biodiversity, biogeography and phylogeography of ordovician rhynchonelliform brachiopods

Chapter 11

Biodiversity, biogeography and phylogeography of Ordovicianrhynchonelliform brachiopods

DAVID A. T. HARPER1*, CHRISTIAN M. Ø. RASMUSSEN2,3, MARIA LILJEROTH2, ROBERT B. BLODGETT4,

YVES CANDELA5, JISUO JIN6, IAN G. PERCIVAL7, JIA-YU RONG8, ENRIQUE VILLAS9 & REN-BIN ZHAN8

1Palaeoecosystems Group, Department of Earth Sciences, Durham University, Durham DH1 3LE, UK2Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, DK-1350 Copenhagen K, Denmark

3Department of Geology, Lund University, Solvegatan 12, SE 223 62 Lund, Sweden4Consultant Geologist, 2821 Kingfisher Drive, Anchorage, AK 99502, USA

5Department of Natural Sciences, National Museums Scotland, Edinburgh, EH1 1JF, UK6Department of Earth Sciences, Western University, London, Canada N6A 5B7

7Geological Survey of New South Wales, Londonderry 2753, NSW, Australia8State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing 210008, China

9Departamento de Ciencias de la Tierra, Facultad de Ciencias, Universidad de Zaragoza, Pedro Cerbuna 10, 50009 Zaragoza, Spain

*Corresponding author (e-mail: [email protected])

Abstract: The phylogeographical evolution and the consequent changing distribution and diversity of rhynchonelliform brachiopodsthrough the Ordovician are linked to the dynamic palaeogeography of the period. The Early Ordovician (Tremadocian and Floian) ischaracterized by globally low-diversity faunas with local biodiversity epicentres, notably on the South China Palaeoplate; low-latitudeporambonitoid-dominated faunas with early plectambonitoid and clitambonitoid representatives, as well as high-latitude assemblagesmostly dominated by orthoids, can be recognized, but many taxa are rooted in Late Cambrian stocks. The Early Ordovician displaysa steady increase in rhynchonelliformean biodiversity, which was mostly driven by the increasing success of the Porambonitoideaand Orthoidea, but the billingsellids and early plectambonitoids also contributed to this expansion. During the Early to Mid Ordovician(Dapingian–Darriwilian), marine life experienced an unprecedented hike in diversity at the species, genus and family levels that firmlyinstalled the suspension-feeding benthos as the main component of the Palaeozoic fauna. However, this may have occurred in response toan early Darriwilian annihilation of existing clades, some of which had been most successful during the Early Ordovician. New cladesrapidly expanded. The continents were widely dispersed together with a large number of microcontinents and volcanic arcs related tointense magmatic and tectonic activity. Climates were warm and sea-levels were high. Pivotal to the entire diversification is the roleof gamma (inter-provincial) diversity and by implication the spread of the continents and frequency of island arcs and microcontinents.The phylogeographical analysis demonstrates that this new palaeogeographical configuration was particularly well explored and utilizedby the strophomenides, especially the Plectambonitoidea, which radiated rapidly during this interval. The porambonitoids, on the otherhand, were still in recovery following the early Darriwilian extinctions. Orthides remained dominant, particularly at high latitudes. Bio-diversity epicentres were located on most of the larger palaeoplates, as well as within the Iapetus Ocean. Provincial patterns were dis-rupted during the Sandbian and early Katian with the migration of many elements of the benthos into deeper-water regimes, enjoying amore cosmopolitan distribution. Later Katian faunas exhibit a partition between carbonate and clastic environments. During the latestKatian, biogeographical patterns were disrupted by polewards migrations of warm-water taxa in response to the changing climate; poss-ibly as a consequence of low-latitude cradles being developed in, for instance, carbonate reef settings. Many clades were well establishedwith especially the strophomenides beginning to outnumber the previously successful orthides, although this process had already begun,regionally, in the mid to late Darriwilian. At the same time, atrypoid and pentameroid clades also began to radiate in low-latitude faunas,anticipating their dominance in Silurian faunas. The Hirnantian was marked by severe extinctions particularly across orthide-strophomenide clades within the context of few, but well-defined, climatically controlled provincial belts.

Supplementary material: The individual localities and a reference list for the data sources are provided at: http://www.geolsoc.org.uk/SUP18667

Overview

A number of nineteenth-century palaeontologists, includingNicholson & Etheridge (1878), noted provincial differencesbetween North American and European Early Palaeozoic faunas.It was not until the 1960s and early 1970s, however, that the bio-geography of Early Palaeozoic faunas was analysed in somedetail with a particular focus on the benthos such as the Brachio-poda (e.g. Spjeldnæs 1960; Williams 1969, 1973; Burrett 1973;Jaanusson 1973, 1979).

Historically many of the discussions related to Ordovician bio-geography have focussed on the better-known, better-sampled andcontrasting European and North American faunas. Tuzo Wilson(1966), in a benchmark paper, provided an explanation for these

differences, based on the existence of a previous AtlanticOcean, the proto-Atlantic that divided Europe from NorthAmerica. Orthogonal opening and closure of this Early Palaeozoicoceanic system formed the basis for the Wilson Cycle. During thelate 1960s, a thorough multivariate investigation, using clusteranalysis, of all the then-known Ordovician brachiopod faunasconfirmed differences between the North American and Europeanbiotas but also indicated important provincial differences withinthe European faunas themselves; for example, the Dapingian bra-chiopods of the island of Anglesey could be associated with thosefrom Baltica, in contrast to those from Shropshire, which appar-ently had affinities with those from the Montagne Noire ofsouthern France (Williams 1969). A later re-evaluation of thesedata (Williams 1973) indicated the presence of a well-defined

From: Harper, D. A. T. & Servais, T. (eds) 2013. Early Palaeozoic Biogeography and Palaeogeography.

Geological Society, London, Memoirs, 38, 127–144. http://dx.doi.org/10.1144/M38.11

# The Geological Society of London 2013. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics

at University of Western Ontario on November 27, 2013http://mem.lyellcollection.org/Downloaded from

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http://mem.lyellcollection.org/


cluster, separate from those of Scoto–Appalachia, northwesternNorth America and the Baltic, characterized by the presence ofRhynchorthis but demonstrating close ties with the Baltic pro-vince. Williams (1973) considered that this, his ‘Celtic province’containing marginal areas of Ireland and Wales, was a distinctbiogeographical entity not necessarily associated with a singlecontinental palaeoplate. Williams (1973) demonstrated areduction of provinces during the Ordovician, from five in theArenig to three in the Ashgill. Moreover, the relative numbersof endemic genera in each province ranged from 80 to 90%during the Arenig and Llanvirn, falling to some 55% during thelater Ashgill (Williams 1973, fig. 12). During the 1970s and1980s Tuzo Wilson’s model was modified to accommodaterates of opening and closure based on faunal data (e.g. McKerrow& Cocks 1976) and a more complex palaeoplate configuration(Cocks & Fortey 1982; Fortey & Cocks 1986) involved the inter-action of the continents of Avalonia, Baltica, Gondwana andLaurentia. None of these models explicitly indicated the presenceof islands; however, Neuman (1984), building on his earlierresearch on the brachiopod faunas within the Caledonian–Appa-lachian orogen (e.g. Neuman 1964, 1972), indicated the existenceof a group of intra-Iapetus islands in his palaeogeographicalreconstructions, now amalgamated within the Caledonianorogen. A large number of the faunas associated with theseisland terranes could now be tied to Williams’s concept of theCeltic province, suggesting origins and positions seawards ofthe main continental palaeoplates. These faunas, however, pre-sented other characteristic features: they contained a high pro-portion of endemics, taxa common to adjacent continents, andsome taxa that are better known from younger rocks in the adja-cent platform provinces. These patterns had also been establishedfor Scandinavian faunas (Bruton & Harper 1981), and later con-firmed by statistical analyses (Harper & Mac Niocaill 2002;Harper et al. 2008).

