Paleobiogeographical extinction patterns of Permian … · of Brachiopoda. The timing of the...

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Paleobiology, 28(4), 2002, pp. 449–463

Paleobiogeographical extinction patterns of Permianbrachiopods in the Asian–western Pacific region

Shen Shu-zhong and G. R. Shi

Abstract.—Spatial and temporal variations in biological diversity are critical in understanding therole of biogeographical regulation (if any) on mass extinctions. An analysis based on a latest da-tabase of the stratigraphic ranges of 89 Permian brachiopod families, 422 genera, and 2059 specieswithin the Boreal, Paleoequatorial, and Gondwanan Realms in the Asian–western Pacific regionsuggests two discrete mass extinctions, each possibly with different causes. Using species/familyrarefaction analysis, we constructed diversity curves for late Artinskian–Kungurian, Roadian–Wor-dian, Capitanian, and Wuchiapingian intervals for filtering out uneven sampling intensities. Theend-Changhsingian (latest Permian) extinction eliminated 87–90% of genera and 94–96% of speciesof Brachiopoda. The timing of the end-Changhsingian extinction of brachiopods in the carbonatesettings of South China and southern Tibet indicates that brachiopods suffered a rapid extinctionwithin a short interval just below the Permian/Triassic boundary.

In comparison, the end-Guadalupian/late Guadalupian extinction is less profound and variestemporally in different realms. Brachiopods in the western Pacific sector of the Boreal Realm nearlydisappeared by the end-Guadalupian but experienced a relatively long-term press extinction span-ning the entire Guadalupian in the Gondwanan Realm. The end-Guadalupian brachiopod diversityfall is not well reflected at the timescale used here in the Paleoequatorial Realm because the life-depleted early Wuchiapingian was overlapped by a rapid radiation phase in the late Wuchiapin-gian. The Guadalupian fall appears to be related to the dramatic reduction of habitat area for thebrachiopods, which itself is associated with the withdrawal of seawater from continental Pangeaand the closure of the Sino-Mongolian seaway by the end-Guadalupian.

Shen Shu-zhong. Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39 EastBeijing Road, Nanjing 210008, P. R. China. E-mail: [email protected]

G. R. Shi. School of Ecology and Environment, Deakin University, Melbourne Campus, 221 BurwoodHighway, Burwood, Victoria 3125, Australia. E-mail: [email protected]

Accepted: 22 April 2002

Introduction

The supercontinent Pangea, formed in thePermian, stretched almost from pole to pole ina meridional orientation. On the easternshelves of Pangea and around the microcon-tinents scattered in the eastern Paleotethys(e.g., South China, Indochina, Sibumasu; seeFig. 1), Permian marine benthic organismswere abundant and exhibited a highly dy-namic history of provincialism. Among them,brachiopods were particularly ubiquitous buthighly varied in geographical distribution.The Permian brachiopods of the Asian–west-ern Pacific region have been the subject of sev-eral detailed paleobiogeographical studies(Nakamura et al. 1985; Shi et al. 1995; Shenand Shi 2000; Shi and Shen 2000). However,only recently has the relationship betweenPermian brachiopod biogeography and themass extinctions in this region attracted atten-tion. Geographic selectivities have been inves-

tigated for the Cretaceous–Tertiary mass ex-tinction (e.g., Raup and Jablonski 1993) andthe end-Ordovician mass extinctions (e.g.,Sheehan and Coorough 1990), and a plea hasbeen raised for similar studies on the Perm-ian–Triassic mass extinction (Valentine andMoores 1973; Erwin 1993). However, it is notknown whether the end-Permian mass extinc-tion varied paleobiogeographically in terms oftiming, magnitude, and taxonomic selectivity,nor whether provincialism had any role inregulating diversity and extinction patternsthrough the Permian.

In this paper, we investigate aspects relatedto the first issue by examining the Permianbrachiopod faunas of the Asian–western Pa-cific region. Specifically we address two ques-tions: (1) Are brachiopod mass extinction pat-terns comparable among different Permianbiogeographical realms in terms of timing,magnitude, and taxonomic groups affected?

