ABSTRACT

A statistical method of discriminating between life and death assemblages of brachiopods in fossil shell beds is demonstrated. The method utilizes the relative numbers of pedicle and brachial or right and left valves present in a sample of shell bed as well as the relative numbers of large and small shells and the relative numbers of articulated and disarticulated specimens.

Application of this method to a brachiopod-rich sample of a shell bed from strata of Early Devonian age in northern Maine shows that two of the contained species are indigenous whereas a third is not. The relationship between the number of articulated and disarticulated valves reveals that one of the two indigenous species has a unit disarticulation rate about eight times greater than the other. The extreme rarity of certain species in any one area is illustrated by the fact that in a sample of almost 5000 specimens, one species is represented by only one specimen.

Theoretical considerations of the transportation of articulated and disarticulated shells suggest that by contouring the amount of disarticulation of a species from a region it should be possible to locate the source area from which the shells came. It should also be possible to locate the source area by contouring the ratio of disarticulated opposite valves of a species from one region.