Eutrephoceras, Hyatt, 1894

Witts, James D., Landman, Neil H., Garb, Matthew P., Irizarry, Kayla M., Larina, Ekaterina, Thibault, Nicolas, Razmjooei, Mohammad J., Yancey, Thomas E. & Myers, Corinne E., 2021, Cephalopods from the Cretaceous-Paleogene (K-Pg) boundary interval on the Brazos River, Texas, and extinction of the ammonites, American Museum Novitates 2021 (3964), pp. 1-52 : 19-20

Eutrephoceras sp.

Figure 7

MATERIAL: One small phragmocone UNM 15495 from the Middle Sandstone Bed ( Yancey, 1996; Hart et al., 2012), Kincaid Formation (Littig Member), from an outcrop just west of a culvert upstream of the waterfall section at AMNH loc. 3620.

DESCRIPTION: The specimen is a wholly septate steinkern 31.6 mm in diameter with a whorl height of 26.5 mm at the adoral end. The septa are closely spaced with 13 septa in the last whorl. The specimen bears traces of another whorl.

REMARKS: The holotype of Eutrephoceras dekayi ANSP 19484 is the original of Morton (1834: pl. 8, fig. 4), from the “marls of Monmouth and Burlington counties, New Jersey,” by subsequent designation by Whitfield (1892: 243, pl. 37, figs. 2 , 3) and is illustrated by Landman et al. (2004a: 41, figs. 17–21). This species was more fully documented by Landman et al. (2017) who relied on conspecific material from the U.S. Western Interior, as Hyatt (1894) had done previously. They concluded that the species is early Maastrichtian, suggesting that younger forms (e.g., late Maastrichtian) should be carefully scrutinized to determine whether they conform to the description of this species. The present specimen is assigned to Eutrephoceras based on its size, shape, and suture pattern. However, because it is only a fragment of a phragmocone, it cannot be identified to species level.

OCCURRENCE: This genus is worldwide and is reported from the Campanian to the Eocene. In Texas, it has been reported from the Upper Cretaceous (Campanian-Maastrichtian) Navarro Group of Hunt, Navarro, and Kaufman counties ( Emerson et al., 1994), and the Eocene Cook Mountain Formation of Leon County ( Miller, 1947). To our knowledge, UNM 15495 is the only reported specimen of Eutrephoceras from the Brazos River localities.

Figures

FIGURE 2.

FIGURE 7. Eutrephoceras sp., UNM 15495, Middle Sandstone Bed, AMNH loc. 3620, basal part of the Paleogene (Danian), Kincaid Formation, Falls County, Texas. A, left lateral; B, ventral; C, apertural.