450 SHEN SHU-ZHONG AND G. R. SHI

FIGURE 1. Schematic reconstruction of Permian paleogeography and paleobiogeography showing the study regionand three major biotic realms. A, Boreal Realm. B, Paleoequatorial Realm. C, Gondwanan Realm. 1 5 Mongoliaand Russian Far East; 2 5 Inner Mongolia and northeast China; 3 5 Tarim Basin; 4 5 Transcaucasia; 5 5 SouthernKitakami and Hida Gaien, Japan; 6 5 South China; 7 5 Southeast China; 8 5 Western Yunnan; 9 5 Qiangtang block;10 5 Iran block; 11 5 Inner Zone, Japan; 12 5 Indochina block; 13 5 Sibumasu Arc; 14 5 Lhasa block; 15 5 WesternAustralia; 16 5 Himalayan terrane; 17 5 Eastern Australia and New Zealand. Base map after Ziegler et al. 1997.

(2) If the brachiopod mass extinctions did ex-hibit paleobiogeographical variations, thenwhat were the likely causes of these varia-tions?

In an earlier report (Shi and Shen 2000), weanalyzed paleobiogeographical patterns ofPermian brachiopod extinctions in this region.The earlier study was based on a series of da-tabases compiled by Shi and colleagues. Theirmain conclusions were (1) that Permian bra-chiopod faunas in the Asian–western Pacificregion suffered two major mass extinctions,respectively at the end-Guadalupian/lateGuadalupian and Changhsingian, and (2) thatthese two extinctions are only broadly com-parable among different Permian biogeo-graphical realms. With respect to the latter, wealso noted that (1) the end-Guadalupian/lateGuadalupian extinction is most pronouncedin the Gondwanan and Boreal Realms and lesswell expressed in the Paleoequatorial Realm,and that (2) the end-Changhsingian extinction

appears to have been much more severe thanthe end-Guadalupian extinction and of short-er duration. However, given its preliminarynature, this initial study suffered from severalpitfalls. First, the brachiopod data for the lateKungurian–Roadian interval was not investi-gated because a detailed international time-scale of the Permian System was not availablewhen the databases were compiled. Second,although we made every effort to ensure thatthe database was both taxonomically and bios-tratigraphically sound, variations in samplingintensity and their potential effect on diver-sity and extinction patterns were not consid-ered. Finally, our initial study was focused ondiversity and extinction patterns only, andwas not intended to consider causal mecha-nisms. These aspects are dealt with in the pre-sent study, which is based on a revised and ex-panded database and uses the recently pro-posed threefold Permian chronostratigraphi-cal timescale (Jin et al. 1997).

451PALEOBIOGEOGRAPHICAL EXTINCTION PATTERNS

FIGURE 2. The newly proposed threefold Permian time-scale (Jin et al. 1997) and the intervals used in this paper.The absolute ages of the Permian/Triassic boundary,Changhsingian/Wuchiapingian boundary, and the baseof Capitanian are from Bowring et al. 1998. The otherages are interpolated based on the timescale of Youngand Laurie (1996).

Data and Methods

This study is restricted to Brachiopoda re-corded from the Permian of the Asian–westernPacific region. This region is ideal as a proxyfor Permian global shallow-marine provincial-ism because the three widely recognized Perm-ian biogeographical realms, i.e., Boreal, Paleoe-quatorial (term of Grunt and Shi 1997), andGondwanan Realms, are all distinctly repre-sented in this region (Fig. 1). The biogeograph-ical characteristics of these realms and theirspatial and temporal ranges/boundaries havebeen discussed in a number of studies (Water-house and Bonham-Carter 1975; Nakamura etal. 1985; Grunt and Shi 1997; Shi and Grunt2000) and will not be repeated here.

The basic database for the present studywas taken from that of Shi and Shen (1999),which was collated and summarized from asuccession of Permian stage-by-stage data setscompiled for the Asian–western Pacific regionby Shi and colleagues since 1992 (see Shi andShen 1999 for references and details of thesepublished databases). However, such databas-es must be updated regularly. We have there-fore updated and expanded the initial data-base by adding the late Kungurian–Roadianinterval and including new Permian brachio-pod faunas published since 1992. Thus, thenew database includes all the time segmentsof the Permian necessary for extinction anal-ysis. The chief sources of additional faunaldata have been the works of Briggs (1998), Shiand Shen (1998), Shen and Jin (1999), andShen et al. (2000, 2001, in press).

