Eutrephoceras Hyatt, 1894

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 : 41-50

Genus Eutrephoceras Hyatt, 1894

TYPE SPECIES: Nautilus Dekayi Morton, 1834, p. 291 , pl. 8, fig. 4, by original designation by Hyatt, 1894, p. 555.

where visible. All specimens were photographed in the conventional manner (with the aperture on top) except for the nautilids, scaphites, and sphenodiscids, which were oriented with the aperture on the bottom, approximating their position in life. Suture ter­ Eutrephoceras dekayi ( Morton, 1834) Figures 17–21

Nautilus Dekayi Morton, 1834: 291 , pl. 8, fig. 4.

Nautilus Dekayi Morton. Whitfield, 1892: 243 , pl. 37, figs. 1–6; pl. 38, figs. 1–4.

Eutrephoceras Dekayi. Hyatt, 1894: 556 , pl. 13, figs. 4–8; pl. 14, fig. 1.

Eutrephoceras dekayi (Morton) . Gardner, 1916: 372, pl. 13, fig. 9.

Eutrephoceras dekayi (Morton) . Miller and Garner, 1962: 102, figs. 1, 2; pl. 65, figs. 1–6; pl. 66, figs. 1, 2; pl. 67, figs. 1–9 (with complete synonymy).

TYPE: The holotype 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: 213, pl. 37, figs. 2, 3) and illustrated (uncoated) in figure 17E–G. It is labeled as being from Burlington or Monmouth County but Whitfield (1892: 244) identified it as being from Monmouth County. Miller and Garner (1962: fig. 1E) referred to it as being from ‘‘the Navesink marl of Monmouth or Burlington County, New Jersey.’’ It was refigured by Meek (1876: text­fig. 67), Whitfield (1892: pl. 37, figs. 2, 3; pl. 38, fig. 1), Miller (1947: pl. 6, figs. 4, 5), and Miller and Garner (1962: pl. 65, figs. 5, 6). It is a large fragment, one­half whorl long, of a body chamber 80.8 mm in diameter. The apertural margin is slightly flared, suggesting it is an adult. It is gray in color with some preserved shell. On the basis of its preservation, it probably does not come from the Merchantville, Marshalltown, or Tinton formations, nor from the basal Navesink Formation at Atlantic Highlands, nor from the MFL at the base of the Hornerstown Formation. It is probably derived from the upper part of the Navesink Formation in Monmouth County.

MATERIAL: Twenty­eight specimens: MAPS A 2012h1 and A2012h2 from AMNH loc. 3346 from the top of the New Egypt Formation 1.5–2 m below the base of the Hornerstown Formation at Parkers Creek, near Eatontown, Monmouth County, New Jersey; MAPS A 2012h3–6 and AMNH 47124–27, 47440–43, and 47463–75 from the top of the New Egypt Formation and the base of the Hornerstown Formation at AMNH loc. 3345 at Parkers Creek, near Eatontown, Monmouth County, New Jersey; and MAPS A 2012f7 from the Tinton Formation at Tinton Falls, Monmouth County, New Jersey.

DESCRIPTION: All of the specimens are internal molds without any trace of original shell. Most of them are phragmocones. The measurements are listed in table 4 and indi­ cate a relatively globose shell with a ratio of whorl width to height of 1.39–1.57. The siphuncle is midwhorl to slightly dorsal of midwhorl. The suture is weakly sinuous with low ventral and lateral lobes (fig. 21).

MAPS A 2012h2 is one­half whorl of a large body chamber and the last chamber of the phragmocone (fig. 18D–F). The maximum diameter is 101.1 mm. The whorl section at the base of the body chamber is depressed reniform. The ratio of whorl width to height is 1.50. The impressed zone is 0.42 times the whorl height. The siphuncle is relatively central.

MAPS A 2012h6 is one­third whorl of a phragmocone 30.0 mm in length consisting of four chambers (fig. 18A–C). The whorl section at the adoral end is depressed reniform with maximum width at one­quarter whorl height. The ratio of whorl width to height is 1.41. The umbilical wall is slightly convex and the umbilical shoulder is fairly abruptly rounded. The flanks and venter are well rounded. The sutures are evenly spaced at distances of approximately 10 mm on the midventer. There are loose fragments of the siphuncle showing the swollen portions between septa and the constricted areas at septal necks.

