Glyptoxoceras texanum, 2001

Ifrim, Christina & Stinnesbeck, Wolfgang, 2021, Ammonoids and their biozonation across the Santonian-Campanian boundary in north-eastern Coahuila, Mexico, Palaeontologia Electronica (a 34) 24 (3), pp. 1-62 : 43-45

Glyptoxoceras texanum

Kennedy, Landman, and Cobban, 2001

Figure 35A–H

1992 Glyptoxoceras sp. ; Cobban and Kennedy, p. 80, plate 4, figures 10-11; plate 6, figures 5-6; plate 7, figures 7-8

1997a Glyptoxoceras sp. ; Kennedy et al., p. 35, figure 22c-e

2001 Glyptoxoceras texanum Kennedy, Landman and Cobban , p. 7, figure 4

Type. The holotype is USNM 490970 , by original designation by Kennedy, Landman and Cobban (2001, figure 4c–e). It is from the top of the Blossom Sand at USGS Mesozoic locality 18120, between Detroit and Bagwell, Red River County, Texas

Material. Two fragments, CPC –2349 from bed TPY48-50 and CPC –2610 from bed TPY73.

Description. Open coil with different intensities of coiling, moderately helicoidal. Whorl section is ovoid, WB/WH is between 0.60 and 0.74, but the ratio may be distorted due to crushing of the shell. Ribs are closely spaced, with a rib index of between 8 and 10, increasing with WH. Ribs are weak and straight across the dorsum, strong and slightly convex across the dorsolateral margin, strong, straight, and rursiradiate on the flanks, and transverse on the venter where they reach their maximum height. CPC–2349 shows a deep constriction which is flanked by a flared adapertural rib.

Dimensions. CPC–2346, WB: 14, WH: 19, WB/ WH 0.74, L: 15, ribs per WH: 8. CPC–2610, smaller end,WB: 12, WH: 20, WB/WH: 0.60, ribs per WH: 10, L: 65 to larger end, there WB: 15, WH: 24, WB/WH 0.63.

Remarks. Our specimens are closely resemble the lower Campanian Glyptoxoceras sp. described by Kennedy et al. (1997b) and Cobban and Kennedy (1992b), which are here included in the present species.

Glyptoxoceras retrorsum (Schlüter, 1972) from the lower Campanian of Germany is similar to our specimens with respect to ribbing and dimensions near the aperture (e.g., Kaplan and Kennedy 2005, p. 310, plate 46, figures 1-3; plate 49, figures 1-2), but lacks flared ribs. Glyptoxoceras novimexicanus ( Reeside, 1927) is morphologically indistinguishable from G. retrorsum and is here regarded as a synonym.

The present material is ribbed more finely than the upper Santonian Glyptoxoceras sp. of ( Kennedy and Cobban, 1991). Glyptoxoceras aquisgranense (Schlüter, 1972) from the lower Campanian of Germany has a lower rib index and a more

mm.

rounded whorl section ( Kennedy and Kaplan, 1995). This species was also recorded from lower Campanian of the Atlantic Coast ( Kennedy et al., 1997b). A more circular section and significantly coarser ribs are present in Glyptoxoceras ellisoni Young, 1963 and Glyptoxoceras rubei ( Reeside, 1927) .

Two groups may thus be distinguished within lower Campanian members of the genus Glyptoxoceras , i.e., delicately ribbed taxa including Glyptoxoceras retrorsum and G. texanum , and coarsely ribbed ones such as G. aquisgranense and G. ellisoni . The presence, or absence, of constrictions may distinguish species in these two groups of Glyptoxoceras , but this cannot be decided to date.

Occurrence. Uppermost Santonian of northeastern Texas , Menabites (Delawarella) delawarensis zone of New Jersey, lower Campanian of northeastern Coahuila , and middle Campanian of Texas .

Figures

FIGURE 35. Glyptoxoceras texanum Kennedy, Landman and Cobban, 2001 from the Tepeyac section. A–D: CPC– 2349, bed TPY48–50; E–F: CPC–2610, bed TPY73. Scale: 50 mm.