diversiﬁcation of atypical paleozoic echinoderms:...

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Paleobiology, 32(3), 2006, pp. 483–510

Diversification of atypical Paleozoic echinoderms: a quantitativesurvey of patterns of stylophoran disparity, diversity,and geography

Bertrand Lefebvre, Gunther J. Eble, Nicolas Navarro, and Bruno David

Abstract.—The analysis of morphological disparity and of morphospace occupation through themacroevolutionary history of clades is now a major research program in paleobiology, and increas-ingly so in organismal and comparative biology. Most studies have focused on the relationshipbetween taxonomic diversity and morphological disparity, and on ecological or developmental con-trols. However, the geographic context of diversification has remained understudied. Here we ad-dress geography quantitatively. Diversity, disparity, and paleogeographic dispersion are used todescribe the evolutionary history of an extinct echinoderm clade, the class Stylophora (cornutes,mitrates), from the Middle Cambrian to the Middle Devonian (about 128 Myr subdivided into 12stratigraphic intervals). Taxonomic diversity is estimated from a representative sample including73.3% of described species and 92.4% of described genera. Stylophoran morphology is quantifiedon the basis of seven morphometric parameters derived from image analysis of homologous skel-etal regions. Three separate principal coordinates analyses (PCO) are performed for thecal outlines,plates from the lower thecal surface, and plates from the upper thecal surface, respectively. PCOscores from these three separate analyses are then used as variables for a single, global, meta-PCO.For each time interval, disparity is calculated as the sum of variance in the multidimensional mor-phospace defined by the meta-PCO axes. For each time interval, a semiquantitative index of paleo-geographic dispersion is calculated, reflecting both global (continental) and local (regional) aspectsof dispersion.

Morphospace occupation of cornutes and mitrates is partly overlapping, suggesting some mor-phologic convergences between the two main stylophoran clades, probably correlated to similarmodes of life (e.g., symmetrical cornutes and primitive mitrocystitids). Hierarchical clustering al-lowed the identification of three main morphological sets (subdivided into 11 subsets) within theglobal stylophoran morphospace. These morphological sets are used to analyze the spatiotemporalvariations of disparity. The initial radiation of stylophorans is characterized by a low diversity anda rapid increase in disparity (Middle Cambrian–Tremadocian). The subsequent diversification in-volved filling and little expansion of morphospace (Arenig–Middle Ordovician). Finally, both sty-lophoran diversity and disparity decreased relatively steadily from the Late Ordovician to the Mid-dle Devonian, with the exception of a second (lower) peak in the Early Devonian. Such a patternis comparable to that of other Paleozoic marine invertebrates such as blastozoans and orthid bra-chiopods. During the Lower to Middle Ordovician, the most dramatic diversification of stylo-phorans took place with a paleogeographic dispersion essentially limited to the periphery of Gond-wana. In the Late Ordovician, stylophorans steadily extended toward lower paleolatitudes, andnew environmental conditions, where some of them radiated, and finally survived the end-Ordo-vician mass extinction (e.g., anomalocystitids). This pattern of paleobiogeographic dispersion iscomparable to that of other examples of Paleozoic groups of marine invertebrates, such as bivalvemollusks.

Bertrand Lefebvre, Gunther J. Eble, Nicolas Navarro,* and Bruno David. Centre National de la RechercheScientifique, UMR 5561 Biogeosciences, Universite de Bourgogne, 6 boulevard Gabriel, 21000 Dijon,France. E-mail: [email protected], E-mail: [email protected], E-mail:[email protected]

*Present address: Faculty of Life Sciences, University of Manchester, Michael Smith Building, Oxford Road,Manchester M13 9PT, United Kingdom. E-mail: [email protected]

Accepted: 16 March 2006

Introduction

The early Paleozoic radiations continue togalvanize debates concerning the tempo andmode of macroevolution. Such debates, as wellas attendant empirical, theoretical, and meth-odological issues, have in turn matured in sev-

eral respects. The Cambrian explosion cannow be placed in the broader context of boththe late Precambrian and the Ordovician fossilrecord, as it involved the origin not only ofmost animal phyla, but also of most classesand orders. The Cambrian explosion has cometo be seen less as a single event and more as

484 BERTRAND LEFEBVRE ET AL.

an ensemble of Cambro-Ordovician eventsand processes relatively clustered in time andmanifested as an unprecedented period ofmajor morphological innovation in the historyof animal life. Furthermore, it is realized thatthe Cambro-Ordovician radiations are onlymeaningful in contrast to what happened ordid not take place afterward, both in the Pa-leozoic and post-Paleozoic. Ecological and de-velopmental explanations involving differen-tial flexibility and enhanced innovation dur-ing the early Paleozoic in particular, and dur-ing evolutionary radiations in general, haveserved as contrasting hypotheses for manystudies, and have been complemented by re-newed attention to the influence of the contextof abiotic environmental change (Valentine2004).

Against this backdrop, the quantification ofmorphological disparity and of morphospaceoccupation emerged as a major research pro-gram in evolutionary paleobiology (e.g., Foote1991, 1997; Gould 1991; Briggs et al. 1992;Wills et al. 1994; Conway Morris 1998; Valen-tine 2004). This alternative view of macroevo-lution effectively revitalized the practice ofevolutionary paleobiology, and represented anew ‘‘way of seeing’’ large-scale evolution,complementary to and enriching of more clas-sical taxonomic diversity descriptors of mac-roevolutionary patterns and processes. Thestudy of disparity and morphospaces wasmainly stimulated by the prospect of more ob-jectively characterizing morphological signa-tures of diversification. In this context, pat-terns of morphological disparity and taxo-nomic diversity are often discordant and forthis very reason highly informative (e.g., Foote1993a).

Despite its scope, this research program isstill a relatively young enterprise, and moststudies have focused on the relationship be-tween taxonomic diversity and morphologicaldisparity through time, and on the ecologicalor developmental meaning of morphologicaland taxonomic signatures of evolutionary ra-diations and diversification in general. A va-riety of groups (arthropods, echinoderms,mollusks, and brachiopods) have been studiedin this manner and, inductively, a few tenta-

tive generalizations have emerged (see Foote1996, 1997; Valentine 2004).

On the other hand, although disparity isnow recognized as an appropriately rigorousmeasure to test hypotheses of differential con-straint over time and to address its causes,geographic correlates of diversification haverarely been incorporated into disparity stud-ies. Theoretically and empirically, the geo-graphic context of morphological diversifica-tion presents itself as potentially important interms of both correlation and causation, and iseminently tractable given the paleogeograph-ic data available. As is already the case withtaxonomic diversity (Jablonski 1986, 1987,1993, 1998; Jablonski and Bottjer 1991), thepossibility of meaningful geographic corre-lates of disparity dynamics could be condu-cive to a better and broader understanding ofthe spatial context of morphological diversi-fication. In this paper, we explicitly addressgeography along with diversity and disparity,and attempt to develop a quantitative index tofacilitate comparisons.

In the arena of quantification of morpholo-gy itself, Gould’s (1991) compelling case for‘‘why we must strive to quantify morpho-space’’ motivated the rigorous characteriza-tion of morphospaces and of the dynamics ofmorphological disparity, understood as a dis-tinct and relatively objective aspect of biodi-versity. However, a real challenge persists:making objects and variables commensurate.

The problem of quantification of data is aperennial one, having already been recog-nized as fundamental 60 years ago, withWoodger’s (1945) critique of D’Arcy Thomp-son’s transformation grids and its limits. Morerecently, Bookstein (1994: p. 220) provided thisassessment regarding morphometric studieson macroevolutionary scales: ‘‘No importantevolutionary change can be captured persua-sively in the language of morphometrics.’’Later, referring to ‘‘the incoherence of any leg-ible geometric metaphor for ‘‘morphospace’’above the species level,’’ he states: ‘‘The fun-damental analogy between a morphospace. . . and a vector space of shape descriptorsquickly becomes untenable as the relevantrange of shapes broadens’’ (Bookstein 1994).Perhaps the survival of disparity and mor-

485DIVERSIFICATION OF ATYPICAL ECHINODERMS

FIGURE 1. Stylophoran morphology: Phyllocystis blayaci (Cornuta), Early Ordovician, Montagne Noire (France),about �2.2 (redrawn and modified after Ubaghs 1970). A, Upper view. B, Lower view. C, Left lateral aspect.

phospace studies lies in the multiple mean-ings of ‘‘shape,’’ a nontrivial issue. In any case,Gould himself also voiced some doubts (1991:p. 421): ‘‘I do confess some fears that, in toto,the question of morphospace may be logicallyintractable, not merely difficult.’’

In other words, a variety of groups withpuzzling morphologies discourage quantifi-cation and do not immediately lend them-selves to a morphometric study with pre-scribed methods. Often, even within a highertaxon, interspecific variation appears difficultto quantify and interpret, given the variousscales of morphological organization and ho-mology. Is there a solution? Perhaps, if one iswilling to consider a pluralistic approach inwhich several techniques are combined andpragmatically explored. We argue that onecan, and must be willing, to abandon the hopeof uniformly applying one’s favored techniquein some instances, whether traditional, out-line-based, or landmark-based. Instead, wemust strive to be pluralistic and flexible in themethods we apply. Exactly how to do so re-mains an open question, and there may beseveral answers. Here we provide an empiri-cal case study to address the issue in a mac-roevolutionary context.

In this paper, the class Stylophora has beenchosen as a model to document the initial di-versification of the phylum Echinodermata.Stylophorans are one of four classes formerlyincluded in the subphylum ‘‘Homalozoa’’

(David et al. 2000). Stylophorans are an extinctclass of echinoderms (about 120 species and 66genera) that offers the possibility to illustratethe complete evolutionary history of an echi-noderm clade, from their initial radiation inthe Middle Cambrian to their decline and fi-nal disappearance in the late Carboniferous.

