lower ordovician (tremadocian) lingulate brachiopods from the house ...

J. Paleont., 79(5), 2005, pp. 884–906 Copyright q 2005, The Paleontological Society 0022-3360/05/0079-884$03.00

LOWER ORDOVICIAN (TREMADOCIAN) LINGULATE BRACHIOPODS FROM THE HOUSE AND FILLMORE FORMATIONS, IBEX AREA, WESTERN UTAH, USA LARS E. HOLMER,1 LEONID E. POPOV,2 MICHAEL STRENG,1

AND

JAMES F. MILLER3

Institute of Earth Sciences, Palaeobiology, Uppsala University, SE-752 36 Uppsala, Sweden, ,[email protected]., ,[email protected]., 2Department of Geology, National Museum of Wales, Cathays Park, Cardiff CF10 3NP, Wales, United Kingdom, ,[email protected]., and 3Geography, Geology, & Planning Department, Missouri State University, Springfield 65804, USA, ,[email protected]. 1

ABSTRACT—Seven genera and eight species of lingulate brachiopods were recovered from the House Limestone and lower Fillmore Formation, Ibex area, Utah, USA. These strata are assigned to the upper Skullrockian Stage and lower Stairsian Stage of the Ibexian Series (Iapetognathus Conodont Zone to Low Diversity Interval) and are correlated with the Tremadocian Series of the Acado–Baltic Faunal Province. The fauna includes two new linguloid species, Spinilingula prisca and Wahwahlingula sevierensis, one new siphonotretoid species, Schizambon obtusus, and two new acrotretoid species, Eurytreta fillmorensis and Ottenbyella ibexiana. The last species is the first record of the genus in North America and suggests a correlation of the basal Fillmore Formation with the Ceratopyge Limestone in Sweden. A Siphonobolus? covered by long hollow spines may be one of the oldest siphonotretides with such ornament. This fauna and those described previously from older Utah strata document the biodiversification of the Cambrian–Ordovician lingulate brachiopods and demonstrate their potential for regional and intercontinental correlation.

INTRODUCTION INGULATE (ORGANOPHOSPHATIC)

brachiopods are poorly documented in lower Ordovician strata in North America. Popov et al. (2002) discussed the taxonomy and established ranges of upper Millardan and lowermost Ibexian brachiopods recovered from conodont samples in the Ibex area of western Utah. In the present report the same authors consider somewhat younger lingulate faunas from the same area. Conodont research by J. F. Miller produced many of the faunas described herein, and Holmer and Miller made additional collections. Brachiopods are from measured sections in which the lithostratigraphy, conodont and trilobite biostratigraphy, and the sequence stratigraphy have been documented (Miller et al., 2001, 2003). Ripperdan and Miller (1995) documented the carbon isotope stratigraphy of some of these strata. Jensen (1967) studied rhynchonelliform (calcitic) brachiopods from Lower Ordovician strata in the same area of Utah, but he did not include data on lingulates.

L

LITHOSTRATIGRAPHY AND MEASURED SECTIONS

Faunas discussed in this report are from the classical Ordovician succession exposed in the House Range and nearby areas in western Millard County, Utah, commonly referred to as the Ibex area. Strata here comprise the type area for the Ibexian Series, the lowest series of the Ordovician System in North America (Ross et al., 1997). The House Range extends ca. 100 km (ca. 60 mi) north-south (Fig. 1) and is a fault-block mountain range that is tilted eastward. Lower Cambrian to lower Triassic strata in the House Range and in the Confusion Range and Wah Wah Mountains to the west were deposited on a rapidly subsiding, tropical, miogeoclinal carbonate platform and are ca. 10.4 km (ca. 34,000 ft) thick (Hintze, 1988, charts 51, 70). Hintze and Davis (2003) discussed all of the stratigraphic units in this thick interval. Evans et al. (2003) discussed the sequence stratigraphy of the portion of this interval that is assigned to the Sauk Sequence. Upper Cambrian and lower Ordovician strata in the central and southern House Range were deformed into a large syncline with gently dipping limbs. The east-west axis of this syncline is located near the position of ‘‘S’’ in the word ‘‘HOUSE’’ on Figure 1. The House Limestone and overlying Fillmore Formation are the lowest of six formations of the Pogonip Group (Hintze, 1951);

exposures of these strata are repeated on both limbs of the syncline. Hintze (1953) discussed the trilobite faunas and biostratigraphy of the Pogonip Group. Hintze (1974a, 1974b) published geologic maps of these areas at scale 1:48,000; Hintze and Davis (2002a, 2002b) published 1:100,000 scale geologic maps. Measured sections on both limbs of the syncline are located on these maps. The type section of the House Limestone is Section A (Hintze, 1951, 1953), which is located on the north limb of the large syncline (location A on Fig. 1). Only three of our collections are from this location (Tables 1, 2); other collections are mostly from exposures on the south limb of the syncline. The Lava Dam North section (location B on Fig. 1) exposes the top 15.2 m (50 ft) of the Lava Dam Member of the Notch Peak Formation, a complete section of the overlying House Limestone, and the basal 1.5 m (5 ft) of the Fillmore Formation (Table 1). Hintze (1973) described the section and Miller et al. (2001, 2003) redescribed it in greater detail. The latter authors divided the House Limestone into the lower Barn Canyon, the middle Burnout Canyon, and the upper Red Canyon members. At Lava Dam North the Barn Canyon Member is 75.6 m (248 ft) thick, the Burnout Canyon Member is 19.5 m (64 ft) thick, and the Red Canyon Member is 69.8 m (229 ft) thick (Fig. 2). The type section of the lower two members is at Lawson Cove in the nearby Wah Wah Mountains (location D on Fig. 1), where Popov et al. (2002) described lingulate brachiopods from the Notch Peak and House Formations. The type section of the Red Canyon Member is at Lava Dam North, where we have one brachiopod collection from the Barn Canyon Member, seven collections from the Red Canyon Member, and two collections from the basal Fillmore Formation (Tables 1, 2). The Fillmore Formation is ca. 550 m (1,800 ft) thick, and the lower half is exposed at the 1965 C section (location C on Fig. 1). Hintze (1973) described this section and indicated it is the type section of the Fillmore Formation; Miller et al. (2003) described the top beds of the House Limestone and redescribed the lower 15.2 m (50 ft) of the Fillmore. At the 1965 C section we have three brachiopod collections from a thick ledge at the top of the Red Canyon Member (see description of lower segment of the 1965 C section in Miller et al., 2003) and 12 collections from the overlying 10.7 m (38 ft) of Fillmore strata (Tables 1, 2). B. F. Dattilo and K. R. Evans (personal commun., 2003) made a reconnaissance of the House–Fillmore interval exposed in the

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Supersequence of Golonka and Kiesling (2002). Sequences 11– 13 are divided into smaller units that Miller et al. (2003) identified as ‘‘packages,’’ which are identified by letters (Fig. 2, Package 11B, 11C, etc.). Those authors identified two prominent intervals of high energy strata that they interpreted as having been deposited during times of low sea level. The first interval includes Packages 11G and 12A (Burnout Canyon Lowstand); the second is Sequence 13 and the lower part of Sequence 14 (Tule Valley Lowstand). Brachiopods have not been recovered from the Burnout Canyon interval, but brachiopods are abundant in strata of the Tule Valley Lowstand. BIOSTRATIGRAPHY

FIGURE 1—Location of measured sections in the House Limestone and lowermost Fillmore Formation, Ibex area, Millard County, Utah. A, Section A of Hintze (1951, 1973) and Miller et al. (2003), type section of House Limestone; B, Lava Dam North section of Hintze (1973) and Miller et al. (2001, 2003), type section for Red Canyon Member of House Limestone; C, 1965 C section of Hintze (1973) and Miller et al. (2003), type section for Fillmore Formation; D, Lawson Cove section of Miller et al. (2001), Popov et al. (2002), and Miller et al. (2003), type section for Barn Canyon and Burnout Canyon members of House Limestone; E, Middle Mountain section.

northwestern Wah Wah Mountains, at Middle Mountain (location E on Fig. 1). They collected and turned over to us a 2 cm thick dark limestone (sample MM in Tables 1, 2) that was covered by hundreds of lingulates. No section was measured, but the sample is from the lower 1–3 m of the Fillmore Formation and is from near the center of the north edge, SE1/4, SW1/4, sec. 28, T23 S, R16 W, Middle Mountain 7.59 Quadrangle, Millard County, Utah, at UTM grid coordinates 269,900 m E, 4,295,450 m N, zone 12. SEQUENCE STRATIGRAPHY

Miller et al. (2003) discussed the sequence stratigraphy of the Sauk III Supersequence and divided most of the Millardan Series and the lower Ibexian Series into 14 sequences. The interval considered in this report include most of their sequence 11, all of sequences 12 and 13, and part of sequence 14 (Fig. 2). Those authors considered sequence 14 to be the base of the Sauk IV

