Liu et al.—Exceptionally preserved Ordovician conodont apparatuses
In many cases, these elements are not hyaline, have somewhat larger denticles, and a carminate rather than bowed blade with a more pointed posterior blade end. An example of this type of albid element is Loxodus dissectus An in An et al., 1983 from the Machiagou Formation in northern China (An et al., 1983, text-figs. 5, 7, 13; Wang et al., 2014, pl. 3, fig. 8). This species is relatively common in this formation and used as a zonal index, but is not associated with archeognathiform elements. It should also be noted that incomplete specimens of the blade-like albid elements of, for example, Appalachignathus Bergström et al., 1974 and Loxodus Furnish, 1938, and the M element of Bergstroemognathus extensus (Graves and Ellison, 1941), could be confused with the S element of Archeognathus primus. Hence, care must be exercised in the identification of coleodi- form elements because this type of element is homeomorphic and probably a component of a variety of multielement taxa.
Family Iowagnathidae new family
Diagnosis.—Large conodonts with individual elements up to 16mm or more in length; complete apparatus with 15 elements somewhat reminiscent of the prioniodinid type; elements with two or three multidenticulated processes and a distinct cusp; denticles hyaline and fibrous, with rare or absent white matter, but without obvious cavity; basal bodies robust, surface with radial ridge-and-groove ornamentation.
Remarks.—Representatives of this family are known only from the Middle Ordovician. Only one referred genus: Iowagnathus new genus.
Genus Iowagnathus new genus Type species.—Iowagnathus grandis new species.
Etymology.—Named for the State of Iowa, the source of the material. Diagnosis.—Same as for species by monotypy.
Remarks.—Iowagnathus n. gen. is strikingly different from Archeognathus and others in the element component and arrangement of the apparatus, aswell as in themorphology of the individual elements (Figs. 5–7, 8.7–8.19, 9.2), suggesting no close affinity at the genus level. In the presence of a denticulated anterior process in some of its elements, Iowagnathus n. gen. is reminiscent of the Darriwilian hyaline genus Paraprioniodus Ethington and Clark, 1981, especially as represented by its type species P. costatus (Mound) (see Ethington and Clark, 1981, p. 77–79; Rexroad et al., 1982, p. 9; Bauer, 2010, p. 16–17). How- ever, as shown by the reconstructions of the P. costatus apparatus by those authors, the significant differences in the morphology of particularly the S0,M, and some S elements of the type species of Iowagnathus n. gen. and Paraprioniodus support separation at the genus level. The elements of Iowagnathus n. gen. also exhibit some general similarity to those of the hyaline genus Erismodus Branson and Mehl, 1933. However, as illustrated by Sweet (1988), the elements of Erismodus lack the long denticulated anterior process in corresponding elements of Iowagnathus n. gen., and the
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appearance of the S0 element is completely different between the two taxa (for further discussion of Erismodus, see Sweet, 1982, p. 1039–1040). Based on the available information, we regard Iowagnathus n. gen. and Erismodus as separate genera. Another genus exhibiting some superficial similarity to Iowagnathus is Erraticodon Dzik, 1978. However, there are significant differences between especially the S and P elements of Erraticodon and those of Iowagnathus n. gen., and these genera are not synonymous.
Iowagnathus grandis new species Figures 5–7, 8.7–8.19, 9.2
?1970 Microcoelodus festivus sp.
nov.Moskalenko, p. 72, pl. 1, fig. 8.
Type specimens.—Holotype: apparatus specimen SUI 139888 (WS18-266) (Fig. 5.2); Paratype: apparatus specimen SUI 139887 (WS18-60) (Fig. 5.1). Both are from the Winneshiek Shale, northeast Iowa.
Material.—Complete or nearly complete apparatuses: SUI 102852,WL151,WS10-347, WS17-273,WS17-275, WS18-79, WS18-246; incomplete apparatuses: WL26, WL60, WL89, WL152, WL156, WL173, WLl79, WS10-72, WS10-195, WS10-197, WS11-21, WS13-1, WS13-656, WS15-71, WS16-82, WS17-2, WS17-287; individual elements: WL208, WS11-342, WS13-587, WS14-553, WS15-342, WS16-80, WS16-235,WS17-296, WS18-265.
Etymology.—Grandis (Latin), big, referring to the large size reached by the elements and apparatus.
Diagnosis.—Hyaline conodonts with an apparatus comprising 15 large ramiform elements, fourteen (P1,P2,M,S1-4) in pairs and one (S0) unpaired (Figs. 5, 6, 9.2). The unpaired S0 element symmetrical and morphologically jaw-like, essentially alate and without posterior or anterior process; cusp short and not prominent. The 14 paired elements more or less digyrate, multidenticulated, with two or three denticulated processes, near symmetrical to asymmetrical; each of the paired elements with a well-developed cusp. Denticles peg-like, sharply pointed, essentially rounded in cross section, and more or less reclined. All elements possess prominent basal bodies and grooves but without cavities.
Occurrence.—Darriwilian (Middle Ordovician, Whiterockian), North America and possibly coeval strata in Siberia.
Description.—Iowagnathus grandis n. gen. n. sp. is one of the most abundant conodont taxa in theWinneshiek collection. The apparatus of this species is composed of 15 large ramiform elements with robust basal bodies, 14 of which are paired and more or less symmetrical to asymmetrical, and one unpaired and essentially symmetrical. The unpaired element (indicated by arrows in Fig. 5.1, 5.2) is referred to as the S0 element. Four pairs of mutually similar S elements form a modified symmetry transition series that includes S1,S2,S3, and S4 elements. The apparatus also has paired M, P1, and P2 elements. Complete apparatuses of this taxon are illustrated in Figure 5.1 and 5.2,
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