In compiling the database, we have exam-ined all available published Permian brachio-pod literature of the region and updated thetaxonomy and age determinations of the pub-lished records in light of the latest develop-ments of Permian brachiopod taxonomy andbiostratigraphy. A total of 89 families, 422genera, and 2059 species in the three realmsare recorded in the revised and updated da-tabase. Seven Permian time intervals are uti-lized in accordance with the recently pro-posed threefold Permian chronostratigraphicscale (Fig. 2). Brachiopods in the early Gries-bachian of the earliest Triassic are also inves-tigated. The seven Permian intervals do not

strictly follow the precise stage boundaries ofthe chronostratigraphical scale. Some group-ing is necessary because the ages of some ofthe brachiopod faunas span stage boundaries.To allow rarefaction analysis for intervals inthe Guadalupian (middle Permian), wegrouped Roadian with Wordian to achievecomparable time durations for the Roadian–Wordian, Capitanian, and Wuchiapingian in-tervals (see below).

To examine the variations in brachiopod di-versity and extinction patterns through time,we used three quantitative measures: raw tax-onomic richness and proportional and totalextinction rates. The proportional extinctionrate refers to the proportion of extinct taxa re-corded in a time interval divided by the totalnumber of taxa recorded in that interval,whereas the total extinction rate is calculatedby the ratio of taxa becoming extinct in a time


FIGURE 3. Simple diversities at familial (m), generic (n),and specific (●) levels in the three realms. Interval num-bers are same as in Figure 2. Interval widths are scaledto duration. A, Boreal Realm. B, Paleoequatorial Realm.C, Gondwanan Realm.

interval over the duration (million years) ofthe interval. These two extinction metrics areselected for this study from many other alter-native measures (Foote 1994) and have alsobeen used in our earlier analysis (Shi and Shen2000).

During the establishment of our database,we found that the sample intensities are clear-ly different in different realms and intervals.Various methodologies are available to assessthe sampling problems. Considering the na-ture of our present brachiopod database, spe-cies/family rarefaction analyses were carriedout to evaluate the actual effects of samplingintensities in the different realms or time in-tervals, following the methodology of Raup(1975). Rarefaction analysis is basically an in-terpolation technique (Sanders 1968), makingit possible to estimate how many specieswould have been found had the sample beensmaller than it actually is. Ideally, to evaluatethe sampling intensities, rarefaction analysisis commonly carried out at the level of num-bers of individual organisms or biomass, butthe fossil record of species and individuals ismuch too spotty for this to be possible, and thenumbers of individual brachiopods were of-ten not recorded in most early publications. Inthis paper, therefore, we use data on the oc-currences of species within families ratherthan specimens within species for rarefactionanalysis. The shift of taxonomic rank does notchange the method mathematically or concep-tually (Raup 1975). That is, numbers of spe-cies, genera, and families in each interval ofeach realm were counted, and each samplewas rarefied so that the brachiopod assem-blages with different number of species/gen-era/families in the same interval in differentrealms, or different intervals with the same/similar durations in the same realm, could becompared by reducing all samples to the sizeof the smallest assemblage. Species/genus orgenus/family rarefaction analysis is not usedherein because rarefaction analysis betweencloser taxonomic ranks may reduce or obscurethe differences among diversity curves withhigh confidence limits. Rarefaction analysisapplied in a single phylum (Brachiopoda inthis paper) clearly meets the basic require-ments as discussed by Tipper (1979).

Two bars—one above the observed valueand one below it—are used to estimate the un-certainties of the rarefaction curves. A confi-dence limit (95%) shows the robustness of theobserved values. To calculate the standard de-viations at any point on the curves, we used thecomputer program compiled by S. M. Hollandreleased on the website http://www.uga.edu/strata/software/index.html.

Results and Discussion

Biogeographical Patterns of Diversity andExtinctions

The diversity and extinction patterns in thethree realms are summarized in Figures 3 and4. Figure 3A shows that the simple diversity


of Permian brachiopods in the Boreal Realmpeaked during the late Artinskian–Kunguri-an, then declined considerably toward the endof the Capitanian (end-Guadalupian). LatePermian marine faunas in the Russian Far Eastare dominated by abundant ammonoids withvery few brachiopods. Only four Tethyan-typegenera and four species (Haydenella sp., Para-crurithyris pigmaea [Liao], Crurithyris flabellifor-mis Liao, Araxathyris minor Grunt) were re-corded, with no description or illustrations(Zakharov and Oleinikov 1994; Zakharov etal. 1995). These warm-water species are con-sidered to have migrated from the moresoutherly Cathysian region during the closureof the Sino-Mongolian seaway and thereforeare assigned to the Paleoequatorial Realm.The diversity curves dropped sharply duringthe Late Permian. Both the proportional andtotal extinction profiles depict troughs for thelate Sakmarian–early Artinskian, then steadyclimbs toward the Capitanian (Fig. 4A).

