This article was downloaded by: [212.26.82.16] On: 24 April 2012, At: 16:20 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Alcheringa: An Australasian Journal of Palaeontology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/talc20 A new bivalve fauna from the Permian–Triassic boundary section of southwestern China Yongqun Gao a , G. R. Shi a & Yuanqiao Peng a a School of Life and Environmental Sciences, Deakin University, Melbourne Campus, 221 Burwood Highway, Burwood, VIC, 3125, Australia Available online: 02 Mar 2009 To cite this article: Yongqun Gao, G. R. Shi & Yuanqiao Peng (2009): A new bivalve fauna from the Permian–Triassic boundary section of southwestern China, Alcheringa: An Australasian Journal of Palaeontology, 33:1, 33-47 To link to this article: http://dx.doi.org/10.1080/03115510802618227 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and- conditions This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.
Transcript
This article was downloaded by: [212.26.82.16]On: 24 April 2012, At: 16:20Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Alcheringa: An Australasian Journal ofPalaeontologyPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/talc20
A new bivalve fauna from thePermian–Triassic boundary section ofsouthwestern ChinaYongqun Gao a , G. R. Shi a & Yuanqiao Peng aa School of Life and Environmental Sciences, Deakin University,Melbourne Campus, 221 Burwood Highway, Burwood, VIC, 3125,Australia
Available online: 02 Mar 2009
To cite this article: Yongqun Gao, G. R. Shi & Yuanqiao Peng (2009): A new bivalve fauna from thePermian–Triassic boundary section of southwestern China, Alcheringa: An Australasian Journal ofPalaeontology, 33:1, 33-47
To link to this article: http://dx.doi.org/10.1080/03115510802618227
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representationthat the contents will be complete or accurate or up to date. The accuracy of anyinstructions, formulae, and drug doses should be independently verified with primarysources. The publisher shall not be liable for any loss, actions, claims, proceedings,demand, or costs or damages whatsoever or howsoever caused arising directly orindirectly in connection with or arising out of the use of this material.
GAO, Y., SHI, G.R. & PENG, Y., March, 2009. A new bivalve fauna from the Permian–Triassic boundary section ofsouthwestern China. Alcheringa 33, 33–47. ISSN 0311-5518.
A new marine bivalve fauna from the continuous Upper Permian Longtan Formation to Lower Triassic YelangFormation of the Zhongzai section in southwestern China is documented. Four bivalve assemblages spanning thePermian–Triassic boundary are recognized and regionally correlated in South China. The bivalve assemblageschanged from elements dominated by Palaeozoic types to those dominated by Mesozoic types. Three new species,Claraia zhongzaiensis sp. nov., Claraia sp. nov. 1 and Claraia sp. nov. 2, are described.
Yongqun Gao [[email protected]], G.R. Shi [[email protected]] & Yuanqiao Peng [[email protected]], School of Life and Environmental Sciences, Deakin University, Melbourne Campus, 221 Burwood Highway,Burwood, VIC 3125, Australia. Received 11.2.2008; revised 21.4.2008; accepted 21.5.2008.
THE CLOSE of the Permian saw the mostprofound alteration of marine and terres-trial faunas in Earth history with losses ofover 90% of marine species and nearly 70%of land vertebrate species (Erwin 1993,1994). Many invertebrate associations werereplaced by quite different faunas in theearliest Triassic. Bivalves are the only majorcomponents of both Late Permian andEarly Triassic invertebrate faunas. Theywere affected by the end-Permian crisis,but survived better than any other group(Fraiser & Bottjer 2005) to become thedominant shelly benthos of the Mesozoic(Hallam & Wignall 1997, Fraiser & Bottjer2007). Bivalve abundance during the EarlyTriassic does not appear to be a taphonomiceffect (Fraiser & Bottjer 2007), hence, thePermian–Triassic Boundary (PTB) is widelyconsidered to mark the transition to thebivalve-dominated Modern Fauna.
The Zhongzai PTB section (Fig. 1; alsonamed the Helaga section by Yao et al.