Trilobite and conodont zones established for the House and Fillmore Formations are summarized in Figure 2. The stratigraphic interval considered herein is assigned to three trilobite zones, which were documented by Miller et al. (2003). The Symphysurina Zone is divided into three subzones, the S. brevispicata (bottom), S. bulbosa (middle), and S. woosteri (top) subzones. The S. brevispicata Subzone comprises the uppermost part of the Lava Dam Member of the Notch Peak Formation and the lower part of the Barn Canyon Member of the House Limestone; these strata are below the interval considered in this report. The S. bulbosa Subzone comprises the upper part of the Barn Canyon Member. Faunas assigned to the S. woosteri Subzone are known only from the relatively thin Burnout Canyon Member. The overlying Bellefontia Zone is quite thick and comprises all but the uppermost 4.9 m (16 ft) of the Red Canyon Member. The top of the Red Canyon Member is a prominent 3.0 m (10 ft) ledge that is present at Lava Dam North, the 1965 C section, Section A, and at Middle Mountain. This ledge includes parts of two trilobite zones. At Lava Dam North the Paraplethopeltis Zone begins 1.8 m (6 ft) below this ledge and includes the lower 0.3 m (1 ft) of the ledge itself; the interval is 178.6–180.7 m (586–593 ft) in the described section of Miller et al. (2001, p. 63; 2003); compare with Table 1. Similar precise trilobite biostratigraphic data for other sections are not available. The Leiostegium– Kainella Zone comprises the upper 2.7 m (9 ft) of the ledge at Lava Dam North, and this zone continues into the lower Fillmore Formation. The ledge is indicated by shading in Figure 2; this ledge and the overlying lowest strata of the Fillmore Formation yielded most of the brachiopod collections discussed in this report. Ranges of conodonts are much better established than ranges of trilobites in Ibex sections because of sampling density, so the conodont biostratigraphy is documented in more detail. Lithostratigraphic intervals assigned to these biostratigraphic units in four sections (excluding Middle Mountain) are shown in Figure 2 and are summarized in Table 1. The oldest brachiopods discussed herein are in a collection from near the middle of the Barn Canyon Member in the thin Iapetognathus Zone at Section A (sample A125; 125 refers to footage above base of measured section A). Popov et al. (2002) described other brachiopod collections from this zone and from the overlying Cordylodus angulatus Zone at Lawson Cove. Two brachiopod collections are from the Cordylodus angulatus Zone at Section A (samples A170.5, A190) and one collection is from this zone at Lava Dam North (sample LD219.5). Most of the remaining brachiopod collections are from the thick Rossodus manitouensis Zone, which comprises the uppermost part of the Barn Canyon Member, all of the Burnout Canyon and Red Canyon members, and the lower 4.0 m (13 ft) of the Fillmore Formation. Miller et al. (2003) divided this conodont zone into two subzones of quite unequal thickness, the lower, thin Loxodus bransoni Subzone and the upper, thick ‘‘Paltodus’’ spurius Subzone. The L. bransoni Subzone includes the uppermost strata of

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TABLE 1—Detailed lithostratigraphic, biostratigraphic, and sample data for brachiopod samples. Thicknesses for Lava Dam North section are based on measured footages painted on strata and correspond to sample numbers; to correct for two small faults below the interval sampled, subtract 11 ft (3.4 m) to convert to Composite Thickness numbers used in Table 2 and Figure 2. Presence of ‘‘1’’ following a number indicates the unit extends into overlying strata. Middle Mountain sample (not shown) is from ca. 1–3 m above the base of the Fillmore Formation in a reconnaissance section and probably is from the ‘‘Paltodus’’ spurius Subzone. Lava Dam North section Fillmore Formation 183.5–185.0 m (602–607 ft) House Limestone 15.2–183.5 m (50–602 ft) Red Canyon Member 113.7–183.5 m (373–602 ft) Burnout Canyon Member 94.2–113.7 m (309–373 ft) Barn Canyon Member 15.2–94.2 m (50–309 ft) Low Diversity Interval Rossodus manitouensis 83.2–184.7 m (273–606 ft) Zone ‘‘Paltodus’’ spurius 98.8–184.7 m (324–606 ft) Subzone Loxodus bransoni Sub83.2–98.8 m (273–324 ft) zone Cordylodus angulatus 64.7–83.2 m (213–273 ft) Zone Iapetognathus Zone 59.2–64.7 m (195–213 ft) Brachiopod sample num- LD219.5, 391, 487, 489, 500, bers compare with 589, 594, 599, 603, 606 footages above

South Extension of 1965 C section 4.3–5.2 m (14–17 ft) 0–4.3 m (0–14 ft) 0–4.3 m (0–14 ft)

Main 1965 C section 0.3–15.21 m (1–501 ft) 0–0.3 m (0–1 ft) 0–0.3 m (0–1 ft)

Section A 0.6–79.21 m (2–2601 ft) 71.3–79.21 m (234–2601 ft) 0.6–71.3 m (2–234 ft)

0–5.2 m (0–17 ft) 0–5.2 m (0–17 ft)

4.3–15.21 m (14–501 ft) 0–4.3 m (0–14 ft) 0–4.3 m (0–14 ft)

60.4–80.21 m (198–2631 ft) 76.5–80.21 m (251–2631 ft) 60.4–76.5 m (198–251 ft) 41.5–60.4 m (136–198 ft)

SEC 3.5, 6, 13.5

the Barn Canyon Member and the lower ca. one-third of the Burnout Canyon Member (Fig. 2). The ‘‘P.’’ spurius Subzone comprises ca. the upper two-thirds of the Burnout Canyon, all of the Red Canyon Member, and the lower 4.0 m (13 ft) of the Fillmore Formation at the 1965 C section. All brachiopod collections from the R. manitouensis Zone are from its ‘‘P.’’ spurius Subzone. The three samples from the Southern Extension of the 1965 C section (abbreviated SEC in Table 2 and Fig. 2) are from the upper thick ledge of the House Limestone. Four samples from the lowermost Fillmore at the 1965 C section (abbreviated 65C) are also from the ‘‘P.’’ spurius Subzone. The Middle Mountain sample presumably is also from this subzone. The youngest conodont biostratigraphic unit considered herein is the Low Diversity Interval, which begins 4.0 m (13 ft) above the base of the Fillmore Formation at the 1965 C section. The unusual name of this interval reflects a major conodont extinction at the top of the Rossodus manitouensis Zone that resulted in a major loss of conodont diversity and abundance in the lower part of the Fillmore Formation. Brachiopod collections from the lower Fillmore Formation reflect this faunal turnover in that six samples from the lower part of the Low Diversity Interval have brachiopod faunas with new taxa. Some samples from the top ledge of the House Limestone and the lower beds of the Fillmore Formation have hundreds to thousands of brachiopod shells (Table 2). These collections are from 1–3 kg of limestone; detailed data for the mass, insoluble residue content, and other fossils from most of these samples are in data tables in Miller et al. (2003). Sample MM from Middle Mountain was less than 1 kg and produced ca. 1,500 shells (Table 2). Graptolites with biostratigraphic potential are known from a thin, olive shale in the House Limestone at Lava Dam North (Miller et al., 2001, p. 65, unit 27). Anisograptus matanensis Ruedemann, 1937 occurs at 63.1 m (207 ft) in the measured section; this horizon is within the middle part of the Barn Canyon Member

65C4, 6.5, 8, 10.5, 13, 14, 16, 20, 21, 26, 28 38

36.3–41.5 m (119–136 ft) A125, 170.5, 190

and in the thin Iapetognathus Zone, 1.8 m (6 ft) below its top. The graptolite occurs 3.8 m (12.5 ft) below our lowest brachiopod collection at Lava Dam North (LD219.5). The lowest occurrence of this graptolite is within the third Tremadocian graptolite assemblage of Cooper (1999) in typical graptolite facies, but ranges of such planktic graptolites are not established in shallow, miogeoclinal carbonate platform deposits such as those in Utah. CHRONOSTRATIGRAPHY

The North American chronostratigraphic classifications of the lowest divisions of the Ordovician System are based on strata in the Ibex area of Utah, including the House and Fillmore formations. Nearly all of the House Limestone is assigned to the Skullrockian Stage, the lowest stage of the Ibexian Series. However, the base of the overlying Stairsian Stage is placed at the base of the Leiostegium–Kainella Trilobite Zone, which at Lava Dam North is at composite meterage 177.4 m (582 ft) (Miller et al., 2003). This horizon is 2.7 m (9 ft) below the top of the House Limestone. The highest beds of the House Limestone and strata of the lower Fillmore Formation are referred to the Stairsian Stage, the second stage of the Ibexian Series. Chronostratigraphic assignment of these strata using other classification schemes is problematic. All brachiopod faunas discussed herein are from the Iapetognathus Zone or are younger. All sections in the Ibex area that expose this zone have near its base a distinctive brown trilobite grainstone bed that contains the widespread olenid trilobite Jujuyaspis borealis Kobayashi, 1955. Acenõlaza and Acenõlaza (1992) considered that this genus occurs at or very close to the base of the Tremadocian Series. Using these data, we consider that all of the brachiopods described in this report are assignable to the Tremadocian Series as that term has been used traditionally in the Acado–Baltic Faunal Province. This conclusion is reinforced by the presence of the graptolite →

FIGURE 2—Stratigraphic ranges of linguliform brachiopods relative to chronostratigraphic, lithostratigraphic, sequence stratigraphic units, and biostratigraphic units. Arrows at bottom of taxon ranges indicate those taxa were found in older strata at Lawson Cove by Popov et al. (2002, fig. 2). Sequence stratigraphy after Miller et al. (2003).? F indicates top of range is based on fragments of taxon that are questionably identified. Letters A, LD, C, and SEC indicate sample horizons (shown by tic marks) from section A, Lava Dam North, 1965 C section, and Southern Extension of 1965 C section, respectively. See Table 2 for details.


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TABLE 2—Summary of distribution of brachiopods showing numbers of specimens in samples from the House Limestone and lowermost Fillmore Formation. Samples with prefix A are from Section A, type section of the House Limestone. Samples with LD prefix are from Lava Dam North section. Samples with SEC prefix are from the Southern Extension of 1965 C section. Samples with 65C prefix are from the main 1965 C section. Composite thicknesses are based on Lava Dam North section; samples from other sections are projected into the measured section based on conodont biostratigraphy. Sample 65C4 is a shell bed of the orthid Nanorthis hamburgensis (Walcott). Frags indicates fragments; ? indicates that specimens are identified with question. MM is a reconnaissance sample from Middle Mountain, ca. 1–3 m above base of the Fillmore Formation. Sample

A125

LD219.5

A170.5

A190

LD391

LD487

LD500

LD589

LD593

Composite thickness in meters Composite thickness in feet Eurytreta cf. bisecta (Matthew) Wahwahlingula sevierensis n. sp. Siphonobolus? sp. Schizambon obtusus n. sp. Conotreta millardensis Popov et al. Zhanatellidae? gen. and sp. indet. Glossellinae gen. and sp indet.

