NEW INSIGHTS ON THE LOCALITY AND MATERIAL FOR THE FIRST PENNSYLVANIAN CONODONT PAPER PUBLISHED IN NORTH AMERICA

Gunnell (1931) described the dominant Pennsylvanian conodont genus, Idiognathodus, and three component species from ‘the shaly middle portion’ of what was then thought to be the Fort Scott Limestone near Lexington, Missouri. Idiognathodus claviformis was designated the type species, and is used sporadically by some workers. Idiognathodus delicatus is used widely, and rather indiscriminately, for generalized flat, lobed forms; one of apparently two cotypes is lost, and both appear to represent incomplete growth. Idiognathodus arcuatus was based on a specimen missing the anterior portion; the holotype is lost, and the taxon has not been used since. Gunnell (1933) described I. fustiformis from a lower bed thought to be Cherokee shale ‘overlying Lexington coal’ in the same area; that holotype is also lost, and the taxon has not been used since.

We are now confident that these Gunnell collections were from the Pawnee Limestone, which lies above the Lexington coal and is the next marine formation above the Fort Scott. The conodont-bearing intervals were re-collected in a ravine where the entire Pawnee and adjacent units are well exposed, providing topotypic material that clarifies these early-named taxa. A gray zone at the top of the basal Anna Shale Member has produced morphotypes resembling Gunnell’s figure of I. fustiformis, from which we will select a neotype. The higher Mine Creek Shale Member and the shaly base of the overlying Coal City Limestone Member contain morphotypes that provide a complete growth series for I. delicatus, which allows us to clearly distinguish adult forms from similar taxa. Ellison (1941) chose the atypically rounded, probably gerontic specimen from cotypes to serve as holotype for I. claviformis, and by extension, the type species for Idiognathodus. Morphologies similar to this holotype are extremely rare in the Pawnee anywhere, so confident ontogenetic interpretation of I. claviformis will require a very large number of samples. Selection of a neotype for the lost, broken I. arcuatus will be more complicated, if it is warranted. These stratigraphic and taxonomic findings will help to delineate biostratigraphically useful taxa among these and subsequently named species of Idiognathodus in the late Desmoinesian.