Menabites (Delawarella) vandaliense ( Young, 1963 )

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 : 23

Menabites (Delawarella) vandaliense ( Young, 1963)

Figure 18A–B

1963 Submortoniceras vandaliense , n. sp.; Young, p. 102, p1. 55, figures 6, 7; text-figures 26a

?1993a Submortoniceras uddeni Young, 1963 ; Kennedy and Cobban, p. 842, figures 10.1, 12.3, 12.4, 12.7, 12.8

Type. The holotype is UT –30638, by original designation by Young (1963, p. 102, plate 55, figures 6, 7; text-figure 26a). It is from the Blossom Sand in Red River County, Texas .

Material. One specimen, CPC –2576 from bed TPY77 .

Description. Involute. Whorl section compressed, with greatest width at mid-flank. Flanks converge moderately towards the subrounded venter. Nineteen pointed umbilical tubercles give rise to branching prorsiradiate ribs which efface on the flanks. They strengthen on the outer flank and form numerous fine oblique bullae on the ventrolateral shoulder. They terminate before reaching the siphonal keel so that the latter is accompanied by narrow smooth grooves.

Dimensions. CPC-2576, D: 90, WB: 12 (0.17), WH: 29 (0.42), WB/WH: 0.41, U: 11 (0.16), number of ribs: 50.

Remarks. This rare species was based on a single specimen with fine ribbing presented by Young (1963), to which another is added here. It differs from Menabites (Delawarella) vanuxemi in the weakening of the outer tubercles at larger diameters and lateral effacing of the ribs. In this aspect it is similar to M. (D.) uddeni , but ventrolateral ornament is finer. Young (1963) already discussed that Submortoniceras vandaliense and S. sancarlosense may be conspecific, but this question cannot be answered here.

The specimen described as Submortoniceras uddeni Young, 1963 , by Kennedy and Cobban (1993a, p. 842, figures 10.1, 12.3, 12.4, 12.7, 12.8) has finer ornament than the nominate species and is better placed in Menabites (Delawarella) vandaliense . It is from the Merchantville Formation exposed on the flanks of the Chesapeake and Delaware Canal 1.65 km (1 mi) east of Summit Bridge on the north side of the canal, New Castle County, Delaware, and thus lacks precise stratification.

Occurrence. Upper Santonian of Texas (but see discussion on the age of the Blossom Sand below), Merchantville Formation of New Castle County, Delaware, USA, and lower Campanian of Tepeyac, Mexico. Where precisely dated the species is from the lower Campanian.

Figures

FIGURE 18. Compressed Menabites (Delawarella) from the Tepeyac section. A–B: Menabites (Delawarella) vandaliense (Young, 1963), CPC–2576 from bed TPY77. Menabites (Delawarella) uddeni (Young, 1963) C–D: CPC– 2399, E–H: CPC–2400, both from bed TPY74; I–J: CPC–2416, K–N: CPC– 2415, both from bed TPY77. Scale: 50 mm.