lingulate brachiopods from the cambrian-ordovician ... - BioOne

J. Paleont., 76(2), 2002, pp. 211–228 Copyright q 2002, The Paleontological Society 0022-3360/02/0076-211$03.00

LINGULATE BRACHIOPODS FROM THE CAMBRIAN-ORDOVICIAN BOUNDARY BEDS OF UTAH LEONID E. POPOV,1 LARS E. HOLMER,2

AND

JAMES F. MILLER3

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

ABSTRACT—Seven genera and eight species of lingulate brachiopods are described from the Cambrian-Ordovician boundary beds (Cambrooistodus minutus Conodont Subzone to Rossodus manitouensis Conodont Zone) at the Lawson Cove and Lava Dam North sections, Ibex area, Utah, USA. The fauna includes one new linguloid genus, Wahwahlingula, and four new species, Lingulella? incurvata, Zhanatella utahensis, Conotreta millardensis, and Quadrisonia? lavadamensis. Lingulate brachiopods from this interval are very poorly known from Laurentia, but the recorded fauna is very similar to that described from coeval beds at Malyi Karatau, Kazakhstan, and both areas contain Eurytreta cf. bisecta (Matthew, 1901); E. sublata Popov, 1988; Zhanatella Koneva, 1986; Schizambon Walcott, 1889; and Wahwahlingula. Eurytreta cf. bisecta is also known from the Lower Ordovician of Avalonian Canada, Britain, and Scandinavia.

INTRODUCTION

of latest Cambrian and earliest Ordovician age are poorly known in North America. This situation is partly because strata of this age in cratonic and platform areas are siliciclastic or are crystalline dolomites in which brachiopods are poorly preserved, and partly because strata of this age are often missing because of hiatus. Many previous faunal studies of Cambrian-Ordovician age concentrated on fossils traditionally used for biostratigraphy, such as trilobites and conodonts. Some studies that dealt mostly with Upper Cambrian and Lower Ordovician trilobites included descriptions of brachiopods (Grant, 1965; Winston and Nicholls, 1967). Jensen (1967) and Freeman and Stitt (1996) described rhynchonelliformean brachiopod faunas from Upper Cambrian and Lower Ordovician strata. Rowell (1966), Kurtz (1971), and Rowell and Brady (1976) discussed lingulate brachiopods from strata of Cambrian-Ordovician age. Lingulate brachiopods and conodonts are often recovered together from limestone samples because of their similar phosphatic composition. In this report we describe taxa from 78 brachiopod collections and establish their stratigraphic ranges. The material was recovered by J. F. Miller from the heavy-liquid concentrations of insoluble residues of limestone conodont samples collected in the classical Ibex area of western Utah. All but one of the samples are from a single measured section, and the additional sample is from a nearby section. These brachiopods occur in strata that preserve a continuous stratigraphic record of latest Cambrian through earliest Ordovician time. These strata contain no obvious major gaps in deposition. Although sequence boundaries have been recognized, no biostratigraphic units known in other parts of North America are missing in this succession. The conodont and trilobite biostratigraphies of these strata are well known, so the ranges of brachiopods discussed herein can be tied into the biozonation.

L

INGULATE BRACHIOPODS

LOCATION OF SAMPLES

Most of the faunas described in this report are from strata exposed in the Lawson Cove section in the Ibex area of western Millard County, Utah; one sample is from the nearby Lava Dam North section. Strata exposed in this area are on public land administered by the United States Bureau of Land Management. The general locations of these sections are shown on Figure 1. The Lawson Cove section is in the northern part of the Wah Wah Mountains (Fig. 1); the Lava Dam North section is in the nearby House Range. The location of the Lawson Cove section is shown

in detail on Figure 2. The section was measured in three overlapping segments, which are referred to as the lower, middle, and upper segments. Brachiopods were obtained from the lower and middle segments. One sample is from the top of the Lava Dam North section in the southern House Range at UTM coordinates 296750 m E, 4302560 m N, zone 12 (Fig. 1). LITHOSTRATIGRAPHY

The Ibex area has a classical succession of North American Upper Cambrian and Lower Ordovician strata. Brachiopods described herein are from the Notch Peak Formation and the overlying House Limestone (Fig. 3). Hintze et al. (1988) divided the Notch Peak Formation into the Hellnmaria, Red Tops, and Lava Dam members and described these strata in the Lawson Cove section. Their report indicates that the Hellnmaria Member consists of 408.4 m (1,340 ft) of stromatolitic and crystalline dolomites with minor limestone. J. F. Miller remeasured and redescribed the Lawson Cove section during study of conodont faunas from the Notch Peak and House formations. The top beds of the Hellnmaria yielded a few conodonts but no brachiopods. Miller concentrated his study on strata above the Hellnmaria Member. His new measurement of the overlying Red Tops Member indicates a thickness of 15.8 m (52 ft); strata consist of skeletal grainstone, flat-pebble conglomerate, stromatolitic boundstone, and minor lime mudstone. Only two brachiopod collections were recovered from the Red Tops Member, which is exposed in the lower segment of the section (Fig. 2). The Notch Peak-House contact (Fig. 3) is placed at a stratigraphically lower horizon than was reported by Hintze et al. (1988); the placement utilized herein is consistent with the contact horizon utilized for descriptions of other sections in the 1988 report. A complete section of the Lava Dam Member is present in the lower segment and is 89.3 m (293 ft) thick. The upper 24.1 m (79 ft) of the Lava Dam Member was measured also at the bottom of the middle segment of the Lawson Cove section (Fig. 3). The Lava Dam Member consists of cherty lime mudstone, lime grainstone, and stromatolitic to thrombolitic boundstone. Many brachiopods were recovered from the Lava Dam Member. Brachiopods occur in all of these lithologies but are rarest in boundstones. The House Limestone was named by Hintze (1951) for exposures in the central House Range. Miller et al. (2001) divided the House Limestone into three members, the Barn Canyon (lower), Burnout Canyon, and Red Canyon (upper) members. The type section of the Barn Canyon Member is the middle segment of the Lawson Cove section; these strata are 86.3 m (283 ft) thick. The Barn Canyon consists of gray cherty lime mudstone, skeletal

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FIGURE 1—Location of measured sections of the Notch Peak Formation and House Limestone in the Ibex area, Millard County, Utah. A, Lawson Cove; B, Lava Dam Five section of Hintze et al., (1988) and Ross and others (1997); C, Lava Dam North section of Hintze (1973). See Figure 2 for detailed locations of lower, middle, and upper segments of the Lawson Cove section.

grainstone, fine-grained grainstone, flat-pebble conglomerate, and minor stromatolitic to thrombolitic boundstone. These strata yielded many brachiopods; most are from lime mudstone and skeletal grainstone. The Burnout Canyon Member is partly exposed in the middle segment of the Lawson Cove section, but the type section is the upper segment, where this member is 16.2 m (53 ft) thick. The Burnout Canyon consists of brown to rusty-brown finegrained grainstone, flat-pebble conglomerate, coarse-grained grainstone, minor lime mudstone to wackestone, rare quartz sandstone, and abundant black to brown to white chert. The lower half of the Red Canyon Member is exposed in the upper segment of the Lawson Cove section (Fig. 3); these strata are 32.2 m (106

FIGURE 2—Portion of Grassy Cove topographic quadrangle (1:24,000) showing location of lower, middle, and upper segments of Lawson Cove measured section. Township and Range grid and UTM grid are shown. Figure 1 shows the general location of this section.

ft) thick. No brachiopods were recovered from the Barn Canyon and Burnout Canyon members at Lawson Cove. One brachiopod collection was recovered from a lime mudstone 0.6 m (2 ft) below the top of the type section of the Red Canyon Member at the Lava Dam North section, at the 600-ft level in the section. The Red Canyon is 71.3 m (234 ft) thick and consists of gray lime mudstone and wackestone, laminated fine-grained grainstone, trilobite grainstone, and flat-pebble and intraclast conglomerate; these strata have up to 20 percent brown to black chert. Miller et al. (2001) provided detailed descriptions of the Lawson Cove and Lava Dam North sections and two other sections in the southern House Range. CHRONOSTRATIGRAPHY

Two different chronostratigraphic frameworks could be used in this report. One choice is the international framework based on a →

FIGURE 3—Stratigraphic ranges of lingulate brachiopods in the Lawson Cove section, Utah (Fig. 1) relative to chronostratigraphic, lithostratigraphic, and biostratigraphic units. Arrows at tops of two taxon ranges indicate those taxa occur near the top of the Red Canyon Member of the House Limestone at the Lava Dam North section (Fig. 1). Hel. indicates Hellnmaria Member of the Notch Peak Formation; B.C. indicates Burnout Canyon Member of the House Limestone.

