FIGURE 1. Telychian conodont zonation based on Baltic fauna with ranges of biostratigraphically important species. Red lines are used for ranges in Iowa when they differ from the Baltic. Wurmiella? polinclinata polinclinata and Aulacognathus bullatus extend lower in Iowa than in the Baltic. Wurmiella? polinclinata estonica does not range as high in Iowa. Dashed lines in Pteropathodus eopennatus ssp. n. 1 Zone indicate uncertainty in stratigraphic range in Iowa. Modified from Männik (2007a).

FIGURE 2. 1, Paleogeographic map showing the locations of the continents during the lower to middle Silurian. Black box indicates approximate location of the Illinois Basin. From Torsvik et al. (1996, figure 13). 2, Map showing the deepest part of the Illinois and East-Central Iowa basins, and trans-Iowa sag in Iowa and nearby states during the Silurian. Shading indicates extent of basins. Modified from Cramer et al. (2006, figure 1).

FIGURE 3. Cross section of Silurian strata in eastern Iowa. The lower two members of the Hopkinton Formation become indistinguishable in the western part of the cross section. The Sweeney and Marcus members are referred to as Hopkinton A, the Farmers Creek Quarry Member as Hopkinton B, and the Picture Rock Member as Hopkinton C in this manuscript. Note the change in datum at the CC core in Linn County. Modified from Witzke (1992, figure 6).

FIGURE 4. Specimens reported from the DX5 outcrop section in Metzger (2005). All specimens in lateral view. 1-3, 5, Pterospathodus eopennatus ssp. n. 2 sensu Männik (1998), Pa element, DLH 4, SUI 132418 (1); Pa element, DLH 6, SUI 132420 (2); Pb element, DLH 6, SUI 132420 (3); and Pa element, DLH 9, SUI 132423 (5). 4, 6-9, Pterospathodus amorphognathoides angulatus, Pa element, DLH 6, SUI 132420 (4); Pb element, DLH 6, SUI 132420 (6); Pa element, DLH 6, SUI 132420 (7); Pb element, DLH 6, SUI 132420 (8); and Pa element, DLH 11, SUI 132425 (9). 10, Aulacognathus bullatus? Pb element, DLH 11, SUI 132425.

FIGURE 5. Stratigraphic column and conodont range chart for the LPC in the Garrison Core. Dashed lines indicate uncertainty in range. M = mudstone, W = Wackestone, P = Packstone, F = Floatstone for carbonate lithologies. L.H. = Lower Hopkinton. Log colors represent the color of the rock. Correlation of conodont biozonation to chronostratigraphic units from Cramer et al. (2011).

FIGURE 6. Stratigraphic column and conodont range chart for the LPC at the DX5 outcrop. Dashed lines indicate uncertainty in range. See Figure 5 for lithology and symbol legend. The samples included from Metzger (2005) included are DLH 4, DLH 6, DLH 11, and DLH 13, in ascending stratigraphic order.

FIGURE 7. Simple cone elements from Garrison Core. All specimens in lateral view except for 6. 1-2, Panderodus equicostatus, graciliform, GC 124.66-124.93 m, SUI 142251 (1) and graciliform, GC 121.92-121.88 m, SUI 142253 (2). 3-5, Panderodus panderi, graciliform, GC 124.66-124.93 m, SUI 142252 (3); arcuatiform, GC 131.95-132.23 m, SUI 142254 (4); and graciliform, GC 111.38-111.63 m, SUI 142255 (5). 6, Psuedooneotodus beckmanni, oral view, GC 135.65-136.10 m, SUI 142256. 7, Panderodus cf. P. unicostatus, falciform, GC 135.65-136.10 m, SUI 142257. 8-11, Panderodus unicostatus, falciform, GC 131.95-132.23 m, SUI 142258 (8); fused cluster of 8 elements, GC 130.20-130.48 m, specimen destroyed processing for SEM (9); fused cluster of 6 elements, GC 131.95-132.23 m, SUI 142260 (10); and tortiform element, GC 131.95-132.23 m, SUI 142261 (11); 12-13, Walliserodus curvatus, dyscritiform, GC 134.06-134.31 m, SUI 142262 (12) and curvatiform, GC 128.85-129.11 m, SUI 142263 (13). 14-15, Panderodus greenlandensis, arcuatiform GC 118.20-118.41 m, SUI 142264 (14) and graciliform, GC 134.06-134.31 m, SUI 142265 (15). White scale bar represents 0.5 mm.

