Late Cretaceous) Rudistids from the Lower Tongue of the Mancos Shale, Lincoln County, New Mexico

Middle Turonian (Late Cretaceous) rudistids from the lower tongue of the Mancos Shale, Lincoln County, New Mexico

Stephen C. Hook, Atarque Geologic Consulting, LLC, 411 Eaton Avenue, Socorro, New Mexico 87801, [email protected]; William A. Cobban, 70 Estes Street, Lakewood, Colorado 80226

Abstract Raton x #20 Mancos Farmington x Thatcher Limestone Rudistids are uncommon fossils in Upper Shale #2 # 27 Lewis Shale (location uncertain) Cretaceous rocks of the Western Interior of x the United States. Since 1856 there have been x fewer than 40 occurrences noted in the litera- x # 14 Niobrara ture, many of these without descriptions or Formation illustrations. Only six of these occurrences x are from New Mexico. Therefore, the discov- x Santa Fe Gallup Las Vegas ery of two fragments of solitary radiolitid x #3 Paguate x x Sandstone rudistids and one fragment of a small bou- x x quet from a sandy concretionary bed in the x x lower tongue of Mancos Shale in Lincoln Albuquerque County, New Mexico, is of some importance. x x Associated fossils in the concretions include x Fence the ammonites Spathites rioensis, Morrowites Lake x depressus, and Collignoniceras woollgari wooll- x x gari x x , placing the rudistid bed in the lower Carthage coal field part of the middle Turonian C. woollgari Zone. Socorro x # 9 Bull Gap Although specifically indeterminate, the rud- Canyon istids are probably conspecific with a large x R x White Oaks Canyon rudistid bouquet composed of Durania cor- -1 x sh nupastoris that was described and illustrated o x Carrizozo re l in from rocks in the same zone in the Greenhorn e Limestone of Colorado. T or C High Nogal Ranch Alamogordo Introduction Silver City

Rudistids (or rudists) are an extinct group of aberrant, inequivalved bivalves that Deming Las Cruces were generally attached to the substrate by either the right or left valve; they could be solitary or gregarious, but not colonial. x Collignoniceras woollgari When gregarious, they could form large 0 50 mi Morrowites depressus # 9 Rudistid locality keyed to wave- and current-resistant structures 0 100 km Appendix called reefs. Since 1775 when they were illustrated for the first time, they have been classed as brachiopods, corals, cephalo- FIGURE 1—Map of New Mexico showing cities, key outcrops (including Bull Gap Canyon), and pods, or cirripeds. Deshayes (1825) appears the approximate position of the regressing (R-1) western shoreline of the Late Cretaceous seaway at to have been among the first naturalists to the beginning of time during which the ammonites Collignoniceras woollgari and Morrowites depres- determine that the group belonged in the sus lived (early–middle Turonian). The shoreline’s position is shown midway between Truth or Bivalvia (Dechaseaux 1969, p. N749). In Consequences—where nonmarine strata of the Carthage Member of the Tres Hermanos Formation most rudistids the larger (attached) valve were being deposited— and Bull Gap Canyon—where marine strata of the lower tongue of the Mancos Shale containing the rudistid bed were being deposited. Modified from Kennedy et al. 2001, fig. 16. ranges from conical to gently curved to spi- rally coiled and from 2 cm to 2 m in length and 8 mm to 0.6 m in diameter. The smaller Formation of Kansas, where rudistids are then, Hall and Meek’s species has been (free) valve ranges from flat to slightly con- relatively abundant (Cobban et al. 1991, p. reassigned to the genus Ichthyosarcolites. vex and lidlike to conical, or coiled. In some D2). Cobban et al. (1991, pp. D2–D3) pro- Caldwell and Evans (1963) redescribed cases the larger (free) valve was coiled and vide a summary of rudistid occurrences in Hall and Meek’s holotype and described the smaller (attached) valve was conical to the Western Interior as of 1990; this sum- a Campanian specimen of I. coraloidea slightly coiled. Shell wall thickness could mary is updated in the Appendix. A web from the Bearpaw Shale of Saskatchewan, vary from less than 2 mm to more than 10 catalog of worldwide occurrences of rudis- Canada, making it the northernmost rudist cm. Their geologic range extends from the tids can be found at http://www.paleotax. in the Western Interior. Upper Jurassic to the Upper Cretaceous. de/rudists/locality.htm#MU. Mudge (1876, p. 216) was probably the Even though Late Cretaceous marine Hall and Meek (1856, p. 380, pl. 1, fig. first to note the occurrence of rudists in the faunas from the Western Interior of the 3a-f) described the first rudist from the Cretaceous chalk of Kansas, where they United States are dominated by mollusks, Western Interior from the Campanian are fairly abundant; Williston (1897, p. 239) rudistid bivalves are uncommon elements Pierre Shale at Sage Creek, South Dakota, referred to these beds as “Rudistes Beds.” (Fig. 1), presumably because the boreal as the new species Caprinella coraloidea. At Logan (1898, p. 494, pl. 115, pl. 119, fig. 1) waters of the Western Interior Seaway were that time, it was the northernmost occur- was the first to describe the Kansas rud- too cold. The lone exception is the Niobrara rence of a rudistid in North America. Since ists as the new species Radiolites maximus

February 2013, Volume 35, Number 1 New Mexico Geology 13 N Top Bridge Creek Limestone Beds of the S N S lower tongue of the Mancos Shale Atarque Sandstone Member Tres Hermanos Formation

D14973—rudistid bed

A B

N Atarque Sandstone Member S Tres Hermanos Formation

D14973 Morrowites depressus (Fig. 3, unit 17)

