Aulacognathus bullatus 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 : 22

Aulacognathus bullatus Nicoll and Rexroad, 1968

Figure 9.11 -14

*1968 Neospathognathodus bullatus Nicoll and Rexroad , pl. 1, figs. 5-7 (Pa element).

1990 Aulacognathus bullatus Nicoll and Rexroad ; Armstrong, pl. 6 figs. 1-2, 4-7 (multielement; synonymy through 1987).

1991 Aulacognathus bullatus Nicoll and Rexroad ; McCracken, pl. 3, fig. 1.

2007a Aulacognathus bullatus Nicoll and Rexroad ; Männik, fig. 8T.

2007b Aulacognathus bullatus Nicoll and Rexroad ; Zhang and Barnes, fig. 13.18.

2015 Aulacognathus bullatus Nicoll and Rexroad ; Bancroft, Brunton, and Kleffner, fig. 5H.

Description. P 1 element consists of a denticulate, blade-like anterior process that continues as nodose or ridged carina on the platform part of the element. Posterior process bifurcated, with longer process deflected strongly inwardly. Two lobate lateral processes extend anteriorly from the middle of the element. The lateral processes are ornamented by ridges and nodes. Ridges more pronounced on larger specimens. P 2 element angulate with a small inner lateral process extending from below the cusp. Cusp is reclined posteriorly. The anterior process is longer than the posterior process and higher in lateral view. Denticles smaller on the posterior process than on the anterior and progressively diminish in size away from the cusp. White matter extends to base of denticles on the anterior process and almost to the base of the element on the posterior process.

Remarks. The P 1 specimen from the Garrison Core ( Figure 9.14 ) has significantly fewer ridges or nodes on the processes than the specimens from the DX5 outcrop. But the slight development of ridges on the bifurcated posterior process, development of paired and uneven nodes on the outer lateral process, and the connection of the nodes on the inner lateral process to the carina justify its assignment to this species. The specimen from the Garrison Core is much smaller than those from the DX5 outcrop, so it is interpreted as being a juvenile. The P 2 specimen from the DX5 outcrop is tentatively assigned to Aulacognathus bullatus because no diagnostic P 1 elements were found in the same sample.

Material examined. One P 2?, four 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.