MAPS A 2012h4 is a small, subglobular phragmocone 32.6 mm in diameter (fig. 19H–K). There are 16 chambers. The three most adoral chambers are missing parts of their flanks. The whorl section at the third to last suture is depressed reniform with maximum width at one­third whorl height. The outer flanks and venter are well rounded. The ratio of whorl width to height is 1.46. The umbilicus is tiny, 1.7 mm in diameter. The ratio of umbilical to shell diameter at the third to last suture is 0.06. The sutures are spaced at equal angular increments and are slightly sinuous with weak lateral lobes (fig. 21A). The distance between sutures on the midventer increases gradually from 3.5 mm on the adapical end to 8 mm on the adoral end of the specimen.

New Jersey. A, Right lateral ; B, apertural; C, ventral; D, left lateral. E–G. ANSP 19484 , holotype, ‘‘marls of Monmouth and Burlington counties, New Jersey’ ’ ( Morton, 1834). E, Apertural ; F, ventral; G, left lateral. All figures are X1.

AMNH 47440 is one­third whorl of a phragmocone 39.0 mm in diameter (fig. 17A–D). It is irregularly broken on the adoral end and consists of parts of nine chambers. Interestingly, five segments of the siphuncle are preserved on the middorsum although this was clearly not their original position in life.

AMNH 47441 is a fragment of the adoral end of a phragmocone and adapical part of the body chamber of a small juvenile 24.3 mm in diameter (fig. 19E–G). It consists of three phragmocone chambers and approximately 0.2 whorls body chamber. The whorl section at the adapical end is depressed reniform but the ratio of whorl width to height cannot be measured because of adhering matrix. The body chamber exhibits the midventral line characteristic of nautilids.

AMNH 47443 is a small phragmocone 20.1 mm in diameter consisting of 13 chambers (fig. 19A–D). The umbilicus is small with a diameter of 0.95 mm at a shell diameter of 17.3 mm (ratio of umbilical diameter to shell diameter = 0.05). The ratio of whorl width to height near the adoral end is 1.39. The sutures are slightly sinuous with weak ventral and lateral lobes and are spaced at equal angular increments.

MAPS A 2012h5 (not illustrated) consists of four septate fragments all belonging to the same individual. The composite diameter is 59.5 mm and represents approximately onehalf whorl consisting of seven chambers. The whorl width at the adapical and adoral ends is approximately 37.3 and 59.8 mm, respectively, implying an increase in whorl width of 1.6 times.

AMNH 47475 (not illustrated) is one­half whorl of a phragmocone 28.3 mm in length. It consists of two pieces representing a total of six chambers. The suture is slightly sinuous with weak lateral and ventral lobes. The venter bears a distinct midline. The siphuncle is dorsal of center on the fifth to last septum.

MAPS A 2012f7 from the Tinton Formation is a globular specimen 84.6 mm in diameter (fig. 19L–N). The last one­half whorl is body chamber. The interior of the phragmocone is filled with fecal pellets. The surface of the phragmocone shows longitudinal ornamentation. The body chamber exhibits a flattened venter.

DISCUSSION: Whitfield (1892) figured five specimens from New Jersey in addition to the type: (1) a small phragmocone from Marlboro, New Jersey (pl. 37, fig. 1), reillustrated by Weller (1907, pl. 100, figs. 2, 3), undoubtedly from the Navesink Formation near Big Brook; (2) a large nearly complete specimen from ‘‘Hillsboro, New Jersey’’ (pl. 37, figs. 5, 6), reinterpreted by Miller and Garner (1962: 110) as probably from ‘‘Hillsdale, Monmouth County, where the Red Bank formation occurs’’, but whose locality is still unknown; (3) another large specimen from an unidentified locality (pl. 37, fig. 4), then in the collections of the Academy of Natural Sciences of Philadelphia, but now apparently lost; (4) approximately one­half whorl of a phragmocone from Marlboro, New Jersey (pl. 38, fig. 2), reillustrated by Weller (1907: pl. 100, fig. 4), and undoubtedly from the Navesink Formation near Big