D14973—rudistid bed

lower tongue Mancos Shale C D

FIGURE 2—Photographic gallery of the rocks and fossils from the Bull Gap foreground on the south is held up by the Atarque Sandstone Member of Canyon area of Lincoln County, New Mexico. A—Outcrop view, looking the Tres Hermanos Formation. Outcrop of the sandy beds containing the east, of the uppermost limestone of the Bridge Creek Limestone Beds of the rudistid support the hill and swale in the center of the photograph. This lower tongue of the Mancos Shale exposed in the SE¼NW¼SE¼ sec. 24 T9S area is 0.4 mi (0.7 km) southeast of that shown in Fig. 2A in SE¼SE¼SW¼ R9E., Bull Gap Canyon 7.5-min quadrangle, Lincoln County, New Mexico. sec. 24 T9S R9E, Bull Gap Canyon 7.5-min quadrangle, Lincoln County, This bed (Fig. 3, unit 10) contains the inoceramid Mytiloides puebloense; its New Mexico. C—Closer view, looking east, of the sandy interval near the base marks the boundary between the Cenomanian Stage (below) and top of the lower tongue of the Mancos Shale shown in Fig. 2B. Hammer the Turonian Stage (above). The 200 ft (61 m) of section between this bed and Yeso for scale on unit 17 of measured section (Fig. 3) that yielded and the sandy beds that contain the rudistid are covered everywhere in the large solitary rudistid (Fig. 4C, D). D—Close-up view, looking east, the area (see Fig. 3). Field companions Eisenhower (front) and Yeso are of internal molds of Morrowites depressus that have weathered out of unit shown for scale. B—View looking east from near the top of the Bridge 17, the sandy concretion bed that yielded the first rudistid. Same locality Creek Limestone Beds across the almost entirely covered outcrop of the as Fig. 2C. upper part of the lower tongue of the Mancos Shale. High area in the near from the Campanian Niobrara Chalk; R. varied from very generalized (“rudistids”) northeastern New Mexico. This occurrence maximus was described in more detail and to a specific identification (Ichthyosarcolites is in the middle Cenomanian Conlinoceras illustrated by Miller (1968, pp. 37–38, pl. 4, coraloidea); and the documentation of the tarrantense Zone, indicating that the rudis- figs. 6–8; 1970 pl. 1, fig. 2). occurrence has varied from an observation, tids established a presence in the Western Since Hall and Meek’s (1856) work on the to placement in a measured section, to a Interior soon after the Late Cretaceous sea- Campanian of South Dakota, rudists from description with illustration(s). way entered New Mexico. This was merely the Western Interior have been reported or an observation made by W. J. Kennedy (in described from every stage of the Upper New Mexico’s Upper Cobban et al. 1991, p. D2) with no locality Cretaceous, with occurrences in New data and no specific determination of the Mexico, Arizona, Colorado, Wyoming, Cretaceous rudistids rudistid. Montana, Kansas, and Saskatchewan The second oldest occurrence is from (Appendix). The six occurrences in New The oldest rudistid occurrence in the dark-brown-weathering sandstone concre- Mexico (Fig. 1) are typical: they range in Western Interior is from the Thatcher tions in the Paguate Tongue of the Dakota age from the Cenomanian to Santonian; the Limestone Member of the Graneros Shale in Sandstone in McKinley County at USGS taxonomic assignment of the specimens has Mesozoic locality D7333. The fragmentary

14 New Mexico Geology February 2013, Volume 35, Number 1 rudistid has affinities to Ichthyosarcolites. Tres Hermanos Fm. Atarque Ss. Member 19 Associated fossils include Inoceramus ruther- lower 3 ft (1 m) [D14971] Collignoniceras woollgari woollgari fordi, Ostrea beloiti, Acanthoceras amphibolum, 18 75 ft (22.9 m) of cover and Turrilites acutus (Cobban et al. 1991, removed (not to scale) 17 D14973 Collignoniceras woollgari woollgari, p. D2). This faunal assemblage places the Morrowites depressus, cf. Durania rudistid in the middle Cenomanian A. 16 cornupastoris, bivalves (see Fig. 2B-D) amphibolum Zone, four standard ammonite 15 D14988 Morrowites depressus, Spathites rioensis zones higher than the previous Graneros 14 13 D14987 Spathites rioensis

Shale specimen. See Cobban et al. (2006, (not to scale) 12 fig. 1) for the standard zonal table for the 288.1 ft (87.8 m) thick Upper Cretaceous of the Western Interior. upper shale unit 200 ft (61 m) of cover The third oldest occurrence is from 11 two localities in the lower tongue of the removed (not to scale) Turonian 10 [D14945] Mytiloides puebloense (see Fig. 2A) Mancos Shale at Bull Gap Arroyo, Lincoln Cenomanian 9 County (Figs. 1–3). The three fragmentary specimens from USGS Mesozoic locali- 8 7 ties D14973 and D15025 are referred to cf. Covered Durania cornupastoris. Associated fossils Partly covered place these rudistids low in the middle Turonian Collignoniceras woollgari Zone, 15 0 0 Marine sandstone l ower tongue