POPOV ET AL.—CAMBRIAN-ORDOVICIAN LINGULATE BRACHIOPODS FROM UTAH

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TABLE 1—Summary of lingulate brachiopod distribution showing numbers of specimens within the Cambrian-Ordovician boundary interval at Lawson Cove, including a single sample (LDN600) from the Lava Dam North locality. For sample numbers, R 5 Red Tops Member of Notch Peak Formation, LD 5 Lava Dam Member of Notch Peak Formation, H 5 Barn Canyon Member of House Limestone. Numbers for cumulative feet and cumulative meters above base of section are measured from 12 feet (3.7 meters) below the base of the Red Tops Member and correspond with scales in feet and meters shown on Figure 3. Sample Number in LOWER SEGMENT

R28

R36

LD5

LD46

LD76

LD100

LD151

LD156

Cumulative feet above base of section Cumulative meters above base of section Quadrisonia? lavadamensis new species Zhanatella utahensis new species Lingulella? incurvata new species Wahwahlingula sp. Eurytreta sublata Popov

50 15.2

58 17.7

67 20.4

108 32.9 13

138 42.1 6

162 49.4

213 64.9

2

3 1

218 66.4 42 2

Sample Number in MIDDLE SEGMENT

LD248

LD251

LD257

H277

H279

H324.5

H328

H336

Cumulative feet above base of section Cumulative meters above base of section Lingulella? incurvata new species Wahwahlingula sp. Eurytreta sublata Popov Eurytreta cf. bisecta (Matthew) Schizambon typicalis Walcott

333 101.5 4 1

336 102.4

342 104.2

362 110.3 3

364 110.9

416.5 126.9

420 128.0

428 130.5

19

19

7

2

7

Sample Number in MIDDLE SEGMENT

H436.5

H437

H438

H440

H451

H452.5

H455

H462

Cumulative feet above base of section Cumulative meters above base of section Lingulella? incurvata new species Wahwahlingula sp. Eurytreta cf. bisecta (Matthew) Schizambon typicalis Walcott Conotreta millardensis new species

528.5 161.1

529 161.2

530 161.5 2

532 162.2

543 165.5

544.5 166.0

547 166.7 3

554 168.9

12

4 2

3

4 2

29

2

6 3

10 28

4

4 1

45

.300

recently approved global stratotype section and point for the Cambrian-Ordovician boundary. The alternative is the regional North American chronostratigraphy for the Upper Cambrian and Lower Ordovician. The International Commission on Stratigraphy recently chose a global stratotype to be the designated boundary for the base of the Ordovician System, the Lower Ordovician Series, and the Tremadocian Stage (redefined and different from the traditional Tremadocian Series). The boundary section is at Green Point in western Newfoundland, Canada. Strata are assigned to the Cow Head Group, and the boundary point coincides with the local lowest occurrence of the conodont Iapetognathus fluctivagus Nicoll et al., 1999. It is difficult to correlate strata at Lawson Cove with the new stratotype because of the mixed-age faunal succession at Green Point. Strata of the Cow Head Group were deposited near the base of the continental slope. These slope strata include in situ shales interbedded with redeposited debris slide breccias, turbidite grainstones, and slump deposits (James and Stevens, 1986, p. 141–143, fig. 13). At Green Point there are numerous collections that yielded graptolites and conodonts, but there are only two trilobite collections, both from redeposited debris-slide breccias (Barnes, 1988, fig. 9, table 6; Miller et al., 1998). At Lawson Cove there are many collections (Miller, Loch et al., 1999) that yielded trilobites, conodonts, organophosphatic brachiopods (this report), and calcitic brachiopods, but no graptolites. The only fossils in common between the Lawson Cove and Green Point are conodonts. However, the only abundant conodont collections below the new boundary horizon at Green Point are from a debris-slide breccia in which different clasts contain trilobites from at least three different zones, and all conodont taxa occurring below the boundary also occur above it. Thus there is essentially no characteristically Cambrian conodont fauna nor any useful Cambrian biozonation. Most of the conodont collections from below the boundary, at the boundary, and for some meters above the boundary horizon occur in redeposited limestones. Conodonts from these collections are of mixed ages and form an inverted homotaxial succession that

includes taxa diagnostic of the upper subzone of the Cordylodus lindstromi s.l. Zone through the Clavohamulus elongatus Subzone of the Cordylodus proavus Zone. Such an inverted succession is prima facie evidence that the conodonts were deposited in shallower (presumably shelf and upper slope) environments, and later they were eroded and redeposited in an inverted sequence on the lower slope at Green Point. Most of the conodonts below, at, and above the boundary horizon are redeposited, and thus they have little biostratigraphic and chronostratigraphic significance. The designated boundary horizon is within an interval in which the conodonts actually become older in successively higher strata due to the redeposited and inverted succession. Miller and Flokstra (1999) discussed these problems and used graphic correlation of Green Point and Lawson Cove conodonts to try to overcome the problem of correlating these sections. They found that graphic correlations between these sections, as well between Green Point and sections in Australia and Kazakhstan, resulted in a line of correlation with no slope. Their interpretation was that the boundary interval at Green Point correlates with more than 90 m of strata at Lawson Cove. Graphic correlations between Lawson Cove and sections in Australia, China, and Kazakhstan had good results, and the lines of correlation have reasonable slope angles. One must conclude that the Green Point section is of little use as a basis for biostratigraphic and chronostratigraphic correlation with strata in the Ibex area of Utah. Because of these problems with the new international standard, we prefer to use regional chronostratigraphic units from Utah to demonstrate the ranges of brachiopods reported herein. Strata in the Ibex area form the basis for the chronostratigraphic subdivision of Upper Cambrian and Lower Ordovician strata in North America. Palmer (1998) proposed a new chronostratigraphic classification of the Cambrian System in North America. In his classification the upper subdivision of the Cambrian is the Millardan Series, named for exposures in Millard County, Utah, where the Ibex area is located. Palmer (1998) recommended use of the term Sunwaptan Stage for the upper stage of the Millardan Series. Ross et al. (1997) subdivided the overlying Ordovician Ibexian Series


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TABLE 1—Extended.

LD157

LD183

LD184

LD185

LD190

LD191

LD193

LD194

LD195

LD277

LD280

LD285

219 66.8 20 1

245 68.9

246 68.9

247 72.5

252 72.5

253 77.1

255 77.7

256 78.0

257 78.3

341 103.9

344 104.9

349 106.4

3

11

6

8

5

10

4

46

1 24

1

H340

H345

H380

H385

H393

H401

H407

H421

H424

H434.5

H436

432 131.7

437 133.2 2

472 143.9

477 145.4

485 147.8 2

493 150.3

499 152.1

513 156.4

516 157.3 4

526.5 160.5

528 160.9 4

8

16

6 18 7

82 7

4

5

3 7

1

32

17

H479

H485

H487

H498

H512

Lava Dam North Section, sample LDN600

571 174.0

577 175.9

579 176.5 2

590 180 3

604 184 4

2 feet below top of House Limestone 0.6 m below top of House Limestone

14

22

53 1 76

into four stages, the lowest of which is the Skullrockian Stage. The boundary between the Millardan and Ibexian Series is placed at the base of the Cordylodus proavus Conodont Zone, near the middle of the Lava Dam Member. Brachiopods described herein are from the upper part of the Millardan Series and from the lower part of the Ibexian Series (Fig. 3), including all of the Skullrockian Stage and the basal ca. one meter of the overlying Stairsian Stage (sample at LDN600). Trilobite and graptolite data from the Ibex area permit correlation with the base of the traditional Tremadocian Series in the Acado-Baltic Faunal Province, as shown on Figure 3. The base of the traditional Tremadocian Series, which is characterized by graptolites and shown on Figure 3, should not be confused with the base of the redefined Tremadocian Stage, which is characterized by conodonts at the new global stratotype at Green Point. Rushton (1982) defined the base of the Tremadocian Series at a point in rock coinciding with the lowest occurrence of the planktic graptolite Rhabdinopora flabelliformis. No graptolites occur at Lawson Cove, but Miller, Berry et al. (1999) reported lower Tremadocian Series planktic graptolites from the upper part of the Iapetognathus Conodont Zone at the Lava Dam North section (Fig. 1). At Lawson Cove the base of the Tremadocian Series is recognized (Fig. 3) by the occurrence of the olenid trilobite Jujuyaspis borealis, which is considered to occur near the base of the Tremadocian Series (Stitt and Miller, 1987; Acenõlaza and Acenõlaza, 1992; Miller and Taylor, 1995). This trilobite occurs in one bed in the Barn Canyon Member of the House Limestone. At Lawson Cove it is at 0.9 m (3 ft) above the base of the Iapetognathus Conodont Zone and 0.3 m (1 ft) above the base of the Symphysurina bulbosa Subzone of the Symphysurina Trilobite Zone (Fig. 3). A similar relationship occurs at Lava Dam North and at several other sections in the Ibex area. BIOSTRATIGRAPHY

Many of the standard North American Upper Cambrian and Lower Ordovician trilobite and conodont zones are based on faunas from the Ibex area. Trilobites from these strata were documented by Hintze (1953) and by Hintze et al. (1988). Miller

6 .1500

(1969) and Ethington and Clark (1981) described conodonts from the Notch Peak and House formations in the Ibex area. These faunas were used to establish trilobite and conodont zones in the House Range and Confusion Range. Ross et al. (1997) summarized these faunas and the trilobite and conodont biostratigraphic units recognized in the House Range. Miller, Loch et al. (1999) summarized the conodont biostratigraphy of the Lawson Cove section; the same zones and their various subzones are shown on Figure 3 herein. This biostratigraphy is based on ca. 210 conodont collections and approximately 45,000 identified conodont elements from the Lawson Cove section. Our biozonation differs slightly from that of Ross et al. (1997) in that herein the Cordylodus lindstromi sensu lato Conodont Zone is divided into lower and upper subzones (Fig. 3). The lower subzone is characterized by the presence of Cordylodus prolindstromi Nicoll, and the upper subzone is characterized by the presence of C. lindstromi Druce and Jones. The lower subzone is equivalent to the C. prolindstromi Conodont Zone of Shergold and Nicoll (1992) from the Black Mountain section in Queensland, Australia, and the upper subzone is equivalent to the lower part of the C. lindstromi Conodont Zone in that section. Herein these units are classified as subzones of one inclusive zone. This classification is used because the species that characterize these subzones are so similar that they cannot be distinguished in sections that do not have large, well preserved collections. Loch et al. (1999) summarized the trilobite biostratigraphy of the Lawson Cove section. The biozonation recognized currently is shown on Figure 3 herein, but research on trilobites from this section is still in progress, and the biozonation is subject to future refinement. Nevertheless, within the stratigraphic interval where collections have been studied, all of the zones and subzones recognized by Ross et al. (1997) have been identified. In addition, it is possible to recognize at Lawson Cove the three subzones of the Symphysurina Trilobite Zone that were established by Stitt (1977) in Oklahoma (Fig. 3). No biozonation of the brachiopods is proposed herein, but the lowest or highest occurrences of some of the taxa approximately

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TABLE 2—Lingulella? incurvata new species, average dimensions and ratios of ventral valves from samples H436, H487, and H512. For abbreviations, see text.

