THE LATE ORDOVICIAN AND EARLY SILURIAN PENTAMERIDE BRACHIOPOD HOLORHYNCHUS KIAER, 1902 FROM NORTH CHINA

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J. Paleont., 78(2), 2004, pp. 287–299Copyright q 2004, The Paleontological Society0022-3360/04/0078-287$03.00

THE LATE ORDOVICIAN AND EARLY SILURIAN PENTAMERIDEBRACHIOPOD HOLORHYNCHUS KIAER, 1902 FROM NORTH CHINA

JIA-YU RONG,1 REN-BIN ZHAN,1 AND JISUO JIN2

1Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China 210008, ,[email protected];[email protected]. and 2Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada, ,[email protected].

ABSTRACT—Holorhynchus giganteus Kiaer, 1902, a common Late Ordovician (mid-Ashgill) pentameride brachiopod in the Balticregion, Kazakhstan, and southern Tien Shan, is documented for the first time from the Badanjilin Formation (mid-Ashgill) of westernInner Mongolia (Alxa block), North China. Serial sections of the Chinese material confirm the presence of a vestigial ventral medianseptum in the early growth stage of H. giganteus, but the septum becomes embedded in the secondary shell thickening at the adultgrowth stage. A survey of the type material from Norway and additional material from other regions indicates that the incipient ventralmedian septum is a much more commonly developed structure than was previously believed. The presence of a well-developedpseudodeltidium in the Tien Shan material of H. giganteus and the absence of such a structure in conspecific material from many otherregions require a systematic revision of the generic group. Holorhynchus has rodlike crura (5brachial processes) that do not formflanges at their junctions with the inner hinge plates (5outer plates 5 crural plates) and outer hinge plates (inner plates). This, togetherwith the development of a crude spondylial comb structure, points to its affinity to the Virgianidae rather than to the Stricklandiidae.Holorhynchus can be regarded as a Lazarus taxon because of its absence during the crisis (Hirnantian) and survival (early-middleRhuddanian) intervals associated with the Late Ordovician mass extinction and its reappearance in Kazakhstan and North China duringthe Early Silurian (late Rhuddanian-early Aeronian). The mid-Ashgill Holorhynchus fauna, typified by a number of large-shelledpentamerides, was common in the Baltic region, the Urals, Kazakhstan, Tien Shan, Alxa, Qaidam, Kolyma, and east-central Alaska,but largely absent from Laurentia and Siberia (except for Taimyr) in the ancient tropical-subtropical regions. This paleobiogeographicpattern agrees with the general pattern of the Late Ordovician brachiopod provincialism.

INTRODUCTION

HOLORHYNCHUS KIAER, 1902 is a large and primarily smooth-shelled pentameride genus that occurs commonly in the Bal-

tic, Kazakhstan, and Tien Shan regions (e.g., St. Joseph, 1938;Rukavishnikova and Sapelnikov, 1973; Kovalevskii et al., 1991;Hints, 1993). Its distinctive shell morphology and relatively shortstratigraphic range in the Late Ordovician make the genus a usefulbiostratigraphic tool for dating and correlating Rawthyan rocks inEurope and Kazakhstan (Kovalevskii et al., 1991; Brenchley etal., 1997). Its stratigraphic utility is hampered only to a minordegree by its limited recurrence in the Early Silurian (Llandovery)in the Kazakhstan paleoplate and its adjacent blocks (Sapelnikovand Rukavishnikova, 1975). Its large, smooth, and biconvex shellled some early workers to regard Holorhynchus as a transverselyextended form of Pentamerus Sowerby, 1813. The lack of a typ-ical pentameroid ventral median septum (usually clearly visiblethrough the semitransparent shell of Pentamerus) and the pres-ence of a minute dorsal cardinalia in Holorhynchus were firstrecognized by Kiaer (1902) as distinctive features among the LateOrdovician and Early Silurian pentameride brachiopods. St. Jo-seph (1938) was the first to study the shell internal structure ofHolorhynchus by means of serial sectioning. Subsequently, Ho-lorhynchus was treated as a virgianid (Amsden and Biernat, 1965)and found to be very common not only in the Upper Ordovicianstrata of the Baltic region but also in the Upper Ordovician and/or Lower Silurian rocks of Kazakhstan and the Tien Shan region.Sapelnikov and his colleagues (e.g., Nikiforova and Sapelnikov,1973; Sapelnikov and Rukavishnikova, 1975) provided furtherimportant information on the shell structures of Holorhynchus.

Despite numerous previous studies, Holorhynchus requires fur-ther investigation partly because it is one of the small number ofLate Ordovician-Early Silurian pentamerides that have been re-ported to lack a ventral median septum. In early works (e.g., St.Joseph, 1938), the shell structures in transverse sections tend tobe illustrated using simple outlines or solid black fills, withoutdistinction between the lamellar and the prismatic shell layers. Asa result, it has been difficult to identify detailed or minute shellstructures embedded in the thick prismatic layer or secondarythickening at the shell posterior. Serial sections and regular thin

sections prepared for the present study indicate that Holorhynchusgiganteus Kiaer, 1902, the type species of the genus, possesses avestigial ventral median septum in small shells or at the earlygrowth stage of adult shells. This has important implications forinterpreting the evolution and taxonomic position of Holorhyn-chus in the family Virgianidae because it is not clear whether ornot such an incipient ventral median septum is consistently de-veloped in the type material of Holorhynchus from Norway. St.Joseph (1938, p. 296, footnote) insisted on the complete absenceof a ventral median septum, whereas the structure appears to bepresent in a specimen illustrated by Cocks (1982, p. 776, pl. 83,fig. 13). Also, St. Joseph (1938) regarded Holorhynchus to beclosely related to Stricklandia Billings, 1859 on the basis of theirdorsal cardinalia, although he formally assigned Holorhynchus tothe Pentameridae. Cocks (1982) carried the argument further byassigning Holorhynchus to the Stricklandiidae. As will be dis-cussed in this paper, our data indicate that the genus has the clos-est affinity to the Virgianidae.

Another area of confusion over the shell structure of Holor-hynchus is the development of a pseudodeltidium, which has beenfound so far only in some Late Ordovician forms of H. giganteusreported from Tien Shan by Nikiforova and Sapelnikov (1973).Data available hitherto suggest that H. giganteus was the onlylarge-shelled Late Ordovician pentameride that survived the Hir-nantian mass extinction event to reappear in the Early Silurian.More detailed morphological and taxonomic study of Holorhyn-chus is critical for determining whether or not H. giganteus wasa true Lazarus species and, if so, to locate a possible extinctionrefugium during the Hirnantian age. In this study, we attempt tocontribute new data and observations regarding this interestingpentameride genus.

MATERIAL AND STRATIGRAPHIC SETTINGS

The specimens used in this study were collected in two lots:one from the Upper Ordovician and the other from the LowerLlandovery (Fig. 1). The Upper Ordovician material of Holor-hynchus giganteus was collected in 2002 from the Badanjilin For-mation (mid-Ashgill) of Danmianshan in the Badanjilin Desert,western Inner Mongolia. The outcrop area, about 45 km south of

288 JOURNAL OF PALEONTOLOGY, V. 78, NO. 2, 2004

FIGURE 1—Location maps of Holorhynchus occurrences in Upper Or-dovician and Lower Silurian rocks of Northwest China. 1, Map ofChina, with inset enlarged as 2 to show the study area. 2, Detailed mapof the two study areas, with the top left inset enlarged as 3, and thelower right inset enlarged as 4. 3, Upper Ordovician locality (solidtriangle) at Danmianshan, Inner Mongolia. 4, Lower Silurian locality(solid square) at Zhaohuajing, Tongxin County, Ningxia.

FIGURE 2—Stratigraphic nomenclature of the Upper Ordovician and Low-er Silurian successions of Danmianshan, Inner Mongolia, and Zhao-huajing, Ningxia, Northwest China.

Yagan and 135 km southeast of the town of Ejin County, is lo-cated in the northeastern part of the Paleozoic Alxa Block (Chenand Rong, 1992).

The Badanjilin Formation (Fig. 2) consists mainly of a 300–500 m thick succession of shallow marine, siliciclastic strata withcarbonate interbeds, suggesting the Badanjilin Desert being anepeiric sea during the Late Ordovician. Holorhynchus occurs inthe coquinitic-crinoidal wackestone and packstone facies of theformation, with well-preserved peloid grains common inside someof the shells (Fig. 3.5). Most shells of Holorhynchus giganteus inthe Badanjilin Formation are broken and disarticulated, suggest-ing their deposition under high-energy water conditions. The spe-cies occurs in a low-diversity brachiopod assemblage, includingH. giganteus (114 specimens), Altaethyrella Severgina, 1978(108), Ovalospira Fu, 1982 (58), Leptellina Ulrich and Cooper,1936 (9), Sowerbyella Jones, 1928 (6), Pectenospira Popov, Ni-kitin, and Sokiran, 1999 (1), atrypide (1), and orthide (1). Cal-culation of the above relative abundance data using the PAST soft-ware (Hammer et al., 2002) indicates that the brachiopod speciesdiversity attains a notably low Shannon index value of 1.3.

Shannon index H 5 2 (Ni/N)ln(Ni/N)O

where Ni is the number of individuals of the ith species in asample, N is the total number of individuals of all species in thesample; a high-diversity assemblage would have a Shannon indexvalue greater than 2.5.

Other fossil groups consist of relatively abundant solitary ru-gose corals and relatively small colonies of tabulate corals (e.g.,Agetolites Sokolov, 1955), rare trilobites and nautiloids, and com-mon crinoid ossicles (Zheng et al., 1987). The sample, however,was collected by means of hand-picking from weathered surfacesand probably carries a certain degree of collection bias.

A combination of abundant shelly-crinoidal bioclastic grains,spherical peloid grains inside relatively well-preserved shells,common corals of relatively small size, and a low to moderatediversity of brachiopods suggests a depositional setting betweennormal and maximum storm wave bases (i.e., 30–70 m). TheHolorhynchus giganteus assemblage from the Badanjilin Forma-tion, therefore, can probably be assigned to Benthic Assemblage3 (sensu Boucot, 1975).

The Holorhynchus giganteus-bearing beds are correlative to theBadanjilin Formation in the No. 4 Section nearby (Zheng et al.,1987), where the occurrence of a Staurocephalus clavifrons An-gelin, 1854 trilobite fauna indicates a mid-Ashgill age (Zhou andZhou, 1982). Neither graptolites nor Holorhynchus have beenfound in the No. 4 Section.

The type material of the Lower Silurian specimens of Holor-hynchus sinicus Fu, 1982 was collected initially by Zhou Zhi-qiang in 1978 from the upper part of the Zhaohuajing Formation(upper Rhuddanian–lower Aeronian) of central Ningxia, NorthChina, and the specimens were subsequently described by Fu

289RONG ET AL.—ORDOVICIAN-SILURIAN HOLORHYNCHUS FROM NORTH CHINA

(1982). In 1995, two of the present authors (JYR and RBZ) car-ried out further field work in the area and collected topotype ma-terial (field collection NX6). The Holorhynchus sinicus-bearingstrata of the Zhaohuajing Formation are exposed in the Zhao-huajing area (Fig. 1), north of the town of Tongxin County, south-ern Ningxia. In addition, Holorhynchus sinicus occurs in thelargely coeval strata at Yezhugou, 20 km south of the town ofZhongning County in central Ningxia.

The Zhaohuajing Formation is composed of dark gray to black,argillaceous, nodular, bioclastic limestone with calcareous sand-stone and siltstone in the basal part. Gao (1987) and He et al.(1987) reported an association of Holorhynchus sinicus with ru-gose corals (e.g., Brachyelasma irregulare He in Kong andHuang, 1978 and Tongxinophyllum tongxinensis Gao, 1987), tab-ulate corals, and a few stropheodontid and atrypide brachiopods.

Below the Holorhynchus sinicus-bearing horizon, a stratigraph-ic unit of dark gray, yellowish gray, or purple gray, argillaceous,bioclastic or nodular limestones yielded a low-diversity and high-abundance brachiopod assemblage characterized by Eospiriferdasifiliformis Fu, 1982, Dolerorthis Schuchert and Cooper, 1931,and Meifodia Williams, 1951. Other fossil groups include diverserugose corals, some tabulate corals, nautiloids, gastropods, andtrilobites.

At the Yezhugou section (about 40 km north of the type areaof Holorhynchus sinicus; Fig. 1) of the Zhaohuajing Formation,H. sinicus occurs in the argillaceous limestone of Bed 7 (31.4 m,upper Zhaohuajing Formation). In a thin bed (25 cm) of inter-calated calcareous shale of this stratigraphic unit, the presence ofa graptolite association, represented by Pseudoclimacograptushughesi (Nicholson, 1867), Normalograptus miserabilis (Ellesand Wood, 1906), and N. minutus (Carruthers, 1868), suggests alate Rhuddanian-early Aeronian age (Gao, 1987; He et al., 1987).The Holorhynchus sinicus-bearing horizon is overlain by theHanxia Formation of siliciclastic facies (sandstone and siltstone)and is underlain by the lower Zhaohuajing Formation of carbonaterocks with interbedded siliciclastic mudstone. A total of 14 brokenventral valves and a single incomplete dorsal valve of Holorhyn-chus sinicus was collected, and the shells range from very small(8 mm in width) to very large (78 mm). The Holorhynchus sinicusbrachiopod assemblage is virtually monospecific, except for a sin-gle additional specimen of eostropheodontid and a trilobite.

TAXONOMIC SIGNIFICANCE OF THE VENTRAL MEDIAN SEPTUM IN

PENTAMEROIDS

In the majority of pentameride genera, the spondylium is sup-ported by a median septum and, in comparison, the lack of aventral median septum is unusual and considered a distinctivefeature for some of the pentamerides. The archetypal pentameride,Pentamerus, has a median septum extending between one-thirdto two-thirds of the shell length, as do many other genera (e.g.,Pentameroides Schuchert and Cooper, 1931, Brooksina Kirk,1922, and Tcherskidium Nikolaev and Sapelnikov, 1969). In manyother pentameride groups, however, the length of the median sep-tum is highly variable. Several genera (e.g., Kirkidium Amsden,Boucot, and Johnson, 1967 and Pentamerifera Khodalevich,1939) possess the longest median septum, which extends almostto the anterior shell margin. (For examples of various medianseptum lengths, see Kirk, 1922, 1925; Nikolaev and Sapelnikov,1969; and Sapelnikov, 1976, 1985a.) There are also pentamerides(e.g., Kulumbella Nikiforova, 1960, Microcardinalia Boucot andEhlers, 1963, and Galeatellina Sapelnikov and Rukavishnikova,1976) that have a short spondylium and median septum restrictedto the posterior one-fifth to one-fourth of the shell. Towards theother end of the spectrum, several genera (e.g., EoconchidiumRozman, 1967, Harpidium Kirk, 1925, and Vosmiverstum Breiveland Breivel, 1970) bear a short median septum confined mainly

to the umbonal area and the spondylium is largely free anteriorly(Nikiforova and Sapelnikov, 1971; Rong and Yang, 1981).

Within the 80 or so genera of the suborder of Pentameridina,there are eight genera that have been reported to lack a ventralmedian septum (Boucot et al., 2002). These genera are scatteredacross two superfamilies: the Stricklandioidea and the Penta-meroidea. Within the former there occur three such genera:Aenigmastrophia Boucot, 1971, Spondylostrophia Sapelnikovand Rukavishnikova, 1975, and Stricklandiella Sapelnikov andRukavishnikova, 1973, all of Llandovery age. Several penta-meroid genera also lack a ventral median septum (e.g., Eokirk-idium Khodalevich and Sapelnikov, 1970, Vagranella Sapelni-kov, 1960, and Subriana Sapelnikov, 1960), all of which areLate Silurian (Ludlow) in age except for Holorhynchus (Boucotet al., 1971; Sapelnikov, 1985b; Kovalevskii et al., 1991). Datapresented in this paper, of course, preclude Holorhynchus fromthis group (see more detailed discussion under systematic de-scription of the genus).

Distribution of the genera without a ventral median septumacross different pentameride superfamilies suggests that a freespondylium is polyphyletic in origin. The first occurrence of sucha septumless condition is found in the three stricklandioid generaduring the Llandovery Epoch, and the second occurrence in thepentamerids and subrianids mainly during the Ludlow. So far, acompletely free spondylium has not been found in the Clorindoi-dea and Gypiduloidea, although some genera in these two super-families may have a very short median septum.

In terms of autecology, those genera that lack a ventral medianseptum almost invariably have a transversely extended, subellip-tical to subtriangular shell (especially the dorsal valve), usuallywith broad costae or plicae (e.g., Spondylostrophia, Vagranella,Eokirkidium, and Subriana). It can be postulated that such shellsrequired a weaker muscular force for opening or closing than didsmooth and elongate shells (longer leverage from the hinge axisto the shell gravity center) with a rectimarginate commissure(which would require a wider opening to achieve the same openarea compared to shells with a zigzag commissure). In otherwords, shells with a reduced shell length probably did not needa median septum to fortify the muscle attachment site on thespondylial floor. It should be pointed out that, in some taxa, suchas Vagranella diversoplicata Sapelnikov, 1960 and Stricklandiellarobusta (Rong and Yang, 1981), the spondylium is supported pos-teriorly by thickened shell substance, even though the medianseptum is absent. The shell thickening would have served thesame supporting function in a weakly biconvex shell as would amedian septum in moderately to strongly convex shells.

In a few pentameroids, the spondylium may be either free orsupported by a very short (apical) median septum. The presenceor absence of a short or incipient median septum can often beobserved in the same population of a species. As will be discussedlater in this paper, Holorhynchus appears to fall into this category.Similar examples of Silurian age include Mariannaella Sapelni-kov and Rukavishnikova, 1975 (Llandovery); Virgianella Niki-forova and Sapelnikov, 1971 (middle Llandovery); Pseudocon-chidium Nikiforova and Sapelnikov, 1971 (middle Llandovery);and Lissidium Lenz, 1989 (Wenlock). To determine the presenceor absence of a ventral median septum, it is crucial to investigatecarefully the lamellar shell layer in the apical areas of both youngand adult forms, especially using the technique of serial section-ing.

CHARACTERISTICS OF THE SPONDYLIUM IN HOLORHYNCHUS

Compared to other genera of the Virgianidae, the spondyliumin Holorhynchus is rather short and shallow, which, together withthe lack or poor development of a median septum, makes a uni-form, single-chambered umbonal cavity (Fig. 3.1–3.3). Also, the


FIGURE 3—Holorhynchus sinicus Fu, 1982 from the Zhaohuajing Formation, lower Llandovery, Tongxin, Ningxia; 1, 2, NIGP135533, thin sectionof arched apical area of ventral valve showing U-shaped spondylium and lamellar layer of median septum (msl) embedded in shell thickening(msp—lateral boundary of prismatic layer of median septum). Note median septum not long enough to divide umbonal cavity; 3, NIGP135534,slightly oblique longitudinal section cutting through both side walls of spondylium and apical median septum (msl); 4, 5, 6, NIGP135535, thin


←

section of dorsal valve showing smooth junctions of crus with inner hinge plate (ihp) and outer hinge plate (ohp); note inner hinge plates fusingsmoothly (not wedged in) with inner surface of valve floor; 7, NIGP135536, cross section showing broad V-shaped spondylium near its midlength;8, NIGP135537, thin section through distal end of spondylium; note comb structure near recurved tip (top of spondylium).

anterior portion of the spondylium in Holorhynchus curvesstrongly to the dorsal direction, with the distal end bending slight-ly backward to the posterior direction in relatively large speci-mens. Cross sections through the distal end of the spondylium,therefore, become an elongate oval structure (Fig. 3.8; see alsoSt. Joseph, 1938; Fu, 1982). A similar configuration of the spon-dylium can be found in other virgianids (e.g., Pleurodium, Wang,1955 and Plicidium Rong and Yang, 1981).

In the serial sections prepared for the present study, the spon-dylial comb structure (s. Jin and Copper, 2000 5 spondylial fil-ament of Rong and Yang, 1977) is observed for the first time inHolorhynchus (Fig. 3.8). The structure is crude and restricted tothe spondylial floor at the distal end resembling that of VirgianaTwenhofel, 1914. In terms of shell microstructure, the lack ofspondylial saw structure, median groove (common in Pentamerusand Pentameroides), and hook structure (common in stricklan-diids; Jin and Copper, 2000) can be regarded as supporting evi-dence for assigning Holorhynchus to the Virgianidae.

The comb structure was originally observed by Rukavishnikovaand Sapelnikov (1973) and, subsequently, Rong and Yang (1981)found the comb structure to be best developed near the anteriorend of the spondylium in some stricklandiids. The structure typ-ically consists of 10 to 30 parallel ridges along the spondylialfloor. Rong and Yang (1981) further pointed out that the combstructure (as small denticles in the transverse sections) is distinc-tive from the spondylium in its optical property, and they postu-lated that the structure may have served as attachment sites ofdorsal diductor muscles, similar to the filamentous structures inthe cardinal pit of certain spiriferides, atrypides, and rhynchonel-lides. Jin and Copper (2000) noted that the comb structure orig-inated from the secondary thickening layer (myotest) and wascommonly buried in this layer. The comb structure has been foundin Pleurodium, Clorinda Barrande, 1879, Plicidium (Rong andYang, 1981), Stricklandia Billings, 1859 (Jin and Copper, 2000),Prostricklandia Rukavishnikova and Sapelnikov, 1973, Procon-chidium Rukavishnikova and Sapelnikov, 1973, Microcardinalia,Tcherskidium (Zhan and Cocks, 1998), and Virgiana Twenhofel,1914 (Jin and Copper, 2000). All these genera appear to be con-fined stratigraphically to rocks of mid-Ashgill to Llandovery age.The comb structure is associated mainly with taxa that have ashallow spondylium. More work is needed to determine the tax-onomic value of this structure, which is absent from the familyPentameridae, although it seems to occur randomly in several oth-er pentameride families.

EVOLUTIONARY, PALEOECOLOGICAL, AND

PALEOBIOGEOGRAPHICAL IMPLICATIONS

Holorhynchus appears to have spread widely in the warm waterregions during the mid-Ashgill. It was commonly associated withabundant corals of relatively high diversity, as recorded in theBadanjilin Formation of Inner Mongolia. So far, Holorhynchushas not been found to associate with the Hirnantia Lamont, 1935Fauna in the Kosov Province during Hirnantian time (Rong andHarper, 1988; Brenchley et al., 1997). Stratigraphically, Holor-hynchus occurs almost invariably immediately below the Hirnan-tia Fauna (e.g., see Kovalevskii et al., 1991), suggesting that thegenus inhabited shallow and warm waters immediately before theHirnantian mass extinction event.

After its absence from the early Hirnantian to middle Rhud-danian, Holorhynchus reappeared during the late Rhuddanian-ear-ly Aeronian, represented by two species, H. cinghizicus Borissiak,1955, from Kazakhstan and H. sinicus from North China. Theabsence of Holorhynchus during the crisis and survival intervalsacross the Late Ordovician mass extinction event indicates thatthe genus is a Lazarus taxon (s. Jablonski, 1986). Survival of largeor gigantic brachiopod taxa across the glacially induced Late Or-dovician mass extinction event (Sheehan, 2001) was a very rarephenomenon because Late Ordovician brachiopod gigantism wascommon only in deposits of shallow tropical waters and the large-shelled species usually became extinct at the onset of the Hirnan-tian glaciation and sea level drawdown (Jin, 2001). In future re-search, it would be interesting to locate the refugium of Holor-hynchus and to determine its environmental characteristics duringthe crisis (Hirnantian) and survival (early-middle Rhuddanian) in-tervals.

During the Late Ordovician (mid-Ashgill, pre-Hirnantian), apentameride brachiopod fauna characterized by one or more ofsuch relatively large forms as Holorhynchus, Proconchidium,Tcherskidium, and Eoconchidium, existed in a group of paleopla-tes including Baltica, Kazakhstan, South China, and their adjacentblocks (e.g., Kolyma, Alaska, Alxa). Holorhynchus was perhapsthe most distinctive and most common member of this fauna andit would be appropriate to call this fauna the ‘‘Holorhynchus fau-na,’’ although Holorhynchus itself could be absent in some re-gions (e.g., South China). In contrast, this fauna is virtually absentfrom the large, tropically located paleoplate Laurentia, except forthe occurrence of Holorhynchus, Tcherskidium, and Eoconchi-dium in the suspect terranes of eastcentral and northeastern Alaska(Blodgett et al., 1987, 1988) and Proconchidium in the CanadianArctic (Rong et al., 1989). In Siberia, only one occurrence of aHolorhynchus-Tcherskidium association is known from the Tai-myr region (Nikiforova, 1989; Cocks and Modzalevskaya, 1997).The complete absence of the Holorhynchus fauna from Gondwanaas well as peri-Gondwana blocks further supports the interpreta-tion that the fauna lived mainly in tropical warm waters (Fig. 4).The pattern of Ashgill brachiopod provincialism can be tracedback to the early Caradoc (Nemagraptus gracilis Biozone) duringthe major global sea level rise and marine transgression (Jin,1996). A similar pattern of provincialism has been observed alsoin some other benthic faunas. The Agetolites coral fauna, for ex-ample, has been found to be common in Kazakhstan, Kolyma,Alaska, North China, South China, Qaidam, Zhungar, and otherregions, but the coral fauna is similarly missing from Laurentiaand Siberia (Lin in Lai et al., 1982). The provincialism was prob-ably not the result of different depositional environments becausethe Foliomena Havlicek, 1952 Fauna, which was partly coeval tothe Holorhynchus fauna but lived in deeper water (BA4–BA6;Sheehan, 1979; Cocks and Rong, 1988; Rong and Harper, 1988),is also absent from Siberia and Laurentia (except for two marginalareas; see Rong et al., 1999). The mid-Ashgill Holorhynchus fau-na of shallow and warm tropical waters was replaced in severalregions (e.g., Kazakhstan and the Baltic region) by the HirnantiaFauna of relatively shallow and cool water environment duringthe Hirnantian glacial interval. The similar absence in Laurentiaand Siberia of these three faunas of widely disparate geological


FIGURE 4—Paleogeographic distribution of Holorhynchus during mid-Ashgill and early Llandovery times (see Appendix). The genus is large-ly absent from the large, tropically located Laurentia and Siberia pa-leoplates as well as from the coldwater Gondwana and peri-Gondwanaregions.

and paleoecological settings implies that the Late Ordovician bra-chiopod provincialism was probably not controlled simply by en-vironmental factors (e.g., water temperature) but rather affectedby the relative positions of the paleoplates, sea level stand, oceancurrents, and availability of oceanic islands as stepping stones offaunal migration (e.g., Fortey, 1984; Jin, 1996).

SYSTEMATIC PALEONTOLOGY

Figured specimens are deposited in the Nanjing Institute ofGeology and Palaeontology (NIGP), Nanjing or in the Xi’an In-stitute of Geology and Mineral Resources (XIGM), Xi’an, China.

Order PENTAMERIDA Schuchert and Cooper, 1931Superfamily PENTAMEROIDEA M’Coy, 1844

Family VIRGIANIDAE Boucot and Amsden, 1963Subfamily VIRGIANINAE Boucot and Amsden, 1963

Genus HOLORHYNCHUS Kiaer, 1902Type species. Holorhynchus giganteus Kiaer, 1902. Langara

Formation (5Langara Shale and Limestone), mid-Ashgill, Osloregion, Norway (St. Joseph, 1938; Cocks, 1982; Brenchley et al.,1997).

Diagnosis (emended herein). Shell medium-sized to verylarge, transversely to longitudinally ellipsoidal to subrhomboidalin outline, nearly equibiconvex to ventribiconvex; usually smoothor with weak, irregular costae; trilobate in some large shells.Spondylium entirely free or supported by minute median septumin apical area (Fig. 3.1–3.3); median septum may be embeddedin prismatic layer or shell thickening at adult growth stage. Innerhinge plates (5outer plates 5 crural plates) short, discrete, sub-parallel to each other; outer hinge plates (5inner plates) slightlylonger than inner hinge plates (Figs. 3.4–3.6, 7); crura (5brachialprocesses) rodlike, circular in cross section, forming smooth junc-tions with outer and inner hinge plates without flanges.

Species assigned. Holorhynchus giganteus, Langara Forma-tion, mid-Ashgill, Oslo region, Norway (Brenchley et al., 1997);

Holorhynchus giganteus latisulcifer Rukavishnikova and Sapel-nikov, 1973, Tolen beds, central and eastern Kazakhstan; Nondiacanadensis Boucot and Chiang, 1974, Nonda Formation, Aeron-ian, Rocky Mountains, northern British Columbia, Canada;Holorhynchus cinghizicus Borissiak, 1955, Alpeis horizon, lower-middle Llandovery, eastern and southern Kazakhstan. Holorhyn-chus sinicus Fu, 1982, Zhaohuajing Formation, upper Rhuddani-an-lower Aeronian, Ningxia, North China.

Species excluded. Holorhynchus lalaensis Sapelnikov, 1963,Wenlock beds, eastern slope of central Urals; excluded from Ho-lorhynchus by Rong and Boucot (1998) because of its triangularand strongly dorsibiconvex shell with laterally directed cruralflanges. Holorhynchus tuberosus Sapelnikov, 1963, Wenlockbeds, eastern slope of central Urals; trilobate shells with extremelywide and shallow spondylium and prominent, laterally directedcrural flanges preclude it from Holorhynchus (Rong and Boucot,1998). Virgianella sogdianica Nikiforova and Sapelnikov, 1973,from the upper Archalyk Formation (lower-middle Llandovery)of the Zeravshan Range, was assigned to Holorhynchus (Nondia)by Rong and Boucot (1998), but it may be best to retain thisspecies in Virgianella because of its strongly convergent innerhinge plates (forming a U-shaped cruralium) in V. sogdianica andother congeneric species (e.g., Rong and Yang, 1981; Sapelnikov,1985a).

Occurrences. Mid-Ashgill to lower Llandovery. Balto-Scan-dia, Urals, Kazakhstan, Tien Shan, North China, Alaska, and Ko-lyma.

Discussion. The lack of a ventral median septum has beenregarded as one of the diagnostic features of Holorhynchus (Bou-cot et al., 2002). The common presence of an incipient medianseptum and the variability of other features of Holorhynchus fromthe Badanjilin Formation, however, requires emendation of thegeneric diagnosis. For the Norwegian type material of Holorhyn-chus giganteus, St. Joseph (1938, p. 296) emphasized the totalabsence of a ventral median septum, despite that a structure inhis serial sections of the apical area superficially resembles a me-dian septum. Cocks (1982, p. 776, pl. 83, fig. 13) illustrated aninternal mould of H. giganteus from the Langara Formation,which showed a minute median septum. A rudimentary ventralmedian septum in this taxon appears to be present in the apicalarea of a specimen figured by Boucot et al. (1971, pl. 5, fig. 2),although these authors stated that a ventral median septum is ab-sent. Sapelnikov (1985b, pl. 14, fig. 2) noted a rudimentary ven-tral median septum embedded in the apical shell thickening in atransverse section of a shell from the Archalyk Formation (Ash-gill) of the Zeravshan-Gissar Range of southern Tien Shan. De-tailed reinvestigation in the future may prove that a rudimentarymedian septum is a much more consistent feature in Holorhyn-chus than was believed in the past.

Holorhynchus giganteus from the type area of Norway andmost other localities appears to have a completely open delthyr-ium and lack a pseudodeltidium (e.g., St. Joseph, 1938; Sapelni-kov and Rukavishnikova, 1975). Shells of Holorhynchus gigan-teus reported in this paper also lack this structure. The conspecificmaterial from the Zeravshan Range of southern Tien Shan (Ni-kiforova and Sapelnikov, 1973; Sapelnikov, 1985a), however, hasa well-developed, ventrally concave pseudodeltidium. It is notclear at the present whether or not the presence or absence of apseudodeltidium is of taxonomic significance at the specific level.In other groups of pentameroids, however, the pseudodeltidium isa consistent structure. Pentamerus and Pentameroides, for ex-ample, invariably have a pseudodeltidium similar to that of Ho-lorhynchus giganteus from Tien Shan (Jin and Copper, 2000).

Nondia Boucot and Chiang, 1974, from the lower Nonda For-mation (upper Rhuddanian-lower Aeronian) of the CanadianRocky Mountains, resembles Holorhynchus in having a smooth


shell and a free spondylium. Boucot and Chiang (1974) distin-guished Nondia from all other genera of the Virgianinae by itssubrhomboidal shell outline and a median ridge in the ventralvalve (mistakenly stated to be in the dorsal valve in Rong andBoucot, 1998). These morphological similarities and differencesled Rong and Boucot (1998) to treat Nondia as a subgenus ofHolorhynchus. Our investigation of Holorhynchus and Nondiasuggests that the ventral median ridge is not sufficiently consistentto be regarded as a diagnostic feature at the generic or subgenericlevels. Thus, it seems that the only differences between Holor-hynchus and Nondia are their shell size and outline—Nondia hasa medium shell size and an elongate, subrhomboidal shell outline,whereas a large shell size and a transversely extended outlinetypify Holorhynchus. At the present, Nondia is treated provision-ally as a subgenus of Holorhynchus (s. Rong and Boucot, 1998)because the presence or absence of a ventral median septum isnot clearly known in the poorly preserved type material of Non-dia.

Holorhynchus is also similar to Virgianella Nikiforova and Sa-pelnikov, 1971 in possessing a large and smooth shell, but Vir-gianella differs in its strongly arched ventral umbo and beak andits inner hinge plates being variously convergent to each othertowards the valve floor or forming a cruralium (Sapelnikov,1985a, pl. 15, figs. 2, 3). An incipient ventral median septum isalso visible (wedged into the thickened prismatic layer) in theapical area in shells of Virgianella (Nikiforova and Sapelnikov,1971, p. 50), although these authors did not regard this structureas a true median septum. The presence of a median septum inVirgianella is corroborated by the presence of a short and strongmedian septum in the serial sections of V. glabella (Rong andYang, 1981) from the upper Xiangshuyuan Formation (Aeronian,Llandovery) of northeastern Guizhou, South China. This led Rongand Yang (1981) to emend the diagnosis of Virgianella to includeforms with a smooth shell and a short median septum. It shouldbe noted also that each of the crura (brachial processes) in Vir-gianella forms a laterally directed flange at its junction with theinner hinge plate (similar to the crura of Pseudoconchidium),whereas in Holorhynchus the junctions of crura with the outer orinner hinge plates are relatively smooth without flanges (similarto those of Virgiana).

HOLORHYNCHUS GIGANTEUS Kiaer, 1902Figures 5.1–5.18, 5.22–5.25, 6, 7

Holorhynchus giganteus KIAER, 1902, p. 63, figs. 1–7; SCHUCHERT AND

COOPER, 1932, pl. 27, fig. 30; ST. JOSEPH, 1938, p. 292, pl. 4, figs. 1–5; BORISSIAK, 1955, p. 44, pl. 4, figs. 1, 2; BORISSIAK, 1964, p. 72,pl. 1, figs. 1–4; GAURI AND BOUCOT, 1968, p. 106, pl. 11, figs. 3, 4;BOUCOT ET AL., 1971, p. 277, pl. 5, figs. 1–9; pl. 6, figs. 1–5; NIKI-FOROVA AND SAPELNIKOV, 1973, p. 68, pl. 1, figs. 8–10; pl. 2, figs.1–5; pl. 3, figs. 1, 2; pl. 4, fig. 1; pl. 5, fig. 1; SAPELNIKOV AND

RUKAVISHNIKOVA, 1975, p. 47, pl. 7, fig. 1–4; pl. 43, fig. 1; NIKITIN

IN APOLLONOV ET AL., 1980, p. 64, pl. 20, fig. 1; COCKS, 1982, p. 774,pl. 83, figs. 12–17; ORADOVSKAYA IN KOREN ET AL., 1983, p. 53, pl.9, fig. 1; HINTS, 1993, p. 121, pl. 1, figs. 5–7; BEZNOSOVA, 1994, p.61, pl. 2, figs. 1–7.

Holorhynchus cf. giganteus; SAPELNIKOV AND BEZNOSOVA, 1980, p. 4,pl. 1, figs. 1–5.

Holorhynchus ex gr. giganteus; NIKIFOROVA, 1989, p. 80, pl. 2, figs. 1–3.Holorhynchus giganteus latisulcifer RUKAVISHNIKOVA AND SAPELNIKOV,

1973, p. 90, pl. 1, figs. 1–14; pl. 2, figs. 9, 10; SAPELNIKOV AND

RUKAVISHNIKOVA, 1975, p. 49, pl. 8, figs. 1–14; pl. 9, figs. 1–5.

Description (Inner Mongolian material). Shell small to verylarge, with many small to medium-sized specimens being trans-versely subelliptical in outline, weakly to moderately ventribicon-vex (Fig. 5); outer shell surface usually smooth, but faint costaemaybe present in relatively large shells. Concentric growth lines

commonly developed, irregular in strength and spacing, inter-rupted by irregular growth lamellae in anterior and lateral areasof large individuals (Fig. 5.25). Narrow and shallow medial fur-row clearly defined in both valves (Fig. 5.13, 5.16, 5.17). Ventralpalintrope uniformly curved and well developed; ventral umboand beak relatively low, strongly curved, arched above dorsalumbo. Delthyrium open, without pseudodeltidium. Anterior mar-gin rectimarginate.

Spondylium broadly V- to U-shaped (Fig. 5.7, 5.8), confinedto posterior one-fourth of shell length; distal portion of spondy-lium bending strongly toward dorsal direction, with its distal endcurving slightly backward to posterior. Median septum present,well-defined in small shells, dividing umbonal cavity into twominute chambers (Fig. 6, 0.2–0.3 mm from apex), becoming em-bedded in apical shell thickening in large shells.

Inner hinge plates short, subparallel to each other in cross sec-tion (Figs. 5.4, 7), extending anteriorly for one-seventh to one-fifth of shell length. Outer hinge plates triangular in shape, robust,equal to or slightly longer than inner hinge plates in length. Crurarodlike, subcircular in cross section, forming smooth junctions(without flanges) with outer and inner hinge plates, with anteriorends unsupported by outer or inner hinge plates (Fig. 7). Low andthin median ridge present in some specimens, extending to mid-length of valve in some large specimens.

Material examined. One hundred twenty-four specimens fromthe Badanjilin Formation (mid-Ashgill), Danmianshan, Yagan,Ejin Banner, western Inner Mongolia. Most specimens are incom-plete and disarticulated, and shell dimensions can be measuredfor only seven specimens (Table 1). There are many larger spec-imens that cannot be measured because of their incompleteness.Figured specimens: NIGP135526, NIGP135527, NIGP135528,NIGP135529, NIGP135530, NIGP135531, NIGP135532,NIGP135546, and NIGP135547 (last two serially sectioned; seeTable 1 and Figs. 6, 7).

Discussion. Our investigation of Holorhynchus giganteusfrom the Baltic region, Kazakhstan, Tien Shan, and North Chinarevealed a number of morphological variations that may have tax-onomic implications:

1. Ventral median septum. As discussed in previous sections,the ventral median septum is present at least in some speci-mens of the mid-Ashgill Holorhynchus giganteus from Nor-way, Tien Shan, and North China and in the Llandovery H.sinicus from North China.

2. Pseudodeltidium. So far, a well-developed pseudodeltidiumhas been found only in the Tien Shan material assigned toH. giganteus by Nikiforova and Sapelnikov (1973), althoughthe type material from Norway appears to lack this structure(St. Joseph, 1938). A restudy of the Norwegian forms bydetailed serial sectioning will be crucial for assessing the var-iability of this feature among different populations of Holo-rhynchus giganteus.

3. Median ridge. A median ridge may be present on the innersurface of some large dorsal valves of the Inner Mongolianmaterial and in some specimens from the Norwegian typearea (see Boucot et al., 1971, pl. 6, fig. 1; Cocks, 1982, pl.83, fig. 14). A reassessment of the consistency of this struc-ture in the Norwegian type material of H. giganteus will beimportant for determining the validity of other Holorhynchusspecies.

4. Median furrow. A narrow and shallow median furrow of var-iable relief can be seen on both valve surfaces in some of theInner Mongolian material (Fig. 5.16, 5.17) and on a dorsalvalve from Norway (Boucot et al., 1971, pl. 5, fig. 5). Sucha median furrow is regarded as one of the diagnostic char-acters of H. giganteus latisulcifer from mid-Ashgill rocks of



FIGURE 6—Serial sections of conjoined shell of Holorhynchus giganteus, NIGP135546, Badanjilin Formation, mid-Ashgill, Inner Monglolia. Noteclearly defined median septum in apical area (0.2–0.3 mm from apex).

←

FIGURE 5—1–18, 22–25, Holorhynchus giganteus Kiaer, 1902 from the Badanjilin Formation, mid-Ashgill, Danmianshan, Inner Mongolia; 1–5,NIGP135525, dorsal, ventral lateral, posterior, and anterior views of immature shell, 32; 6–10, NIGP135526, dorsal, ventral, lateral, posterior, andanterior views of small shell; note open delthyrium, 32; 11–15, NIGP135527, ventral, lateral, dorsal, posterior, and anterior views of relativelysmall shell, 32.5; 16–18, NIGP135528, dorsal, ventral, and lateral view of medium-sized shell with damaged posterior, 32; 22, NIGP135529,lateral view of posterior fragment, 32.4; 23, NIGP135530, exterior of ventral valve with cracked surface, 32; 24, NIGP135531, exterior of ventralvalve, 31.9; 25, NIGP135532, lateral view of weathered shell, 31.8. 19–21, 26, 27, Holorhynchus sinicus, Zhaohuajing Formation, lower Llan-dovery, Tongxin, Ningxia; 19–21, paralectotype, XIGM-B911, dorsal, lateral, and posterior views of relatively small shell, 31.5; 26, 27, lectotype,XIGM-B910, ventral and lateral views of large ventral valve, 31.

southern Kazakhstan (Rukavishnikova and Sapelnikov,1973), although the furrow may vary from prominent to in-conspicuous in the Kazakhstan species. Thus, the wide rangeof variation in the median furrow development implies thatthe structure is not reliable for species-level classification.

5. External ribbing. Although Holorhynchus usually has asmooth shell, irregular, faint to moderately developed radialribbing is not uncommon in H. giganteus (St. Joseph, 1938,pl. 4, fig. 1; Nikiforova and Sapelnikov, 1973), H. latisulcifer(Rukavishnikova and Sapelnikov, 1973, pl. 1, fig. 1), and H.sinicus (Fig. 5.26).

In summary, a detailed restudy of the type material of H. gi-ganteus and its comparison with conspecific material from otherregions with respect to the five variable characters discussedabove are important not only for clarifying the confusions overHolorhynchus taxonomy, but also for determining whether or notH. giganteus is a Lazarus taxon at the species level.

HOLORHYNCHUS SINICUS Fu, 1982Figure 5.19–5.21, 5.26, 5.27

Holorhynchus sinicus FU, 1982, p. 135, pl. 38, figs. 1, 2; FU, 1985, p.93, pl. 1, figs. 4, 5.

Types. Syntypes, XIGM B910 and XIGM B911. ZhaohuajingFormation (upper Rhuddanian-lower Aeronian), Tongxin County,Ningxia, North China. Fu (1982) selected two syntypes but did

not designate a holotype. Specimen B910 is a large ventral valve(for measurements see Table 2) and is selected herein as the lec-totype (Fig. 5.26, 5.27) and B911 as a paralectotype (Fig. 5.19–5.21).

Other material examined. Approximately 15 specimens col-lected by Rong and Zhan from the type locality in 1995; mostspecimens are incomplete ventral valves. Figured hypotypes:NIGP135533, NIGP135534, NIGP135535, NIGP135536, andNIGP135537.

Discussion. Fu (1982) described Holorhynchus sinicus fromthe upper Zhaohuajing Formation (upper Rhuddanian-lowerAeronian) of Ningxia, North China. Reinvestigation of the typeand topotype material of Fu’s species suggests its close affinityto H. giganteus in shell size, outline, and weak costae in largeforms. Fu (1982) separated H. sinicus from H. giganteus on thebasis that the spondylium is less strongly curved to the dorsaldirection in H. giganteus than in H. sinicus, although this is mostlikely a result of different orientations of the transverse sections.In the present paper, the spondylial curvature is not considered tobe of any taxonomic significance. Some large shells of H. sinicushave pronounced trilobation, which is common in the Early Si-lurian Pentamerus but usually absent or poorly developed in theLate Ordovician Holorhynchus of the Baltic region. On the otherhand, the degree of consistency of such structures as the ventralmedian septum, pseudodeltidium, and the median ridge inside


FIGURE 7—Serial sections of dorsal valve of Holorhynchus giganteus, NIGP135547, Badanjilin Formation, Danmianshan, Inner Mongolia. Note thatthe distal portions of the crura were not preserved in the disarticulated dorsal valve.

TABLE 1—Measurements (mm) of Holorhynchus giganteus from the Badanjilin Formation, Inner Mongolia.

12. NIGP135546 3 4

5. NIGP135547 6 7

LengthWidthThicknessMedian septumInner hinge plate length

5.86.13.4P

0.8

5.97.63.4P

0.8

8.58.8*4.8

P1.6

13.2*14.1*7.5?

3.1

14.613.88.7??

15.618.5*

—?

4

20.5*25.0*11.2

?5.2

* 5 estimate; P 5 present; ? 5 not visible from shell exterior.

each valve is not fully understood in H. giganteus from the Nor-wegian type area. Pending further detailed investigation, there-fore, H. sinicus is retained provisionally as a separate species.Should it be confirmed that the Norwegian forms are completelydevoid of a pseudodeltidium but have a consistently developedincipient median septum, H. sinicus would be considered a juniorsynonym of H. giganteus, but the Tien Shan forms of H. gigan-teus with a pseudodeltidium (Nikiforova and Sapelnikov, 1973)would require systematic revision.

ACKNOWLEDGMENTS

Z.-C. Zheng of the Geological Surveying Team of Ningxia Au-tonomous Region, Z.-G. Zhou of the Xi’an Institute of Geologyand Mineral Resources, X. Chen, H.-K. Xu, and Y. Wang of theNanjing Institute of Geology and Palaeontology (NIGP) providedinvaluable field assistance. L.-P. Fu of the Xi’an Institute of Ge-ology and Mineral Resources generously gave access to the typematerial of Holorhynchus sinicus. Z.-Y. Zhou (NIGP) kindly iden-tified the trilobites associated with H. sinicus in the ZhaohuajingFormation. Y.-G. Ren and Z.-G. Chen (NIGP) assisted in prepar-ing the line drawing and photographic illustrations. This researchproject is funded by the Major Basic Research Project(G2000077700) from the Ministry of Science and Technology ofChina (Rong and Zhan), Senior Visiting Scientist Fellowship fromthe Chinese Academy of Sciences (Jin), and the Natural Sciencesand Engineering Research Council of Canada (Jin).

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APPENDIX

Fossil data for paleobiostratigraphic discussion.

Baltica and adjacent blocks. Horizon 5b (Langara Shale and Lime-stone), mid-Ashgill, Asker, Norway (H. giganteus Kiaer, 1902; St. Joseph,1938; Boucot et al., 1971; Brenchley et al., 1997). Mid-Ashgill beds,Sweden (Jaanusson, 1982; Pedersen et al., 1992). Yaptikshor beds, Kyra

horizon, mid-Ashgill, western slope of Boreal Urals (H. giganteus; Mod-zalevskaya and Sapelnikov, 1973; Sapelnikov and Beznosova, 1980; Bez-nosova, 1994). Kabala and Taucionys Formations, Pirgu Stage, mid-Ash-gill, Estonia, Latvia, and Lithuania, eastern Baltic region (H. giganteus;H. sp. Paskevicius, 1982; Kovalevskii et al., 1991; Hints, 1993).

Kazakhstan and adjacent blocks. Tolen horizon, mid-Ashgill, Chingizand Tarbagatai ranges, Chu-Illi Mountains, and Dzhungar Alatai (H. gi-ganteus, H. giganteus latisulcifer, Rukavishnikova and Sapelnikov, 1973;Sapelnikov and Rukavishnikova, 1975). Akadombak beds, mid-Ashgill,Chingiz Range, eastern Kazakhstan (H. giganteus; Klenina, 1984).Chashmanklon and Archalyk beds, Ashgill, Zeravshan-Gissar ranges,Tien-Shan (H. giganteus; Nikiforova and Sapelnikov, 1973; Rozman,1978; Kim et al., 1978). Lower Archalyk beds, mid-Ashgill, ZeravshanRange, Tian-Shan (H. giganteus; Nikiforova and Sapelnikov, 1973). Al-peis horizon, lower Llandovery, Kazakhstan (Chingiz-Tarbagatai andChu-Ili Mountains) (H. cinghizicus, Borissiak, 1955, 1964; Rukavishni-kova and Sapelnikov, 1973; Sapelnikov and Rukavishnikova, 1975). Bad-anjilin Formation, mid-Ashgill, western Inner Mongolia (H. giganteus,Alxa block; this paper). Zhaohuajing Formation, lower Llandovery, Ni-ngxia (H. sinicus, Alxa block; this paper).

Laurentia and adjacent blocks. Nonda Formation, lower Llandovery,northern British Columbia, Canada (Nondia norfordi Boucot and Chiang,1974). Tirekhtyakh Formation, beds N and O, mid-Ashgill, Omulev High-land, Kolyma (H. giganteus; Oradovskaya, 1983; Kovalevskii et al.,1991). Fossil Creek Volcanic Suite (upper part, Ashgill), east-centralAlaska (Holorhynchus n. sp. Blodgett et al., 1987).

Siberia and adjacent blocks. Ashgill beds, central Taimyr, Siberia (H.ex gr. giganteus, H. giganteus; Nikiforova, 1989; Cocks and Modzalev-skaya, 1997).

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THE LATE ORDOVICIAN AND EARLY SILURIAN PENTAMERIDE BRACHIOPOD HOLORHYNCHUS KIAER, 1902 FROM NORTH CHINA