59.1 194 27 2

63.6 208.5

72.1 236.5

77.4 254

115.8 380

145.1 476

149.0 489

4

?3

5

3

176.2 578 18 3

177.4 582 87 1

12 1 18

10 4 1 1

4 1 10

Sample

SEC3.5

LD594

SEC6

LD599

LD600

SEC13.5

LD603

65C4

LD606

Composite thickness in meters Composite thickness in feet Eurytreta cf. bisecta (Matthew) Wahwahlingula sevierensis n. sp. Glossellinae gen. and sp. indet. Eurytreta fillmorensis n. sp. Nanorthis hamburgensis (Walcott) Discinidae? gen. and sp. indet. Spinilingula prisca n. sp. Ottenbyella ibexiana n. sp.

177.5 582.5 ?3 ?frags

177.7 583 ?;200 ?frags 10

178.3 585 ?;300 ?frags

179.2 588 ?frags

179.5 589 .1,500 6

180.0 590.5

180.4 592

181.1 594

181.4 595

?frags

4 4 39

Sample

65C6.5

65C8

65C10.5

65C13

65C14

65C16

65C20

65C21

65C26

181.8 596.5

182.3 598

183.0 600.5

183.8 603

184.1 604

184.7 606

185.9 610 ?frags

186.2 611

187.8 616

?frags

13

2

?frags

?3 ?frags

3 29

;70 .2,000

?frags ?frags

Composite thickness in meters Composite thickness in feet Eurytreta cf. bisecta (Matthew) Wahwahlingula sevierensis n. sp. Spinilingula prisca n. sp. Eurytreta fillmorensis n. sp. Ottenbyella ibexiana n. sp.

?frags ?10

many 1 19 39

4 2 ;1,000 ;400

34 ?;20 ;160

?frags ?frags

?frags ?frags

?frags ?frags

Sample

65C28

65C38

MM

Composite thickness in meters Composite thickness in feet Wahwahlingula sevierensis n. sp. Eurytreta fillmorensis n. sp. Ottenbyella ibexiana n. sp.

188.4 618 ?frags ?frags ?frags

191.4 628 ?frags

?ca. 181.4 ?ca. 595 ?frags

Anisograptus matanensis in the Iapetognathus Zone at Lava Dam North. Recently the term Tremadocian was redefined as the lowest stage of the Lower Ordovician Series, and a Global Stratotype Section and Point (GSSP) was chosen to mark the base of the Ordovician System. The boundary stratotype section is at Green Point in western Newfoundland, Canada; strata are part of the Cow Head Group. The boundary point was chosen in the rock sequence 4–5 m below the lowest planktic graptolites so as to coincide with the lowest local occurrence of the conodont Iapetognathus fluctivagus Nicoll, Miller, Nowlan, Repetski, and Ethington, 1999 (Cooper et al., 2001). Correlation of this boundary point to sections in Utah is a complex problem. Miller et al. (2003, p. 104–113) discussed this problem thoroughly, but a brief summary is appropriate. The Cow Head Group is a well-known stratigraphic me´lange that was deposited on the continental slope. Strata at Green Point were deposited near the base of the continental slope and include in situ shales interbedded with redeposited slump deposits, debris slides, and distal turbidites (James and Stevens, 1986). No brachiopods are reported from the Green Point section. Trilobites occur in only two beds; both are debris-slide breccias, one below and one above the boundary horizon. Different limestone clasts from the breccia located below the boundary horizon contain trilobites diagnostic of at least three different zones. Shales yield mostly long-ranging

.1,500

protoconodonts and paraconodonts that are not used for correlation (Barnes, 1988). Biostratigraphically useful euconodonts begin to occur only slightly below the designated boundary. Euconodonts below and above the boundary horizon mostly occur in redeposited slump, slide, and turbidite strata. These conodonts have ranges that indicate they have been redeposited so as to form mixed-age associations, but generally the homotaxial succession is inverted (Miller et al., 2003, fig. 63). The defined base of the Ordovician System is within this redeposited, inverted succession and is 4–5 m below the oldest biostratigraphically useful graptolites. The problems with redeposited fossils at Green Point were documented at three conferences (Miller et al., 1998a, 1998b; Miller and Flokstra, 1999), but the section was nevertheless designated as the global stratotype for the Cambrian–Ordovician boundary (Cooper et al., 2001). We cannot say where in the Utah stratigraphic succession we should correlate the Cambrian–Ordovician boundary established at Green Point. Our brachiopod faunas are from the upper Skullrockian and lower Stairsian stages of the Ibexian Series, and they can be correlated with the traditional Tremadocian Series of the Acado–Baltic faunal province. However, we cannot determine which of our brachiopod faunas are from strata that may correlate with the uppermost Cambrian strata at Green Point and which faunas may correlate with the lowermost Ordovician.

HOLMER ET AL.—LOWER ORDOVICIAN LINGULATE BRACHIOPODS FROM UTAH DEPOSITIONAL ENVIRONMENTS

The House Limestone and lowest Fillmore Formation include many varieties of limestone, but most of the conodont samples that yielded brachiopods are from either lime mudstones or finegrained lime grainstones. These lithologies indicate low to moderate energy levels and depositional environments slightly above to slightly below fair-weather wave base. Three samples represent higher energy, shallower-water facies, probably considerably above fair-weather wave base. Of the three high-energy samples, LD219.5 and LD589 are fine-grained lime grainstones from two different sea-level lowstand intervals. The third sample, 65C10.5, is from a flat-pebble conglomerate that is clast-supported and has clasts up to 23 cm (9 in) across, indicating very high energy levels, although the clasts consist of lime mudstone. This sample is from the interval that Miller et al. (2003) interpreted as the shallowest part of the Tule Valley Lowstand. The lime mudstone in the clasts suggests relatively low-energy conditions, and the clasts may have formed during a subsequent storm. The entire interval shown in Figure 2 was sampled for conodonts, and all but one sample horizon yielded conodonts. However, most of the samples that yielded brachiopods are clustered near the top (Fig. 2). Many collections and also several extremely abundant brachiopod collections are from the thick ledge at the top of the House Limestone and from the lowermost beds of the Fillmore Formation. These strata are mostly very dark limestone (mostly lime mudstone) interpreted by Miller et al. (2003) as deposits of the Tule Valley Lowstand. The lowest part of the overlying Low Diversity Interval is also part of this lowstand and also has abundant linguliform brachiopods. Most of our brachiopod collections and the most abundant collections are from relatively shallow-water facies with moderate- to low-energy conditions. The lack of specimens from shallower, high-energy facies could be due to unfavorable environmental conditions or to excessive fragmentation of specimens. Nearly all of the brachiopods are from conodont samples that were processed in a uniform manner, so abundance of shells is unlikely to be due to variations in processing technique. Two shell beds with abundant rhynchonelliform brachiopods also occur near the House–Fillmore boundary. The lower bed at LD591.5 is near the top of the House Limestone. Jensen (1967) documented the occurrence of calcitic brachiopods and reported the orthids Syntrophina campbelli (Walcott, 1908) and Nanorthis hamburgensis (Walcott, 1884) from this bed, which is within the thin Paraplethopeltis Zone. The second shell bed is 1.2 m (4 ft) above the base of the 1965 C section; this bed is 0.9 m (3 ft) above the base of the Fillmore Formation and also contains Nanorthis hamburgensis. These two shell beds beds are from geographically close sections and are separated by only about 4.9– 5.5 m (16–18 ft) of strata. Miller et al. (2003) interpreted both shell beds to be within the Tule Valley Lowstand. The depositional environment of one sample, 65C21, is of special interest because the weathered surface has abundant sponge spicules in addition to numerous lingulate brachiopods. The spicules are mostly monaxons and retain their original calcite composition (Fig. 3.5, 3.6), so they are never present in acid residues of samples processed for conodonts. Thus, the distribution and abundance of spicules could not be checked using standard etching techniques. The spicules are not clearly observable on polished sections, peels, and thin sections, possibly due to recrystallization. Consequently, one bedding surface from sample 65C21 (Fig. 3) was partially etched in the laboratory in order to examine the distribution of brachiopods and sponge spicules over the surface. More than 2,000 brachiopods where obtained from the sample, over 90% of which represent Ottenbyella ibexiana n. sp. (Table 2). It is also clear from the partially etched surface that the

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shells of O. ibexiana are concentrated and best preserved (including complete articulated shells) in the area with the densest accumulation of sponge spicules (Fig. 3.7, 3.8). K. Rigby Sr. examined photographs of this association (Fig. 3.1–3.6) and suggested (personal commun., 2003) that the spicules are from root tufts of sponges. This sample is from only ca. 8 ft (2.4 m) above the shallowest part of the Tule Valley Lowstand, but the sample is from the transgressive part of the next sequence and formed in somewhat lower energy, deeper-water conditions compared with underlying strata. The delicate nature of the well-preserved spicules and shells (Fig. 3) indicates that the assemblage cannot have been transported any significant distance, and the association may be more or less in situ. The close association between lingulate brachiopods and sponge-dominated environments has been noted previously by Popov et al. (1994) from Upper Ordovician strata of Estonia, as well as most recently by Mergl (2002) from the Ordovician of Bohemia (see also Percival et al., 1999 for a discussion of this life habit). Direct evidence for the lingulate-sponge association comes mainly from the Cambrian Burgess Shale, where the paterinid Micromitra Meek, 1873 is attached to the sponge Pirania Walcott, 1920 (e.g., Conway Morris et al., 1982, p. 25, pl. r), as well as from the Silurian of Canada, where the enigmatic linguloid Paterula Barrande, 1879 is found attached around the oscular margin of sponges (Lenz, 1993). SIGNIFICANCE OF THE FAUNA

