A COMPLETE APPARATUS FOR IDIOPRIONIODUS CONJUNCTUS FROM THE EXCELLO SHALE OF IOWA

A moderately well-preserved conodont fauna from calcareous concretions in the Excello Shale Member of the Mouse Creek Formation of the Marmaton Group (upper Desmoinesian, Pennsylvanian) was recovered from two localities: near the towns of Booneville in Dallas County and Medora in Warren County, south-central Iowa. Acid residues of these concretions contain radiolarians, conodonts, agglutinated foraminifers, fish remains, bivalves, microgastropods, and sponges. The concretions contain a significant amount of hydrocarbons and are difficult to breakdown. By letting the concretions naturally weather on a campus quadrangle, the hydrocarbons were significantly degraded/removed so that the weathered rind would breakdown and these parts yielded conodonts that are nearly all unbroken with the denticles intact. The apparatus of Idioprioniodus conjunctus is easy to pick out as the elements are robust, more than the twice the size of the other contained conodont species, and are nearly completely hyaline. The unbroken material shows the processes on I. conjunctus are not short as commonly reported, but are relatively long, and that most previously illustrated specimens were broken. The apparatus has previously been reported to be a seven element apparatus, but in our interpretation it is in fact an eight member apparatus. Given this new material the best apparatal plan for modeling the Idioprioniodus apparatus is that of contemporaneous species of Gondolella. Both Idioprioniodus and Gondolella can occur abundantly together in Middle and Upper Pennsylvanian black shales of the Midcontinent, but are relatively rare in other lithofacies.