standard ammonite zones above the pre- Mancos Shale Marine limestone upper 339 ft (103 m ) vious Dakota Sandstone specimen. These Concretions Bull Gap rudistids will be discussed in 6 2m detail in the next section of the paper. Marine noncalcareous shale 10 ft The third youngest occurrence is from 50 Marine calcareous shale 46.2 ft (14.1 m) thick ft (15 m) above the base of the lower shale Bridge Creek Marine silty/sandy shale unit of the Smoky Hill Shale Member of the Limestone Beds Niobrara Formation in Colfax County. Scott et al. (1986, p. 31) report only that a rudist had been discovered. Cobban et al. (1991, p. 5 D10640 Inoceramus sp. D2) assign this oyster-encrusted specimen to Durania aff. D. austinensis from USGS Mesozoic locality D11432. Scott et al. (1986, 4 p. 14) report Cremnoceramus browni from the D14871 Pycnodonte newberryi same interval as the rudist, which places 3 the interval in the lower Coniacian Scaphites 2 ventricosus Zone, 11 standard ammonite 1 D10640 Metoicoceras geslinianum zones above the Bull gap rudistids. lower shale unit The second youngest occurrence is from upper 5 ft (1.5 m) 658 ft (200 m) below the top of the Mancos Shale in San Juan County. Reeside (1924, p. 11) records Sauvagesia cf. S. austinensis from the middle Santonian Clioscaphites FIGURE 3—Graphic section of the upper 339 ft (103 m) of the lower tongue of the Mancos Shale vermiformis Zone, three standard ammonite showing lithology and positions of key fossil collections (collection numbers shown in [brackets] if zones above the previous occurrence. projected into this section). The rudistid (Fig. 4C, D) was recovered from unit 17, a 6 inch- (15 cm-) The youngest occurrence in New Mexico thick concretionary sandstone that also yielded Morrowites depressus (Fig. 2D) and Collignoniceras woollgari woollgari (Fig. 4A, B). is from 25 ft (7.6 m) below the Huerfanito Bentonite in the Lewis Shale in Rio Arriba County at USGS Mesozoic locality D13719. 7.5-min quadrangle. Geographically, local- the sandy beds containing the rudistid Fassett et al. (1997, p. 230) referred this ity D15025 is 0.32 mi (0.51 km) due east of produced only an approximate set of specimen to Hall and Meek’s (1856) species, D14973; geologically, it lies in the hanging measurements. The much better exposed, Ichthyosarcolites coraloidea, and placed it in the wall block of a normal fault that juxtaposes but lithologically and biostratigraphically upper Campanian Didymoceras nebrascense the rudistid bed against the base of the Bridge similar, section at the Carthage coal field, Zone, 18 standard ammonite zones above the Creek Limestone Beds in the footwall. 40 mi (65 km) to the northwest (Fig. 1; previous occurrence. The rudistid bed at locality D14973 is Hook et al. 2012, fig. 5), suggests that the 213 ft (65 m) above the top of the Bridge stratigraphic interval between the base of Bull Gap Canyon rudistids Creek Limestone Beds of the lower tongue the Bridge Creek Limestone and the base of of the Mancos Shale and 75 ft (23 m) below the Atarque Sandstone Member at Bull Gap The three rudistid fragments collected from the base of the Atarque Sandstone Member could be about 20% too great. This interval sandy limestone concretions in the lower of the Tres Hermanos Formation (Fig. 3). at Carthage is 275 ft (84 m), whereas at Bull tongue of the Mancos Shale south of Bull Although much of the Mancos Shale sec- Gap Canyon, it is 339 ft (103 m). Gap Canyon, Lincoln County, New Mexico, tion both above and below the rudistid are from two localities approximately 0.32 occurrence is covered, the section between Measured section mi (0.51 km) apart. The largest and best the base of the Bridge Creek Limestone preserved fragment is from USGS Mesozoic Beds and the base of the Atarque Sandstone The graphic section at Bull Gap Canyon locality D14973 in the SE1/4 SE1/4SW1/4 sec. 24 Member of the Tres Hermanos Formation (Fig. 3) is drawn to emphasize: (1) the T9S R9E, Bull Gap 7.5-min quadrangle. The appears to be stratigraphically complete. relative position of the rudistid bed within two smaller fragments are from the same However, reliable dip and strike measure- the upper part of the lower tongue of the level at USGS Mesozoic locality D15025 in ments could be made on only the limestone Mancos Shale; (2) the lithology and thick- the SE1/4SW1/4SW1/4 sec. 24 T9S R9E, Bull Gap beds within the Bridge Creek interval; ness of the sandy beds in which the rudistid occurs; (3) the lithology and thickness of

