Menabites (Delawarella) tequesquitense ( 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 : 10-13

Menabites (Delawarella) tequesquitense ( Young, 1963)

Figure 6A–B , Figure 7A–C , Figure 8 , Figure 9 ,

Figure 10A–C , Table 5

1963 Submortoniceras tequesquitense , n. sp.; Young, p. 97, plate 28, figure 1; plate 42, figures 1, 2; plate 44, figures 4, 5; plate 51, figures 1, 2; plate 52, figures 1-4; plate 57, figure 4; plate 70, figure 1; text-figures 12b, 28b

1991 Submortoniceras tequesquitense Young, 1963 ; Cobban and Kennedy, p. B3, plate 1, figures 1, 2

1997 Submortoniceras tequesquitense Young, 1963 ; Kennedy et al., p.23, figures 14, 15

Type. The holotype is TMM 34742 by original designation of Young (1963, p. 97, plate 42, figures 1-

2; plate 52, figures 1-2, 4, text-figure 28b). It is from

PALAEO- ELECTRONICA.ORG the upper part of the Dessau Chalk, "downstream from the concrete spillway of the new (1932) Del Rio-Eagle Pass highway crossing on Tequesquite Creek , Kinney County, Texas " ( Young, 1963, p. 97) .

Material. Eight specimens, CPC-2381,–2383, – 2387, –2422, –2550,–2551, –2564,–2567, in addition to uncollected specimens, from beds TPY 25 to TPY 50.

Description. Evolute shell with a moderately high expansion rate and a relatively wide U (U/D of 0.29-0.41). The umbilical wall seems to be undercut. 24 sharp umbilical bullae are present per whorl and project into the umbilicus. Sharp single or paired ribs arise from these bullae. They are broad and low, straight to slightly prorsiradiate, and efface markedly on the flanks. A row of sharp lateral tubercles is situated near mid-flank and separated by a row of weaker, ventrolateral tubercles. Each of these tubercles is connected by a low and broad rib to stronger elongate clavi; the latter are separated from the strong siphonal keel by a

IFRIM & STINNESBECK: CAMPANIAN AMMONOID BIOZONATION smooth sulcate-shaped zone. The external clavi thus flank the bisulcate-carinate venter. In adult specimens the clavi and keel are replaced by weaker, broad rounded tubercles, and the ribs cross a moderately wide rounded venter.

Dimensions. Table 5.

Remarks. The well-developed ribs on the inner whorls readily distinguish this species from all other Gulf Coast representatives of the genus described by Young (1963) as Submortoniceras , including S. sancarlosense , S. mariscalense , S. uddeni , and S. vandaliaense .

Klinger and Kennedy (1980) suggested Menabites (Delawarella) tequesquitense to be closely allied if not conspecific with Submortoniceras woodsi , because dimensions of the two species overlap. Apart from a slightly narrower whorl section, denser and more forwardly curved costation, there seems to be little difference between M. (D.) tequesquitense and S. woodsi . However, this difference is here considered to be sufficient for specific differentiation. Young (1963, p. 98) suggested that M. (D.) tequesquitense could be derived from Plesiotexanites shiloensis . However, affinities of Menabites (Delawarella) tequesquitense with the

PALAEO- ELECTRONICA.ORG

South African T. soutoni seem closer than with P. shiloensis . In this view M. (D.) tequesquitense would also be derived from T. soutoni and then give rise to the North American succession of species. It nevertheless appears that both lineages are closely connected and that a repeated interchange of these species occurred between the South African – Madagascar Southern Ocean and the Ancient Gulf of Mexico.

Occurrence. Menabites (Delawarella) tequesquitense is the index fossil of the identical uppermost Santonian-lowermost Campanian ammonite zone, introduced for the Gulf Coast region by Young (1963). The zone has been recorded in Mississippi, Alabama, and Texas ( Young, 1963; Kennedy et al., 1997a). A single specimen documented by Kennedy et al. (1997a) from New Mexico, has been collected from the Scaphites (Scaphites) hippocrepis I zone.

Figures

FIGURE 6. Menabites (Delawarella) tequesquitense (Young, 1963) from bed TPY33 of the Tepeyac section. A–B: CPC–2381. Scale: 50 mm.

FIGURE 7. Menabites (Delawarella) tequesquitense (Young, 1963) from the middle Tepeyac section. A: CPC–2381, TPY33, B–C: CPC-2383, TPY36. Scale: 50 mm.

FIGURE 8. Menabites (Delawarella) tequesquitense (Young, 1963) from bed TPY36 of the Tepeyac section. CPC- 2383, left lateral view. Scale: 50 mm.

FIGURE 9. Menabites (Delawarella) tequesquitense (Young, 1963) from bed TPY36 of the Tepeyac section. CPC- 2383, right lateral view. Scale: 50 mm.

FIGURE 10. Menabites (Delawarella) tequesquitense (Young, 1963) from the Tepeyac section. CPC-2422, bed of ori- gin unknown. Scale: 50 mm.