Stylophorans are a major component of LateCambrian to Early Ordovician echinodermfaunas (Guensburg and Sprinkle 2000; Lefeb-vre and Fatka 2003). They have been recordedfrom all around the world, with the exceptionof Antarctica. A relatively good phylogeneticframework is available for the class, which isusually subdivided into the two monophyleticorders Cornuta and Mitrata (Ubaghs 1968;Parsley 1988; Lefebvre 2001; Sprinkle andGuensburg 2004). All stylophorans share thesame basic anatomical organization, withtheir body consisting of two well-defined re-gions: the aulacophore and the theca (Fig. 1)(Ubaghs 1961, 1981; Chauvel 1981; Parsley1988; Lefebvre 2001). The aulacophore is a del-icate, flexible, tripartite appendage. It is afunctional, composite structure comprising afeeding arm (distal regions), and an exothecalextraxial extension (proximal portion; Davidet al. 2000). The mouth is located at the baseof the feeding arm (Ubaghs 1961; Nichols1972; David et al. 2000). The theca is a massive,flattened, asymmetrical extraxial calcite box,which enclosed most organs in life. This ana-tomical interpretation of stylophorans is root-


FIGURE 2. Stylophoran taxonomic diversity: compari-son of sampled and total number of described species.

ed in the Extraxial Axial Theory (Mooi et al.1994; Bergstrom et al. 1998; David and Mooi1999; David et al. 2000). However, the resultsof this paper are not conditioned on this the-ory, and the only prerequisite is that Stylo-phora corresponds to a monophyletic group,which is now widely accepted (e.g., Peterson1995; Parsley 1997; Sumrall 1997; Ruta 1999a).Number, morphology, and arrangement ofthecal skeletal elements (plates) are constantand diagnostic of a given species of stylo-phoran (Lefebvre 2001). A solid, well-estab-lished model of homologies has been pro-posed to identify equivalent skeletal elementsamong stylophorans (Lefebvre et al. 1998; Le-febvre and Vizcaıno 1999; Lefebvre 2000a,b,2001). Such a model of plate homologies al-lows direct interspecific comparisons and theuse of a variety of morphometric methods toquantify disparity. Although disparity couldbe quantified in terms of total change withphylogenetic measures (Smith 1994; Wills etal. 1994; Wagner 1995; Eble 2000), no mor-phospace would be made explicit, and its dif-ferential exploration would be difficult toevaluate in terms of phylogeny alone. In con-trast, disparity as net change (Foote 1995,1996) emphasizes both actual and possible lo-cations of taxa in a multidimensional space oftraits. Thus, morphospace itself is made ex-plicit in discourse, analysis, representation,and interpretation. The patterns documentedby using this approach are independent of anygiven phylogeny and of the phylogenetic po-sition of the Stylophora as a group, whetherwithin or outside the echinoderms.

Material and Methods

Sampling. Data were collected at the spe-cies level, based on a comprehensive, nearlycomplete sample of stylophoran taxa. Thischoice was motivated by the small number ofspecies described so far in the class (about120), by the presence of great morphologicalvariation within some genera (e.g., in Scotiae-cystis), and so as to avoid problems related tothe definition of genera, given that there ismore consensus about the identity of speciesthan of genera. For example, all workers dis-tinguish the four species P. africana, P. buretti,P. flemingi, and P. garratti, included here in the

genus Placocystella (following Lefebvre 2001),even though they were traditionally consid-ered as belonging to four different genera(Caster 1983; Parsley 1991, 1997; Ruta 1999b;Ruta and Jell 1999e). In this context, stylo-phoran disparity has been estimated from thelargest possible sample of well-preservedforms, including 88 species and 61 genera, andcorresponding, respectively, to 73.3% and92.4% of all forms described to date. This sam-ple includes the two most primitive knownstylophoran species (genus Ceratocystis) andrepresentatives of the two monophyletic or-ders Cornuta and Mitrata. Here we considercornutes and mitrates as clades, followingphylogenetic analyses by Lefebvre and Viz-caıno (1999) and Lefebvre (2001). The identi-fication of plate homologies within stylophor-ans strongly supports the view that the ‘‘an-kyroids’’ of Parsley (1997) are a polyphyleticassemblage based on superficial similarities(Lefebvre 2001). In our analysis, 38 of 49 spe-cies (77.5%), and 27 of 30 genera of cornutes(90%), and 48 of 69 species (69.6%), and 33 of35 genera of mitrates (94.3%) have been con-sidered (see supplementary materials onlineat http://dx.doi.org/10.1666/05044.s1).

Thirty-two species (five genera) were ex-cluded from the analysis. However, this didnot affect the pattern of stylophoran diversitythrough time (Fig. 2). Taxa were excluded forthe following reasons: (1) they are known onlyfrom isolated skeletal elements (e.g., the cor-nute Babinocystis dilabidus, most kirkocystid


mitrates); (2) they were described from a sin-gle, incomplete specimen (e.g., the cornutesHanusia obtusa, Thoralicystis zagoraensis, Tri-gonocarpus singularis); (3) their morphology istoo poorly known, owing to disarticulation,poor preservation, and/or difficulty in dis-cerning plate boundaries (e.g., the cornuteAcuticarpus delticus, the mitrates Dalejocystiscasteri and Mongolocarpos minzhini); (4) there isno reconstruction of their morphology avail-able in the literature (e.g., the mitrates Eno-ploura balanoides, and ?Mitrocystites styloideus);(5) they possibly represent junior synonyms oftaxa included in the analysis (e.g., Anomalo-cystites disparilis is a possible junior synonymof A. cornutus, after Parsley 1991). Further-more, the exclusion of about 26.7% of stylo-phoran taxa for mostly preservational reasonsappears to be unbiased with respect to thetwo major stylophoran groups, as comparableproportions of cornutes (22.5%) and mitrates(30.4%) were not sampled. However, a closerexamination of excluded taxa suggests thatthe occurrence of poorly preserved species isnot completely random within subgroups: forexample, 66.7% of peltocystid mitrates havebeen excluded from the analysis, as most oftheir species were described on the basis ofisolated skeletal elements (e.g., most species ofthe genus Anatifopsis). It should be stressed,however, that the small number of peltocys-tids included in the analysis is not expected toalter the overall pattern of stylophoran dis-parity, as morphologies are very conservativein this group of mitrates. For example, themorphologies of excluded taxa such as Anati-fopsis balclatchiensis (Upper Ordovician) and?Mitrocystites styloideus (Early Devonian) lookvery similar to that of the included species A.trapeziiformis (Early Ordovician).

Whenever complete specimens were notavailable, we relied on composite reconstruc-tions, which are widely accepted. This wasnecessary because fossil remains of stylophor-ans are almost always found more or less dis-articulated, distorted, and/or incomplete, sothat reconstruction of their morphology is fre-quently based on several individuals. Thiswas possible because intraspecific morpholog-ical variation, when documented in stylo-phorans, is in most cases very limited and can

be neglected in comparison with interspecificvariation (Chauvel 1941; Ubaghs 1968, 1979;Jefferies 1984; Ruta 1998; Lefebvre 1999; Rutaand Jell 1999d). Similarly, ontogenetic varia-tion was not considered because it is very lim-ited, with isometric growth being character-istic of most stylophorans. Reconstructions ofstylophorans used in this analysis have beenextracted from the relevant literature (see sup-plementary materials).

Choice of Anatomical Scheme. The stylophor-an theca (Fig. 1) is an extraxial ‘‘box’’ with astable plate pattern, made of a reduced num-ber of plates but still having the potential forlocal variation (extraxial regions are relativelyfree of constructional limitations as comparedto regions associated with the axial compo-nent [Mooi and David 1998; David and Mooi1999]). This stability allows the identificationof homologous skeletal thecal elements in allstylophorans (Lefebvre et al. 1998), thus per-mitting the comparison of the wide array ofthecal morphologies exhibited by cornutesand mitrates. Here, we classically treat the flatsurface of the theca as homologous in cornutesand mitrates (Ubaghs 1968, 1981; Chauvel1981; Parsley 1988, 1997; Lefebvre 2000a, 2001;but see Jefferies 1968, 1999). The aulacophorehas been discarded from the study for twomain reasons: (1) it is the most delicate andbrittle portion of the organism, and it is thusseldom preserved (Lefebvre et al. 1998; Ruta1999a)—the precise length and morphology ofthe distalmost portion of the aulacophore hasbeen only rarely documented (Ubaghs andRobison 1988; Ruta and Bartels 1998; Sumralland Sprinkle 1999); (2) its morphology, and es-pecially that of its distal portion (arm), is part-ly composed of axial skeleton and thus ismuch less variable than the extraxial theca; themorphology of the appendage is accordinglyvery conservative and uniform across all sty-lophorans (Ubaghs 1968, 1981; Lefebvre 2001).

Plate Homologies. Three main systems ofplate homologies have been proposed for sty-lophorans: the ‘‘calcichordate’’ (Jefferies andProkop 1972; Jefferies 1986; Cripps and Daley1994), the ‘‘ankyroid’’ (Parsley 1997; Ruta1999a), and the ‘‘Ceratocystis’’ models (Lefeb-vre and Vizcaıno 1999; Lefebvre 2000b, 2001).The calcichordate system of plate homologies


FIGURE 3. Theca of the primitive stylophoran Ceratocystis perneri, Middle Cambrian, Bohemia (Czech Republic),about �1.5 (redrawn and modified after Ubaghs 1968). A, B, Identification of plate homologies. A, Upper surface.B, Lower surface. C, D, Surfaces used for morphometric analysis. C, Upper surface. D, Lower surface. See text forabbreviations.

is well suited for recognizing homologieswithin each stylophoran order, but it fails inidentifying equivalent skeletal structures incornutes and mitrates (Ubaghs 1981; Ruta1999a; Lefebvre 2000a; Marti-Mus 2002). Inturn, the identification of homologous ele-ments is sometimes ambiguous in the anky-roid system because of superficial similaritiesin shape and/or position (Lefebvre 2001). Incontrast, the Ceratocystis system suggests thatthe identification of homologies can be de-duced in all stylophorans from a comparisonof their morphology with that of the mostprimitive known member of the class, Cerato-cystis (Fig. 3A,B). This system, which is adopt-ed below, consistently allows the identification

of homologous skeletal elements in both cor-nutes and mitrates, whatever their number ofplates and the shape of their theca (e.g., boot-shaped, heart-shaped). The Ceratocystis modelof plate homologies uses the plate terminolo-gy first applied to mitrates by Jaekel (1901)and later extended to cornutes (Ubaghs 1963).In this terminology, the insertion of the aula-cophore is considered as a reference point,such that all marginals (M) and adorals (A) tothe right of it are designated Mn and An, andthose to the left of it, M’n and A’n (with n asa number indicating the position of the plateaway from the insertion of the aulacophore; n� 0 in the case of a plate in central position).However, this terminology was adjusted (fol-


lowing Lefebvre and Vizcaıno 1999) so thatputatively homologous plates are given thesame name.