1980) was first studied by Yao et al. (1980),who documented abundant fossil bivalvesfrom the PTB strata. Around twenty yearslater, Wang & Yin (2001) restudied thesection and first introduced it as theZhongzai section. This section possesses asimilar PTB sequence to the Meishan GSSPsection (Fig. 2), as indicated by thePermian–Triassic Boundary StratigraphicSet (PTBST) in Peng et al. (2001). Inaddition, the Early Triassic conodont indexfossilHindeodus parvus (Kozur & Pjatakova,1976) has been found in the limestone of thePTBST at the Zhongzai section (Nicoll &Metcalfe 2005), making the PTB of thissection readily correlative to the MeishanGSSP. Consequently, this section has beenthe focus of much recent attention becauseof its potential as a bridge to correlate thePTB (and even the terrestrial PTB) sectionsin southwestern China to southeasternChina, where the Meishan GSSP section islocated (Peng et al. 2002).
Abundant fossils have been found acrossthe PTB at the Zhongzai section in recentyears, and in this study, we document itsdiverse bivalve fauna. Four bivalve
ISSN 0311-5518 (print)/ISSN 1752-0754 (online)� 2009 Association of Australasian PalaeontologistsDOI: 10.1080/03115510802618227
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assemblages are recognized, described andregionally correlated across South China.Three newClaraia species are also described.
The changing pattern of bivalve faunasfollowing the end-Permian mass extinctionis also documented and discussed.
Fig. 1. Location of the Zhongzai section, southwestern China. Solid lines represent roads, coarsely dashed lines arerailways and finely dashed lines are provincial boundaries.
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StratigraphyThe Zhongzai section is located 5 km northof Zhongzai Village, Landai Town, LiuzhiCounty, Guizhou Province (Fig. 1). Thesection is exposed along a newly builtcountry road from Landai Town to Zhong-zai Town. It is well exposed and readilyaccessible. The sediments in the Zhongzaisection are composed mainly of shallowmarine carbonates and littoral clastics. Thelithostratigraphy of the Zhongzai sectionincludes, in ascending order, the conform-
able Upper Permian Longtan Formationand the Lower Triassic Yelang Formation.The Longtan Formation is characterized bymixed lithologies of marine and terrestrialclastics, together with minor shallow marinecarbonate interbeds. There are interbeddedcoal seams in the lower part of the LongtanFormation. The upper part of the YelangFormation is dominated by fossiliferousmarine clastic rocks, locally intercalatedwith marine carbonates.
The Early Triassic index fossilHindeodusparvus has been reported from the PTB
Fig. 2. PTB sequence of the Zhongzai section in southwestern China and its correlation with the Meishan section, theGlobal Stratotype Section and Point (GSSP) of the PTB (after Peng et al. 2001).
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sequence at the Zhongzai section (Nicoll &Metcalfe 2005), much like its occurrence inthe Meishan GSSP section (Fig. 2). Thus,the PTB of the Zhongzai section can bebiostratigraphically subdivided with high-resolution (Fig. 2). A typical Late Permianfossil assemblage has been found in theUpper Permian Longtan Formation,including cephalopods: Lopingoceras sp.,Pernodoceras sp., Pleuronodoceras sp., Pseu-dogastrioceras sp.; bivalves: Astartella am-biensis (Waagen, 1881), A. symmetrica Liu,1976, Etheripecten sp., Guizhoupecten sp.,Isognomon sinensis (Frech, 1911),Palaeolimasichuanensis Liu, 1976, Palaeolima sp.,Palaeoneilo guizhouensis Chen & Lan (in
Nanjing Institute of Geology and Palaeon-tology, 1976), Pernopecten sichuanensisLiu, 1976; brachiopods: Cathaysia chone-toides (Chao, 1927), Crurithyris speciosaWang 1956, Neochonetes strophomenoides(Waagen, 1884), N. substrophomenoides(Huang, 1932), Orthothetina ruber (Frech,1911), Spinomarginifera alpha (Huang,1932), S. chenyaoyanensis Huang, 1932, S.sp., Tethyochonetes guizhouensis (Liao,1980), T. soochowensis (Chao, 1928),T. wongiana (Chao, 1928), T. liaoi Chen,Shi, Shen & Archbold, 2000; and a trilobite:Pseudophillipsia sp. The Yelang Formationis dominated by Early Triassic faunas, espe-cially the thin-shelled bivalveClaraia. Small-
Fig. 3. Bivalve assemblages of the Zhongzai section and their regional correlations.