The simple diversities in the Paleoequato-rial Realm (Fig. 3B) show no late Guadalupiandeclines. The number of families, genera, andspecies increase from the late Artinskian–Kungurian to the Changhsingian and thendrop abruptly at the end of Changhsingian.Only 22 small and thin-shelled Permian-typebrachiopod species of 12 genera persisted intothe earliest Triassic (Griesbachian). Althoughthe proportional extinction rates are slightlyhigher at specific level (54%) in the Capitanianthan those in the preceding Roadian–Wordian(50%) and succeeding Wuchiapingian (49%)intervals, they were clearly dwarfed by thepeak extinction rates of the end-Changhsin-gian (96%). Proportional extinction ratesbased on the generic data and the total extinc-tion rates show an acceleration from the lateArtinskian–Kungurian to the Changhsingian(Fig. 4B). However, the subdued extinctionsignal at the end-Guadalupian in the Paleoe-quatorial region may be an artifact related touse of a coarse timescale (see discussion be-low). It is interesting to note that some Earlyand middle Permian brachiopod genera of an-titropical (term of Grunt and Shi 1997) distri-bution (e.g., Attenuatella, Waagenites, Strophal-osiina, Comuqia) appeared in the Paleoequato-rial Realm for the first time in the latest mid-

dle Permian (late Capitanian) and persistedinto the Late Permian.

The simple diversities at familial, generic,and specific levels in the Gondwanan Realmall peaked in the late Artinskian–Kungurian,then dropped significantly toward the end ofCapitanian, indicating a long-term press ex-tinction (term of Erwin 1996), which is fol-lowed by a modest recovery in the Wuchia-pingian and a significant drop again after theWuchiapingian (Fig. 3C). Only three species(Pustula sp., Linoproductus lineatus Waagen,and Retimarginifera sp.) are recorded in theearliest Triassic (Griesbachian) in the Gond-wanan Realm (Nakazawa et al. 1975; Shimizu1981). Both the proportional extinction rateand the total extinction rate clearly demon-strate a two-phase extinction pattern at boththe generic and specific levels (Fig. 4C) for theGondwanan Realm.

Testing by Rarefaction Analysis

It is worth noting that rarefaction analysisbetween species and families is sensitive to in-terval durations because of the likely effect ofinterval length on taxonomic richness of sam-ples (Raup 1975; Tipper 1979). Among the sev-en Permian intervals that we investigated inthis study, the Roadian–Wordian, Capitanian,and Wuchiapingian intervals are similar induration (5–6 Myr), as are the Asselian–earlySakmarian, late Sakmarian–early Artinskian,and late Sakmarian–Kungurian intervals (9–9.5 Myr). But the latter three intervals are notrelated to the middle and end-Permian massextinctions, and were therefore not tested byrarefaction analysis in this study. Thus, weanalyzed only the upper three intervals(Roadian–Wordian, Capitanian, and Wuchia-pingian) by rarefaction analysis, in an attemptto assess the veracity of the diversity changeand extinction patterns recognized above byusing diversity and extinction measures andto compare these patterns between the Gond-wanan and Paleoequatorial Realms (Fig. 5A,B) (the Boreal Realm in northeast Asia was notincluded because it lacks Late Permian, Bore-al-type brachiopod faunal data). All threerealms were also compared for specific timeintervals (Fig. 5C–F).

As exhibited in Figure 5A, the diversity tra-


FIGURE 4. Proportional extinction and total extinction rates at generic (n) and specific (●) levels in the seven in-tervals of the Permian for the three realms. Interval widths are scaled to duration. Proportional extinction rateequals the number of taxa that become extinct in the interval divided by the total number of the taxa in the interval;total extinction rate equals the number of taxa that become extinct in the interval divided by the duration of theinterval in millions of years. A, Boreal Realm. B, Paleoequatorial Realm. C, Gondwanan Realm.

jectories for time intervals 3–6 of the Gond-wanan Realm clearly indicate the lowest di-versity in the Roadian–Wordian interval, fol-lowed by the Capitanian and Wuchiapingian

intervals. The Capitanian rarefaction curvesignificantly differs in length from those of theRoadian–Wordian and Wuchiapingian inter-vals, implying that the Capitanian is poorly


FIGURE 5. Species/family rarefaction curves for different intervals or realms (numbers on the curves of A and Bare the interval numbers as shown in Fig. 2). Vertical bars depict the deviation with 95% confidence limits basedon the program compiled by S. M. Holland.


sampled, and therefore its trend is difficult topredict. This curve also may indicate that themiddle Permian extinction began earlier in theGondwanan Realm, an implication that is re-flected also in the raw diversity (see Fig. 3C).