Biogeographical studies of Ordovician Brachiopoda have fol-lowed three parallel approaches. First, many analyses havefocussed on the occurrences of key genera or families to helpmap provincial data (Cocks & Fortey 1982). Second and by wayof contrast, a number of authors have used the whole-dataapproach, analysing statistically all the available data from given

time slices using a range of multivariate methods (Williams1969, 1973; Harper 1992). Third, the biogeographical distributionsof taxa have been mapped onto phylogenetic trees for some areasof the phylum (Popov et al. 2001; Candela 2011). Moreover theconcept and application of provinces have differed betweenauthor groups (see below), with some authors basing their pro-vinces entirely on the distribution of taxa whereas others havetied them to continental palaeoplates.

In this study we have access to the most comprehensive databaseof brachiopod occurrences through the Ordovician. The database(see Supplementary material), assembled in the University ofCopenhagen by M. Liljeroth and C. M. Ø. Rasmussen and sup-plemented with data from all the other co-authors, is locality-basedand grouped into seven time slices, and includes the mostup-to-date generic assignments of taxa. These data have been con-verted to presence–absence matrices for the seven time slices:Tremadocian, Floian, Dapingian–Darriwilian (the late Arenig–early Lanvirn brachiopods are difficult to precisely date in someparts of the world, particularly within the marginal and oceanicterranes), Sandbian, Lower Katian, Upper Katian and Hirnantian.The database has also been used to access the diversity ofthe rhynchonelliformean brachiopods through the Ordovician(Fig. 11.1) to specifically unravel the phylogeographical evolutionwithin the clade (Fig. 11.16).

The data have been mapped onto BugPlates (http://www.geodynamics.no/bugs/SoftwareManual.pdf), but these, like manyreconstructions, have shortcomings. In particular, the ongoingwork on the Australasian part of the Gondwanan margin togetherwith the Central Asian orogenic belt is not integrated with thecurrently available software and will be subject to much revi-sion over the coming years (see e.g. Popov et al. 2009).

Biogeographical provinces

The data are analysed by a number of multivariate techniques.There are, however, a number of challenges interrogating suchsubstantial databases that by their nature contain a great deal ofnoise and are not free from errors. First, a number of the major con-tinental blocks (e.g. Laurentia, Baltica and South China) that are

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Fig. 11.1. Changing diversity through the

seven time slices, indicated by maximum

number of genera and maximum number of

localities together with extinction and

origination curves. For a more detailed

diversity curve, see Figure 11.16.

D. A. T. HARPER ET AL.128


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particularly rich in data from many localities across a range offacies commonly present a range of confusing and sometimesdifferent biogeographical signals. Even within single basins, forexample the Appalachians and adjacent areas (Jaanusson &Bergstrom 1980) and the Baltic basin (Jaanusson 1976), thereare many different biofacies ranging from shallow to deep water,typified by a spectrum of substrates from varieties of carbonatesto siliciclastic sediments. For these larger, more complex conti-nental units data have been combined from the large numbers oflocalities available in the database to provide a more average butnevertheless comprehensive biogeographical signal. For the pur-poses of biogeographical analyses this process is defensible;however, from the Sandbian onwards the diversification of deeper-water, marginal and more cosmopolitan faunas requires thepartition of some continental areas into shallower- and deeper-water faunas.

Second, in grouping together faunas into possible provinces,endemic taxa (essentially singletons) from individual localitiesor suites of adjacent localities have been eliminated. Admittedlyprovinces are defined on the basis of their endemic taxa;however, the numbers of endemic taxa are discussed under eachof the time slices. Third, use of data at this resolution will onlydelineate the major brachiopod provinces and we have notattempted in most cases to identify in detail marginal faunasassociated with the major continents.

Here, we also introduce the term ‘species pump’, to describeregions with great species diversity, which have acted as centresthat allowed the extra-regional spread of taxa. This term isadapted from its use in modern biogeographical studies, and isthus preferred over terms such as ‘hot spots’, which have a differ-ent meaning in present-day biogeography. Further, we use the term‘biodiversity epicentre’. This term is applied to regions with highbiodiversity, but without any evidence of faunal migrations toneighbouring regions. Lastly, the term ‘cradle’ is applied toregions where early signs of developing species pumps or biodi-versity epicentres are located. This tri-partite division of evolvingspecies-rich regions may thus be viewed as a progressive develop-ment of a faunal region, going from ‘cradle’, where key taxaemerge, through ‘biodiversity epicentre’ with high levels of a-and b-diversity to finally a fully developed ‘species pump’, result-ing in the increase in g-diversity.

Time slices

Tremadocian

There have been few attempts to assess articulate brachiopodbiogeography during the Tremadocian. For example, brachiopodsdid not merit mention in Jaanusson’s review of Ordovician bio-geography (1979). In addition, a number of previous studiesprior to the establishment of the current base of the system andinternational stadial divisions (e.g. Williams 1973) included theTremadoc Series within the Cambrian, whereas some studies(e.g. Cocks 2001) included discussion of these faunas with thoseof the Arenig Series. The articulate brachiopod assemblagesfrom this stage are relatively few in number and represented bylow-diversity associations strongly rooted in the Late Cambrian.Overall, based on currently available data, the mid Cambrian toTremadocian seems to have been an interval of evolutionarystasis within the rhynchonelliforms. Nevertheless pockets ofendemism and regions of high local diversity suggest that thesubsequent Great Ordovician Biodiversification Event (GOBE)was already firmly rooted. As noted above, previous authorshave largely ignored this interval with the exception of Jaanusson(1973), who noted the remarkable similarity amongst many Tre-madocian assemblages although a distinctive Southern Fauna(essentially the Mediterranean Province) characterized by Poram-borthis can be recognized.

Fifty localities with some 40 genera have been recorded glob-ally. There is marked endemicity at local levels with 20 generareported from only one site whereas one genus, Nanorthis, isreported from 25 sites. One site, Guizhou (South China Palaeo-plate), contains the most diverse assemblage with 10 genera,while 12 sites are represented by only one genus. The standardizeddiversity for the Tremadocian is 0.82. Sample sizes are thus smalland biogeographical patterns are far from robust. Nevertheless afew comments are possible based on the biogeographical dis-tribution of taxa (Figs 11.2 & 11.3). High-latitude (SouthernFauna), low-latitude (Northern Fauna) and Baltic provinces arerecognized. The last provided the initial immigrants that estab-lished the high-latitude Mediterranean Province (Havlıcek 1989).The low-latitude faunas are dominated by orthidine and syntro-phoid brachiopods, whereas higher-latitude assemblages arecharacterized by an array of polytoechioids associated with afew orthidines. Bassett et al. (2002), in a detailed analysis of thebiogeography and diversity of brachiopod faunas through theCambrian–Ordovician transition, identified a high-latitude groupof faunas within the siliciclastic facies of the Gondwananmargins; a number of polytoechioids, probably derived from theearlier Billingsella fauna, dominated the margins, later migratingto the Urals. Lower-latitude faunas were dominated by the syntro-phoids and orthidines. This partially confirms Benedetto’s (2001)identification of high-latitude orthidine-dominated assemblagesand low-latitude pentameride faunas during the Early Ordovician.

