NEW TAXONOMIC AND PALEOAUTECOLOGIC INSIGHTS INTO MIDDLE AND UPPER DEVONIAN AMBOCOELIIDS FROM NORTHEASTERN NORTH AMERICA

Ambocoeliid brachiopods are a common occurrence throughout Middle and Upper Devonian strata across northeastern North America. With the exception of the Middle Devonian deposits of New York State, no taxonomic work on Ambocoeliids has been undertaken since the time of James Hall in the late 1800's, and most of the names he gave for the New York Ambocoeliids have been applied to similar brachiopods elsewhere in northeastern North America without any corresponding taxonomic analysis.

In this study we present taxonomic revision of two taxa of the genus Ambocoelia based on material collected from the Upper Devonian of western New York and the Middle Devonian of northwestern Ohio. In the Northern Appalachian Basin deposits of New York State, collection of additional material from the type locality of Ambocoelia umbonata var. gregaria has resulted in the recognition of this form as a species discrete from Ambocoelia umbonata, and allows for the taxonomic elevation of this form back to Ambocoelia gregaria. Furthermore, comparison of adult and juvenile forms and environmental preference of A. umbonata and A. gregaria suggests that the latter exhibits a paedomorphic morphology that likely evolved from A. umbonata, and that these taxa likely exhibited completely different life orientations. Study of Ambocoeliids from the Silica Shale of Ohio, which were assigned by previous workers to the Appalachian Basin form, Ambocoelia umbonata, has resulted in the identification of a new species of Ambocoelia. Ambocoeliids from the Silica Shale are planoconvex to ventribiconvex, with an inconspicuous ventral sulcus and no visible fold. Similar to Ambocoelia umbonata, the shells of this new form are extraordinarily thick for their size, in particular in the umbonal area, which is incurved. In adult forms, the delthyrial gap is relatively large compared to other species of Ambocoelia, and partially covered by secondary shell material. This form possesses a bilobed, tuberculate cardinal process, inconspicuous crural plates, and spires with 4-5 coils. Additionally, this species possesses concentric rows of spines along growth lamellae, a feature uncommon in Ambocoelia. This work represents an initial step in further understanding the evolution, paleoecology, and biogeography of Middle and Upper Devonian Ambocoeliids.