Abstract

Brachiopods belonging to Ambocoelia occur ubiquitously in Middle and Upper Devonian strata of the northern Appalachian Basin. Originating during the Eifelian, Ambocoelia umbonata persisted through numerous biocrises, but went extinct during the late Frasnian Kellwasser Crisis. Ambocoelia umbonata var. gregaria, the only other form of this genus that is present within the New York Devonian succession, originated around the time of the Kellwasser Crisis and persisted locally into at least the latest Famennian. Examination of syntypic material of A. umbonata var. gregaria has resulted in the taxonomic revision of this form and elevation to Ambocoelia gregaria. Comparison of ontogenetic stages and environmental preferences of A. umbonata and A. gregaria suggests that the latter exhibits a paedomorphic morphology that may have evolved from A. umbonata through neoteny. Furthermore, these comparisons also give new autecological insights for Ambocoelia, suggesting that A. umbonata was capable of living in a diversity of environments by using a variety of life positions, whereas A. gregaria was likely more specialized. This taxonomic revision provides the necessary framework for revising the biostratigraphic range of Ambocoelia and, furthermore, the evolutionary history of this genus in relation to the Lower Kellwasser Event.

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