Palaeogeography, Palaeoclimatology, Palaeoecology 361–362 (2012) 38–48

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Palaeogeography, Palaeoclimatology, Palaeoecology

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Macroevolutionary transition in crinoids following the Late Ordovician extinctionevent (Ordovician to Early Silurian)

William I. Ausich a,⁎, Bradley Deline b

a School of Earth Sciences, 125 South Oval Mall, The Ohio State University, Columbus, OH 43210, United Statesb Department of Geosciences, University of West Georgia, Carrollton, GA 30118, United States

⁎ Corresponding author.E-mail addresses: ausich.1@osu.edu (W.I. Ausich), bd

0031-0182/$ – see front matter © 2012 Elsevier B.V. Allhttp://dx.doi.org/10.1016/j.palaeo.2012.07.022

a b s t r a c t

a r t i c l e i n f o

Article history:Received 8 May 2012Received in revised form 12 July 2012Accepted 20 July 2012Available online 27 July 2012

Keywords:MacroevolutionCrinoidOrdovicianSilurianExtinction

The end-Katian (Late Ordovician) crinoid mass extinction triggered the change from the Early to the Middle Pa-leozoic crinoid evolutionary faunas (CEFs). This was a change from diplobathrid camerate-disparid-hybocriniddominated faunas to faunas dominated by monobathrid camerate, cladid, and flexible crinoids. All clades suf-fered extinctions at the end-Katian event, but diplobathrid camerates, disparids, and hybocrinids suffered higherrates of extinction. The primary amount of diversification occurred in clades that would become dominant dur-ing the Silurian. However, the formation of the characteristic Middle Paleozoic CEF was protracted beyond theLate Ordovician extinction event. Monobathrid camerates and flexibles diversified through the Llandovery, butboth dendrocrinid and cyathocrinid cladids did not diversify until later. Monobathrid camerate genera and fam-ilies diversified, the flexible diversification was largely at the genus level, cyathocrine diversification was largelyamong families, and dendrocrinids did not diversify significantly until after the Llandovery. Overall disparity de-creased during the end-Katian extinction by reducing the disparity within each clade. Disparity remained fairlyconstant during the Hirnantian but increased significantly during the Llandovery by both increasing disparitywithin clades and expanding the morphospace of the disparids due to the radiation of families with new mor-phologies. North America was the biogeographic center of origination for the families that survived to becomedominant Silurian clades.

© 2012 Elsevier B.V. All rights reserved.

1. Introduction

A significant discontinuity in crinoid evolutionary history occurredbetween the Ordovician and Silurian. This macroevolutionary changehas been recognized since at least byMoore (1950) andwas recognizedmore recently as the transition between the Early andMiddle Paleozoiccrinoid evolutionary faunas (CEF) (Baumiller, 1993; Ausich et al., 1994).Most primary crinoid cladeswere part of both evolutionary faunas, suchthat the transition represented a change in dominance between crinoidclades. Assemblages of the Early Paleozoic CEF were typically dominat-ed by disparid, diplobathrid camerate, and hybocrinid crinoids (Fig. 1,Table 1). In contrast, typical middle Silurian examples of theMiddle Pa-leozoic CEF were characterized by assemblages dominated bymonobathrid camerates, flexibles, and primitive cladids. The advanced,pinnulate cladid crinoids became important during the Mississippian,following the transition to the Late Paleozoic evolutionary fauna(Ausich et al., 1994; Kammer and Ausich, 2006).

This contribution considers the demise of the Early Paleozoic CEFand the radiation of the Middle Paleozoic CEF. We examine the disas-sembly of the Early Paleozoic CEF, the recovery response of elementsof the Early Paleozoic CEF versus those of the Middle Paleozoic CEF,

eline@westga.edu (B. Deline).

rights reserved.

and the timing of the assembly of the newMiddle Paleozoic CEF follow-ing the end-Katian extinctions. There are several models for evolution-ary transitions such as refilling a vacated niche following an extinctioncompared with direct competition between clades. With a transitionthat occurs near a mass extinction it is assumed that faunal transitionwas largely facilitated by the extinction, which can be tested by aclose examination of the faunal changes through the interval.

Historically, the most notable aspect of the Hirnantian (latest Or-dovician) to Llandovery (Early Silurian) crinoids has been the lackof information. Although authors have typically not discussed thispoint directly, it is evident from published diagrams depicting crinoidevolutionary history (e.g., Moore and Laudon, 1943; Moore, 1950;Moore and Teichert, 1978). Diverse, shelly faunas have also been rel-atively poorly known globally during this interval, because epiconti-nental sea habitats were largely eliminated due to sea level fallassociated with the end-Ordovician glaciation on Gondwana. Since1980, a concerted effort to discover new latest Ordovician and earliestSilurian crinoid faunas has been successful. For example, the numberof Llandovery species has increased from 26 to 140 (Fig. 2). Withthese new data, the transition between crinoid macroevolutionaryfaunas can now be examined in much greater detail both in termsof taxonomic diversity as well as morphologic disparity.

The examination of both diversity and disparity can give a morethorough view of macroevolutionary changes. These two metrics are

Fig. 1. Spindle diagrams of generic diversity of major Ordovician to Llandovery crinoid clades.