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sized (‘dwarfed’) lingulid brachiopods arealso very common (Peng et al. 2007, Peng &Shi 2008), as is the microgastropod Polygyr-ina assemblage (He et al. 2008). Together,the thin-shelled bivalves, ‘dwarfed’ brachio-pods and microgastropods constitute ahighly distinctive low-diversity and high-abundance neritic fauna of earliest Triassicage at the Zhongzai section.
Bivalve biostratigraphyBivalves are abundant in both Upper Per-mian and Lower Triassic strata in theZhongzai section. Four bivalve assemblagesfrom the Late Permian to the Early Triassiccan be recognized based on the variedstratigraphic ranges of the bivalve species inthe section. In general, these four bivalveassemblages can be readily correlated withsimilar bivalve assemblages/zones from otherPTB sections in South China (Yin 1982 1985,Long et al. 1991, Fang 2004; Fig. 3).
Tambanella–Pernopecten Assemblage (beds1–11 of the Zhongzai section)Besides the zonal elements, this LatePermian bivalve assemblage is composedof a diverse Late Permian bivalvefauna, including the genera: Palaeoneilo,Towapteria, Guizhoupecten, Wilkingia, Avi-culopecten, Euchondria, Astartella, Palaeoli-ma, Nuculopsis, Limipecten, Ptychopteria,Phestia, Stutchburia, Isognomon, Etheripec-ten, Girtypecten, Taimyria, Septimyalina,Streblochondria, Streblopteria and Lepto-chondria. This bivalve assemblage is wellcorrelated with the Late Permian Tamba-nella–Claraioides Assemblage proposed byFang (2004). However, Claraioides might bea synonym of the Late Permian genusClaraia, both of which have a very limiteddistribution in southwestern China (seereviews by Yang et al. 2001, Gao et al.2004). Therefore, given the uncertainty overthe validity of Claraioides, Pernopecten ispreferred over Claraioides as a nominal
taxon for the Late Permian bivalve assem-blage in South China. Pernopecten is a verycommon element of Late Permian bivalvefaunas of South China, as indicated by Yin(1982, 1985) and Long et al. (1991).Hunanopecten is another very commonelement of most of these faunas but hasnot been recovered at Zhongzai. Never-theless, most other key species of the SouthChina Late Permian bivalve assemblage,including Palaeoneilo, Towapteria, Guizhou-pecten, Aviculopecten and Palaeolima, occurin the Zhongzai section, among others.
Pteria ussurica variabilis Assemblage (beds12–15a of the Zhongzai section)This assemblage spans the Permian–Triassicboundary. It is composed mainly of newtaxa of Early Triassic aspect, but retainsminor Late Permian relicts (e.g. Palaeoneilosp.). Pteria ussurica variabilis is widelydistributed through the shallow marinedeposits of South China and is mostlyfound in neritic clastic facies. Long et al.(1991) recognized a Pteria ussurica varifur-cata-Towapteria scythicum Assemblage forthe earliest Triassic of Guizhou Provincebased on the old designation of the PTB inthis area. Likewise, the Pteria-Towapteria-Promyalina Assemblage has been proposedby Fang (2004) for the latest Permian toearliest Triassic bivalve suites in SouthChina. These assemblages are interpretedto correlate with our newly establishedPteria ussurica variabilis Assemblage in theZhongzai section.
