498 Materials and methods
Among the 5,354 numbered specimens collected from the Winneshiek Shale, 2,749 are conodonts and more than 10% of these conodont specimens are bedding-plane assemblages. As mentioned above, this study focuses on the apparatuses of two taxa identified as Archeognathus Cullison and a new genus Iowagnathus. Each taxon is represented by multiple, apparently complete or nearly complete apparatuses. Based on their position in the section, the specimens
collected from the top to the base of the excavated section are labeled WS1 through WS18, each number representing a stratum thickness of about 20 cm. Other specimens were collected from random slabs that were washed out from the river bed during flooding. These specimens are labeled WL.
Repository and institutional abbreviation.—The specimens described and illustrated herein are reposited in the Paleonto- logy Repository of the Department of Earth and Environmental Sciences, the University of Iowa, and are labeled SUI.
Systematic paleontology Conodonta Eichenberg, 1930
Family Archeognathidae Miller, 1969
Diagnosis.—Large conodonts with individual elements that can be longer than 10mm; a highly modified apparatus consisting of only three pairs of elements, one pair of coleodiform and two pairs of archeognathiform; all elements containing robust basal bodies with distinctive radial or oblique ridge-and-groove surface ornamentation; denticles hyaline and fibrous, with rare or absent white matter.
Remarks.—Representatives of this family are currently known only from the Darriwilian to Sandbian interval of the Ordovician. There is only one referred genus: Archeognathus Cullison, 1938. Pending revision of relevant taxa (see Klapper and Bergström, 1984; Miller, 1969; Sweet, 1988), we assign Archeognathus to Archeognathidae Miller, 1969, following Klapper and Bergström (1984).
Genus Archeognathus Cullison, 1938
Type species.—Archeognathus primus Cullison, 1938, by original designation.
Diagnosis.—Complete apparatus consisting of three pairs of large elements. One pair of coleodiform (S) elements long and elongate; thick basal body slightly curved with numerous small denticles along the upper (convex) margin to form a saw-blade shape. Two other pairs of archeognathiform elements (P1 and P2) smaller, with fewer but much more robust denticles, none developed as a cusp; prominent basal bodies of P1 and P2 ele- ments with conspicuous handle-like projection from a more or less straight lower margin.
Journal of Paleontology 91(3):493–511
Remarks.—In all important morphological features, including the appearance of the basal body, the P elements of this appa- ratus are identical with the holotype of A. primus from the Dutchtown Formation (Cullison, 1938, pl. 29, figs. 10a, b). However, in accordance with taxonomic priority rules, it is necessary to assess whether any other element in the Archeognathus apparatus was assigned to a new genus prior to 1938. The fact that this apparatus contains only one other type of paired element, here referred to as the S element, would appear to make it an easy task to establish priority. In previous conodont faunal studies, blade-like specimens of similar appearance to the S element in the Winneshiek taxon have in most cases been referred to the form genus Coleodus Branson and Mehl, 1933. Unfortunately, as noted by Klapper and Bergström (1984), Branson and Mehl’s (1933) cotypes of C. simplex, the type species of Coleodus, which were collected from the Harding Sandstone of Colorado, are too fragmentary to permit a full description and confident identification, and it has never been revised in terms of multielement taxonomy. Inspection of Branson and Mehl’s (1933, pl. 1, fig. 22) illustration of the most complete specimen, which we here select as the lectotype of C. simplex, shows that its denticulation and the shape of both the lower margin and lateral face of the process differ markedly from the corre- sponding features in the coleodiform element (S element) of A. primus. Thus, it is unlikely that they represent the same species. In addition, the Harding Sandstone is of late Sandbian age and substantially younger than both the Dutchtown and Winneshiek formations. Coleodus has been used as a genus designation for several
Middle, and even Late, Ordovician taxa of both hyaline and albid types of conodonts based on a superficial general similarity to C. simplex in descriptions of North American, Baltoscandic, and Chinese faunas that completely lack arche- ognathiform elements (e.g., Moskalenko, 1970; An et al., 1983; Bauer, 2010). This suggests that Coleodus has become a wastebasket genus for homeomorphic but not closely related conodont elements, and that these species are not congeneric with A. primus. Thus, although Coleodus was established a few years earlier, we use Archeognathus as the generic designation for our Winneshiek taxon. Winneshiek apparatuses of this taxon include elements clearly representing Youngquistina Miller, 1969 and this genus is here regarded as a junior synonym of Archeognathus. Neocoleodus spicatus Branson and Mehl, 1933, the type
species of Neocoleodus, has been recorded from several formations but is currently poorly known. It may be related to Archeognathus at the family level, but this type of element is not present in ourWinneshiek collections.
Archeognathus primus Cullison, 1938 Figures 2–4, 8.1–8.6, 9.1
1969 Youngquistina mitteni Miller, p. 505, fig. 1. 1984 Archeognathus primus Cullison, 1938; Klapper and Bergström, p. 954, figs. 3–8, 9A, B, 10 (includes further synonyms).
1938 Archeognathus primus Cullison, p. 227, pl. 29, figs. 16a, b.
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