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inherently related, but they may have dramatically different patternsthrough time (Foote, 1993). A decrease in disparity can be caused byeither by an overall reduction in the range of morphologies present orby filling of morphospace with morphologically similar organisms. Incontrast, an increase in disparity can be caused by the evolution ofnew morphologic features or by diluting the morphospace leavingonly morphologically distinctive organisms. Therefore, the couplingof these two measures can better document the Early Paleozoic tran-sition in crinoid communities.

2. End-Ordovician extinctions

The second-most devastating collapse of the marine biosphere oc-curred during the transition from the Ordovician to the Silurian(Sepkoski, 1981; Raup and Sepkoski, 1982; Brenchley, 1989; Brenchleyet al., 1994, 2003; Bambach et al., 2004; and others). As many as 57%of genera and 25% of families are estimated to have suffered extinction,which dramatically affected the diversity of major groups and changedthe evolutionary fortunes of many clades, including the Crinoidea. Ex-amples of clades that were significantly impacted include brachiopods(Harper and Rong, 1995; Sheehan, 2001), conodonts (Barnes andBergström, 1988), crinoids (Eckert, 1988; Donovan, 1989, 1994;Sprinkle and Guensburg, 2004; Ausich and Peters, 2005; Peters andAusich, 2008), graptolites (Chen et al., 2003), reef faunas (Copper,2001), and many other clades (e.g., Hallam and Wignall, 1997; Finneyet al., 1999; Sheehan, 2001; Kaljo et al., 2008).

The Late Ordovician global climate cooled, culminating in aGondwanan glaciation (Brenchley et al., 2003). The catastrophiclosses of marine habitats during eustatic sea level drop associated

Table 1Major crinoid clades discussed in this paper.

Class CrinoideaSubclass ProtocrinidaSubclass AethocrinidaSubclass CamerataOrder DiplobathridaOrder Monobathrida

Subclass CladidaOrder DendrocrinidaOrder Cyathocrinida(primitive cladids are non-pinnulate)(advanced cladids are pinnulate dendrocrinids)

Subclass FlexibiliaSubclass Disparida

with ice buildup are generally regarded as the proximate causes of bio-sphere collapse (Berry and Boucot, 1973; McKerrow, 1979; Sheehan,2001). However, the ultimate cause for climate cooling is much lessclear. Many hypotheses have been forwarded including, among others,nutrient levels in the ocean, uplift of the continents, silicate and carbon-ate weathering, reduction in poleward heat transfer in the oceans,orbital eccentricity cycles, and gamma ray bursts (e.g., Kump et al.,1999; Sutcliffe et al., 2000; Sheehan, 2001; Herrmann et al., 2004a,b;Melott and Thomas, 2009; and Young et al., 2010). One puzzle aboutthis glaciation is that it occurred during a greenhouse Earth; andwhen originally recognized, the Hirnantian glaciation was regarded asan unusually short glacial epoch (Brenchley, et al., 1994). However,the Hirnantian glaciation is now recognized to have continued throughthe Llandovery (Grahn and Caputo, 1992, 1994; Brenchley et al., 2003;Ghienne, 2003; Herrmann et al., 2004a,b). Also, this glaciation is nowrecognized as geographically widespread, with glacial deposits knownin northern Africa (Ghienne, 2003; Ghienne et al., 2007), South America(Grahn and Caputo, 1992, 1994; Schönian and Egenhoff, 2007), and re-cently as far north as southeastern Europe (peri-Gondwana during theOrdovician) (Gutiérrez-Marco et al., 2010).

3. Previous work

3.1. Diversity counts of Ordovician crinoid radiations and extinctions

At least as early as Bassler and Moodey (1943) and Moore andLaudon (1943) authors have recognized an adaptive radiation in themiddle portion of the Ordovician. This radiation is referred to hereinas the Sandbian (Bergström et al., 2006, 2009) radiation; but using

Fig. 2. Cumulative percentage of described (and valid) Llandovery crinoid species fromthe 1840s through 2010.

Fig. 3. Ordovician through Llandovery genus biodiversity from sampled standardizedresampling (modified from Peters and Ausich, 2008). Note analysis with differentstage level chronostratigraphy, with end-Rawtheyan (R) equal to the end-Katian ofthe present manuscript. Mean values with plus or minus one standard error aregiven. Points to left of vertical dashed line are raw values, because occurrences orbiofacies were too few for meaningful analyses. A, sample standardized using occur-rences. B, sample standardized using biofacies.

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previous chronostratigraphic schemes, this has also been regarded asthe Caradoc, Mohawkian, or other radiations. This radiation wasdepicted in diagrams or discussed in detail by authors includingMoore and Laudon (1943), Moore (1950), Moore (1952), Mooreand Teichert (1978), Eckert (1988), Donovan (1994), Ausich (1998),Sprinkle and Guensburg (2004), Ausich and Peters (2005), andPeters and Ausich (2008). This middle Ordovician radiation was alsoexpressed in the data compendium of Sepkoski (2002) and the Paleo-Biology Database bpaleobd.org/cgi-bin/bridge.pl>.

3.2. New Hirnantian to Llandoverian crinoid faunas and resampling sta-tistical analyses

As discussed above, prior to 1980 Hirnantian and Llandoveriancrinoids were known from a limited number of localities. For example,Hirnantian crinoidswere described fromNorth America in the GirardeauLimestone of Missouri (Brower, 1973). Llandovery faunas known before1980 were few and typically isolated specimens rather than part of a di-verse assemblages, such as Calceocrinus pustulosus Brower, 1966(Manitoulin Formation, Ontario) or Calceocrinus centervillensus Foerste,1936; Calceocrinus insertus Foerste, 1919; Eomyelodactylus rotundatus(Foerste, 1919); and Clidochirus ulrichi Foerste, 1919 (Brassfield Forma-tion, Ohio).