N X S MIN MAX

L

W

B

Il

Iw

Pl

Pw

L/W

B/L

Il/L

Iw/W

6 1.56 0.562 0.86 2.38

6 0.92 0.273 0.66 1.36

4 1.08 0.243 0.86 1.38

6 0.41 0.188 0.16 0.66

6 0.67 0.304 0.4 1.14

6 0.27 0.127 0.1 0.42

6 0.14 0.073 0.06 0.24

6 169.0% 33.6 104.9% 205.3%

4 59.0% 4.9 55.1% 66.2%

6 25.3% 4.3 18.6% 30.8%

6 70.8% 15.4 48.8% 83.8%

coincide with important chronostratigraphic boundaries. The highest occurrences of Zhanatella utahensis and Quadrisonia? lavadamensis are near the top of the Millardan Series. The lowest occurrence of Eurytreta Rowell is only slightly above the base of the Ibexian Series. The change in the brachiopod faunas in this interval appears to be useful in characterizing the Millardan-Ibexian boundary, which is the level at which the Ordovician biodiversification began (Miller, Loch et al., 1999). The lowest occurrences of Eurytreta cf. bisecta and Schizambon typicalis are only slightly below the occurrence of the trilobite Jujuyaspis borealis and near the base of the Iapetognathus Conodont Zone. These brachiopods appear to be useful in recognizing the approximate base of the traditional Tremadocian Series. AFFINITIES OF THE LINGULATE FAUNA

At Lawson Cove the lingulate brachiopod fauna generally is of low diversity in the Cambrian-Ordovician boundary interval (Cambrooistodus minutus Conodont Subzone to Cordylodus angulatus Conodont Zone). Only seven genera and eight species of lingulates are described below. New taxa include one new linguloid genus, Wahwahlingula, and four new species, Lingulella? incurvata, Zhanatella utahensis, Conotreta millardensis, and Quadrisonia? lavadamensis. Nearly all of the brachiopod samples from the Cambrooistodus minutus Conodont Subzone (with the exception of R36; Table 1) are monospecific and contain a low number of specimens of Quadrisonia? lavadamensis, which occasionally co-occurs with even fewer specimens of Zhanatella utahensis and Wahwahlingula sp. (Table 1). In the Hirsutodontus hirsutus Conodont Subzone and upward to the base of the Cordylodus lindstromi Conodont Zone, Quadrisonia? lavadamensis is replaced by Eurytreta sublata, which also forms mostly monospecific faunas, and it co-occurs with very rare specimens of Lingulella? incurvata in only three samples (H280, H380, H393; Table 1). The latter species otherwise is also monospecific in samples from the Fryxellodontus inornatus Conodont Subzone, but sometimes it is replaced by Wahwahlingula sp. In the Cordylodus lindstromi s.l. Conodont Zone and upwards, most samples are strongly dominated by Eurytreta cf. bisecta, which commonly

forms monospecific or nearly monospecific faunas, but sometimes it co-occurs with Schizambon typicalis, Wahwahlingula sp., and Lingulella? incurvata. Eurytreta cf. bisecta is lacking in only four of 18 samples from this interval (Table 1). A detailed comparison with coeval faunas across the world is difficult due to the lack of data from most areas. The described fauna is most similar in composition to that recorded from coeval beds at Malyi Karatau, Kazakhstan (Holmer et al., 2001), which is the only other section where the succession of lingulates has been studied in detail from carbonate strata. In this part of Kazakhstan, the lingulate brachiopod fauna is also of low diversity in the Cambrian-Ordovician boundary interval. At Malyi Karatau, Eurytreta sublata Popov is also found within the Upper Cambrian (Euloma-Leiostegium beds) and, as at Lawson Cove, it is replaced by Eurytreta cf. bisecta in the Lower Ordovician (Dikelokephalina and Szechuanella-Apatokephalus beds). In addition, the Cambrian–Ordovician boundary beds at Malyi Karatau have yielded numerous fragments of an indeterminable species of Wahwahlingula as well as Zhanatella, and Schizambon appears in the Lower Ordovician (Dikelokephalina beds). Eurytreta cf. bisecta is otherwise also known from the Lower Ordovician of Avalonian Canada, Britain, and Scandinavia (e.g., Popov and Holmer, 1994). Wahwahlingula antiquissima and an indeterminable species of Eurytreta are also known from the Cambrian-Ordovician boundary beds of the East Baltic (Popov et al., 1989). 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; Cw, Cl 5 width, length of cardinal muscle field; Sa 5 length of median septum; Sm 5 position of maximum height of dorsal median septum; B 5 position of maximum width of the valve; X 5 average value; S 5 standard deviation; N 5 number of measurements; MAX, MIN 5 maximum and minimum values. The material illustrated and discussed is deposited in National

← FIGURE 4—1–11, Lingulella? incurvata new species Notch Peak Formation, Lava Dam Member, Fryxellodontus inornatus Conodont Subzone, sample LD195 (5); House Limestone, Barn Canyon Member, Cordylodus lindstromi s.l. Conodont Zone, sample H424 (1, 2, 3, 4, 6, 10, 11); House Limestone, Barn Canyon Member, Cordylodus angulatus Zone, sample H498 (7, 8); 1, 2, USNM 516723, ventral valve exterior, 342, lateral view of 1, 344; 3, 4, USNM 516724, ventral valve exterior, 329, oblique lateral view, 332; 5, USNM 516725, dorsal valve exterior, 331; 6, USNM 516726, dorsal valve interior, 338; 7, 8, Holotype, USNM 516727, dorsal valve interior, 327, oblique lateral view, 331; 9, USNM 516728, dorsal valve interior, 330; 10, 11, USNM 516729, oblique lateral view of ventral valve interior, 322, detail of ventral pseudointerarea, 354. 12–17, Wahwahlingula antiquissima (Jeremejew, 1856) Upper Cambrian, upper Cordylodus proavus Biozone, Tosna Formation, Syas River south of Rebrovo village, north-western Russia; 12, CNIGR 182/12348, ventral valve interior, 311; 13, CNIGR 12348, dorsal valve interior, 310; 14, Neotype, CNIGR 180/12348, ventral valve exterior, 33; 15, 16, GLAHM 101691, exterior of fragmentary valve, showing pitted ornamentation with pitted ornamentation, 3500, details of pits, 3800 (see also Cusack et al. 1999, pl. 1); 17–27, Wahwahlingula sp. Notch Peak Formation, Lava Dam Member, Cambrooistodus minutus Conodont Subzone, sample LD156 (22–27); House Limestone, Barn Canyon Member, Cordylodus lindstromi s.l. Conodont Zone, sample H407 (20, 21); Barn Canyon Member, Rossodus manitouensis Conodont Zone, sample LDN600 (17–19); 17–19, USNM 516737, dorsal valve exterior, 321, detail of umbonal region, 347, detail of post larval pitting, 3346; 20, 21, USNM 516738, ventral valve exterior, 342, oblique lateral view, 344; 22–25, USNM 516739, ventral valve exterior, 388, oblique lateral view, 391, detail of larval shell, 3227, detail of post larval pitting, 3455; 26, USNM 516741, ventral valve interior, 343; 27, USNM 516742, oblique lateral view of ventral valve interior, 335.

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TABLE 3—Lingulella? incurvata new species, average dimensions and ratios of dorsal valves from samples LD248–H512. For abbreviations, see text.

N X S MIN MAX

L

W

B

Il

Iw

Pl

L/W

B/L

Il/L

Iw/W

5 1.34 0.431 0.78 1.8

5 0.92 0.325 0.54 1.26

4 0.90 0.274 0.6 1.2

5 0.28 0.177 0.1 0.54

5 0.60 0.238 0.32 0.84

5 0.13 0.044 0.08 0.16

5 147.4% 8.8% 138.1% 161.8%

4 59.6% 6.4% 54.5% 69.0%

5 19.6% 7.2% 12.7% 30.0%

5 64.7% 5.9% 58.8% 72.7%

Museum of Natural History, Washington (USNM), in the National Museum of Wales, Cardiff (NMW), in the Hunterian Museum, Glasgow (GLAHM), and in the Central Scientific Geological Exploration Museum (Tschernyschev Museum), St. Petersburg, Russia (CNIGR). Class LINGULATA Gorjansky and Popov, 1985 Order LINGULIDA Waagen, 1885 Superfamily LINGULOIDEA Menke, 1828 Family OBOLIDAE King, 1846 Genus LINGULELLA Salter, 1866 Remarks.The concept of Lingulella found in Sutton et al. (2000) is followed here. LINGULELLA? INCURVATA new species Figure 4.1–4.11 Diagnosis.Shell dorsibiconvex, inequivalved, strongly elongate suboval in outline, with the maximum width somewhat anterior to mid-length; ventral pseudointerarea long, triangular, occupying about one quarter of sagittal valve length, with narrow and shallow pedicle groove and propareas; dorsal valve shorter than ventral, with crescent-shaped pseudointerarea; interior characters of both valves weakly impressed, but with large ventral visceral area extending anteriorly to mid-valve and fine dorsal median ridge. Description.Shell dorsibiconvex, inequivalved, and elongate suboval in outline. Ventral valve acuminate, on average 169 percent as long as wide, with the maximum width on average located at 59 percent of the valve length from posterior margin. Ventral pseudointerarea elongate triangular, almost orthocline, concave in transverse section, occupying on average 25 percent of the valve length and 71 percent of the valve width. Pedicle groove shallow and flattened. Propareas only slightly raised above the valve floor. Inner sides of propareas between the flexure lines and outer margins of the pedicle groove bear strongly wrinkled growth marks, whereas the outer sides of propareas are nearly smooth. Dorsal valve strongly and evenly convex in transverse and lateral profiles, on average 147 percent as long as wide, with a somewhat swollen umbonal area. Dorsal pseudointerarea, occupying on average 20 percent of the valve length and 65 percent of the valve width, forming crescent-shaped strip along the posterior margin, with broad concave median groove along the valve floor; propareas rudimentary and slightly raised, lacking flexure lines. Larval and postlarval shell smooth, not clearly differentiated from each other. Ventral interior with weakly impressed visceral area, extending anteriorly to mid-valve and bisected by weak, slightly diverging impressions of pedicle nerve. Other characters weakly impressed, with exception of slightly thickened posterolateral muscle fields, comprising scars of transmedian and anterior lateral muscles. Dorsal interior with weakly impressed visceral area, occupying about three-fifths of valve length, bisected by fine median ridge and slightly raised, strongly elongated anterolateral muscle field. Etymology.Latin incurvatus, incurved. Type.Holotype, USNM 516727, dorsal valve: House Limestone, Cordylodus angulatus Conodont Zone, sample H498, Lawson Cove section, Utah.