The brachiopod faunas are significant from several perspectives. The faunas are important taxonomically because five new species are present (Fig. 2). Conotreta millardensis Popov, Holmer, and Miller, 2002 is now known from additional samples and localities, so its range is better established than when Popov et al. (2002) named it from a single abundant sample. The evolutionary lineage of Eurytreta Rowell, 1966 has been extended from the base of the Ibexian Series (middle Lava Dam Member) into the lower Stairsian Stage (lower Fillmore Formation). The overall fauna is not very diverse compared with coeval faunas from central Asia documented by Holmer et al. (2001), but this low diversity is typical of slightly older faunas described from the Ibex area by Popov et al. (2002). The most significant biogeographical information is the occurrence in Utah of Ottenbyella Popov and Holmer, 1994, which previously was known only from the Ceratopyge Limestone at ¨ land in southeast Sweden, from the Ottenby on the island of O Bjørka˚sholmen Limestone of Sweden and the Oslo Region, Norway, and from apparently coeval strata in the Malyi Karatau in Kazakhstan. The presence of Ottenbyella in Utah also provides a biostratigraphic link to Sweden, Norway, and Kazakhstan and suggests that the lowest part of the Fillmore Formation in Utah correlates with the Ceratopyge Limestone in Sweden and the Bjørka˚sholmen Limestone in Sweden and Norway. Ottenbyella occurs through 6.6 m (21.5 ft) of the lowermost Fillmore Formation in the 1965 C section (Table 2), at 363 and 382 m in the Batyrbay section in Kazakhstan (Holmer et al., 2001), and through a little more than one meter of strata in Sweden. The potential biostratigraphic usefulness of the brachiopods is enhanced because most of the material was recovered from thick, well-described sections in which the trilobite and conodont biostratigraphy are well known. Some taxa described from slightly older strata in Utah by Popov et al. (2002) are now known to extend somewhat higher, e.g., Eurytreta cf. bisecta (Matthew, 1901), Conotreta millardensis, and Wahwahlingula sevierensis n. sp. These faunas help to characterize strata that comprise the type areas of the Millardan Series and the Ibexian Series.

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FIGURE 3—1–8, Partially etched bedding surfaces from sample 65C21 showing distribution of brachiopods (mostly Ottenbyella ibexiana n. sp.) and sponge spicules. 1–6, USNM 526090, 1, complete ventral valve of O. ibexiana, 313, 2, accumulation of mostly fragmented sponge spicules, 328, 3, two long spicules, 345, 4, accumulation of mostly fragmented sponge spicules, 328, 5, detail of calcite spicule, 3850, 6, detail of calcite matrix, 3360; 7, 8, USNM 526091, bedding surface with accumulation of well-preserved and mostly complete shells of O. ibexiana in area with densest accumulation of sponge spicules (indicated by dashed lines and arrows) (white bar scale is 1 mm), 37, detail of two complete articulated shells of O. ibexiana, 330, respectively.

HOLMER ET AL.—LOWER ORDOVICIAN LINGULATE BRACHIOPODS FROM UTAH BRACHIOPOD FAUNAL ASSOCIATIONS

By combining data of this report with data from Popov et al. (2002, fig. 3), we identify several distinct brachiopod faunal associations in the Notch Peak, House, and lower Fillmore Formations. These faunas appear to have potential for biostratigraphic correlation, although no zones can be established at this time. The association of Quadrisonia lavadamensis Popov, Holmer, and Miller, 2002 and Zhanatella utahensis Popov, Holmer, and Miller, 2002 is confined to the uppermost Millardan Series (Upper Cambrian); these taxa disappear at the base of the Ibexian Series. No linguliform brachiopods are known at present from the thin Eurekia apopsis Trilobite Zone at the base of the Ibexian Series. The next interval of strata, the Cordylodus proavus and C. intermedius conodont Zones, is characterized by Eurytreta sublata Popov in Koneva and Popov, 1988, which apparently is the oldest species of the genus. The third brachiopod association consists of Eurytreta cf. bisecta and Schizambon typicalis Walcott, 1884 and occurs in the Cordylodus lindstromi sensu lato and C. angulatus conodont Zones. These brachiopods are joined in the Cordylodus angulatus Zone by Siphonobolus? sp., Schizambon obtusus n. sp., and Conotreta millardensis to form a fourth association; the last species continues to near the top of the House Limestone. The fifth brachiopod association is in the lowermost Fillmore Formation and includes Eurytreta fillmorensis n. sp., Ottenbyella ibexiana n. sp., and Spinilingula prisca n. sp., although the tops of the ranges of these species are not established. These changing faunal associations document the biodiversification of linguliform brachiopods in Laurentia during latest Cambrian and earliest Ordovician time. Two major events punctuated this biodiversification. The first is at the base of the Ibexian Series, where a major faunal turnover among trilobites and conodonts is accompanied by a change in both linguliform and rhynchonelliform brachiopods. The Skullrockian Stage is characterized by diversification in the Eurytreta evolutionary lineage, which continued into the Stairsian Stage. This diversification pattern is similar to that of Skullrockian trilobite and conodont faunas (Miller et al., 1999). The second punctuation event in the development of Ordovician linguliform brachiopods is a faunal turnover at the base of the Fillmore Formation (Fig. 2). This brachiopod turnover is slightly above the trilobite turnover at the top of the Skullrockian Stage and slightly below the conodont turnover at the top of the Rossodus manitouensis Zone. These two intervals of major faunal turnover, near the base and near the top of the Skullrockian Stage, were identified by Stitt (1983) as trilobite biomere boundaries and by Miller et al. (2003) as major sequence boundaries associated with sea-level lowstands. These two faunal turnovers affected brachiopods, conodonts, and trilobites and were utilized by Ross et al. (1997) as important chronostratigraphic boundaries for the base of the Ibexian Series and for the base of the Stairsian Stage. SYSTEMATIC PALEONTOLOGY

Measurements (in millimeters if not stated otherwise) are as follows (for location of measurements, see Holmer et al., 1996, fig. 2): W, L, T 5 width, length, height of valve; Iw, Il 5 width, maximum length of pseudointerarea; Pw 5 width of median groove or pedicle groove; Pl 5 median length of pseudointerarea; Il, Iw 5 maximum length and width of pseudointerarea; Cw, Cl 5 width, length of cardinal muscle field; Vl 5 length of visceral area; Sa 5 length of median septum; Sm 5 position of maximum height of dorsal median septum; Sp 5 point of origin of median septum; OR 5 observed range, X 5 average value; S 5 standard deviation, N 5 number of measurements, MAX, MIN 5 maximum and minimum values. The illustrated and discussed material is deposited in National

891

Museum of Natural History, Washington (USNM), and in National Museum of Wales, Cardiff (NMW). Class LINGULATA Gorjansky and Popov, 1985 Order LINGULIDA Waagen, 1885 Superfamily LINGULOIDEA Menke, 1828 Family OBOLIDAE King, 1846 Subfamily OBOLINAE King, 1846 Genus SPINILINGULA Cooper, 1956 SPINILINGULA PRISCA new species Figure 4 Diagnosis.Elongate Spinilingula with strongly acuminate ventral posterior margin; ventral pseudointerarea narrow and high, subtriangular; dorsal pseudointerarea undivided, crescent-shaped; oblique ribs forming a divaricate pattern with terraces. Description.Shell slightly dorsibiconvex, inequivalved, strongly elongate suboval in outline, with maximum width somewhat anterior to midvalve. Ventral valve very gently convex in sagittal profile, about 160%–180% as long as wide. Ventral posterior margin strongly acuminate, with gently curved lateral sides diverging from the apex. Ventral pseudointerarea narrow and high, subtriangular, about 70%–80% as long as wide, and occupying up to about 30% of the valve length and 60%–70% of the valve width. Pedicle groove narrow and shallow, with anterior median projection dividing ventral umbonal muscle scar. Propareas slightly raised, divided by flexure lines. Dorsal valve about 130%–150% as long as wide, with rounded posterior margin and gently convex sagittal profile, with maximum height posterior to midvalve. Dorsal pseudointerarea undivided, crescent-shaped, not raised above the valve floor, occupying about 20%–30% of the valve length and 60%–70% of the valve width. Ventral interior lacking distinctive features, apart from divided umbonal muscle scars. Dorsal interior with weakly impressed visceral area, extending as a narrow anterior tongue slightly anterior to midvalve. Shell surface covered by numerous thin growth lamellae bearing short, flattened marginal spines at the end of the oblique ribs, about 60–100 mm apart, forming a characteristic divaricate ornamentation with terraces. Etymology.After Latin priscus, ancient. Type.Holotype, USNM 526098, dorsal valve, lower part of Fillmore Formation, ‘‘Paltodus’’ spurius Subzone, sample LD606, from Lava Dam North section, Utah. Other material examined.Total of 21 ventral and dorsal valves. Occurrence.Lower part of Fillmore Formation, upper part of ‘‘Paltodus’’ spurius Subzone and lower part of Low Diversity Interval, Lava Dam North and 1965 C sections (Fig. 2, Table 2). Discussion.Spinilingula prisca is the earliest known species of the genus. It is easily discernable from S. bracteata Krause and Rowell, 1975, which occurs in the Middle Ordovician (Whiterockian) Antelope Valley Limestone of Nevada, in having a distinctly elongated shell with a strongly acuminate posterior ventral margin, as well as oblique ribs forming a divaricate pattern with terraces. In contrast, the ribbing pattern of S. bracteata is arranged in a more regular radial manner. In ornamentation, S. prisca resembles S. radiolamellosa Holmer, 1989, from the Ordovician Furudal and Ka¨lla limestones of Sweden, but the former can be easily distinguished from the latter in having a more elongated shell outline with an acute ventral umbonal area, a high, triangular ventral pseudointerarea, as well as a wide, undivided, crescentshaped dorsal pseudointerarea. Subfamily GLOSSELLINAE Cooper, 1956 Genus and species INDETERMINATE Figure 5.1–5.5 Material examined.Six ventral and 19 dorsal valves. Occurrence.Barn Canyon and Red Canyon members and