February 2013, Volume 35, Number 1 New Mexico Geology 15 the Bridge Creek Limestone Beds; and (4) the paleontology of this part of the lower tongue of Mancos Shale and the overly- ing Atarque Sandstone. At the same time, Figure 3 de-emphasizes the thickness of the two large covered intervals in the upper shale unit of 200 ft (61 m) and 75 ft (22.9 m), which together comprise not only 81% of the measured section, but also 100% of the thickness error. Three thin, resistant, concretionary sandstones interbedded with silty shale (Fig. 3, units 13–17) form an inconspicu- ous hill about three-quarters of the way between the base of the Bridge Creek Limestone and the base of the Atarque Sandstone Member of the Tres Hermanos Formation (Fig. 2B). The rudistid (D14973) A B is in a 6 inch- (15 cm-) thick sandy concretionary bed (unit 17) at the top of this series that forms a prominent dip slope. A 200 ft- (61 m-) thick, soft, covered interval (unit 11) separates this outcrop from the top of the Bridge Creek; a 75 ft- (23 m-) covered interval (unit 18) separates it from the base of the Atarque. The Bridge Creek Limestone Beds of the lower tongue of the Mancos Shale are 46.2 ft (14.1 m) thick and consist of five thin limestone beds interbedded with four highly calcareous shale beds (Fig. 3, units 1–10). The lowest bed (unit 1) is a hard, dense, very dark gray, almost lithographic limestone that weathers pale yellowish orange and is 8 inches (20 cm) thick. It breaks with a conchoidal fracture and forms a prominent ledge. The other lime- C D stone beds are not as hard or resistant, are a lighter gray, weather to an off white, and do not form as conspicuous an outcrop. All five limestone beds tend to pinch and swell FIGURE 4—Plate of two key fossils from unit 17, a 6 inch- (15 cm-) thick concretionary sandstone along strike. that is 213 ft (65 m) above the top of the Bridge Creek Limestone Beds and 75 ft (22.9 m) below the base of the Atarque Sandstone Member (see Fig. 3). A, B—Top (ventral) and side views, respectively, Surprisingly, the Bridge Creek Limestone of a whitened fragment of Collignoniceras woollgari woollgari (USNM 558703), X1. Top view shows Beds are only sparsely fossiliferous in the clavate keel in which there is one clavus for each set of double ventrolateral tubercles. The the Bull Gap Canyon area, especially the inner ventrolateral tubercles are bullate, and the outer tubercles are clavate. The side view reveals lower four limestone beds. The hard, dense a moderately evolute ammonite with prosoradiate ribs that arise from bullate umbilical tubercles. limestone at the base of the beds has yielded C, D—Top and side views, respectively, of the rudistid cf. Durania cornupastoris (USNM 558700), only one ammonite species, Metoicoceras ges- unwhitened, X0.6. Top view reveals a transverse section across the rudistid showing the thick shell linianum (D10640), indicative of the upper wall composed of polygonal cells (inset X2) and an elliptical mantle cavity that was filled with sedi- Cenomanian Euomphaloceras septemseriatum ment. Side view reveals a fractured, irregular longitudinal section that shows the shell and mantle Zone. Only a few very small Pycnodonte new- cavity tapering downward. The rudistid is shown unwhitened because the whitening agent obscured berryi the telltale polygonal wall structure. Both specimens are from USGS Mesozoic locality D14973 in the shells (D14871) have been collected SE¼SE¼SW¼ sec. 24 T9S R9E, Bull Gap Canyon 7.5-min quadrangle, Lincoln County, New Mexico. as float from the shale (unit 4) between the second and third limestones in the sequence. However, this collection constitutes the east- boundary; its top is the upper lithologic oldest of three chronologic species in central ernmost occurrence of P. newberryi in New boundary of the Bridge Creek Limestone New Mexico and is indicative of the lower Mexico. Fragments of inoceramids have Beds in the area. The higher, thin calcaren- part of the lowermost middle Turonian been observed in the lower four limestone ites that lie in the Mammites nodosoides Zone Collignoniceras woollgari Zone, four standard beds, but are specifically indeterminate, e.g., and form the top of the Bridge Creek at ammonite zones higher than the Watinoceras D10640 from unit 5. Carthage are not present at Bull Gap. These devonense Zone. Fragments of the very large The uppermost of the five limestone calcarenites are either covered or, more ammonite Morrowites depressus (D14988) are beds (unit 10) is quite fossiliferous in Bull likely, not developed at Bull Gap. present with S. rioensis in a 6 inch- (15 cm-) Gap Canyon itself, where several very nice The next higher fossil in the section occurs thick concretionary sandstone, 2.0 ft (61 cm) internal molds of the inoceramid Mytiloides at the base of the sandy interval that contains higher. Approximately 4.5 ft (1.37 m) higher, puebloense (D14945) have been collected from the rudistid. Several very well preserved the best rudistid fragment (D14973) was an inch or so below the top of the bed. In internal molds of Spathites rioensis (D14987) found in a 6 inch- (15 cm-) thick concretion- New Mexico, M. puebloense is the most com- have been recovered from unit 13, a 7 inch- ary sandstone (unit 17). Associated fossils mon indicator of the basal lower Turonian (18 cm-) thick, light-brown-weathering, fine- include Collignoniceras woollgari woollgari, Watinoceras devonense Zone. The base of grained sandstone. Spathites rioensis is the Morrowites depressus, calcareous worm unit 10 is the Cenomanian–Turonian stage

16 New Mexico Geology February 2013, Volume 35, Number 1 Genus Durania (Des Moulins 1826)

Type species—Hippurites cornupastoris Des Moulins 1826

Right valve is cylindrical but can be short or elongate; left valve is operculiform. Siphonal bands can be concave, smooth, or ribbed. The ligamental ridge is absent, but bifurcating radial furrows are present on the upper surface of the outer wall in many species. Stratigraphic range: Upper Cretaceous (Turonian–Maastrichtian). Geographic range: Europe, North Africa, Asia, South America, and North America.

cf. Durania cornupastoris (Des Moulins 1826) L.O.G. 2013 Figure 4C, D

Durania cornupastoris (Des Moulins); Skelton in Cobban et al. (1991, pp. D3– D7, fig. 1, pls. 1–3)

