the fossil is also preserved as sections of stems with distinctive segmentation marks. Occasionally, it is possible to find the aboral cup, which protected the animal’s soft body with a symmetrical “petal pattern” of calcium-rich plates atop the stem. Rarely are crinoids preserved in their entirety: once the soft parts of the animal decayed, sea currents generally scattered the skeletal segments. By far the most common crinoid fossils are the stem pieces.
Did you know...?
Crinoids are so abundant in Missouri that one species – Delocrinus missouriensis – was named the official state fossil by the Missouri General Assembly on June 16, 1989 (RSMo 10.090).
EARTHCACHE TASKS
You will need a ruler that measures inches to complete this Earthcache. A quarter will do quite good as well, since it’s almost exactly an inch across.
The posted coordinates should place you in front of (or very near) two basement windows at almost sidewalk level. Above these windows, you will find building stones with abundant crinoid fossils in them. Study one of these stones and answer the questions below. Send those answers to me via email or a message through my profile. Any “found it” logs that fail to complete the tasks and send me the relevant answers will be quietly deleted.
1. During what time did crinoids peak in abundance?
2. Relate the average size of the crinoids you see in this stone (i.e., size of a BB, pea, marble, etc.). How big are they on average?
3. In addition to the typical discs, you should be able to see stem portions preserved. Using your ruler or quarter, tell me how long (in inches) the biggest section of stem you can find is.
4. How would you describe the stone itself? Does it seem mostly composed of visible fossils or do the fossils seem more sparse?
5. Knowing that these blocks were quarried locally, and given the fossils present, what do you think that this area was like hundreds of millions of years ago?
6. A picture of yourself in this area would be nice, but it’s not required.
