Discoscaphites jerseyensis, LANDMAN, NEIL H., JOHNSON, RALPH O., GARB, MATTHEW P., EDWARDS, LUCY E. & KYTE, FRANK T., 2007

LANDMAN, NEIL H., JOHNSON, RALPH O., GARB, MATTHEW P., EDWARDS, LUCY E. & KYTE, FRANK T., 2007, CEPHALOPODS FROM THE CRETACEOUS / TERTIARY BOUNDARY INTERVAL ON THE ATLANTIC COASTAL PLAIN, WITH A DESCRIPTION OF THE HIGHEST AMMONITE ZONES IN NORTH AMERICA. PART III. MANASQUAN RIVER BASIN, MONMOUTH COUNTY, NEW JERSEY, Bulletin of the American Museum of Natural History 303 (1), pp. 1-122 : 1-122

Discoscaphites jerseyensis , new species figures 47F, 52

ETYMOLOGY: Named after the state of New Jersey, which has produced more scaphites than anyone would have dreamed of just a few years ago.

TYPES: The holotype and paratype are AMNH 50393 and 50774, respectively, from the Pinna Layer at the top of the Tinton Formation, Manasquan River Basin, Monmouth County, New Jersey. Both specimens are macroconch body chambers. In AMNH 50393, there is a small healed injury at the adapical end.

MATERIAL: Two incomplete macroconch body chambers ( AMNH 50393 and 50774), part of a hook of a microconch ( MAPS A2061a1), and a piece of a phragmocone ( AMNH 51312), possibly of a macroconch, from the Pinna Layer at the top of the Tinton Formation, Manasquan River Basin, Monmouth County, New Jersey.

DIAGNOSIS: Body chamber with very depressed whorl section. Ornament consists of three rows of small tubercles (umbilicolateral and inner and outer ventrolateral tubercles), a single row of small midflank bullae, and long, straight, closely spaced ribs on the hook.

MACROCONCH DESCRIPTION: The body chamber is very depressed. The intercostal ratio of whorl width to height at midshaft is 1.07 and 1.19 in AMNH 50393 and AMNH 50774, respectively (table 11). The umbilical wall is broad and convex and the umbilical shoulder is fairly abruptly rounded. The inner flanks are broadly rounded and divergent, the midflanks are broadly rounded and convergent, and the outer flanks are nearly flat and more steeply convergent. Maximum width occurs at the umbilicolateral margin. The ventrolateral shoulder is broadly rounded and the venter is nearly flat. Both whorl width and height decrease adorally, producing a depressed whorl section at the aperture. The intercostal ratio of whorl width to height at the aperture is 1.13 and 1.17 in AMNH 50393 and 50774, respectively.

The small piece of phragmocone (AMNH 51312) bears long narrow ribs with four rows of tubercles (not illustrated). The body chamber is ornamented with umbilicolateral tubercles that give rise to straight rectiradiate to prorsiradiate ribs bearing weak midflank bullae. In AMNH 50393 ( fig. 52A–D ), these bullae disappear at the adoral end of the shaft, but in AMNH 50774 ( fig. 52E–H ), they persist to the aperture. Inner and outer ventrolateral tubercles are present on the entire body chamber. In AMNH 50393, in which the tubercles can easily be counted, there are 15 inner and 15 outer ventrolateral tubercles, although the body chamber is incomplete. These tubercles are strongest and most widely spaced on the adapical part of the body chamber, and weaker and more closely spaced on the hook; they develop into bullae in AMNH 50393. The hook is covered with fine dense ribbing. The ribs are prorsiradiate on the flanks and straight on the venter; there are 15 ribs/cm on the venter of the hook in AMNH 50393. Part of the suture is preserved in AMNH 51312 and is similar to that of other species of Discoscaphites ( fig. 47F).

DISCUSSION: Discoscaphites jerseyensis , n. sp., differs from D. sphaeroidalis in having very fine ribbing on the hook and a row of midflank bullae instead of tubercles. It differs from D. minardi in having a much more robust body chamber. The difference between D. jerseyensis and D. minardi is analogous to that between D. sphaeroidalis and D. iris .

OCCURRENCE: Pinna Layer , top of the Tinton Formation, Manasquan River Basin, central Monmouth County, New Jersey.

APTYCHI (LOWER JAWS) figures 53, 54

MATERIAL: There are 17 aptychi in the AMNH and MAPS collections ( AMNH 51298, 51300, 51313, MAPS A2062a1–14) from the Pinna Layer at the top of the Tinton Formation, Manasquan River Basin, central Monmouth County, New Jersey. Based on their shape and ornament, these specimens are interpreted as the lower jaws of scaphites. MAPS A2062a8 is preserved inside the body chamber of a macroconch of Discoscaphites iris ( fig. 53D, E). MAPS A2062a7 ( fig. 53A– C) and MAPS A2062a9 ( fig. 53F) are closely associated with a macroconch and microconch of the same species, respectively. The rest of the jaws are isolated ( fig. 54), but were probably associated with the shells from which they were derived, although this was not noted at the time they were collected. We attribute all of the isolated jaws to D. iris because this is the most abundant scaphite in the Pinna Layer. In general, the jaws are preserved with only one of the wings exposed, although the other wing is probably embedded in the matrix. Sometimes, the jaw is folded together [‘‘folio’’ preservation of Seilacher (1993)] exposing both wings of the jaw. In two specimens ( MAPS A2062a7, 10), the lower jaw forms a U-shaped structure, which probably approximates its shape in life.

