MULTIPLE FORMS OF BIOIMMURATION IN A CORAL-CRINOID-BRYOZOAN ASSOCIATION FROM THE MIDDLE DEVONIAN ONONDAGA FORMATION OF SOUTHERN ONTARIO

Large, flat-topped favositid tabulate corals are common in biostromal lithofacies of the Middle Devonian Edgecliff Member of the Onondaga Formation near Port Colborne, southernmost Ontario. One such tabulate colony, collected from dark brown, crinoid-rich, mud matrix, is described herein because of several noteworthy paleontological features preserved via overgrowth by the coral. The initial substratum colonized and subsequently overgrown by the favositid is a large solitary rugose coral; several other macrofossils—including other solitary rugosans, a platyceratid gastropod, and three relatively long portions of large-diameter (probably camerate) crinoid columns—were encrusted and incorporated into the base of the coral as it grew outward. The crinoid columns, which likely represent portions of robust, recumbent dististelar attachment structures, are otherwise known almost entirely from isolated columnals at the collection locality and similar high-energy biostromal lithofacies in the Edgecliff Member elsewhere. One of the crinoid columns is encrusted by a laminar stenolaemate bryozoan containing several examples of the parasitic bioclaustration structure Catellocaula. Hence, the composite coral-crinoid-bryozoan association contains two forms of bioimmuration: preservation of the relatively intact crinoid columns via overgrowth (i.e., substratum bioimmuration) and preservation of the outline of the Catellocaula-forming organism, potentially an ascidian tunicate, via embedment in the bryozoan skeleton (i.e., bioclaustration). This specimen therefore represents an example of how bioimmuration by colonial organisms can improve the preservational quality of well-mineralized multi-element macrofossils in high-energy settings as well as foster moldic preservation of soft-bodied organisms.