The rarefaction curves for the Paleoequato-rial Realm show that family diversities in thethree time intervals are not significantly dif-ferent, as evidenced by the overlapping of thestandard deviations with 95% confidence limit(Fig. 5B), suggesting that the differences insimple diversity among the Roadian–Wordi-an, Capitanian, and Wuchiapingian (see Fig.3B) are most likely due to sampling intensi-ties. Rarefaction curves comparing the threerealms during the different intervals (Fig. 5C–F) demonstrate that the three realms had com-parable family diversities during both the lateArtinskian–Kungurian and the Wuchiapingi-an intervals (Fig. 5C,F). However, the rarefac-tion curves of the Roadian–Wordian (Fig. 5D)and the Capitanian (Fig. 5E) intervals showclearly that the family diversities of the Pa-leoequatorial Realm are higher than those ofthe Boreal and Gondwanan Realms. There-fore, the important conclusion to be drawnfrom Figure 5 is that the Guadalupian declineof familial diversities in the Boreal and Gond-wanan Realms is statistically robust and mostlikely true.

The End-Guadalupian/Late GuadalupianExtinction

The scenario that some major mass extinc-tions are associated with, and may be a directconsequence of, large-scale or global marineregressions (e.g., Simberloff 1972; Jablonski1985; Hallam 1989) appears particularly ap-plicable to the middle Permian, when majorland masses assembled together to form Pan-gea and, as a consequence, a major worldwideregression was initiated (Holser and Margar-itz 1987). This global regression subsequentlyled to the withdrawal of seawater from a largepart of the Pangean shelves and epicontinen-tal seas. One of the earliest attempts to revealthe relationship between the distribution ofepicontinental sea areas and diversities wascarried out by Schopf (1974), who plotted di-versities against epicontinental sea areas us-ing then available paleogeographical recon-

struction maps. Schopf (1974) was able todemonstrate that a sharp decrease in the per-centage of the continents covered by shallowmarine seas, from 40% in the Early Permian toabout 15% at near the P/T boundary, then fol-lowed by a rapid recovery to 34% in the EarlyTriassic, was closely matched by variations indiversity. Since Schopf’s study, many versionsof Permian global reconstruction maps havebeen published with varied accuracy, but in-variably they all suggest that the total globalcontinental shelf area was reduced signifi-cantly after the end-Guadalupian (see, for ex-ample, the reconstruction maps in Ziegler etal. 1997) (Fig. 6). This reduction, we believe,may have been the direct cause of the end-Guadalupian/late Guadalupian mass extinc-tion, particularly with respect to the Borealand Gondwanan Realms where this middlePermian mass extinction manifested itself best(see below).

Boreal Realm. The brachiopod faunas in theEarly and middle Permian in the BorealRealm were widely distributed on the RussianPlatform, the Urals, the Sino-Mongolian sea-way between the North China Platform andthe Siberian Platform, the Russian Far East,and northeast Japan. However, the end-Guad-alupian regression eliminated most of theshelf areas (Fig. 6), and this could have beenthe direct cause of the almost total extinctionof Brachiopoda in the Late Permian in the Bo-real Realm. Although it might be argued thatsome of the Boreal taxa could have migratedinto other realms or deep seas during or fol-lowing the regression, an extensive search inthe available stratigraphic records indicatesthat 37% genera and 78% species known fromthe Capitanian in the Boreal Realm never oc-curred anywhere in the later intervals of allrealms in the Asian–western Pacific region.Elsewhere in the Boreal Realm (e.g., EastGreenland) Late Permian brachiopods mayhave persisted in some local areas althoughinformation on such faunas is still very scanty.Throughout the Late Permian and Early Tri-assic a narrow seaway probably extendeddown to the northeast coast of Greenlandfrom the Arctic Ocean, in which some marinedeposits accumulated with a low-diversitybrachiopod fauna (Dunbar 1955). Another


