Goniatites multiliratus Gordon, 1962

Titus, A. L., Korn, D., Harrell, J. E. & Lambert, L. L., 2015, Late Viséan (late Mississippian) ammonoids from the Barnett Shale, Sierra Diablo Escarpment, Culberson County, Texas, USA, Fossil Record 18 (2), pp. 81-104 : 91-92

Goniatites multiliratus Gordon, 1962 ( Fig. 9 )

1909 Goniatites choctawensis . – Shumard, 1863; Girty, p. 59 (part), pl. 13, fig. 1.

1962 Goniatites multiliratus Gordon , p. 356, text-fig. 1A.

1964 Goniatites choctawensis . – Branson, figs. 1–2.

1965 Goniatites multiliratus . – Gordon, p. 186, pl. 18, figs. 8–12 [for more synonymy].

Holotype: Specimen USNM 119499 ; illustrated by Gordon (1965, pl. 18, figs. 9–12).

Type locality and horizon: USGS locality 6619A, 2 km south of Buckhorn (Murray County, Oklahoma); Caney Shale, Goniatites multiliratus Biozone.

Material: Three specimens ( NPL 68494 through NPL 68496 from sample 00TXCU-25) .

Diagnosis: Goniatites with a globular conch between 2 and 8 mm diameter (ww / dm 0.85–1.10) and thickly pachyconic to globular conch (ww / dm 0.80–0.85) at 20 mm diameter. Umbilicus moderately wide in early ontogeny (uw / dm = 0.30–0.35 at 2 mm diameter) and very narrow in all stages larger than 4 mm diameter (uw / dm 0.02–0.10). Umbilical wall convexly rounded in all stages. Aperture low or moderately high ( WER = 1.60–1.80 at 20 mm diameter). Ornament with more than 200 spiral lines and crenulated, slightly biconvex, and rectiradiate growth lines; external sinus shallow. Suture line at 25 mm conch diameter with narrow external lobe (0.55 of the external lobe depth; 1.00 of the ventrolateral saddle width), and moderately low median saddle (0.45 of the external lobe depth). External lobe Y-shaped with very narrow, V-shaped prongs; ventrolateral saddle subacute.

Description: The largest specimen ( NPL 68494) has a partly crushed body chamber, but the phragmocone appears to be uncrushed ( Fig. 9 ). The conch is, at 30 mm diameter, thinly pachyconic (ww / dm = 0.70) with a very narrow umbilicus. Shell fragments are visible at some places. They show fine spiral lines, which in accompany with crenulated growth lines form a spider web-like pattern. The steinkern is smooth except for wide, shallow constrictions.

The smallest specimen ( NPL 68495) is partly crushed and has a diameter of 15 mm. Faint traces of spiral ornament show that this feature has developed by this diameter. Like both of the other specimens, the phragmocone is extensively recrystallized. The medium sized specimen was difficult to extract and the only useful data that can be obtained is that it shows strong spiral lines, with a density of 13 per 2 mm, at an estimated diameter of 25 mm.

Discussion: This species can easily be confused with the stratigraphically older species G. deceptus , which occurs in Nevada and Utah sections of Chainman Shale. The main differences between the two species are the generally wider conch in G. multiliratus (ww / dm = 0.80–0.85 at 20 mm diameter in G. multiliratus in contrast to 0.65–0.70 in G. deceptus ) and the wider external lobe with higher median saddle in G. multiliratus .

G. multiliratus is the stratigraphically youngest species of Goniatites known from North America, and certain features of its conch ontogeny (prolonged subevolute juvenile stage) and suture line (relatively high median saddle and angular flanks of the adventive lobe) may foreshadow the evolution of a Choctawites -like form, although there would clearly be other intermediate stages.

Figures

Figure 9. Goniatites multiliratus Gordon, 1962 from the Figure 2 Ranch section, Sierra Diablo. Specimen NPL 68494 from bed 17 (sample OOTXCU-25); × 2.0.