Texanites lonsdalei 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 : 6

Texanites lonsdalei Young, 1963

Figure 4A–G , Table 2

1963 Texanites lonsdalei n. sp.; Young, 1963, p. 90, plate 34, figure 1; plate 51, figures 3-7; plate 58, figures 5, 6; text-figures 22a, d

1967 Texanites lonsdalei Young, 1963 ; Wolleben, p. 1152, p1. 147, figures 4, 5; text-figures 8c,d

1997 Texanites (Texanites) lonsdalei Young, 1963 ; Kennedy and Cobban, p. 17, figures 9-12

Type. The holotype is TMM-UT 30474 by original designation by Young (1963: 90, plate 34, figure 1;

plate 51, figures 3-7; plate 58, figures 5, 6; text-figures 22a, d). It is from the Dessau Chalk of Kitch-

ens Ranch, Travis County, Texas .

Material. CPC –2375, –2377, –2584, IGM 12796,

and 12797, and uncollected specimens from beds

TPY 21 to TPY 53.

Description. Evolute shell with U/D of about 0.4.

28 to 33 sharp ribs rise on the umbilical wall and strengthen into pointed bullae that project into the umbilicus. These bullae give rise to sharp, straight, moderately prorsiradiate ribs, which are occasionally intercalated by secondary ribs. A row of strong, lateral tubercles is located dorsal of midflank and separated from the umbilical row of bullae. A third slightly weaker row of tubercles is present ventrolaterally; they are rounded to feebly clavate. A fourth row of larger tubercles, respectively coarse clavi, is seen on the venter, next to a siphonal keel from which they are separated by a smooth zone. The secondary ribs also show these outer rows of tubercles, resulting in 36 ventral clavi per whorl. The keel and lateral clavi disappear at largest diameters, and ribs in these large-sized specimens cross the venter in a moderately narrow arch.

Dimensions. Table 2.

Remarks. Klinger and Kennedy (1980) casted doubt on the validity of Texanites lonsdalei , but subsequently, Kennedy et al. (1997a) discussed the species in detail and presented characters for distinction from similar taxa. According to these latter authors, T. lonsdalei is distinguished by sharper, straighter ribs than coeval species of Plesiotexanites or Menabites (Delawarella) .

Occurrence. Uppermost Santonian and lowermost Campanian Menabites (Delawarella) tequesquitense Zone of Texas. At Tepeyac, the species occurs in the uppermost Plesiotexanites shiloensis zone of the Santonian and in the top of the lower Campanian M. (D.) delawarensis Zone.

Figures

FIGURE 4. Texanites lonsdalei Young, 1963 from the Tepeyac section. A: in bed TPY11; B: IGM 12796, bed TPY 21 C–D: IGM 12797, bed TPY 14; E–G: CPC–2377, bed TPY33. Scale: 50 mm.