FIGURE 6. Changes in habitat area from the Wordian (middle Guadalupian) to Wuchiapingian (early Lopingian).Reconstruction map after Ziegler et al. 1997. Brachiopod habitat area is indicated by oblique dotted lines. Area withstars indicate habitat areas for brachiopods present during the Guadalupian but lost in Wuchiapingian. A, BorealRealm. B, Paleoequatorial Realm. C, Gondwanan Realm.

possible area of Late Permian shallow-marinesediments with brachiopods is represented bythe Kapp Starostin Formation in westernSpitsbergen, but the upper age limit of thisformation is still controversial (Stemmerik1988; Gruszczynski et al. 1989; Malkowski etal. 1989; Nakamura et al. 1992). However, evenif we accept the Spitsbergen and Greenlandfaunas as Late Permian, as argued by Stem-merik (1988), these faunas contain a total of 43species from 26 genera (Dunbar 1955; Naka-mura et al. 1992), which would constitute only29.5% species and 42.6% genera for Capitan-ian faunas of the Boreal Realm in the Asian–western Pacific sector. The actual percentagesfor both species and genera would be muchlower if calculated relative to the whole BorealRealm.

Gondwanan Realm. Sea level dropped dur-ing the middle Permian and through the LatePermian over much of Gondwana (Fig. 6), assuggested by the formation of extensive coalmeasures in Australia and India (Veevers et al.1994; Mishra 1996), South Africa (Visser 1995),and South America (Harrington 1962). Thetiming of this eustatic event agrees well withthe Guadalupian brachiopod extinction in theGondwanan Realm. For instance, in Western

Australia, Early Permian and early middlePermian strata bearing abundant marine fau-nas are replaced by late middle and LatePermian sandstone-dominated strata in manybasins (see Archbold 1999: Fig. 3). In the Syd-ney Basin of eastern Australia, the youngestmarine Permian faunal horizon is Midian (5Capitanian) in age (Briggs 1998), lying im-mediately below the Late Permian IllawarraCoal Measures. However, there are limited ar-eas in the Gondwanan Realm where marinedeposition occurred during the Late Permian.One case is the Himalayan region includingsouthern Tibet, Nepal, and northern India.Here, Late Permian deposits used to be con-sidered absent, but they have been confirmedby recent studies based on faunas from the up-per part of the Kuling Group in northern India(Garzanti et al. 1996), the Thini Chu Group incentral Nepal (Garzanti et al. 1994), and theSelong Group in southern Tibet (Shen et al.2000). It is interesting to note that in this peri-Gondwanan region Guadalupian brachiopodfaunas are actually very limited. This may bedue to a prolonged period of low sea-levelstand and erosion, as suggested by Garzantiet al. (1996). However, a significant transgres-sion beginning in the early Wuchiapingian


FIGURE 7. Diversity pattern of Permian–Triassic bra-chiopods in South China. Original data from Shen andShi (1996). Vertical error bars depict the deviation with95% confidence limits based on the program of Raup1991.

brought about extensive marine depositionacross the region, and with it, a flourishingbrachiopod fauna.

Paleoequatorial Realm. Differing from thetwo realms mentioned above, the Paleoequa-torial Realm experienced only a short, but dis-tinct, regression at the end-Guadalupian, asmarked by a regional unconformity betweenthe Guadalupian and the Lopingian Series incentral Iran, South China, and Japan. In SouthChina, this event has long been recognizedand known as the Dongwu Movement, whichresulted in the Longtan Coal Measures over-lying directly and unconformably on the mid-dle Permian Maokou and/or Lengwu Lime-stones (Formations). Only in the central partof the Jiangnan Basin in southwest China werethere localized areas (e.g., the Laibin area inGuangxi of southwest China) where marinedeposition continued across the Guadalupi-an/Lopingian boundary. Even in these areas,the end-Guadalupian regression is evidentand clearly marked by the deposition of cri-noid grainstones with oncolites and skolithostrace fossils, indicating a nearshore high-en-ergy environment (Jin et al. 1998). However, asconstrained by conodonts across the Guadal-upian and boundary at the Laibin section (Meiet al. 1998), this shallowing event was rela-tively short lived, lasting no more than 2 mil-lion years (see Jin et al. 1998: Fig. 3). This rapidevent resulted not only in a significant reduc-tion of epicontinental seas on South China (seeWang and Jin 2000: Fig. 3F,G) and consequent-ly a crisis for the middle Permian marine ben-thos (Jin et al. 1994), but also in profoundchanges in the paleogeographical settings ofSouth China. Despite this rapid eustatic event,the end-Guadalupian extinction in the wholePaleoequatorial Realm of the Asian–westernPacific region is not well expressed relative tothe Boreal or Gondwanan Realm. In fact, asshown in Figures 3–5 and also discussedabove, the extinction is rather weak in com-parison with the extinctions at that time in theother two realms. But this subdued extinctionsignal from the Paleoequatorial region may bean artifact because the timescale is coarse rel-ative to the rapidity of the actual geologicalevent, as can be explained using the exampleof South China. Shen and Shi (1996) docu-

