Aulacognathus angulatus Bischoff, 1986

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 : 22

Aulacognathus angulatus Bischoff, 1986

Figures 8.20 , 9.9-9.10

*1986 Aulacognathus angulatus ; Bischoff, pl. 3, figs. 15-24 (P 1 and P 2 elements)

Description. P 1 element consists of a blade with two anteriorly oriented lateral processes that intersect the blade at nearly the same point. Blade denticulate. Anterior portion of the blade bowed. Posterior portion curved and slightly deflected outwardly. Lateral processes narrow, with aligned nodes. A small, very steep platform is developed between the lateral processes and the blade. P 2 element angulate. Posterior process deflected inwardly. White matter distributed almost to the base of the element on both the anterior and posterior processes. S 1/2? element alate, with arched, excavated, and thickly-walled basal cavity. Denticles are widely separated and oval shaped in cross section. White matter extends below denticles in near-rectangles and is separated by translucent material.

Remarks. This rare species has been previously recovered only from an unnamed limestone unit in New South Wales, Australia ( Bischoff, 1986, p. 9, locality number 9). Bischoff assigned the unit to the Stimulograptus sedgwickii or Spirograptus turriculatus graptolite biozones, which correlate to the upper Aeronian to lower Telychian ( Cramer et al., 2011). Our specimens were recorded with conodonts from the lower Telychian Pt. eopennatus Superzone.

Material examined. One S 1/2, one P 2, one P 1 element.

Figures

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); 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.