Wurmiella? polinclinata polinclinata ( Nicoll and Rexroad, 1968 )

Waid, Christopher B. T. & Cramer, Bradley D., 2017, Telychian (Llandovery, Silurian) conodonts from the LaPorte City Formation of eastern Iowa, USA (East-Central Iowa Basin) and their implications for global Telychian conodont biostratigraphic correlation, Palaeontologia Electronica 42 (6), pp. 1-37 : 29-30

Wurmiella? polinclinata polinclinata ( Nicoll and Rexroad, 1968)

Figures 9.1-9.8 , 11.1 -12, 11.14

*1968 Spathognathodus polinclinatus ; Nicoll and Rexroad, pl. 2, figs. 19-20 (P 1 element).

1992 Ozarkodina polinclinata polinclinata Nicoll and Rexroad ; Männik, figs. 4.1-4.28, 5.1-5.7, pl. figs. 8, 10-20 (multi-element; synonymy of P 1 elements through 1992).

1994 Ozarkodina polinclinata Nicoll and Rexroad ; Kleffner, fig. 10.1.

2005 Ozarkodina polinclinata polinclinata Nicoll and Rexroad ; Metzger, pl. 1, fig. 24.

2006 Ozarkodina polinclinata polinclinata Nicoll and Rexroad ; Hints, Killing, Männik, and Nestor, pl. 3, fig. 5.

2007a Ozarkodina polinclinata polinclinata Nicoll and Rexroad ; Männik, fig. 9I.

2007b Ozarkodina polinclinata Nicoll and Rexroad ; Zhang and Barnes, fig. 12.30-12.31.

Description. P 1 elements blade-like with an identi-

fiable cusp. Denticles along the anterior part oriented upwards and mostly evenly sized. In some specimens the most anterior denticles may be taller and wider, and rarely, the anterior-most two or three denticles may be completely fused. Denticles over basal cavity larger and reclined posteriorly. Denticles are partially fused creating grooves between each denticle. Some grooves extend almost to base of element. Aboral margin anterior to basal cavity straight to slightly curved. Basal cavity flares out into a small, unornamented basal platform. Basal platforms restricted to the posterior one third of the total length of the blade. Blade posterior to cusp deflected slightly inwards. P 2 elements slightly angulate with a posteriorly reclined cusp that is much larger than the other denticles. Denticles on anterior process oriented upwards to slightly reclined posteriorly. Denticles on posterior process reclined posteriorly at the same angle as the cusp. Posterior process deflected slightly inwards. M element dolabrate, with a slightly twisted posterior process extending straight behind cusp. Basal cavity widest under cusp and extends along posterior process. S 0 elements alate, with closely spaced compressed denticles. Basal cavity small. S 1/2 elements have a central cusp with two lateral processes extending down and away at different angles. Inner lateral process slightly wider than outer. Denticles closely spaced and triangular. S 3/4 elements bipennate. Posterior process extends straight behind the cusp. Anterior process inclined inwards. Denticles closely spaced, short, and triangular.

Remarks. The M elements are very similar to those of Psl. fluegeli , but can be distinguished by their narrower basal cavities and slightly straighter posterior process.

Murphy et al. (2004) reassigned polinclinata from genus Ozarkodina to Wurmiella without elaboration. We tentatively agree with this assignment, because the P 2 elements exhibit the slight asymmetry in the basal platform that characterizes species of Wurmiella . The P 1 elements, however, differ considerably from the morphology of the type species of Wurmiella , as well as the diagnosis of Murphy et al. (2004), page 8, who state that Wurmiella is a “…genus whose species have a sexmembrate apparatus characterized primitively by processes without strong variation of adjacent denticles.” The denticles on W.? polinclinata can greatly vary in size on some specimens, particularly those adjacent to the cusp and at the posterior end of the blade ( Figures 9.7, 9.8 , 11.1, 11.2 ), in contrast to the very evenly-sized and oriented denticles on Wurmiella tuma ( Murphy et al., 2004, figure 2.16- 19).

