CONODONT APPARATUSES FROM THE MIDDLE ORDOVICIAN WINNESHIEK SHALE, IOWA, USA
Many Winneshiek conodont apparatus elements are of huge size (up to 10 mm or more) suggesting that these conodont animals may have been 0.5-1.0 m in length. Two of the most common apparatus types are referred to Archeognathus primus Cullison, 1938 and to a new genus and species. The former has a 6-element apparatus composed of two pairs of archeognathiform (P) and one pair of coleodiform (S) elements. The 15-element apparatus of the latter contains only ramiform elements of alate (one element) and angulate or bipennate, and tertiopedate types (seven pairs). Elements of both taxa are hyaline and provided with robust basal plates. They are the first hyaline conodont apparatuses described from the Ordovician. Compared with the few previously described Ordovician conodont apparatuses, these apparatuses from the Winneshiek are very distinctive. Whereas the Archeognathus apparatus is quite unlike any previously described conodont apparatus, that of the new genus and species is superficially similar in its 15-element architecture to that of prioniodiform conodonts but differs in the placement, appearance, and presumed function of the elements. Based on their apparatuses, both genera appear to occupy an isolated taxonomic position. Some other conodont apparatuses comprising hyaline elements also occur in the Winneshiek fauna.