Number, morphology, and arrangement ofthecal plates are constant and diagnostic forany given species of stylophoran, but highlyvariable from one species to another. A stylo-phoran theca basically comprises two infra-central areas (left and right), one supracentralarea, and 16 major plates, consisting of fivepairs of left and right marginals, three ador-als, one posterior zygal plate (Z), and two pos-terior elements (glossal and digital). However,additional plates are sometimes present: co-thurnocystid marginal (Mc) in some cornutes,and posterior plates (PP1, PP2) in some mitro-cystitid mitrates. Consequently, the theca ofsome stylophorans comprises more than 16major plates (e.g., 17 in the primitive cornuteCothurnocystis fellinensis). Moreover, the rightinfracentral area and/or several major skele-tal elements are frequently lost in derivedforms, typically characterized by a theca con-sisting of a reduced number of elements (e.g.,only ten major plates in the cornute Lyricocar-pus, and in kirkocystid mitrates). The numberof plates seems to be particularly reduced inthe most recent stylophoran, Jaekelocarpus okla-homaensis, with only nine major plates and asingle integumentary area (Kolata et al. 1991;Domınguez et al. 2002).

To perform the analysis of stylophoran dis-parity optimally, it was necessary to groupsome plates, so as (1) to minimize the effect oflarge variation in the number of major skeletalelements and integumentary areas in cornutesand mitrates, and (2) to reduce the uncertaintyassociated with the identification of some the-cal plates. Whatever the adopted model ofplate homologies (‘‘calcichordate,’’ ‘‘anky-roid,’’ or ‘‘Ceratocystis’’), several thecal ele-ments (e.g., M1, M�1, adorals) are consideredas equivalent by most authors (see Marti-Mus2002: Fig. 9 for an overview of unambiguousplate homologies within cornutes). In thisstudy, each region of ‘‘problematic’’ thecal el-ements was treated as if it constituted a singlethecal plate: for example, the left portion of themarginal frame delimited by M�1, the left in-fracentral area, and M�4 was treated as a sin-gle morphological unit (‘‘left marginals’’ or

‘‘LM’’), whatever its number of elementaryplates and their putative identification. Con-sequently, not only do such groupings of the-cal elements follow the homology of subsets ofplates, but they also dramatically reduce thesensitivity of the analysis to the adoption ofone particular model of plate homologies.

All in all, 17 surfaces have been retained forthe analysis (see Fig. 3C,D): (1) thecal outline,TH; (2) M1; (3) M�1; (4) right marginals, RM(M2 � M3 � Mc); (5) left marginals, LM (M�2

� M�3); (6) M4; (7) M�4; (8) glossal, G; (9) dig-ital, D; (10) posterior zygal plate, Z; (11) pos-terior marginals, PM (M5 � M�5 � PP1 � PP2);(12) plates of the right infracentral area, RIA;(13) plates of the left infracentral area, LIA;(14) right adoral A1; (15) median adoral, A0;(16) left adoral, A�1; and (17) plates of the su-pracentral area, SA. The central marginal M0

of Ceratocystis has not been considered in thestudy because it is an autapomorphy of thisgenus.

The profile of the theca is sufficiently low sothat it is possible to consider that projections(drawings) of the plate patterns are withoutdistortion. Portions of plates or groups ofplates shared by both the lower and the upperthecal surfaces were considered as indepen-dent elements in each case and treated sepa-rately. This is justified because in most casestheir extension is different on the lower andupper thecal surfaces. The only example ofsurfaces showing similar extensions in upperand lower views are the glossal (G) and digital(D), where these skeletal elements occur in theform of exothecal processes, articulated to theposterior end of theca (e.g., in the cornute Co-thurnocystis, and in most anomalocystitid mi-trates). The three adorals (A1, A�1, A0), and thesupracentral area (SA) are restricted to the up-per thecal side in almost all stylophorans.However, A1 and A�1 can extend onto the low-er side (e.g., Ceratocystis), and sometimes over-lap the lateral edges of the underlying mar-ginals (e.g., Anatifopsis, Balanocystites). Exten-sion of supracentrals onto the lower side oc-curs in the mitrate Lagynocystis. Consequently,so as to avoid redundancy and autocorrelationrelated to the extension of surfaces from theupper side toward the lower side of the theca(e.g., overlap of marginal elements), no por-


tions of A1, A�1, and SA located on the lowerside of the theca have been considered in theanalysis.

Quantification of Form. Stylophoran mor-phology has been quantified with morpho-metric parameters derived from image anal-ysis of homologous skeletal regions: plates, onthe one hand, and outlines of the theca, on theother. The aim is to use the geometry of boththe whole theca and its individual plates asmorphological descriptors to measure stylo-phoran disparity. This combined approachalso makes it possible to compare global andlocal aspects of stylophoran shape. Stylophor-ans constitute an appropriate model for theapplication of such morphometric methods, asthey are a relatively small group with clearlyidentified plate homologies, and with all spe-cies sharing a standard organization. Conse-quently, given the aim of the study and the in-trinsic characteristics of stylophoran mor-phology, it appears that morphometric meth-ods based on the geometry of both thecaloutlines and homologous individual platesconstitute a good compromise approach toquantify disparity in the group. However, oth-er descriptors of shape could have been used.Procrustes methods based on landmarks, forexample, would have allowed us to estimatemorphological variety among stylophorans bycomparing actual architectural relationshipsbetween sets of plates, rather than on plate-by-plate geometry per se. However, Procrustesmethods would not have permitted a compar-ison between thecal and plate geometries.Fourier methods are another powerful tool al-lowing precise description of outlines of sur-faces such as the theca or individual plates,but such precision is achieved at a cost of bi-ological interpretability; this is particularlytrue in the present situation, where the num-ber of distinct surfaces is considerable, and thetoo numerous Fourier coefficients would havebeen almost impossible to relate to morpho-logical differences. In addition, the presenceof distorted specimens inevitably leads to im-precise reconstructions with uncertain reli-ability of the fine details that Fourier analysesare supposed to capture. Therefore, we pre-ferred to use variables that convey informa-

tion more roughly, but are also more reliableat the level of the whole organism.

Morphometric variables were measured us-ing the software OPTIMAS (version 6). Themeasurements chosen were a subsample ofthe total number available, and the choice wascarefully made in light of the stylophoranbody plan. Finally, seven parameters (out ofabout 40) were specifically chosen for theirability to characterize all surfaces concerned.Together, they capture distinct yet comple-mentary aspects of plate and thecal morphol-ogy. Special emphasis was placed on variablesconsidered the most pertinent for describingthe large array of plate outlines in stylophor-ans (e.g., sub-circular to elliptical, sub-quad-rate to polygonal, rodlike, Y-, T-, or C-shaped).Redundant, uninformative, and/or uninter-pretable (from a biological point of view) pa-rameters were discarded. Of the seven re-tained parameters, four (1 to 4 below) wereapplied to all 17 areas, two (5 and 6 below)only to the 16 plates and groups of plates, andone (7 below) only to the whole theca. Defi-nitions for these variables are as follows: (1)Circularity (C) expresses the ratio of thesquare perimeter divided by the area. Circu-larity is minimum for a circle (C � 12.57),which represents the smallest perimeter for agiven area. Low circularity values correspondto rounded, massive surfaces, and high valuesto long, narrow, and/or digitated surfaces. (2)Rectangularity (R) corresponds to the ratio ofthe surface area divided by the area of thesquare box (parameterized by the major andminor axes) including it. (3) Relative lengthmajor axis (RLMA) is the ratio of the surfacearea divided by the square length of the majoraxis of the corresponding surface. (4) Coeffi-cient of variation of Feret diameters (CVFD)represents the standard deviation as a pro-portion of the mean of 16 successive diametersmeasured every 11.5� around the surface. (5)Relative area (RA) expresses the ratio of a giv-en surface area divided by the area of thewhole theca. (6) Relative perimeter (RP) cor-responds to the ratio of a given surface perim-eter divided by the thecal perimeter. (7) Scaledarea (SA) is expressed in mm2 (chosen size es-timate of the whole theca).

These variables were used to produce three


FIGURE 4. Diagram illustrating the degree of pairwiseindependence between the 84 variables of the upper sur-face using Van Valen’s (1974) measure of dimensionality(D). Mean value of D is shown for each variable, as wellas the 95% confidence interval. The degree of non-in-dependence is highly significant (p � 0.0001, sign testwith expected null value of 1.5).

separate raw data matrices: (1) for the wholetheca, comprising 88 species and five morpho-metric variables (C, R, RMAL, CVFD, SA); (2)for plates and groups of plates of the lowersurface, including 88 species and 72 morpho-metric variables (six variables measured foreach of the 12 plates or groups of plates: C, R,RMAL, CVFD, RA, RP); and (3) for plates andgroups of plates of the upper surface, includ-ing 88 species and 84 variables (six variablesmeasured for each of 14 plates or groups ofplates).

Missing plates occasionally reflect imper-fect preservation of posterior thecal region (Dand G), but in most cases they reflect true ab-sences. Coding in such situations proceededas follows. When due to imperfect preserva-tion, entries were coded as missing values.When due to true plate absence, entries werecoded as zero when logically interpretable(RLMA, CVFD, RA, RP), or as a missing valuewhen this was mathematically impossible (Cand R).

