500
Journal of Paleontology 91(3):493–511 Both the P1 and P2 elements are provided with very
prominent basal bodies. The most conspicuous feature of these bodies is what Klapper and Bergström (1984) referred to as a downward projection, oriented more or less obliquely to the denticle row. Based on the shape, we refer to this structure as a “handle-like” base projection. This projection is broader and located in a more central position in the P1 element than that in the P2 element (Figs. 2, 3.1, 3.2, 4, 8.1–8.3). In all the three pairs of elements of the A. primus apparatus, ridge-and-groove ornaments commonly occur on the surface of the basal bodies (Figs. 2.1, 2.3, 8.1–8.3). Where preserved, they are obliquely arranged on the S elements and roughly radiate from the base projection in the P1 and P2 elements.
Remarks.—The holotype of Youngquistina mitteni Miller, 1969, the type species of Youngquistina, which was collected from the Harding Sandstone in Colorado, agrees in all significant mor- phological features with the P1 element of A. primus and we consider Youngquistina to be a junior synonym of Archeognathus. The unidentified specimen with prominent basal body described by Mosher and Bodenstein (1969) from the lower part of the Chickamauga Limestone of Alabama is clearly a P element of an archeognathid. With a total size of ~ 1mm long, this Chickamauga specimen is less than half the size of many Winneshiek examples of this element. Although coleodiform elements are widespread in Middle
Figure 4. Schematic illustration of the architecture of the 6-element Archeognathus primus apparatus.
opposite direction to those in the S elements (Fig. 2.1, 2.2). Because this difference in denticle direction often occurs in our Archeognathus apparatuses, it may reflect the position of the elements in the living animal. In most specimens, the denticles of the P1 element are straighter than those in the P2 element. The space between adjacent denticles may vary slightly in the archeognathiform P1 and P2 elements, but their bases are connected by a continuous lamina. Longitudinal striae, which were described by Cullison (1938, p. 227) and later illustrated by Miller et al., (1947, pl. 1), are not evident in our specimens.
and early Late Ordovician faunas, this is the first report of a natural apparatus in which they are associated with arche- ognathiform elements. However, some possible co-occurrences of coleodiform and archeognathiform elements have been reported from other Ordovician strata, such as in the conodont faunas of the St. Peter Sandstone of Iowa (Witzke and Metzger, 2005). Webers (1966) reported Neocoleodus spicatus and Coleodus simplex (Webers, 1966, pls. 4.5, 5.11; also cf. elements identified as species of Lonchodus illustrated by Stauffer, 1935, pl. 10, figs. 1–7, 9–12) from the Glenwood Formation of Minnesota, which may represent elements of a species of Archeognathus. Mound (1965, pl. 4) reported Polycaulodus reversus and Pravognathus idoneus from the Joins Formation of Oklahoma, which possibly also represent a species of Archeognathus. Klapper and Bergström (1984) discussed other records of possible archeognathiform specimens from North America and Siberia. Because we have not had the opportunity to reexamine these taxa, we cannot add further information but note that the specimens illustrated by Moskalenko (1983, figs. 3L, N, but not M) as Neocoleodus dutchtownensis Youngquist and Cullison show some similarity to archeognathiform elements. These and other co-occurrences of coleodiform and archeognathiform elements suggest that there were additional Ordovician archeognathid taxa, but far more extensive collecting is needed to confirm this observation. Coleodiform elements have been recorded as species of
Coleodus or Loxodus from a variety of formations in North America, Baltoscandia, Siberia, and China, where they are not associated with archeognathiform elements. Three examples of this are records of a species of Coleodus from the Winnipeg Formation of South Dakota (Sweet, 1982), the Mystic Forma- tion of Quebec (Barnes and Poplawski, 1973), and the Hølonda Limestone of the Norwegian Caledonides (Bergström, 1980).
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