Measurements.See Tables 2, 3. Other material examined.Total of 41 dorsal valves, 28 ventral valves, and one complete shell. Occurrence.Eoconodontus notchpeakensis Conodont Subzone to Cordylodus angulatus Conodont Zone (Fig. 3; Table 1). Discussion.This species is represented exclusively by juvenile, larval, and early postlarval shells; however, they have diagnostic features which clearly distinguish them from other Late Cambrian and Early Ordovician species of Lingulella, including the type species (see Sutton et al., 2000). Lingulella? incurvata differs from all other species of the genus in having a somewhat swollen dorsal umbonal area, strongly and evenly convex transverse and lateral dorsal valve profiles, and an acuminate and strongly elongate ventral valve which has an elongate triangular pseudointerarea. The only similar species is Oepikites? elongatus Popov and Khazanovich (in Popov et al., 1989, p. 104) from the Upper Cambrian Ladoga Formation of northwestern Russia. Both species have a strongly elongated inequivalved shell, an elongate, concave ventral pseudointerarea with narrow and shallow pedicle groove, as well as a fine dorsal median ridge bisecting nearly all the visceral field. Lingulella? incurvata differs from the Russian species by its outline, by having the maximum width anterior to mid-length, and by the absence of dorsal flexure lines. However, Lingulella? incurvata is here represented exclusively by juvenile specimens, which are one-third to one-fourth the size of Oepikites? elongatus; the differences in the morphology of the dorsal pseudointerareas of these two species probably reflect preservational differences, and the two species are considered congeneric. In that case they may represent a separate new genus, different both from Lingulella and Oepikites. Family ZHANATELLIDAE Koneva, 1986 Genus WAHWAHLINGULA new genus Type species.Lingula antiquissima Jeremejew, 1856. Diagnosis.Shell slightly dorsibiconvex, elongate, suboval to subtriangular in outline; ventral valve with orthocline, subtriangular pseudointerarea bisected medially by narrow and shallow pedicle groove; ventral propareas crossed by fine flexure lines; dorsal valve with crescent-shaped orthocline pseudointerarea, not raised above valve floor; dorsal propareas rudimentary, undivided; ventral interior with weakly impressed visceral area bearing pedicle nerve impression and baculate, arcuate vascula lateralia that are situated close to the lateral margins of the valve; dorsal interior with weakly impressed visceral area extending anteriorly to mid-valve, and bisected by long, fine median ridge; dorsal vascula lateralia arcuate, peripheral; vascula media short, diverging; larval and postlarval shell finely pitted with subcircular and suboval pits of varying size. Species included.Lingula antiquissima Jeremejew, 1856, Upper Cambrian–Lower Ordovician (Cordylodus proavus to Cordylodus lindstromi s.l. Conodont Zones), Tosna Formation, northwestern Russia; Wahwahlingula sp., Lower Ordovician (Paroistodus proteus Conodont Zone), Leetse Formation, northwestern Russia. Etymology.After the Wah Wah Mountains in Utah, and Latin lingula, little tongue.


219

FIGURE 5—1–19, Zhanatella utahensis new species Notch Peak Formation, Lava Dam Member, Cambrooistodus minutus Conodont Subzone, sample LD156 (1–6); Red Tops Member, Cambrooistodus minutus Conodont Subzone, sample R36 (7–19); 1–4, USNM 516733, ventral valve exterior, 360, lateral view, 387, detail of larval shell, 3242, detail of larval pitting, 3483; 5, USNM 516734, dorsal valve interior, 338. 6, USNM 516735, dorsal valve interior, 372; 7–9, USNM 516736, dorsal valve exterior, 373, oblique posterior view of larval shell, 3185; detail of larval shell, 3165; 10–12, USNM 516776, dorsal valve exterior, 347, detail of postlarval ornamentation, 3185, detail of postlarval pits, 3750; 13–15, USNM 516777, ventral valve exterior, 3125, oblique posterior view, showing emarginature, 3185, detail of anterior margin of larval shell, 3250; 16– 18, Holotype, USNM 516778, ventral valve interior, 395, oblique lateral view, 395, detail of ventral pseudointerarea and emarginature, 3185. 19, USNM 516740, dorsal valve exterior, 3115.

Discussion.This new genus is nearly indistinguishable from Lingulella (as redescribed by Sutton et al., 2000) in external characters of the shell, morphology of the pseudointerareas in both valves, as well as in the internal morphology of both valves. The main difference is that the larval and postlarval microornamentation is pitted in Wahwahlingula, whereas the external shell

surface of Lingulella is smooth. The new American material described below is represented by a limited number of juveniles, and thus the better-known Lingula antiquissima Jeremejew is chosen as the type species and is redescribed below. The pitted microornament of the shell in Wahwahlingula (see also Cusack et al., 1999) is a characteristic feature of the Family Zhanatellidae

220


FIGURE 6—1–15, Conotreta millardensis new species House Limestone, Barn Canyon Member, Cordylodus angulatus Conodont Zone, sample H498; 1, 2, USNM 516716, dorsal valve exterior, 334, oblique lateral view, 335; 3, 4, USNM 516717, dorsal valve interior, 354, oblique lateral view, 366; 5, Holotype, USNM 516718, dorsal valve interior, 332; 6, 7, oblique lateral views of 5, 335; 8–10, USNM 516719, ventral valve exterior,

POPOV ET AL.—CAMBRIAN-ORDOVICIAN LINGULATE BRACHIOPODS FROM UTAH TABLE 4—Conotreta millardensis new species, average dimensions and ratios of ventral valves from sample H498. For abbreviations, see text.

N X S MIN MAX

L

W

T

L/W

T/L

5 0.65 0.174 0.34 0.97

5 0.72 0.077 0.66 0.84

5 0.39 0.061 0.34 0.48

5 87.8% 6.9% 78.6% 97.0%

5 61.2% 7.7% 54.8% 72.7%

as defined by Holmer and Popov (2000). Among the zhanatellids the closest genus is Fossuliella Popov and Ushatinskaya (in Popov et al., 1992), but Wahwahlingula differs from the latter mainly in the absence of an emarginature and in having an elongate, triangular, ventral pseudointerarea with a narrow pedicle groove and wide propareas. WAHWAHLINGULA ANTIQUISSIMA (Jeremejew, 1856) Figure 4.12–4.16 Lingula antiquissima JEREMEJEW, 1856, p. 1, fig. 6. Lingulella antiquissima Jeremejew. POPOV AND KHAZANOVICH (in POPOV ET AL., 1989), 1989, p. 124, pl. 4, figs. 1–2, 4; pl. 8, figs. 6–10, text-fig. 22. Lingulella antiquissima Jeremejew. POPOV AND HOLMER, 1994, p. 42 (in part), figs. 47I–M, not figs. 45, 46, 47A–H. ‘‘Lingulella’’ antiquissima Jeremejew. CUSACK ET AL., 1999, p. 809, pl. 1, figs. 1–7.

Type.Neotype, CNIGR 180/12348 (selected by Popov and Khazanovich in Popov et al., 1989), ventral valve; Upper Cambrian, upper Cordylodus proavus Biozone, Tosna Formation, Syas River south of Rebrovo village, northwestern Russia. Diagnosis (emended).Shell subtriangular to elongate suboval, about 130 percent as long as wide, with maximum width anterior to mid-valve; ventral interarea narrow triangular, occupying about half of total valve; propareas slightly raised, divided medially by strong flexure lines; dorsal interarea narrow, concave, crescentshaped, undivided; ventral interior with weakly impressed visceral area, extending to about one third the valve length; ventral vascula media arcuate, submarginal; dorsal interior with short, narrow median tongue and long, fine median ridge bisecting all visceral area; dorsal scars of central and outside lateral muscles placed close to each other; microornament of close-packed hemispherical to semi-ellipsoidal pits about 6–8 microns across. WAHWAHLINGULA sp. Figure 4.17–4.27 Description.Shell elongate suboval to subtriangular, juvenile shells with finely pitted microornament. Ventral pseudointerarea well developed, with narrow pedicle groove and large propareas with flexure lines. Dorsal pseudointerarea crescent-shaped, with reduced propareas lacking flexure lines. Interior characters of both valves indiscernible. Other material examined.Total of 25 dorsal valves and 21 ventral valves. Occurrence.Cambrooistodus minutus Conodont Subzone to Rossodus manitouensis Conodont Zone (Fig. 3; Table 1).

221

Discussion.Apart from microornament, the only recognizable difference from the smooth shells of Lingulella? incurvata, which occur in the same samples, is the short, somewhat tubular apical projection of the ventral valve at the end of the pedicle groove. The specimens vary in shell outline and characters of pitted microornament, which suggest that they may belong to several different lingulide species. In particular, shells from the Cambrooistodus minutus Conodont Subzone are only slightly longer than wide (Fig. 4.26) and have a subtriangular outline, whereas specimens from the Cordylodus lindstromi s.l. Conodont Zone and higher are strongly elongated (Fig. 4.20). Genus ZHANATELLA Koneva, 1986 Type species.Zhanatella rotunda Koneva, 1986. Diagnosis.Shell subequally biconvex, circular; ornamented by evenly spaced, concentric rugellae. Ventral pseudointerarea wide, with deep, narrow pedicle groove; propareas flattened, elevated with well defined flexure lines. Dorsal pseudointerarea with wide, lens-shaped median groove. Ventral visceral field slightly thickened anteriorly, not extending to mid-length; ventral vascula lateralia submedianly placed, widely divergent in posterior half, becoming arcuate anteriorly. Dorsal visceral field small, with narrow median tongue, not extending to mid-length, bordered laterally by low ridges; dorsal vascula lateralia subperipheral, arcuate; vascula media long, divergent (Popov and Holmer, 1994). ZHANATELLA

new species Figure 5 Diagnosis.Ventral pseudointerarea apsacline; pseudointerareas of both valves lacking well defined flexure lines. Ventral larval shell with rounded emarginature, about 50 microns across, and with short median ridge with two divergent lateral ridges. Dorsal larval shell bisected by two low ridges, and with oval raised area close to posterior margin. Description.Shell gently ventribiconvex of varying outline. Ventral pseudointerarea apsacline, occupying about half of total valve width, with raised propareas lacking well defined flexure lines. Pedicle groove deep, forming emarginature. Dorsal pseudointerarea crescent-shaped with broad, concave median plate and slightly raised narrow propareas lacking flexure lines. Interior characters of both valves poorly impressed, but with slightly raised visceral areas. Dorsal visceral area with short median tongue, extending somewhat anterior to mid-valve. Larval shell of both valves about 0.3 mm across, commonly marked by ring of growth disturbance and covered by shallow circular pits about 3 microns across. Ventral larval shell with rounded emarginature, about 50 microns across, and with short median ridge with two divergent lateral ridges. Dorsal larval shell bisected by two low ridges, and with oval raised area close to posterior margin. Postlarval shell ornamented by lenticular pits, up to about 11 microns across, most commonly with the largest dimension arranged perpendicular to the growth direction. The raised areas separating the larger pits have a fine microornament of circular pits less than 1 micron across. Etymology.After the occurrence in Utah. UTAHENSIS