Since 1980, new Hirnantian crinoids have been described from fivestratigraphic levels on Anticosti Island, Quebec (Ausich and Copper,2010). Two small faunas from Missouri are also recognized asHirnantian in age (Ausich, 1987c).

Knowledge of Llandovery crinoid faunas has expanded greatly since1980 (Ausich, 2009). Important new faunas include the Brassfield For-mation of Ohio (Aeronian) (Ausich, 1984a,b, 1985, 1986a,b,c, 1987a,b); Hopkinton Formation of Iowa (Telychian) (Witzke and Strimple,1981); the Bear Creek Shale, Cabot Head Formation, Reynales Forma-tion, and Wolcott Limestone of New York and Ontario (Eckert, 1984,1990; Eckert and Brett, 2001); and several new faunas from the UnitedKingdomand Ireland (Donovan and Sevastopulo, 1989; Donovan, 1993;Donovan and Harper, 2003; Donovan and Lewis, 2005; Fearnhead andDonovan, 2007a–d; Donovan et al, 2009).

Most recently, Ausich and Copper (2010) described Llandoverycrinoids from Anticosti Island, Quebec, Canada. A total of 44 generawere described from throughout the Llandovery of Anticosti Island,which has a nearly complete stratigraphic section through this inter-val. Despite these new discoveries, very few latest Ordovician andEarly Silurian crinoids are known from anywhere outside of NorthAmerican and western Europe. The latest set of analyses describedbelow incorporated these new data. This revised compendium pro-vides a new perspective on the transition from the early to the middlePaleozoic CEF.

3.3. End-Ordovician extinction analysis

After describing new Early Silurian crinoid faunas (Eckert, 1988;Eckert and Brett, 2001), Eckert (1988) considered the crinoid transitionbetween the Ordovician and Silurian to be a two-step decline based oncrinoid richness. The first step was the Caradoc/Ashgill “biotic crisis” inwhich approximately 50% of generic diversity attained in the previousradiation was lost. The second step for Eckert (1988) was theend-Richmondian (end-Rawtheyan of Peters and Ausich, 2008;end-Katian herein) extinction event in which only 30% genera ofcontained within his database survived from the Richmondian to theHirnantian.

Donovan (1988, 1989) clarified aspects of the paleogeographyfrom (Eckert, 1988), and he examined this transition using formtaxa based on only columnals and columns (Donovan, 1994). Thislargely independent column taxonomy was used to examine Ordovi-cian extinctions. Donovan (1994) also recognized a two-step

Ordovician extinction, but his two steps were the end-Rawtheyan(=end-Katian, herein) and the end-Hirnantian.

An earlier version of the data used for this study was evaluated inmany ways. Ausich and Peters (2005) examined rates of originationand extinction of genera from the basal Ordovician through theLlandovery and compared this to the compendium of Sepkoski(2002). Ausich and Peters (2005) concluded that previous interpreta-tions of the end-Ordovician interval had overestimated the rates ofextinction at the end-Ordovician and underestimated richness duringthe Early Silurian. This conclusion was significantly different from thesame analysis using only Sepkoski (2002) data, indicating netnon-random errors do occur within the Sepkoski compendium.

Peters and Ausich (2008) evaluated these data further usingsample-standardized subsampling. The rapid rise in crinoid biodiver-sity as recorded by previous authors (Sandbian, herein) was con-firmed. However, these methods identified only a single, statisticallysignificant extinction among Ordovician crinoids at the end-Katian(=end-Richmondian or end-Rawtheyan in previous stratigraphicusage) (Fig. 3). Therefore, the only statistically significant decline incrinoid genus richness occurred during the onset of glaciation andhabitat loss. This was the second step of extinction interpreted byEckert (1988) and the first step recognized by Donovan (1994).Neither a middle Ordovician decline nor an end-Hirnantian extinctionwas confirmed by Peters and Ausich (2008).

Morphological patterns have also been closely examined through-out this interval. Foote examined crinoid disparity throughout the

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Early Paleozoic (1994) and later the entire Phanerozoic (1999) andfound a rapid morphospace occupation during the Middle Ordovicianfollowed by little variation in the morphologic disparity during thistransition despite large fluctuations in taxonomic diversity. This stasisin disparity was hypothesized to be the result of constraints in ecolo-gy or development (Foote, 1994, 1999). Further, Deline (2009),Deline and Ausich (2011), and Deline et al. (2012) re-examined cri-noid morphological disparity through this interval with a higher tax-onomic and temporal resolution and found a larger degree ofvariation in disparity than was previously reported. These resultsare described in conjunction with the revised crinoid history below.

