POPULATION DYNAMICS OF THE FOSSIL CRAB DAKOTICANCER OVERANUS

Study of population dynamics of an assemblage of more than 2500 fossil crabs, Dakoticancer overanus (Dakoticancridae), from the Late Cretaceous Pierre Shale in South Dakota provides a unique insight into the genus. It is rare to find a collection this sizeable of a single species of crabs. Studies of population dynamics have rarely been conducted on fossil decapods, whereas many such studies have been done on molluscan species. On this collection of specimens, measurements will be taken of sternal elements to compare size differences between males and females. Differences in numbers of individuals and in growth rates between males and females will be examined. Preliminary analysis suggests that the population contains many more males than females. Determination of whether or not the decapod collection is an assemblage of molts or corpses representing a portion of a living community is of interest. However, it can be difficult to determine whether or not a fossil crab is a molt or a corpse. To attempt to resolve this question, thin sections will be made to look at cuticle thickness and structure. We hypothesize that most molts have a thinner cuticle than intramolt animals because the endocuticle will have been resorbed. Comparison of cuticle thin sections of the fossil crabs with cuticle thin sections of extant animals in molt and intramolt condition will shed light on the question. This is a new area for cuticle structure research, as thus far, cuticle research on decapod fossils has been concerned with implications for systematics and taphonomy.