Claraia wangi–C. griesbachi Assemblage(beds 15b–17 of the Zhongzai section)Claraia species are very common in thisassemblage. The assemblage is especiallymarked by the first appearance of Claraiawangi and C. griesbachi. Apart from thesenominal taxa, other bivalve species includeClaraia guizhouensis, C. yunnanensis, C.concentrica, C. aurita and Eumorphotisspecies. In the Zhongzai section Claria
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griesbachi is not confined to this assemblagebut extends into the overlying Claraiaaurita–C. stachei Assemblage. Elsewhere inSouth China, this same bivalve assemblageis recognizable at most localities in LowerTriassic rocks, although C. griesbachi hasnot been included as a nominal zonal taxonby some workers (Yin 1982, 1985, Longet al. 1991, Tong & Yin 2002, Fang 2004).The Claraia wangi–C. griesbachi Assem-blage attains a global distribution (Yin1985) in the earliest Triassic marine realmin the aftermath of the end-Permian massextinction (Hallam & Wignall 1997).
Claraia aurita–Claraia stachei Assemblage(beds 18–30 of the Zhongzai section)This is a cosmopolitan assemblage domi-nated by Claraia species. Both Claraiaspecies and other Early Triassic bivalvesare diverse at this stage in South China andall over the world. Besides Claraia species,other bivalves recognized regionally includeEumorphotis, Leviconcha, Promyalina,Towapteria, Neoschizodus, Leptochondria,Palaeoneilo, Bakevellia and Gervilla. Thisbivalve assemblage has been recognized inGuizhou Province (Long et al. 1991). It isalso correlatable to the Claraia stachei Zoneand the Claraia aurita Zone in South China(Tong & Yin 2002), and part of the Claraiawangi–Eumorphotis Fauna (Fang 2004).
Pattern of bivalve changeacross the PTBAlthough bivalves are abundant in both theLate Permian and Early Triassic faunas ofthe Zhongzai section, few genera andspecies are shared. In general, the bi-valve assemblages change from elementsdominated by Palaeozoic types to thosedominated by Mesozoic types following theend-Permian mass extinction. Among the 24Late Permian genera (49 species) present inthe Zhongzai section, only 3 genera and
species (Pteria ussurica variabilis, Eumor-photis illyrica, Towapteria sp.) extend intothe Early Triassic (Fig. 4). Confirming theobservation made by Yin (1982), the Pecti-nacea are predominant, comprising abouthalf of the total genera and species of LatePermian bivalves. The earliest Triassic rockscontain an impoverished, intermediate fau-na, which does not closely resemble youngerTriassic faunas. Seven genera are found inthe Lower Triassic of the Zhongzai section,among which Claraia and Eumorphotis havethe most species.
The end-Permian mass extinction eventnot only reduced the gross diversity ofbivalve faunas, it also changed the grouprepresentation. The Late Permian bivalvefauna of the Zhongzai section includes 24genera and 49 species, whereas the EarlyTriassic bivalve fauna comprises only 7genera and 23 species. Of these, only threegenera survived into the earliest Triassic:Aviculopecten and Palaeoneilo extend up tothe PTB bed but disappeared soon there-after, whereas Towapteria occurs consis-tently below and above the PTB.Excluding these genera, all Late Permianbivalve genera disappeared during the end-Permian mass extinction, resulting in anextinction rate of around 88% of generaand 94% of species at Zhongzai.
There were also profound changes inthe morphology of bivalves across thePermian–Triassic transition including a sig-nificant decrease in shell size, shell thicknessand a tendency to much flatter shells. Thesechanges are reminiscent of morphologicaladjustments in some other marine inverte-brate groups of Permian–Triassic age. Forexample, various workers have noted mor-phological changes in brachiopods andconodonts that have been interpreted as aresponse to stressful environments and theshortage of primary productivity (foodsupply) during the Permian–Triassic transi-tion (Hayami 1997, Luo et al. 2006, He et al.2007b, Peng et al. 2007, Twitchett 2007).
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Although bivalve faunas changed dra-matically during the end-Permian massextinction, as a clade they persisted intothe earliest Triassic, with low diversity andhigh abundance (Erwin 1993, Hallam &Wignall 1997). The rapid evolutionaryturnover of bivalves was probably one oftheir successful attributes for recoveryfollowing the end-Permian event. In parti-cular, the bivalves Claraia and Eumorpho-tis evolved rapidly, attaining at least 30species each in the Griesbachian (less than1 Ma in duration) in South China (Yanget al. 1991). Thus, on average, a newspecies evolved about every 0.03 Maduring that time, much faster than thetypical evolutionary rate for bivalves(0.061 new species per Ma, Stanley1979). Consequently, these bivalve speciesrapidly dominated the shallow seas inthe aftermath of the end-Permian massextinction.
