chapter 13 cambrian echinoderm diversity and...

Chapter 13

Cambrian echinoderm diversity and palaeobiogeography

SAMUEL ZAMORA1*, BERTRAND LEFEBVRE2, J. JAVIER ALVARO3, SEBASTIEN CLAUSEN4, OLAF ELICKI5,

OLDRICH FATKA6, PETER JELL7, ARTEM KOUCHINSKY8, JIH-PAI LIN9, ELISE NARDIN10, RONALD PARSLEY11,

SERGEI ROZHNOV12, JAMES SPRINKLE13, COLIN D. SUMRALL14, DANIEL VIZCAINO15 & ANDREW B. SMITH1

1Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD, UK2UMR CNRS 5276, Universite Lyon 1 & ENS-Lyon, 69622 Villeurbanne, France

3Centro de Astrobiologıa (CSIC/INTA), Ctra. de Torrejon a Ajalvir km 4, 28850 Torrejon de Ardoz, Spain4Geosystemes, UMR 8157 and 7207 CNRS, Universite des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq, France

5Geological Institute, Freiberg University, Bernhard-von-Cotta Street 2, 09599 Freiberg, Germany6Department of Geology and Palaeontology, Faculty of Science, Charles University, Albertov 6, Praha 2, 128 43 Czech Republic

7Queensland Museum, PO Box 3300, South Brisbane, Queensland 4101, Australia8Department of Palaeozoology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden

9State Key Laboratory of Paleobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology,

Chinese Academy of Sciences, 39 East Beijing Road, Nanjing 210008, China10UMR CNRS-UPS-IRD 5563 Geosciences Environnement Toulouse, Observatoire Midi-Pyrenees, F-31400 Toulouse, France

11Department of Earth and Environmental Sciences, Tulane University, New Orleans, LA 70118, USA12Paleontological Institute RAS, Profsoyuznaya St 123, 117997 Moscow, Russia

13Department of Geological Sciences, Jackson School of Geosciences, University of Texas, Austin, TX 78712-0254, USA14Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, USA

157 rue J.-B. Chardin, Maquens, 11090 Carcassonne, France

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

Abstract: The distribution of all known Cambrian echinoderm taxa, encompassing both articulated specimens and taxonomically diag-nostic isolated ossicles, is documented for the first time. The database described by 2011 comprises 188 species recorded from 65 for-mations from around the world. Formations that have yielded articulated echinoderms are unequally distributed in space and time. OnlyLaurentia and West Gondwana provide reasonably complete records at the resolution of Stage. The review of the biogeographical dis-tributions of the eight major echinoderm clades shows that faunas from Laurentia and Northeast Gondwana (China and Korea) are dis-tinct from those of West Gondwana and Southeast Gondwana (Australia); other regions are too poorly sampled to make firmpalaeobiogeographical statements. Analysis of alpha diversity (species per formation) shows that diversity rose initially to CambrianStage 5, declined into Guzhangian and Paibian before returning to Stage 5 levels by the end of the Cambrian. This pattern is replicatedin Laurentia and West Gondwana. We show that taxonomically diagnostic ossicles found in isolation typically occur significantly earlierthan the first articulated specimens of the same taxa and provide important information on the first occurrence and palaeobiogeographicaldistribution of key taxa, and of the phylum as a whole.

Supplementary material: Articulated Cambrian echinoderms and Isolated plates of Cambrian echinoderms are provided at: http://www.geolsoc.org.uk/SUP18668

The Cambrian represents a crucial period in the evolution ofmany groups of Metazoa, and echinoderms are no exception.During this period, echinoderms made their first appearance inthe fossil record and underwent their initial diversification thatestablished many of the major lines of the later Palaeozoic. Theexistence of putative Ediacaran (Late Neoproterozoic) echino-derms (i.e. Arkarua: Gehling 1987; David et al. 2000) remainsspeculative and far from widely accepted. As a result, the oldestundisputed members of the Phylum Echinodermata, based onarticulated specimens, are from Cambrian Stage 3 and representedby helicoplacoids and edrioasteroids in Laurentia and by gogiidblastozoans in Gondwana. Because of their sturdy calcitic skel-eton, echinoderms have left a rich fossil record; however, completeand articulated specimens are typically to be found associated withvery specific facies in ‘echinoderm Lagerstatten’ (Smith 1988).Our knowledge of Cambrian echinoderm Lagerstatten has been

greatly improved in the last two decades, with many new occur-rences reported from palaeogeographical areas where few if anyechinoderms had been previously documented, notably in EastGondwana (e.g. China, Korea), West Gondwana (e.g. Morocco,Spain and Wales), and Siberia.

Despite this improved knowledge, facies from which echino-derm remains have been reported remain unequally distributedthrough time and space, and thus the fossil record of early echino-derms suffers from a strong sampling bias that could confoundthe analysis of the Cambrian echinoderm palaeobiogeography.Figure 13.1a tabulates the chronological distribution of the 65 for-mations known to have yielded 188 species of articulated or par-tially articulated Cambrian echinoderms. The distribution offormations is clearly patchy, with only North America providingan unbroken record of fossiliferous formations through the Cam-brian. West Gondwana is the next best-sampled region, albeit

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

Geological Society, London, Memoirs, 38, 157–171. http://dx.doi.org/10.1144/M38.13

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

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with European localities providing a more complete record thanNorth Africa. Particularly poorly sampled are Siberia, Baltica andsome Gondwanan regions, such as South America and the Ara-bian margin. While Siberia and South America are undoubtedlypoorly explored and undersampled, others, such as Baltica andAvalonia, lie in geologically well-studied regions of the world;the dearth of echinoderm-bearing formations in these two regionsprobably reflects something other than simple sampling bias.

Taking all palaeocontinents together (Fig. 13.1b), it is clear thatechinoderm-bearing formations are much more common in Cam-brian Stage 5 and Drumian, whereas they are particularly poorlyrepresented at the start of the Furongian. This must partiallyreflect major retrogradational–progradational shifts over thecontinental blocks (megacycles; Spencer & Demicco 2002, fig.1). Comparing the pattern of fossil-bearing formations from thetwo best-sampled regions (Laurentia and West Gondwana;Fig. 13.1c), we see that a similar bias exists in both regions, butwith a better Furongian record in Laurentia. In western NorthAmerica this pattern is also reflected in a shift in echinodermbearing facies from fine-grained siliclastics to shelf storm-dominated carbonates (Sumrall et al. 1997). Most notably, thenumber of species recorded through this time interval shows astrong correspondence to sampling patterns (Fig. 13.1d, e).

With these difficulties in mind, the aim of this collaborativeproject is to produce the most up-to-date documentation andanalysis of the palaeobiogeographical distribution of Cambrianechinoderms, drawing together all published and available unpub-lished data that are known to us. Furthermore, we have triedto incorporate all sources of information up to June 2011,

focusing not just on articulated fossil occurrences, but also includ-ing the frequently overlooked record of isolated plates obtainedafter limestone etching. Particular attention has been devotedto establishing the palaeobiogeographical distribution of firstoccurrences of the major echinoderm clades in the fossil record.

