Jeletzkytes Riccardi, 1983

LANDMAN, NEIL H. & COBBAN, WILLIAM A., 2003, Ammonites from the Upper Part of the Pierre Shale and Fox Hills Formation of Colorado, American Museum Novitates 3388, pp. 1-46 : 35-39

Genus Jeletzkytes Riccardi, 1983

TYPE SPECIES: Scaphites nodusus Owen, 1852: 481, pl. 18, fig. 4, by original designation .

Jeletzkytes dorfi Landman and Waage, 1993

Figures 20A–D, 23

Jeletzkytes dorfi Landman and Waage, 1993: 184 , figs. 141–148.

Jeletzkytes dorfi Landman and Waage, 1993 . Jagt and Kennedy, 1994: 242, fig. 3A–E.

TYPE: The holotype is YPM 23175, a macroconch, as originally designated by Landman and Waage, 1993: 184, fig. 141A–E, from a bluff­forming bioturbated sandstone in the lower Fox Hills Formation , SE ¼, SW ¼ to SE ¼, SE ¼ sec. 18, T 37N, R 62 W, Niobrara County, Wyoming .

MATERIAL: There are six microconchs: USNM 519513 from the Fox Hills Formation, NE ¼, SW ¼ sec. 2, T9 S, R76 W, Park County, Colorado; USNM 519514 from the Fox Hills Formation near Round Butte , Larimer County , Colorado (fig. 1, loc. 6); USNM 519512 from the Fox Hills Formation just south of the Wyoming border and east of Round Butte , Larimer County , Colorado (fig. 1, loc. 9); USNM 519515 from the Fox Hills Formation , center sec. 31, T6 N, R58 W, Morgan County , Colorado (fig. 1, loc. 8); CSM 7797 from the Fox Hills Formation , 4 mi (6.4 km) north and 7 mi (11.3 km) east of Fort Collins , Larimer County , Colorado (fig. 1, loc. 1); and USNM 519516 from near the top of the Pierre Shale or lower part of the Fox Hills Formation, SW ¼, SE ¼ sec. 35, T6 N, R67 W, Weld County , Colorado (fig. 1, loc. 20). There are also four specimens too fragmentary to determine the dimorph: CSM 7799 from the Fox Hills Formation , 11 mi (17.7 km) north of Wellington , Larimer County , Colorado (fig. 1, loc. 3); AMNH 47399 from the upper transition member of the Pierre Shale , sec. 11, T4 N, R70 W, Jefferson County , Colorado (fig. 1, loc. 22); AMNH 47400 from the Fox Hills Formation, SW ¼, NE ¼ sec. 31, T6 N, R58 W, Morgan County , Colorado (fig. 1, loc. 23); and AMNH 47398 from the Milliken Sandstone Member of the Fox Hills Formation, SE ¼, NE ¼ sec. 7, T2 N, R68 W, Boulder County , Colorado (fig. 1, loc. 24) .

MICROCONCH DESCRIPTION: USNM 519512 is an internal mold with part of the phragmocone and aperture missing (fig. 23E–G). The base of the body chamber is not apparent. The umbilical shoulder of the shaft of the body chamber is curved in side view. The cross section at midshaft is subquadrate to trapezoidal with maximum width at the umbilical shoulder in both costal and intercostal section. The umbilical wall is broad and inclined outward and the umbilical shoulder is sharply rounded. The flanks are nearly flat and converge toward the venter. The ventrolateral shoulder is sharply rounded and the venter is very broadly rounded to flat.

The specimen is characterized by coarse ribbing and large umbilicolateral and ventrolateral tubercles, in addition to small flank tubercles on the adoral part of the phragmocone. Ribs on the phragmocone are coarse and widely spaced. Near the adoral end of the phragmocone, they swing slightly backward across the umbilical wall and shoulder, then forward, increasing in strength and crossing the flanks with a weak convexity. They bifurcate or intercalate at midwhorl height. Ribs are broad and weak on the venter, which they cross with a very slight adoral projection. There are 5 ribs/cm on the venter at the adoral end of the phragmocone/adapical end of the body chamber. Ribs are barlike on the umbilical wall of the shaft. They are weakly convex on the flanks with broad interspaces between them; the distance between successive rib crests at midflank is 3– 4 mm. The venter is smooth but undulose, with swellings joining pairs of ventrolateral clavi on either side of the venter. Primary ribs swell into fairly massive umbilicolateral clavi, which are especially noticeable on the right side, where there are four of them. The two most adoral clavi are spaced approximately 9 mm apart. Ventrolateral tubercles are also very prominent and are projected outward and backward and become more widely spaced and larger toward the adoral end of the specimen. They are spaced at distances of 3–5 mm on the adapical end of the specimen and 9 mm on the adoral end. The tubercles are clavate in shape with steep adapical sides and more gently sloping adoral sides. Tubercles are generally paired across the venter. Two short rows of flank tubercles occur on the adapical end of the specimen. On the left side, there are two pairs of tubercles, one pair on each of two ribs; on the right side, there is a pair of tubercles on one rib and single tubercles on each of two ribs.