← 337, oblique posterior view of, 343, oblique lateral view, 343; 11–13, USNM 516720, ventral valve exterior, 399, oblique lateral view of ventral valve exterior, 3130, detail of larval shell, 3199; 14, USNM 516721, ventral valve interior, 346; 15, USNM 516722, detail of apical process, 385. 16–26, Schizambon typicalis Walcott; Barn Canyon Member, Cordylodus lindstromi s.l. Conodont Zone, sample H421 (16, 17); Cordylodus angulatus Conodont Zone, H498 (18, 19, 20); Pogonip Limestone (21–26), Nevada, Eureka district; 16, 17, USNM 516730, dorsal valve exterior, 333, oblique posterior view, 336; 18, 19, USNM 516731, dorsal valve exterior, 322, detail of larval shell, 398; 20, USNM 516732, dorsal valve interior, 332; 21, USNM 143025d, dorsal valve interior, 312; 22–26, USNM 459671a, ventral valve exterior, 311, detail of ornamentation, 355, lateral view, 312, detail of pedicle track, 350; 26, USNM 459671b, ventral valve interior showing pseudointerarea and internal foramen, 337.

222


Type.Holotype, USNM 516778, ventral valve: Notch Peak Formation, Red Tops Member, sample R36, Lawson Cove section, Utah. Other material examined.Total of nine dorsal valves and three ventral valves. Occurrence.Cambrooistodus minutus Conodont Subzone (Fig. 3; Table 1). Discussion.The fragmentary material of this species was previously (Miller, Loch et al., 1999) misidentified as a species (referred to Lamanskya?) of the Elkaniidae in view of the similar type of pitted ornamentation. However, the new more abundant material described here preserves ventral valves with a semicircular emarginature, which is the most characteristic feature of the Zhanatellidae and Zhanatella. Zhanatella utahensis can be compared only to the type species, Zhanatella rotunda, which is the only other named species of the genus, and the American species is clearly different in having a ventral larval shell with three distinctive ridges in addition to a much smaller emarginature. Moreover, the pseudointerareas of both valves in Zhanatella utahensis lack well defined flexure lines, and the postlarval shell lacks the characteristic rugellae of the type species. At Malyi Karatau, the type species also occurs in the Upper Cambrian (‘‘Pseudagnostus curtarae’’—Irvingella tropica to Eurudagnostus ovaliformis— ‘‘Pareuloma’’ beds; Holmer et al., 2001). Order SIPHONOTRETIDA Kuhn, 1949 Superfamily SIPHONOTRETOIDEA Kutorga, 1848 Family SIPHONOTRETIDAE Kutorga, 1848 Genus SCHIZAMBON Walcott, 1884 SCHIZAMBON TYPICALIS Walcott, 1884 Figure 6.16–6.26 Schizambon typicalis Walcott. ROWELL, 1962, p. 147, pl. 30, figs. 10, 11, 15–17. Schizambon typicalis Walcott. HOLMER AND POPOV, 2000, p. 145, figs. 80:1a–f.

Description.Shell only somewhat dorsibiconvex, suboval, and almost as long as wide. Ventral valve flattened, only slightly convex with maximum height somewhat anterior to umbo, and having a marginal beak. Pedicle foramen small, subcircular, up to about 0.4 mm across, situated at the end of an elongate, triangular pedicle track, the posterior part of which is covered by a plate. Ventral pseudointerarea low, narrow and short, undivided, apsacline to orthocline. Dorsal valve somewhat sulcate. Dorsal pseudointerarea low, with poorly defined median groove. Larval shell smooth, nearly circular, about 0.25 mm across. Ornamentation of closely spaced rugellae, short discontinuous costellae, and evenly spaced, fine, short spines. Visceral areas of both valves slightly thickened. Dorsal visceral area extending anteriorly to mid-valve, with central and anterior lateral muscle scars; vascula lateralia of both valves marginal, arcuate. Other material examined from Utah.Total of 14 dorsal valves and five ventral valves. Occurrence in Utah.Cordylodus lindstromi s.l. Conodont Zone; Iapetognathus Conodont Zone; Cordylodus angulatus Conodont Zone (Fig. 3; Table 1). Discussion.The above description is based both on the new material from Utah (Fig. 6.16–6.20) as well as on topotype material of the type species from the Lower Ordovician of Nevada, included here for comparative purposes (Fig. 6.21–6.26). The specimens from both areas are indistinguishable in all observable characters. The material from Utah is mostly represented by fragmentary specimens. The type species is very similar to the rare Schizambon sp. recorded from the Lower Ordovician (Agalatas Formation) of the Kendyktas Range (Popov and Holmer, 1994)

and the Lower Ordovician (Dikelokephalina beds) at Malyi Karatau (Holmer et al., 2001). Order ACROTRETIDA Kuhn, 1949 Superfamily ACROTRETOIDEA Schuchert, 1893 Family ACROTRETIDAE Schuchert, 1893 Remarks.In addition to the species described below, fragmentary dorsal valves of an undeterminable Acrotretidae occurs in one of the lowest samples (R36; Table 1). Genus CONOTRETA Walcott, 1889 Remarks.The concept of Conotreta found in Holmer (2000) is followed here. CONOTRETA

MILLARDENSIS new species Figure 6.1–6.15 Diagnosis.Ventral valve widely conical; ventral pseudointerarea almost catacline, with narrow, poorly defined interridge; apical process low, ridge-like, grooved medially. Dorsal pseudointerarea low, wide, slightly anacline, with wide median groove occupying more than half the width of pseudointerarea; dorsal cardinal muscle scars occupying about two-thirds of the maximum valve width; dorsal median septum with single septal rod. Description.Shell subcircular in outline, on average 88–89 percent as long as wide. Ventral valve widely conical, on average 61 percent as high as long, with maximum height near the apex. Ventral pseudointerarea almost catacline, poorly defined laterally with the umbonal region slightly inclined posteriorly. Interridge poorly defined. Anterior and lateral slopes of valve gently and evenly convex in cross section. Pedicle foramen within larval shell. Dorsal valve very gently convex with the maximum height at about one quarter of the valve length from the umbo. Dorsal pseudointerarea low, slightly anacline, occupying on average 54 percent of total valve width. Median groove wide, gently concave, occupying on average 54 percent of the width of pseudointerarea. Apical process low, ridge-like, grooved medially, situated anterior to internal foramen. Ventral mantle canals poorly impressed. Dorsal cardinal muscle scars occupying on average 64 percent of the valve width and 37 percent of the valve length, somewhat elongate suboval in outline and weakly impressed, bordered anteriorly and laterally by low rim. Median septum triangular, bladelike, extending for on average 75 percent of valve length, with single septal rod. Maximum height of septum located at on average 64 percent of the valve length from the anterior margin. Median buttress trapezoidal, widening posteriorly. Etymology.After the occurrence in Millard County, Utah. Type.Holotype, USNM 516718, dorsal valve; Ordovician, Ibexian, Cordylodus angulatus Conodont Zone, House Limestone, sample H498, Lawson Cove section, Utah. Measurements.See Tables 4, 5. Other material examined.Total of 11 ventral valves and 65 dorsal valves. Occurrence.As for holotype (Fig. 3; Table 1). Discussion.This species resembles Conotreta shidertensis Popov and Holmer (1994, p. 90) from the Lower Ordovician Olenty Formation in the general shell shape, in characters of the ventral pseudointerarea, and in height and lateral profile of the ventral valve. However, it can be distinguished by being half as large, by a lower, ridge-like apical process, wide median groove, weakly impressed dorsal cardinal muscle scars, as well as by having a median septum with a single septal rod. Conotreta millardensis differs from all other species of the genus (see review by Holmer 2000) in having a less conical valve with a lower apical process, and poorly impressed ventral mantle canals. Conotreta millardensis is the oldest known species of the genus recorded so far.


223

TABLE 5—Conotreta millardensis new species, average dimensions and ratios of dorsal valves from sample H498. For abbreviations, see text. L N 16 X 0.77 S 0.250 MIN 0.40 MAX 1.20

W

Il

Iw

Pw

Cl

Cw

Sm

Sa

L/W

Iw/W

Pw/Iw

Sa/L

SM/L

Cl/L

Cw/W

16 0.89 0.269 0.44 1.24

19 0.10 0.041 0.04 0.18

17 0.49 0.151 0.24 0.72

18 0.28 0.109 0.12 0.48

18 0.30 0.102 0.14 0.46

16 0.57 0.193 0.28 0.88

14 0.52 0.197 0.2 1.02

19 0.61 0.185 0.28 0.84

12 88.7% 5.6% 81.3% 100.0%

16 53.7% 4.3% 43.9% 61.5%

17 54.1% 8.3% 36.4% 73.1%

16 75.4% 8.1% 63.3% 89.7%

11 63.6% 9.0% 50.0% 85.0%

14 36.9% 3.9% 29.0% 44.0%

16 64.1% 10.3% 32.3% 74.6%

Genus EURYTRETA Rowell, 1966 Diagnosis.Shell with short, slightly convex posterior margin. Ventral valve strongly convex to subconical; pseudointerarea apsacline to catacline, poorly defined laterally, and divided by poorly defined intertrough or interridge. Pedicle foramen small, apical, within larval shell, and usually forming short tube. Dorsal valve slightly convex to deeply convex, sulcate; pseudointerarea short, divided by wide median groove. Ventral interior with subtriangular apical process, placed anterior to pedicle foramen, and bearing semicircular depression. Dorsal interior with triangular median ridge or septum; dorsal cardinal muscle fields small, rounded, placed relatively close together, and not extending far anteriorly; median buttress wide; dorsal central muscle scars usually well defined, small, rounded (Popov and Holmer, 1994). EURYTRETA cf.