Palaeogeographical units and chronostratigraphical

nomenclature

As outlined in Alvaro et al. (2013), the tectonostratigraphical unitsinto which we place Cambrian echinoderms represent a mixtureof palaeogeographical and palaeobiogeographical areas. Thetectonostratigraphical units that we employ here are: Baltica, Laur-entia (including Sonora, Mexico), the Siberian Platform, WestGondwana [Avalonia, the Mediterranean region (from West toEast: Morocco, Ossa–Morena, Iberia, Montagne Noire, Sardinia,Saxo-Thuringia and Bohemia) and its transition to the Arabianmargin (Jordan and Turkey)] and East Gondwana (Iran, SouthChina and Australia). For our biogeographical analyses of echino-derm distribution we arbitrarily separate West Gondwana intoNorth Africa and Europe, and the Arabian margin and East Gond-wana into the Near East (Turkey and Iran), Far East (China andKorea) and Australia.

Only the Terreneuvian and Furongian of the proposed four-foldSeries division of the Cambrian System have been defined by theInternational Subcommission on Cambrian Stratigraphy and rati-fied by the International Union of Geological Sciences (Peng

(a)

(b)

(d) (e)

(c)

Fig. 13.1. Analysis of Cambrian formations

that have yielded articulated echinoderms.

(a) Number of formations per stage plotted

for six biogeographical regions (Laurentia,

South America, Baltica, West Gondwana

(Morocco, Newfoundland and Gondwanan

Europe), Siberia and East Gondwana

(Australia, Middle East and Far East)).

(b) Global number of formations per stage.

(c) Number of formations plotted for

Laurentia and West Gondwana. (d) Global

number of articulated echinoderm species

known per stage. (e) Number of articulated

echinoderm species known from each

Cambrian stage in Laurentia and West

Gondwana.

S. ZAMORA ET AL.158




et al. 2004; Landing et al. 2007; Peng & Babcock 2008). The twoseries remaining to be defined are provisionally termed CambrianSeries 2 and 3. A tentative global correlation chart is givenin Figure 13.2, summarizing the regional chronostratigraphicalnomenclature followed in this chapter.

Palaeogeographical distribution of Cambrian echinoderms

The supplementary material to this paper lists all reported echino-derm occurrences from the Cambrian, along with their age and dis-tribution with reference to major palaeobiogeographical areas.During the Cambrian, echinoderms diversified, giving rise toeight major groups (Figs 13.3 & 13.4): (1) helicoplacoids; (2)eocrinoids; (3) edrioasteroids; (4) rhombiferans; (5) cinctans; (6)ctenocystoids; (7) solutans; and (8) stylophorans. This diversitycoincides with the Cambrian groups classically identified in the lit-erature (e.g. Ubaghs 1971, 1975; Derstler 1981; Paul & Smith1984; Smith 1988; Sprinkle 1992). However, there are severalnotable differences from these earlier works. First, we now includerhombiferans as members of the Cambrian biota, whereas tra-ditionally they have not been reported before the Early Ordovician.Several recent finds suggest that basal members of this groupappeared by Cambrian Series 3 (Ubaghs 1998; Zamora 2010;Zamora & Smith 2012). Second, two problematic taxa, Echma-tocrinus and Eldonia, are omitted here. The putative crinoidaffinities of Echmatocrinus remain controversial; this lightly ske-letized fossil was originally described as a primitive Cambriancrinoid (Sprinkle 1973), but later reinterpreted as an octocoral(Ausich & Babcock 1998; Reich 2009). Sprinkle & Collins(1998, 2011) compared these two interpretations, and argued thata basal crinoid assignment is much more likely than an early octo-coral assignment, but the discussion is still open. Several species ofEldonia have been interpreted as pelagic sea cucumbers (Walcott1911; Durham 1974; questionably by Sprinkle 1992), whereasPaul & Smith (1984) and Reich (2005) strongly disagreed withthis assignment (Reich 2010). Ossicles of Holothuroidea frommiddle and upper Cambrian strata were mentioned by Bell

(1948) and Mankiewicz (1992), but without description and dis-tinct record and thus remain questionable (Reich 2010). Recently,hemichordate affinities were proposed for Eldonia and allied forms(Caron et al. 2010). Finally, echinoderm affinities have beensuggested for the vetulocystids from the Cambrian Series 2 Lager-statte of Chengjiang, China (Shu et al. 2004, 2010). However,these fossils lack plating and are probably better interpreted asclose relatives of vetulicolians and thus as possible stem groupdeuterostomes (Smith 2004; Swalla & Smith 2008; Clausenet al. 2010). Most of these problematic taxa are restricted tosingle localities and horizons (Eldonia is an exception), so theirexclusion here makes little difference to our subsequent palaeobio-geographical analyses and discussion.

Each group of Cambrian echinoderms is reviewed separatelybelow, with comments on their palaeogeographical distribution.

Helicoplacoidea

Helicoplacoids are a relatively small clade of exclusivelyCambrian Series 2 echinoderms. They have a spirally plated,spindle- to bulb-shaped theca (Fig. 13.3a) constructed from numer-ous rows of interambulacral plates and just three ambulacra(Durham & Caster 1963; Sprinkle & Wilbur 2005). The mouthis thought to be situated at mid-height on the lateral side, andthe anus at the distal pole (Derstler 1981; Paul & Smith 1984;Sprinkle & Wilbur 2005; Smith 2008). Helicoplacoids probablylived with one of the thecal poles (the one opposite the anus)either inserted into relatively firm, stabilized substrates (Dornbos2006) or attached to bioclasts on these substrates (Sprinkle &Wilbur 2005).

The three currently valid genera of helicoplacoids, Helicopla-cus, Polyplacus and Waucobella (Durham 1967; Wilbur 2006),all come from Laurentia (western USA). A helicoplacoid specimenwas reported from central British Columbia, Canada (Durham1993), but it is now missing (Wilbur 2006); other undescribedmaterial from here exists (Sprinkle, pers. obs. 2010). Helicopla-coids are also known in the Cambrian Series 2 of Sonora,Mexico (Zamora & Clausen, pers. comm.).

Fig. 13.2. Correlation chart of the Cambrian showing the global chronostratigraphical series and stages compared with regional usage in major areas of the world;

modified from Peng et al. (2004), Landing et al. (2007) and Peng & Babcock (2008). *Siberian regional ‘horizons’ not yet officially erected for the Furongian.

CAMBRIAN ECHINODERMS 159




Of the eight Cambrian echinoderm groups, helicoplacoids arethe clade with both the shortest stratigraphical range (restrictedto Cambrian Stage 3) and the most restricted palaeobiogeographi-cal distribution (western Laurentia).

Edrioasteroidea

Edrioasteroids are an extinct group of sessile forms with a globularto discoidal theca lacking exothecal appendages (Fig. 13.3f, j, k).They have five ambulacra arranged in a 2–1–2 pattern around a

central mouth, with the anal pyramid situated orally between theC and D ambulacra. Edrioasteroids first appeared in CambrianStage 3 of Laurentia (Durham 1967). The oldest named speciesis ‘Stromatocystites’ walcotti from Stage 4 of Newfoundland(Schuchert 1919; Smith 1985; Zhao et al. 2010). Other occurrencesfrom the same stage that may be approximately coeval or slightlyyounger are Stromatocystites reduncus and Edriodiscus primoticus(Smith & Jell 1990) from Queensland and ?Stromatocystites sp.from the Bilbilian of northern Spain (S. Zamora, pers. obs. 2006).

Like many other echinoderm groups, edrioasteroids were muchmore diverse in Cambrian Series 3. Typical Stromatocystites-like

Fig. 13.3. Representative Cambrian

echinoderms. (a) Helicoplacus gilberti

(BMNH E27094) from the Cambrian

Series 2 of North America.