USNM 519513 is a microconch still embedded in the matrix with most of the phragmocone missing (fig. 23O, P). It is an internal mold 53.8 mm in maximum length. The umbilical shoulder is curved in side view and follows the curvature of the venter. The whorl section at midshaft is compressed subquadrate with maximum width at the umbilical shoulder in costal section and at onethird whorl height in intercostal section. The umbilical wall is broad and inclined outward and the umbilical shoulder is sharply round­ ed. Flanks are very broadly rounded, and the ventrolateral shoulder is sharply rounded. The venter is very broadly rounded to nearly flat.

As in other microconchs of Jelezkytes dorfi , this specimen is characterized by coarse ribbing, prominent umbilicolateral and ven­ trolateral clavi, and partial rows of flank tubercles on the adoral portion of the phragmocone. Ribs are strong, prorsiradiate, and straight on the preserved part of the phragmocone, with intercalation at one­third whorl height. Several ribs bear one or two small flank tubercles, and all ribs, at least those preserved, bear ventrolateral tubercles. The ribs cross the venter with a weak adoral projection, and there are 7 to 8 ribs/cm on the venter on the adoral part of the phragmocone. Primary ribs are straight, prorsiradiate, and barlike on the umbilical wall of the shaft. They merge into prominent umbilicolateral clavi that are fairly uniformly spaced at distances of 4–5 mm. One clavus clearly shows a steep, concave adapical side and more gradually sloping adoral side. Two prorsiradiate ribs branch from each clavus, the more adoral one of which is more prorsiradiate and convex. These ribs are separated by broad interspaces. Branching and intercalation occur on the outer one­third of the flanks, especially on the adoral part of the shaft and hook. As a consequence, the ribbing is dens­ er on the ventrad part of the shell. Large clavi occur on the ventrolateral margin. They increase in size adorally, reaching their largest size (3.5 mm in height) at midshaft, after which they diminish in size. They also gradually become more widely spaced adorally; the distance between successive clavi at midshaft is 9–10 mm. The clavi are sharp and projected backward and outward. Each shows a steep adapical side and more gently sloping adoral side. Two clavi show small grooves along their midlines. There are no ribs on the venter but it is slightly undulose, with swellings joining pairs of ventrolateral clavi on either side of the venter.

USNM 519514 is an impression of a microconch in a chunk of sandstone (fig. 23N). The specimen is approximately 56 mm in maximum length. Like the other microconchs, it is characterized by coarse ribbing and prominent umbilicolateral and ventrolateral tubercles/clavi, in addition to a partial row of flank tubercles on what is presumably the adoral part of the phragmocone. Ribs are widely spaced and rectiradiate or prorsiradiate on the midshaft. Ribs become more closely spaced and prorsiradiate on the adoral part of the shaft and hook. Intercalation and branching occur on the outer one­third of the flanks on the midshaft and nearer the middle of the flanks on the hook. Approximately 9 ribs/cm are present on the flanks on the adoral part of the shaft. Eight more or less evenly spaced umbilicolateral tubercles occur at distances of 5–6 mm; they attain their maximum height at midshaft. Ventrolateral clavi are also approximately evenly spaced on the shaft at distances of 7 mm. They disappear abruptly (or diminish to a tiny tubercle) at the adoral end of the shaft.