mented an 87% proportional extinction rate ofbrachiopods near the Maokouan/Lopingianboundary in South China. Their study wasbased on various measured stratigraphic sec-tions with relatively higher biostratigraphicresolution. They were therefore able to ana-lyze the brachiopod extinction rates using bio-zones/substages rather than stages or super-stages as in the present study. Thus they rec-ognized that the end-Maokouan extinctionwas in fact concentrated in the late Maokouan(or Lengwuan); its appearance as a boundaryextinction had been enhanced by the paucityof life in the subsequent early Wuchiapingian.The following late Wuchiapingian is markedby a radiation of numerous new taxa (Fig. 7).In the current study, however, the whole of theMaokouan Stage is treated as one time inter-val, as is the Wuchiapingian Stage. This treat-ment, which is inevitable with the muchbroader regional scale of the present study,has combined two substages, hence lumpingdiversities and condensing the pattern of di-versity variation that would otherwise bemore varied on a finer time resolution. In oth-er words, it remains reasonable to suggest anend-Guadalupian extinction of some magni-


FIGURE 8. Stratigraphic ranges of brachiopod species (by vertical lines with dots indicating the occurrences ofbrachiopods) at the Beifengjing section near Chongqing City of Sichuan Province, South China. Fossil ranges scaledto thickness of the Changhsing Formation. Data after Shen and He 1991.

tude for the Paleoequatorial Realm, but themanifestation of this event is not well recog-nized in this study because the extinction wasrapid and quickly replaced by a rapid phaseof origination in late Wuchiapingian. Never-theless, the end-Guadalupian/late Guadalu-pian extinction is probably taxonomically se-lective. Fusulinids and corals apparently suf-fered heavy losses (Stanley and Yang 1994;Wang and Sugiyama 2000), whereas gastro-pods were less affected (Erwin 1996). How-ever, studies on these taxa did not mention thelife-depleted early Wuchiapingian, so it ishard to make comparisons with the brachio-pods in this study.

The End-Changhsingian Extinction

The brachiopod disappearance pattern dur-ing the end-Changhsingian in the shallow-water carbonate sequences (e.g., ChanghsingFormation) of South China appears to supporta scenario of rapid extinction process as ad-vocated by Rampino and Adler (1998) and Jinet al. (2000). For example, the abruptness ofthe mass extinction is well exhibited at the Bei-fengjing section in Chongqing City of South

China (Fig. 8). Here, the Permian/Triassicboundary is well defined by the first appear-ance of the Triassic index conodont Hindeodusparvus (Yin 1985; Yang et al. 1987). The totalthickness of the Changhsingian strata is 91.5m. Shen and He (1991) identified 155 brachio-pod species in the Changhsing Formation. Ofthese, 126 species disappeared within an in-terval of 0.91 m below the Permian/Triassicboundary, only 29 species disappeared wellbelow (56.47 m) the Permian/Triassic bound-ary, and 2 species persisted across the Perm-ian/Triassic boundary (Shen and He 1991)(Fig. 8). Evidence indicating paleoenviron-mental deterioration within the top 0.91 m ofthe Changhsingian includes the occurrence offramboidal pyrites, a lithologic shift fromthick-bedded biosparite into middle/thin-bedded argillaceous limestone, a decrease inthe density of bioclasts and the diameter ofburrows (Wignall and Hallam 1996), and achangeover from brachiopod communitieswith numerous pro-reef forms to those withstress-tolerant forms (Shen and He 1991).There is also evidence for contemporaneousvolcanism, as shown by the occurrence of sev-


FIGURE 9. Stratigraphic ranges of brachiopod species atthe Selong Xishan section in southern Tibet. Data afterShen et al. 2000 and Shen and Jin 1999.

eral clay layers of illite/smectites with mi-crospherules (Yang et al. 1987). It is thus clearthat the end-Changhsingian mass extinctionwas concentrated within the very end of theChanghsingian now represented by 0.91 m inthe stratigraphic record at this section. Al-though the sedimentation rate within theChanghsing Formation at this section is notexactly known, a rapid extinction clearly oc-curred at the very end of the Changhsingian.In fact, because of the Signor-Lipps effect (Si-gnor and Lipps 1982; Rampino and Adler1998) and the artifact of incomplete preser-vation (Marshall 1995), the extinction mayhave been even more rapid than it appears.