(b) Guizhoueocrinus yui (KW-08) from

Cambrian Series 2 of China. (c) Kinzercystis

durhami (MCZ 581) from Cambrian Series

2 of North America. (d) Cambroblastus

enubilatus (QMF17872) from the Furongian

of Australia. (e) Sinoeocrinus lui (GM

9-3-1382) from the Cambrian Series 3 of

China. (f) Protorophus hispanicus

(MPZ2009/1233) from the Cambrian

Series 3 of Spain. (g) Ubaghsicystis segurae

(MNCN-I-30849) from Cambrian Series 3

of Spain. (h) Velieuxicystis ornata (VCMN

523a) from the Furongian of France. (i)

Lichenoides priscus (BMNH E29346) from

the Cambrian Series 3 of Bohemia. ( j) New

stromatocystitid edrioasteroid (MPZ2007/

1890) from the Cambrian Series 3 of Spain.

(k) Kailidiscus chinensis (GM 2146) from

the Cambrian Series 3 of China. All

photographs with the exception of D are

taken from latex casts whitened with NH4Cl

sublimate. Abbreviations: BMNH, Natural

History Museum (UK); MCZ, Museum of

Comparative Zoology, Harvard University

(USA); QMF, Queensland Museum,

Brisbane (Australia); GM and KW, The

Paleontological Museum, Guizhou

University (China); MPZ, Museo

Paleontologico Universidad Zaragoza

(Spain); VCMN, Collection Vizcaino,

Carcassonne (France); USNM, US National

Museum (USA); PIW, Institut fur

Palaontologie der

Julius-Maximilians-Universitat Wurzburg

(Germany); IGR, Institut de Geologie,

Universite de Rennes (France); NMP,

Narodnı Muzeum, Prague (Czech

Republic); MNCN, Museo Nacional

Ciencias Naturales Madrid (Spain); SNUP,

Seoul National University Palaeontology

(Korea); TX, Nonvertebrate Paleontology

Laboratory, University of Texas at Austin

(USA); MNHN, Museum National

d’Histoire Naturelle, Paris (France).

S. ZAMORA ET AL.160




taxa (with a fully plated aboral surface and biserial flooring plates)occur in West Gondwana (Fig. 13.3j). Stromatocystites has beenfound in Australia, Bohemia, Morocco, Spain and Turkey (Pom-peckj 1896; Jell et al. 1985; Smith & Jell 1990; Lefebvre et al.2010), as well as in Baltica (Dzik & Orłowski 1995). Theclosely related genus Cambraster has been reported from Austra-lia, France and Spain (Jell et al. 1985; Smith 1985; Zamora et al.2007b). Totiglobus is the Laurentian counterpart of Stromatocys-tites and Cambraster, but represents a distinct clade with veryreduced secondary cover plates, a more domed theca and no epis-pires (Bell & Sprinkle 1978; Sprinkle 1985). A third clade ofedrioasteroids, with quadriserial flooring plates, an uncalcified

aboral surface and pedunculate zone, is present in both NorthAmerica (Walcottidiscus) and China (Kailidiscus, Fig. 13.3k;Smith 1985; Zhao et al. 2010). The oldest members of the OrderIsorophida (with uncalcified aboral surface and uniserial floor-ing plates) are known from West Gondwana, where they are repre-sented by the genus Protorophus (Fig. 13.3f) and an indeterminatetaxon, both from Cambrian Stage 5 of North Spain (Zamora &Smith 2010). Finally, the fossil record of isolated plates assignedto edrioasteroids (Kouchinsky et al. 2011, in press) suggests thisgroup was in Stages 3 (Kouchinsky et al. in press) and 5 (Kou-chinsky et al. 2011) of Siberia, although no articulated specimenshave yet been described.


echinoderms. (a) Coleicarpus sprinklei

(USNM 423877) from the Cambrian

Series 3 of North America. (b) Ctenocystis

utahensis (BMNH E63150) from the

Cambrian Series 3 of North America.

(c) Lignanicystis barriosensis (MPZ2007/776) from the Cambrian Series 3 of Spain.

(d) Trochocystites bohemicus (NMP 9066)

from the Cambrian Series 3 of Bohemia. (e)

Gyrocystis badulesensis (PIW92V6I) from

the Cambrian Series 3 of Spain. (f)

Undatacinctus undata (IGR 1033a) from

the Cambrian Series 3 of Morocco. (g)

Minervaecystis? sp. (1791TX4) from the

Furongian of North America. (h)

Lobocarpus vizcainoi (VCMN 656) from

the Furongian of France. (i) Ceratocystis

perneri (NMP.L.10392) from the Cambrian

Series 3 of Bohemia. (j) Cornute

stylophoran indet. (SNUP 2563) from the

Furongian of Korea. (k) Courtessolea

monceretorum (MNHN.F.A45783) from

the Cambrian Series 3 of France. All

photographs with the exception of (a) and

(g) were taken from latex casts whitened

with NH4Cl sublimate. For abbreviations:

see caption to Figure 13.3.





The Furongian record of edrioasteroids is, by comparison,extremely poor and includes only a handful of species. How-ever, the little available evidence suggests that edrioasteroidscontinued to diversify through the Furongian. Only four edrio-asteroids have been recorded so far from the Furongian: oneindeterminate edrioasteroid from North America (Sumrall et al.1997), a possible stromatocystitid from France (Ubaghs 1998)and two isorophids from Australia, Chatsworthia and Hadro-discus (Smith & Jell 1990), both of which have unplatedaboral surfaces. Finally, edrioblastoids (a derived clade ofedrioasteroids) first appeared in the Furongian (Fig. 13.3d); theyhave been reported so far only from Australia (Cambroblastusenubilatus; Smith & Jell 1990).

Eocrinoids

The ‘Class’ Eocrinoidea is a paraphyletic assemblage compris-ing stem-group members of most other blastozoan clades(Ubaghs 1968a; Sprinkle 1973; Smith 1984; Paul 1988; Sumrall1997; David et al. 2000). The body of eocrinoids generally con-sists of three parts (Fig. 13.3b): a sack-like theca that enclosed themain viscera, the feeding appendages (brachioles) and an aboralstalk or stem used for attachment and to elevate the theca abovethe sea floor. In the most primitive taxa (e.g. Gogia and relatives),this appendage consists of a long, multiplated stalk. In morederived forms (e.g. Ubaghsicystis) it is a columnal-bearing stem.This aboral appendage is absent in other taxa (e.g. Lichenoides).Simple respiratory structures (epispires) occur frequently, more orless extensively, over the theca of eocrinoids (Fig. 13.3b, c). Thepresence of epispires is a plesiomorphic feature within echino-derms, which is lost in more advanced eocrinoids and otherblastozoans.