Description—The best preserved of the three rudistid specimens from Bull Gap Canyon is a fragment of the right (attached) valve of a large solitary individual (USNM 558700) from USGS Mesozoic locality D14973 (Fig. 4C, D). The specimen appears to be conical and has an elliptical cross section with a maximum diameter of 98.6 mm, a height of 81.4 mm, and a maximum shell wall thickness of 20.9 mm. This rudistid is FIGURE 5—Hypothetical reconstruction of the middle Turonian (Late Cretaceous) sea floor at Bull the nucleus of a cannonball-type concretion Gap Canyon, Lincoln County, New Mexico. The lone rudistid from USGS Mesozoic locality D14973 is with a diameter of at least 100 mm. The shown attached to an exhumed, “prefossilized “ internal mold of the ammonite Morrowites depressus. sandy limestone concretion is broken to See text (p. 18) for details. Living bivalves shown on the sea floor include the genera Phelopteria, expose a transverse section of the rudistid, Mytiloides, and Cymbophora. Rudistid is based on Kauffman and Sohl’s (1979, fig. 1G) line drawing of revealing the telltale polygonal structure Durania. Bivalves are based on drawings in Stanton (1893, pl. 9, fig. 7; pl. 14, fig. 2; and pl. 27, fig. 17). of a sauvagesinae radiolitid (Fig. 4C). The Reconstruction by Leo Gabaldon (New Mexico Bureau of Geology and Mineral Resources). longitudinal (radial) structures necessary to place the specimen in a genus or species are not preserved or obscured by the outer tubes, and a few fragments of large, but Systematic paleontology part of the concretion. The elliptical mantle indeterminate bivalve internal molds. These cavity of the specimen, which filled with ammonites reveal the C. woollgari woollgari Family Radiolitide sediment after the death of the individual, Subzone, just as S. rioensis did at the base of Gray 1847 has a maximum diameter of 49.6 mm and a the interval. minimum diameter of 37.2 mm. A 1979 collection made by the authors Inequivalve rudistids in which the right The other two specimens (not illustrated) from this entire sandy interval (units 13, (attached) valve is conical and the left are of right valves of smaller individuals 15, and 17) contained a more diverse fauna (free) valve is operculiform; the surface of from USGS Mesozoic locality D15025. The but did not include a rudistid. Cobban the right valve is without furrows but has solitary rudistid (USNM 558702) is pre- (1986, p. 81) listed the following fossils two concave, flat, or convex siphonal bands served in a portion of a sandy limestone from USGS locality D10643: calcareous separated by an interband. The ligamental concretion 51 mm long by 42 mm wide worm tubes, Phelopteria gastrodes, Mytiloides ridge can be present or absent. Stratigraphic by 16 mm deep. A broken surface formed hercynicus, Camptonectes platessa, Cymbophora range: Lower Cretaceous (Barremian) within the concretion cuts across the rud- sp., Tragodesmoceras socorroense, Placenticeras through Upper Cretaceous (Maastrichtian). istid in a transverse orientation and reveals cumminsi, Spathites rioensis*, Morrowites an elliptical cross section with a maximum depressus*, Collignoniceras woollgari woollgari*, Subfamily Sauvagesinae diameter of 18.33 mm and a minimum and Baculites yokoyamai. An asterisk indicates Douvillé 1908 diameter of 15.03 mm; the shell wall is 1.33 that Cobban (1986) illustrated a specimen mm thick. The second specimen (USNM from locality D10643. Right valve is composed of cells that are 558701) is a small association of two closely A specimen of Collignoniceras woollgari polygonal in transverse section and pris- spaced individuals that are preserved on woollgari (D14971) collected as float from the matic in longitudinal section. Stratigraphic the outer surface of a fragment of sandy basal part of the Atarque Sandstone Member range: Lower Cretaceous (Albian) through limestone concretion that is 73 mm long of the Tres Hermanos Formation indicates Upper Cretaceous (Maastrichtian). by 65 mm wide by 26 mm deep. The better that both Atarque Sandstone and the upper preserved of the two has an elliptical cross part of the lower tongue of the Mancos Shale section with a maximum diameter of 20.32 lie within the C. woollgari woollgari Subzone.