892


FIGURE 4—Spinilingula prisca n. sp., Fillmore Formation, ‘‘Paltodus’’ spurius Subzone, sample LD606, Lava Dam North section. 1, 2, USNM 526092, ventral valve exterior, 312, lateral view, 322, respectively; 3, USNM 526093, ventral valve exterior, 324; 4, 5, USNM 526094, ventral valve interior, 317, detail of pseudointerarea, 334, respectively; 6, USNM 526095, dorsal valve interior, 324; 7, USNM 526096, dorsal valve interior, 317; 8, USNM 526097, ventral valve interior, 315; 9–14, Holotype, USNM 526098, dorsal valve exterior, 39, lateral view, 310, oblique posterior view, 320, details of ornamentation, 380, 3200, 340, respectively.

lower beds of Fillmore Formation, ‘‘Paltodus’’ spurius Subzone, Section A and Lava Dam North section (Fig. 2, Table 2). Discussion.The dorsal posterior margin is only thickened, and a well-defined pseudointerarea is absent, which indicates that this form belongs within the subfamily Glossellinae. If this is correct, the rare and invariably fragmented valves illustrated here represent the oldest record of this group, which is otherwise know only from the Arenigian through the Ashgillian (Holmer and Popov, 2000, p. 54). Family ZHANATELLIDAE Koneva, 1986 Genus and species INDETERMINATE Figure 5.6–5.9 Material examined.Two dorsal valves. Occurrence.In two samples, one from the Barn Canyon Member, Cordylodus angulatus Zone, Section A; the other from

the Red Canyon Member, upper part of ‘‘Paltodus’’ spurius Subzone, Lava Dam North section (Fig. 2, Table 2). Discussion.The dorsal valve of this extremely rare form is closely similar to that of the Zhanatellidae, which are characterized by having finely pitted microornamentation on the juvenile and adult shell. Popov et al. (2002) described Zhanatella utahensis from the Upper Cambrian Millardan Series at Lawson Cove, but the new Ordovician form clearly differs from the Cambrian species in details of the microornament; the mature shell of Z. utahensis is covered by lenticular pits (up to 11 mm across), with smaller circular interspatial pits (less than 1 mm across), whereas the Ordovician form only has lenticular pits (ca. 7–11 mm across), but lacks the interspatial pits (Fig. 5.8). The larger and smaller pits in the Zhanatellidae were interpreted as the imprints of proteinaceous and mucinous vesicles, respectively, by Williams (2003). One of the dorsal valves has a circular hole, about 50 mm


893

FIGURE 5—Glossellinae genus and species indeterminate, Fillmore Formation, ‘‘Paltodus’’ spurius Subzone, samples LD593 (1, 2), LD606 (3–5), Lava Dam North section. 1, 2, USNM 526099, dorsal valve exterior, 332, detail of ornamentation, 3130, respectively; 3, USNM 526100, oblique posterior view of dorsal valve exterior, 340; 4, USNM 526101, lateral view of dorsal valve interior, 330; 5, USNM 526102, lateral view of dorsal pseudointerarea, 336. 6–9, USNM 526103, Zhanatellidae, genus and species indeterminate, Red Canyon Member, sample LD593, Lava Dam North section; dorsal valve exterior, 336, oblique posterior view, 340, detail of pitted mature ornamentation, 3600, possible predatory drill hole, 3150, respectively.

across, with a countersunk rim (Fig. 5.9); the morphology is consistent with other reported predatory drilling holes (e.g., Kowalewski et al., 1998). Genus WAHWAHLINGULA Popov, Holmer, and Miller, 2002 WAHWAHLINGULA SEVIERENSIS new species Figures 6, 7 Wahwahlingula sp. POPOV, HOLMER, 4.17–4.19 (partim).

AND

MILLER, 2002, p. 221, fig.

Diagnosis.Ventral pseudointerarea subtriangular, occupying more than half of the valve width; propareas low, narrow, with fine flexure lines; dorsal pseudointerarea low and not raised above the valve floor; median groove poorly defined; ventral visceral area occupying about half of the valve length; dorsal median ridge poorly defined to completely absent; mature shell with up to five fine growth lamellae, and microornament of close-packed hemispherical to semiellipsoidal pits, 1–3 mm across; first-formed and brephic shells present on both valves, covered by circular to oval, sometimes cross-cutting, flat-bottomed pits up to about 2.5 mm across. Description.Shell slightly dorsibiconvex, elongate suboval to subtriangular in outline, with maximum width slightly anterior to midlength (in mature specimens more than 5 mm in length). Ventral valve gently convex, on average 130% as long as wide, with acuminate umbo. Ventral pseudointerarea subtriangular, occupying up to about 60% of total valve width and 25% of the valve length. Pedicle groove shallow, triangular, occupying up to about 15% of width of pseudointerarea. Propareas low, narrow; adults have fine flexure lines expressed by a deflection of growth lines.

Dorsal valve, on average 118% as long as wide, gently convex in lateral profile, with rounded umbonal area. Dorsal pseudointerarea low and not raised above the valve floor. Median groove weakly defined and usually observed only in the largest specimens. Visceral areas, muscle scars, and baculate mantle canals weakly impressed in both valves and observable only in the largest specimens. Ventral visceral area occupying up to about 50% of the valve length and bisected by impression of pedicle nerve (becoming obscured in the largest shells). Ventral vascula lateralia arcuate, submarginal. Dorsal visceral area occupies up to about 75% of the valve length, terminating with long narrow anterior tongue bearing a pair of small elongate suboval impressions of the outside lateral muscle scars near its distal end. Dorsal vascula media short, closely placed, subparallel; vascula lateralia arcuate, submarginal. Median ridge poorly defined to completely absent. Possible first-formed shell present on both valves, transversely oval, about 100–130 mm wide, delineated from the brephic shell by raised rim. First-formed shell covered by circular to oval, sometimes cross-cutting, flat-bottomed pits up to about 2.5 mm across. Ventral first-formed shell with well-defined raised area forming a tubular apical projection around the pedicle notch (Fig. 6.19). Brephic shell of both valves up to about 250–300 mm wide, with pitted microornamentation identical to that of the firstformed shells. Mature shell with up to five fine growth lamellae. Mature microornament of close-packed hemispherical to semiellipsoidal pits, varying in size, 1–3 mm across. Etymology.After Sevier Lake, near the type locality. Type.Holotype, USNM 526104, dorsal valve, lower part of

894


HOLMER ET AL.—LOWER ORDOVICIAN LINGULATE BRACHIOPODS FROM UTAH Fillmore Formation, upper part of ‘‘Paltodus’’ spurius Subzone, sample 65C8, 1965 C section, Utah. Measurements.See Table 3. Other material examined.Ninety-six ventral and dorsal valves and numerous fragments. Occurrence.Barn Canyon and Red Canyon members and lower part of Fillmore Formation; Iapetognathus and Cordylodus angulatus Zones, ‘‘Paltodus’’ spurius Subzone, Low Diversity Interval; Sections A and C, Lava Dam North section, and Middle Mountain (Fig. 2, Table 2). Discussion.This species is comparable only with the type species Wahwahlingula antiquissima (Jeremejew, 1856) as described by Popov et al. (1989, 2002) in general shell shape and outline, in morphology of pseudointerareas, and in having a finely pitted microornament. However, it can be distinguished from W. antiquissima in having a very poorly developed to absent dorsal median groove, and in possessing a larger ventral visceral area, occupying up to half the valve width. The first-formed and juvenile shells have not been observed in the type species. The flatbottomed circular and cross-cutting pits on the juvenile (firstformed plus brephic) shell of W. sevierensis (Fig. 6.22, 6.23) are similar to those found on the juvenile shell of some linguloids (e.g., Paterula) and acrotretoids (e.g., Opsiconidion Ludvigsen, 1974). Williams (2003) interpreted these pits as imprints of mineralized tablets, and this interpretation is accepted here. The mineralogy of the tablets could have been either calcitic or phosphatic. The mature pitted microornamentation of W. sevierensis differs from that of the type species in having a smaller size range of 1–3 mm compared to 6–8 mm, respectively (Cusack et al., 1999, p. 809, pl. 1). The mature pits can be interpreted as the imprints of proteinaceous vesicles (Williams, 2003); however, the interspaces and larger pits of W. antiquissima are provided with shallow, flat-bottomed, subhexagonal smaller pits (0.6–1.2 mm across) that sometimes actually contain the phosphatic tablets that caused the imprints (Cusack et al., 1999, pl. 1; see also Williams, 2003, pl. 4, fig. 8, text-fig. 5). The latter type of imprint was not observed in W. sevierensis. The specimens of Wahwahlingula sp. described by Popov et al. (2002) from the Upper Cambrian Cambrooistodus minutus Conodont Subzone to the Lower Ordovician Rossodus manitouensis Conodont Zone may represent at least two closely related species, but they were represented only by juvenile specimens, which makes their precise taxonomic discrimination impossible. However, the specimens from the Barn Canyon Member of the Lava Dam North section of Utah illustrated by Popov et al. (2002, fig. 4.17–4.19) most likely belong to Wahwahlingula sevierensis. ?Family DISCINIDAE Gray, 1840 Genus and species INDETERMINATE Figure 8 Material examined.One incomplete dorsal valve. Occurrence.Lower beds of Fillmore Formation, ‘‘Paltodus’’ spurius Subzone, sample LD606, Lava Dam North section.