Eocrinoids commonly form the dominant echinoderm groupin Cambrian assemblages. The earliest eocrinoids include repre-sentatives of the ‘orders’, Imbricata and Gogiida. Imbricate eocri-noids are probably the most basal blastozoans (Sprinkle 1973; Paul& Smith 1984). Their stalk is an unorganized, polyplated struc-ture built of numerous imbricate elements (Fig. 13.3c). CambrianSeries 3 imbricate eocrinoids are restricted to Laurentia (NorthAmerica) where there are just two genera, Lepidocystis and Kin-zercystis (Sprinkle 1973). The oldest gogiid eocrinoid is Gogiaojenai from the Stage 4 of Laurentia (Durham 1978). Earlygogiids from Gondwana are of approximately the same age astheir Laurentian counterparts. They are represented by Alanisi-cystis andalusiae and Alanisicystis sp. from the Marianian andBanian stages of South Spain and Morocco, respectively(Ubaghs & Vizcaıno 1990; Nardin & Lefebvre 2005), as well asby Guizhoueocrinus yui (Fig. 13.3b) and Wudingeocrinus rarusfrom Stage 4 of China (Zhao et al. 2007; Hu et al. 2007; Hu &Luo 2008; Luo et al. 2008). Other West Gondwanan occurrencesof gogiids are based on isolated plates and their stratigraphicalrange is comparable to that of articulated specimens. Isolatedgogiid plates have been recorded from the Comley of Britain(Series 2; Donovan & Paul 1982), Germany (Elicki & Schneider1992), from the slightly younger Bilbilian Stage of Jordan andNorth Spain (Clausen 2004; Shinaq & Elicki 2007), and fromthe Laurentian part of Newfoundland (Skovsted & Peel 2007).Finally, other Cambrian Series 2 eocrinoid skeletal elements arealso known from Siberia (Rozanov & Zhuravlev 1992, p. 248;Rozhnov et al. 1992; Kouchinsky et al. 2012, in press).

Eocrinoid faunas from Cambrian Series 3 strata show that basalblastozoans had become more diversified. Imbricate eocrinoidssurvived, but their only record is from the Prıbram-Jince Basin(Vyscystis ubaghsi; Fatka & Kordule 1990). This region has alsoyielded a new, as yet unpublished, basal blastozoan, intermediatein morphology between imbricates and gogiids (Nardin 2007). Incontrast, gogiids (Fig. 13.3e) are relatively common in siliciclasticplatforms of both Laurentia (Mexico and USA; Sprinkle 1973;

Sprinkle & Collins 2006; Nardin et al. 2009) and Gondwana(China, Czech Republic, France and Spain; Fatka & Kordule1984; Ubaghs 1987; Zhao et al. 2008; Zamora et al. 2009;Parsley & Zhao 2010). Some morphological innovations in eocri-noids appeared apparently earlier in West Gondwana than inLaurentia (Zamora 2010). For example, the possession ofcolumnal-bearing stems is documented both in Spain (Ubaghsicys-tis, Fig. 13.3g; Gil Cid & Domınguez 2002) and in the Prıbram-Jince Basin (O. Fatka, pers. obs. 2010) as early as CambrianStage 5, instead of the Guzhangian in Laurentia (e.g. Eustypocys-tis; see Sprinkle 1973). This earlier occurrence of holomeric stemsin articulated Gondwanan eocrinoids is also mirrored by the fossilrecord of isolated columnals. Columnals are known from variousGondwanan regions (Australia, Morocco, Sardinia and Turkey)in levels very close to the boundary of Cambrian Series 2–3(Elicki 2006; Clausen & Smith 2008; Clausen et al. 2009; Guens-burg et al. 2010). They have been also reported from Baltica (Berg-Madsen 1986; Hinz-Schallreuter 2001). Lichenoidids are a groupof stemless eocrinoids that were apparently endemic to WestGondwana (Fig. 13.3i). They are known from Bohemia (Ubaghs1953) and Spain (Zamora 2010), and related plate taxa (Cymbio-nites and Peridionites) are known from Stage 5 in Australia(Smith 1982; J. Sprinkle, pers. obs. 2013). Finally, long-stalkedeocrinoids appeared at the same time in both Laurentia and Gond-wana. They include Balangicystis from China (Parsley & Zhao2006; Sprinkle et al. 2011) and Lyracystis from North America(Sprinkle & Collins 2006). Cambrian Series 3 eocrinoids are veryrare from Baltica, where only the enigmatic Cigara and isolatedthecal plates (assigned to Crucicystis) have been described(Franzen-Bengston, in Berg-Madsen 1986; Hinz-Schallreuter 2001).

The Furongian marks a dramatic turnover in blastozoan assem-blages, with the appearance of new clades able to colonize carbon-ate hardgrounds, which for the first time were becomingwidespread in warm to temperate shallow-water environments(Brett et al. 1983). Unfortunately, the fossil record for this impor-tant time interval is extremely poor in most parts of the world(Fig. 13.1). Apparently, eocrinoids with holomeric stems(adapted to life on firm grounds and shell fragments), which firstappeared at the base of Cambrian Series 3 in West Gondwana,expanded into these new niches (hardgrounds) during the Furon-gian (Zamora et al. 2010). Trachelocrinids are an example ofsuch rapidly diversifying eocrinoids adapted to life on hardgroundsacross the shallow carbonate platforms of Laurentia (Sprinkle1973; Sumrall et al. 1997). In the Furongian of Siberia, Sumrallet al. (2003) identified at least six different eocrinoid taxa (includ-ing both gogiids and columnal-bearing forms) based on poorlyarticulated and disarticulated material.

Rhombifera

Rhombiferans are one of the dominant groups of Ordovician echi-noderms (Lefebvre et al. 2013), but the roots of this clade can betraced back into the Cambrian. Unlike their Ordovician relatives,Cambrian rhombiferans lacked specialized respiratory structures(rhombs), and their thecal plates were not standardized intoregular rows (Fig. 13.3h). Basal members include a newgroup called dibrachicystids (Zamora & Smith 2012) bearingtwo feeding appendages, thecal plates with respiratory folds anda tripartite stem with distal holomeric columnals. Dibrachicystidswere originally described from isolated plates (Ubaghs 1967,1987). These distinctive plates displaying a strong radial ornamen-tation are frequently reported under the name ‘Eocystites’. Articu-lated specimens of dibrachicystids have been found in CambrianStage 5 rocks of both France and Spain (Zamora 2010; Zamora& Smith 2012). Disarticulated dibrachicystid-like plates of thesame age have been reported from many other areas of West Gond-wana, such as Germany, Morocco, Sardinia and Ossa–Morena(southern Iberian Peninsula; Loi et al. 1995; Gil Cid & Domınguez

S. ZAMORA ET AL.162




1998; Sdzuy 2000). Finally, Kouchinsky et al. (2011, fig. 38A–F)described a series of isolated plates from the Drumian Stage ofSiberia that fit in size and morphology with the proximal stemplates of dibrachicystids.

In the Furongian, more glyptocystitid-like rhombiferansappeared both in Baltica (e.g. Cambrocrinus from Poland; Dzik& Orłowski 1993) and Gondwana, such as Australia (Ridersia wat-sonae; Jell et al. 1985) and southern France (Velieuxicystis,Fig. 13.3h, and Barroubiocystis; Ubaghs 1998). The widespreaddistribution of glyptocystitid-like Gondwanan taxa in Furongiantimes is confirmed by the presence of isolated plates in both Koreaand Wales (B. Lefebvre & S. Zamora, pers. obs. 2002, 2011).

Cincta

Cinctans are a small but distinctive clade of Cambrian Series 3echinoderms. The cinctan skeleton consists of two parts: themain body (or theca) and a posterior appendage (or stele;Fig. 13.4d). The theca is constructed of a ring of large marginalplates, the so-called cinctus. It is dorsally and ventrally coveredwith two membranes of tessellate plates. The main body orificesare situated in the anterior part of the theca, the mouth piercingthe cinctus and the anus piercing the supracentral integument.One or usually two food grooves run laterally around the anteriorpart of the cinctus. These grooves converge onto the mouth, whichis situated in the anterior right part of the cinctus. The stele is a pos-terior appendage, considered to be a prolongation of the cinctus(Jefferies 1990; Friedrich 1993; Zamora & Smith 2008).