The rapid extinction event in the Paleoequa-torial Realm is also well expressed in theGondwanan Realm. The Selong Xishan sectionin southern Tibet (Fig. 9) may serve as a goodexample to compare relatively high-latitude ex-tinction patterns with that of the Paleoequato-rial Realm. At this section, 49 Wuchiapingianto Changhsingian brachiopod species havebeen recorded (Shen and Jin 1999; Shen et al.2000). Brachiopods, corals, and bryozoans be-came extinct within a short interval beneath thePermian/Triassic boundary (Fig. 9). The end-Changhsingian transgression begins at thebase of the Waagenites Bed (Shen and Jin 1999)of the Kangshare Formation. Below the Waa-genites Bed, a caliche bed is present (Jin et al.1996), indicating a regression event, which inturn is underlain by the topmost part of the Se-long Group consisting of nearshore bioclasticlimestone with bioclasts dominated by brachio-pod, coral, and crinoid fragments. TheChanghsingian strata at this section are only0.17 m thick (Wang et al. 1989; Shen and Jin1999) or, at most, no more than 2.25 m thick(Shen et al. 2000). The lithology of the Changh-singian strata is predominantly well-sortedbioclastic grainstone containing 35–80% bio-clastics (Jin et al. 1996). The reduced thicknessand extremely high content of bioclastics in-dicate that the Changhsingian strata at this sec-tion were deposited during a period of sedi-ment starvation (Shen and Jin 1999). Accordingto Jin et al. (1996), the uppermost Permian Waa-genites Bed represents carbonate depositsformed in shallow, medium-energy shoals. Theoverlying Early Triassic Otoceras Bed consists

of stylo-compacted corroded packstone withcrinoid fragments and bioturbation structure.A dramatic drop in d13C value from 13.2 in theCaliche Bed to 22.89 per mil (‰) in the Waa-genites Bed is evident (Wang et al. 1997). Thisisotopic excursion is very similar to signalsknown from many other P/T boundary sec-tions (e.g., the Meishan section [Cao et al.2001]), and it suggests that the depletion ofd13C value may not reflect a single triggeringevent but a complex web of causality (Erwin1993).

Conclusions

Our analysis indicates that Permian bra-chiopods in the Asian–western Pacific regionsuffered two discrete, closely spaced extinc-


tions, at the end-Guadalupian/late Guadalu-pian and at the end-Changhsingian, but pos-sibly with different causes. The end-Guadal-upian/late Guadalupian extinction can be re-lated to a reduction of the habitable shelf areasleading to decreased population sizes.

The end-Changhsingian extinction hap-pened rapidly in both the Paleoequatorial andthe Gondwanan Realms. Shallow-water car-bonate settings of South China and southernTibet show evidence of a rapid and severemain extinction within a short interval just be-low the Permian/Triassic boundary. This ex-tinction appears to be proceeded by a rapidregression event, as evidenced by the presenceof highly diverse plant fossils at the Penglai-tan section (Jin et al. 2001) and the Caliche Bedat the Selong Xishan section in the very lateChanghsingian (Jin et al. 1996), which is fol-lowed by a rapid transgression event resultingin the occurrence of framboidal pyrites, a lith-ologic shift from thick-bedded biosparite intomiddle/thin-bedded argillaceous limestone,and a faunal shift from diverse pro-reef formsto monotonous stress-tolerant forms.

Acknowledgments

We especially thank D. H. Erwin for readingan earlier draft of this paper and providing ahelpful discussion. A. I. Miller and P. B. Wig-nall provided valuable reviews, commentsand information. The rarefaction programcompiled by S. M. Holland is used. This paperwas supported by the Major Basic ResearchProjects of the Ministry of Science and Tech-nology (G2000077700) of the People’s Republicof China; the Chinese Academy of SciencesHundred Talents Program; a National ScienceFoundation grant (40072012) to Shen Shu-zhong; and an Australia Research Councilgrant to G. R. Shi.

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