3.4. Additional analysis of Anticosti Island crinoids

The upper Katian through at least the early Telychian is well ex-posed on Anticosti Island, Quebec; and, as mentioned above, crinoidsfrom Anticosti Island are now well known through this interval(Ausich and Copper, 2010). Two further questions have been askedof crinoids from the Anticosti Basin through this interval, i.e., are cri-noids well sampled and did crinoid size decrease significantlythrough the extinction interval? Ausich (2010) evaluated samplingand concluded that, although additional collecting would undoubted-ly reveal new material, the Anticosti crinoid fauna was sampled wellenough to allow meaningful analyses of evolutionary and paleoeco-logic patterns. Further, Borths and Ausich (2011) concluded thatAnticosti Island crinoids display the Lilliput Effect, through the extinc-tion interval. The estimated volumes of crinoid calyxes became signif-icantly smaller at the Katian–Hirnantian boundary, coinciding withthe only interval of significant extinction identified by Peters andAusich (2008). Calyx volume did not recover until the Aeronian(Borths and Ausich, 2011).

4. Methods

The data used here are an updated version of the compendiumused by Ausich and Peters (2005) and Peters and Ausich (2008).The updates are 1) inclusion of new data published since 2004, asdiscussed above, and 2) the data organized using the new Ordovicianchronostratigraphy. Ordovician stages now include, from bottom totop, Tremadoc, Floian, Dapingian, Darriwilian, Sandbian, Katian, andHirnantian (Bergström et al., 2006). The Llandovery stages remain,from bottom to top, Rhuddanian, Aeronian, and Telychian (Crameret al., 2010) (Table 2).

For this analysis, generic richness was tabulated using generic datafor each stage and plotted on spindle diagrams that are organized bylarger taxonomic categories. These diagrams include range-throughdata of genera. For a family that is a Lazarus taxon, only known generaknown to occur on both before and after the gap are counted. Differ-ent evolutionary patterns between the major clades were analyzed

Table 2Chronostratigraphy with duration of series that are used in this paper (Bergström et al.,2009).

Series Age at base Duration (Ma)

SilurianSheinwoodian 428.2Telychian 436.0 7.8Aeronian 439.0 3.0Rhuddanian 443.7 4.7

OrdovicianHirnantian 445.6 1.9Katian 455.8 10.2Sandbian 460.9 5.1Darriwilian 468.1 7.2Dapingian 471.8 3.7Floian 478.6 6.8Tremadoc 488.3 9.7

based on correlation of diversity data and first differences betweentemporal stages. In addition, the generic richness of the families wasanalyzed using correspondence analysis to examine the patterns offaunal change throughout this interval.

In addition to the revision in taxonomic diversity,morphologic dispar-ity was also updated based on the new Ordovician chronostratigraphy.Crinoid morphology is characterized loosely based on the charactersuite assembled by Foote (1999) presented by Deline (2009) andDeline and Ausich (2011). The dataset consists of discrete charactersencompassing the entire morphology of the organisms based on anadditive coding scheme of 479 species of Laurentian Ordovicianthrough Early Silurian crinoids. The dataset was analyzed using Prin-cipal Coordinate Analysis using Gower's similarity metric (Gower,1971). The use of Gower's similarity allows for a differentiation be-tween non-applicable, absent, and missing data (Deline, 2009; Delineand Ausich, 2011). Principle Coordinate Analysis is preferred because ofthe flexibility in choosing similarity metrics as well as its ability tobetter handle missing data compared with Principle ComponentAnalysis (Lofgren et al., 2003). For a detailed examination of the codingscheme please refer to Deline and Ausich (2011). Disparity was thencalculated as the average squared distance between crinoids that werepresent in each time interval. This metric is preferred because itshows the most stable patterns with small sample sizes (Ciampaglioet al., 2001). Analyses and statistics were computed using R 2.15 (RDevelopment Core Team, 2012).

5. Early to Middle Paleozoic crinoid evolutionary faunal changes

5.1. Crinoid evolutionary faunas

These new data clearly support the distinction between the EarlyandMiddle Paleozoic CEF (Baumiller, 1993; Ausich et al., 1994), despitethe fact that several taxon ranges have been expanded across theboundary. For example, the recent study on Anticosti Island (Ausichand Copper, 2010) recognized Eomyelodactylus and Xenocrinus asboundary crossers. Similarly, the following families are now known tocross the O–S boundary, as compared with Moore and Teichert(1978): Cincinnaticrinitidae, Myelodactylidae, and Xenocrinidae(Ausich and Copper, 2010).

5.2. Early Ordovician crinoid evolution

The oldest crinoids recognized are from the Tremadocian, and thenumber of major clades represented during this time has increasedrecently with more work (e.g., Guensburg and Sprinkle, 2003,2009, 2010; and others). Monobathrida, Cladida, and Disparida firstappeared during the Tremadoc (Fig. 1). Further, the protocrinids(Guensburg and Sprinkle, 2003) and the aethocrinids (Ausich,1996, 1998) also appeared during the Tremadocian, although theseclades are controversial. All major crinoid clades, except theCyathocrinida and Flexibilia evolved by the Floian (Fig. 1). Tremadocto Floian crinoid generic biodiversity was dominated by disparid cri-noids, especially members of the Eustenocrinidae, Iocrinidae; theProtocrinida; and the cladid Dendrocrinidae (Figs. 4–6). A somewhatmore diverse crinoid fauna began to emerge during the Dapingianand Darriwilian, but overall biodiversity remained low. During theDapingian and Darriwilian, a modest diversification occurred in theRhodocrinitidae (Diplobathrida); Colpodecrinidae (Cladida); Iocrinidae,Maenillocrinidae, and Tetragonocrinidae (Disparida), Hybocrinidae andCornucrinidae (Hybocrinida).