Cinctans apparently underwent rapid evolution within a shorttime range (Cambrian Series 3; Smith & Zamora 2009), andhave a relatively restricted palaeobiogeographical distribution(West Gondwana and Siberia). They have not been reportedfrom either Baltica or Laurentia. The oldest undisputed cinctanremains correspond to isolated plates from the Leonian (Stage 5)Mansilla Formation (Iberian Chains, Spain). The oldest namedspecies is Protocinctus mansillaensis (Rahman & Zamora 2009)from the same formation, but slightly younger beds (upperLeonian). The Czech species ‘Asturicystis’ havliceki is probablyalso of similar age (late Leonian), although a precise stratigraphi-cal correlation remains difficult to establish between Bohemiaand Spain (Fatka & Kordule 2001). Slightly younger are Asturicys-tis jaekeli and Sotocinctus ubaghsi from the Cambrian Stage 5 ofthe Cantabrian Mountains (North Spain; Sdzuy 1993). Drumiancinctan assemblages are more diverse and widespread in manyWest Gondwanan areas (France, Germany, Morocco, Sardiniaand Wales), and are characterized by Elliptocinctus, Gyrocystis(Fig. 13.4e), Lignanicystis (Fig. 13.4c), Progyrocystis, Sucocys-tis, Undatacinctus (Fig. 13.4f) and several species left in opennomenclature (Cabibel et al. 1959; Schroeder 1973; Termier &Termier 1973; Friedrich 1993, 1995; Gil Cid & DomınguezAlonso 1995a, b; Loi et al. 1995; Zamora et al. 2007a; Zamora& Smith 2008; Zamora & Rahman 2008; Smith & Zamora 2009;Zamora & Alvaro 2010). The Drumian cinctans Trochocystitesbohemicus (Fig. 13.4d) and Trochocystoides parvus are endemicfrom Bohemia. Another endemic genus was reported in theDrumian of Wales, based on poorly preserved material (Friedrich1993). The Siberian record of cinctans consists of two endemicgenera, Nelegerocystis and Rozanovicystis, both described fromthe Drumian (Rozhnov 2006).

Cinctans become extinct close to the Drumian–Guzhangianboundary. The youngest species include Undatacinctus melendezi,U. aff. quadricornuta, and Sucocystis acrofera, all from Franceand Spain (West Gondwana).

Ctenocystoidea

Ctenocystoids are possibly the most puzzling and enigmatic groupof Cambrian echinoderms. They have a nearly bilateral theca,

framed by one, or more frequently, two superposed rings of mar-ginal plates (Fig. 13.4b), and lack a stem. As in cinctans, bothupper and lower thecal surfaces are covered by relatively flexi-ble, tessellated membranes. The anterior part of the ctenocystoidtheca is formed by a ctenidium, a specialized organ covering themouth composed of a series of highly modified, tooth-like plates.A single posterior aperture represents the anus (Robison & Sprin-kle 1969; Domınguez Alonso 1999; David et al. 2000; Rahman &Clausen 2009). Ctenocystoids were relatively short-ranged fos-sils, restricted to Cambrian Series 3 but achieving a remarkablycosmopolitan palaeobiogeographical distribution. They may, how-ever, have a longer range as one possible Late Ordovician cteno-cystoids has been described (Domınguez Alonso 2004).

Ctenocystoids with a double-plated marginal ring have beenreported from western Laurentia (Ctenocystis utahensis,Fig. 13.4b, and C. colodon; Robison & Sprinkle 1969; Ubaghs &Robison 1988), and several Gondwanan regions, such as Australia(Ctenocystis jagoi; Jell et al. 1985), Bohemia (Etoctenocystisbohemica; Fatka & Kordule 1985), France (C. smithi; Ubaghs1987) and Wales (Pembrocystis gallica; Domınguez Alonso2004). Undescribed ctenocystoid species are known in bothMorocco (S. Clausen, pers. obs. 2011) and northern Spain (e.g.Ctenocystis sp. and Etoctenocystis sp.; Zamora 2011). Ctenocys-toids with a single-plated marginal ring are restricted to WestGondwana. They were originally reported from Cambrian Stage5 of southern France (Montagne Noire; Courtessolea moncere-torum; Domınguez Alonso 2004; Fig. 13.4k). Courtessolea hasbeen found in Bohemia and Spain but awaits formal description(Zamora 2010; O. Fatka, pers. obs. 2011). A distinctive form,bearing highly reduced thecal plating, occurs in Poland (Jugoszo-wia; Dzik & Orłowski 1995). Isolated ctenocystoid plates havebeen reported from Baltica (Sweden; Domınguez Alonso 2004).

Soluta

Solutans are a small, extinct clade of echinoderms that range fromthe Cambrian to the Early Devonian. They have two unequalappendages, inserted at opposite ends of the body (theca)(Fig. 13.4a). The short, anterior appendage is made from biserial(rarely uniserial) flooring plates and two opposite sets of coverplates. It has been interpreted either as an arm (e.g. Smith 2005)or a brachiole (e.g. David et al. 2000). The long posterior appen-dage is a stalk-like structure called a stele. In the most primitivegenus (Coleicarpus; Fig. 13.4a), the stele is a polyplated, unorga-nized holdfast. In all other taxa (including the contemporary Cas-tericystis), this appendage is organized into a highly flexible,proximal region and a rigid, distal portion whose plating differson upper and lower surfaces. The mouth was located at the baseof the feeding appendage. In most taxa, both the gonopore andthe hydropore are close to the insertion of the feeding appendage.In all solutans, the anus forms a large thecal orifice, opening later-ally, and close to the insertion of the stele.

The Cambrian record of solutans is extremely poor, andrestricted to Laurentia. Solutans did not appear in Gondwanauntil the Early Ordovician, and in Baltica until the Mid Ordovician(see Lefebvre et al. 2013). The earliest record of this class is aquestionable unnamed and unillustrated form from the CambrianSeries 2 of Pennsylvania (Derstler 1975, 1981). Two generawere described from Cambrian Series 3 deposits of Utah: Colei-carpus and Castericystis (Ubaghs & Robison 1985, 1988; Daley1995, 1996). Coleicarpus is the most primitive solutan knownso far (Daley 1996; David et al. 2000). It attached to skeletaldebris on the sea floor and/or to any hard object by its stele. Cas-tericystis is identical in age but has a more derived stele mor-phology, which was used for attachment only during juvenilestages (Daley 1995). A third unnamed species based mostly onseparate steles was mentioned and illustrated from CambrianSeries 3 deposits in Nevada (Sprinkle 1973, plate 28, fig. 4).





Their Furongian record is limited to two complete but unnamedsolutans that were briefly described from northern Alabama (Laur-entia) and an unnamed species (Fig. 13.4g), also from Laurentia,described from two isolated steles (Bell & Sprinkle 1980;Sumrall et al. 1997).