USNM 519515 is a small body chamber fragment, mostly an internal mold, part of which is worn away (fig. 23A–D). The umbilical shoulder is curved in side view. The apertural margin is slightly flexuous with a weak adoral projection at the venter; the dorsal lappet is not preserved. The whorl section at midshaft is subquadrate. The umbilical wall is broad and slanted outward and the umbilical shoulder is sharply rounded. Flanks are very broadly rounded with maximum width at the umbilicolateral tubercles in costal section and at one­third whorl height in intercostal section. Flanks gradually converge toward the venter. The ventrolateral shoulder curves gently into a moderately well­rounded venter. The ratio of whorl width to whorl height in intercostal section at midshaft is 0.83. The aperture is more ovoid in cross section, with an intercostal ratio of whorl width to whorl height of 0.91.

The body chamber is covered with ribs and umbilicolateral tubercles. Ribs on the shaft are broad and slightly prorsiradiate with wide interspaces between them, becoming more prorsiradiate and closely spaced on the hook. Intercalation and branching occur on the middle and outer flanks. Ribs cross the venter with a moderately strong adoral projection; there are 10 ribs/cm on the venter of the hook. The body chamber bears five umbilicolateral tubercles, which are sites of branching and intercalation. These tubercles occur at equal distances of approximately 5 mm. Ventrolateral tubercles are worn off but there are still swellings on the shaft.

CSM 7797 is a small slightly distorted microconch with half of the phragmocone missing (fig. 23H–J). It is approximately 47.4 mm in maximum length and is elongate in outline with only a slight gap between the hook and phragmocone. The umbilicus is large, 3.9 mm in diameter, and the umbilical shoulder is curved in side view. The aperture is slightly flexuous with part of the dorsal lappet exposed. The right side of the midshaft is inflated, possibly due to a healed injury. The whorl section at midshaft, based on the left side of the specimen, is nearly quadrate, with maximum width at the umbilical shoulder in costal section and at one­third whorl height in intercostal section. The umbilical wall is broad, convex, and inclined outward. The umbilical shoulder is sharply rounded and the flanks are broadly rounded, converging toward the venter. The ventrolateral shoulder is sharply rounded and the venter is very broadly rounded. The ratio of whorl width to whorl height at mid­shaft is approximately 0.76.

Ribs on the adapical part of the phragmocone are coarse and widely spaced. They are equally widely spaced on the middle of the shaft, but become more closely spaced and prorsiradiate on the adoral part of the shaft and hook, with intercalation and branching occurring on the middle and outer flanks. Ribs cross the venter with a weak adoral projection; there are 9 ribs/cm on the venter of the hook. Six umbilicolateral tubercles are perched on the umbilical shoul­ der. They are spaced at equal distances of approximately 5 mm at midshaft. There are nine ventrolateral tubercles on the body chamber, which are more or less evenly spaced at distances of 6–8 mm. The largest and most clavate tubercles occur at midshaft.

DISCUSSION: Jeletzkytes dorfi is characterized by moderately widely spaced ribbing, which becomes more closely spaced on the hook, umbilicolateral and ventrolateral tu­ bercles/clavi, and partial rows of flank tubercles on the adoral part of the phragmocone. These features are well illustrated in specimens from Niobrara County, Wyoming (fig. 20A–D; Landman and Waage, 1993: figs. 141–146). The specimens in our collection match those from Wyoming with two exceptions. USNM 519515 lacks ventrolateral tubercles. However, this is a worn specimen and the tubercles have probably eroded away. CSM 7797 is a very small specimen with an estimated maximum length of 47.4 mm. However, it is only slightly smaller than the smallest specimen from Wyoming (48.9 mm) recorded by Landman and Waage (1993: 192).

OCCURRENCE: AMNH 47400 occurs at the same locality as YPM 202272, a small belemnite. USNM 519516 is in the same lot as USNM 519510 and 519519, both specimens of Sphenodiscus pleurisepta . Jeletzkytes dorfi occurs in the upper part of the Pierre Shale and Fox Hills Formation in Larimer, Weld, Morgan, Park, Boulder, and Jefferson counties, Colorado, and in the Fox Hills Formation in Niobrara County, Wyoming ( Landman and Waage, 1993). It occurs in the Hoploscaphites birkelundae Zone and is commonly associated with the ammonites Hoploscaphites birkelundae , Coahuilites sheltoni , and Sphenodiscus pleurisepta . Jeletzkytes dorfi has also been reported from the lower upper Maastrichtian of Belgium ( Jagt and Kennedy, 1994).