February 2013, Volume 35, Number 1 New Mexico Geology 17 mm, a minimum diameter of 15.26 mm, Paleoecology—Radiolitid rudistids are on the sea floor (Fig. 5). The mere presence and a shell wall thickness of 2.01 mm. It an extinct group of sessile, filter-feeding, of internal molds of at least two species is separated by 11 mm of matrix from the epifaunal bivalves with massive shells that of ammonites in this bed (Fig. 3, unit 17) second individual. The orientation of the were attached as larvae to objects on the indicates that their sediment-filled shells outer surface of the concretion relative to sea floor and grew erect, perpendicular accumulated on the sea floor. Before com- the rudistid makes it impossible to get exact to the sea floor. They preferred shallow, plete burial, these shells could have acted measurements, but the two individuals warm, clear water of normal salinity and as heavy, attachment sites for the rudistids, are of similar size. Both individuals show are commonly found in carbonate depos- regardless of whether the internal molds polygonal structures. its. Although gregarious, they were not were later prefossilized and eroded from No left (free) valves of rudistids have colonial. They lived as individuals and in the sediment. been found in the concretionary bed that conjoined groups that could contain a small yielded the right valves at Bull Gap Canyon. number of individuals called bouquets or Geologic occurrence—Middle Turonian a large number of individuals called reefs. lower tongue of the Mancos Shale, Discussion—Skelton (in Cobban et al. 1991, The large size of the illustrated specimen Collignoniceras woollgari woollgari Subzone pp. D3–D7) described a rudistid bouquet (Fig. 4C, D) suggests that it had lived for of the C. woollgari Zone, 75 ft (22.9 m) below from the Greenhorn Limestone of Colorado some time, perhaps a year or so, and was the base of the Tres Hermanos Formation and assigned the 28 conjoined individu- attached to some large, heavy object on the and 213 ft (65 m) above the top of the als in the bouquet to Durania cornupastoris sea floor. The attachment point would have Bridge Creek Limestone Beds of the lower (Des Moulins 1826). The largest individuals been at the small end of its slightly conical tongue of the Mancos Shale. in the bouquet had conical to cylindrical shell. If it had been attached to a smaller or right valves as much as 80 mm in length. lighter object—such as a small ammonite’s Geographic occurrence—D14973: SE1/4SE 1/4 He noted (p. D5) that “The regular ribbing shell or clam’s shell—the rudistid’s high SW1/4 sec. 24 T9S R9E, Bull Gap 7.5-min and the more finely ribbed radial bands of center of gravity and large surface area quadrangle, Lincoln County, New Mexico; these specimens, together with their clear would have allowed currents to push it and D15025: SE¼SW¼SW¼ sec. 24 T9S polygonal cell structure, immediately iden- over into an unfavorable living position. R9E, Bull Gap 7.5-min quadrangle, Lincoln tify them as sauvagesinae radiolitids….The The paleogeography and stratigraphy at County, New Mexico. absence of any ligamentry invagination the measured section indicate that the rud- places them in the genus Durania….Thusfar, istid lived in a nearshore environment— Acknowledgments their classification presents no problems. probably less than 35 mi (56 km) from the Species assignment is problematical, how- strand line (see Fig. 1)—on a relatively soft We thank the U.S. Geological Survey for ever, because the species level taxonomy of bottom of silty to sandy clay (Fig. 3). The use of facilities and access to fossil collec- the genus is in serious need of revision. At relatively soft bottom conditions lead to the tions stored at their repository in Denver, present, the literature is cluttered with typo- question of the nature of the holdfast object Colorado. We owe a special debt of grati- logically (and commonly stratigraphically) for a large, erect, heavy animal such as the tude to K. C. McKinney, U.S. Geological defined species, most of which deserve the illustrated rudistid (Fig. 4C, D). Kauffman Survey, Denver, for his friendship and oblivion of synonymy; far too many are and Sohl (1979, fig. 1) refer to Durania as a expertise, without which this paper would based on small numbers of specimens, little “…large, barrel-shaped [genus],” suggest- not have been possible. He also sponsored allowance being made of the extent of intra- ing that it had a fairly large attachment area Hook as an adjunct at the U.S. Geological specific variability that might reasonably be relative to other rudistid genera that would Survey working on the Upper Cretaceous expected in such sessile epifaunal forms by provide more stability on the sea floor. They stratigraphy and paleontology of New analogy with, for example, oysters.” (Kauffman and Sohl 1979, p. 725) state that Mexico. Caitlin Lewis, under the supervi- Skelton (p. D5) felt that the Colorado the “…open cellular structure of the rudist sion of K. C. McKinney, photographed specimens could have been assigned to shell permitted rapid growth without great the fossils in Figure 4. We thank Robbie either Durania cornupastoris (Des Moulins expenditure of calcium carbonate, and this Hooten for allowing us access to the 1826) or D. arnaudi (Choffat 1891), which co- resulted in the construction of very large Bull Gap Canyon area. Donald Wolberg occur in the Turonian in Europe and form massive shells in short periods of time. (adjunct, New Mexico Institute of Mining a morphological continuum. He further Filling of these cells with fluid would have and Technology) and Gretchen Hoffman suggested that the two had been divided provided the necessary density to make (geologist, New Mexico Bureau of Geology arbitrarily into two typological species that the rudist shells stable on the sea floor as and Mineral Resources) provided thought- could be synonymized under the older spe- exposed epifaunal organisms.” ful reviews that improved the manuscript. cies name, D. cornupastoris. One possibility as an attachment object Primary field support for this study was The material from Bull Gap Canyon con- is presented by the large ammonite provided by Atarque Geologic Consulting, sists of three specimens, two of which are of Morrowites depressus (Fig. 2D; see Cobban, LLC. Fossil collections have been assigned solitary individuals, and one in which two 1986, fig. 10 for a large specimen from the U.S. Geological Survey Mesozoic locality individuals may be part of a small bouquet. area). An oyster-encrusted internal mold numbers; they begin with the prefix “D” All three are not preserved well enough to of M. depressus was collected at USGS for Denver and are housed at the Federal show the longitudinal bands. The assign- Mesozoic locality D15025 along with the Center in Denver, Colorado. Illustrated and ment of the Bull Gap specimens to cf. two unfigured rudistid specimens. Hook described specimens have been assigned Durania cornupastoris is based primarily and Cobban (1981, p. 13) interpret similar USNM numbers and are reposited in the on stratigraphic occurrence in the middle oyster-encrusted molds in New Mexico as U.S. National Museum in Washington, D.C. Turonian Collignoniceras woollgari Zone and evidence for discontinuity surfaces. The We are indebted to the editorial and partially on overall resemblance to the mate- scenario they envision involves burial of the drafting staff of New Mexico Geology for rial illustrated by Cobban et al. (1991, pls. sediment-filled ammonite shell; dissolution their competence and excellence. Leo 1–3). The rarity of rudistids in the Western of the aragonitic shell resulting in prefos- Gabaldon drew the reconstruction of the Interior suggests very strongly that the Bull silization of the sediment filling (internal Late Cretaceous sea floor shown as Figure 5. Gap Canyon occurrence is conspecific with mold); erosion of the sediment surrounding that of the Colorado occurrence; both are in the hardened internal mold; and coloniza- the C. woollgari woollgari Subzone. tion by oysters (and, here, rudistids) of the discontinuous hardground provided by the internal mold(s), which form a lag deposit

