BURROW MORPHOMETRY OF THE BLUE LAND CRAB (CARDISOMA GUANHUMI): A FIELD-BASED NEOICHNOLOGICAL APPROACH

Blue land crab (Cardisoma guanhumi Latreille, 1825) is a keystone species and a prolific burrower in a variety of low-latitude supratidal habitats, however few efforts have been made to address the ichnology of this decapod. We present a detailed morphological assessment of C. guanhumi burrows and make comparisons to Macanopsis plataniformis, a trace fossil thought to be constructed by a similar brachyuran. Using ten burrow casts from a mangrove wetland on San Salvador Island, Bahamas, 29 dimensionless morphological parameters were compared. Measurements were taken from the casts and 2D photogrammetry, with 117 additional published measurements included. Key architectural metrics were analyzed using the Bray-Curtis similarity test to determine morphometric indices representative of the biogenic structures produced by C. guanhumi. The attributes were compared to measurements taken from published images of M. plataniformis. Results show high overall similarity index (0.8) between all casts, with complexity, tortuosity, and opening inclination angle having moderate to high similarity (>0.7). The end chamber angle of the blue land crab has the highest similarity both within the modern dataset (0.9) and to that of M. plataniformis (0.9). The large terminal chamber is particularly important due to its preservation potential, repository of vegetation matter and potential skeletal remains, and a reliable water table (~sea-level) indicator. Our findings demonstrate how a quantitative assessment of modern biogenic structures and their likely counterparts from the sedimentary record can help constrain tracemaker identity.