895

TABLE 3—Wahwahlingula sevierensis n. sp., average dimensions and ratios of ventral and dorsal valves from samples C8 and LD219.5. For abbreviations, see text. Ventral valves N X S Min Max

Dorsal valves

L

W

L/W

L

W

L/W

5 4.05 3.12 1.00 7.90

5 3.17 2.55 0.88 6.24

5 130.4% 17.0 113.6% 158.4%

4 4.28 3.46 0.64 7.36

4 3.63 3.00 0.60 6.48

4 118.6% 12.5 106.7% 133.3%

Discussion.The single fragmentary dorsal valve has a very distinctive ornamentation with strong, regular concentric rugellae, 80–140 mm apart, superposed on lower radial capillae, 30–80 mm apart. The juvenile shell is not preserved, but the mature shell has a microornament with circular to oval hemispherical pits about 2–6 mm across; this pitted microornament is quite similar to that of the Zhanatellidae, but a radial capillate ornament is unknown within this group and suggests affinity to the Discinidae. Order SIPHONOTRETIDA Kuhn, 1949 Superfamily SIPHONOTRETOIDEA Kutorga, 1848 Family SIPHONTRETIDAE Kutorga, 1848 Genus SIPHONOBOLUS Havlıćˇek, 1982 SIPHONOBOLUS? sp. Figure 9 Material examined.One dorsal valve. Occurrence.Barn Canyon Member, Cordylodus angulatus Zone, sample LD219.5, Lava Dam North section. Discussion.The single fragmentary dorsal valve with long hollow spines is possibly among the oldest-known siphonotretides with that kind of ornament. Its precise generic assignment cannot be defined because of lack of information on the morphology of the ventral valve. However, the raised anacline undivided dorsal interarea suggests that it may belong to Siphonobolus, otherwise known from the late Tremadocian and early Arenigian of Bohemia (Havlıćˇek, 1982), South Urals (Popov and Holmer, 1994), and Holy Cross Mountains, Poland (Holmer and Biernat, 2002). Family SCHIZAMBONIIDAE Havlıćˇek, 1982 Genus SCHIZAMBON Walcott, 1884 SCHIZAMBON OBTUSUS new species Figure 10 Diagnosis.Shell strongly ventribiconvex with slightly sulcate dorsal valve; pedicle track short and narrow, partly covered by short posterior plate; ventral pseudointerarea apsacline; ornament of nodes, pustules, and solid blunt ‘‘spines’’ formed at intersection of concentric lamellae and radial parvicostellae. Description.Shell strongly ventribiconvex, subcircular in outline. Ventral valve strongly convex, with maximum height between midlength and one-quarter of valve length from the umbo,

← FIGURE 6—Wahwahlingula sevierensis n. sp., Fillmore Formation, ‘‘Paltodus’’ spurius Subzone, sample 65C8 (1–17), 1965 C section; sample LD606 (19–23), Lava Dam North section; Low Diversity Interval, sample 65C21 (18). 1–5, Holotype, USNM 526104, ventral valve exterior, 350, lateral view, 355, oblique posterior view, 3120, edge of brephic shell, 3240, pitted ornamentation, 3500, respectively; 6–9, USNM 526105, ventral valve exterior, 324, oblique posterior view, 330, oblique posterior view of umbo, 3120, ornamentation of brephic and early mature shell, 3240, respectively; 10, USNM 526106, ventral valve interior, 328; 11, USNM 526107, ventral pseudointerarea, 324; 12, USNM 526108, dorsal valve exterior, 324; 13, 14, USNM 526109, dorsal valve interior, 326, oblique anterolateral view, 330, respectively; 15, 16, USNM 526110, ventral valve interior, 324, oblique anterolateral view of pseudointerarea, 355, respectively; 17, USNM 526111, lateral view of dorsal umbo, 3170; 18, USNM 526112, dorsal valve interior, 334; 19, USNM 526113, oblique posterolateral view of ventral umbo, 390; 20–23, USNM 526114, lateral view of dorsal umbo with position of 23 indicated, 3110, first-formed shell, with position of 22 indicated, 3200, pitted ornamentation of firstformed shell, 32,000, pitted ornamentation of brephic shell, 3360, respectively.

896


FIGURE 7—Wahwahlingula sevierensis n. sp., House Limestone, Cordylodus angulatus Zone, Barn Canyon Member, sample LD219.5 (1–13), Red Canyon Member, sample LD593 (14–17), Lava Dam North section, Utah. 1, USNM 526115, ventral valve exterior, 38; 2, 3, USNM 526116, ventral valve exterior, 39, lateral view, 310, respectively; 4, 5, USNM 526117, ventral pseudointerarea, 39, lateral view of pseudointerarea, 39, respectively; 6–9, USNM 526118, oblique anterior view of dorsal valve interior, 37, oblique anterior view of dorsal pseudointerarea, 312, dorsal valve interior, 39, lateral view of dorsal interior, 313, respectively; 10, 11, USNM 526119, oblique anterior view of ventral valve interior, 38, oblique anterior view of ventral pseudointerarea, 313, respectively; 12, 13, USNM 526120, lateral view of dorsal valve exterior, with position of 13 indicated, 38, detail of pitted mature ornamentation, 3280, respectively; 14–16, USNM 526121, dorsal brephic valve exterior with position of 15 indicated, 375, boundary between first-formed and brephic shell with position of 16 indicated, 3320, pitted ornamentation of first-formed shell, 31,300, respectively; 17, USNM 526122, oblique posterolateral view of dorsal first-formed shell, 3150.


897

FIGURE 9—1–3, USNM 526124, Siphonobolus? sp., Cordylodus angulatus Zone, Barn Canyon Member, sample LD219.5, Lava Dam North section; dorsal valve exterior, 315, lateral view, 322, posterior view, 315, respectively.

FIGURE 8—1–5, USNM 526123, ?Discinidae genus and species indeterminate, ‘‘Paltodus’’ spurius Subzone, Fillmore Formation, sample LD606, Lava Dam North section, dorsal valve exterior, 330, lateral view, 336, ornamentation, 370, detail showing concentric rugellae, superposed on lower radial capillae, 3144, pitted mature ornamentation, 3560, respectively.

about 90%–95% as long as wide, and less than 20% as high as long. Ventral pseudointerarea strongly apsacline, convex in transverse profile, low, undivided, poorly delineated laterally, occupying less than half the valve width. Pedicle foramen short, elongate oval to triangular, up to about 340 mm long and 200 mm wide in the largest specimen (2.5 mm long), and covered posteriorly by a very poorly developed short plate (about 70 mm wide and 100 mm long). In one specimen also the anterior end of the foramen is partly covered by a narrow, concave plate. Pedicle foramen leads into internal tube. Dorsal valve about 80%–85% as long as wide, gently convex, less than 10% as high as long, with shallow sulcus originating in the umbonal area and fading anterior to midvalve. Dorsal pseudointerarea close to orthocline, low and narrow, occupying somewhat more than half of the valve

width and less than 10% of the valve length. Median groove triangular, occupying about 40% of the width of the pseudointerarea. Ventral interior with rather weakly impressed visceral area, occupying slightly less than one-third of the valve length. Ventral muscle fields tripartite, with a large oval central field, posterolateral and umbonal fields. Internal tube circular, 200 mm across, inclined anteromedially, with umbonal muscle field directly posterolateral to tube. Dorsal visceral area weakly impressed, dominated by a pair of large elongate suboval central muscle scars, directly posterior to the proximal end of the short median tongue, projecting anterior to midvalve, and terminating with a pair of small anterior lateral muscle scars. Juvenile shells of both valves smooth, about 200–300 mm wide. Dorsal juvenile shell with two low bulbous lateral nodes and a median depression. Ventral juvenile shell with central bulbous node projecting over pseudointerarea. Juvenile pedicle foramen partly closed by small plate. Mature shell with concentric lamellae (ca. 30–40 mm apart) with upturned edges, about 1 mm high, superimposed on sharp parvicostellae (ca. 20–30 mm apart), less than 2 mm high. Ornament of low nodes (on early mature shell) to higher pustules, more than 5 mm high, and ‘‘spines,’’ up to 59 mm high (on late mature shell), forming at the intersection between lamellose and parvicostellate ornament. Etymology.Latin obtusus, blunt, obtuse, referring to the blunt ‘‘spines’’ of this species. Type.Holotype, USNM 526127, ventral valve; Barn Canyon

TABLE 4—Eurytreta fillmorensis n. sp., average dimensions and ratios of dorsal valves from sample LD606. For abbreviations, see text.

N X S Min Max N X S Min Max

L

W

T

Il

Iw

Cl

Cw

Sa

Sm

Sp

10 0.97 0.224 0.52 1.30

10 1.09 0.265 0.58 1.54

10 0.19 0.076 0.08 0.54

10 0.10 0.032 0.06 0.14

10 0.48 0.130 0.24 0.64

10 0.29 0.075 0.14 0.40

10 0.65 0.173 0.30 0.92

10 0.75 0.239 0.34 1.10

8 0.59 0.109 0.34 0.68

10 0.20 0.058 0.10 0.30

L/W

T/L

Iw/W

Cl/L

Cw/W

Sm/L

Sa/L

Sp/L

10 89.5% 5.47 82.1% 96.2%

10 18.9% 5.34 13.7% 30.9%

10 44.0% 3.80 39.6% 50.0%

10 30.5% 3.16 25.0% 34.8%

10 62.5% 8.96 51.7% 80.2%

8 56.2% 5.14 48.6% 61.8%

10 76.2% 9.06 65.4% 87.3%

10 21.1% 2.30 17.4% 23.5%

898



899

TABLE 5—Eurytreta fillmorensis n. sp., average dimensions and ratios of ventral valves from sample LD606. For abbreviations, see text.