18 New Mexico Geology February 2013, Volume 35, Number 1 References Regina, New Mexico; in Anderson, O. J., Kues, Kennedy, W. J., Cobban, W. A., and Landman, N. B. S., and Lucas, S. G. (eds.), Mesozoic geology H., 2001, A revision of the Turonian members and paleontology of the Four Corners region: of the ammonite Subfamily Collignonicerati- Caldwell, W. G. E., and Evans, J. K., 1963, A Cre- New Mexico Geological Society, Guidebook nae from the United States Western Interior taceous rudist from Canada, and a redescrip- 48, pp. 229–232. and Gulf Coast: American Museum of Natural tion of the holotype of Ichthyosarcolites coraloi- Gray, J. E., 1847, A list of genera of recent Mollus- History, Bulletin 267, 148 pp. dea (Hall and Meek): Journal of Paleontology, ca, their synonyms and types: Zoological Soci- Logan, W. N., 1898, The invertebrates of the Ben- v. 37, no. 3, pp. 615–620. ety of London, Proceedings, v. 15, pp. 129–219. ton, Niobrara, and Fort Pierre Groups: Kansas Choffat, P., 1891, Crétacique de Torres Vedras. Griffitts, M. O., 1949, A new rudist from the Nio- University Geological Survey, v. 4, pt. 8, pp. Recueil d’études paléontologiques sur la faune brara of Colorado: Journal of Paleontology, v. 431–518. crétacique du Portugal: I. Espéces nouvelles ou 23, no. 5, pp. 471–472. Miller, H. W., 1968, Invertebrate fauna and envi- peu connues, Comunicaçoes dos Serviços geo- Hall, J., and Meek, F. B., 1856, Descriptions of ronment of deposition of the Niobrara Forma- logicos de Portugal, pp. 203–211. new species of fossils from the Cretaceous for- tion (Cretaceous) of Kansas: Fort Hays Studies Cobban, W. A., 1986, Upper Cretaceous mollus- mations of Nebraska, with observations upon (new series), Science Series 8, 90 pp. can record from Lincoln County, New Mexi- Baculites ovatus and B. compressus, and the pro- Miller, H. W., 1970, Additions to the fauna of the co; in Ahlen, J. L., and Hanson, M. E. (eds.), gressive development of the septa in baculites, Niobrara Formation of Kansas: Transactions of Southwest section of AAPG transactions and ammonites, and scaphites: American Academy the Kansas Academy of Science, v. 72, no. 4, guidebook of 1986 convention, Ruidoso, New of Arts and Science Memoir, new series, v. 5, pp. 533–546. Mexico: New Mexico Bureau of Mines and pp. 379–411. Mudge, B. F., 1876, Notes on the Tertiary and Mineral Resources, pp. 77–89. Hattin, D. E., 1982, Stratigraphy and deposition- Cretaceous periods of Kansas: US Geological Cobban, W. A., Skelton, P. W., and Kennedy, W. al environment of Smoky Hill Chalk Member, and Geographical Survey of the Territories, J., 1991, Occurrence of the rudistid Durania Niobrara Chalk (Upper Cretaceous) of type Bulletin 2, no. 3, pp. 211–221. cornupastoris (Des Moulins, 1826) in the Upper area, western Kansas: Kansas Geological Sur- Reeside, J. B., Jr., 1924, Upper Cretaceous and Cretaceous Greenhorn Limestone in Colorado: vey, Bulletin 225, 108 pp. Tertiary formations of the western part of the U.S. Geological Survey, Bulletin 1985-D, pp. Hook, S. C., and Cobban, W. A., 1981, Late Green- San Juan Basin, Colorado and New Mexico: D1–D8. horn (mid-Cretaceous) discontinuity surfaces, U.S. Geological Survey, Professional Paper 134, Cobban, W. A., Walaszczyk, I., Obradovich, J. southwest New Mexico; in Hook, S. C. (comp.), pp. 1–70. D., and McKinney, K. C., 2006, A USGS zonal Contributions to mid-Cretaceous paleontology Reeside, J. B., Jr., 1955, Revised interpretation table for the Upper Cretaceous middle Ceno- and stratigraphy of New Mexico: New Mexico of the Cretaceous section on Vermilion Creek, manian–Maastrichtian of the Western Interior Bureau of Mines and Mineral Resources, Cir- Moffat County, Colorado; in Anderman, G. G. of the United States based on ammonites, inoc- cular 180, pp. 5–21. (ed.), Green River Basin: Wyoming Geological eramids, and radiometric ages: U.S. Geological Hook, S. C., Mack, G. H., and Cobban, W. A., Association, Guidebook 10, pp. 85–88. Survey, Open-file Report 2006–1250, 46 pp. 2012, Upper Cretaceous stratigraphy and bio- Richards, P. W., 1955, Geology of the Bighorn Dane, C. H., Pierce, W. G., and Reeside, J. B., stratigraphy of south-central New Mexico; in Canyon–Hardin area, Montana and Wyoming: Jr., 1937, The stratigraphy of the Upper Cre- Lucas, S. G., McLemore, V. T., Lueth, V. 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(ed.), Jurassic–Cre- tion, Cretaceous (Maastrichtian), South Dako- Society of America and the University of Kan- taceous biochronology and paleogeography ta, pt. 2, Systematics of the Bivalvia: Yale Uni- sas Press, pp. N749–N751. of North America: Geological Association of versity, Peabody Museum of Natural History, Des Moulins, C., 1826, Essai sur les spherulites Canada, Special Paper 27, pp. 273–306. Bulletin 33, 222 pp. qui existent dans les collections de MM F. Kauffman, E. G., 1985, Depositional history of Stanton, T. W., 1893 [1894], The Colorado forma- Jouannet et C. Moulins, et considerations sur the Graneros Shale (Cenomanian), Rock Can- tion and its invertebrate fauna: U.S. Geological la famille à laquelle ces fossiles appartienment: yon anticline; in Pratt, L. M., Kauffman, E. G., Survey, Bulletin 106, 288 pp. Bulletin de l’Histoire Naturelle Société Lin- and Zelt, F. (eds.), Fine-grained deposits and Williston, S. 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Appendix Compilation of Upper Cretaceous rudistid occurrences in the Western Interior of the United States from published records and unpublished collections housed in the USGS Mesozoic Invertebrate collections in the Denver Federal Center. These occurrences are arranged stratigraphically from lowest (no. 1) to highest (no. 37). Although rudistids are rare faunal elements in the Upper Cretaceous of the Western Interior, there is at least one occurrence from each stage. Geographically, they range from New Mexico (NM) on the south to Saskatchewan (SK), Canada, on the north. CSK = Cobban, W. A., Skelton, P. W., and Kennedy, W. J. (1991).

