Scaphites (Scaphites) depressus Reeside, 1927

Landman, Neil H., Plint, A. Guy & Walaszczyk, Ireneusz, 2017, Allostratigraphy And Biostratigraphy Of The Upper Cretaceous (Coniacian-Santonian) Western Canada Foreland Basin, Bulletin of the American Museum of Natural History 2017 (414), pp. 1-173 : 139-159

Scaphites (Scaphites) depressus Reeside, 1927

Figures 9D, E, 17–32

1894. Scaphites ventricosus Meek and Hayden. Stanton : 186 (pars), pl. 44, fig. 10 only.

1898. Scaphites ventricosus Meek and Hayden. Logan : 476, pl. 104, fig. 10 only.

1927a. Scaphites ventricosus Meek and Hayden var. depressus Reeside : 7, pl. 5, figs. 6–10.

1927a. Scaphites ventricosus Meek and Hayden var. stantoni Reeside : 7, pl. 3, figs. 19, 20; pl. 4, figs. 5–10.

1927a. Scaphites ventricosus Meek and Hayden var. oregonensis Reeside : 7, pl. 6, figs. 11–15.

1952. Scaphites depressus Reeside. Cobban : 32, pl. 15, figs. 6–8.

1952. Scaphites depressus Reeside var. stantoni Reeside. Cobban : 33, pl. 15, figs. 1–5.

1952. Scaphites depressus Reeside var. oregonensis Reeside. Cobban : 33.

1964. Scaphites depressus var. stantoni Reeside. Scott and Cobban , pl. 5, fig. 2.

1970. Scaphites depressus Reeside. Jeletzky , pl. 26, fig. 2.

non 1976 Scaphites ex. gr. ventricosus Meek and Hayden. Szász : 204, pl. 3, fig. 2.

1976. Scaphites depressus Reeside. Kennedy and Cobban , pl. 7, fig. 4.

1977. Scaphites depressus Reeside. Kauffman : 263, pl. 24, figs. 9, 10.

1994. Scaphites depressus Reeside. Braunberger : 117–118, pl. 14, figs. 1–4; pl. 15, figs. 1–3; pl. 16, figs. 1–3.

1994. Scaphites depressus Reeside. Hills et al. : 735, pl. 1, figs. 2, 4.

DIAGNOSIS: Macroconchs globular and massive, with closely coiled body chamber and broadly rounded to flattened flanks, with a reduced aperture; apertural angle averaging 70°; ornament consisting of numerous, straight, closely spaced primary and secondary ribs; microconchs smaller with more loosely uncoiled body chamber; suture complex with asymmetrically bifid first lateral lobes.

TYPES: Holotype YPM 6417 from 244 m above the base of the Cody Shale on the Oregon Basin Oil Field in sec. 6, T. 51N., R. 100W., Park County, Wyoming.

MATERIAL: Approximately 77 specimens, all of which are adult specimens, comprising 45 macroconchs and 32 microconchs.

TABLE 7

Measurements of Scaphites (Scaphites) depressus macroconchs.

See figure 2 for description of measurements. All measurements are in mm, except for apertural angle (AA) and septal angle (SA), which are in degrees. Rib density is reported to the nearest 0.25 ribs/cm on the adapical and adoral parts of the phragmocone, the midshaft, and the hook, depending upon the preservation of the specimen. Height (m) is the height in the measured stratigraphic section.

Study Height LMAX/ LMAX/ WP/ WS/ WH/ Rib density

TMP No. Loc. LMAX AA SA UD

No. (m) HP HS HP HS HH Adap. Adoral Shaft Hook Ram

2 2016.041.0004 132.5 89.9 – – – – – – – – – 4 4 5 Riv.

Ram

5 2016.041.0007 132.5 88.8 – – – – – – – – – 3 4 4.5 Riv.

Ram

7 2016.041.0009 132.5 91.4 2.38 2.51 – – – 1.32 1.48 1.32 – 3.25 4 4 Riv.

Ram

8 2016.041.0010 132.5 76.8 2.50 2.33 – – – 1.38 1.44 1.42 – 4 4.5 4.5 Riv.

Ram

9 2016.041.0011 132.5 95.5 2.34 2.14 77 -7 – 1.41 1.34 1.69 – 3.25 3.25 3.5 Riv.

Ram

10 2016.041.0012 132.5 – – – – – – – – – – – 3 4 Riv.

Ram

12 2016.041.0014 110.7 89.7 – – – – – – – 1.49 – 3 3 4 Riv.

Ram

14 2016.041.0016 112.7 92.0 – – – – – – – – – 3 4 4 Riv.