It was not necessary to take into accountmeasurement error given that, at the scale ofthis study, observed interspecific differencesare several orders of magnitude larger thanthose induced by drawing error in the recon-struction of plate architecture.

To evaluate the persistence of correlationsamong the variables considered in the threemodules, we calculated Van Valen’s measureof dimensionality or non-redundancy (VanValen 1974) for all pairwise comparisons be-tween variables pertinent to each of the threemodules. Figure 4 illustrates the result for theupper surface only, but the degree of non-in-dependence is highly significant for the threemodules, although weaker for the theca.

Data Analyses. Gower’s coefficient of simi-larity (Gower 1971) and principal coordinatesanalysis (PCO; Gower 1966) were used to an-alyze the data. Although all variables werecontinuous, Gower’s coefficient and PCO areappropriate here so as to allow every speciesto be considered regardless of missing values.In addition, given that the variables are not allstrictly commensurate, PCO is the techniqueof choice. PCO axes were used to project theoriginal, raw multidimensional space onto asmaller, more informative number of dimen-

sions. In this PCO space, species are naturallyordinated in proportion to morphological dis-tance. Here, we treat PCO ordinations as pro-viding a useful graphical representation of thegeneral patterns of empirical morphospace oc-cupation.

A separate PCO analysis (using Gower’sdistance-transformed coefficient for quantita-tive characters) was performed on each of thethree data matrices referred to above. Theseinclude (1) whole theca, (2) plates of lower the-cal surface, and (3) plates of upper thecal sur-face. Given that our purpose was to considerall taxa and all three morphological contextstogether in a single, comprehensive analysis,we performed a ‘‘meta-PCO’’ (similar to thatproposed by Klingenberg [1996] for ‘‘meta-PC’’) based on the PCO axes (treated as newvariables) retained from each of the threeanalyses above. A meta-PCO allows for a bal-ance between the three anatomic modulesconsidered (whole theca, upper surface, lowersurface), although they are each depicted byvery different numbers of variables (5, 84, and72 respectively). The number of PCO axes re-tained was based on the decay of the eigen-values. The quality of the reduced space rep-resentation (analogous to the cumulative pro-portion of variance in principal componentsanalysis) was estimated as the ratio of the sumof the eigenvalues of the retained axes to thetotal sum of the eigenvalues. Because of neg-


TABLE 1. Timescale, total number of stylophoran genera and species, and sample sizes. Age at base of intervals inmillions years before present (Ma), and durations in millions of years (Myr) based on data from the InternationalStratigraphic Chart (Gradstein et al. 2004), and the new Ordovician stratigraphic chart (Webby et al. 2004a). Ab-breviations in parentheses are also used in the figures and the online appendix.

Stratigraphic intervalAge at base

(Ma)Duration

(Myr)

No. of genera

Total Sampled

No. of species

Total Sampled

Pennsylvanian (Pe) 318.1 19.1 1 1 1 1Middle Devonian (MD) 397.5 12.2 4 3 4 3Emsian (Em) 407.0 9.5 7 6 9 7earliest Devonian (eD) 416.0 9 6 6 7 6late Silurian (lS) 422.9 6.9 4 3 4 3early Silurian (eS) 443.7 20.8 2 2 2 2Ashgill (As) 449 5.3 8 8 11 8Caradoc (Ca) 460.9 11.9 10 9 18 11Middle Ordovician (MO) 471.8 10.9 19 19 27 21Arenig p.p. (Ar) 478.6 6.8 21 19 29 23Tremadocian (Tr) 488.3 9.7 7 7 9 7Late Cambrian (LC) 501.0 12.7 6 4 7 4Middle Cambrian (MC) 513.0 12 4 4 5 5

ative eigenvalues resulting from imbalance inthe distance matrices due to missing valuesand non-Euclidean property of the resultingdistance, these sums were corrected accordingto the absolute value of the largest negative ei-genvalues (see Legendre and Legendre 1998).Approximately 70% of the cumulative vari-ance corresponded to most of the structure inall three analyses. Therefore, using this crite-rion, five PCO axes were retained for thewhole theca, eight for the lower surface, and 8for the upper surface, yielding 21 ‘‘meta-var-iables’’ for the meta-PCO. In this way, a globalmorphospace projection reflecting differentaspects and scales of stylophoran variationwas possible. All retained axes have larger val-ues than the absolute value of the largest neg-ative eigenvalues. Therefore, the Euclidean ap-proximation of the reduced space is meaning-ful (Legendre and Legendre 1998).

In addition, cluster analysis was used toidentify morphological clusters. This analysiswas performed using Euclidean distances andunweighted pair-group method using arith-metic averages as aggregation rule. A thresh-old was identified according to the impor-tance of steps on the aggregation graph, andthe fine-scale structure of the dendrogramwas not kept. The resulting 11 morphologicalgroups are hierarchically clustered into threemain sets (I to III), and were used in turn asmorphological units in further analyses.

Stratigraphic Intervals and Resolution. The

time frame of the analysis (about 215 Myr) en-compasses the entire evolutionary history ofthe class Stylophora, from the Middle Cam-brian (Archaeocothurnus, Ceratocystis, Ponticu-locarpus, Protocystites), to the Pennsylvanian(Jaekelocarpus). It is worth pointing out that therecent discovery of Jaekelocarpus has consider-ably extended the stratigraphic range of theclass from the Middle Devonian to the lateCarboniferous (Kolata et al. 1991; Domınguezet al. 2002). However, the presence of a singlespecies more than 65 million years after theMiddle Devonian is uninformative. Thus, forthe purposes of reconstructing disparity his-tory, this interval was discarded from thestudy. Even so, the species was retained for itscontribution to the total empirical morpho-space. The 12 stratigraphic intervals used inthe analysis represent a compromise betweensample size and time resolution (Table 1).Ages and durations of time intervals werebased on the IUGS timescale produced byGradstein et al. (2004), and the revised Or-dovician stratigraphic chart of Webby et al.(2004a). The duration of intervals is between5.3 and 20.8 Myr, with a mean value of 10.7Myr, and duration of 9–13 Myr for 8 of 12 ofthem. The duration of intervals and the num-ber of taxa per interval (total number and/ornumber of sampled taxa) are clearly not cor-related (r2 � 0.198, p � 0.128; Table 1).

Quantification of Geographic Space Occupa-tion. The aim was to define a semiquantita-


tive index that could be used to draw curvesof paleo(bio)geographic dispersion throughtime, comparable to curves of taxonomic andmorphological diversity. Specifically, our goalwas to use a biogeographic index that both isrelevant for large-scale studies and displaysthe same degree of generality with which di-versity and disparity changes were docu-mented (only 12 stratigraphic intervals be-tween the Middle Cambrian and the MiddleDevonian). Therefore, such an index differsfrom most ‘‘traditional’’ paleogeographic in-dices, usually designed for comparison of fau-nal compositions and/or quantification of bio-geographic affinities between regions. Geo-graphic space occupation was quantified onboth a global and a regional scale.

The global scale reflects overall colonizationand dispersion patterns around continentalmargins, with high precision but low resolu-tion, given the relatively small number of sam-pling units (continents). Estimation of global-scale dispersion is based on available dataconcerning the absence/presence of stylo-phorans around paleocontinents (as definedon paleoreconstructions; e.g., Scotese andMcKerrow 1990; Scotese 2001), which reflectgeneral dispersion events. In contrast, the lo-cal scale expresses the number of distinct re-gional occurrences around the same paleocon-tinent. Although the local approach is moreprecise, and conveys more information thanthe global one, the signal is more influencedby preservational biases: the presence of sty-lophorans in a regional entity is partly corre-lated to outcrop area (volume and accessibil-ity of rock strata), number of echinoderm Lag-erstatten, and effort of sampling (see Smith1988). Several weighting combinations be-tween continental and regional entities havebeen explored. All combinations are stronglycorrelated to each other (r2 � 0.90) and lead tovery similar ‘‘paleogeographic curves.’’ Forthe purpose of this paper, a ‘‘mixed’’ paleo-geographic index [Bi] was calculated for eachtime interval, as the sum of both relative glob-al dispersion (number of distinct ‘‘continen-tal’’ occurrences [Co] divided by total numberof paleocontinents [NC] ever colonized) andrelative local dispersion (number of distinctregional occurrences [Ro] divided by total

number of regions ever occupied [NR]).Therefore, Bi � Co/NC � Ro/NR.

All stylophorans included in this studywere collected on the continental margins ofthree paleocontinents: Baltica (Russia, Scan-dinavia), Gondwana (Africa, South America,Australia, southwestern Europe, Korea), andLaurentia (North America, northern Ireland,Scotland). However, by late Silurian times,Baltica and Laurentia had collided (Scandianorogeny) to form a single paleocontinent, Lau-russia. The estimate of stylophoran global dis-persion is not affected by the reduction in thenumber of major continental masses after theSilurian, as only one Laurussian species isconsidered (Anomalocystites cornutus). Duringthe Ordovician, Avalonia (Belgium, England,most of Nova Scotia and New Brunswick,Wales) formed a fourth, separate, short-livedpaleocontinent, which split off from the north-western margin of Gondwana (Early Ordovi-cian), drifted northward, and finally collidedwith Baltica (Ashgill to early Silurian; Cockset al. 1997; Nance et al. 2002; Verniers et al.2002). Consequently, Avalonian faunas exhibitstrong Gondwanan affinities in the Early Or-dovician, and increasing Baltic influences inthe Late Ordovician (Cocks and Fortey 1990;Cocks et al. 1997). In this study, Avalonian sty-lophorans were considered as ‘‘Gondwanan’’from the Middle Cambrian to the Darriwilian,and as ‘‘Baltic’’ from the Caradoc to the Mid-dle Devonian. A fifth paleocontinent, Siberia,was not considered because the single knownstylophoran reported so far from this regionwas too poorly preserved to be included (Mon-golocarpos minzhini).

