INTENSE DRILLING PREDATION ON THE BRACHIOPOD CARDIARINA CORDATA (COOPER 1956) FROM THE PENNSYLVANIAN OF NEW MEXICO

Intense drilling predation (>20%) is a common phenomenon in Late Mesozoic and Cenozoic fossil assemblages. However, the Paleozoic drilling frequencies documented so far rarely exceed 10%. Cooper (1956), when describing the Pennsylvanian brachiopod Cardiarina cordata (Otero Fm., New Mexico), noted that many specimens displayed a small round hole and suggested that the holes represent gastropod borings. Analysis of a bulk collection of the specimens of C. cordata housed in the Smithsonian reveals that these small brachiopods (<2 mm size) display small (<0.2mm), single, round, often beveled holes with a drilling frequency (32.7%; n=400 specimens) comparable with rates observed in the Late Mesozoic and Cenozoic. Of the 131 drilled specimens, only 8 displayed multiple boreholes. Pedicle valves display twice as many boreholes (n=86) as brachial valves (n=43). Landmark-based morphometric analysis shows that boreholes on brachial valves are commonly found in the central area of the valve while those in pedicle valves show a wider range of location. Two other species, both notably larger than C. cordata, were included in the same bulk collection. Out of 73 specimens of Coledium bowsheri, none were drilled. Out of 89 specimens of Oligothyrina alleni, only 1 was drilled (1.1%). The results point to a Pennsylvanian drilling organism (predator or parasite) that intensely drilled small brachiopods and displayed high species, valve, and site selectivity. The high drilling frequency indicates that Cenozoic-level predation intensities may have locally affected Late Paleozoic benthic communities. The results also suggest (see also Leighton, 2001) that the high Paleozoic rates may be unique to small prey with small boreholes and may record different predators than those that generate relatively larger, but less frequent drillholes, previously documented for the Paleozoic brachiopods, echinoderms, and mollusks.