On the carbonate shelves along the margins of Gondwana, bill-ingselloid, polytoechioid and syntrophoid associations developedin the equatorial zone and migrated later to Laurentia, Siberiaand the Uralian margins of Baltica (Bassett et al. 2002). Theseand subsequent faunas dominating the Floian have parallels withthe composition, distribution and structure of the Ibexian trilobitefaunas, associated with late Cambrian–Early Ordovician carbon-ate facies. South China, situated in equatorial latitudes adjacentto the western-facing margins of Gondwana, was a local biodiver-sity epicentre, exhibiting unusually high levels of diversity (theFinkelnburgia and Tritoechia faunas; Wang & Xu 1966; Zhan &Harper 2006). These faunas are very similar to those from Lauren-tia and related regions. Overall, however, many of the taxa arelinked directly with precursors in the later Cambrian (althoughin general the faunal compositions are quite different), consolidat-ing the concept of an Ibexian brachiopod fauna, prior to the majorchange-over at the base of the Whiterock.

Floian

Some 30 localities have been identified globally for this stagecontaining 87 genera. One site, Guizhou, in South China, contains38 genera whereas the remaining 29 sites have between one and 11genera. Some 35 genera occur at only one site whereas two genera,Hesperonomia and Tritoechia, occur at 11 and 12 sites, respect-ively. The standardized diversity for the Floian is 2.90, animportant increase from levels in the Tremadocian. The rhyncho-nelliform brachiopods of the Floian interval are to date poorlystudied. These are, however, known from a large number of equa-torial localities, dominated by orthidines such as Archaeorthis,Apheoorthis and Finkelnburgia together with camerelloids, associ-ated with the isolation of Laurentia from the other major continents(Hansen & Holmer 2010). Higher latitudes were typified by adifferent group of orthidines, including Paurorthis, Prantlinaand Ranorthis. South China remained a locus for high diversity(Zhan & Harper 2006), manifested by the Sinorthis fauna (atypical regional brachiopod fauna in late Early Ordovician repre-senting the first radiation acme in South China; see Zhan & Jin2008; Zhan et al. 2011). However, a major change in brachio-pod faunal affinities occurred at the beginning of the Floian(Tetragraptus approximatus Biozone). Whereas Tremadocianbrachiopods of South China show close linkages to those of

ORDOVICIAN RHYNCHONELLIFORM BRACHIOPODS 129




Laurentia, during the Floian to Darriwilian interval, as the SouthChina block drifted away from Gondwana, its faunal affinitygradually shifted to closer relationships with the terranes ofBaltica, Avalonia, Sibumasu and southern Kazakhstan (Zhanet al. 2011); nevertheless it displayed strong endemism, markedby the presence of Pseudomimella, Pseudoporambonitoides,Sinorthis, Xinanorthis and Yangtzeella (Xu & Liu 1984). In thisstudy (Figs 11.4 & 11.5) we recognize high- and low-latitude pro-vinces together with a Baltic Province.

Dapingian–Darriwilian

This is a key interval for brachiopod diversification and conti-nental disparity (Harper et al. 2009). The Dapingian and Darriwi-lian have been grouped into one time slice since operationally ithas been difficult to separate some of their respective brachiopodfaunas, especially those within the late Arenig–early Llanvirninterval and particularly those from the world’s mountain beltsthat lack other age constraints. Some 65 localities have been ident-ified globally for this stage, containing over 230 genera. Two sitesin the East Baltic have diversities approaching 40 genera, whereassome 35 sites have diversities ranging from one to seven genera.

60oS

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Tarim

Fig. 11.2. Palaeogeographical map for the Tremadocian time slice based on BugPlates and using a Mollweide projection. The individual localities are listed in the

supplementary material.

Low-latitude provinceHigh-latitude province Baltic province

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Fig. 11.3. Cluster analysis for a selection of faunas for the Tremadocian time

slice using the Raup–Crick (Hammer & Harper 2006) similarity coefficient and

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Over 100 genera occur at only one site, whereas two genera, Tritoe-chia and Paralenorthis, occur at over 15 and 20 sites respectively.The standardized diversity for the Dapingian–Darriwilian intervalis 3.57, another significant increase from levels in the Floian.

A disparate group of continental fragments and island arcsloosely assigned to the Celtic province has been identified, con-taining a distinctive suite of shelly faunas that formed a testablebiogeographical unit. The Celtic faunas are characterized by alarge number of endemic brachiopod taxa, some cosmopolitanforms and taxa at the beginning or end of their stratigraphicalranges. Multivariate analyses of many of the Dapingian–earlyDarriwilian (late Arenig–early Llanvirn) brachiopod faunas(Neuman & Harper 1992; but see also Harper 1992) have con-firmed the discrete and distinctive grouping of both the sites andtaxa constituting the Celtic province (Figs 11.6 & 11.7). This bio-geographical unit has been tested by both new data and modernstatistical techniques, and its integrity remains consistently repro-ducible (Harper et al. 1996, 2008). The concept of the Celtic pro-vince was, however, challenged by McKerrow & Cocks (1993),who suggested that the term should be abandoned on the basis ofthe very widespread distribution of its brachiopod genera and thelack of an obvious pool of cross-province endemics. Implicit intheir argument was the suggestion that some groups of brachiopodswere better biogeographical indicators than others, a concept that

has been applied to a number of other fossil groups (e.g. Fortey& Mellish 1992; Servais & Sintubin 2009). This argument was,however, not based on any particular taxonomic groups withinthe Brachiopoda, rather it was only those associated with theCeltic province that were clearly of limited value as they occurredalong the same volcanic arc as localities with the marginalLaurentia Toquima–Table Head fauna. The single BronsonHill–Tetagouche–Lushs Bight Island arc, however, proposed byMcKerrow & Cocks (1993) is in fact at least two separate arcs:one part (with the Toquima–Table Head taxa) was associatedwith marginal Laurentia, whereas the other (associated with theCeltic province) developed at higher latitudes, within the IapetusOcean (Neuman et al. 1994). A more detailed analysis of thisinterpretation and an alternative model was provided by Harperet al. (1996) and Williams et al. (1996).

More recently, support for the Celtic province has accumulatedfrom three sources of data. First, new faunas particularly fromSouth America, for example, Argentina (Benedetto & Sanchez2003), Bolivia and Peru (Gutierrez-Marco & Villas 2007), haveprovided new occurrences of taxa associated with the Celtic pro-vince, supporting its extension along a high- to mid-latitude belt.Second, new data from already well-documented sites such asOtta, central Norway (Harper et al. 2008), continue to providetaxa that anchor these faunas within the province. Third, new

TarimTarim

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Fig. 11.4. Palaeogeographical map for the Floian time slice based on BugPlates and using a Mollweide projection. The individual localities are listed in the






data from the platform provinces such as Baltica (Harper & Hints2001; Sturesson et al. 2005; Rasmussen et al. 2007) and SouthChina (Rong et al. 2005; Zhan & Harper 2006) confirm the differ-ences between these faunas and those of the Celtic province. Thebrachiopod faunas of Dapingian and Darriwilian age are rep-resented by the Yangtzeella and the Saucrorthis faunas, respect-ively, in South China, both of which are regional brachiopodfaunas with very important palaeobiogeographical significance(Zhan et al. 2007, 2010). Multivariate analyses of the globaldataset consistently identify the Celtic group as distinct from theplatform provinces associated with Baltica and Laurentia (low lati-tude), and separate them from the marginal Laurentian Toquima–Table Head realm (e.g. Harper 2006a).