Seventeen distinct regional entities wereconsidered: (1) eastern North America (Illi-nois, Indiana, Kentucky, Maryland, Missouri,New York State, Ohio, Oklahoma, Ontario,Quebec, Pennsylvania, Tennessee, Virginia,Wisconsin); (2) western North America (Ne-vada, Utah); (3) Argentina; (4) Australia (Vic-toria); (5) Bohemia; (6) Brazil (Parana Basin);(7) England (Shropshire and Worcestershire)and Wales; (8) Germany; (9) Ibero-Armorica(western France, Spain, Portugal); (10) Korea;(11) Montagne Noire (southern France); (12)Morocco (Anti-Atlas); (13) New Zealand; (14)


FIGURE 5. Plot of the global morphospace of the 88sampled stylophoran species on the first two principalcoordinates axes of the meta-PCO, with distinction be-tween primitive forms, and representatives of the twomain clades, cornutes and mitrates.

Norway; (15) Scotland and Northern Ireland;(16) South Africa; (17) Tasmania.

Results and Discussion

Morphospace Ordination. Principal coordi-nate analysis of the 21 ‘‘meta-variables’’ re-veals considerable structure in the data, withabout 27.5% of the variation expressed in thefirst three ‘‘meta-axes.’’ At face value, theamount of information conveyed in this com-pound analysis is smaller than that obtainedin each of the three ‘‘source’’ analyses per-formed independently on the theca (63% ofthe variance in the first three axes), the lowersurface (51.5% of the variance in the first threeaxes), and the upper surface (48.2% of the var-iance in the first three axes). Nevertheless, de-spite an unavoidable loss of resolution, themeta-PCO analysis has the advantage of con-stituting an integrative and heuristic ap-proach allowing representation and visuali-zation, however obliquely and partially, of a‘‘global’’ morphospace that takes simulta-neously into account three different aspects ofstylophoran morphology. These three aspectsare here viewed as the relevant organizationaland variational modular regions of the phe-notype (Eble 2004, 2005), and each modularregion in turn can be expressed in terms of apartial morphospace. Combining partial mor-phospaces allows the portrayal of all sampledspecies in a single global morphospace, whichis not the case for the source PCO analyses ofthe lower surface (six missing species) and ofthe upper surface (12 missing species; see sup-plementary materials). The meta-axes of theglobal PCO analysis reflect a multidimension-al space in which ordination is possible for allsampled stylophorans, including partiallypreserved forms.

The projection of this multidimensionalspace in the plane defined by the first twometa-axes, i.e., meta-PCO1 (10.5% of the var-iance) and meta-PCO2 (9.5% of the variance),allows a partial yet still heuristically infor-mative and practical visualization of broadmorphospace occupation among stylophorans(Fig. 5). Occupation in general is not homo-geneous, with several ‘‘clouds’’ or groupingssituated at the periphery of an almost emptycentral ‘‘zone,’’ occupied only by a primitive

form, Ceratocystis vizcainoi. The partitioning ofthe two main clades of stylophorans in thismorphospace is relatively clear: cornutesshow great variability along meta-PCO1 butreduced dispersion along meta-PCO2 (withalmost exclusively positive values), whereasmitrates are characterized by great variabilityalong the metaPCO2, and to a lesser extentalso along meta-PCO1 (Fig. 5). As plotted, thetwo groups are relatively distinct, althoughthere is a large zone of overlap representingconvergent morphologies among certain mi-trocystitid mitrates (e.g., Ovocarpus, Vizcaino-carpus) and various derived cornutes (e.g.,Amygdalotheca, Lyricocarpus). It is interestingto point out that the two primitive forms of thegenus Ceratocystis appear in a position rough-ly intermediate between the clouds of pointscorresponding to cornutes and to mitrates.The partitioning of cornutes and mitrates inthis global reference morphospace reflectsquite well the preliminary results previouslyobtained by principal components analyses ofthe thecal outlines and of the lower surface(Lefebvre et al. 2003). In fact, those resultssuggested that although the distinction be-tween cornutes and mitrates was very clearwith respect to the morphology of plates inthe lower surface, these two groups could notbe distinguished on the basis of their thecaloutlines. This indicates that very similar thecaloutlines were independently achieved by the


two clades, but with plates having differentmorphologies (Lefebvre et al. 2003). Similarly,the existence of a region of overlap betweencornutes and mitrates in the global morpho-space defined by the meta-PCO axes can beexplained by the fact that variables describingthecal outline and variables describing platemorphology were both taken into account. Inany case, the present study seems to confirmthe existence of form convergences betweenthe two groups (see Lefebvre 2001).

In order to minimize a priori taxonomic as-sumptions, and so as to better characterize theheterogeneities in occupation of stylophoranmorphospace (the existence of a large zone ofsuperposition between its two componentgroups suggesting that the classical distinc-tion between cornutes and mitrates is not nec-essarily the most pertinent for describing dis-parity), several morphological subgroups ofstylophorans were identified a posteriori, onthe basis of hierarchical clustering of all pair-wise distances. The application of this cluster-ing procedure yielded a dendrogram of dis-tances among different stylophoran species inthe multidimensional space defined by theaxes of the meta-PCO (Fig. 6). Eleven morpho-logical subgroups (understood as operationalsubsets) were revealed. These 11 subsets canthemselves be grouped into three main sets (I,II, and III), containing five (Ia–Ie), four (IIa–IId), and two subsets (IIIa, IIIb), respectively.Seven subsets comprise at least six species, butfour subsets are small and contain only one(IIc, IId), two (Id), or three (Ie) taxa.

The first axis of the meta-PCO is mainly in-fluenced by the general morphology of thecalcontours (Fig. 7). This axis discriminates clear-ly stylophorans belonging to sets II and III,characterized by very asymmetrical and dig-itated thecal contours (thecal outgrowths,such as digital, glossal, and spinal; positivevalues of scores in meta-PCO1), from those inset I, which have symmetrical and massivethecae, without outgrowths (negative valuesin meta-PCO1). The second axis of the meta-PCO appears to reflect more the relative im-portance of integumentary areas (especiallyinfracentral; Fig. 7). Meta-PCO2 thus sepa-rates quite clearly forms with large integu-mentary surfaces and, consequently, with a

relatively large thecal width (set III, subsets Ia,Ic–Ie, and IIb), from forms with reduced or ab-sent integumentary surfaces and with a nar-rower and more elongated theca (subsets Ib,and IIa, IIc, IId). The third axis of the meta-PCO is more difficult to interpret, but it showsa distinction between two ensembles of sub-sets: in one case, Ia, Ib, and IIIa (positive val-ues), and in the other case, Ic–Ie, IIb, and IIIb(negative values); the remainder subset, IIa, isspread all along meta-PCO3 (taking both pos-itive and negative values).

Set I comprises 36 stylophorans (10 cornutesand 26 mitrates), all characterized by massivethecae, symmetrical and without outgrowths,and with integumentary areas at times re-duced (subset Ib), but more often relativelylarge (subsets Ia, Ic–Ie). The second set com-prises 38 stylophorans (two primitive forms,14 cornutes, and 22 mitrates) with an asym-metrical theca, sometimes with extensive out-growths and infracentral areas (subset IIb),but more often reduced (subsets IIa, IIc, IId).Finally, set III comprises 14 cornutes that arevery strongly asymmetric (boot-shaped the-ca), characterized by large integumentary ar-eas (subset IIIa) and by large exothecal out-growths (subset IIIb).

It is interesting to note that the general as-pect of the dendrogram produced by hierar-chical clustering for purely operational rea-sons resembles the general aspect of the clad-ogram produced by Parsley (1997, 1998). In ef-fect, sets I and II bring together the‘‘ankyroid’’ stylophorans (mitrates and sym-metrical cornutes), whereas set III corre-sponds to cornutes with a boot-shaped theca.These observations suggest that the phyloge-netic tree produced by Parsley (1997, 1998),which takes into account numerous charactersbased on the general morphology and theasymmetry of the theca, may be more similarin structure to a dendrogram than to a clad-ogram (see Lefebvre 2001).

The existence of convergent morphologiesamong cornutes and mitrates, for example be-tween mitrocystitids and symmetrical cor-nutes (set I) or between asymmetrical cornutesand mitrates with posterior processes (set II),brings to the fore the issue of a possible rela-tion between morphology and mode of life.


FIGURE 6. Dendrogram resulting from the hierarchical clustering of the global stylophoran morphospace (see Fig.5), and showing the disconnection into three well-defined main morphological sets (I, II, and III), consisting of five(Ia–Ie), four (IIa–IId), and two (IIIa, IIIb) subsets, respectively. Morphologies included in each subset are illustratedby some significant taxa (all thecae illustrated in lower view, and showing surfaces used for morphometric analysis):1, Adoketocarpus acheronticus; 2, Aspidocarpus bohemicus; 3, Chinianocarpos thorali; 4, Mitrocystites mitra; 5, Ovocarpusmoncereti; 6, Ateleocystites guttenbergensis; 7, Barrandeocarpus jaekeli; 8, Eumitrocystella savilli; 9, Mitrocystella incipiens;10, Yachalicystis triangularis; 11, Amygdalotheca griffei; 12, Lyricocarpus courtessolei; 13, Nanocarpus milnerorum; 14, Re-ticulocarpos hanusi; 15, Ampelocarpus landeyranensis; 16, Prochauvelicystis semispinosa; 17, Lobocarpus vizcainoi; 18, Viz-cainocarpus dentiger; 19, Balanocystites primus; 20, Ceratocystis perneri; 21, Diamphidiocystis drepanon; 22, Lagynocystispyramidalis; 23, Placocystella africana; 24, Arauricystis primaeva; 25, Chauvelicystis spinosa; 26, Hanusia prilepensis; 27,Ponticulocarpus robisoni; 28, Protocystites menevensis; 29, Jaekelocarpus oklahomaensis; 30, Diamphidiocystis sp.; 31, Ar-auricystis occitana; 32, Cothurnocystis fellinensis; 33, Phyllocystis blayaci; 34, Scotiaecystis jefferiesi; 35, Thoralicystis griffei ;36, Cothurnocystis elizae; 37, Galliaecystis ubaghsi; 38, Scotiaecystis collapsa; 39, Scotiaecystis curvata.


