TAPHONOMIC ANALYSIS OF CRINOIDS FROM THE STANTON FORMATION (LATE PENNSYLVANIAN, MISSOURIAN) OF THE NORTH AMERICAN MIDCONTINENT: EVIDENCE FOR PREDATION, PARASITISM, AND COMMENSALISM

The most common epifauna on Stanton crinoids includes encrustations; pits/borings; sinuous grooves or cuts; sharply delineated, deep cuts or gashes; and punctures. Some of these markings such as pits and borings are observed almost exclusively on crinoids whereas some, such as encrusting organisms, are seen on many other invertebrates.

Encrusters include algae, worms, bryozoans, brachiopods, and other echinoderms. Brachiopods are usually productoids, chonetoids, or strophomenoids and echinoderms may be other crinoids or ?edrioasteroids. Encrustations or cuts that cross articulations or sutures and borings are post mortem. Cuts or borings that cross suture junctions or articulations are also post mortem.

Encrusting organisms are more commonly observed on crinoids from the southern region of the study area than in the northern region.

Pits/borings are commonly on the exterior of plates and do not cross sutures or articulations. Pits or borings are commonly observed at tri-suture junctions or in the anal area of crinoids. Different genera of crinoids commonly have different kinds of pits/boring, suggesting host specificity. For example: catacrinids and diphuicrinids have large, cylindrical pits/borings without a rim whereas pirasocrinids commonly have smaller, parabolic pits/borings with a highly swollen outer rim. Pits/borings have rarely been observed on crinoid cups smaller than about 10 mm in diameter, suggesting body mass of the host as a criterion for a parasite or commensal organism selecting its living space.

Cuts or slashes on the exteriors of plates may have been either the result of post mortem scavenging or made while the crinoid was still living. Either scavengers or predators including gastropods, cephalopods, or fishes may have made cuts or slashes. Puncture wounds are usually single but some possible pairs have been observed.