Stylophora

Stylophorans are an extinct class of echinoderms (Cambrian Series3–Late Carboniferous), characterized by a bipartite body organiz-ation (Fig. 13.4i), consisting of a single appendage and a flattened,fundamentally asymmetrical theca. Their phylogenetic positionwithin the Phylum Echinodermata remains controversial. Theymay represent primitive, relatively basal echinoderms (Ubaghs1968b; Smith 2005) or a highly derived clade possibly related toblastozoans (Sumrall 1997) or to arm-bearing echinoderms (e.g.asterozoans and crinoids; David et al. 2000; Lefebvre 2003). Theclass Stylophora is traditionally subdivided into two orders,Cornuta (Jaekel 1901) and Mitrata (Jaekel 1918). The cornutes(Cambrian Series 3–Late Ordovician) have a relatively rigidappendage, and a generally light, delicate theca framed bynarrow marginal plates, whereas the mitrates (Furongian–LateCarboniferous) have a comparatively more highly flexible distalappendage and a more massive theca made from enlarged andthickened marginals and centrals (Lefebvre 2001).

Stylophorans first appeared in Cambrian Series 3. The oldestand most primitive members of the class are heavily plated(‘armoured’) Ceratocystis-like taxa (Fig. 13.4i), which wereapparently adapted to relatively warm to temperate, shallowwaters (Lefebvre 2007). These basal stylophorans were restrictedto Baltica and West Gondwana. In Baltica, Ceratocystis-liketaxa are represented by isolated plates from Denmark (Berg-Madsen 1986) and several complete, fully articulated specimensfrom Sweden (B. Lefebvre, pers. obs. 2009). Armoured stylophor-ans are much more abundant in West Gondwana, where they havebeen reported from Bohemia (Pompeckj 1896; Jaekel 1901; Bather1913; Ubaghs 1967; Jefferies 1969), southern France (Ubaghs1987), Germany (Sdzuy 2000; Rahman et al. 2010), Morocco(Clausen & Smith 2005), Sardinia (Loi et al. 1995), Spain (GilCid & Domınguez Alonso 1998; Zamora 2010) and Wales (Jeff-eries et al. 1987). Like cinctans and several clades of trilobites,the armoured stylophorans disappeared before the Furongian,probably as a consequence of habitat loss related to a globalregression (Zamora & Alvaro 2010).

The first cothurnocystid cornutes appeared slightly later,although still in Cambrian Series 3, and are found in what wereonce soft substrates deposited in relatively deep, quiet

environments (Lefebvre 2007). Cothurnocystids were thus prob-ably ‘psychrospheric’ (cold water-adapted) taxa, with a near-cosmopolitan distribution. They have been reported fromwestern Laurentia (e.g. Archaeocothurnus bifida, Ponticulocarpusrobisoni; Ubaghs & Robison 1988; Sumrall & Sprinkle 1999),Siberia (Ponticulocarpus sp.; S. Rozhnov, pers. obs. 2002) andGondwana, such as Iran (Ponticulocarpus sp.; S. Rozhnov, pers.obs. 2002) and Spain (Zamora 2010).

The Furongian record of stylophorans is relatively rich com-pared with that of most other echinoderm groups. Although stillinsufficiently documented, this time interval marks a major turn-over in stylophoran assemblages. Cothurnocystid cornutes arethe dominant and most diverse Furongian stylophorans (Fig.13.4j). Their distribution is near-cosmopolitan, with occurrencesreported from Laurentia (e.g. Cardiocystella prolixora; Sumrallet al. 1997, 2009) and various Gondwanan regions such as SouthChina (Han & Chen 2008), southern France (Ubaghs 1998) andKorea (e.g. Sokkaejaecystis serrata; Lee et al. 2005). The Furon-gian interval also has recorded the first occurrences of severalnew clades of stylophorans. For example, Drepanocarpos austra-lis (Australia; Smith & Jell 1999) is the oldest and most primitiveknown member of hanusiid cornutes (Lefebvre 2001, 2007).Mitrates, long thought to originate in the Early Ordovician, arenow known to extend back at least to the Furongian. The heavilyplated stylophoran Lobocarpus vizcainoi (Fig. 13.4h) fromsouthern France (Ubaghs 1998) has been reinterpreted as a poss-ible basal mitrate (Lefebvre 2000, 2001), while isolated plates ofpeltocystids and several fully articulated specimens of primitivemitrocystitids close to Chinianocarpos and/or Vizcainocarpusare now known from Korea (Lefebvre 2007) and South China(B. Lefebvre, pers. obs.).

The conspicuous record of disarticulated

echinoderm ossicles

Until recently, our understanding of echinoderm diversity andevolution was based almost entirely on analysis of the distributionof well-preserved, articulated specimens. These, however, comepredominantly from relatively deep-water palaeo-environmentsbelow storm-wave base, where taphonomic conditions weremore favourable for such preservation. Because the distributionof articulated specimens is possibly taphonomically biased, animportant and possibly more complete record of echinoderms isprovided by isolated plates, as these are much more commonlyencountered than articulated specimens in a much wider range ofpalaeo-ecological settings (Fig. 13.5, see Supplementary material).


isolated plates (scanning electron

microscope photographs). (a, e). Uniserial

element from the Cambrian Series 2 of

Siberia (SMNH X 4047). (b, c) Stem

columnals from the Cambrian Series 3 of

Sardinia (FG 535/4_3, FG 535/4_5). (d)

Epispire bearing plate from the Cambrian

Series 3 of Jordan (FG 619/7_115). (f, g)

‘Eocystitid’ proximal stem plate from the

Cambrian Series 3 of Siberia (SMNH X

4016). (h) Ambulacral flooring plate from

the Cambrian Series 3 of Siberia (SMNH X

4046). Abbreviations: SMNH, Swedish

Museum of Natural History, Stockholm

(Sweden); FG, Geological Institute of the

Technische Universitat Bergakademie

Freiberg (Germany).

S. ZAMORA ET AL.164




Some Cambrian limestones are packed full of echinoderm ele-ments, and those preserved as iron oxide, glauconite, phosphateor silica replacements can be isolated and studied in 3D afteracid etching (e.g. Berg-Madsen 1986; Clausen & Smith 2005,2008). Preliminary investigation of how isolated skeletal elementsfrom Cambrian limestones are distributed in space and timesuggests that they provide important additional information. Thestudy of isolated elements enhances our understanding of echino-derm palaeobiogeography in two major ways.

(1) Echinoderm plates with their distinctive stereom structureare easily identified from polished rock sections, and theirappearance in the rock record provides evidence of whenechinoderms first appeared across different palaeobiogeogra-phical regions. Figure 13.6 summarizes the first occurrenceof echinoderm plates in the rock record in five major biogeo-graphical regions. In two of the five regions, isolated echino-derm plates have been found in significantly to slightly olderdeposits than those yielding articulated specimens. Thistabulation (Fig. 13.6) demonstrates that the echinodermsfirst appeared approximately contemporaneously (slightlyabove the Terreneuvian-Stage 3 boundary) in Laurentia,Siberia and Gondwana, later in the geological record thanother phyla, such as arthropods, brachiopods or molluscs(Landing et al. 2010).