N X S Min Max

L

W

T

L/W

T/L

6 1.08 0.157 0.90 1.30

6 0.97 0.130 0.80 1.14

6 0.85 0.263 0.54 1.20

6 89.4% 0.031 84.6% 93.7%

6 87.9% 0.216 60.0% 114.6%

Member, Cordylodus angulatus Zone, sample A190, Section A, Utah. Other material examined.Twenty-eight ventral and dorsal valves. Occurrence.Barn Canyon Member, upper half of Cordylodus angulatus Zone, Section A (Fig. 2, Table 2). Discussion.This species differs from the type species, Schizambon typicalis (occurring in the Barn Canyon Member, Cordylodus lindstromi Zone to lower Cordylodus angulatus Zone; Popov et al., 2002), in having a strongly ventribiconvex shell, with a shorter and narrower pedicle foramen, which is covered posteriorly by a much smaller plate, and a higher apsacline ventral pseudointerarea that is highly raised above the valve floor and convex in transverse profile. Moreover, the later mature ornamentation of S. obtusus differs from that of the type species in that high, solid blunt ‘‘spines’’ are formed at the intersection of concentric lamellae and radial parvicostellae. It is also important to note that (contrary to the description of Popov et al., 2002) neither S. obtusus nor S. typicalis have true hollow siphonotretoid spines (see Williams et al., 2004). Order ACROTRETIDA Kuhn, 1949 Superfamily ACROTRETOIDEA Schuchert, 1893 Family ACROTRETIDAE Schuchert, 1893 Genus CONOTRETA Walcott, 1889 CONOTRETA MILLARDENSIS Popov, Holmer, and Miller, 2002 Figure 11 Conotreta millardensis n. sp. POPOV, HOLMER, 222, fig. 6.1–6.15.

AND

MILLER, 2002, p.

Type.Holotype, USNM 516718, dorsal valve, Barn Canyon Member, Cordylodus angulatus Zone, sample H498, Lawson Cove section, Utah. Material examined.Eight ventral and dorsal valves. Occurrence.Barn Canyon and Red Canyon members; Cordylodus angulatus Zone and ‘‘Paltodus’’ spurius Subzone; Section A, Lawson Cove, and Lava Dam North sections (Fig. 2, Table 2; Popov et al., 2002). Discussion.Popov et al. (2002) recently published a detailed description of this species.

FIGURE 11—Conotreta millardensis Popov, Holmer, and Miller, 2002, Cordylodus angulatus Zone, Barn Canyon Member, sample A190, Section A. 1–3, USNM 526132, dorsal valve exterior, 326, posterior view of dorsal first-formed shell, 3210, lateral view, 334, respectively; 4– 6, USNM 526133, ventral valve exterior, 334, lateral view, 334, posterior view, 334, respectively; 7, USNM 526134, lateral view of dorsal valve interior, 354.

Genus EURYTRETA Rowell, 1966 EURYTRETA cf. BISECTA (Matthew, 1901) Figure 12 Eurytreta cf. bisecta (MATTHEW, 1901). POPOV 106, fig. 86g–h (with synonymy).

AND

HOLMER, 1994, p.

← FIGURE 10—Schizambon obtusus n. sp., Cordylodus angulatus Zone, Barn Canyon Member, samples A170.5 (1–13, 17–20), A190 (14–16, 21), Section A. 1–5, USNM 526125, dorsal valve exterior, 318, oblique posterolateral view, 324, dorsal umbo and juvenile shell, 350, ‘‘spinose’’ mature ornamentation, 3260, anterior margin with ‘‘spinose’’ ornamentation, 365, respectively; 6, 7, USNM 526126, dorsal valve interior, 318, lateral view of dorsal interior, 318, respectively; 8–13, USNM 526127, holotype, lateral view of ventral exterior, 324, ventral valve exterior, 317, oblique posterolateral view, 324, posterior view of pedicle foramen and juvenile shell, 390, ventral umbo and pedicle foramen, 395, mature ornamentation with low nodes directly anterior of pedicle foramen, 3110, respectively; 14, 15, USNM 526128, ventral valve exterior, 315, pedicle foramen, 3150, respectively; 16, USNM 526129, lateral view of dorsal valve exterior, 324; 17–20, USNM 526130, lateral view of ventral valve interior, 318, anterior view of internal pedicle tube and visceral area, 345, oblique anterolateral view of ventral interior, 336, ventral pseudointerarea, 334, respectively; 21, USNM 526131, exfoliated primary layer of ventral valve exterior, 3150.

900


FIGURE 12—Eurytreta cf. bisecta (Matthew, 1901), Cordylodus angulatus Zone, Red Canyon Member, sample LD593, Lava Dam North section. 1, 2, USNM 526135, dorsal valve exterior, 326, posterior view of dorsal first-formed shell, 3160, respectively; 3–7, USNM 526136, ventral valve exterior, 345, lateral view, 355, posterior view, 355, detail of first-formed shell, 3200, detail of pustulose mature ornamentation, 3180, respectively; 8, USNM 526137, dorsal valve interior, 340; 9, USNM 526138, oblique anterior view of ventral valve interior, 336.

Eurytreta cf. bisecta (MATTHEW, 1901). HOLMER, POPOV, KONEVA, AND BASSETT, 2001, p. 92, pl. 25, figs. 3, 5–11. Eurytreta cf. bisecta (MATTHEW, 1901). POPOV, HOLMER, AND MILLER, 2002, p. 223, fig. 7.

Material examined.At least 2,135 dorsal and ventral shells; many are fragmentary. Occurrence.Barn Canyon and Red Canyon members, lower part of Fillmore Formation; Cordylodus lindstromi, Iapetognathus, and Cordylodus angulatus Zones, and ‘‘Paltodus’’ spurius Subzone; Section A, Lava Dam North and 1965 C sections (Fig. 2, Table 2; Popov et al., 2002). Discussion.Popov et al. (2002, p. 223) recently provided a detailed description and discussion of the shells of this species from Utah. The new and younger material from the Cordylodus angulatus and Rossodus manitouensis zones differs somewhat from the older specimens in that some of the examined valves (in particular from sample LD593; Fig. 12) have a pustulose ornamentation. This type of ornamentation has been recorded from

the type species, E. curvata (Walcott, 1902) (see Popov and Holmer, 1994, fig. 81), but E. cf. bisecta clearly differs in having a broadly subconical ventral valve with a catacline pseudointerarea, whereas the ventral valve of the type species is low, recurved, and has a strongly apsacline pseudointerarea. EURYTRETA

new species Figure 13 Diagnosis.Ventral valve high, up to more than 1.1 times as high as long, and cone-shaped, with apsacline pseudointerarea, bisected by an indistinct interridge. Pedicle foramen at the end of short tube. Dorsal valve evenly convex, only slightly sulcate. Ventral apical process low, elongate. Dorsal cardinal muscle scars wide, forming low platforms, occupying about three-fifths of valve width and one-third of valve length. Dorsal median septum thick, high, subtriangular, extending for four-fifths of valve length, with maximum height near midvalve. Description.Shell strongly ventribiconvex, transversely oval FILLMORENSIS

→ FIGURE 13—1–25, Eurytreta fillmorensis n. sp., ‘‘Paltodus’’ spurius Subzone, Fillmore Formation, sample LD606 (1–11, 15, 18–25), Lava Dam North section, sample 65C21 (12–14, 17), 1965 C section; Low Diversity Interval. 1, 2, USNM 526139, dorsal valve exterior, 324, oblique posterolateral view, 330, respectively; 3, 4, USNM 526140, dorsal valve interior, 340, oblique anterolateral view, 355, respectively; 5–8, holotype, USNM 526141, ventral valve exterior, 330, oblique posterolateral view, 348, oblique posterolateral view, 340, detail of first-formed shell, 3280, respectively; 9, USNM 526142, dorsal valve interior, 317; 10, 11, USNM 526143, dorsal valve interior, 317, lateral view, 322, respectively; 12– 14, USNM 526144, posterior view of ventral valve exterior, 350, lateral view, 345, detail of first-formed shell, 3300, respectively; 15, USNM 526145, ventral valve interior, 360; 16, USNM 526146, ventral valve interior, 345; 17, USNM 526147, detail of ventral apical process, 375; 18, 19, USNM 526148, dorsal valve interior, 330, lateral view, 336, respectively; 20–23, USNM 526149, ventral valve exterior, 340, lateral view of first-formed shell, 3280, detail of first-formed shell, 3220, pitted ornamentation of first-formed shell, 3750, respectively; 24, 25, USNM 526150, dorsal valve interior, 326, lateral view, 330, respectively.


901

902



903

TABLE 6—Ottenbyella ibexiana n. sp., average dimensions and ratios of dorsal valves from sample C21. For abbreviations, see text.

