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

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

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Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo

Macroevolutionary transition in crinoids following the Late Ordovician extinction event (Ordovician to Early Silurian) William I. Ausich a,⁎, Bradley Deline b a b

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

a r t i c l e

i n f o

Article history: Received 8 May 2012 Received in revised form 12 July 2012 Accepted 20 July 2012 Available online 27 July 2012 Keywords: Macroevolution Crinoid Ordovician Silurian Extinction

a b s t r a c t The end-Katian (Late Ordovician) crinoid mass extinction triggered the change from the Early to the Middle Paleozoic crinoid evolutionary faunas (CEFs). This was a change from diplobathrid camerate-disparid-hybocrinid dominated faunas to faunas dominated by monobathrid camerate, cladid, and flexible crinoids. All clades suffered extinctions at the end-Katian event, but diplobathrid camerates, disparids, and hybocrinids suffered higher rates of extinction. The primary amount of diversification occurred in clades that would become dominant during the Silurian. However, the formation of the characteristic Middle Paleozoic CEF was protracted beyond the Late Ordovician extinction event. Monobathrid camerates and flexibles diversified through the Llandovery, but both dendrocrinid and cyathocrinid cladids did not diversify until later. Monobathrid camerate genera and families diversified, the flexible diversification was largely at the genus level, cyathocrine diversification was largely among families, and dendrocrinids did not diversify significantly until after the Llandovery. Overall disparity decreased during the end-Katian extinction by reducing the disparity within each clade. Disparity remained fairly constant during the Hirnantian but increased significantly during the Llandovery by both increasing disparity within clades and expanding the morphospace of the disparids due to the radiation of families with new morphologies. North America was the biogeographic center of origination for the families that survived to become dominant Silurian clades. © 2012 Elsevier B.V. All rights reserved.

1. Introduction A significant discontinuity in crinoid evolutionary history occurred between the Ordovician and Silurian. This macroevolutionary change has been recognized since at least by Moore (1950) and was recognized more recently as the transition between the Early and Middle Paleozoic crinoid evolutionary faunas (CEF) (Baumiller, 1993; Ausich et al., 1994). Most primary crinoid clades were part of both evolutionary faunas, such that the transition represented a change in dominance between crinoid clades. Assemblages of the Early Paleozoic CEF were typically dominated by disparid, diplobathrid camerate, and hybocrinid crinoids (Fig. 1, Table 1). In contrast, typical middle Silurian examples of the Middle Paleozoic CEF were characterized by assemblages dominated by monobathrid 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 CEF and the radiation of the Middle Paleozoic CEF. We examine the disassembly of the Early Paleozoic CEF, the recovery response of elements of the Early Paleozoic CEF versus those of the Middle Paleozoic CEF, ⁎ Corresponding author. E-mail addresses: [email protected] (W.I. Ausich), [email protected] (B. Deline). 0031-0182/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.palaeo.2012.07.022

and the timing of the assembly of the new Middle Paleozoic CEF following the end-Katian extinctions. There are several models for evolutionary transitions such as refilling a vacated niche following an extinction compared with direct competition between clades. With a transition that occurs near a mass extinction it is assumed that faunal transition was largely facilitated by the extinction, which can be tested by a close examination of the faunal changes through the interval. Historically, the most notable aspect of the Hirnantian (latest Ordovician) to Llandovery (Early Silurian) crinoids has been the lack of information. Although authors have typically not discussed this point directly, it is evident from published diagrams depicting crinoid evolutionary history (e.g., Moore and Laudon, 1943; Moore, 1950; Moore and Teichert, 1978). Diverse, shelly faunas have also been relatively poorly known globally during this interval, because epicontinental sea habitats were largely eliminated due to sea level fall associated with the end-Ordovician glaciation on Gondwana. Since 1980, a concerted effort to discover new latest Ordovician and earliest Silurian crinoid faunas has been successful. For example, the number of Llandovery species has increased from 26 to 140 (Fig. 2). With these new data, the transition between crinoid macroevolutionary faunas can now be examined in much greater detail both in terms of taxonomic diversity as well as morphologic disparity. The examination of both diversity and disparity can give a more thorough view of macroevolutionary changes. These two metrics are

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

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

inherently related, but they may have dramatically different patterns through time (Foote, 1993). A decrease in disparity can be caused by either by an overall reduction in the range of morphologies present or by filling of morphospace with morphologically similar organisms. In contrast, an increase in disparity can be caused by the evolution of new morphologic features or by diluting the morphospace leaving only morphologically distinctive organisms. Therefore, the coupling of these two measures can better document the Early Paleozoic transition in crinoid communities. 2. End-Ordovician extinctions The second-most devastating collapse of the marine biosphere occurred during the transition from the Ordovician to the Silurian (Sepkoski, 1981; Raup and Sepkoski, 1982; Brenchley, 1989; Brenchley et 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 changed the evolutionary fortunes of many clades, including the Crinoidea. Examples of clades that were significantly impacted include brachiopods (Harper and Rong, 1995; Sheehan, 2001), conodonts (Barnes and Bergström, 1988), crinoids (Eckert, 1988; Donovan, 1989, 1994; Sprinkle and Guensburg, 2004; Ausich and Peters, 2005; Peters and Ausich, 2008), graptolites (Chen et al., 2003), reef faunas (Copper, 2001), and many other clades (e.g., Hallam and Wignall, 1997; Finney et al., 1999; Sheehan, 2001; Kaljo et al., 2008). The Late Ordovician global climate cooled, culminating in a Gondwanan glaciation (Brenchley et al., 2003). The catastrophic losses of marine habitats during eustatic sea level drop associated

with ice buildup are generally regarded as the proximate causes of biosphere collapse (Berry and Boucot, 1973; McKerrow, 1979; Sheehan, 2001). However, the ultimate cause for climate cooling is much less clear. Many hypotheses have been forwarded including, among others, nutrient levels in the ocean, uplift of the continents, silicate and carbonate 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 about this glaciation is that it occurred during a greenhouse Earth; and when originally recognized, the Hirnantian glaciation was regarded as an unusually short glacial epoch (Brenchley, et al., 1994). However, the Hirnantian glaciation is now recognized to have continued through the Llandovery (Grahn and Caputo, 1992, 1994; Brenchley et al., 2003; Ghienne, 2003; Herrmann et al., 2004a,b). Also, this glaciation is now recognized as geographically widespread, with glacial deposits known in northern Africa (Ghienne, 2003; Ghienne et al., 2007), South America (Grahn and Caputo, 1992, 1994; Schönian and Egenhoff, 2007), and recently as far north as southeastern Europe (peri-Gondwana during the Ordovician) (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 and Laudon (1943) authors have recognized an adaptive radiation in the middle portion of the Ordovician. This radiation is referred to herein as the Sandbian (Bergström et al., 2006, 2009) radiation; but using

Table 1 Major crinoid clades discussed in this paper. Class Crinoidea Subclass Protocrinida Subclass Aethocrinida Subclass Camerata Order Diplobathrida Order Monobathrida Subclass Cladida Order Dendrocrinida Order Cyathocrinida (primitive cladids are non-pinnulate) (advanced cladids are pinnulate dendrocrinids) Subclass Flexibilia Subclass Disparida

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

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previous chronostratigraphic schemes, this has also been regarded as the Caradoc, Mohawkian, or other radiations. This radiation was depicted in diagrams or discussed in detail by authors including Moore and Laudon (1943), Moore (1950), Moore (1952), Moore and Teichert (1978), Eckert (1988), Donovan (1994), Ausich (1998), Sprinkle and Guensburg (2004), