Discoscaphites sphaeroidalis Kennedy and Cobban 2000
Creators: name: Witts, James D.
name: Landman, Neil H.
name: Garb, Matthew P.
name: Irizarry, Kayla M.
name: Larina, Ekaterina
name: Thibault, Nicolas
name: Razmjooei, Mohammad J.
name: Yancey, Thomas E.
name: Myers, Corinne E.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Cephalopoda
Ammonitida
Scaphitidae
Discoscaphites
Discoscaphites sphaeroidalis

description: Discoscaphites sphaeroidalis Kennedy and Cobban, 2000
Figure 12O, P
Discoscaphites sp. Stephenson, 1955: 135, pl. 23, figs. 20–22.
Discoscaphites sphaeroidalis Kennedy and Cobban, 2000: 185, pl. 1, figs. 1–11, text-fig. 6
Discoscaphites sphaeroidalis Kennedy and Cobban, 2000. Kennedy et al., 2001: 169, fig. 4b, c. Discoscaphites iris (Conrad, 1858). Landman et al., 2004b: 71, fig. 34A–D.
Discoscaphites sphaeroidalis Kennedy and Cobban, 2000. Landman et al., 2007a: 92, figs. 47D, 48.
TYPE: The holotype is USNM 465615, a macroconch missing part of the hook. It is from the Owl Creek Formation at its type locality, 4 km northeast of Ripley, Tippah County, Mississippi.
MATERIAL: The material from Brazos consists of six specimens, three of which are identifiable as adult microconchs (AMNH 108185, 111957, and 116345) and three of which are fragments of adult microconchs (AMNH 108174, 108184, and 133094) from the top of the Corsicana Formation in Darting Minnow and Cottonmouth creeks (AMNH locs. 3620 and 3621), Falls County, Texas.
MICROCONCH DESCRIPTION: The three nearly complete specimens range in size from 31.6 to 36.1 mm. The phragmocone extends slightly below the line of maximum length and the body chamber occupies approximately one-half whorl. As shown in AMNH 116345 (fig. 12P), the aperture is constricted with a weak ventral projection.
The ornamentation on the phragmocone is well preserved in AMNH 11957 (fig. 12O). The ribs are narrow, long, and uniformly spaced. They bear four rows of tubercles, of which the inner ventrolateral row is the most prominent. The ribs on the body chamber are weaker, but the tubercles are stronger than those on the phragmocone. The tubercles are widely spaced on the shaft and more closely spaced on the hook. Both rows of ventrolateral tubercles extend to the aperture.
REMARKS: Because these specimens are crushed, no information is available about the shape of the whorl section, which is important for identifying this species and distinguishing it from Discoscaphites iris. However, the ornamentation on the phragmocone is well preserved and consists of narrow, long ribs, one of the defining features of this species. It is curious that our collection consists only of microconchs whereas other collections of this species contain both dimorphs (Kennedy and Cobban, 2000; Kennedy et al., 2001; Landman et al., 2007a). If macroconchs were present, they would be easily recognizable. Their absence is probably due to the small size of the collection.
OCCURRENCE: This species is known from the upper part of the Corsicana Formation along the Brazos River and its tributaries in Falls County, Texas. Kennedy et al. (2001) reported it as occurring throughout the top ~ 8 m of the Corsicana Formation. Elsewhere on the Gulf Coastal Plain, it occurs in the Owl Creek Formation in Mississippi and Missouri (Stephenson, 1955; Kennedy and Cobban, 2000). On the Atlantic Coastal Plain, it occurs in the upper part of the Tinton Formation and as reworked material at the base of the Hornerstown Formation, central Monmouth County, and in the upper part of the New Egypt Formation and as reworked material at the base of the Hornerstown Formation in northeastern Monmouth County (Landman et al., 2007a).
description: Published as part of 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, pp. 1-52 in American Museum Novitates 2021 (3964) on pages 34-35, DOI: 10.1206/3964.1, http://zenodo.org/record/4566589