Whereas the existence and integrity of the Celtic group of bra-chiopod faunas has been demonstrated by a range of multivariatestatistical analyses, the precise pre-drift positions of the terranes,and by implication the geographical extent of the Celtic pro-vince, require a more multidisciplinary approach. Early to MidOrdovician palaeogeography has been refined by a series ofrecent studies based on both palaeontological and palaeomag-netic data (Harper et al. 1996). More recent publications haveemphasized again the role of shallow-water, marine benthos indefining provinces, for example, those by Cocks (2000, 2001)and Fortey & Cocks (2003). These workers, although recogniz-ing the existence of marginal and peripheral sites to Avalonia,Baltica and Laurentia, opposed the concept of marginal oroceanic provinces based on a lack of province-wide endemics;nevertheless, they have accepted that these faunas cannotreadily be accommodated within the platform provinces associ-ated with major continental palaeoplates. Further, modernpalaeogeographical analyses (e.g. for Baltica, Cocks & Fortey1998; Cocks & Torsvik 2005; for Avalonia, Cocks et al. 1997;for Siberia, Cocks & Torsvik 2007) have consistently recognizedthe complexity of Ordovician geography and the existence andlocation of marginal terranes. Current palaeogeographicalstudies have also emphasized the existence and significance ofother comparable archipelagos. The Toquima–Table Head pro-vince (Toquima–Table Head Realm of Ross & Ingham 1970)includes a number of Laurentian marginal terranes now part ofthe Caledonian Appalachian belt. Parts of western Irelandtogether with SW Scotland and a chain of localities along the

eastern seaboard of the USA have also yielded a distinctivefauna with some endemics and very different from the carbonateplatform faunas of the adjacent Laurentian craton (Neuman &Harper 1992; Harper & Mac Niocaill 2002).

Typical of the province are the genera Aporthophyla, Idiostro-phia, Leptella, Leptellina, Neostrophia, Taphrodonta, Toquimia,Trematorthis and Trondorthis. However, Aporthophyla and anumber of other typical members of the Toquima–Table Headprovince are known from outside the margins of Laurentia.Aporthophyla occurs together with Leptellina in South China,together with a number of endemic taxa such as Parisorthis(Zhan et al. 2005). Aporthophyla apparently had a widespread dis-tribution across broadly low-latitude sites from Laurentia to equa-torial peri-Gondwanan sites. On the other hand, Paralenorthiswas widely distributed across higher latitudes as well as somelocalities of lower latitude (e.g. in southern Tibet and SouthChina; Rong et al. 2005; Zhan et al. 2005). Both taxa occur interranes from South Kazakhstan, providing an interface betweenthe two provinces (Zhan et al. 2005; Nikitina et al. 2006). Themany terranes associated with central Asia have their own distinc-tive faunas. For example, the early Darriwilian brachiopod faunasof the Chu-Ili range and the West Balkhash region of SouthKazakhstan contain some 60 genera distributed across at leastfive palaeocommunity types. The faunas are highly endemic butshow strong links with South China at this time. The early tomid–Darriwilian (late Arenig–early Llanvirn) was an interval ofintense magmatic and tectonic activity. This is reflected in thepresence of a large variety of island arcs and microcontinents dis-persed across a spectrum of latitudes that interacted with a range ofoceanic currents (Christiansen & Stouge 1999) associated withradiations (Droser & Sheehan 1997; Bottjer et al. 2001; Harperet al. 2004), causing g-diversity to increase rapidly.

Many of the data evaluated here are derived from the distri-butions of articulated (rhynchonelliform) brachiopods. The inten-sive study of sites associated with the Celtic province is relativelyrecent, essentially since the early 1960s, compared with those ofthe coeval platform provinces, many of which have been documen-ted since the late 1800s and early 1900s (Harper 1998). This,coupled with the relative rarity of localities and the imperfect pres-ervation of material, has contributed to the difficulties in definingthis biogeographical unit. Moreover, some of the new generadescribed from this province are difficult to relate to existingtaxa because of their poor preservation, the lack of some taxo-nomic information and their different and distinctive mor-phologies. Nevertheless, since the 1990s a critical mass of datahas been available for analysis. The majority of these earlier Ordo-vician faunas were developed in relatively shallow-water facies(e.g. Lockley 1983; Cocks 1996) and thus in most cases assem-blages from similar depths are compared. Multivariate analysesof large datasets of brachiopod distributions (Harper 1992,2006a, b; Neuman & Harper 1992; Harper et al. 1996, 2008)have consistently isolated a cluster of brachiopods, identifiableas the Celtic province (Figs 11.6 & 11.7). About 15 taxa occur attwo or more of the Celtic sites; four taxa (Paralenorthis, Produc-torthis, Tritoechia and Rugostrophia) are relatively widespread,whereas some, such as Famatinorthis, Ffynnonia, Monorthis, Pla-tytoechia, Rhynchorthis and Treiroria, are relatively restricted,occurring only at two or three sites. A number of genera, such asFistulogonites, Ottadalenites, Rutrumella and Schedophyla, arereported only from single sites. Many of these sites have been sub-sequently amalgamated into allochthonous complexes and are thuslocated in Caledonian or coeval orogenic belts so that today, unlikethe coherent platform provinces, they have a very disjunct distri-bution. Nonetheless, where assembled in their pre-drift positions,the majority of sites form a high- to mid-latitude belt marginal toor seawards of Gondwana. The position of North China here andin many reconstructions is anomalous. More data are requiredfrom this microcontinent to establish its exact positions throughthe Ordovician.

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Fig. 11.5. Cluster analysis for a selection of faunas for the Floian time slice

using the Raup–Crick (Hammer & Harper 2006) similarity coefficient and a

neighbour-joining algorithm.





The brachiopods experienced a marked diversification at thespecies, genus and family levels during the early and mid Ordovi-cian (Harper et al. 2004; Zhan & Harper 2006; Rasmussen et al.2007). It is clear, however, that the distributional patterns andranges of the two main informal groups within the Brachiopoda,the non-articulated (Bassett et al. 1999; Popov et al. 1999) andarticulated stocks (Harper et al. 1999, 2004), developed indepen-dently during the biodiversification and, moreover, ecologicalevents within the phylum were not always correlated with taxo-nomic expansions. These groups have different zoogeographicalpatterns based on the behaviour of their respective larvae. Nonar-ticulate brachiopod larvae have a well-developed lophophore thatallows them to feed in the plankton and live as plankton formonths, whereas rhynchonelliform brachiopod larvae are lecitho-trophic, and they do not feed in the water column and settle out ofthe plankton in only a few days.

Globally, the order Rhynchonellida first appeared during thelate Darriwilian (Llanvirn) and underwent a modest diversificationrepresented by Rostricellula, Ancistrorhyncha, Dorytreta, Spheno-treta and Lenatoachia, widely distributed in Laurentia, Siberia,Avalonia and Kazakhstan (Jin 1996). These newly evolved taxa,being unspecialized small shells and without complications ofhold-over stratigraphical ranges, are particularly significant forbiogeographical analysis. Their distribution suggests a semi-

cosmopolitanism of the brachiopod faunas among Laurentia andits adjacent palaeoplates.