N X S Min Max N X S Min Max

L

W

T

Il

Iw

Cl

Cw

Sa

Sm

Sp

10 0.97 0.224 0.52 1.30

10 1.09 0.265 0.58 1.54

10 0.19 0.076 0.08 0.54

10 0.10 0.032 0.06 0.14

10 0.48 0.130 0.24 0.64

10 0.29 0.075 0.14 0.40

10 0.65 0.173 0.30 0.92

10 0.75 0.239 0.34 1.10

8 0.59 0.109 0.34 0.68

10 0.20 0.058 0.10 0.30

L/W

T/L

Iw/W

Cl/L

Cw/W

Sm/L

Sa/L

Sp/L

10 89.5% 5.47 82.1% 96.2%

10 18.9% 5.34 13.7% 30.9%

10 44.0% 3.80 39.6% 50.0%

10 30.5% 3.16 25.0% 34.8%

10 62.5% 8.96 51.7% 80.2%

8 56.2% 5.14 48.6% 61.8%

10 76.2% 9.06 65.4% 87.3%

10 21.1% 2.30 17.4% 23.5%

to subcircular in outline. Ventral valve high, strongly coneshaped, on average 88% as high as long, and 89% as long as wide. Ventral pseudointerarea apsacline, rounded in cross section, bisected by an indistinct interridge accentuated laterally by a pair of shallow grooves. Pedicle foramen small, circular, about 37 mm across, at the end of short tube, situated within the larval shell. Anterior and lateral slopes of the ventral valve evenly convex in profile. Dorsal valve evenly convex, on average 20% as high as long and 90% as long as wide. Dorsal valve only slightly sulcate, with very shallow sulcus originating in the umbonal area. Dorsal pseudointerarea low, anacline, occupying on average 44% of the valve width. Dorsal median groove broad, triangular, occupying up to about 75% of the width of pseudointerarea. Ventral interior with low, elongate, subtriangular apical process. Ventral vascula media baculate, slightly diverging and curved distally, without recognizable bifurcations. Dorsal cardinal muscle scars wide, strongly impressed, and forming low platforms, occupying on average 62% of valve width and 30% of valve length. Dorsal cardinal buttress variably developed, but commonly robust. Dorsal median septum thick, high, subtriangular, originating at on average 21% of the valve length from the posterior margin, and extending for on average 76% of valve length, with maximum height near midvalve. First-formed shell of both valves subcircular, about 120–170 mm wide, with microornament of hemispherical pits, varying in size, about 1–3 mm across, and occasionally with smaller interspatial pits, less than 1 mm across. Etymology.After the occurrence in the Fillmore Formation. Type.Holotype, USNM 526141, ventral valve, lower Fillmore Formation, upper part of ‘‘Paltodus’’ spurius Subzone, sample LD606, from Lava Dam North section, Utah. Measurements.See Tables 4, 5. Other material examined.More than 1,000 ventral and dorsal valves, mostly fragmentary. Occurrence.Lower part of Fillmore Formation; upper part of ‘‘Paltodus’’ spurius Subzone, Low Diversity Interval (Fig. 2, Table 2).

Discussion.Eurytreta fillmorensis can be easily distinguished from E. cf. bisecta, E. sublata, and E. curvata, which also occur in the uppermost Cambrian and lower Ordovician of Utah (Popov et al., 2002) in that E. fillmorensis has a high, apsaconical ventral valve. The only similar species is E. chabakovi (Lermontova in Lermontova and Razumovskii, 1933) from the Lower Ordovician Akbulaksai and Alimbet Formations of South Urals (Popov and Holmer, 1994); however, E. fillmorensis can be easily distinguished from the former in having an even higher ventral valve, with a straight lateral profile of the ventral pseudointerarea divided by an interridge, as well as having less thickened, but wider and shorter dorsal cardinal muscle scars. The maximum size of the Uralian species is about two times larger than that recorded from E. fillmorensis. Genus OTTENBYELLA Popov and Holmer, 1994 OTTENBYELLA IBEXIANA new species Figures 3, 14 Diagnosis.Ventral valve high conical, up to nearly four-fifths as high as long. Ventral pseudointerarea catacline to slightly procline, bisected by broad, weak interridge. Pedicle tube not differentiated; foramen facing posteroventrally. Dorsal valve flattened with very broad sulcus. Apical process weakly defined, elongate subtriangular directly anterior to the internal foramen. Dorsal cardinal muscle scars relatively small, short, weakly impressed, occupying about half of the valve width and one-third of valve length. Dorsal median septum, low and thin, bladelike, extending for about four-fifths of valve length. Dorsal median buttress well developed, with two lateral nodes. Description.Shell strongly ventribiconvex, transversely oval to subcircular in outline. Ventral valve high conical, on average 83% as long as wide and 66% as high as long. Ventral anterior and lateral slopes gently and evenly convex in profile. Ventral pseudointerarea catacline to slightly procline, bisected by broad, weak interridge. Pedicle tube not differentiated; foramen circular, about 57 mm across, within the larval shell, facing posteroventrally. Dorsal valve flattened, on average 89% as long as wide

← FIGURE 14—Ottenbyella ibexiana n. sp., ‘‘Paltodus’’ spurius Subzone, Fillmore Formation, samples 65C8 (1–7) 65C16 (10, 11), 1965 C section; sample LD606 (23, 25, 26), Lava Dam North section, Low Diversity Interval, sample 65C21 (8, 9, 12–22, 24). 1–4, USNM 526151, dorsal valve exterior, 334, lateral view, 340, detail of first-formed shell, 3360, detail of umbo, 3140, respectively; 5–7, USNM 526152, dorsal valve interior, 330, oblique anterolateral view, 340, detail of pseudointerarea and visceral area, 380, respectively; 8, 9, holotype, USNM 526153, ventral valve exterior, 330, posterior view, 330, respectively; 10, 11, USNM 526154, ventral valve exterior, 345, lateral view, 340, respectively; 12, 13, USNM 526155, lateral view of dorsal interior, 340, dorsal valve interior, 338, respectively; 14, USNM 526156, oblique posterolateral view of ventral exterior, 334; 15, USNM 526157, ventral valve interior, 330; 16–19, USNM 526158, dorsal valve exterior, 340, lateral view, 355, detail of first-formed shell, 3280, detail of pitted ornamentation of first-formed shell, 3550, respectively; 20–22, USNM 526159, ventral valve exterior, 370, oblique posterolateral view, 390, detail of first-formed shell, 3300, respectively; 23, USNM 526160, posterior view of ventral exterior, 340; 24, USNM 526161, ventral valve interior, 334; 25, 26, USNM 526162, lateral view of dorsal exterior, 360, detail of first-formed shell, 3240, respectively.

904


TABLE 7—Ottenbyella ibexiana n. sp., average dimensions and ratios of ventral valves from sample C21. For abbreviations, see text.

N X S Min Max

L

W

T

L/W

T/L

8 1.84 0.169 1.58 2.04

8 2.22 0.222 1.88 2.62

8 1.20 0.156 1.02 1.42

8 82.9% 0.031 71.8% 94.7%

8 65.5% 0.216 54.2% 73.3%

and 19% as high as long, with very broad sulcus. Dorsal pseudointerarea low, occupying on average 45% of valve width and 31% of valve length. Dorsal median groove wide and shallow, occupying less than half of width of pseudointerarea. Ventral interior with weakly defined, elongate subtriangular apical process directly anterior to the internal foramen. Ventral vascula lateralia baculate, slightly diverging distally. Dorsal cardinal muscle scars relatively small, short, weakly impressed, occupying on average 53% of the valve width and 31% of valve length. Dorsal median septum low and thin, bladelike, originating at on average 22% of the valve length from the posterior margin, and extending for on average 79% of valve length. Dorsal median buttress well developed, with two lateral nodes. First-formed shell of both valves subcircular, about 130–150 mm wide, with microornament of hemispherical pits, varying in size, about 1–3 mm across. Etymology.After the Ibex site near the type locality. Type.Holotype, USNM 526153, ventral valve, lower part of Fillmore Formation, Low Diversity Interval, sample 65C21, 1965 C section, Utah. Measurements.See Tables 6, 7. Material examined.More than 4,000 ventral and dorsal valves; many are fragmentary. Occurrence.Lower part of Fillmore Formation; upper part of ‘‘Paltodus’’ spurius Subzone, Low Diversity Interval; Lava Dam North and 1965 C sections and Middle Mountain (Fig. 2, Table 2). Discussion.This species differs from the type species, Ottenbyella carinata (Moberg and Segerberg, 1906), from the Bjørka˚sholmen Limestone of Sweden and the Oslo Region, Norway (Popov and Holmer, 1994), in having a more catacline ventral pseudointerarea, divided by a less pronounced interridge, as well as in the complete lack of an external pedicle tube. Moreover, the apical process of O. ibexiana is lower and less well defined, and the dorsal cardinal muscle scars are proportionally wider and somewhat longer, and the dorsal median septum higher as compared with the type species. Ottenbyella ibexiana differs from O. evanda (Popov in Koneva and Popov, 1988), known from the Szechuanella–Apatokephalus beds of the Malyi Karatau Range, southern Kazakhstan (Holmer et al., 2001), in having a wider dorsal pseudointerarea and a longer, higher median septum. Moreover, the ventral pseudointerarea of the Kazakhstanian species is invariably procline. Juvenile and fragmented specimens of O. ibexiana are difficult to distinguish from both Eurytreta cf. bisecta and E. fillmorensis n. sp. ACKNOWLEDGMENTS

Grants from the Swedish Research Council (VR) supported Holmer’s work. Popov’s work is financed by fellowships from the Royal Society of London and the National Museum of Wales. Miller’s research was funded by National Science Foundation grants EAR 8108621, EAR 8407281, and EAR 8804352; additional funds were provided by Faculty Research Grants and other funds from Missouri State University. Miller prepared parts of the manuscript during a sabbatical leave at Uppsala University that was funded in part by a grant from the Wenner-Gren Foundation.

A. J. Rowell, M. Mergl, and K. Dewing reviewed a draft of the manuscript and offered suggestions that improved the final report. This paper is a contribution to IGCP Project 410. REFERENCES

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