Fossil clusters in the Ludlowville Shale near Buffalo, New York, are nearly circular in bedding-plane outline and plano-convex (convex down) in cross section, the dimensions being about 1 m across and 2 cm thick. The clusters contain several brachiopod species and less abundant bryozoans, trilobites, crinoids, ostracods, bivalves, gastropods, and solitary corals. Their consistent presence across a considerable geographic area and their high diversity suggest that they are an in situ "life" assemblage, but their shape and distinct boundaries may be interpreted as evidence that they are not an in situ "life" assemblage.

The spiriferid brachiopod Ambocoelia umbonata was sampled quantitatively in successive 0.5-cm layers within the fossil clusters. Shell distortion, shell fragmentation, and valve ratios illustrate no vertical trends. Therefore these phenomena must be related to factors that have acted uniformly throughout the clusters. Consistent trends in shell disarticulation, shell position, shell density, and pyrite content are related to factors controlling cluster development. This relation, together with random beak orientations and bimodal size-frequency distributions, favors a biologic origin. The clusters apparently record establishment and succession of organisms on a soft substrate.

End_of_Article - Last_Page 709------------