Punctal density in the Ordovician orthide brachiopod Paucicrura rogata: anatomical and paleoenvironmental variation

摘要

In the orthide brachiopodPaucicrura rogata, from the Upper Ordovician of New York, the density of punctae (small perforations in the shell) increases from about 350 to about 450 per mm2of shell in the transition from shallow‐water limestones to black graptolitic shales down the outer slope of the Taconic Trench. Punctal density is significantly correlated with water depth, as measured by distance downslope along individual volcanic ash layers, and by reciprocal averaging score for macroinvertebrate fossil assemblages (p