FIGURE 8. Conodonts from the Garrison Core. 1-12, 19, Psuedolonchodina sp. n., Sa element, posterior view, GC 115.51-115.76 m, SUI 152266 (1); Sa element, posterior-aboral view, GC 121.62-121.88 m, SUI 142267 (2); Sb element, anterior view, GC 134.06-134.31 m, SUI 142268 (3); Sc element, lateral view, GC 130.20-130.48, SUI 142269 (4); Sc/M? element fragment, lateral view, GC 128.85-129.11 m, SUI 142270 (5); M element, lateral-posterior view, GC 131.95-132.23 m, SUI 142271 (6); M element, anterior-lateral view, GC 134.06-134.31 m, SUI 142272 (7); Pa element, oral view, GC 134.06-134.31 m, SUI 142273 (8); Pa element, oral view, GC 130.79-131.09m, SUI 142274 (9); Sc element, lateral view, GC 135.65-136.10 m, SUI 142259 (10); Pb element, lateral, and lateral-aboral views, GC 115.51-115.76 m, SUI 142275 (11 and 12); and Pb element, lateral view, GC 130.79-131.09 m, SUI 142276 (19). 13, 15, Oulodus sp. indet., Sa element, anterior-lateral view, GC 137.12-137.40 m, SUI 142277 (13) and Pa element, posterior view, GC 135.65-136.10 m, SUI 142278 (15). 14, 16-17, Oulodus cf. Ou. petilus pacificus, Sc element, lateral view, GC 134.06-134.31 m, SUI 142279 (14); Sb element, posterior-oral view, GC 130.20-130.48 m, SUI 142280 (16); and Pb element, anterior-lateral view, GC 130.79-131.09 m, SUI 142281 (17). 18, 21-22, Distomodus staurognathoides, Sb element, posterior view, GC 134.06-134.31 m, SUI 142282 (18); Pa element, oral view, GC 135.65-136.10 m, SUI 142283 (21); and Pa element, oral view, GC 135.65-136.10 m, SUI 142282 (22). 20, Aulacognathus angulatus, P₂ element, lateral view, GC 135.65-136.10 m, SUI 142285.

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); S_1/2 element, posterior view, GC 115.51-115.79 m, SUI 142287 (2); S_3/4 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 S_1/2 ? 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 10. Conodonts from the Garrison Core and DX5 outcrop. 1-7, Pterospathodus amorphognathoides angulatus, Sc1 element, posterior view, GC 115.51-115.76 m, SUI 142304 (1); Pb₁ ? element, lateral view, GC 115.51-115.76 m, SUI 142305 (2); Pb2 element, GC 111.38-111.63 m, SUI 142306 (3); Pb1 element, inner lateral, and oral views, GC 115.51-115.76 m, SUI 132410 (4 and 5); Pa element, oral view, DX5 3.49-3.59 m, SUI 142307 (6); and Pa element, lateral view, DX5 4.59-4.61 m, SUI 142308 (7). 8-19, Pterospathodus eopennatus ssp. n. 2 sensu Männik (1998), Sb2 element, posterior, and lateral views, GC 130.79-131.09 m, SUI 142309 (8 and 9); Sc ₁ element, lateral view, GC 130.79-131.09 m, SUI 142310 (10); M element, GC 130.79-131.09 m, SUI 142311 (11); Pb1 element, lateral view, GC 128.85-129.11 m, SUI 142312 (12); Pc element, lateral view, GC 130.20-130.48 m, SUI 142313 (13); Pb1 element, lateral view, GC 130.20-130.48 m, SUI 142314 (14); Pa element, lateral view, GC 128.85-129.11 m, SUI 142315 (15); Pb1 element, lateral view, GC 130.20-130.48 m, SUI 142316 (16); Pa element, lateral, and oral views, GC 130.79-131.09 m, SUI 142317 (17 and 18); and Pa element fragment, oral view, GC 130.20-130.48 m, SUI 142318 (19). 20-21, Aulacognathus sp., juvenile P1 element, oral, and lateral-anterior views, GC 135.65-136.10 m, SUI 142319. 22-23, Kockelella cf. K. abrupta, P1 element, oral, and lateral views, DX5 0.67-0.74 m, SUI 142320.

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).