Overall crinoid disparity was stable throughout the Ordovicianwith a wide array of morphologic forms present in the depauperatefaunas of the Tremadoc (Fig. 7) as has been previously reported byFoote (1994, 1999). Much of this early disparity is contained withinthe aforementioned protocrinids, which have unique thoughnon-uniform morphologies. In addition, diplobathrids and cladids

Fig. 4. Family spindle diagrams of generic diversity of Ordovician to Llandovery Disparida and Hybocrinida.

Fig. 5. Family spindle diagrams of generic diversity of Ordovician to Llandovery Dendrocrinida, Cyathocrinidae, and Flexibilia.

42 W.I. Ausich, B. Deline / Palaeogeography, Palaeoclimatology, Palaeoecology 361–362 (2012) 38–48

have their highest Early Paleozoic disparities during the Early Ordovi-cian (Floian), with high initial disparity also present in the disparids(Fig. 8). This pattern of low diversity with high disparity indicates

Fig. 6. Family spindle diagrams of generic diversity of Ordovician

rapid evolutionary change in morphologically plastic organismssuch that the first representatives of different clades are substantiallypartitioned.

to Llandovery Protocrinida, Aethocrinida, and Diplobathrida.

Fig. 7. Ordovician through early Silurian crinoid disparity. Crinoid disparity is calculat-ed as the average squared distance between crinoids in morphospace for each stage.Crinoid morphologic data was compiled and described in Deline and Ausich (2011).Error bars are calculated as the standard error of 1000 bootstrap resamples (Efron,1982). The gap in the Darriwilian is caused by a lack of described Laurentian crinoidspecies during this interval.

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5.3. Sandbian radiation

The Sandbian radiation was dominated by diplobathrid camerates(Fig. 6) and disparids (Fig. 4), but both dendrocrinids and cyathocrinidsalso diversified considerably (Fig. 5). Important aspects of the Sandbianradiation were 1) origination of the Porocrinidae (Cladida) and theDimerocrinitidae (Diplobathrida); 2) radiation of the important disparidfamilies Calceocrinidae, Cincinnaticrinidae, Homocrinidae, and Iocrinidae;and 3) radiation of the diplobathrid family Rhodocrinitidae. Lesssignificant in terms of biodiversity, but still important were furtherradiations by themonobathrid family Glyptocrinidae, origination of themonobathrid family Patelliocrinidae (Fig. 9), and the origination of thedisparid family Pisocrinidae (Fig. 4). The Cyathocrinida originated dur-ing the Sandbian, and the Flexibilia originated during the Katian. Forthemost part, Sandbian through Katian, generic diversity of families ex-perienced relatively minor fluctuations (Fig. 5).

Familial extinction at the close of the Sandbian was restricted tothe Cyathocrinidae and the Disparida. The Cyathocrinida family that

Fig. 8. Disparity and generic diversity from the Ordovician through Early Silurian for the fourbetween crinoids in morphospace for each stage. Crinoid morphologic data was compiled anof 1000 bootstrap resamples (Efron, 1982). Disparity is represented by solid lines while div

became extinct was the Agostocrinidae; and the following disparidfamilies became extinct: Acolocrinidae, Dulkumnocrinidae, andColumbicrinidae.

This major Ordovician diversification of crinoids resulted in only aminor expansion of the boundaries of morphospace, but was typifiedmostly by a filling in the space around the taxa that first appeared dur-ing the Tremadoc and Floian (Figs. 7, 8). This filling of morphospace re-duced the overall disparity during this expansion as crinoids becamemore diverse and stereotypical within the different crinoid orders.Disparids are the exception to this pattern, the large taxonomic diversi-fication is coupled with an increase in disparity, which is caused by theorigination of several new body plans within the group (e.g.calceocrinids and acolocrinids) that differ markedly from the averagemorphology of those from the Tremadoc (e.g. iocrinids).

5.4. End-Katian extinctions

The end-Katian extinction devastated crinoid faunas (Eckert,1988; Donovan, 1994; Peters and Ausich, 2008) (Fig. 1) in a singlemajor extinction event (Peters and Ausich, 2008) (Fig. 3). Further,this extinction coincided with the change to a fauna composed of sig-nificantly small individual crionoids (Lilliput Effect) (Borths andAusich, 2011). The three dominant Ordovician clades experienced atleast 75% generic extinction (Diplobathrida 76.3%, Disparida 75.7%,and Hybocrinida 100%) (Figs. 4, 6). No new diplobathrid and disparidgenera originated during the Hirnantian, resulting in Hirnantian di-versities of 6 and 9 respectively. Thus, these clades dramatically de-creased from the Katian to the Hirnantian (Table 3).

The clades that would eventually dominate post-Ordovicianfaunas (Monobathrida, Cyathocrinida, Dendrocrinidae, and Flexibilia)also experienced less but significant extinction. Similar to thediplobathrids and disparids, more than 76% of Katian dendrocrinidgenera became extinct; and 60% of monobathrids, 66.6% of cyathocrinids,and 60.0% of flexibles became extinct. Overall disparity decreasedslightly during the end-Katian extinction, this is largely an effect ofretaining the major clades of crinoids while reducing the disparitycontained within each subgroup (Figs. 7, 8). The orders most affectedmorphologically are the disparids and diplobathrids indicating that

major orders of crinoids. Crinoid disparity is calculated as the average squared distanced described in Deline and Ausich (2011). Error bars are calculated as the standard errorersity is presented as a dashed line.

