Multiple forms of bioimmuration in a coral–crinoid–bryozoan association from the Middle Devonian Onondaga Formation of southeastern Ontario

Abstract

A large favositid tabulate coral colony from the Middle Devonian Edgecliff Member of the Onondaga Formation, collected from Port Colborne, southernmost Ontario, 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 was a large solitary rugose coral; and outward growth resulted in overgrowth of multiple macrofossils, including relatively long portions of large-diameter (probably camerate) crinoid columns. 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 stenolaemate bryozoan containing several examples of a parasitic bioclaustration structure similar to Catellocaula. Hence, the composite coral-crinoid-bryozoan association contains two forms of bioimmuration: preservation of the relatively intact crinoid columns via overgrowth and eventual incorporation into the base of the tabulate coral and preservation of the outline of the bioclaustrated organism (potentially an ascidian tunicate) via embedment in the bryozoan. This specimen serves as a testament to the diversity of biotic interactions and preservational mechanisms that occurred in Paleozoic carbonate buildups.