Discoscaphites gulosus ( Morton, 1834 )

Landman, Neil H., 2004, Cephalopods From The Cretaceous / Tertiary Boundary Interval On The Atlantic Coastal Plain, With A Description Of The Highest Ammonite Zones In North America. Part 2. Northeastern Monmouth County, New Jersey, Bulletin of the American Museum of Natural History 2004 (287), pp. 1-107 : 92-94

Discoscaphites gulosus ( Morton, 1834) Figures 39Y–Z, a, b , 41E

Ammonites conradi var. petechialis Morton, 1834: 39 , 40, pl. 16, fig. 1.

Ammonites conradi var. gulosus Morton, 1834: 39 , pl. 16, fig. 2.

Ammonites conradi var. navicularis Morton, 1834: 40 , pl. 19, fig. 4.

Discoscaphites gulosus ( Morton, 1834) . Landman and Waage, 1993: 212, figs. 156, 157, 159, 160, 167–180 (with full synonymy).

Discoscaphites gulosus ( Morton, 1834) . Cobban and Kennedy, 1995: 29, figs. 10.4, 10.5, 19.20– 19.24, 20.8–20.12, 20.14–20.17, 21.18–21.21.

Discoscaphites gulosus ( Morton, 1834) . Kennedy et al., 1997: 21, figs. 20k–o, 21d, e.

TYPE: The holotype is ANSP 51552 from the Prairie Bluff Chalk at Prairie Bluff, Alabama.

MATERIAL: AMNH 47106, an internal mold of part of a phragmocone from the Main Fossiliferous Layer at the New Egypt / Hornerstown formational contact at AMNH loc. 3345 at Parkers Creek, near Eatontown, Monmouth County, New Jersey.

DESCRIPTION: AMNH 47106 is one­half of a phragmocone with part of the venter and flanks missing on the adapical end (fig. 39Y– Z, a, b). The specimen is 30.4 mm in diameter. The whorl section at the adoral end is compressed ovoid with maximum width at one­quarter whorl height. The ratio of whorl width to height is 0.72. The umbilical wall is convex and the umbilical shoulder is fairly sharply rounded. The inner flanks are well rounded and the outer flanks are broadly rounded and converge toward the venter. The ventrolateral shoulder is fairly abruptly rounded and the venter is nearly flat.

The ornament consists of five rows of tubercles that occur on swollen prorsiradiate ribs. Intercalation and branching occur at one­third whorl height. The umbilical tubercles occur just outside the umbilical shoulder. The two most adoral tubercles are 5 mm apart. The two rows of inner and outer flank tubercles are not as prominent as the umbilical tubercles. They are evenly spaced and occur on every rib. These rows are more closely spaced to each other than the inner flank row is to the umbilical row (2.5 mm versus 4 mm as measured on a single rib on the right side 45° from the adoral end). The inner ventrolateral tubercles are as prominent as the umbilical tubercles and more prominent than the flank tubercles and are spaced at distances of 2.5 mm on the adapical part, becoming more widely spaced (5 mm) on the adoral part, as measured on the left side. The distance between the inner ventrolateral row and the outer flank row (3 mm as measured on the same rib as previously described) is slightly larger than that between the two flank rows. The outer ventrolateral tubercles are close to the inner ventrolateral tubercles, approximately 2.5 mm apart on the same rib as previously described. The outer ventrolateral tubercles are slightly smaller than the inner ventrolateral ones. The two most adoral outer ventrolateral tubercles are 3.5 mm apart. The outer ventrolateral tubercles are slightly offset from one side of the venter to the other. The suture shows part of a narrow first lateral lobe (L) and U 2 (fig. 41E). It is simplified but this is due perhaps to poor preservation.

DISCUSSION: This specimen, although fragmentary, matches in its shape and ornament other specimens of Discoscaphites gulosus illustrated by Jeletzky and Waage (1978) and Landman and Waage (1993). It is notable that there is no midventral row of tubercles on this specimen, which is characteristic of D. gulosus from the Prairie Bluff Chalk (e.g., Jeletzky and Waage, 1978, pl. 3, figs. 13, 14), although, in fact, this feature may be retricted to the body chamber.

OCCURRENCE: Top of the New Egypt Formation and base of the Hornerstown Formation, AMNH loc. 3345, Parkers Creek, near Eatontown, Monmouth County, New Jersey. A single specimen has also been re­ ported from the Navesink Formation (New Egypt Formation according to our usage) at the Inversand Pit, Gloucester County, New Jersey (Kennedy et al., 2000). On the basis of its preservation, it was probably derived from the lower part of the New Egypt Formation (W.B. Gallagher, personal commun., 2003). Discoscaphites gulosus occurs in several localities on the Gulf and Atlantic Coastal Plains including the Severn Formation, Prince Georges County, Maryland ( Kennedy et al., 1997); the Peedee Formation, Brunswick County, North Carolina ( Landman et al., 2004); and the Prairie Bluff Chalk, Alabama ( Cobban and Kennedy, 1995). In the Western Interior, D. gulosus occurs in both the Hoploscaphites nicolletii and Jeletzkytes nebrascensis Zones of the Fox Hills Formation, South Dakota ( Landman and Waage, 1993). However, it is more abundant in the lower of these two zones.

Figures

Fig. 39. A–P. Discoscaphites iris (Conrad, 1858), uppermost New Egypt Formation and basal Hornerstown Formation, AMNH loc. 3345, northwest of Eatontown, Monmouth County, New Jersey. A– D. AMNH 47105, microconch. A, Right lateral; B, apertural; C, ventral; D, left lateral. E–H. AMNH 51056, microconch. E, Right lateral; F, apertural; G, ventral; H, left lateral. I, J. AMNH 37359, dimorph indeterminate. I, Ventral; J, left lateral. K–M. AMNH 47368, dimorph indeterminate. K, Right lateral; L, ventral; M, left lateral. N–P. AMNH 47105, dimorph indeterminate. N, Right lateral; O, apertural; P, ventral. Q–T. Discoscaphites minardi Landman et al., 2004, AMNH 47369, microconch, same locality as A–P. Q, Right lateral; R, apertural; S, ventral; T, left lateral. U–X, c–f. Discoscaphites spp., same locality as A–P. U–X. AMNH 47371. U, Right lateral; V, apertural; W, ventral; X, left lateral. c– f. AMNH 47374. c, Right lateral; d, apertural; e, ventral; f, left lateral. Y–Z, a, b. Discoscaphites gulosus (Morton, 1834), AMNH 47106, same locality as A–P. Y, Right lateral; Z, apertural; a, ventral; b, left lateral. All figures are X1.

Fig. 41. A–D. Discoscaphites iris (Conrad, 1858), uppermost New Egypt Formation and basal Hornerstown Formation, AMNH loc. 3345, northwest of Eatontown, Monmouth County, New Jersey. A, B. AMNH 47365, a fragment of a macroconch, part of the last suture at a whorl height of approximately 18.2 mm and internal lobe of another suture on the inner whorls. C. AMNH 51060, a macroconch, part of the last suture at a whorl height of 19.7 mm. D. AMNH 51059, a macroconch, part of a composite of two sutures at a whorl height of 7.9 mm. E. Discoscaphites gulosus (Morton, 1834), AMNH 47106, same locality as A–D, part of a composite of two sutures at whorl heights of 17.3 mm and 17.6 mm. F. Discoscaphites sp., AMNH 47107, a fragment, same locality as A–D, part of a suture at a whorl height of approximately 10.3 mm.