FIGURE 7. Plot of the global morphospace of the 88sampled stylophoran species on the first two principalcoordinate axes of the meta-PCO, with distinction be-tween the 11 morphological subsets identified by hier-archical clustering (see Fig. 6).

FIGURE 8. Plot of the global morphospace of the 88sampled stylophoran species on the first two principalcoordinate axes of the meta-PCO, with distinction be-tween infaunal and various epibenthic forms.

Four major modes of life among stylophoranshave been identified (Lefebvre 2003): one isendobenthic (theca buried under the sub-strate), and three are epibenthic, with the an-imal attaching itself to the substrate by meansof thecal protuberances, spines arranged onthe perimeter of the theca, or the arm. A gen-eral relationship seems to exist between mor-phology and mode of life (Fig. 8). In fact,meta-PCO1 discriminates quite well the epi-benthic forms anchored with the arm (andhaving a rather symmetric theca; left of dia-gram) from the endobenthic and epibenthicforms clinging to the sediment by means ofthe theca (asymmetric forms and/or formshaving exothecal outgrowths; right of the di-agram). Similarly, meta-PCO2 separates quitewell, on the right portion of the diagram, theepibenthic forms anchored by means of thetheca or of spines (large integumentary areas,thecae staggered transversally; positive val-ues on meta-PCO2) from the endobenthicforms (reduced integumentary areas, thecaestaggered anteroposteriorly; negative valueson metaPCO2). Therefore, it is probable thatvery similar morphologies, independentlyevolved in some cornutes and mitrates, showvery similar modes of life, as exemplified inset I (epibenthic mode of life with anchoringby the arm). On the other hand, in set II thepresence of exothecal outgrowths correspondsto two very distinct modes of life: epibenthic

with anchoring by the theca (IIb in cornutesand IId in mitrates), or else endobenthic (onlymitrates, IIa). A certain correspondence be-tween thecal morphology and mode of lifecould be expected, given that the latter waspartly deduced from the general aspect of thetheca (Lefebvre 2003). However, there is no di-rect correspondence between thecal morphol-ogy and presumed mode of life, as the latterwas also largely deduced from the morphol-ogy of the appendage (Lefebvre 2003), whichis not considered herein. Moreover, several as-pects of stylophoran thecal morphology arenot correlated with functional morphology(e.g., asymmetry of lower thecal surface, withthe zygal bar), but possibly reflect construc-tional constraints.

It is also interesting to note that certainmorphological types were never developed inmitrates (e.g., set I), perhaps because suchtypes are associated with a mode of life in-herently uncommon in this clade (epibenthicwith anchoring by the theca; e.g., Diamphidi-ocystis). Likewise, neither of the two mainmorphological types characteristic of burrow-ing forms was adopted by cornutes (subsets Iband IIa). This suggests the existence, in eachof the two clades, of functional limits and/orstructural constraints intrinsic to their bodyplans, and impervious to convergent evolu-tion. Thus, although convergence is relativelycommon, it is conditioned on the degrees of


freedom established in the history of theclade.

Spatiotemporal Pattern of Stylophoran Diversi-fication in Morphospace. The spatiotemporalevolution of taxonomic and morphologic di-versity may be followed in simplified fashion,by representing, for each of the 12 stratigraph-ic intervals considered (representing about128 Myr from the base of the Middle Cambri-an to the end of the Givetian), the distributionof various forms in the projection of the globalmorphospace and the corresponding paleo-geographic dispersion. Thus, inspection of thetemporal sequence of 12 morphospace projec-tions on the meta-PCO1–metaPCO2 plane be-side 12 associated ‘‘snapshots’’ of paleogeo-graphic partitioning allows a generalized butheuristic assessment of the broad evolutionarydynamics of this class of echinoderms. A suc-cession of five main phases is apparent andexplained below.

Initially, from the Middle Cambrian to theTremadocian (Fig. 9), stylophorans under-went an apparent increase in disparity, inspite of the relatively small sample sizes. Al-though members of only one main morpho-logical set (II) were represented in the MiddleCambrian (subsets IIa and IIb), they were fol-lowed by two (I and II) in the Late Cambrian(subsets Ic, Ie, and IIb), and finally three (I, II,and III) in the Tremadocian (subsets Ic, Id, Ie,IIa, IIb, and IIIa). Therefore, in less than 35Myr, stylophorans occupied all three distinctzones in morphospace; no other main mor-phological set would appear in the ensuing180 Myr. This expansion in morphospace wasaccompanied by an even greater paleogeo-graphic dispersion during the Cambrian, butit must be emphasized that disparity re-mained low within each of the three zonesconsidered. Conversely, in the Tremadocian,disparity increased strongly, while paleogeo-graphic dispersion was extremely low (re-stricted to the northern-Gondwanan margin).

During the early and middle Arenig (Fig.9), stylophorans displayed a marked increasein taxonomic diversity, yet disparity remainedcomparable to that of the Tremadocian, de-spite the appearance of two additional mor-phological subsets (Ia and IIIb). This intervalseems to correspond to a simple filling of mor-

phospace previously partitioned in the Tre-madocian. This important Arenigian phase oftaxonomic diversification occurred exclusivelyon the north-Gondwanan margin, i.e., thesame paleogeographic region as in the Tre-madocian.

Stylophoran taxonomic diversity steadilydecreased from the Middle Ordovician to theend of the Ashgill (Fig. 10). Nevertheless, mor-phological disparity was maintained, with thepersistence of the three main morphologicalsets even as the number of subsets representedregularly declined (eight in the Middle Or-dovician, four in the Caradoc, and three in theAshgill) and intermediate forms among thethree sets disappeared. In the Ashgill, thesethree sets were represented only by extrememorphologies, such as those of the stronglyasymmetric cornutes Cothurnocystis elizae orScotiaecystis curvata. In parallel with the de-cline in taxonomic diversity and the evacua-tion of morphospace, stylophorans showed anincrease in paleogeographic dispersion fromthe Middle Ordovician to the Ashgill, with ex-pansion into Avalonia, then Laurentia, and fi-nally Baltica and the east-Gondwanan mar-gin). This paleogeographic expansion was ac-companied by a decrease in disparity withinthe region of origin (the north-Gondwananmargin) and by a relatively low disparitywithin each of the different zones occupied atthe end of the Ordovician. It is also apparentthat one of the three main morphologies re-maining in the Ashgill (IIa, anomalocystitids)exhibited a vast paleogeographic distributionat lower paleolatitudes, on both sides of theequator. This type of stylophoran dispersionseems very different from that of the Earlyand Middle Ordovician, almost exclusivelylimited to high paleolatitudes. The paleogeo-graphic expansion toward low paleolatitudes,observed from the Middle Ordovician, mightconceivably correspond to the adaptation ofcertain forms to new environmental condi-tions.

The early Silurian (Fig. 10) was character-ized by a profound reduction not only of tax-onomic diversity, but also of disparity, as thereremained only one morphological type (II),represented by a single subset (IIa). Throughthis time interval, by far the longest in this


FIGURE 9. Evolution of stylophoran morphospace occupation and paleogeographic dispersion from the MiddleCambrian to the end of the Early Ordovician.


FIGURE 10. Evolution of stylophoran morphospace occupation and paleogeographic dispersion from the MiddleOrdovician to the early Silurian (Llandovery–Wenlock).


study (20.8 Myr), paleogeographic distribu-tion was also strongly reduced, with one spe-cies from the Llandovery of Tasmania (Placo-cystella buretti) and one species from the Wen-lock of England (Placocystites forbesianus).These two anomalocystitid mitrates are fromregions then situated at very low paleolati-tudes and they belong to the same morpho-logical type (IIa) as that of Ashgillian stylo-phorans present in those regions. This wasalso the first time since the Middle Cambrianthat stylophorans were absent from the vari-ous regions of the northern-Gondwanan mar-gin. In fact, in the early Silurian these regionswere characterized by extensive deposits ofblack shale, indicating the existence (and per-sistence) of anoxic oceanic conditions follow-ing the major climatic perturbations of theend-Ordovician (Cocks and Fortey 1990; Parisand Le Herisse 1992; Storch et al. 1993). It istherefore possible that the presence of a singlestylophoran morphological type in the earlySilurian signaled not only the disappearanceof types I and III from high paleolatitudes, byvirtue of unfavorable environmental condi-tions (anoxia), but also the persistence of typeII only at low paleolatitudes, given that pa-leoenvironmental conditions were more favor-able (Cocks and Fortey 1990; Robardet et al.1990), and given that this type became estab-lished in the end-Ordovician. Curiously, theonly morphological type that survived the bi-ological crisis at the end of the Ordovician (setII) was precisely the same that was initiallypresent in the Middle Cambrian.

Finally, from the late Silurian to the MiddleDevonian (Fig. 11), stylophorans underwent asecond phase of diversification, which corre-sponded to an increase in disparity with thereappearance of the type I morphology. Con-sequently, in contrast to the Cambro-Trema-docian radiation, no fundamentally newforms evolved during the Siluro-Devonian di-versification—as if somehow mitrates werelimited in their evolution and could only pro-duce morphologies of types I and II. This sec-ond phase was characterized by a peak of di-versity and disparity (two morphologicaltypes, represented by three subsets, Ia, Ib, andIIa) in the Early Devonian (Lochkovian to Em-sian), as well as by an increase in paleogeo-

graphic dispersion. This phase was followedby a slight decrease in diversity and disparity(two morphological types each represented byonly one subset) and reduced paleogeograph-ic dispersion in the Middle Devonian. Also, asecond important difference from the Cam-bro-Tremadocian radiation concerns the pa-leogeographic context of the Siluro-Devoniandiversification: whereas the former occurredessentially in a single region (the northern-Gondwanan margin), the latter was character-ized by strong paleogeographic dispersion.