(2) While the majority of echinoderm plates are non-diagnosticand offer little information other than simply the presence/absence of echinoderms, some are distinctive and taxon-diagnostic (i.e. ctenoidal plates from ctenocystoids, stylo-cones from stylophorans, marginal frame and opercularplates of cinctans, marginal plates from some edrioasteroids,holocolumnals from eocrinoids or the proximal stem platesfrom ‘eocystitids’). These can provide important evidencefor the occurrence of certain taxa at times or in palaeogeogra-phical regions where no articulated material is known(Fig. 13.6). For example, diagnostic plates from eocrinoidsprovide the only records we have that members of thisgroup existed in Baltica and Australia during the Cambrian.In Australia, distinctive silicified holocolumnals can beextracted after etching of bioclastic limestones long beforethe earliest record of articulated blastozoans with holomeric

stems. Isolated stylocones in Morocco provide the earliestrecord of ceratocystid stylophorans in West Gondwana(Clausen & Smith 2005). Finally, numerous localities areknown where isolated cinctan marginal plates are abundantyet from where named species have yet to be recorded. Iso-lated elements can also reveal unexpected diversity, as inthe case of the variety of distinct holocolumnal morphotypesfound by Clausen & Smith (2008) in Cambrian Stage 5 con-densed levels of Morocco. The recognition that many groupsappeared earlier in shallow carbonate platforms than in off-shore clayey substrates indicates that an important part ofthe early record of echinoderm evolution from relativelyshallow settings is missing.

Palaeobiogeographical patterns

First appearances in Laurentia and Gondwana

Figure 13.6 charts the first occurrence data for our eight echino-derm clades in space and time. Evidence for echinoderms firstappears at same time in different palaeocontinents (early Series2). However, there is a strong endemic constraint in the earliestrecords, with the first identifiable echinoderms from Laurentiabeing helicoplacoids and edrioasteroids. Eocrinoids (Imbricataand Gogiida) appeared one stage later. In contrast, the earliestrepresentatives from Gondwana of similar age (Cambrian Stage3) are gogiid eocrinoids (Alanisicystis from Ossa–Morena andMorocco). Edrioasteroids are present but do not appear in theGondwanan record until slightly later (?Stromatocystites sp.from Northern Spain and Edriodiscus and Stromatocystites fromAustralia). Despite these differences, gogiid eocrinoids andedrioasteroids are consistently the first to appear in the fossilrecord across all regions (Fig. 13.6).

Cinctans, ctenocystoids, solutans, stylophorans and most othergroups of radiate echinoderms all appear in Cambrian Stage 5.The clear distinction that exists between these groups right fromthe very start of their records, and their near synchronicity of appear-ance, strongly suggests that we are missing the earliest part oftheir history and that all these groups most likely diverged during

Fig. 13.6. Table charting the first

occurrences of eight major groups of

echinoderm in each of five biogeographical

regions. The first record of stereom in plates

and of holomeric columnals in the rock

record is marked.





Cambrian Series 2 or earlier. Consequently, the order in whichgroups appear in the fossil record must be treated with caution.

Biogeographical relationships of echinoderm assemblages

The closeness of relationships shown by the Cambrian echino-derms can be assessed by analysing the biogeographical distribu-tion of individual clades. Although there is no agreed globalphylogeny for all echinoderms, many of the constituent groupsare widely recognized and accepted as potentially monophyletic.For example, there has never been any disagreement that cinctansand ctenocystoids form well-defined clades. Each of these cladesinhabited one or more biogeographical regions; by analysing thepattern of shared occurrences, the degree of similarity of thoseregions can be established using Parsimony Analysis of Endemism(Rosen & Smith 1988; Da Silva & Oren 2008).

Here we map the distribution of 21 Cambrian clades(Table 13.1) across seven palaeogeographical regions [Laurentia(USA and western Canada), West Gondwana (Morocco, southernEurope and Bohemia), Far East Gondwana (China and Korea),Australia, Arabian margin (Turkey and Iran), Baltica andSiberia]. The distribution of each clade is summarized inTable 13.1. Figure 13.7 shows the results of a Parsimony Analysisof Endemism carried out under Dollo Parsimony (which prohibitsthe same taxon from arising more than once independently indifferent geographical areas). Only four of these regions (Lauren-tia, West Gondwana, East Gondwana and Australia) are suffi-ciently densely sampled to provide reliable patterns; in other,poorly sampled, regions our inability to distinguish betweengenuine absences from the region and absences from inadequatesampling makes interpretation problematic.

Turning first to the four regions for which we have a moderatelygood sample, our analysis clearly distinguishes between a pairingof Laurentia and East Gondwana and a pairing of Australia andWest Gondwana. Laurentia and East Gondwana both uniquelyhave lyracystids and kailidiscid edrioasteroids as part of theirfauna, while Australia and West Gondwana share isorophids,stromatocystitids and cambrasterids. Baltica has representativesof just three echinoderm clades, one of which is shared with Aus-tralia and West Gondwana, and another (glyptocystitid-like rhom-biferans) shared uniquely with West Gondwana. The Arabianmargin of Gondwana has just two clades, the near-cosmopolitancothurnocystid stylophorans and one shared with Baltica, Austra-lia and West Gondwana (stromatocystitids). The pairing of theArabian margin with Baltica is probably a bias of poor samplingas they are united only by implied secondary losses of lineages.Finally, Siberia has representatives of four clades and providesa mixed signal. Stylophorans are present in Siberia, but thesedisplay a near-cosmopolitan distribution. Column-bearing eocri-noids are also present, but these are shared with both Laurentiaand West Gondwana and are therefore uninformative. The same

is true for early glyptocystitids, a taxon that Siberia shareswith West and East Gondwana, as well as with Australia. How-ever, Siberia uniquely shares with West Gondwana the presenceof cinctans, suggesting that the Siberian echinoderm fauna maybe closer to that of West Gondwana and Australia than to that ofLaurentia and East Gondwana.

Laurentia has the longest branch of any region, possibly reflect-ing the better sampling available there. Four of the six endemicclades in our analysis come from Laurentia.

Alpha diversity in space and time

The Cambrian fluctuations of echinoderm diversity is partlydriven by the distribution of appropriate facies where echinodermshave been preserved as articulated specimens (Smith 1988;Zamora & Alvaro 2010) and in part by important ecologi-cal changes (i.e. the so-called Cambrian Substrate Revolution;Dornbos 2006; Zamora et al. 2010). This means that a directreading of the fossil record may inform us just as much aboutsampling in space and time as it does about echinoderm evolu-tion. A simple plot of the raw data (Fig. 13.1d, e) might betaken to imply that Cambrian Series 3 was a time of palaeobio-geographical expansion for many echinoderm classes, while the

Fig. 13.7. Biogeographical relationships of seven regional Cambrian faunas

based on a Parsimony Analysis of Endemism of 21 echinoderm clades

(Table 13.1) under Dollo Parsimony. Important shared clades are indicated on the

diagram that link two or more regions. Note that very low numbers of taxa

recorded from Baltica and the Arabian margin mean that these regions are united

only by shared secondary losses, absences that probably reflect undersampling of

these regions rather than biogeographical signature. Boxes indicate important

echinoderm taxa that characterize different regions of the tree.

