Menabites (Delawarella) danei ( 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 : 18

Menabites (Delawarella) danei ( Young, 1963)

Figure 14A–B

1929 Mortoniceras delawarensis (Morton) , Dane, 1929, pI. 10, figures 1, 2

1963 Delawarella danei , n. sp.; Young, 1963, p. 114, plate 57, figure 6, plate 62, figures 1, 2; p1. 64, figures 1, 5; p1. 65, figures 1, 2; plate 66, figures 3, 4; text-figures 24e, 33b

1992a Menabites (Delawarella) danei ( Young, 1963) ; Cobban and Kennedy, p. 74, plate 2, figures 5-8; plate 3, figures 1-3; plate 4, figures 1, 12

1992b Menabites (Delawarella) danei ( Young, 1963) ; Cobban and Kennedy, p. 448, figures 3.2-3.4, 5.5, 5.10

1997 Menabites (Delawarella) danei ( Young, 1963) ; Kenned y et al., p. 29, figures 19, 20

Type. The holotype is UT –30646 by original designation by Young (1963, p. 114, plate 57, figure 6;

plate 62, figures 1, 2; plate 65, figure 1; plate 66, figure 4; text-figure 33b). It is from “a formation equivalent in age to the Gober chalk,” in McCurtain County, Oklahoma , 1 mile west of the Oklahoma- Arkansas state boundary on Route 3 from Foreman , Arkansas , to Tom, Oklahoma .

Material. Three specimens, CPC –2409 and –2421 from beds TPY 75 and TPY 77, CPC –2590 from bed TPY83, in addition to an uncollected specimen from bed 50 .

Description. Evolute coiling, with an U/D ratio of 0.43. The WB/WH ratio is 0.67, with greatest breadth at about mid-flank. Seventeen strong umbilical bullae per whorl give rise to coarse, blunt, prorsiradiate ribs, which efface at mid-flank and again strengthen on the outer flank, where they develop coarse, submarginal tubercles. Broad, coarse ribs link to a row of clavi, with about the same number of additional clavi intercalated. A deep ventral groove separates the row of clavi from the siphonal keel. Faint tubercles at mid-rib are present on the last half whorl, and a second row of ventrolateral tubercles is seen on the last three ribs.

Dimensions. CPC-2421, D: 117, WB: 29 (0.25), WH: 43 (0.37), WB/WH: 0.67, U: 50 (0.43). CPC-2590, WB: 16, WH: 24, WB/WH: 0.67.

Remarks. Specimens of this species show a prolonged Australiella stage and a transition to a typically penta-tuberculate Delawarella ornamentation at large diameters. Menabites (Delawarella) danei is distinguished from all other American Delawarella by the unique coarseness of tuberculation and ribbing. The species is closely related to M. (D.) sabinalensis ( Young, 1963) , which has no tubercles and intercalated secondaries, instead of the bifurcating ribs and strong tuberculation of M. (D.) danei .

Traces of septate spines as described by Kennedy et al. (1997a) cannot be identified in the Tepeyac specimens, although the tubercles seem to be extended.

Occurrence. Upper lower Campanian of Oklahoma, Texas, Colorado (zone of Baculites obtusus ), and now north-eastern Mexico.

Figures

FIGURE 14. Menabites (Delawarella) danei (Young, 1963) from bed TPY77. A–B: CPC– 2421. Scale: 50 mm.