Sandbian

The basal Sandbian is signalled by a massive marine transgres-sion that encouraged the migration of many deeper-water bra-chiopod taxa onto the cratons, for example the draboviidOanduporella (Rasmussen 2011) and the strophomenoid Folio-mena (Rong et al. 1999). The Sandbian also marks the firstmajor migration of benthic shelly communities into deeper-water environments (Sepkoski & Sheehan 1983), reflected in asecond peak in global diversification during the GOBE(Harper et al. 1999; Harper 2006a; Servais et al. 2010). In par-ticular, the Foliomena fauna, characterized by minute-sizedspecies, lived in relatively deep water, mainly outer-shelf,slope and basin, in many parts of the world (Rong et al.1999). The advent of deeper-water faunas, with their own dis-tinctive biogeographical signals, adds a further complexity tothe distributional patterns of the global brachiopod fauna (Figs11.8 & 11.9). Attempts at seriation of these data against a lati-tudinal gradient (Parkes et al. 1990) were unsatisfactory,

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Celtic province

Baltic province


Tarim

Fig. 11.6. Palaeogeographical map for the Dapingian–Darriwilian time slice based on BugPlates and using a Mollweide projection. The individual localities are listed in

the supplementary material.





indicating that the brachiopods were already participating in awide range of complex community types across a range ofdepth zones and facies. Detrended correspondence analysis(Harper 1992) and cladistic analysis (Fortey & Mellish 1992)provided more consistent and conclusive results, althoughthese studies largely excluded deeper-water assemblages suchas the Foliomena fauna (Rong et al. 1999).

Some 70 localities have been identified globally for this stage,containing over 240 genera. Two sites on the Laurentian marginhave diversities approaching 70 genera, reflecting Cooper’s(1956) monographic burst, whereas some 28 sites have diversitiesranging from one to seven genera. Over 100 genera occur at onlyone site whereas one genus, Sowerbyella, occurs at over 30 sites.The standardized diversity for the Sandbian stage is 3.48, aslight drop from levels in the Dapingian–Darriwilian. Jaanusson(1973) recognized Northern and Southern faunas, correspondingto low- and high-latitude assemblages, but he also isolated a separ-ate Scoto-Appalachian fauna, succeeding in part the earlierToquima–Table Head fauna, around the margins of Laurentia;the Balto-Scandian fauna was now quite distinct. In the sametime interval, Williams (1973) identified clusters relating to Amer-ican, Baltic, Anglo-French and Bohemian faunas, whereas Havlı-cek (1989) noted that the Mediterranean Province is firstunambiguously defined during the Sandbian.

The integrity and distinctive character of the high-latitude peri-Gondwanan faunas are confirmed, dominated by dalmanellidinessuch as Drabovia, Heterorthina, Svobodaina and Tafilaltia.There are now strong faunal links between the mid-latitude conti-nents of Avalonia and Baltica, suggesting that well-developedspecies pumps were operating on both continents. These faunaswere distinct from those of Laurentia and its margins. The deep-water Foliomena fauna was still limited to South China and partsof southern Kazakhstan (Rong et al. 1999).

Lower Katian

A recent detailed investigation of the biogeography and geo-graphy of this interval, essentially the late Caradoc (Candela2006), interrogated a matrix of some 180 genera from nearly 30localities around the world using cluster and detrended

correspondence analyses. Key conclusions included theclear division of Kazakhstan into a number of independent terranesduring this interval, with different faunal affinities and histories,the prevalence of deep-water Foliomena faunas in South Chinaand a peri-equatorial location for the Gornoi-Altai terrane whichwould facilitate the westward migration of taxa. This migrationroute is in line with published palaeo-ocean current models forthe late Ordovician (see Rasmussen 2011 and references therein).

More recently, Rasmussen et al. (2012) mapped out the relation-ships amongst, between and within; (a) the tropical platforms, ter-ranes and temperate margins including Avalonia, deep-waterfaunas of Baltica, Laurentia and associated terranes, as well asSiberia and Altai; (b) tropical Gondwana and (c), high-latitudeGondwana. The Kazakh terranes are most similar to shallow-waterfacies in South China, and shallow-water assemblages in theBaltic form their own disparate branch signalling that althoughfaunas are gradually becoming more cosmopolitan, there arestill strongly endemic regions, primarily restricted by facies pre-ferences. Earlier studies such as Williams (1973) identified Amer-ican (mid-continent), circum-American, Baltic and Bohemianclusters, whereas Jaanusson (1973) noted his persistent South-ern fauna together with American mid-continent and marginalScoto-Appalachian faunas.

A palaeobiogeographical analysis of the early Katian (Trento-nian) brachiopod faunas of Laurentia and its surrounding palaeo-plates by Sohrabi & Jin (2013a, b) confirmed the existence of aunique Scoto-Appalachian fauna from the Sandbian to earlyKatian (see also Jaanusson & Bergstrom 1980); whereas theNorth American epicontinental brachiopod fauna, which startedto become distinct during the early Katian, was most closelyrelated to the shallow platform brachiopod fauna of Baltica (seealso Harper & Hints 2001).

Some 70 localities have been identified globally for this stagecontaining some 240 genera. Two sites in the Kazakh arc havediversities approaching 50 whereas the majority of sites havediversities ranging from one to almost 25 genera. One genus,Sowerbyella, occurs at 25 sites whereas the majority of generaoccur at between one and four sites. The standardized diversityfor the Lower Katian interval is 3.43 (Figs 11.10 & 11.11).

During the Late Ordovician, the orthern path of South Chinais reflected by changing faunal affinities, with increasing linkages

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Low-latitude province Celtic provinceBaltic provinceM

Fig. 11.7. Cluster analysis for a selection

of faunas for the Dapingian–Darriwilian

time slice using the Raup–Crick (Hammer

& Harper 2006) similarity coefficient and a






to Kazakhstanian terranes developing from the Sandbian, andstrong affinities to eastern Gondwana (New South Wales) faunasbecoming evident by the mid to late Katian as South China inter-sected migration pathways defined by surface currents. Also,throughout this interval, the Chu–Ili Terrane of Kazakhstanstands out as a cradle for a number of biogeographically significantgenera, with the Chingiz–Tarbagatai, Boshchekul and Selety ter-ranes providing secondary centres of origination (Percival et al.2011).

Upper Katian

This interval, essentially the pre-Hirnantian Ashgill, is markedby widespread development of carbonate mudmound facies andthe marked migration of tropical faunas into the temperate andhigher-latitude climatic belts (Boucot et al. 2003). Williams(1973) recognized a diversity of provinces, including NorthEuropean, North American and Bohemian clusters. Jaanusson(1973), in addition to his Early Katian provinces, added theHiberno-Salairian fauna that essentially included the belt of mud-mounds which stretched at this time across northern Europe.Some 70 localities have been identified globally for this intervalcontaining nearly 250 genera. Four sites, one in southeastern

South China (Rong & Zhan 2004), one in Avalonia and twoon the Laurentian margin (e.g. Harper 2006b), have diversitiesexceeding 55 genera whereas the majority of sites have diversi-ties ranging from one to 20 genera. One genus, Christiania,occurs at over 20 sites. The standardized diversity for theUpper Katian is 3.49, a slight increase from levels in theLower Katian. A recent analysis by Rasmussen et al. (2012) indi-cated that later Katian faunas had a more definite cosmopolitanstamp, although tropical shelf margins, tropical platforms andassociated terranes, together with Gondwana and adjacentterranes, are still clearly differentiated (Rasmussen et al. 2012,fig. 6).