February 2013, Volume 35, Number 1 New Mexico Geology 19 CSK CSK CSK new CSK CSK CSK CSK CSK CSK CSK CSK CSK CSK CSK CSK CSK CSK CSK CSK CSK CSK CSK new new CSK CSK new CSK CSK CSK Source Same CSK CSK CSK CSK CSK Reference CSK (1991, p. D3-D7) Dane et al. (1937, p. 214) This paper CSK (1991, p. D2) (1984, p. 291) Kauffman CSK (1991, p. D2) CSK (1991, p. D2) observed CSK (1991, p. D2) Hattin (1982, fig. 32) (1949, pp. 471-472) Griffitts CSK (1991, p. D2) Scott et al. (1986, p. 31) CSK (1991, p. D2) Reeside (1955, p. 87) (1984, pp. 293-294) Kauffman CSK (1991, p. D3) This paper Richards (1955, p. 61) Richards CSK (1991, p. D3) (1984, p. 295) Kauffman This paper Reeside (1924, p. 11) Hattin (1982, fig. 31) CSK (1991, p. D3) Fassett et al. (1997, p.229) (1984, p. 295) Kauffman CSK (1991, p. D3) CSK (1991, p. D3) Caldwell and Evans (1963) CSK (1991, p. D3) Speden (1970, p. 157) Logan (1898, p. 494) Hall and Meek (1856, p. 380) Hattin (1982, fig. 31) This paper Kauffman (1985, p.95) Kauffman ------USGS # USGS D11226 D14973, D15025 D9019 D7333 D3467 D6051-52 D11432 D13098 23641 D7763 21214 22177 D9059 D2630, D3567 D13719 D3576 23054 D1349 D88 coraloidea coraloidea coraloidea coraloidea coraloidea coraloidea S. austinensis Taxon cf. Sauvagesia Ichthyosarcolites Durania cornupastoris Sauvagesia ? Durania cornupastoris Durania cornupastoris* aff. aff. rudistids radiolitid rudistids cf. Durania niobrarensis * Durania niobrarensis rudist Durania maxima Durania Sauvagesia cf. S. austinensis Durania D. austinensis Durania aff. Durania rudist ? Ichthyosarcolites Durania Sauvagesia Durania maxima rudist rudist Ichthyosarcolites coraloidea Ichthyosarcolites ? Ichthyosarcolites Durania ? coraloidea Ichthyosarcolites ? Ichthyosarcolites ? Ichthyosarcolites ? Ichthyosarcolites ? sp. Ichthyosarcolites maximus Radiolites Caprinella coraloidea Durania maxima rudist ? Ichthyosarcolites radiolitid State(s) CO CO CO AZ NM NM CO NM CO CO KS CO CO WY NM WY MT MT CO NM KS CO CO NM MT CO, KS, WY MT SK MT MT SD KS SD KS CO CO CO ------Member/Bed Bridge Creek Member Bridge Creek Bridge Creek Member Bridge Creek Limestone Bridge Creek Paguate Tongue Thatcher Limestone lower tongue Fort Hayes Member Fort Hayes Limestone Smoky Hill Member Fort Hayes Limestone Smoky Hill Member Gammon Member Gammon Member Smoky Hill Member Claggett Member Monument Hill Member Matador Sand Member Trail City Member Trail Smoky Hill Member Thatcher Limestone ------Formation Greenhorn Limestone Greenhorn Greenhorn Limestone Greenhorn Formation Greenhorn Shale Mancos Dakota Sandstone Shale Graneros Mancos Shale Mancos Niobrara Formation Niobrara Formation Niobrara Formation Niobrara Formation Mancos Shale Mancos Niobrara Formation Cody Shale Pierre Shale Pierre Shale Pierre Mancos Shale Mancos Shale Mancos Niobrara Lewis Shale Cody Shale Pierre Shale Pierre Bearpaw Shale Bearpaw Shale Bearpaw Shale Niobrara Chalk Fox Hills Sandstone Shale Pierre Niobrara Chalk Shale Pierre Shale Pierre Graneros Shale Graneros ? ------Zone sp. (weak flank ribs) upper? middle Collignoniceras woollgari Collignoniceras woollgari Euomphaloceras septemseriatum Acanthoceras amphibolum Conlinoceras tarrantense Collignoniceras woollgari Cremnoceramus deformis ? Cremnoceramus Scaphites mariasensis ? Cremnoceramus deformis Cremnoceramus Scaphites depressus Scaphites ventricosus Scaphites preventricosus Scaphites hippocrepis Scaphites hippocrepis lower Baculites III Scaphites hippocrepis all Clioscaphites vermiformis Clioscaphites saxitonianus "of Niobrara age" Baculites scotti Baculites asperiformis Exiteloceras jenneyi Exiteloceras jenneyi Didymoceras stevensoni Baculites compressus Hoploscaphites nicolleti [upper] lower Baculites compressus Baculites compressus Conlinoceras tarrantense Stage Cenomanian Cenomanian Turonian Turonian Cenomanian Cenomanian Cenomanian Turonian Coniacian Turonian Coniacian Coniacian Coniacian Coniacian Coniacian Campanian Coniacian Campanian Campanian Santonian Santonian Santonian Coniacian? Campanian Campanian Santonian? Campanian Campanian Campanian Campanian Maastrichtian Campanian Campanian Campanian Campanian Campanian Cenomanian 6 5 8 7 4 3 2 9 1 11 12 10 13 16 15 14 23 17 25 24 22 20 19 18 27 26 21 30 29 28 31 37 36 35 34 33 32 No.

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