Fig. 9. Family spindle diagrams of generic diversity of Ordovician to Llandovery Monobathrida.

44 W.I. Ausich, B. Deline / Palaeogeography, Palaeoclimatology, Palaeoecology 361–362 (2012) 38–48

the extinction is not uniformly thinning the previous morphologies(which would result in an increase in disparity), but the loss ofmorphotypes which would contract the range of morphologiescontained within an order. The extinction has the smallest effect onmonobathrids and their disparity remains static along with theirdiversity.

5.5. Hirnantian and end-Hirnantian extinctions

Very few new genera arose during the Hirnantian. The two cladeswith the least generic end-Katian extinctions experienced the mostHirnantian origination, i.e. Monobathrida (four new genera, 37.5%)(Fig. 9) (Table 2) and Flexibilia (two new genera, 50%) (Fig. 5). Forthe characteristic Ordovician clades, Diplobathrida and Disparida,only a single genus originated during the Hirnantian in each clade,which represents 16.6 and 11.1% new Hirnantian genera, respec-tively. Interestingly, generic diversity was most volatile for theDiplobathrida and Disparida, the two major Ordovician clades(Fig. 1). During the Hirnantian, three diplobathrid genera became ex-tinct, but one originated. Disparids experienced no Hirnantian extinc-tion of genera, and six genera arose (four were ghost lineages, soknown generic biodiversity only increased by two) (Table 3). Threenew families originated during the Hirnantian, all of which were themonobathrids. Compared to the end-Katian, relatively little changeoccurred at the end-Hirnantian (Peters and Ausich, 2008). Only fivetotal genera became extinct; in contrast, 7 genera originated duringthe Hirnantian.

Disparity remained fairly constant which is consistent with thelack of taxonomic change across this interval. A marginal increase inoverall disparity is observed because of an origination of new cladeswithin the disparids.

Table 3Generic diversity, generic extinction, and percent extinction for the Katian and generic dive

Crinoid clade Katian genericdiversity

Katian genericextinction

Percent Katianextinction

Diplobathrida 19 14 73.6%Monobathrida 10 6 60.0%Dendrocrinida 13 10 76.9%Cyathocrinida 6 4 66.6%Flexibilia 5 3 60.0%Disparida 33 25 75.7%Hybocrinida 4 4 100.0%

5.6. Llandovery crinoid radiation

All major clades that survived into the Rhuddanian expandedthrough the entire Llandovery, except the Disparida that maintaineddiversity until after the Aeronian. Monobathrids, cyathocrinids, andflexibles all increased in both generic and familial diversity from theRhuddanian through the Telychian, which is consistent with the radi-ation of the middle Paleozoic CEF (Baumiller, 1993; Ausich et al.,1994) (Fig. 1). Genus level biodiversity rebounded to pre-extinctionlevels during the Aeronian (Fig. 3), which coincided with significantlylarger crinoid individuals (Borths and Ausich, 2011).

During the Llandovery, monobathrid camerates increased in genericdiversity from 7 to 28 (Fig. 9). Of the boundary crossers, four persistedthrough the Llandovery and two became extinct (Tanaocrinidae andGlyptocrinidae, which had been important Ordovician families). How-ever, ten new monobathrid families originated during the Llandovery.Among the Dendrocrinida, one family that crossed the boundary be-came extinct and others persisted through the Llandovery. Onedendrocrinid family originated during the Llandovery. Of the boundarycrossers among the Cyathocrinida, one family became extinct and sixnew families originated (Fig. 5). All Flexibilia families that crossed theHirnantian–Rhuddanian boundary continued through the Llandovery,and two new families originated (Fig. 5). Diplobathrids experienced amodest increase in generic diversity due to the Aeronian expansion ofthe Rhodocrinitidae (followed by a Telychian decline), Telychian radia-tion of the Dimerocrinitidae, and the origination of a few low-diversity,short-lived families (Fig. 6). The increased diversity of theDisparidawasdue largely to the radiation of the Calceocrinidae, which was themost diverse disparid clade during the Llandovery (Fig. 4). Other di-versity among disparids remained basically stable with extinction ofimportant Ordovician families (Eustenocrinidae and Iocrinidae) andminor expansion of clades that would remain important during the

rsity, generic origination, and percent origination for the Hirnantian.

Hirnantian genericorigination

Percent Hirnantianorigination

Hirnantian genericdiversity

1 16.6% 63 37.5% 80 0.0% 30 0.0% 22 50.0% 41 11.1% 90 0.0% 0

Table 4Generic diversity, generic extinction, and percent extinction for the Hirnantian and generic diversity, generic origination, and percent origination for the Rhuddanian.

Crinoid clade Hirnantian genericdiversity

Hirnantian genericextinction

Percent Hirnantianextinction

Rhuddanian genericorigination

Percent Rhuddanianorigination

Rhuddanian genericdiversity

Diplobathrida 6 3 50.0% 4 57.1% 7Monobathrida 8 1 12.5% 2 28.6% 7Dendrocrinida 3 1 33.3% 0 0.0% 2Cyathocrinida 2 0 0.0% 0 0.0% 2Flexibilia 4 0 0.0% 0 0.0% 4Disparida 9 0 0.0% 5 35.7% 14

45W.I. Ausich, B. Deline / Palaeogeography, Palaeoclimatology, Palaeoecology 361–362 (2012) 38–48

Silurian (Myelodactylidae and Pisocrinidae). The Calceocrinidae,Myelodactylidae, and Pisocrinids (the latter two relatively minor) di-versified during the Llandovery. All three of these families persistedfor some time (Myelodactylidae into the Devonian, Pisocrinidae intothe Devonian, and Calceocrinidae into the Permian).