Spatiotemporal Pattern of Stylophoran Diversi-fication: Comparison of Quantitative Indices.The three main aspects of the stylophoran di-versification of interest in this study, i.e., tax-onomic diversity, morphological disparity,and paleogeographic dispersion, can be ana-lyzed in a more rigorous manner by means ofcomparisons through time of quantitative in-dices summarizing the general signal con-veyed by each of these aspects. The taxonomicdiversity curve expresses temporal variationsin number of species. The morphological dis-parity curve indicates, for each interval con-sidered, the sum of the variances of the prin-cipal coordinates scores as calculated by thesoftware MDA (Navarro 2003). Other relevantdisparity measures, such as the total range,were explored, but the results did not differmuch, or else demanded the use of rarefactionwith a baseline sample size too small to allowmeaningful interpretation, owing to the largeerror bars. The sum of the variances wastherefore chosen as the reference disparitymeasure because it is relatively insensitive tosample size differences, and more directlycomparable and interpretable with a numberof other studies of disparity in the literature.Error bars for disparity values were estimatedby bootstrapping (Efron and Tibshirani 1993).For each stratigraphic interval, species coor-dinates on PCO axes were resampled with re-placement and the sum of variance was cal-culated. This procedure was repeated 500times, and the mean and standard deviationwere calculated. Standard deviation of thebootstrap samples provides an estimate of thestandard error, which, in paleobiological stud-ies, essentially reflects an estimate of analyti-cal error (Foote 1993b). Finally, the curve sum-


FIGURE 11. Evolution of stylophoran morphospace occupation and paleogeographic dispersion from the late Si-lurian (Ludlow–Pridoli) to the Middle Devonian.


FIGURE 12. Patterns of stylophoran disparity (thickline) and taxonomic diversity (thin line) from the Mid-dle Cambrian to the Middle Devonian. Disparity is mea-sured as the sum of variances. Diversity is the numberof sampled species. Errors bars on disparity were esti-mated by bootstrap (500 replications). MC, Middle Cam-brian. LC, Late Cambrian. Tr, Tremadocian. Ar, Arenigpro parte. MO, Middle Ordovician. Ca, Caradoc. As,Ashgill. eS, early Silurian. lS, late Silurian. eD, earliestDevonian. Em, Emsian. MD, Middle Devonian.

FIGURE 13. Patterns of stylophoran disparity (thickline) and paleogeographic dispersion (dotted line) fromthe Middle Cambrian to the Middle Devonian. Disparityis measured as the sum of variances. Paleogeographicdispersion measured as indicated in the text. Errors barson disparity were estimated by bootstrap (500 replica-tions). Abbreviations as in Figure 12.

marizing general paleogeographic dispersionthrough time was constructed by calculatingfor each stratigraphical interval an index ofdispersion reflecting the distribution of bothglobal (paleocontinents) and local (regions)samples (see above).

The comparison of diversity and disparitycurves (Fig. 12) quantitatively confirms thevarious patterns revealed by the qualitativeexamination of the details of morphospace oc-cupation in the metaPCO1-metaPCO2 projec-tion (Figs. 9–11). A very clear discordance ex-isted between disparity and diversity in thefirst half of stylophoran history, although itwas manifested in several ways. During theinitial radiation phase (Cambro-Tremado-cian), disparity greatly increased while diver-sity remained relatively low. From the earliestArenig to the Middle Ordovician, disparityremained elevated and relatively constant,while diversity strongly increased andreached its peak (Fig. 12). Finally, from theLate Ordovician (Caradoc) to the Middle De-vonian disparity and diversity show relativelygood concordance, with both decreasing mo-notonously, despite a second peak in the EarlyDevonian (though much smaller than the Ear-ly to the Middle Ordovician).

The comparison between the signals of dis-

parity and paleogeographic dispersion re-veals two distinct diversification phases (Fig.13). During the first phase, which correspondsto the principal radiation (Middle Cambrianto Middle Ordovician), the signals of dispar-ity and paleogeographic dispersion appear in-versely related: dispersion was maximal whendisparity was lowest (Cambrian) and, con-versely, dispersion was minimal when dispar-ity was highest (Early to Middle Ordovician).During the second phase (Late Ordovician toMiddle Devonian), the relationship betweenthe two signals was reversed.

Conclusions

The disjunction between the peaks of dis-parity and diversity during the initial radia-tion of stylophorans is in itself an interestingresult, given that a similar pattern character-izes a number of other marine invertebrateclades, including arthropods (Gould 1989;Briggs et al. 1992; Foote and Gould 1992; Willset al. 1994), brachiopods (Carlson 1992;McGhee 1995), gastropods (Wagner 1995),blastozoans (Foote 1992, 1993a), and crinoids(Foote 1994, 1995, 1999). Nevertheless, the op-posite pattern has also been described, for ex-ample in trilobites whose Cambrian diversitypeak clearly preceded the Ordovician dispar-ity peak (Foote 1991, 1993a). In the case of sty-lophorans, it seems that diversification was


characterized by a relatively rapid saturationof morphospace, with initially few species inthe Cambro-Tremadocian occupying rapidlybut sparsely the main morphospace regions,later followed, in the Arenig-Middle Ordovi-cian, by an important phase of diversificationthat nonetheless only filled in an already oc-cupied morphospace.

The macroevolutionary pattern of stylo-phorans is quite similar to that documentedfor several other marine invertebrate groups,which began to diversify comparatively slow-ly during the Cambrian, achieving a diversitypeak in the Ordovician, and then declined inrelatively consistent manner until their dis-appearance during the late Paleozoic (Car-boniferous–Permian), but still displayed a sec-ond disparity peak in the Early Devonian.This is the case of blastozoans (Foote 1992,1993a) and orthid brachiopods (Harper andTychsen 2004). The similarity in macroevolu-tionary patterns might have involved commoncauses (e.g., paleoenvironmental) to particularfluctuations and/or reflect more general mac-roevolutionary trends, of intrinsic (increase inconstraint through time) or extrinsic character(replacement of the Paleozoic fauna by themodern fauna). Preservational and samplingbiases cannot be completely excluded, notablywith respect to the strong decline in both tax-onomic and morphological diversity in the Si-lurian and to the diversity peak in the EarlyDevonian. Indeed, as with stylophorans, anumber of echinoderm groups relatively com-mon in the Ordovician were virtually absentin the Silurian, only to reappear in Lazarus-like fashion in the Early Devonian. This wasthe case, for example, of solutes and of pleu-rocystitid rhombiferans. Thus, the rarity ofcertain echinoderm groups in the Silurianmay be tied to the lack of preservation (or un-derrepresentation) of certain types of environ-ments or Lagerstatten. Finally, stylophoransdiffer from other groups with an otherwisesimilar pattern by the fact that their diversityclearly peaked earlier: earliest Arenig (‘‘un-named stage 2’’ [Sprinkle and Guensburg2004]) instead of Middle to Late Ordovician(Foote 1992; Harper and Tychsen 2004).

The apparent inverse relationship betweenpaleogeographic dispersion and diversity

(both taxonomic and morphologic) during theinitial history of stylophorans runs converselyto the hypothesis of diffusion on a globalscale, which entails an expectation of positivecorrelation between the two signals. This re-lationship suggests that the colonization ofnew geographic areas, and putatively of newenvironments, is not necessary for speciationand morphological differentiation. The stylo-phoran pattern is reminiscent of other groupsof marine invertebrates, in particular bivalvemollusks. Bivalves apparently radiated in theCambrian, diversified extensively in the Earlyand Middle Ordovician, but remained ex-tremely restricted paleogeographically (Babin1993; Cope and Babin 1999; Cope 2004). Fromthe Caradoc onward, bivalves extended theirrange toward lower paleolatitudes, where asecond major diversification occurred, thoughthey became rarer and less diverse in the re-gion of origin (notably the northern-Gond-wanan margin). The similarity of the stylo-phoran and bivalve macroevolutionary pat-terns suggests perhaps the influence of com-mon paleoenvironmental controls of thepaleogeographic dispersion of these twogroups.

More generally, results of the threefold ap-proach (diversity, disparity, geography) pur-sued in this study suggest that the relation-ships among the three signals can be complexand at times too idiosyncratic for simple in-terpretation. Still, the explicit consideration ofthe geographic context of taxonomic and mor-phological diversification has enhanced ourunderstanding of the macroevolutionary dy-namics of stylophorans by providing an im-portant additional perspective for the char-acterization and interpretation of biodiversity.Biodiversity is inherently complex, havingmultiple aspects, measures, and contexts. Ac-cordingly, different patterns are likely to becollectively informative in novel and valuableways, complementing the rich body of knowl-edge stemming from generally accepted stud-ies focusing on a particular aspect, measure,and context.

Although comparisons of diversity and dis-parity have yielded important insights aboutmacroevolution, more work is needed becausegeneralizations have emerged mostly in an in-


ductive fashion, and many groups still awaitstudy. An eventual theory of biodiversity dy-namics cast in terms of diversity and disparityremains possible, but would remain inevitablypartial given the heterogeneity of biodiversi-ty. It may well be that some components ofbiodiversity are less informative and of lim-ited interest or applicability in paleobiology,yet factors such as biogeography are well es-tablished in their empirical and theoreticalvalue for understanding diversification and itscontrols.

Biogeography should be more widely con-sidered in studies of diversity and disparity,and a threefold approach is almost self-evi-dently appealing, notwithstanding that (1)data resolution and the relevance of various bi-ases would hardly be equivalent among thethree given the very nature of the signals andtheir estimation; (2) as a consequence the sig-nal-to-noise the ratio will be uneven for dif-ferent patterns, thus limiting the types of com-parison possible as well as the content of gen-eralizations; (3) the array of possible discor-dances or concordances among signals maynot be equally likely, because different signalsare not completely independent and have dif-ferent degrees of freedom. In any case, com-parisons of multiple signals of biodiversitycan be informative provided that the issueslisted above are taken into account. In the caseof biogeography, a richer characterization ofmacroevolutionary pattern was possible here,facilitating the inference of mechanisms andcauses. However, additional case studies willbe needed to produce generalizations aboutthe paleoecological trinity that is diversity-disparity-geography.

