Restudy of conodonts (Late Ordovician – Early Silurian) from the Edgewood Group, Clarksville, Missouri

Study of Late Ordovician – Early Silurian conodonts from Anticosti Island, Quebec prompted the re-interpretation of conodonts from the Edgewood Group (Noix Limestone, Bowling Green Dolomite) near Clarksville, Missouri. Eleven 1 kg samples yielded 1565 conodonts of which 1269 are from four Ordovician samples.Ordovician conodonts from the Noix Limestone are similar to those of Fauna 12 from Anticosti Island and the western United States. The notable difference is the multielement genus Noixodontus n. gen., which has an apparatus that consists of a, b, c, d, f, and g elements. The a–d elements have a long cusp and denticles and an adenticulate posterior process; the other processes have only one denticle. An e element may have been previously documented. The f and g elements are prioniodontiform and blade-like, respectively. This new genus differs from Gamachignathus and Prioniodus in apparatus plan and element morphology. A Richmondian age is suggested by the fauna rather than a latest Ordovician Gamachian age. Both lithological and paleontological data suggest a post-Richmondian hiatus.The Silurian Bowling Green Dolomite fauna is dominated by undiagnostic simple cones, which suggests re-occupation after transgression by generalized opportunistic species. This fauna may represent an early Llandovery age, either the Distomodus kentuckyensis Zone or the older Oulodus? nathani Zone.