Menabites (Bererella) walnutensis ( 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 : 25-28

Menabites (Bererella) walnutensis ( Young, 1963)

Figure 19A–G , Figure 20A–F , Figure 21A–F ,

Figure 22 , Figure 23A–C , Table10

1963 Menabites s.l. walnutensis n. sp.; Young, p.109, plate 58, figures 1, 4; text-figures 20e–f, 26k

1963 Submortoniceras chicoense (Trask, 1856) , Young, p. 106, plate 57, figures 13; text-figures 11e–f, 12d

1993? Menabites (Bererella) sp., Kennedy and Cobban, p. 841, figures 14.36, 14.38, 14.39

1997b Menabites (Bererella) walnutensis ( Young, 1963) ; Kennedy et al., p. 4, figure 3a–k, figures 4a–f, 5a-k, 6a-c

Type. The holotype is UT-18, by original designation by Young (1963, p. 109, plate 58, figures 1, 4; text-figures 20ef, 26k). It is from Bureau of Economic Geology locality 226-T- 4 in Travis County, Texas .

Material. Twenty-eight specimens, CPC –2392, – 2394, –2395, –2398, –2403, –2406 to –2414, – 2417 to –2420, –2549, –2551, –2570, –2572, – 2573, –2577, –2580, –2581, –2583, and –2589 from beds TPY46 upwards, but mostly in beds TPY73 to TPY77 .

Description. Medium-sized, moderately involute shells (U/D between 0.21 and 0.46, increasing with D). The fifth, submarginal row of tubercles is always weak.

Dimensions. Table 10.

Remarks. Menabites (Bererella) walnutensis ( Young, 1963) is based on a stout specimen (WB/ WH ca. 0.9) with coarse ribbing and strong tuberculation. Nevertheless, Kennedy et al. (1997b) demonstrated a wide intraspecific variation and morphological dimorphism between stout and gracile forms of this species. Our specimens thus majorly correspond to the stout specimens and show a similarly wide range of morphologies ( Figure 23 ). This suggests a wide intraspecific variation, as reported for Pseudoschloenbachia (P.) mexicana (see Ifrim et al., 2013). With this in mind

IFRIM & STINNESBECK: CAMPANIAN AMMONOID BIOZONATION we assign the Tepeyac specimens to M. (B.) walnutensis .

Occurrence. Merchantville Formation. New Jersey; central and western Texas ( Young, 1963; Kennedy et al., 1997b), and now northeastern Coahuila.

Figures

FIGURE 19. Menabites (Bererella) walnutensis (Young, 1963) from beds TPY54 to TPY60. A–B: CPC–2392, TPY54- 56. C–D: CPC–2581, TPY60. E–G: CPC– 2549, TPY69top. Scale: 50 mm.

FIGURE 20. Menabites (Bererella) walnutensis (Young, 1963) from bed TPY74. A–B: CPC–2404. C–F: CPC– 2406. Scale: 50 mm.

FIGURE 21. Menabites (Bererella) walnutensis (Young, 1963) from bed TPY77. A–C: CPC–2394 from bed TPY73; D– F: CPC–2419 from bed TPY77. CPC– 2582 from bed TPY77. Scale: 50 mm.

FIGURE 22. Menabites (Bererella) walnutensis (Young, 1963) from bed TPY77. A–C: CPC–2580. Scale: 50 mm.

FIGURE 23. Morphometry of Menabites (Bererella) walnutensis (Young, 1963). Full Diamonds: WB/WH for TPY, empty diamonds: WB/WH from Kennedy et al. (1997b), full circles: U/D for TPY, empty circles: U/D from Kennedy et al. (1997b).