The late Katian was also a time when cradles for many of thepost-extinction forms were being developed. Particularly, earlyvirgianid brachiopods, such as Brevilamnulella, appear to haveevolved from deep-water mound settings at lower latitudes, suchas the Boda Mounds in Sweden, to become very important in theaftermath of the extinctions (Wright & Rong 2008; Rasmussenet al. 2010). Thus, the basic characters of Brevilamnulellaprobably gave rise to the rest of the pentameroid group, whichbecame very successful in shallow-water settings. At the sametime, the clorindoids – possibly also derived from a Brevilamnu-lella-like ancestor closely related to Clorilamnulella – maintaineda deeper water preference. Another virgianid of late Katian age,

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Fig. 11.8. Palaeogeographic map for the Sandbian time slice based on BugPlates and using a Mollweide projection. The individual localities are listed in the






Deloprosopus (very similar to Tcherskidium) was evolved insoutheastern South China, and may be the local ancestor for theSilurian pentameroids in South China (Jin et al. 2006). Thus, habi-tats like the Boda Mounds seem to have been of profound impor-tance as cradles and subsequently species pumps for opportunistictaxa that were to play a pivotal role in restoring the biodiversitylevels in the wake of the Hirnantian extinctions.

Pronounced brachiopod provincialism is well known for themiddle–late Katian (e.g. Sheehan & Coorough 1990). This iswell demonstrated by the newly evolved rhynchonellide fauna ofLaurentia during this time interval. For example, the ubiquitousNorth American brachiopod fauna represented by Hiscobeccus,Lepidocyclus and Hypsiptycha in the Maysvillian–Richmondianwas virtually confined to Laurentia, except for a few isolated, puta-tive occurrences elsewhere (see Jin 1996, 2001; Rasmussen 2013;Sohrabi & Jin 2013a, b; Figs 11.12 & 11.13).

Hirnantian

Since recognition of the widespread distribution of the Hirnantiabrachiopod fauna in the mid-1960s (e.g. Temple 1965; Marek &Havlıcek 1967; Bergstrom 1968; Wright 1968), there have beena number of analyses of the global distributions of the Hirnantianbrachiopod fauna (e.g. Rong 1984; Rong & Harper 1988; Harperet al. 2013). There is a clear division between the low-latitudeEdgewood Province (Amsden 1974) and those of the higher-latitude Bani and Kosov provinces dominated by variants of theHirnantia fauna, although clear elements of the Edgewoodprovince are present in, for example, Estonia and the OsloRegion, arriving to colonize suitable warm-water carbonatefacies. The differentiation between the Bani and Kosov provinces

is more subtle, the former characterized by low-diversity faunasand differences at the species level from comparable taxa in themore-diverse Kosov Province (Villas et al. 1999). Some 50localities have been identified globally for this stage, containingover 140 genera. One site, Estonia, has a diversity approaching40 genera whereas the remaining sites have diversities rangingfrom one to 25 genera. Seven key genera, Cliftonia, Dalmanella,Eostropheodonta, Hindella, Hirnantia, Leptaena and Plectothyr-ella, each occur at over 15–25 sites. The standardized diversityfor the Hirnantian Stage is 2.8; a drop from levels in the UpperKatian.

Rasmussen & Harper (2011b) pinpointed a number of regionsand settings that acted as safe havens for various groups of brachio-pods. The Yangtze Platform, for instance, played a pivotal role inpreserving the mid-shelf stocks, whereas the Oslo Region inBaltica apparently housed an unusually large number of deep-water taxa during the crisis interval. This may explain why alarge number of holdover or Lazarus taxa are found in theseregions during the earliest Silurian Rhuddanian Stage (Baarli &Harper 1986; Rong et al. 2006; Figs 11.14 & 11.15).

Brachiopod biodiversity and phylogeography during

the Ordovician

The rhynchonelliformean brachiopods comprise a major constitu-ent of the GOBE (Harper 2006a). Their diversity through theperiod has previously been assessed in some detail (e.g. Harperet al. 2004 and references therein). The current study, based on anew, much more comprehensive, dataset, roughly mirrors thediversity curve produced by previous studies (Fig. 11.16a),

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Fig. 11.9. Cluster analysis for a selection of faunas for the Sandbian time slice using the Raup–Crick (Hammer & Harper 2006) similarity coefficient and a






although the current dataset reveals an overall higher diversitylevel throughout the period, possibly reflecting the more recentintense sampling and research being conducted within this field.

The Ordovician Period commenced with a relatively slow, butsteady increase in generic diversity which continued through theFloian Stage and into the Dapingian. The persistence and slightdiversification of Cambrian stocks were responsible for thisslow rise in diversity, which occurred despite the demise of thebillingselloids. It was primarily driven by radiations within theOrthoidea and Porambonitoidea. However, from the Floianonwards, the strophomenides gradually became more and moreimportant, notably as the Plectambonitoidea was established.The phylogeographical map for the Tremadocian Stage (Fig.11.16b) shows that the orthoids were present as a dominant con-stituent of the faunas in all regions at this time, notably, aroundhigh- and low-latitude Gondwana, as well as on the more southerlylocated continents of Avalonia and Baltica. Adjacent to Gond-wana, Perunica hosted a somewhat more phylogeneticallydiverse fauna where orthoids were associated with billingsellids.In the Northern Hemisphere, however, the faunas were morecomplex. The South China Palaeoplate seems to have been acradle for many clades, such as the clitambonitoids, which had astrong component together with porambonitoid taxa mixed withorthoids. Moreover, some of the earliest occurrences of the stro-phomenide clades were also present, whose cradles seem to havebeen located in equatorial settings. Porambonitoid and clitamboni-toid genera are also found in parts of Gondwana (Tasmania) at this

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Fig. 11.10. Palaeogeographical map for the Lower Katian time slice based on BugPlates and using a Mollweide projection. The individual localities are listed in the


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Fig. 11.11. Cluster analysis for a selection of faunas for the Lower Katian

time slice using the Raup–Crick (Hammer & Harper 2006) similarity

coefficient and a neighbour-joining algorithm.





time. Along with the Orthoidea, the porambonitoids were impor-tant constituents throughout lower latitudes, commonly alongwith the billingselloids, or, as seen on the Salair Terrane and inLaurentia, together with plectambonitoids. In Laurentia, thepentameride taxa, again characterized by the porambonitoids,dominated the faunas, with the orthoids being less important. Bill-ingselloids were also present as a minor part of the fauna. Laurentiaand South China are apparently two of the cradles for the Stropho-menoidea and some of the main biodiversity epicentres for thesubsequent radiation of the superfamily. In Salair and SouthChina, the plectambonitoids were firmly established in otherwiseporambonitoid-dominated low-latitude regions.

This earliest Ordovician phylogeographical distribution contin-ued into the Floian. The porambonitoids continued to radiate andthus reached a generic diversity almost at the same level as theorthoids. However, this diversification ceased within the Dapin-gian when one-third of the porambonitoid stocks disappeared.However, the Orthoidea continued to radiate. In addition the Cli-tambonitoidea began to radiate. However, the trajectories of theorthoids and porambonitoids were subsequently modified byextinctions within the early Darriwilian. The overall generic diver-sity reached a plateau, which primarily was caused by a genericloss within these two superfamilies. This was an interval whenonly the clitambonitoid and strophomenide clades displayed a

net diversification. Although the strophomenoids continued toradiate, they could not compensate for the major loss of taxawithin the porambonitoids and the orthides, as well as the demiseof the Billingselloidea, which went extinct by the Dapingian. Basedon the phylogeographical maps for the Tremadocian (Fig. 11.16b)and Dapingian–Darriwilian (Fig. 11.16c) intervals, it is evidentthat there was a drastic change in the phylogeographical compo-sition in especially the low-latitude regions. The porambonitoidsclearly suffered a large loss on Laurentia, but the demise of theorthoids is somewhat more difficult to locate geographically.

