Kaim, A. 2010: Non-actualistic wood-fall associations from Middle Jurassic of Poland. Lethaia, Vol. 44, pp. 109–124.
The oldest modern-type wood-fall (sunken wood) associations so far known, were reported from the Upper Cretaceous of Japan. Here, four Middle Jurassic fossil associations collected from logs of sunken driftwood are documented from clay and silt sediments of the Częstochowa Ore-bearing Clay Formation in Poland. The associations are composed of almost entirely different set of molluscs when compared to modern examples of wood-fall communities. The exceptions are leptochitonid polyplacophorans and alleged cocculinoid gastropods, both of which are typical of modern sunken wood communities. It is hypothesized here that the associations represent Jurassic wood-fall communities, which in contrast to their modern counterparts do not contain associated chemosymbiotic animals. This disparity results from the absence of xylophagain wood-boring bivalves, which since the Cretaceous have produced significant amounts of faecal pellets, the decomposition of which increases the amount of sulphide around sunken driftwoods. The associations are considered as benthic rather than pseudoplanktonic because the wood logs were colonized only on their upper side, the abundant crinoids belong to benthic genera rather than to pseudoplanktonic, associations include numerous infaunal organisms, and there are too many clingers in the associations. The most typical and numerous members of the investigated associations are the gastropods Cosmocerithium and Astandes, both having uncertain taxonomic positions. It is suggested here that Cosmocerithium could be a grazer of bacterial mats, and represents an ecological counterpart of modern Provannidae. □chitons, cocculinoids, deep sea, ecology, evolution, Wood-fall communities.