Menabites (Delawarella) delawarensis ( Morton, 1830 )

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 : 13-18

Menabites (Delawarella) delawarensis ( Morton, 1830)

Figure 11 , Figure 12 , Figure 13 , Table 6

1830 Ammonites delawarensis Morton , p. 244, plate 2, figure 4.

IFRIM & STINNESBECK: CAMPANIAN AMMONOID BIOZONATION

1948 Menabites (Delawarella) delawarensis Morton ; Collignon, p. 29 (86) (with synonymy)

1986 Menabites (Delawarella) delawarensis ( Morton, 1830) ; Kennedy, p. 81, plate 3, figures 3, 4 (with synonymy)

1992a Menabites (Delawarella) delawarensis ( Morton, 1830) ; Cobban and Kennedy, p. 73, plate 6, figure 9

1992b Menabites (Delawarella) delawarensis ( Morton, 1830) ; Cobban and Kennedy, p. 445, figures 4.6-4.9, 5.1, 5.2, 5.6, 5.7, 5.11-5.13

1993a Menabites (Delawarella) delawarensis ( Morton, 1830) ; Kennedy and Cobban, p. 836, figures 5.10, 5.11, 9.5-9.13, 10.3, 11.1, 11.2, 11.4- 11.6, 11.8, 11.9, 11.11

1996 Menabites (Delawarella) delawarensis (Morton) ; Wiese, plate 1, figure 1a-b

1997 Menabites (Delawarella) delawarensis ( Morton, 1830) ; Kennedy et al., p. 23, figures 16, 17, 18d-e

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Types. The types are lost (see Reeside, 1962 p. 132, and Kennedy, 1986 p. 81).

Material. Fourteen specimens, CPC-2382,–2386, –2388, –2389, –2550, –2551, –2552, –2564, – 2568,–2569, –2573,–2584, –2585, and –2586 from beds TPY33 to above TPY 60, in addition to uncollected specimens.

Description. Evolute coiling, with U/D between 0.32 and 0.51 and a depressed whorl section. Greatest WB occurs below mid-flank intercostally and at the lateral tubercles costally. The umbilicus is deep, with a flat, vertical wall and narrowly rounded umbilical shoulder. The inner flanks are flattened and subparallel, the outer flanks broadly rounded and convex, and the venter is broadly arched. Sharp umbilical bullae on the umbilical shoulder give rise to 27 to 36 broad, slightly rursiradiate single or paired ribs, their number increasing with diameter. These bullae give rise to strong, straight prorsiradiate ribs. Each submarginal tubercle splits into a marginal clavus and conical submarginal tubercle, while a lateral tubercle is situated near mid-flank. A broad, smooth sulcate zone separates the external clavi from the siphonal keel, which is only preserved in smaller specimens.

Dimensions. Table 6.

Discussion. Menabites (Delawarella) delawarensis is similar to M. (D.) tequesquitense from which it differs by coarser ribbing. M. (D.) danei Young, 1963 is characterized by even coarser ribbing, stronger umbilical, submarginal, and external tubercles only. M. (D.) vanuxemi ( Morton, 1834) , also described below, is more compressed and involute, and tubercles are subordinate to ribs.

Our specimens present a slightly lower WB/ WH ratio than specimens published by other authors. This may partially be due to diagenetic compression but majorly reflects wide intraspecific variation, as known for Schloenbachia varians ( Wilmsen and Mosavinia, 2011) and Pseudoschloenbachia mexicana (see Ifrim et al., 2013).

Occurrence. Middle lower Campanian Menabites (Delawarella) delawarensis zone in Delaware and New Jersey, Texas, and Oklahoma ( Young, 1963; Cobban and Kennedy, 1992b; Kennedy and Cobban, 1993a; Kennedy et al., 1997a; Kennedy et al., 1997b). Isolated specimens are also reported from the lower Campanian of Aquitaine, France, from Spain, the lower Campanian of Zululand ( South Africa) and, possibly, Madagascar ( Besaire, 1930; Klinger and Kennedy, 1980; Kennedy, 1986), but not in western Coahuila ( Ifrim et al., 2013).

Figures

FIGURE 11. Menabites (Delawarella) delawarensis (Morton, 1830) from bed TPY35 of the Tepeyac section. A–D: CPC-2382. Scale: 50 mm.

FIGURE 12. Menabites (Delawarella) delawarensis (Morton, 1830) from the middle Tepeyac section. A–C: CPC– 2386, TPY40. D–G: CPC–2388, TPY50. Scale: 50 mm.

FIGURE 13. Menabites (Delawarella) delawarensis (Morton, 1830) from bed TPY50. A–D: CPC–2388. Scale: 50 mm.