Ram

17 2016.041.0019 132.9 – – – – – – – – – – – 4 5 Riv.

Ram

18 2016.041.0020 132.9 – – – – – – – – – – 4.25 3 5 Riv.

Ram

21 2016.041.0023 132.9 78.6 – – – – – – – – – 5 – 5 Riv.

Ram

22 2016.041.0024 127.3 81.7 – – – – – – – – 4.75 4.25 4 4.75 Riv.

Ram

23 2016.041.0025 127.3 – – – – 2 5.1 1.35 1.27 – 5 4.5 3.25 4 Riv.

Ram

24 2016.041.0026 127.3 – – – – – – – – – – 4 – – Riv.

Ram

25 2016.041.0027 119.6 74.5 – – – – – – – – 5 5 4.5 5.25 Riv.

E. This-

37 2016.041.0069 83.3 90.1 2.40 2.10 79 0 4.9 1.39 1.31 1.35 5.5 4 3.75 4 tle Ck.

E. This-

38 2016.041.0070 83.3 74.4 – 2.11 – -12.5 – – – – – – 3.5 – tle Ck.

E. This-

39 2016.041.0071 83.3 82.1 2.85 2.17 – – – 1.60 1.40 – 5 – – 3.5 tle Ck.

James

58 2016.041.0156 92.9 – – – – – – – – – – 5 4 5 Riv.

W. This-

76 2016.041.0210 100.9 102 2.76 2.38 – -16 – 1.54 1.42 – – 4 3.5 3.5 tle Ck.

W. This-

77 2016.041.0211 101.3 93.3 – – – – – – – - 4.5 4 – 4 tle Ck.

MACROCONCH DESCRIPTION: In the mea- trolateral shoulder is sharply rounded; and the sured sample, LMAX averages 90.6 mm and venter is broadly rounded. WS/HS averages 1.39 ranges from 74.3 to 122.7 mm (table 7). The ratio and ranges from 1.27 to 1.58. Adoral of the midof the size of the largest specimen to that of the shaft, the whorl width and, especially, the whorl smallest is 1.65. The size distribution is unimodal height abruptly decrease. As a result, the whorl with a peak between 90 and 95 mm (fig. 17). section at the point of recurvature is much more Adults are robust with a circular outline in side depressed than that at midshaft. WH/HH averages view. The exposed phragmocone occupies 1.54 and ranges from 1.32 to 1.87. The umbilical approximately one whorl and terminates slightly wall is flat and slopes outward, the flanks are below or slightly above the line of maximum sharply rounded, and the venter is broadly length. The septal angle averages -2.5°. The rounded. The shell culminates in a constricted umbilical diameter of the phragmocone is small aperture with a dorsal lappet. and averages 5.4 mm. The body chamber consists On the exposed phragmocone, primary ribs of a short shaft and recurved hook. The umbilical emerge at the umbilical seam and are straight shoulder of the shaft is straight in side view. and rectiradiate on the umbilical wall and shoul- LMAX/HS averages 2.23 and ranges from 2.01 to der. They develop into broad elongate swellings 2.51. The body chamber is tightly coiled leaving that gradually reach their maximum strength at hardly any gap between the phragmocone and one-third whorl height, but never form nodes. hook. LMAX/HP averages 2.55 and ranges from They each subdivide into two or three secondary 2.34 to 2.85. TMP 2016.041.0298–.0300 from ribs, with another one or two longer secondary Sheep River, which occur in the lower part of the ribs intercalating between them. Ribs are sharp Scaphites (S.) depressus Zone , are slightly more and uniformly strong on the broadly rounded loosely uncoiled than most specimens of this venter, which they cross with a slight adoral prospecies, and are reminiscent of S. (S.) ventricosus . jection. They are closely spaced on the adapical In all of our specimens, the aperture is reduced end of the phragmocone with a rib density of in size relative to that at midshaft. The apertural 3.75 to 6 ribs/cm. They become more widely angle averages 70.2° and ranges from 61° to 81°. spaced on the adoral end of the phragmocone

