ABSTRACT
The origination of Paleozoic epibiont communities is temporally constrained through an investigation of encrusters and borers on brachiopods (and some trilobites) older than the Late Ordovician. Well preserved brachiopods from the Arenigian (Kanosh Shale, Utah) and Llandeilan (Bromide Formation, Oklahoma; Benbolt Formation, Virginia) were examined for epibionts. Kanosh brachiopods contained no epibionts; Bromide and Benbolt specimens had numerous encrusters but few borings. For each encrusted host, the percent cover of various epibionts was computed and ecological interactions (i. e., overgrowth relationships) were noted. Bromide and Benbolt epibiont communities were closely similar to each other and to previously described Late Ordovician communities in relative abundance of taxa and ecological structure. They were spatially dominated by several species of mat trepostome bryozoans and the cyclostome Corynotrypa. Other encrusters include craniids, cornulitids, crinoids and edrioasteroids. Mat trepostomes were most common on convex surfaces of host Strophomena and Corynotrypa was most common on concave surfaces and trilobite exuviae. Epibiont growth patterns suggest these assemblages encrusted the upper and lower surfaces, respectively, of live strophomenids. Similarity between Llandeilan and later Ordovician brachiopod epibionts, and the paucity of epibionts on Arenigian specimens suggest that typical epibiont faunas, like many other Paleozoic faunas, arose through rapid diversification of various taxonomic groups during the Arenigian-Llanvirnian.