Table 13.1. Distribution of 21 Cambrian echinoderm groups in seven palaeogeographical regions

Major clades 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Laurentia 1 0 1 1 0 1 0 0 0 0 1 0 1 1 1 1 1 0 0 1 0

Baltica 0 0 0 1 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0

West Gondwana 0 1 0 1 1 1 1 1 1 1 0 1 1 1 0 0 1 1 0 0 1

Arabian margin 0 0 0 0 0 1 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0

Siberia 0 1 0 0 0 1 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0

East Gondwana (Australia) 0 0 0 1 0 1 0 1 0 1 0 1 0 0 0 0 0 1 1 0 0

East Gondwana (China and Korea) 0 0 0 0 0 1 1 1 0 0 0 0 0 1 0 1 0 0 0 1 0

Taxa numbered as follows: 1, helicoplacoids; 2, cinctans; 3, solutans; 4, ctenocystoids; 5, ceratocystitid stylophorans; 6, cothurnocystid stylophorans; 7, mitrate

stylophorans; 8, primitive glyptocystitid rhombiferans; 9, eocystitid rhombiferans; 10, stromatocystitid edrioasteroids; 11, edrioasterid-like edrioasteroids; 12, isorophid

edrioasteroids; 13, imbricate eocrinoids; 14, gogiid eocrinoids; 15; trachelocrinid eocrinoids; 16, lyracystid eocrinoids; 17, column-bearing eocrinoids; 18, cambrasterid

edrioasteroids; 19, edrioblastoid edrioasteroids; 20, kailidiscid edrioasteroids; 21, lichenoidid eocrinoids.

S. ZAMORA ET AL.166




Furongian recorded a marked decline. Assemblages in CambrianSeries 3 were dominated by cinctans in many West Gondwananareas and by gogiid eocrinoids in East Gondwana (China) andLaurentia. Gondwanan assemblages from offshore and relativelyshallow-water environments are apparently more diverse thanthose from deeper-water settings of East Gondwana and Laurentia.There are other groups that dominate benthic assemblages insome specific levels but are very rare in others. This is the casefor edrioasteroids (e.g. Stromatocystites), ctenocystoids (e.g. Cte-nocystis utahensis) or stylophorans (e.g. Ceratocystis perneri).

Furongian communities are dominated by eocrinoids andstylophorans, with fewer solutans and edrioasteroids, in Laurentia(Sumrall et al. 1997). Development of the first carbonate hard-grounds in Laurentia may have allowed the immigration ofGondwanan faunas that were pre-adapted to such substrates inCambrian Series 3 firmgrounds (Zamora et al. 2010). In France,rhombiferans and stylophorans were the dominant groups inmixed (carbonate–siliciclastic) environments.

However, we know that sampling is possibly much better inCambrian Series 3 than in lower Furongian strata. To reduce thebias introduced by uneven sampling, we use counts of thenumber of species recorded from single formations. This measuresalpha diversity (i.e. within formation species richness), and allowsus to compare diversity patterns across regions that have verydifferent numbers of echinoderm-bearing formations. The resultsare shown in Figure 13.8 and there are several notable featuresto emerge from this:

(1) Cambrian Series 2 formations typically yield two species,each from its own monotypic level. The Poleta Formation(Cambrian Stage 4) of Laurentia appears to be an anomaly,as it has yielded four species (three helicoplacoids and oneedrioasteroid). However, in this case one helicoplacoid andthe edrioasteroid (which is known from numerous isolatedplates) completely dominate the assemblage and the othertwo are known only from single specimens. Formationsthat contain a significant alpha diversity first appeared inCambrian Stage 5 of West Gondwana where, for the firsttime, we begin to find as many as eight species representedby numerous specimens and preserved in a single bed (e.g.the Purujosa section; Zamora 2010). This implies that therewas a genuine increase in echinoderm diversity going intoCambrian Series 3. Part of the reason why there are so

many formations yielding echinoderms in Series 3 isbecause echinoderms themselves were becoming more abun-dant and widespread.

(2) Lower Furongian formations show diversity levels that are aslow as those of the Stage 3, suggesting that there is a genuinedrop in diversity at this time. This pattern is repeated in Laur-entia, West Gondwana and China. However, we cannotdiscount the possibility that this drop is because we aresampling a smaller range of palaeo-environments than forother time spans. There is no doubt that in many regionsthis is an interval characterized by regional regressionswhich induced the onset of stratigraphical gaps and arecord of coarse-grained substrates that precluded the pre-servation of fossiliferous strata.

(3) Later Furongian formations on average have the highestlevels of alpha diversity (Fig. 13.8c) of any Cambrian stagein Laurentia, but in West Gondwana and China alpha diver-sity only returns to match levels achieved in CambrianSeries 2.

Conclusions

The compilation of a complete inventory of fossil echinodermoccurrences throughout the Cambrian comprises records of botharticulated specimens and isolated echinoderm plates. Analysisof these data shows that:

(1) The Cambrian record of echinoderms spans something like30 million years. During this time faunas changedcompositionally.

(2) The distribution of formations yielding fossil echinoderms isnot evenly spread through space and time. Siberia, theArabian margin of Gondwana, South America and Balticaare particularly under-represented and only Laurentia pro-vides an unbroken record throughout the Cambrian.

(3) The record of isolated echinoderm plates, although oftenoverlooked, yields important data on echinoderm distributionin space and time. Specifically, it provides the only evidenceof eocrinoids from Australia and Baltica.

(4) The earliest echinoderms, known from isolated stereom-bearing plates, appear contemporaneously in Laurentia,Siberia and Gondwana.

(a)

(b) (c)

Fig. 13.8. Echinoderm alpha diversity

through the Cambrian based on articulated

specimens. (a) Table of mean alpha

diversity (average number of species per

formation per stage) for six major

biogeographical regions (as in Fig. 13.1

colours indicate relative level of alpha

diversity). (b) Mean global alpha diversity

in the 10 Cambrian stages. (c) Comparison

of mean alpha diversity per stage in West

Gondwana and Laurentia.





(5) Evidence for a number of groups is first provided by iso-lated elements, and only later by articulated fossils.Onshore environments, such as shallow-water carbonateplatforms, have a comparatively poor record of articulatedspecimens, and thus our view of echinoderm evolution atthis time is biased.

(6) Raw diversity over time points to a major increase in diver-sity, concentrated in West Gondwana, during CambrianStage 5 and to very low diversity levels during the Guzhan-gian and Paibian. However, analysis of alpha diversityshows that much of this variation may reflect samplingbiases, although there is a genuine rise in diversity throughthe Cambrian in both Laurentia and Gondwana.

(7) Parsimony Analysis of Endemicity indicates a close relation-ship between the echinoderm faunas of Australia and WestGondwana and between those of East Gondwana (Chinaand Korea) and Laurentia. Low sampling in other regionsmakes interpretation problematic.

This work is a contribution to the Projects Consolıder MURERO number

CGL2006-12975/BTE from MEC and to the project CGL 2010-19491 from

MICINN-FEDER, INSU (SYSTER) project AO2012-786879 ‘contextes tem-

poral, environnemental et ecologique de l’initiation de l’intervalle glaciaire au

Paleozoıque inferieur’, and to the team ‘Couplages Lithosphere-Ocean-Atmos-

phere’ (UMR CNRS-UPS-IRD 5563). This paper is also a contribution of the

team ‘Vie Primitive, biosignatures, milieux extremes’ of UMR CNRS 5276,

and to the ANR project RALI ‘Rise of Animal Life (Cambrian–Ordovician) –

organization and tempo: evidence from exceptionally preserved biota’. We

thank I. Perez (MEC-FSE) for preparing the plates and some photographs of

this paper and A. Rushton (London) for his information about the Cambrian of

Wales. A. Kouchinsky acknowledges support from the NordCEE project grant

DNRF53 to D. Canfield from Danish National Research Foundation (Danmarks

Grundforskningsfond). Two reviewers, T. Guensburg (USA) and M. Reich

(Germany), provided important comments that greatly improved the resulting

manuscript.

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