I've given special treatment to the crinoids simply because you're going to find so many of them. As fossils, the calcite "skeletons" of these mostly stalked echinoderms can be so abundant in a limestone strata that they essentially make up a fossil breccia comprised of stalk segments, tubular sections of stalks, isolated plates and bits of their feathery arms. Crinoids must have exited in some cases in vast fields, bending into the current in unison to catch plankton with their open net-like feeding behavior.
Often misnamed sea lilies,
the crinoids form a large class of echinoderms. Generally, the body plan of the crinoid is similar to that of the cystoid. The crinoid is more advanced in having a symmetrical arrangement of calyx plates and well-developed arms and pinnules. In addition, a long stem supports the crown and serves as an anchor for the animal. Most fossil forms were attached to the sea bottom. In both fossil and modern forms, the stem and arms were flexible, allowing graceful movements in the gentle currents in which they lived. The oldest positively known crinoid comes from the Lower Ordovician rocks. By Middle Ordovician times the representatives of the major groups had evolved. They flourished in the Paleozoic, especially in the Mississippian Period, and then were almost wiped out in the Permian period. A few stragglers repopulated the seas to their present numbers. Crinoid fossils are very abundant in Arizona.


All fossil collectors would like to find a complete crinoid, from root to arms, but they are very rare in Arizona. More often in Arizona Paleozoic rocks, you are more likely to find crinoid pieces, as shown to the right of the crinoid illustration; one or multiple arms, a cup (usually with arms not attached), stems...lots of stems, and possibly a anchor or root. That said, a complete crinoid is a beautiful fossil, and you can purchase a whole specimen from Crawfordsvill, Indiana or from another country at a reasonable price from one of several dealers that you can link to on the AAPS website.

Rays (arms)
Calyx (cup)
Stems
Holdfast (root)
The stems of crinoids are a stack of interlocking disks or columnals of a variety of shapes. Often the columnals are arranged in a repeating series of smaller disks periodically interrupted by larger cirri bearing columnals.
Living crinoid on left, fossil crinoid has above
Cirri are hair-like protrusions constructed much like a stem but with smaller columnals. Each columnal is centrally perforated creating a stem lumen leading into the coelomic cavities housed in the calyx.
The stems of crinoids end in a variety attachment structures. Some have a root-like system of cirri while others utilize a cementing disk to attach to hard substrates. There are crinoids that have an anchor-like holdfast while others produced bulbs.
There are so may species of crinoids that I've given up the thought of showing enough examples of fossils to be really very useful to a collector. To help you in your quest for the ever evasive taxonomy of a new fossil, I really recommend you get hold of the book Index Fossils of North America by Hervey W. Shimer and Robert Rakes Shrock (MIT Press). I've had this book, now a bit dog-eared, since I got it as a Christmas present from my brother when I was 13 years old. This book, still and tremendously useful identification too, is a must for any serious fossil collector. This classic is the best single volume reference for the identification of fossil invertebrates. It was a staple for working field geologists for decades. This is because the identification of "index fossils" was, and is, the handiest way to date strata in the field.
Index Fossils of North America is organized by phyla: Protozoa, Porifera, Coelenterata, Echinoderma, Annelida, Conodonts, Bryozoa, Brachiopoda, Mollusca, and Arthropoda. There are also sections on fossil plants and miscellaneous objects of somewhat strange or really unknown classification.
COLLECTING FOSSIL ECHINODERMS
Any plate or large fossil fragment which exhibits well-developed, uniform calcite cleavage may be part of a fossil echinoderm, and this characteristic of the echinoderm's skeleton is said to be the most useful field criterion for the recognition of fossil echinoderms. Also, because of this characteristic cleavage, special care must be taken to avoid hitting any echinoderm fossil with a hammer or hitting too hard on an adjacent bit of matrix. Crinoid parts are pretty tough and survive well as fossils.
Acids in rainwater did the preparation of this specimen for me
Echinoderm fossils can literally explode along a thousand cleavage lines, rendering the specimen into useless and unidentifiable fragments. Seen in the photo above, a single crinoid stalk had fallen onto the sea floor and many of the bead-like segments separated as the muscle tissue which held them together in life disintegrated. The Paleozoic seafloors were littered with these crinoid body parts, and in most cases, in Arizona's outcrops, you will mostly find incomplete specimens. Rare, more complete fossils crinoids have been found, but very special depositional conditions were needed for their preservation. Ocean currents or the activity of other animals prowling around in the mud usually caused crinoids to break apart. A fossil crinoid collector works the odds; if he or she looks at enough rocks, eventually a real prize is found. A head (calyx) or even a completely articulated crinoid, stem to stern, is a real scientific prize. Seek and ye shall find!
Obviously, most common acids cannot be used to remove specimens from encrusting matrices because both the rock and the echinoderm fossil are both composed of calcite, and calcite dissolves in hydrochloric acid. You specimen will simply vanish before your eyes, so a collector must rely on careful work with fine needles and dental tools for final preparation. If you find an intact calyx you'll notice that the arms appear very delicate. They are! If the matrix is soft shale, you may be able to use a fine needle to work away the surrounding shale. If the specimen is in tougher rock, and you feel the specimen is rare, you may want to enlist the help of a friendly professional museum preparator, or contact one of the talented commercial dealers and preparators who do this kind of thing for a living. You'll find a link to these on the AAPS webpage.
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