Systematic palaeontologyAll specimens described in this paper arehoused at Museum Victoria, Melbourne,Australia, and are registered with theprefix NMVP. Each number represents onespecimen. Most specimens are preserved assingle valves. Conjoined specimens of bothright and left valves are very rare, especiallyfor the Early Triassic bivalves. Of thebivalves identified in this paper (Fig. 5),only the new species are described. Theclassification of Pterinopectinidae followsNewell (1937).
Discussion. The familial position of Claraiahas long been debated. It has been asso-ciated with several bivalve families since itsestablishment as reviewed by Waterhouse(2000). These include Aviculidae (Patte1935), Aviculopectinidae (Pseudomonoti-nae) (Dickins & McTavish 1963, Ichikawa1958), Pseudomonotidae (Ciriacks 1963,Ichikawa & Yin 1966, Nakazawa 1977,1981), Aviculopectinidae (Hertlein et al.1969), Aviculopectinidae (Aviculopectini-nae) (Newell 1969, Kulikov & Tkachuk1979), Pectinidae (Li & Ding 1981) andLimidae (Muromtseva 1984). The familialposition of Claraia was most clearlyresolved to the Pterinopectinidae Newell,1937, after the hinge structure of chevronwas discovered in the genus (Zhang 1980).Consequently, Claraia and the morphologi-cally similar Dunbarella Newell, 1937 areconsidered to be sister groups within thisfamily (Zhang 1980, Waterhouse 2000).
The hinge areas of most Claraia-likespecimens are not well preserved, especiallyamong Early Triassic samples, which areusually flat and thin-shelled (Waterhouse2000). Thus, it is usually impractical todefine Claraia-like species on the basis ofhinge structures. Nevertheless, Gavrilova(1996) constructed an elaborate classifica-tion of Late Permian to Early TriassicClaraia-like bivalves. Three subfamilies weredefined, in which the number of chevrons,their shape, and character of alteration withshell growth were applied as criteria for theaggregation of Claraia-like genera andspecies into subfamilies (Gavrilova 1996).On this basis, Pseudoclaraia has beenconsidered to be a junior synonym ofClaraia (Yang et al. 2001, Chen & Komatsu2002, Chen 2004, Fang 2004, He et al.2007a), as has Claraioides (Yang et al. 2001).Thus far, Claraia-like species with well-developed ligament areas include Claraiaperthensis Dickins & McTavish, 1963,‘Pseudoclaraia’ aurantiformis Zhang, 1980,Claraia primitiva Yin, 1985, Guichiella
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angulata Li & Ding, 1981, ‘Claraioides’guizhouensis Fang, 1993 and Claraia wangi(Patte) of Chen & Komatsu (2002). Accord-ing to Gavrilova’s subdivision, the otherknown Claraia-like species can only betentatively included in this genus if primeattention is laid on the structure of theligament (Waterhouse 2000). In this paper,greater emphasis is placed on the traditionalmorphology of Claraia-like species. This is amore practical approach and features can bereadily recognized from all well-preservedmaterials. These include byssal attachment,nature of the ornament and the degree ofauriculation.
Claraia zhongzaiensis sp. nov. (Fig. 5S, T)
Material. Holotype (NMVP 309753:Fig. 5S). One well-preserved right valve(NMVP 309753), one inner mould of rightvalves (NMVP 309754) and several brokenright valves.
Type unit and locality. Bed 24, YelangFormation (Lower Triassic); Zhongzai sec-tion, Liuzhi, Guizhou Province, China.
Etymology. Refers to Zhongzai village, afterwhich the host section is also named.
Diagnosis. Valves roughly circular, ca17 mm both in length and width. Distinctright anterior auricle and a moderatelydeveloped byssal notch.
