CHANGING FREQUENCIES OF INFESTATION TRACES AND REACTION FEATURES IN PALEOZOIC CRINOID COLUMNS

Epibiosis and parasitism are found in a great variety of organisms from as early as the Ordovician. In particular, both modern and ancient crinoids are known to have harbored a variety of infesting organisms, including annelids, gastropods, crustaceans, other crinoids, and various unidentified makers of trace fossils. A trend of increasing intensity of both lethal and grazing predation on crinoids and other organisms over the course of the Paleozoic has been well-documented, and it has been postulated that the same “arms race” of reciprocal evolution implicated in predatory escalation could apply to other antagonistic relationships. However, rates of parasitism are more difficult to determine, due not only to the typically low preservation potential of parasitic organisms, but also to the inherent difficulty in distinguishing different modes of interaction between hosts and infestors; thus, previous work has had difficulties in addressing the question of whether parasitism has also undergone an escalation. In particular, galling and other reaction features resulting from infestation of crinoid columnals are a paleopathology found throughout the Paleozoic and Mesozoic in the crinoid fossil record, but there is an ongoing debate over whether or not this interaction harmed the host. In this study, rather than attempting to identify "true" parasitism, we instead examine the continuum of features resulting from infestation of crinoid columns to determine whether the frequency of column infestation changes over the course of the diversifications and extinctions in crinoids. Here we present results from an analysis of the frequencies of encrustation, boring, embedment, and reaction features on crinoid columnal fragments from the Silurian through Pennsylvanian of North America.