(Matthew, 1901) Figure 7

BISECTA

Eurytreta cf. bisecta (MATTHEW, 1901). POPOV 106, fig. 86G–H (with synonymy).

AND

HOLMER, 1994, p.

Description of specimens from Utah.Shell ventribiconvex, subcircular in outline, on average 91 percent as long as wide. Ventral valve broadly subconical, about 70 percent as high as long, with maximum height at the apex. Anterior and lateral slopes evenly and gently convex in cross section. Ventral pseudointerarea catacline, bisected by shallow intertrough. Pedicle foramen within larval shell, facing posteroventrally. Dorsal valve gently convex with maximum height somewhat posterior to midlength and weakly sulcate with sulcus originating about at umbo. Dorsal pseudointerarea low, slightly anacline, occupying on average 52 percent of the valve width, with shallow, broad median groove, occupying on average 60 percent of the width of pseudointerarea. Larval shell about 180 microns wide covered by rounded pits of two varying sizes, with the larger pits about 2–3 microns, and smaller ones less then 1 micron in diameter. Apical process thickened, elongate subtriangular, directly anterior to the internal foramen. Ventral vascula lateralia straight, diverging, baculate. Dorsal interior with robust trapezoidal median buttress, separating strongly impressed cardinal muscle scars, bordered by the distinct rim; cardinal scars occupying on average 40 percent of valve length and 65 percent of valve width. Median septum extending for on average 76 percent of valve width, low subtriangular in profile, with angular tip at on average 57 percent from the posterior margin. Measurements.See Table 6. Other material examined.Total of more than 2,000 dorsal and ventral valves.

Occurrence in Utah.Cordylodus lindstromi s.l. Conodont Zone; Iapetognathus Conodont Zone; Cordylodus angulatus Conodont Zone; Rossodus manitouensis Conodont Zone (Fig. 3; Table 1). Discussion.It is difficult to compare specimens of Eurytreta from clastic rocks with those dissolved from carbonates because of their different preservation (see e.g., Popov and Holmer, 1994, p. 95). In particular, these preservational differences cause problems in comparing the specimens of Eurytreta cf. bisecta from the Lawson Cove section with the types of E. bisecta from the McLeod Brook Formation (Dictyonema shale) of Cape Breton, Nova Scotia (see Owens et al., 1982). The specimens from Utah appear to be somewhat smaller and to have a more circular commissural outline, and the dorsal median ridge is usually about three-fourths of the valve length, which is comparable with data provided by Owens et al. (1982) for Eurytreta sabrinae (Callaway), but it is somewhat shorter than in Eurytreta bisecta. However, no measurements accompany the existing descriptions of Eurytreta bisecta. The observed difference in average size is more likely caused by the fact that tiny acrotretide shells preserved in clastics are usually affected by compression and distortion. Our observations also suggest that among the features (e.g., somewhat larger sizes, more transverse outline of the shell, more convex lateral profile of the dorsal valve, and large widely spaced dorsal cardinal muscle scars) listed by Owens et al. (1982) as diagnostic for Eurytreta bisecta in comparison with Eurytreta sabrinae, only the difference in characters of the dorsal cardinal muscle scars can be used with confidence. Data provided by Popov and Holmer (1994) clearly suggests that the dorsal cardinal muscle scars usually do not exceed one-third of the valve length and half of the valve width in the specimens from south Kazakhstan and in Eurytreta cf. sabrinae from the upper Tremadocian of the South Urals and Sweden. The species from Utah is also similar to the somewhat older Eurytreta sublata Koneva and Popov (1988), which is characteristic for the Cordylodus proavus to Cordylodus lindstromi Conodont Zones of the Batyrbay section in the Malyi Karatau Range, Kazakhstan and in the Lawson Cove section of Utah. In the Lawson Cove section there is almost a gradual morphological transition between these two species. The comparative discussion is given below. EURYTRETA SUBLATA Popov, 1988 Figure 8.10–8.28 Eurytreta sublata POPOV (in KONEVA 8, pl. 3.11, fig. 3.

AND

POPOV, 1988), p. 60, pl. 2.4–

TABLE 6—Eurytreta cf. bisecta (Matthew), average dimensions and ratios of dorsal valves from samples H451, H462, and H487. For abbreviations, see text. L N 16 X 0.90 S 0.304 MIN 0.58 MAX 1.78

W

Il

Iw

Pw

Cl

Cw

Sm

Sa

L/W

Iw/W

Pw/Iw

Cl/L

Cw/W

Sa/L

Sm/L

16 1.00 0.319 0.62 1.65

18 0.11 0.054 0.06 0.22

18 0.56 0.184 0.34 0.9

18 0.34 0.107 0.2 0.6

19 0.39 0.129 0.22 0.66

18 0.72 0.243 0.4 1.2

8 0.67 0.220 0.3 1.06

18 0.743 0.318 0.3 1.54

13 91.1% 4.7 83.3% 100.0%

15 51.5% 13.9 4.8% 63.1%

18 60.2% 6.8 48.5% 68.4%

16 40.3% 5.0 34.2% 53.1%

15 64.7% 18.0 6.9% 95.1%

16 75.5% 10.5 46.9% 87.5%

7 57.1% 10.2 37.5% 65.5%

224



225

TABLE 7—Eurytreta sublata Popov, average dimensions and ratios of dorsal valves from samples LD185, LD191, LD277, and H279. For abbreviations, see text.

N X S MIN MAX

L

W

Il

Iw

Pw

Cl

Cw

Sa

L/W

Iw/W

Pw/Iw

Sa/L

Cl/L

Cw/W

16 0.92 0.211 0.54 1.25

14 1.03 0.291 0.64 1.56

15 0.10 0.038 0.04 0.16

12 0.50 0.131 0.34 0.72

14 0.28 0.077 0.18 0.42

16 0.30 0.075 0.16 0.46

14 0.65 0.191 0.38 1.08

16 0.68 0.231 0.32 1.04

13 86.4% 5.7 80.1% 97.7%

11 51.7% 3.9 45.9% 57.5%

12 54.3% 8.6 42.9% 75.0%

15 74.2% 15.1 38.5% 97.1%

15 33.1% 3.1 25.0% 37.5%

13 62.6% 5.9 55.8% 74.5%

Emended diagnosis.Ventral valve about half as high as long, with maximum height at umbo; ventral pseudointerarea usually catacline, with weak interridge or undivided; apical process subtriangular, directly anterior to internal foramen; median buttress high, transversely subrectangular; dorsal median septum low subtriangular, extending anteriorly between two-thirds and threefourths of valve length, lacking an angular tip. Description of specimens from Utah.Shell slightly transversely oval in outline, on average 86 percent as long as wide. Ventral valve broadly conical, slightly more than half as high as long, with maximum height at the umbonal apex. Ventral pseudointerarea catacline, rarely slightly procline, divided by weak interridge or undivided. Ventral anterior and lateral slopes nearly straight in cross-section. Dorsal valve gently convex, with the maximum height at about one-fourth of the valve length from the umbo. Dorsal sulcus poorly defined. Dorsal pseudointerarea low, occupying on average 52 percent of valve width, with shallow median groove occupying on average 54 percent of the width of pseudointerarea. Ventral interior with somewhat elongate subtriangular apical process that is anterior to the internal foramen. Ventral vascula lateralia baculate, diverging. Dorsal median septum low subtriangular, but not forming angular tip on the highest point near midvalve, extending forward for on average 74 percent of the valve length from the posterior margin. Median buttress high, transversely subrectangular in outline. Dorsal cardinal muscle scars elongate suboval, slightly raised and bordered by high rim, occupying on average 33 percent of valve length and 63 percent of valve width. Type.Holotype, CNIGR 13/12034; dorsal valve; figured by Koneva and Popov (1988, pl. 2.1); Late Cambrian (Euloma-Leiostegium beds); Malyi Karatau Range, Batyrbay Section (131 m level), Malyi Karatau, southern Kazakhstan. Measurements.See Table 7. Other material examined from Utah.Total of 154 dorsal valves and 41 ventral valves. Occurrence in Utah.Hirsutodontus hirsutus Conodont Subzone; Fryxellodontus inornatus Conodont Subzone; Clavohamulus elongatus Conodont Subzone; Clavohamulus hintzei Conodont Subzone (Fig. 3; Table 1). Discussion.Eurytreta sublata is somewhat comparable with E. sabrinae (Callaway), as well as with the specimens of E. cf.

sabrinae described by Popov and Holmer (1994), in the external morphology of both valves and in having a relatively short dorsal median ridge. The most distinctive features of E. sublata include a low and narrow interridge, rather than a weak intertrough or undivided ventral pseudointerarea as in E. sabrinae, nearly straight ventral lateral slopes, a strong, narrow subtriangular apical process, and wider dorsal cardinal muscle scars. Eurytreta sublata differs from E. cf. bisecta by having somewhat shorter cardinal dorsal muscle scars, extending anteriorly for about onethird of the valve length, and a median septum that is more ridgelike. The septum usually lacks an angular tip, which is characteristic of adult Eurytreta cf. bisecta. Moreover, the ventral pseudointerarea of Eurytreta sublata has a very weak interridge (mostly in the specimens from the Cordylodus proavus Conodont Zone) or it is undivided, whereas in E. cf. bisecta the ventral pseudointerarea usually possesses a weak intertrough. Genus QUADRISONIA Rowell and Henderson, 1978 Diagnosis.Shell transversely oval, with relatively short, straight posterior margin. Ventral valve low subconical to conical; ventral pseudointerarea procline to catacline, undivided or with very shallow intertrough. Dorsal valve slightly convex, with short, orthocline pseudointerarea, divided by wide median groove. Ventral interior with elongate subtriangular apical process, perforated posteriorly by internal pedicle tube. Dorsal interior with variably developed median ridge; dorsal cardinal muscle fields small, subcircular in outline, closely spaced; dorsal central muscle scars well defined (Popov and Holmer, 1994). QUADRISONIA?

LAVADAMENSIS new species Figure 8.1–8.9 Diagnosis.Ventral valve somewhat more than half as high as long; ventral pseudointerarea catacline to somewhat apsacline, flattened, almost lacking intertrough. Apical process low, elongate, subtriangular. Ventral vascula lateralia widely divergent. Description.Shell ventribiconvex, somewhat transversely oval, somewhat more than 90 percent as long as wide. Ventral valve somewhat more than half as high as long, with maximum height at apex. Ventral pseudointerarea catacline to apsacline and flattened, almost lacking intertrough. Pedicle foramen forming very short tube within larval shell. Dorsal valve gently convex in lateral view. Dorsal pseudointerarea orthocline, occupying about

← FIGURE 7—1–26, Eurytreta cf. bisecta (Matthew, 1901). House Limestone, Barn Canyon Member,Cordylodus lindstromi s.l. Conodont Zone, samples H407 (15), H424 (5, 6, 12, 13, 16, 25); Barn Canyon Member, Cordylodus angulatus Conodont Zone, samples H462 (1, 2, 17, 18, 20, 21, 26), H485 (22–24), H487 (3, 4, 10, 11, 19); Red Canyon Member, Rossodus manitouensis Conodont Zone, sample LDN600 (7–9, 14); 1, 2, USNM 516743, dorsal valve exterior, 351, oblique lateral view, 358; 3, 4, USNM 516744, dorsal valve interior, 331, oblique lateral view, 338; 5, 6, USNM 516745, dorsal valve interior, 329, oblique lateral view, 331; 7–9, USNM 516746, ventral valve exterior, 326, oblique lateral view, 333, detail of larval shell, 3280; 10, USNM 516747, ventral valve exterior, 349; 11, USNM 516748, dorsal valve interior, 346; 12, 13, USNM 516749, dorsal valve exterior, 332, oblique lateral view, 342; 14, USNM 516750, oblique lateral view of ventral valve interior, 324; 15, USNM 516751, dorsal valve exterior, 329; 16, USNM 516752, oblique lateral view of ventral valve exterior, 343; 17, 18, USNM 516753, dorsal valve interior, 351, oblique lateral view, 361; 19, USNM 516754, ventral valve interior, 343; 20, 21, USNM 516755, dorsal valve interior, 349, oblique lateral view, 356; 22–24, USNM 516756, oblique lateral view of ventral valve exterior, 394, oblique posterior view, 3125, detail of larval shell, 3398; 25, USNM 516757, ventral valve interior, 389; 26, USNM 516758, ventral valve interior, 361.

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POPOV ET AL.—CAMBRIAN-ORDOVICIAN LINGULATE BRACHIOPODS FROM UTAH half of the valve width; median groove broadly triangular, occupying more than half of width of pseudointerarea. Ventral interior with low elongate, subtriangular apical process. Ventral vascula lateralia baculate, widely divergent. Dorsal cardinal muscle fields suboval, widely spaced, occupying more than 60 percent of the valve width and somewhat more than 30 percent of the length. Dorsal median ridge low and triangular, originating directly anterior to median buttress and extending anterior to midvalve. Etymology.After the occurrence in the Lava Dam Member. Type.Holotype, USNM 516760, dorsal valve; Upper Cambrian, Cambrooistodus minutus Conodont Subzone, sample LD156, Lawson Cove section, Utah. Other material examined.Total of 68 dorsal valves and 23 ventral. Occurrence.Cambrooistodus minutus Conodont Subzone (Fig. 3; Table 1). Discussion.Quadrisonia? lavadamensis differs from all other species of the genus in having a catacline to apsacline ventral valve, whereas the type and most species of Quadrisonia have a procline ventral valve. In the morphology of the dorsal valve, it is most similar to Quadrisonia declivis Koneva and Popov from the Upper Cambrian of Kazakhstan (Popov and Holmer, 1994), but the latter species has a procline ventral valve. ACKNOWLEDGMENTS

L. E. Popov acknowledges two grants from the Swedish Natural Sciences Research Council (NFR) and three grants from the Royal Swedish Academy of Sciences (KVA) that have enabled him to work as a visiting scientist in Uppsala. L. E. Popov’s work in Cardiff is financed by fellowships from the Royal Society of London and the National Museum of Wales. Grants from the Swedish Natural Science Research Council (NFR) and the Magnus Bergwall Foundation (Stockholm) have supported Holmer’s work. Miller’s research was funded in part by National Science Foundation grant EAR 88-04352 and by Faculty Research Grants from Southwest Missouri State University. K. R. Evans of StratiGraphix prepared Figures 1, 2, and 3. J. D. Loch and J. H. Stitt provided data on trilobite biostratigraphy for the Lawson Cove and Lava Dam North sections. A. J. Rowell and A. R. Palmer reviewed the manuscript and offered suggestions that improved the final submission. This paper is a contribution to IGCP Project 410. REFERENCES

ACENÕLAZA, F. G., AND G. F. ACENÕLAZA. 1992. The genus Jujuyaspis as a world reference fossil for the Cambrian-Ordovician boundary, p. 115–120. In B. D. Webby and J. R. Laurie (eds.), Global Perspectives on Ordovician Geology, Balkema, Rotterdam. BARNES, C. R. 1988. The proposed Cambrian-Ordovician global boundary stratotype and point (GSSP) in western Newfoundland, Canada. Geological Magazine, 125(4):381–414.

227

CUSACK, M., A. WILLIAMS, AND J. O. BUCKMAN. 1999. Chemico-structural evolution of linguloid brachiopod shells. Palaeontology, 42(5): 799–840. ETHINGTON, R. L., AND D. L. CLARK. 1981. Lower and Middle Ordovician conodonts from the Ibex Area, western Millard County, Utah. Brigham Young University Geology Studies, 28(2):1–155. FREEMAN, R. J., AND J. H. STITT. 1996. Upper Cambrian and lowest Ordovician articulate brachiopods from the Arbuckle and Wichita Mountains, Oklahoma. Journal of Paleontology, 70(3):355–372. GORJANSKY, V. YU., AND L. E. POPOV. 1985. Morfologiya, systematicheskoye polozheniye i proiskhozhdeniye bezzamkovykh breakhiopod s karbonatnoy rakovinoy: Paleontologicheskiy Zhurnal, 3:3–14. GRANT, R. E. 1965. Faunas and stratigraphy of the Snowy Range Formation (Upper Cambrian) in southwestern Montana and northwestern Wyoming. Geological Society of America Memoir, 96, 171 p. HINTZE, L. F. 1951. Lower Ordovician detailed stratigraphic sections for western Utah. Utah Geological and Mineralogical Survey Bulletin, 39, 99 p. HINTZE, L. F. 1953. Lower Ordovician trilobites from western Utah. Utah Geological and Mineralogical Survey Bulletin, 48, 249 p. HINTZE, L. F. 1973. Lower and Middle Ordovician stratigraphic sections in the Ibex area, Millard County, Utah. Brigham Young University Geology Studies, 20(4):3–36. HINTZE, L. F., M. E. TAYLOR, AND J. F. MILLER. 1988. Upper Cambrian– Lower Ordovician Notch Peak Formation in western Utah. U.S. Geological Survey Professional Paper, 1393, 30 p. HOLMER, L. E. 2000. Redescription of the Ordovician brachiopod Conotreta Walcott, 1889. GFF, 122:313–318. HOLMER, L. E., AND L. E. POPOV. 2000. Subphylum Linguliformea, p. H30–H146. In R. L. Kaesler (ed.), Treatise on Invertebrate Paleontology, Pt. H (Brachiopoda). Geological Society of America and University of Kansas Press, Lawrence. HOLMER, L. E., L. E. POPOV, AND R. WRONA. 1996. Early Cambrian brachiopods from King George Island (South Shetland Islands), West Antarctica. Palaeontologica Polonica, 55:37–50. HOLMER, L. E., L. E. POPOV, S. KONEVA, AND M. G. BASSETT. 2001. Cambrian-Early Ordovician brachiopods from Malyi Karatau, the western Balkhash region, and Tien Shan, Central Asia. The Palaeontological Association, Special Papers in Palaeontology, 65, 180 p. JAMES, N. P., AND R. K. STEVENS. 1986. Stratigraphy and correlation of the Cambro-Ordovician Cow Head Group, western Newfoundland. Geological Survey of Canada Bulletin, 366, 143 p. JENSEN, R. G. 1967. Ordovician brachiopods from the Pogonip Group of Millard County, western Utah. Brigham Young University Geology Studies, 14:67–100. JEREMEJEW, P. 1856. Geognostische Beobachtungen an den Ufern des Wolchow. Russisch-Kaiserliche Mineralogische Gesellschaft zu St. Petersbourg, Verhandlungen, 10:63–84. KING, W. 1846. Remarks on certain genera belonging to the class Palliobranchiata. Annals and Magazine of Natural History (London), 18: 26–42. KONEVA, S. P. 1986. Novoje semeistvo kembriiskikh bezzamkovykh brakhiopod. Paleontologicheskii Zhurnal, 1:49–55. KONEVA, S. P., AND L. E. POPOV. 1988. Akrotretidy (bezzamkovye brakhiopody) iz pogranichnykh otlozhenii kembriia-ordovika khrebta Malyi Karatau (iuzhnyi Kazakhstan). Ezhegodnik Vsesoiuznogo Paleontologicheskogo Obshchestva (St. Petersburg), 31:52–72.

