Bevahites costatus Collignon, 1948

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 : 8

Bevahites costatus Collignon, 1948 coahuilaensis Young, 1963

Figure 5D–F , Table 4

1963 Bevahites costatus Collignon, 1948 , subsp. coahuilaensis , n. subsp.; Young, p. 96, plate 47, figures 1-4, plate 71, figure 5; text-figures 34b

1967 Bevahites costatus coahuilaensis Young, 1963 ; Wolleben, p. 1156, plate 150, figure 8

Type. The holotype is BEG-20288 through original designation by Young (1963, p. 96, plate 47, figures 1–4, plate 71, figure 5, text-figure 34b), from Arroyo Tecolote near Jiménez , Coahuila .

Material. Three specimens, CPC –2372, –2546, and –2548 from beds TPY27 to TPY44 .

Description. Moderately involute, with subrectangular whorl section and a maximum WB at mid-flank. Blunt ribs arise from umbilical tubercles and reach to mid-flank where they bifurcate at a rounded tubercle. From here, secondaries reach to the venter and wear two rows of shallow, ventrolateral tubercles, as well as a third ventrolateral row of clavi. The venter is keeled, with a smooth area between the ventrolateral clavi and the keel.

Dimensions. Table 4.

Remarks. Young’s (1963) type specimens are from the Arroyo Tecolote, located at about 5 km north of Tepeyac. Wolleben (1967) noted that this subspecies of Bevahites costatus is rare in the area, but that it occurs in several stratigraphic levels. It differs from Bevahites behavensis in a stout whorl section and ribs bifurcating at D of about 130 mm.

Occurrence. Bevahites costatus coahuilaensis occurs at about the Santonian-Campanian boundary in the Ojinaga Formation of eastern Chihuahua and in the Jiménez area of Coahuila, Mexico, as well as in western Texas. At Tepeyac, it was identified in beds 27, 36, and 44-46, i.e., in the interval across the Santonian-Campanian boundary. The species was also reported from the lower Campanian of Madagascar ( Collignon, 1969).

Figures

FIGURE 5. Bevahites from the Tepeyac section. A–B, G–J: Bevahites bevahensis, A–B: CPC–2374; G–J: CPC–2547, both bed TPY26; C–F: Bevahites costatus coahuilaensis, C–D: CPC–2372, bed TPY27; E–F: CPC–2548, beds TPY40-46. Scale: 50 mm.