CONODONT BIOSTRATIGRAPHY OF LOWER AND MIDDLE PENNSYLVANIAN STRATA IN THE TYPE AREA OF THE DERRYAN SERIES, SOUTHERN NEW MEXICO
Some idiognathodontids exhibit discontinuous transverse ridges on the oral surface of the Pa element, a characteristic commonly associated with Streptognathodus. These transitional morphologies are present throughout the Desmoinesian, and we consider them to represent reiterative evolution in response to stress conditions. Hindeodus, Idioprioniodus, and Adetognathus are common where transitional idiognathodid morphologies are present. They are elevated in numbers in some units that do not contain transitionals, but they are otherwise generally rare.
Conodont biofacies associations reflect a shallow shelf, marine environment of generally low to moderately elevated energy. Elevated numbers of Hindeodus reflect localized energy variations, and locally elevated numbers of Adetognathus, Idioprioniodus, and Idiognathoides indicate stress conditions.