GYPIDULA COEYMANENSIS SCHUCHERT, 1913, THE WIDESPREAD AND COMMONLY CITED INDEX BRACHIOPOD FOR HELDERBERGIAN (EARLY EARLY DEVONIAN) STRATA OF SOUTHEASTERN LAURENTIA IS REALLY A MEMBER OF THE GENUS SIEBERELLA OEHLERT, 1887

Gypidula coeymanensis is a widely cited brachiopod for Helderberg Group rocks in southeastern North America (Laurentia). It is the most common brachiopod in the Group, especially in the Coeymans Limestone, but it is also found in all other formations. Its abundance is remarkable in the Coeymans where it occurs in shell banks that have often been illustrated in the literature. It was originally established by Schuchert in 1913 as Gypidula (Sieberella) coeymansis, however subsequently it was almost always referred simply as Gypidula coeymanennsis. The only other citations to it belonging to Sieberella were in two publications by Winifred Goldring, former State Paleontologist at the New York State Museum, published in 1933 and 1935 who simply cited them as Sieberella coeymanensis.

Based on our extensive review of the literature focused on this species, as well as examination of specimens gathered by one of us (Feldman), we believe this species should correctly be referred to as Sieberella coeymanensis. Both Gypidula and Sieberella are members of the subfamily Gypidulinae but differ in the former having a relatively coarsely pauciplicate shell with ribs restricted to the anterior margins, whereas Sieberella is almost entirely plicate with numerous angular costae. Internally Sieberella differs in having inner hinge plates variably united to form a cruralium or even low median septum.

We intend to continue our study to carefully examine dorsal interiors of Sieberella coeymansis and the several subspecies attributed to it. S. coeymanensis is widespread in the Appalachian Basin, and occurrences are noted even as far west as western Tennessee and western Texas. The species disappears at the end of the Helderbergian, along with all other gypidulinids in the Lower Devonian of eastern North America. Their disappearance from the remainder of the Lower Devonian in eastern North America appears to be attributed to a major climatic cooling event, when many other warm-water faunal elements become restricted.