The Darriwilian extinctions apparently helped pave the wayfor an explosion in strophomenide clades. In many of the majorextinctions clearing ecospace was clearly important for some sub-sequent radiations. The Plectambonitoidea and Strophomenoideadoubled their generic diversity by the mid Darriwilian and thiscontinued through the rest of the Darriwilian, a trend that wasmirrored by the dalmanelloids, a plexus that constituted thebackbone of the brachiopod radiation during the GOBE. By thelate Darriwilian more and more clades increased in generic diver-sity and geographical distribution, probably derived from low- tomid-latitude species pumps situated on the more diverse habi-tats of the larger continental palaeoplates, such as Baltica (seeRasmussen et al. 2007), but also on the emerging intra-oceanicpalaeoplates. The Dapingian–Darriwilian phylogeographical

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Fig. 11.12. Palaeogeographical map for the Upper Katian time slice based on BugPlates and using a Mollweide projection. The individual localities are listed in the






map clearly demonstrates the shift from orthoid/porambonitoiddominated Tremadocian world (dark orange and purple colours)to a strophomenoid-dominated Mid Ordovician brachiopod fauna(green colours). Although orthide and pentameride losses werestabilized, mostly owing to the ever more successful dalmanelloidsand camerelloids, it was the strophomenides that underpinnedthe main diversity peak. These taxa were now the main constitu-ents in most regions, except for mid- and high-latitude Gondwana.On the larger continents, particularly Avalonia and Laurentia,orthoid biodiversity epicentres persistently dominated alongwith the new clades. Cradles for rhynchonellides and triplesiids,for example, were almost exclusively located on Avalonia andLaurentia as important parts of the overall phylogenetic compo-sition of these continents. The clitambonitoids reached the acmeof their distribution, constituting large proportions of the generain Avalonia and Baltica and possibly acting as species pumps forthe neighbouring regions, where the clitambonitoids to a lesserextent were recruited within the remainder of low- to mid-latituderegions. The dalmanelloids, in contrast, seem to have been quitesuccessful in high-latitude Gondwana, which may have acted asa species pump, possibly facilitating their spread to the nearbypalaeoplates of Avalonia and South China and then farther northto the Northern Precordilleran terrane and Perunica, as well asthe intra-Iapetus terranes, such as the Leinster and Midland Val-ley terranes. Baltica and the North China Palaeoplate, however,were not characterized by the same dalmanelloid radiation dur-ing the Darriwilian. The most phylogenetically diverse regionswere Avalonia, Laurentia and South China, but particularly theintra-Iapetus island arcs and microcontinents also held a widerange of clades, many carrying the new dominant strophomenideand clitambonitoid groups mixed with the older orthoid andporambonitoid stocks.

The GOBE reached its plateau during the early Sandbian,mainly constructed by the overwhelmingly successful strophome-nides. However, a number of new clades contributed to this diver-sity spike, together with the older Cambrian stocks, such as theorthides, with radiations within all major clades, recovering fromthe early Darriwilian extinctions. Within the previously successfulpentamerids, the camerelloids also managed to stage a notable

recovery. By the earliest Sandbian, rhynchonelliformean diver-sity constituted more than 200 genera, of which about 80%belonged to either the Orthida or Strophomenida. This expansionin biodiversity continued well into the Katian, with some fluctu-ations, before one final hike during the latest Katian. This wasbolstered by a final radiation of the orthoids and strophomenides,new pentameroids, and the atrypoids.

The Katian phylogeographical map (Fig. 11.16d) clearlyshows this wealth of new clades, which occupied both the equator-ial and boreal belts. By the late Katian, Baltica, with more than 20superfamilies present, surpassed Laurentia and South China as themost phylogenetically diverse region. Strophomenoids, account-ing for more than 40 genera, were overwhelmingly dominantwith more than twice as many genera than the second largestgroup, the plectambonitoids. Compared with the Darriwilianmap for Baltica, the atrypides, rhynchotrematoids and pentamer-ides radiated, whereas clitambonitoids and orthoids became lessimportant. This appears to have been the more general pictureglobally. Although still dominated by strophomenides, manyother clades gained a permanent foothold around the larger conti-nents, which thus acted as large biodiversity epicentres and sub-sequent species pumps. This included new pentameroid taxa, theatrypids and athyridids, as well as a whole suite of other clades.Orthoid-dominated regions were now exclusively located in low-diversity, high latitudes, alongside the dalmanelloid and stropho-menoid clades that remained; these were cosmopolitan at thistime. Avalonia was still, with 16 superfamilies, a very phylogeneti-cally diverse region, as elsewhere, mostly dominated by the stro-phomenoids and plectambonitoids together with dalmanelloidsand orthoids. The eastern part of the continent had a somewhatdifferent phylogenetic signature, lacking rhynchotrematoids andmeristelloids.

In Laurentia, the plectorthoids were nearly as diverse as the dal-manelloids and orthoids. In addition, rhynchotrematoids, camerel-loids and pentameroids were similarly diverse. For the Katian map,the phylogenies for the Anticosti Basin, Newfoundland and theFranklinian Basin are also shown, to give an impression ofwhich clades were present on the Laurentian margins. Whereasthe Franklinian fauna clearly demonstrates a strong pentameroidcomponent (purple), within the strophomenide and orthide domi-nated fauna, the more southerly basins have only rare pentamer-oids, instead being dominated by rhynchotrematoids, atrypidsand athyridids.

Off the western margin of Laurentia, the Klamath terrane washeavily dominated by the Orthida with many orthoids and plec-torthoids, together with some dalmanelloids and enteletoids. Plec-tambonitoidea was less dominant here than was usual for thisinterval. Thus, in general, this distribution is likely to reflect temp-erature, with the pentameroids preferring the tropical settings, andother clades being more adaptable to temperate regions. Interest-ingly, the Eastern Klamath terrane appears to have acted as amuseum, retaining clades that were dominant earlier in theOrdovician.

In the Iapetus Ocean, terranes such as the Midland ValleyTerrane exhibit a substantial phylogenetical diversity, possiblyconveying clades from either side of the extremely diverse sur-rounding continents, or providing stepping stones to migrations.The Midland Valley Terrane exhibits an unusually high numberof remnants from the earlier Ordovician (Clitambonitoidea) anda greater orthide component dominated by Orthoidea than seenelsewhere. However, these were mixed with new clades, such asthe Rhynchotrematoidea and Triplesioidea, which also were unu-sually diverse here. Also several atrypid and athyridid superfami-lies were present, but only few pentamerides (Camerelloidea).

The regions that were the most conspicuous, during this timeslice, were the Farewell and Kolyma terranes, with their unusuallyhigh concentration of pentameride stocks (Camerelloidea and Pen-tameroidea). Notably, for the Farewell Terrane, Anazygoidea wasalso unusually well represented. Plectambonitoidea, however, was

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Low-latitude province Mid-latitude province High-latitude province

Fig. 11.13. Cluster analysis for a selection of faunas for the Upper Katian

time slice using the Raup–Crick (Hammer & Harper 2006) similarity

coefficient and a neighbour-joining algorithm.





the most dominant group, although with only a few more generathan the pentameroids. Orthoids were not particularly importantand strophomenoids were represented by only one genus.

