Paleoecology of Subulites; a gastropod in the middle Ordovician of central Tennessee

The distribution and abundance patterns of Subulites in gastropod assemblages of the Carters Limestone, a Middle Ordovician shallow-water sequence in the Black River Group of Central Tennessee, exhibit a close correlation with carbonate facies. Environmental interpretation of these carbonate facies indicates a subtidal environment characterized by a soft mud substrate. In some areas where Subulites is exceedingly abundant, this substrate was subject to frequent winnowing, and generally turbid water conditions were produced. In comparison with the associated gastropods, shell features of Subulites such as a straight anterior siphonal canal, a columellar fold, and the shape of the aperture, indicate an advanced type of soft part anatomy capable of dealing more efficiently with flocculent mud substrates. It is suggested that this functional advantage, inherent in Subulites, enabled it to numerically dominate in an environment less conducive to the inhabitation of other gastropods. Careful study of the functional morphology of Subulites as deduced from shell features, along with abundance and distributional trends, permits a comparison with functions, life habits, and distributions of living gastropods. These comparisons suggest possible feeding analogies with predators and scavengers. The interpretation of specific feeding functions in Subulites poses difficulties and in some respects appears incompatible with modern findings. Nevertheless the life habits of Subulites, based on the presumed functional morphology of the shell as well as information derived from the associated biota and the enclosing carbonates, is in agreement with the life habits of extant forms. This favors the role of Subulites as an infaunal or semi-infaunal scavanger.