A significant change in disparity occurred during the modestLlandovery recovery with an increase in disparity in all four orders ofcrinoids in concert with the increases in taxonomic diversity (Figs. 7,8). Diplobathrids and cladids had similar patterns with an increase indisparity during the Aeronian, but no further increase during theTelychian as the rate of recovery slows. Monobathrids had a large in-crease in diversity through this interval that was not present withinits disparity. This could be caused by two factors; first, the diversifica-tion could be occurring within the previously established Ordovicianmorphospace and the unique morphologies of later monobathridswere yet to appear, which is consistent with the disparity during theAeronian. However, distinctive monobathrid crinoids originated duringthe Telychian (e.g. Eucalyptocrinites and Marsupiocrinus), but occurredlargely in the Hopkinton Formation preserved as molds, thus manyof their morphologically distinctive features are not well preserved(Witzke and Strimple, 1981). Disparids have very little turnoverduring the recovery, but the dominant crinoids within the group(Calceocrinidae, Myelodactylidae, and Pisocrinids) are all morphologi-cally distinctive, such that an extinction of many of the more ‘average’bodyplans creates a large distance between taxa and a spike in disparitywithout a large turnover or diversification.

Table 5Generic diversity, generic extinction, and percent extinction, generic origination, andpercent origination for the Aeronian.

Crinoid clade Aeroniangenericorigination

PercentAeronianorigination

Aeroniangenericdiversity

Aeroniangenericextinction

PercentAeronianextinction

Diplobathrida 8 66.7% 12 7 58.3%Monobathrida 14 77.8% 18 11 61.1%Dendrocrinida 2 66.7% 3 2 66.7%Cyathocrinida 4 66.7% 6 4 66.7%Flexibilia 3 42.9% 7 2 28.6%Disparida 7 38.9% 18 6 33.3%

Table 6Generic diversity, generic extinction, and percent origination, generic origination, andpercent origination for the Telychian.

Crinoid clade Telychiangenericorigination

PercentTelychianorigination

Telychiangenericdiversity

Telychiangenericextinction

PercentTelychianextinction

Diplobathrida 10 66.7% 15 7 46.7%Monobathrida 21 75.0% 28 10 35.7%Dendrocrinida 1 25.0% 4 2 50.0%Cyathocrinida 6 75.0% 8 2 25.0%Flexibilia 6 54.5% 11 2 18.2%Disparida 4 25.0% 16 3 18.8%

6. Discussion

The macroevolutionary discontinuity between early and middlePaleozoic CEFs was mediated by extinction coincident with the globalclimate change at the close of the Ordovician. A single significantgenus-level extinction interval at the close of the Katian was recog-nized (Peters and Ausich, 2008). However, the subclass and ordertransitions between CEFs were not a simple change. A statistical com-parison of the diversity trends in and correlations among the differentclades of crinoids is given in Tables 3–7. The lack of negative correla-tion values between clades in Table 7 (with the exception of a mar-ginally negative coefficient between diplobathrids and flexibles) isinitially surprising. The lack of negative correlation is caused by theorigination of all of the clades in this interval, such that they allstart with a low number of genera followed by diversifications andfluctuations in diversity. There are no groups that originated with ahigh diversity then diminished, which would be required to have anegative correlation in with the raw data or first differences.

The overall pattern in faunal change as indicated by correspon-dence analysis (Fig. 10) indicates that the change in familial diversitythrough this interval is relatively constant and not concentrated atthe end of the Katian. This pattern indicates that even though amass extinction occurred during this interval, the faunal transitionwas not a result of the extinction, but rather longer-term ecologicaland environmental pressures.

Unique Ordovician clades, such as the Hybocrinids, aethocrinids(sensu Ausich, 1996), and protocrinids (sensu Guensburg andSprinkle, 2003) all became extinct well before the end of the Ordovi-cian. The other two dominant early Paleozoic clades were theDiplobathrida and Disparida. At the end-Katian extinction threediplobathrid families became extinct, and the remaining two familiessuffered generic extinctions. The Rhodocrinitidae were the dominantfamily of Ordovician diplobathrids. They declined at the end-Katian,diversified again during the Aeronian (primarily because of their ex-pansion in reef/encrinites facies of the Brassfield Formation, seeAusich, 1986c), and declined again during the Telychian. The most

Table 7Statistical comparison of diversity patterns among major clades of crinoids during theEarly Paleozoic. Different diversity patterns were tested based on linear correlation ofraw data and first differences and correlation coefficients are presented (statisticallysignificant values are shaded in gray).