Kolyma also had a very unusual phylogenetic composition. Itwas almost a ‘Silurian fauna’, being dominated by pentameroids,atrypids and athyridids and with a total absence of orthides. InSiberia, an odd mix of strophomenides, rhynchotrematoids andatrypids co-occurred with a few orthoids and plectorthoids. Dalma-nelloids were lacking – to some extent this composition is alsoseen in the nearby, very phylogenetically diverse, Altai Terrane.Here, however, the camerelloids and pentameroids were alsoimportant constituents. Interestingly, on both the Siberia andAltai terranes, dalmanelloids seem to have been rare, havingbeen replaced by orthoid and plectorthoid clades. In the Taimyrregion of Siberia, orthoids were also rare, with dalmanelloids,the most common orthides, marked by only four genera – thesame number as both the plectambonitoids and strophomenoids.Atrypoids were unusually diverse, as were the pentameroidsand triplesioids.

Farther east from the Altai terrane, the Kazakh terranes,along with the North China Palaeoplate, were dominated by thestrophomenides. In particular, the Tien–Shan terrane was domi-nated by plectambonitoids, with atrypoids and strophomenoids asthe second, most-diverse constituents. Pentameroids were alsoimportant but only one orthoid genus was present. The Chu–Iliterrane displayed quite different phylogenies, including large pen-tameroid, meristelloid and enteletoid components mixed with theplectambonitoids. In between the Tien–Shan and Chu–Ili terranes,

60oS

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Fig. 11.14. Palaeogeographical map for the Hirnantian time slice based on BugPlates and using a Mollweide projection. The individual localities are listed in the


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Fig. 11.15. Cluster analysis for a selection of faunas for the Hirnantian time

slice using the Raup–Crick (Hammer & Harper 2006) similarity coefficient and

a neighbour-joining algorithm.





the Chinghiz Terrane was very diverse, phylogenetically, withmany clades derived from the nearby North China Palaeoplate.

During the rest of the Ordovician Period, the South ChinaPalaeoplate was one of the most diverse regions containingmany unusual stocks and notably a high number of atrypoidgenera represented by the Altaethyrella fauna (a regional brachio-pod fauna of late Katian age mainly in South China, NorthChina and southern Kazakhstan terranes; Rong & Zhan 2004).

In Gondwana, the low-latitude, equatorial regions stand out asbeing most phylogenetically diverse. These regions were stronglydominated by the Strophomenida, but with a rare large compo-nent of atrypides, camerelloids and rhynchotrematoids, althoughpossibly linked to the siliciclastic facies dominant here, not asimportant constituents, as seen elsewhere in the tropics. Plec-torthoids are the most dominant orthides. In high-latitude Gond-wana, Orthoidea and Dalmanelloidea still dominated, whereas

EichwaldioideaCyr�oideaSpiriferida

DayioideaRetzioideaAthyrididinaMeristelloidea

LissatrypoideaAnazygoideaAtrypoideaProtozygoideaUncinuloidea

ClorindoideaStricklandioideaPentameroidea

UNCERTIANRhynchospirinoideaChonetoideaChilidiopsoidea

Legend

Rhynchotrematoidea

Camerelloidea

Poram

bonitoidea

Strophomenoidea

Plectambonitoidea

Enteletoidea

Dalmanelloidea

Plectorthoidea

Orthoidea

Billingselloidea

Ancistrorhynchoidea

Clitambonitoidea Polytoechioidea

50

250

200

150

100

Gen

eric

div

ersi

ty

Ma/ Global Stage

KatianSandbian Hir.P RC

453.0 445.2 443.8458.4

DarriwilianDap.FloianTremadocian

467.3470.0477.7485.4

OrthidaOrthida

BillingsellidaBillingsellida

StrophomenidaStrophomenida

Pentamerida

Pentamerida

Triplesioidea

Triplesioidea

Rhynchonellida

Rhynchonellida

Skenidioidea

Atrypida

Atrypida

(a)

(b)

(c)(d)

Fig. 11.16. (a) Ordovician generic brachiopod diversity and phylogeographical distribution through the Ordovician Period. Genera are grouped into superfamilies, and in

some cases higher groupings. Related phylogenetic groups share the same colour shades. These shades are also used in the phylogeographical time-slice maps (b–d).

Radial colourings indicate dominance of each superfamily in a given region, going from least dominant (centre of circles) to most dominant (outermost part of circles).

Abbreviations: Dap., Dapingian; Hir., Hirnantian. See legend for names of superfamilies not written on the biodiversity graph.





strophomenoids and triplesiids were minor constituents and somecamerelloids, porambonitoids and plectorthoids were present onlyregionally.

Following this late Katian explosion in numbers of clades, theHirnantian extinctions excised a significant number of theancient stocks, clearing ecospace for new clades, such as the pen-tameroids and the atrypids, to expand rapidly during the sub-sequent Llandovery. Having mostly been located on relativelyisolated intra-oceanic, low-latitude terranes during the latestKatian, these clades suddenly were able to gain a foothold on,for instance, the Laurentian margins once the recumbent faunashad been stressed, if not removed entirely (Sheehan 1975; Rasmus-sen & Harper 2011a, b).

Conclusions

(1) Low global diversities of Tremadocian and Floian faunaswere typical: the main biodiversity epicentres were locatedin South China, where the first spike of the GOBE manifestedin the lower Floian.

(2) Bursts of diversity within the Dapingian–Darriwilian inter-val were associated with dispersed island arcs, microconti-nents and continents but retarded by subsequent regionalextinctions in the early Darriwilian.

(3) There was a mid-Darriwilian onset of a massive radiationwithin the strophomenide and dalmanelloid clades, constitut-ing the main phylogenetical component of the GOBE. Mainspecies pumps were located on Avalonia and Baltica.

(4) Sandbian offshore and other migrations of faunas and thedevelopment of the Foliomena faunas occurred: many newclades had now emerged.

(5) Katian development of cradles in carbonate mound environ-ments contributed to migrations of fauna poleward. Particu-larly during the latest Katian, this caused a great expansionin pentameroid clades, as well as the atrypids and athyridids.

(6) End-Ordovician (Hirnantian) glaciations coincided withwell-defined, climatically controlled provinces and massiveextinctions in the ‘Ordovician brachiopod fauna’.

David A. T. Harper, Christian M. Ø. Rasmussen thank the Danish Council for

Independent Research, and Natural Sciences for financial support. Ian G. Percival

publishes with permission of the Executive Director, NSW Trade and Investment,

Department of Resources and Energy. J.-Y. Rong and R.-B. Zhan thank the

National Natural Science Foundation of China (41221001, 41290260). This

paper is also a contribution to the IGCP project 591 ‘Early to Middle Paleozoic

Revolution’. We gratefully acknowledge the help of R. Cocks in providing us

with the brachiopod data of Lees et al. (2002). Insightful and thoughtful

reviews by L. Popov and P. Sheehan considerably improved the manuscript.

M. McCorry helped consolidate our reference lists and the supplementary data.

The reconstructions are based on BugPlates with some minor modifications.

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http://dx.doi.org/10.1016/j.palaeo.2013.02.027

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biodiversity, biogeography and phylogeography of ordovician rhynchonelliform brachiopods

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