Description. Shell subrounded, right anteriorauricle large, distinct, triangular and coveredwith fine growth lines. Byssal notch moder-ate and clear, tapering posteriorly. Umbolarge, occupying almost one-third of thewhole shell. Right valve flat. Shell coveredwith fine growth lines that are grouped intoseveral concentric wrinkles (Fig. 5S, T).
Discussion. The new species is similar toseveral other Early Triassic Claraia speciesthat are characterized by a prominent rightanterior auricle, conspicuously developedbyssal notch and concentric wrinkles. Clar-aia sp. of Gan & Yin (1978, pl. 114, fig. 23)from Guizhou Province differs only by itslong oblong right anterior ear, wider byssalnotch with parallel sides and relatively ovalshape. Claraia anulata Yin & Gan (Gan &Yin, 1978, pl. 114, figs 8, 9, 16), Claraiaconcentric (Yabe) of Gan & Yin (1978, pl.113, fig. 17) and Claraia orbicularis(Richthofen) of Gan & Yin 1978, pl. 114,fig. 6) are also distinct from this new speciesin their rectangular right anterior ears and
Fig. 4. Lithostratigraphic column for the Zhongzai section and distribution of bivalves. Stars refer to specimenscollected from the bed in this study, dashed lines indicate the full known stratigraphic ranges of bivalve species fromthis section including information from previous studies, and the solid lines represent the actual ranges of thesespecies as observed in the present study. 1, Pernopecten symmetricus curtus; 2, Palaeolima dieneri; 3, Pernopectenguizhouensis; 4, P. hayingshanensis; 5, Towapteria equicosta; 6, T. minima; 7, Streblochondria zhongyingensis; 8,Nuculopsis sp.; 9, Limipecten globules; 10, Euchondria longtanensis; 11, Phestia sp.; 12, Ptychopteria (Actinopteria)problematica; 13, P. sichuanensis; 14, Nuculopsis darlingensis; 15, N. wymmensis; 16, Aviculopecten beipeiensis; 17,Euchondria dalongensis; 18, Etheripecten fasciculicostatus; 19, Nuculopsis yangtzeensis; 20, Palaeolima sichuanensis;21, Schizodus lopingensis; 22, Stutchburia sp.; 23, Tambanella sp.; 24, Limipecten sp.; 25, Tambanella subquadrata; 26,Pernopecten sp.; 27, Schizodus sp.; 28, Astartella symmetrica; 29, Euchondria sp.; 30, Astartella sp.; 31, Pernopectensichuanensis; 32, Palaeolima sp.; 33, Isognomon sp.; 34, Etheripecten sp.; 35, Girtypecten sp.; 36, Astartella ambiensis;37, Guizhoupecten sp.; 38, Isognomon sinensis; 39, Leptochondria virgalensis; 40, Palaeoneilo guizhouensis; 41,Septimyalina sp.; 42, Schizodus pinguis; 43, S. schlotheimi; 44, Streblopteria sp.; 45, Taimyria sp.; 46,Wilkingia sp.; 47,Aviculopecten sp.; 48, Palaeoneilo sp.; 49, Pteria ussurica variabilis; 50, Eumorphotis illyrica; 51, Claraia wangi; 52,Myophoria (Leviconcha) orbicularis; 53, Palaeonucula qinganensis; 54, Palaeonucula sp.; 55, Towapteria sp.; 56,Claraia hunanica,; 57, C. guizhouensis; 58, C. yunnanensis; 59, Entolium discites; 60, Claraia zhenanica; 61, C.hubeiensis; 62, Pteria sp.; 63, Claraia sp.; 64, C. griesbachi; 65, Eumorphotis sp.; 66, Claraia concentrica; 67,Eumorphotis telleri; 68, C. aurita; 69, C. stachei; 70, C. decidens; 71, C. tumida; 72, C. longyanensis.