The whorl section of the phragmocone along with a rib density of 3 to 5 ribs/cm. the line of maximum length is depressed and The same pattern of ornamentation persists subquadrate with maximum whorl width at one- onto the body chamber. Primary ribs are rectiradithird whorl height. The umbilical wall is steep ate on the umbilical wall and shoulder. They and subvertical; the flanks are broadly rounded develop into elongate swellings that follow the cur- and nearly parallel; the ventrolateral shoulder is vature of the flanks and never culminate in nodes. sharply rounded; and the venter is broadly They are prominent, rectiradiate, and equally rounded. WP/HP averages 1.46 and ranges from spaced on the shaft, becoming weaker, prorsiradi- 1.32 to 1.74. As the shell passes from the phrag- ate, and more closely spaced on the hook. At onemocone into the body chamber, the whorl width half whorl height coincident with the ventrolateral and height increase only slightly, so that the shoulder, each rib subdivides into two secondary whorl section at midshaft is nearly the same as ribs, with two to four longer secondary ribs interthat along the line of maximum length. It is calating between them. Ribs are uniformly strong depressed and subquadrate with maximum and wirelike on the venter of the shaft, which they whorl width at one-third whorl height. The cross with a slight adoral projection. They are umbilical wall is steep and subvertical; the flanks widely spaced with a rib density of 2 to 4.5 ribs/cm, are broadly rounded and nearly parallel; the ven- becoming more closely spaced on the venter of the

TABLE 8

Measurements of Scaphites (Scaphites) depressus microconchs. See figure 2 for description of measurements.

All measurements are in mm. Rib density is reported to the nearest 0.25 ribs/cm on the adapical and adoral parts of the phragmocone, the midshaft, and the hook, depending upon the preservation of the specimen. Height (m) is the height in the measured stratigraphic section.* = above measured section.

Study Height LMAX/ WP/ WS/ WH/ Rib density

TMP No. Locality LMAX UD

No. (m) HP HP HS HH Adap. Adoral Shaft Hook

1 2016.041.0003 Ram Riv. 132.5 62.2 – – – 1.28 1.69 6 5.5 – 6

3 2016.041.0005 Ram Riv. 132.5 59.4 2.35 – 1.23 1.37 1.39 – 5 5 5.5

4 2016.041.0006 Ram Riv. 132.5 – – – – – – – 4.5 4.5 5

6 2016.041.0008 Ram Riv. 132.5 – – 3.5 – – – – – – –

11 2016.041.0013 Ram Riv. 132.5 75.8 2.49 – 1.22 – – – 5 4.5 5

13 2016.041.0015 Ram Riv. 111.4 – – – – – – – 4 –

20 2016.041.0022 Ram Riv. 132.9 – – – – 1.43 1.46 – 5 5 E. Thistle

36 2016.041.0068 82.0 58.0 – – – – – 6 5 4.5 6 Ck.

W. Thistle

75 2016.041.0209 100.3 68.5 – – – 1.40 – – 4 4.5 5 Ck.

W. Thistle

86 2016.041.0220 118.7 – – – – – – – – 4 5 Ck.

W. Thistle

87 2016.041.0221 121.0 64.8 2.67 5.1 – 1.13 – – 5 4 5 Ck.

W. Thistle

89 2016.041.0223 121.0 56.0 2.51 – 1.37 1.38 1.50 – 4.25 4 5 Ck.

Cardinal

100 2016.041.0274 96.8 70.8 2.30 3.8 1.46 1.42 – 4.5 4.5 3.75 5 Riv.

Cardinal

102 2016.041.0276 121.0 60.1 – – – – – – – – – Riv.

Cardinal

103 2016.041.0277 139.0 58.0 2.47 – 1.38 1.31 1.36 – 4 4 4.75 Riv.

Cardinal 141.5–

104 201.041.0278 70.3 2.42 3.5 1.58 1.40 – 5 4 3.75 4.5 Riv. 143.5

Cardinal 141.5–

106 2016.041.0280 55.9 – – – – – 6 5 4.5 5 Riv. 143.5

109 2016.041.0297 Sheep Riv. – – – – – – – – – 4

113 2016.041.0301 Sheep Riv. 149.0 73.0 2.63 – – – – 5 4 3.5 –

114 2016.041.302 Sheep Riv. 149.0 55.8 – – – – – – 4.5 4.25 5

117 2016.041.0305 Sheep Riv. 158.8 76.2 2.53 Bighorn

123 2016.041.0352 142.2 62.9 2.50 Riv.

Bighorn

124 2016.041.0353 142.2 69.1 – Riv.

Bighorn

125 2016.041.0354 Above* 70.0 – Riv.

– – 1.31 1.29 – 5 3.5 5

– – 1.48 1.57 – 4 – 6

– – 1.53 1.62 – 4 4 5

– – – – – 5 4 5

hook, with a rib density of 3.25 to 5.25 ribs/cm. They cross the venter of the hook with a slight to strong adoral projection.

A suture is not well enough preserved in any of the specimens in our study, but according to Cobban (1952), it is complex with asymmetrically bifid first lateral lobes (fig. 9D, E).

