Predatory and non-predatory borings in echinoids from the upper Ocala Formation (Eocene), North-Central Florida, U.S.A
Abstract Predation is one of the more likely types of biotic interactions to be preserved in the fossil record, because a physical record of the event is usually left behind in the form of borings, bite traces, shell repair, or rejuvenated anatomy. The other types of interactions, such as symbiosis (commensalism, parasitism, mutualism), are less obvious unless some physical record of the association is preserved. In spite of their enormous paleoecological potential, we still know very little about symbiotic and predator-prey relationships for most groups of fossil marine organisms, especially echinoids. Sixty-five speciments belonging to five species of irregular echinoids from the Ocala Limestone (Upper Eocene, north-central Florida) were examined for evidence of boring activity. Eight types of borings were delineated based on morphological characteristics and the distribution of the types on the echinoid tests mapped. These data suggest that five types of boring activity are present, which include symbiosis and predation. Three categories of predator-prey relationship are present: (1) a species-specific (non-random) gastropod-echinoid association that may have resulted from coevolution, (2) opportunistic predation by gastropods on echinoids encountered by change and (3) gastropod attacks in which the intended victim was not the echinoid, but rather, another organism encrusting the echinoid test. Not all of the gastropod borings represent predation. One species of echinoid contains clusters of borings that resemble those made by Recent symbiotic gastropods suggesting that a coevolved symbiotic relationship between echinoids and gastropods may have been established as early as the Eocene. Finally, probable annelid borings are also present and if the host were alive at the time of infestation, may represent a symbiotic relationship also, but one that was facultative. Alternatively, the annelid borings may represent the simple use of the empty echinoid test as a suitable substrate for the annelid to bore into, in which case, no biotic interaction exists between the two organisms.