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byssal notches with parallel sides. Com-pared with this new species, Claraia con-centrica (Yabe) of Nakazawa (1977, pl. 3,fig. 9) has a relatively short byssal notchthat tapers more sharply and has much
clearer concentric wrinkles. Claraia long-yanensis Chen (Chen 2004, pl. 4.4.2, fig. 4) isalso distinguished from the new species byits widely spaced concentric wrinkles andlack of concentric lines on the right anterior
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auricle. Claraia dieneri Nakazawa(Nakazawa 1977, Waterhouse 2000, fig.1D) differs from this new species by itsnarrow anterior auricle above an evenlyconcave byssal notch. Claraia songpanensisXu (Xu 1978, pl. 105, fig. 20) differs by itsrounded shape, shorter right anterior ear andshallower byssal notch. The well-developedradial lines or wrinkles of Claraia bioniNakazawa (Nakazawa 1977, pl. 3, fig. 3),Claraia diana Guo (1985, pl. 10, figs 1–9),Claraia stacheiBittner (Chen 1976, pl. 31, fig.28), Claraia yunnanensis (Yin & Hsu) ofChen (1976, pl. 32, fig. 17), Claraia zhiyunicaYang, Gao et Peng (Yang et al. 2002, fig. 2,B–L, K–N) easily separate them from thenew species although they all have rightanterior ears. Claraia primitiva Yin (Yin1982, pl. 29, 4–6) and Claraia shabaonica(Fang 1993) can be easily recognized fromthis new species by their deep and wide byssalnotch with the inner end extending to theventral or rear ventral margin (Yang et al.2002, Fang 1993, pl. I, figs 10, 11, 13 – 15).The concentric wrinkles of the new speciesalso readily separate it from Claraia griesba-chi (Chen 1976, pl. 32, figs 9–13, Nakazawa1977, pl. 3, figs 13, 14), which additionallyhas a small right anterior ear that is eithersmooth or with obscure concentric lines.Claraia hubeiensis Chen (Chen 1976, pl. 33,fig 24) and Claraia aurita (Hauer) of Chen(1976, pl. 32, fig 1) differ from the new speciesby their smaller right anterior ears that areusually extended in the direction of the
ventral margin, and their byssal notches thatare oblique to the anterior margin. Claraiawangi (Patte) of Chen (1976, pl. 32, fig. 20)can be distinguished from the new species byits obscure byssal notch that is undifferen-tiated from the body. The new species has asimilarly conspicuous right anterior ear to C.liuqiaoensisHe et al., 2007a, but the shape ofthe ear is different.
Claraia sp. 1 (Fig. 5M)
Material. One right valve (NMVP309748)
Host unit and locality. Bed 30, YelangFormation (Lower Triassic); Zhongzai sec-tion, Liuzhi, Guizhou Province, China.
Description. This specimen (Fig. 5M) is16 mm long and 15 mm high. Right shellsub-rounded, flat; hinge line straight andhalf of the shell length with one obscureparallel hinge groove imprint; umbo occu-pying half of the body. Right anteriorauricle small and well formed, covered byconcentric lines, extending at the end andset off from body by a groove-like auricularsulcus lower than the adjacent umbonalfold, thus resulting in an obscure byssalnotch. Right posterior wing large, lessdifferentiated from body of shell. Sculpturedwith concentric lines and wrinkles. Radiallines conspicuous in the middle part of theshell, intersecting with the concentric linesto form a lattice.
Fig. 5. Bivalves of the Zhongzai section, Liuzhi, Guizhou Province, China. A, Claraia griesbachi (Bittner), rightvalve,6 3.4, NMVP309737. B, Claraia dieneri Nakazawa, right valve,6 2.4, NMVP309738. C, Claraia griesbachi(Bittner), right valve mould,6 3, NMVP309739. D, Claraia griesbachi (Bittner), right valve,6 4, NMVP309740. E,Eumorphotis sp., right valve,6 4, NMVP309741. F, Claraia wangi (Patte), right valve mould,6 2.8, NMVP309742.G, Claraia wangi (Patte), right valve,6 4, NMVP309743. H, Claraia griesbachi (Bittner), right valve,6 3.5,NMVP309744. I, Claraia griesbachi (Bittner), right valve mould,6 3.5, NMVP309745. J, Claraia griesbachi(Bittner), right valve,6 3.5, NMVP309755. K, Claraia griesbachi (Bittner), right valve mould,6 3.8, NMVP309746.L, Claraia wangi (Patte), right valve,6 2.5, NMVP309747. M, Claraia sp. nov. 1, right valve,6 3, NMVP309748. N,Claraia griesbachi (Bittner), right valve,6 2.7, NMVP309749. O, Eumorphotis sp. nov, right valve,6 4,NMVP309750. P, Claraia sp. 1, right valve mould,6 3, NMVP309756. Q, Eumorphotis sp., right valve,6 7,NMVP309751. R, Claraia sp. 2, right valve,6 2.3, NMVP309752. S, Claraia zhongzaiensis sp. nov., rightvalve,6 1.6, NMVP309753. T, Claraia zhongzaiensis sp. nov., right valve mould,6 1.6, NMVP309754.