DESCRIPTION: In well preserved specimens, the length of the jaw ranges from 8.4 to 12.6 mm, and averages 10.3 mm (table 12). The width of the wing ranges from

TABLE 12 Measurements of the Lower Jaws of Discoscaphites iris ( Conrad, 1858) , Tinton Formation, Manasquan River Basin, Monmouth County, New Jersey a

5.4 to 7.6 mm, and averages 6.2 mm. The ratio of jaw width (5 twice wing width) to length ranges from 0.98 to 1.48, and averages 1.23. The symphysal edge is straight and forms a flange that increases in height posteriorly. The anterior margin is nearly straight, the lateral margin is broadly round- ed, and the posterior margin is sharply rounded. The wings are ventrally convex and covered with small folds that parallel the posterior margin.

DISCUSSION: This is the first record of the lower jaws of ammonites from the Upper Cretaceous strata of the Atlantic Coastal Plain. These specimens closely resemble the lower jaws of scaphites illustrated from Maastrichtian deposits of South Dakota ( Landman and Waage, 1993: figs. 37– 41 , 167E–I) and northern Europe (Birkelund, 1982: pl. 2, figs. 6 , 7 ; Birkelund, 1993: pl. 17, figs. 2–4 ; Machalski, 2005: fig. 26 ). The presence of these jaws in the Pinna Layer suggests minimal transport and relatively rapid burial.

Figures

Fig. 52. Discoscaphites jerseyensis, n.sp., macroconchs, Pinna Layer, top of the Tinton Formation, Manasquan River Basin, Monmouth County, New Jersey. A–D. AMNH 50393, holotype. A. Right lateral; B. apertural; C. ventral; D. left lateral. E–H. AMNH 50774, paratype. E. Right lateral; F. apertural; G. ventral; H. left lateral. All figures X1.

Fig. 37. Eubaculites latecarinatus (Brunnschweiler, 1966), Pinna Layer, Tinton Formation, Manasquan River Basin, central Monmouth County, New Jersey. A–E. AMNH 51877. A. Right lateral; B. dorsal; C. ventral; D. left lateral; E. whorl section at adoral end. F–I. AMNH 51876. F. Right lateral; G. dorsal; H. ventral; I. left lateral. J–M. AMNH 51862. J. Right lateral; K. dorsal; L. ventral; M. left lateral. N–Q. AMNH 51875. N. Right lateral; O. dorsal; P. ventral; Q. left lateral. All figures X1.

Fig. 38. Top. Size histogram of a sample of Eubaculites latecarinatus (Brunnschweiler, 1966), Pinna Layer, Tinton Formation, Manasquan River Basin, central Monmouth County, New Jersey. Most of the specimens are fragments of juvenile body chambers. Bottom. Scatter plot of whorl width versus height in the same sample of E. latecarinatus. Measurements are at the adoral ends of the specimens.

Fig. 6. A–D. Cluster of Discoscaphites iris (Conrad, 1858), Pinna Layer, Tinton Formation, Manasquan River Basin, Monmouth County, New Jersey. All of the pieces fit together and form the

Fig. 7. Fish teeth and spines, Pinna Layer, upper part of the Tinton Formation, Manasquan River Basin, Monmouth County, New Jersey. A. Rostral tooth of a sawfish (photo mosaic of two images), AMNH 51310. B. Fish tooth, probably not of a shark, MAPS A1043a1. C, D. Tooth of a lamniform

Fig. 2. Detailed locality map of the Manasquan River Basin, central Monmouth County, New Jersey, showing the Tinton Formation and overlying Hornerstown Formation. Numbers correspond to AMNH localities described in the text.

Fig. 3. Simplified stratigraphic section in the Manasquan River Basin, central Monmouth County, New Jersey, showing the upper part of the Tinton Formation and the lower part of the Hornerstown Formation. The unit at the top of the Tinton Formation (the Pinna Layer) contains a rich assemblage of fossils and represents an autochthonous deposit. (The fossils are not as abundant as illustrated.) The iridium spike occurs at the base of the Pinna Layer, and represents the Cretaceous/Tertiary boundary, assuming no postdepositional remobilization of iridium (but see text). A concentration of siderite nodules occurs at the base of the Hornerstown Formation and is associated with a hiatus. A ‘‘Burrowed Unit’’ is present at some downdip sites and is sandwiched between the top of the Pinna Layer and the overlying part of the Hornerstown Formation. The biostratigraphic ranges of five key species are illustrated on the right (D. iris 5 Discoscaphites iris; E. latecarinatus 5 Eubaculites latecarinatus; D. galeata 5 Deflandrea galeata; P. grallator 5 Palynodinium grallator; O. pulaskensis 5 Ostrea pulaskensis).

Fig. 4. Stratigraphic section at AMNH loc. 3372, Manasquan River Basin, Monmouth County, New Jersey, showing the upper part of the Tinton Formation, including the Pinna Layer, and the overlying Hornerstown Formation, including the Burrowed Unit. The reworked nodules (arrows) in the basal Hornerstown Formation contain Cretaceous fossils. The position of the iridium spike at the base of the Pinna Layer is indicated by an asterisk.

Fig. 26. Sphenodiscus lobatus (Toumey, 1856). MAPS A2002g2, Pinna Layer, Tinton Formation, Manasquan River Basin, Monmouth County, New Jersey. A. Apertural; B. ventral. C. left lateral. All figures X1.