Transitional morphologies absent in the Baltic between Wurmiella? polinclinata estonica Männik (1992 ; see below) and W.? polinclinata polinclinata may be present in the specimens from the Garrison Core. Männik (1992) differentiated the stratigraphically lower W.? p. estonica from the higher W.? p. polinclinata based on the character of the denticulation of P 1 elements. Most W.? p. estonica specimens lack a cusp, have denticles that are uniformly sized, completely fused, oriented straight to very slightly reclined anteriorly at the anterior end of the blade and posteriorly at the posterior end, and lack a cusp ( Männik, 1992, figure 3). Wurmiella ? p. polinclinata , in contrast, has a cusp, the denticles vary in size, are only slightly fused to not fused, and progressively recline more posteriorly closer to the posterior end of the blade. Specimens from 135.65–136.10 m (445.66–446.53ft) in the Garrison Core ( Figure 11.15 -17) can be confidently assigned to W.? p. estonica. Two from GC 134.06– 131.31m (439.83–440.66ft; Figure 11.12, 11.14 ) show some characteristics of both subspecies. The characteristics of W.? p. estonica are that the denticles on each of the specimens recline slightly, if at all, and the denticles are fused with the exception of the most posterior two denticles. The characteristics of W.? p. polinclinata shown by the specimens are the relatively large size difference between the anterior and posterior denticles, and the development of a cusp. The W.? polinclinata polinclinata specimens illustrated in Männik (1992) show much more morphological variability than those illustrated as W.? polinclinata estonica , so we suggest that specimens that do not conform strictly to the diagnosis of W.? p. estonica be assigned to W.? polinclinata polinclinata .

Material examined. Seven S 0, fourteen S 1/2, six S 3/4, two M, eighteen P 2, twenty-one P 1 elements.

Figures

FIGURE 9. Conodonts from the Garrison Core and DX5 outcrop. 1-8, Wurmiella? polinclinata polinclinata, S0 element, anterior view, GC 130.79–131.09 m, SUI 142286 (1); S1/2 element, posterior view, GC 115.51–115.79 m, SUI 142287 (2); S3/4 element, lateral view, GC 115.51–115.76 m, SUI 142288 (3); M element, lateral view, GC 130.20– 130.48 m, SUI 142289 (4); P2 element, lateral view, GC 130.20–130.48 m, SUI 142290 (5); P2 element, GC 130.79– 131.09 m, SUI 142291 (6); P1 element, lateral view, DX5 4.59–4.61 m, SUI 142292 (7); and P1 element, lateral view, DX5 3.49–3.59 m, SUI 142293 (8). 9-10, Aulacognathus angulatus, P1 element, oral view, GC 135.65–136.10 m, SUI 142294 (9) and S1/2? element, posterior view, GC 135.65–136.10 m, SUI 142295 (10). 11-14, Aulacognathus bullatus, P2 element, lateral view, DX5 1.34–1.54 m, SUI 142296 (11); P1 element, oral view, DX5 4.59–4.61 m, SUI 142297 (12); P1 element, oral view, DX5 0.67–0.74 m, SUI 142298 (13); and P1 element, oral view, GC 120.88– 121.13 m, SUI 142299 (14). 15-16, Aulacognathus kuehni, P1 element, oral view, GC 131.95–132.23 m, SUI 142300 (15) and juvenile P1 element, oral view, GC 131.95–132.23 m, SUI 142301 (16). 17, Astrolecignathus cf. milleri, Pa element, oral view, GC 121.92–121.88 m, SUI 142302. 18, Apsidognathus tuberculatus, Pa element, oral view, DX5 1.34–1.54 m, SUI 142303.

FIGURE 11. P1 elements of Wurmiella? polinclinata estonica and Wurmiella? polinclinata polinclinata. 1-11 are classified as W.? polinclinata polinclinata. 12 and 14 show some characteristics of each subspecies, but compare most closely to W.? polinclinata polinclinata. 13, 15-17 are classified as W.? polinclinata estonica. All specimens in lateral view. 1, GC 121.92–121.88 m, SUI 142321; 2, GC 128.85–129.11 m, SUI 142322; 3-5, GC 130.20–130.48 m, SUI 142323 (3), 142324 (4), and 142325 (5); 6, GC 130.79–131.09 m, SUI 142326; 7-11, GC 131.95–132.23 m, SUI 142327 (7), 142328 (8), 142329 (9), 142330 (10), and 142331 (11); 12-14, GC 134.06–134.31 m, SUI 142332 (12), 142333 (13), and 142334 (14); and 15-17, GC 135.65–136.10 m, SUI 142335 (15), 142336 (16), and 142337 (17).