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Discussion. This informally named speciesclosely resembles Claraia wangi (Patte) ofChen & Komatsu (2002, pl. 3, figs 3a, 5a, 6)in its hinge groove imprint but differs bybeing covered with radial lines. Claraiastachei Bittner of Chen (1976, pl. 31, fig 28)is distinct from this new species in possessinga conspicuous byssal notch and clearer radiallines. The well-developed anterior ear of thepresent species readily separates it fromClaraia guizhouensis Chen (1976, pl. 32, figs26–28) despite the latter sharing similarsculptures. The sub-rounded shape of thenew species is also distinct from Claraiazhenanica Chen & Liu of Chen (1976, pl. 32,figs 7–8). Despite the differences with itsclosest allies, clearly more material is neededbefore a new species can be formally erected.
Claraia sp. 2 (Fig. 5R)
Material. One complete right valve (NMVP309752)
Host unit and locality. Bed 28, YelangFormation (Lower Triassic); Zhongzai sec-tion, Liuzhi, Guizhou Province, China.
Description. The specimen is 19 mm longand 13 mm high (Fig. 5R). Right shell sub-rounded, flat. Hinge line straight and two-thirds of the shell length. Right anteriorauricle small and well formed, covered withconcentric lines that extend to the terminus.Byssal notch large and clear. Right poster-ior wing large, less differentiated from bodyof shell. Sculptured with concentric wrin-kles. Radial lines conspicuous on the middlepart of the shell, intersected by the con-centric lines to form a lattice.
Discussion. The new species is similar to theLate Permian Claraia zhiyunica Yang, Gao& Peng (Yang et al. 2002, pl. 3) and Claraiaprimitiva Yin (Yin 1982, pl. 29, figs 1–7) inthe nature of its byssal notch, but differs byhaving shallower and irregular concentric
wrinkles, and radial lines that cover onlythe middle part of the whole valve, thusthe lattice is not so conspicuous. Given thesimilar byssal notch and sculpture of thisEarly Triassic species, it may have evolvedfrom either C. zhiyunica or C. primitiva, bothof which are restricted to the Late Permian.
ConclusionsThe continuous clastic shallow marinePermian–Triassic sequence at the Zhongzaisection in southwest China and its well-preserved fossil assemblages provide usefuldata for the correlation of latest Permianand earliest Triassic zones between theshallow-water sedimentary successions ofSouth China. Bivalves are abundant in thissection, with four assemblages recognizedand correlated with other PTB bivalvefaunas of South China. The bivalve assem-blages change from elements dominated byPalaeozoic types to Mesozoic types follow-ing the end-Permian mass extinction. Thisevent not only dramatically reduced diver-sity of the bivalve faunas, it also changedthe representation of genera. Bivalves alsoexperienced significant morphologicalchanges across the Permian–Triassic transi-tion, shifting towards thinner, smaller andflatter shells in the earliest Triassic.
AcknowledgementsThis work is a part of the researchprograms supported by the NationalScience Foundation of China (Grant nos.40172012 and 40232025). Yongqun Gaoand Yuanqiao Peng acknowledge supportof the Australian Commonwealth Govern-ment and Deakin University for the awardof International Postgraduate ResearchScholarships (IPRS). GRS acknowledgessupport from the Australian ResearchCouncil (DP0772161), Chinese Academyof Sciences (CAS 2006-1-16) and DeakinUniversity.
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