Correlation of First DifferencesMonobathrida Dendrocrinida Cyathocrinida Flexibilia Disparida

Diplobathrida 0.504 0.657 0.95 -0.037 0.833Monobathrida 0.388 0.704 0.598 0.27

0.9080.4110.622Dendrocrinida0.7440.188Cyathocrinida

DendrocrinidaCyathocrinida

Flexibilia 0.089CorrelationMonobathrida Dendrocrinida Cyathocrinida Flexibilia Disparida

Diplobathrida 0.588 0.73 0.929 0.498 0.921Monobathrida 0.076 0.83 0.951 0.367

0.8750.0650.5280.7630.737

Flexibilia 0.35

Fig. 10. A comparison of faunal composition and generic diversity through the Early Pa-leozoic. Faunal composition is quantified as the primary axis of a correspondence anal-ysis of the percent transformed generic diversity within the 78 Early Palaeozoic crinoidfamilies compiled for this study. Error bars for generic diversity are calculated as thesquare root of diversity following Sepkoski and Raup (1986).

46 W.I. Ausich, B. Deline / Palaeogeography, Palaeoclimatology, Palaeoecology 361–362 (2012) 38–48

important Silurian diplobathrid family was the Dimerocrinitidae thatwas diverse during the Katian, maintained diversity through theAeronian, and diversified further during the Telychian.

Similarly, among disparids one family with Ordovician origins di-versified significantly through the Llandovery. Here, the calceocrinidradiation began during the Katian and continued on into theWenlock. Also, the Myelodactylidae and Pisocrinidae experiencedrelatively minor diversification during the Llandovery. DominantOrdovician disparids, such as the Cincinnaticrinidae, Homocrinidae,and Iocrinidae, survived through the end-Ordovician extinction butwere never again significant clades. As presently known, all disparidfamilies that survived the end-Katian extinction survived into theLlandovery.

The monobathrid camerates, cladids, and flexibles dominated themiddle Paleozoic CEF, although the assembly of this evolutionaryfauna was protracted. With the exception of the monobathridcamerates described from the Tremadoc and Arenig (Guensburg andSprinkle, 2003), all eight Ordovician monobathrid families that hadevolved during the Ordovician continued into the Silurian. Further,twelve new monobathrid families arose during the Llandovery,establishing this order as a dominant middle Paleozoic clade. Bothmonobathrid families and genera diversified during the Llandovery.

The subclass Flexibilia history was somewhat similar to themonobathrids. All five Ordovician flexible families that survived intothe Silurian diversified during the Llandovery (note theHomalocrinidaere-appeared during the Wenlock). Two new Llandovery families arose.However, flexibles primarily experienced a generic diversification.

In contrast, the radiation of Silurian cladids occurred largely afterthe Telychian. At least six families of dendrocrinids existed duringthe Ordovician. Three families existed after the end-Katian extinctionand two of these survived into the Silurian. Only one new dendrocrinid

Table 8Percentage biogeographic origination of families (based on oldest recorded taxon) forfamilies that survived in the Rhuddanian, Aeronian, Telychian, and Wenlock.

Families surviving into the Laurentia Baltica Gondwana Avalonia China

Wenlock 82.5% 12.5% 0.0% 5.0% 2.5%Telychian 88.6% 11.4% 0.0% 4.5% 2.3%Aeronian 79.4% 14.7% 0.0% 8.8% 2.9%Rhuddanian 80.6% 12.9% 0.0% 6.9% 0.0%

family, the Botryocrinidae, arose during the Llandovery, and only theDendrocrinidae and Botryocrinidae were present during the Aeronianand Telychian, both of which had limited diversity. The primarycyathocrinid Ordovician family, the Porocrinidae, went extinct by theend of the Katian. Two families crossed the Ordovician–Silurian bound-ary, and five families arose during the Llandovery. Although their over-all diversity was low, all cyathocrinid families that persisted into orarose during the Llandovery continued into the Wenlock. Therefore,unlike monobathrids and flexibles, the radiation of cladids was de-layed largely until later. Through this interval, the cyathocrine diver-sification was largely among families, and little diversificationoccurred at any level among dendrocrines. Later during the Silurian,cladid assemblages were dominated by cyathocrinid and primitivedendrocrinid clades. The advanced, pinnulate cladids evolved duringthe Lower Devonian, and became a dominant component of the latePaleozoic CEF beginning during the Mississippian, and gave rise tothe post-Paleozoic Crinoidea.

In general, Ordovician faunas are more endemic than those fromthe Silurian faunas. The biogeographic origination of other Silurianclades and subclades is quite variable (e.g., Sheehan, 1988; Sheehanand Coorough, 1990; Berry et al., 1995; Harper and Rong, 1995;Sheehan et al., 1996; Sheehan, 2001). Unfortunately, the data for cri-noids are largely limited to North America and Europe. However,given the face-value data, the biogeographic origins of the Silurianfauna were overwhelmingly from Laurentian Ordovician faunas.More than 80% of the families that survived into the Rhuddanianhad Laurentian originations, more than 79% of the families that sur-vived into the Aeronian had Laurentian originations, more than 88%of the families that survived into the Telychian had Laurentian origi-nations, and more than 82% of the families that survived into theWenlock had Laurentian originations (Table 8).

Acknowledgments

Thisworkwas partially supported by theNational Geographic Society6789‐00 and the National Science Foundation EAR-0205968 and DEB1036416 to WIA along with an NSF ROA supplement DEB 1036416(WIA-PI) to BD.Wewould like to thankM. Foote for sharing unpublisheddata and T. Guensburg and F. Gahn for making undescribed specimensavailable for morphologic analyses.

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