← FIGURE 8—1–9, Quadrisonia? lavadamensis new species Notch Peak Formation, Lava Dam Member; Cambrooistodus minutus Conodont Subzone, sample LD156. 1, 2, USNM 516759, dorsal valve exterior, 356, detail of larval shell, 3304; 3, Holotype, USNM 516760, dorsal valve interior, 353; 4, USNM 516761, ventral valve interior, 352; 5–7, USNM 516762, ventral valve exterior, 372; oblique lateral view, 373, detail of larval shell, 3273; 8, USNM 516763, oblique lateral view of ventral valve exterior, 388; 9, USNM 516764, ventral valve interior, 386. 10–28, Eurytreta sublata Popov, 1988, Lava Dam Member, Fryxellodontus inornatus Conodont Subzone, sample L191 (10–14); Clavohamulus elongatus Conodont Subzone, sample H277 (17–22); House Limestone, Barn Canyon Member, Clavohamulus hintzei Conodont Subzone, samples H340 (23), H385 (15, 16, 24–28). 10, USNM 516765, dorsal valve interior, 329; 11, USNM 516766, oblique lateral view of dorsal valve interior, 340; 12, 13, USNM 516767, dorsal valve exterior, 335, oblique lateral view, 340; 14, USNM 516768, dorsal valve interior, 342; 15, 16, USNM 516769, dorsal valve exterior, 330, oblique lateral view, 333; 17–19, USNM 516770, dorsal valve interior, 346, oblique lateral view, 345, oblique posterior view, 351; 20, USNM 516771, ventral valve interior, 355; 21, 22, USNM 516772, ventral valve exterior, 339, oblique posterior view, 349; 23, USNM 516773, dorsal valve interior, 326; 24, 25, USNM 516774, dorsal valve interior, 333, oblique lateral view, 333; 26–28, USNM 516775, ventral valve exterior, 381, oblique posterior view, 397, detail of larval shell, 3316.

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KUHN, O. 1949. Lehrbuch der Palaözoologie. Schweizerbart, Stuttgart, 326 p. KURTZ, V. E. 1971. Upper Cambrian Acrotretidae from Missouri. Journal of Paleontology, 45:470–476. ¨ ber die Brachiopoden-Familie der SiphonotreKUTORGA, S. S. 1848. U taeae. Russisch-Kaiserliche Mineralogische Gesellschaft zu St. Petersbourg, Verhandlungen, 1847:250–286. LOCH, J. D., J. H. STITT, AND J. F. MILLER. 1999. Trilobite biostratigraphy through the Cambrian-Ordovician boundary interval at Lawson Cove, Ibex, western Utah, USA. Quo vadis Ordovician—Short papers of the Eighth International Symposium on the Ordovician System. Acta Universitatis Carolinae, Geologica, 43(1/2):13–16. MATTHEW, G. F. 1901. New species of Cambrian fossils from Cape Breton. New Brunswick Natural History Society, Bulletin, 4:269–286. MENKE, C. T. 1828. Synopsis methodica Molluscorum generum omnium et specierum earum, quae in Museo Menkeano Adservantur. Pyrmonti, 91 p. MILLER, J. F. 1969. Conodont Fauna of the Notch Peak Limestone (Cambro-Ordovician), House Range, Utah. Journal of Paleontology, 43:413– 439. MILLER, J. F., AND B. R. FLOKSTRA. 1999. Graphic correlation of important Cambrian-Ordovician boundary sections. Quo vadis Ordovician—Short papers of the Eighth International Symposium on the Ordovician System. Acta Universitatis Carolinae, Geologica, 43(1/2):81– 84. MILLER, J. F., AND M. E. TAYLOR. 1995. Biostratigraphic significance of Iapetognathus (Conodonta) and Jujuyaspis (Trilobita) in the House Limestone, Ibex Area, Utah, p. 109–112. In J. D. Cooper (ed.), Ordovician Odyssey: Short Papers for the Seventh International Symposium on the Ordovician System. Pacific Section of Society for Sedimentary Geology (SEPM), Book 77. MILLER, J. F., W. N. B. BERRY, J. D. LOCH, AND J. H. STITT. 1999. Tremadocian graptolites from the Lower Ibexian Iapetognathus Zone (Skullrockian Stage), House Limestone, Ibex area, western Utah. Geological Society of America, Abstracts with Programs, 31(7):A-235. MILLER, J. F., K. R. EVANS, J. D. LOCH, R. L. ETHINGTON, AND J. H. STITT. 2001. New lithostratigraphic units in the Notch Peak and House formations (Cambrian-Ordovician), Ibex area, western Millard County, Utah. Brigham Young University Geology Studies, 46:35–69. MILLER, J. F., K. R. EVANS, J. D. LOCH, J. E. REPETSKI, R. L. RIPPERDAN, J. H. STITT, AND J. F. TAYLOR. 1998. Mixed-age redeposited conodonts and trilobites in the proposed global stratotype for the base of the Ordovician System at Green Point, western Newfoundland, Canada. Geological Society of America, Abstracts with Programs, 30(7):A-144. MILLER, J. F., J. D. LOCH, J. H. STITT, R. L. ETHINGTON, L. E. POPOV, K. R. EVANS, AND L. HOLMER. 1999. Origins of the great Ordovician biodiversification: The record at Lawson Cove, Ibex area, Utah, USA. Quo vadis Ordovician—Short papers of the Eighth International Symposium on the Ordovician System. Acta Universitatis Carolinae, Geologica, 43(1/2):459–462. OWENS, R. M., R. A. FORTEY, J. C. W. COPE, A. W. A. RUSHTON, AND M. G. BASSETT. 1982. Tremadoc faunas from the Carmarthen District, South Wales. Geological Magazine, 119(1):1–38. PALMER, A. R. 1998. A proposed nomenclature for stages and series for the Cambrian of Laurentia. Canadian Journal of Earth Science, 35:323– 328. POPOV, L. E., AND L. E. HOLMER. 1994. Cambrian-Ordovician lingulate brachiopods from Scandinavia, Kazakhstan, and South Ural Mountains. Fossils and Strata, 35:1–156. POPOV, L. E., G. T. USHATINSKAYA, AND YU. PELMAN. 1992. Nekotorye

voprosy morfologii i evoliutsii otdelnykh grupp drevneishikh brakhiopod, p. 51–74. In L. N. Repina and A. Yu. Rozanov (eds.), Drevneishie Brakhiopody Territorii Severnoi Evrazii, Novosibirsk. POPOV, L. E., K. K. KHAZANOVITCH, N. G. BOROVKO, S. P. SERGEEVA, AND R. F. SOBOLEVSKAYA. 1989. Opornye razrezy i stratigrafiya kembro-ordovikskoj fosforitonosnoj obolovoj tolshch na severo- zapade Russkoj platformy. AN SSSR, Ministerstvo Geologii SSSR, Mezhvedomstvennym stratigraficheskij komitet SSSR, Trudy 18, 1-222. Nauka, Leningrad. ROSS, R. J., JR., L. F. HINTZE, R. L. ETHINGTON, J. F. MILLER, M. E. TAYLOR, AND J. E. REPETSKI. 1997. The Ibexian, lowermost series in the North American Ordovician. U.S. Geological Survey Professional Paper, 1579-A, 50 p. ROWELL, A. J. 1962. The genera of the brachiopod superfamilies Obolellacea and Siphonotretacea. Journal of Paleontology, 36(1):136–152. ROWELL, A. J. 1966. Revision of some Cambrian and Ordovician inarticulate brachiopods. University of Kansas Paleontological Contributions, Paper 7, 36 p. ROWELL, A. J., AND M. J. BRADY. 1976. Brachiopods and biomeres, p. 165–180. In R. A. Robison and A. J. Rowell (eds.), Paleontology and Depositional Environments: Cambrian of Western North America. Brigham Young University Geology Studies, 23(2). ROWELL, A. J., AND R. A. HENDERSON. 1978. New genera of acrotretids from the Cambrian of Australia and United States. The University of Kansas Paleontological Contributions, 93:1–12. RUSHTON, A. W. A. 1982. The biostratigraphy and correlation of the Merioneth-Tremadoc Series boundary in North Wales, p. 41–59. In M. E. Bassett and W. T. Dean (eds.), The Cambrian–Ordovician Boundary: Sections, Fossil Distributions, and Correlations. National Museum of Wales (Cardiff), Geological Series no. 3. SALTER, J. W. 1866. On the fossils of North Wales, p. 239–381. In A. C. Ramsay (ed.), The Geology of North Wales. Memoirs of the Geological Survey of Great Britain and of the Museum of Practical Geology, 3. SCHUCHERT, C. 1893. A classification of the Brachiopoda. American Geologist, 11(3):141–167. SHERGOLD, J. H., AND R. S. NICOLL. 1992. Revised Cambrian-Ordovician boundary biostratigraphy, Black Mountain, western Queensland, p. 81– 92. In B. D. Webby and J. R. Laurie (eds.), Global Perspectives on Ordovician Geology. Balkema, Rotterdam. STITT, J. H. 1977. Late Cambrian and earliest Ordovician trilobites, Wichita Mountains area Oklahoma. Oklahoma Geological Survey Bulletin, 124, 79 p. STITT, J. H., AND J. F. MILLER. 1987. Jujuyaspis borealis and associated trilobites and conodonts from the Lower Ordovician of Texas and Utah. Journal of Paleontology, 61:112–121. SUTTON, M. D., M. G. BASSETT, AND L. CHERNS. 2000. The type species of Lingulella (Cambrian Brachiopoda). Journal of Paleontology, 73: 426–438. WAAGEN, W. 1885. Salt Range Fossils, Pt. 4(2), Brachiopoda. Memoirs, Palaeontologia Indica, Series 13, 1, Part 5:729–770. WALCOTT, C. D. 1884. Paleontology of the Eureka District. United States Geological Survey Monographs, 8:1–298. WALCOTT, C. D. 1889. Description of a new genus and species of inarticulate brachiopod from the Trenton Limestone. United States National Museum, Proceedings (Washington, DC), 12(775):365–366. WINSTON, D., AND H. NICHOLLS. 1967. Late Cambrian and Early Ordovician faunas from the Wilberns Formation of central Texas. Journal of Paleontology, 41:66–96. ACCEPTED 15 APRIL 2001