Acknowledgments

This paper is a contribution to the GDRCNRS ‘‘Morphometrie et Evolution desFormes,’’ and to team C ‘‘Macroevolution etdynamique de la biodiversite’’ of the UMRCNRS Biogeosciences. The authors are verygrateful to T. Baumiller, A. W. Hunter, and T.Chone for their precious help. G. Eble wassupported in part by postdoctoral fellowshipsfrom the Regional Council of Burgundy (Di-jon, France, with sponsorship by the CNRS)and from the Konrad Lorenz Institute for Evo-

lution and Cognition Research (Vienna, Aus-tria), as well as by research grants from theDeutsche Forschungsgemeinschaft to the In-terdisciplinary Centre for Bioinformatics(University of Leipzig, Germany). We thankour referees, M. Foote and M. A. Wills, fortheir detailed critique and insightful sugges-tions.

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Appendix

List of species included in the analysis, with corresponding taxonomic group, stratigraphic ranges, illustrationsources for reconstructions used in morphometric analysis, and studied areas. MC � Middle Cambrian; LC � LateCambrian; Tr � Tremadocian; Ar � Arenig pro parte (Early Ordovician, stage 2 of Webby et al. 2004); MO � MiddleOrdovician (stages 3 and 4); Ca � Caradoc; As � Ashgill; eS � early Silurian (Llandovery and Wenlock); lS � lateSilurian (Ludlow and Pridoli); eD � early Devonian (Lochkovian and Praguian); Em � Emsian; MD � MiddleDevonian (Eifelian and Givetian); Pe � Pennsylvanian. Abbreviations for bibliographic references are: 1 � Beis-swenger (1994); 2 � Chauvel (1966); 3 � Craske and Jefferies (1989); 4 � Cripps (1988); 5 � Cripps (1989a); 6 �Cripps (1989b); 7 � Cripps (1990); 8 � Cripps and Daley (1994); 9 � Daley (1992); 10 � Gil Cid et al. (1996); 11 �Haude (1995); 12 � Jefferies (1968); 13 � Jefferies (1986); 14 � Jefferies and Lewis (1978); 15 � Jefferies and Prokop(1972); 16 � Jefferies et al. (1987); 17 � Kolata and Guensburg (1979); 18 � Kolata and Jollie (1982); 19 � Kolata etal. (1991); 20 � Lee et al. (2005); 21 � Lefebvre (1999); 22 � Lefebvre (2000b); 23 � Lefebvre (2000c); 24 � Lefebvreand Gutierrez-Marco (2003); 25 � Lefebvre and Vizcaıno (1999); 26 � Marti Mus (2002); 27 � Parsley (1991); 28 �Ruta (1997); 29 � Ruta (1999a); 30 � Ruta (1999b); 31 � Ruta and Bartels (1998); 32 � Ruta and Jell (1999a); 33 �Ruta and Jell (1999b); 34 � Ruta and Jell (1999c); 35 � Ruta and Jell (1999e); 36 � Ruta and Theron (1997); 37 �Smith and Jell (1999); 38 � Sumrall and Sprinkle (1999); 39 � Ubaghs (1963); 40 � Ubaghs (1968); 41 � Ubaghs(1970); 42 � Ubaghs (1979); 43 � Ubaghs (1983); 44 � Ubaghs (1987); 45 � Ubaghs (1991); 46 � Ubaghs (1994); 47� Ubaghs and Robison (1988); 48 � Woods and Jefferies (1992). These references are listed in the Literature Citedsection. Abbreviations for studied surfaces: TH � Theca; LTS � Lower Thecal Surface; UTS � Upper Thecal Surface.

Species Order Range Refs. Studied areas

Adoketocarpus acheronticus mitrate lS 33 TH, LTS, UTSAdoketocarpus janeae mitrate eD 33 TH, LTSAmpelocarpus landeyranensis cornute Ar 25 TH, LTS, UTSAmygdalotheca griffei cornute Tr–Ar 41 TH, LTSAnatifopsis barrandei mitrate MO–Ca 21 TH, LTS, UTSAnatifopsis minuta mitrate MO 23 TH, UTSAnatifopsis trapeziiformis mitrate Tr–MO 21 TH, LTS, UTSAnomalocystites cornutus mitrate eD 27 TH, LTS, UTSArauricystis occitana cornute Ar 46 TH, LTS, UTSArauricystis primaeva cornute Ar 41 TH, LTSArchaeocothurnus bifida cornute MC 47 TH, LTS, UTSAspidocarpus bohemicus mitrate Ca 42 TH, LTS, UTSAspidocarpus discoidalis mitrate MO 7 TH, LTS, UTSAspidocarpus riadanensis mitrate Ca 22 TH, LTSAteleocystites guttenbergensis mitrate Ca 18 TH, LTS, UTSAteleocystites huxleyi mitrate Ca 40 TH, LTSBalanocystites primus mitrate Ar–MO 23 TH, LTS, UTSBarrandeocarpus jaekeli mitrate Ca 42 TH, LTS, UTSBarrandeocarpus norvegicus mitrate As 3 TH, LTS, UTSBeryllia miranda cornute MO 8 TH, LTS, UTSBokkeveldia oosthuizeni mitrate Em 36 TH, UTSCeratocystis perneri primitive MC 40 TH, LTS, UTSCeratocystis vizcainoi primitive MC 44 TH, UTSChauvelicystis spinosa cornute Ar 41 TH, LTS, UTSChauvelicystis ubaghsi cornute Ar 2 TH, LTS, UTSChauvelicystis vizcainoi cornute Ar 9 TH, LTSChinianocarpos thorali mitrate Ar 13 TH, LTS, UTSCothurnocystis courtessolei cornute Ar 41 TH, LTS, UTSCothurnocystis elizae cornute As 40 TH, LTS, UTSCothurnocystis fellinensis cornute Tr–Ar 41 TH, LTS, UTSDiamphidiocystis drepanon mitrate As 17 TH, LTS, UTSDiamphidiocystis sp. mitrate MO 23 TH, LTSaDomfrontia pissotensis cornute MO 8 TH, LTS, UTSDrepanocarpos australis cornute LC 37 TH, LTS, UTSEnoploura popei mitrate Ca–As 27 TH, LTS, UTSEumitrocystella savilli mitrate MO 1 TH, LTS, UTSFlabellicarpus rushtoni cornute Tr 26 TH, LYS, UTSGalliaecystis ubaghsi cornute Ar 41 TH, LTS, UTSHanusia prilepensis cornute MO 6 TH, LTS, UTSJaekelocarpus oklahomaensis mitrate Pe 19 TH, LTS, UTSKierocystis inserta mitrate Ca 27 TH, UTSKopficystis kirkfieldi mitrate Ca 27 TH, UTSLagynocystis pyramidalis mitrate Ar–MO 40 TH, LTS, UTSLobocarpus vizcainoi mitrate LC 22 TH, LTSLyricocarpus courtessolei cornute Ar 25 TH, LTS, UTS

510

Appendix. Continued.

Species Order Range Refs. Studied areas

Milonicystis kerfornei cornute MO 8 TH, LTS, UTSMitrocystella incipiens mitrate MO 12 TH, LTS, UTSMitrocystites mitra mitrate MO 40 TH, LTS, UTSNanocarpus dolambii cornute Ar 45 TH, LTS, UTSNanocarpus milnerorum cornute As 29 TH, LTS, UTSNevadaecystis americana cornute LC 39 TH, LTS, UTSOccultocystis koeneni mitrate eD–Em 11 TH, UTSOvocarpus moncereti mitrate Ar–MO 24 TH, LTS, UTSParanacystis petrii mitrate Em 40 TH, LTS, UTSParanacystis simoneae mitrate MD 21 TH, LTSPeltocystis cornuta mitrate Ar 41 TH, LTS, UTSPhyllocystis blayaci cornute Ar 41 TH, LTS, UTSPhyllocystis crassimarginata cornute Tr–Ar 41 TH, LTS, UTSPlacocystella africana mitrate Em–MD 36 TH, LTS, UTSPlacocystella buretti mitrate eS 30,35 TH, LTS, UTSPlacocystella flemingi mitrate Em 30,35 TH, LTS, UTSPlacocystella garratti mitrate lS 30,35 TH, LTS, UTSPlacocystites forbesianus mitrate eS 14 TH, LTS, UTSPonticulocarpus robisoni cornute MC 38 TH, LTS, UTSProchauvelicystis semispinosa cornute Tr 9 TH, LTS, UTSProcothurnocystis owensi cornute MO 48 TH, LTS, UTSProkopicystis mergli cornute MO 5 TH, LTS, UTSPromitrocystites barrandei mitrate MO 40 TH, LTS, UTSProscotiaecystis melchiori cornute Ar 43 TH, LTSProtocystites menevensis cornute MC 16 TH, LTS, UTSProtocytidium elliotae mitrate As 32 TH, LTS, UTSPseudovictoriacystis problematica mitrate eD 34 TH, LTS, UTSReticulocarpos hanusi cornute MO 15 TH, LTS, UTSRhenocystis latipedunculata mitrate Em 31 TH, LTS, UTSScotiaecystis collapsa cornute As 4 TH, LTS, UTSScotiaecystis curvata cornute As 12 TH, LTS, UTSScotiaecystis guilloui cornute MO 25 TH, LTS, UTSScotiaecystis jefferiesi cornute Ca 10 TH, LTS, UTSSokkaejaecystis serrata cornute LC 20 TH, LTS, UTSThoralicystis bouceki cornute MO 40 TH, LTS, UTSThoralicystis griffei cornute Ar 41 TH, LTS, UTSVictoriacystis hulmesorum mitrate eD 34 TH, LTS, UTSVictoriacystis wilkinsi mitrate lS 28 TH, LTS, UTSVizcainocarpus dentiger mitrate Ar 22 TH, LTS, UTSVizcainocarpus rutai mitrate Tr 22 TH, LTSWillmanocystis denticulata mitrate Ca 18 TH, LTS, UTSYachalicystis triangularis mitrate eD–Em 11 TH, LTS, UTSYachalicystis sp. mitrate MD 21 TH, LTS

diversiﬁcation of atypical paleozoic echinoderms:...

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