New Jersey. A, Right lateral; B, apertural; C, ventral. D–F. MAPS A 2012h2, top of the New Egypt Formation, 1.5–2 m below the base of the Hornerstown Formation, AMNH loc. 3346, northwest of Eatontown, Monmouth County, New Jersey. D, Apertural; E, ventral; F, left lateral. All figures are X1. Brook; and (5) a large piece of a phragmocone, approximately one­half whorl, from the ‘‘Middle Marls at J. S. Cook’s pits, near Tinton, New Jersey’’ (pl. 38, figs. 3, 4), reillustrated by Weller (1907: pl. 100, fig. 5), who gave the locality as the ‘‘Hornerstown marl; Cook’s pits near Tinton Falls, New Jersey’’, and again by Miller (1947: pl. 6, figs. 1–3), who gave the locality as ‘‘the Hornerstown marl near Tinton Falls, New Jersey’’, and probably from the top of the New Egypt Formation or base of the Hornerstown Formation in this area.

Several other specimens of Eutrephoceras dekayi have been illustrated from New Jersey. Weller (1907: pl. 100, fig. 1) figured an internal mold of an incomplete specimen of a phragmocone and body chamber from the ‘‘Red Bank sand; Shrewsbury River’’. Miller and Garner (1962: pl. 67, figs. 4, 5) figured a small broken juvenile (SUI 8741) from ‘‘the Navesink marl at Glassboro, N.J.’’ and called it Eutrephoceras dekayi perlatum . Miller and Garner (1962: pl. 65, figs. 1, 2) also illustrated a larger, broken adult (ANSP 19680) from ‘‘Burlington County, N.J.,’’ as the same variety. It appears to be the same specimen figured by Whitfield (1892: pl. 37, fig. 4).

Our specimens, with the exception of MAPS A 2012f7, all occur in the upper 2 m of the New Egypt Formation and as reworked material in the basal 6 cm of the Hornerstown Formation. There is little variation in the suture among specimens, which is not unexpected for Eutrephoceras . A comparison of the suture of MAPS A 2012h4 with anoth­ er specimen of E. dekayi (AMNH 50381) from the basal Navesink Formation at Atlantic Highlands reveals no differences (fig. 21).

On the basis of material from the U.S. Western Interior and Gulf and Atlantic Coastal Plains, Miller and Garner (1962) subdivided Eutrephoceras dekayi into three varieties: the nominate variety E. dekayi dekayi ; E. dekayi perlatum after N [autilus] per­ latus originally proposed by Morton (1834: 33, pl. 13, fig. 4) for specimens from the Prairie Bluff Chalk of Alabama; and E. dekayi alcesense after Eutrephoceras alcesence originally proposed by Reeside (1927: 7, pl. 1, figs. 1–3; pl. 2, fig. 1; pl. 3, figs. 1–5; pl. 5, figs. 1, 2) for specimens from the Eagle Sandstone of Montana, Wyoming, Utah, and New Mexico. Miller and Garner (1962) distinguished these varieties on the basis of degree of whorl compression, degree of involution (= depth of impressed zone), and the position of the siphuncle.

We measured the drawings of the whorl sections of the eight specimens figured by Miller and Garner (1962: figs. 1, 2) to obtain a more quantitative understanding of these varieties (table 5). Eutrephoceras dekayi dekayi is the most globose of the three varieties with a ratio of whorl width to height of 1.46– 1.53. It is moderately involute and the siphuncle is just dorsal of center. The ratio of whorl width to height ranges from 1.18 to 1.26 in E. dekayi perlatum but this variety resembles the nominate variety in the other two features. Eutrephoceras dekayi alcesense is the most compressed variety with a ratio of whorl width to height of 1.04 to 1.18. It is also the least involute and is characterized by a siphuncle midway between the center and the dorsum.

On the basis of these measurements, the specimens in our study clearly fall in the variety Eutrephoceras dekayi dekayi . However, we hesitate to use the varietal names until we perform a more thorough analysis of the variation within a large sample of specimens from a single horizon at one locality. It is possible that the range of variation exhibited by these three varieties is characteristic of a single population. Differences in the degree of whorl compression may reflect sexual dimorphism, as documented in Recent Nautilus by Saunders and Spinosa (1978). The position of the siphuncle changes during ontogeny ( Stumbur, 1975), and it is important to

A–D. AMNH 47443. A, Right lateral; B, apertural; C, ventral; D, left lateral. E–G. AMNH 47441. E, Apertural; F, ventral; G, left lateral. H–K. MAPS A 2012h4. H, Right lateral; I, apertural; J, ventral; K, left lateral. L–N. MAPS A 2012f7, Tinton Formation, AMNH loc. 3348, near Tinton Falls, Monmouth County, New Jersey. L, Apertural; M, ventral; N, left lateral. All figures are X1.

take such information into account in collecting data.

