Quantitative ichnology of triassic crayfish burrows (Camborygma eumekenomos): Ichnofossils as linkages to population paleoecology

Analysis of 201 crayfish burrows (Camborygma eumekenomos) from three fluvial beds of the Chinle Formation (Upper Triassic, Utah, U.S.A.) provides results consistent with knowledge of Holocene crayfish ecology. Thus, many aspects of their population ecology may have remained unchanged since the early Mesozoic. A significant increase in crayfish size away from the fluvial channel reflects size (age) segregation along an environmental gradient. The high lateral (within-bed) variation in burrow density may have been caused by spatial heterogeneity in water table and soil moisture levels. In each of the three analyzed beds, the burrows record a single ecologic generation of a monospecific crayfish population. The three beds differ in terms of the mean burrow diameter (this may reflect differences either in the average size/age of the resident crayfish or in the lateral extent of sampling). However, the overall shape of the burrow-size distribution is similar for all three beds (unimodal and close-to-normal). This reflects similar paleohydrologic and paleoecologic conditions through time, as substantiated by independent ichnologic and sedimentologic evidence.