MICROCONCH DESCRIPTION: Many of the microconchs are simply miniatures of the macroconchs. For example, TMP2016.041.0278 is simply a scaled-down version of TMP2016.041.0069. Other microconchs such as TMP2016.041.0221 are not only smaller than the macroconchs, but are also more elongate with a more concave umbilical shoulder in lateral view. LMAX averages 65.3 mm and ranges from 55.8 to 77.5 mm (table 8). The size distribution is unimodal with a peak between 60 and 65 mm (fig. 17).

The shell proportions of microconchs are similar to those of macroconchs. The whorl section of the phragmocone along the line of maximum length is depressed and subquadrate with maximum whorl width at one-third whorl height. The umbilical wall is steep and subvertical; the flanks are broadly rounded and nearly parallel; the ventrolateral shoulder is sharply rounded; and the venter is broadly rounded. WP/HP averages 1.42 and ranges from 1.22 to 1.69. As the shell passes from the phragmocone into the body chamber, the whorl width and height increase only slightly, so that the shape of the whorl section at midshaft is nearly the same as that along the line of maximum length. It is depressed subquadrate with maximum whorl width at one-third whorl height. The umbilical wall is steep and subvertical; the flanks are broadly rounded and nearly parallel; the ventrolateral shoulder is sharply rounded; and the venter is broadly rounded. WS/ HS averages 1.38 and ranges from 1.13 to 1.58. Adoral of the midshaft, the whorl width and height decrease slightly, resulting in a slightly more depressed whorl section at the point of recurvature. WH/HH averages 1.52 and ranges from 1.29 to 1.77. The umbilical wall is flat and slopes outward, the flanks are sharply rounded, and the venter is broadly rounded. The shell culminates in a constricted aperture.

The pattern of ornamentation on microconchs is the same as that on macroconchs. On the exposed phragmocone, primary ribs emerge at the umbilical seam and are straight and rectiradiate on the umbilical wall and shoulder. They develop into broad elongate swellings that are straight or weakly concave or convex. They branch into two secondary ribs, with another longer secondary rib intercalating between them. Ribs are sharp and uniformly strong on the broadly rounded venter, which they cross with a slight adoral projection. They are closely spaced on the adapical end of the phragmocone with a rib density of 4.5 to 6 ribs/ cm. They become slightly more widely spaced on the adoral end of the phragmocone with a rib density of 4 to 5.5 ribs/cm.

The same pattern of ribbing persists onto the body chamber. Primary ribs are rectiradiate on the umbilical wall and shoulder. They form elongate swellings that are widely spaced on the shaft, becoming more closely spaced on the hook. In a few, more compressed specimens, these ribs develop into bullae at the ventrolateral shoulder before branching into two or three secondary ribs, with one longer secondary rib intercalating between them. Ribs are uniformly strong and wirelike on the venter of the shaft, which they cross with a slight adoral projection. The rib density ranges from 3.5 to 5 ribs/cm. The ribs become more closely spaced on the venter of the hook, with a rib density of 4 to 6 ribs/cm. They cross the venter of the hook with a slight adoral projection.

The suture of the microconchs is the same as that of the macroconchs.

REMARKS: Dimorphism is present in Scaphites (S.) depressus . The microconchs have previously been referred to as the co-occurring variety Scaphites (S.) depressus var. stantoni by Reeside (1927a) but we argue that they are simply microconchs of the typical form. The size distribution of microconchs and macroconchs is each unimodal with a peak between 60 and 65 mm and 90 and 95 mm, respectively (fig. 17). The average size of microconchs is 72.1% that of macroconchs (or conversely, the average size of macroconchs is 138.7% that of microconchs).

Two macroconchs of Scaphites (S.) depressus are encrusted with cheilostome bryozoans belonging to the genus Conopeum (fig. 32). The colonies are sheetlike and cover an area of approximately 2 cm 2. They occur on the internal molds of the ammonites near the apertural margin, indicating that they must have encrusted the inside surfaces of the body chambers after the ammonites died. This suggests that the shells must have rested on the sea floor for at least several months.

Outside the study area, Scaphites (S.) depressus is widely distributed in the Kevin Member of the Marias River Shale in north-central Montana and the Cody Shale in western Wyoming. It is rare in the Smoky Hill Chalk Member of the Niobrara Formation in southwestern Colorado and in the Mancos Shale in western Colorado and eastern Utah.

Scaphites (S.) depressus co-occurs with Clioscaphites saxitonianus at several sites in Alberta and Montana. At Cardinal River, Alberta, the two species co-occur at a height of 141.5– 143.5 m and at West Thistle Creek, Alberta, they co-occur at a height of 121.0 and 123.6 m. Cobban et al. (2005) also noted the co-occurrence of these two species in the Bad Heart Sandstone in central western Alberta and in the Virgelle Sandstone in southwestern Montana.