OCCURRENCE: This species occurs in the top 2.0 m of the New Egypt Formation and as reworked material in the basal 6 cm of the Hornerstown Formation, near Eatontown, and in the Tinton Formation, near Tinton Falls, northeastern Monmouth County, New Jersey. It also occurs in the upper part of the Navesink Formation and lower part of the New Egypt Formation in the Crosswicks Creek Drainage, central Monmouth County (Landman et al., in prep. b). It is rare in the Merchantville and Marshalltown formations but relatively common at the base of the Navesink Formation at Atlantic Highlands. Miller and Garner (1962: 109) reported that ‘‘In the Cretaceous of New Jersey this species is not abundant, but it occurs in the Navesink marl and the Red Bank sand.’’ They listed six lo­ calities from the Navesink Formation in Monmouth, Burlington, Camden, and Gloucester counties and one locality from the Red Bank Sand in Monmouth County (as originally reported by Weller, 1907). They speculated that the specimen from the Hornerstown Formation near Tinton Falls, illustrated by Whitfield (1892: pl. 38, figs. 3, 4) and Weller (1907: pl. 100, fig. 5) but unavailable to them for study was a different species. Gallagher (1993: 92) reported that Eutrephoceras dekayi is not common in New Jersey but occurs ‘‘from the Navesink up into the Hornerstown’’ and argued that a fragment from the upper part of the Hornerstown Formation at the Inversand Pit probably belongs to this species. Outside of New Jersey, E. dekayi is widespread in Campanian to Maastrichtian strata on the Gulf and Atlantic Coastal Plains and in age­equivalent strata in the Western Interior.

TABLE 4 Measurements (mm) of Eutrephoceras dekayi ( Morton, 1834) a TABLE 5 Measurements of Eutrephoceras dekayi ( Morton, 1834) Described by Miller and Garner (1962: figs. 1, 2) a

ORDER AMMONOIDEA ZITTEL, 1884

SUBORDER AMMONITINA HYATT, 1889

SUPERFAMILY ACANTHOCERATACEAE DE GROSSOUVRE, 1894

FAMILY SPHENODISCIDAE HYATT, 1900

Figures

Fig. 17. Eutrephoceras dekayi (Morton, 1834). A–D. AMNH 47440, uppermost New Egypt Formation and basal Hornerstown Formation, AMNH loc. 3345, northwest of Eatontown, Monmouth County,

Fig. 18. Eutrephoceras dekayi (Morton, 1834). A–C. MAPS A2012h6, uppermost New Egypt Formation and basal Hornerstown Formation, AMNH loc. 3345, northwest of Eatontown, Monmouth County,

Fig. 19. Eutrephoceras dekayi (Morton, 1834). A–K. Uppermost New Egypt Formation and basal Hornerstown Formation, AMNH loc. 3345, northwest of Eatontown, Monmouth County, New Jersey.

Fig. 20. Eutrephoceras dekayi (Morton, 1834). Uppermost New Egypt Formation and basal Hornerstown Formation, AMNH loc. 3345, northwest of Eatontown, Monmouth County, New Jersey. A– D. AMNH 47442. A, Right lateral; B, apertural; C, ventral; D, left lateral. E–H. MAPS A2012h3. E, Right lateral; F, apertural; G, ventral; H, left lateral. All figures are X1.

Fig. 21. Eutrephoceras dekayi (Morton, 1834). A. Suture of MAPS A2012h4 at a diameter of 25.7 mm, AMNH loc. 3345, uppermost New Egypt Formation and basal Hornerstown Formation, northwest of Eatontown, Monmouth County, New Jersey. B. Suture of AMNH 50381 at a whorl width of 43.8 mm, basal Navesink Formation, Atlantic Highlands, Monmouth County, New Jersey.