Menabites (Delawarella)

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 : 18-20

Menabites (Delawarella) sp.

Figure 15A–C

Material. Two specimens, CPC –2588 from bed TPY77 and –2590 from bed TPY80 .

Dimensions. CPC-2588, D: 140, WB: 40(0.29), WH: 62 (0.44), WB/WH: 0.65, U: 43 (0.31), ribs per whorl: 34.

Remarks. This morphotype has no tubercles and strong, simple ribs, contrasting with all other species in this genus. The two specimens may or may not belong to the same species. CPC–2590 has has a polygonal whorl section comparable to M. (D.) danei but has more convergent flanks, and ribbing is finer. Menabites (Delawarella) sabinalensis ( Young, 1963, p. 112, PI. 54, figure 2, PI. 63, figures 1, 3, 4, text-figures 20c, 2 le, 26c) is a boldly and distantly ribbed species, with weakly developed tubercles and quadri-tuberculate ornamentation in adults. However, tubercles are absent in our specimens.

Occurrence. Only known from the upper Tepeyac section close to the early-middle Campanian boundary.

Menabites (Delawarella) vanuxemi ( Morton, 1830)

Figure 16A–F , Table 7

1830 Ammonites vanuxemi Morton , p. 244, plate 3, figures 2–4.

1962 Submortoniceras vanuxemi (Morton) ; Reeside, p. 133, plate 72, figures 4, 5 (with synonymy)

1963 Submortoniceras vanuxemi (Morton) ; Young, p. 98, plate 54, figure 3; plate 56, figure 2; plate 57, figure 7; plate 58, figure 3; plate 67, figure 3; plate 69, figure 1, 2, 6; text-figures 12c, 12e, 26d– 26e (with synonymy)

1967 Submortoniceras vanuxemi (Morton) ; Wolleben, p. 1156, plate 17, figure 1, plate 148, figure 3

1992b Menabites (Delawarella) vanuxemi (Morton) ; Cobban and Kennedy, p. 76, plate 2, figures 2–4 (with additional synonymy) 1993a Menabites (Delawarella) vanuxemi ( Morton,1830) ; Kennedy and Cobban, p. 838, figures 11.3, 11.7, 11.10, 11.11, 11.12, 12.5, 12.6, 12.17-12.19, 13.1

1997a Menabites (Delawarella) vanuxemi ( Morton, 1830) ; Kennedy et al., p. 27, figure 18a

2013 Menabites (Delawarella) vanuxemi ( Morton, 1830) ; Ifrim et al., p. 889, figures 3.8, 3.9, 4.5, 4.6

Types. The holotype, by monotypy, is No. 19492 in the collection of the Academy of Natural Sciences in Philadelphia ( Morton, 1830, plate 3, figures 2–4; refigured by Reeside, 1962, plate 72, figures 4, 5). It is from the Chesapeake and Delaware Canal in Delaware, USA.

Material. Eight specimens, CPC-2379, –2390, – 2391, –2575, –2578, –2579, –2587, and –2591, and numerous uncollected specimens from bed TPY33 to TPY77.

Description. Moderately involute shell with compressed whorls; the WB/WH ratio is between 0.43 and 0.67 and descreases upsection; U/D is between 0.16 and 0.27. The umbilical wall bends narrowly into parallel, then convergent flanks; greatest whorl width is below mid-flank. The ventrolateral shoulders are narrowly rounded. Eight to nine umbilical bullae per half whorl give rise to pairs of straight, moderately prorsiradiate ribs. Secondaries are intercalated. Weak but pointed tubercles are present on the ventrolateral shoulder. Ribs terminate at small external clavi; there is a smooth zone between these and the siphonal ridge.

Dimensions. Table 7.

Remarks. Among the finely ornamented species of this subgenus, this is the least compressed form. Menabites (Delawarella) mariscalense is almost smooth at similar diameters, M. (D.) uddeni and the other compressed species differ in their type of ribbing at similar diameters.

Occurrence. Records are from the upper lower Campanian of the Atlantic Coast, northern and western Gulf Coastal Plain, and the Western Interior of North America ( Reeside, 1962; Young, 1963; Wolleben, 1967, 1977; Cobban and Kennedy, 1992 a, 1992b; Larson et al., 1997; Ifrim et al., 2013). The species was described to be restricted to the upper lower Campanian, but at Tepeyac it was identified near the base of the Campanian.

IFRIM & STINNESBECK: CAMPANIAN AMMONOID BIOZONATION

Figures

FIGURE 15. Menabites (Delawarella) n. sp. from the upper Tepeyac section. A–C: CPC– 2393, TPY73. D–F: CPC– 2560, TPY74. Scale: 50 mm.

FIGURE 16. Menabites (Delawarella) vanuxemi (Morton, 1830) from the middle Tepeyac section. A–D: CPC–2379, TPY33. E: CPC–2390, TPY50. F: CPC–2391, TPY50. Scale: 50 mm.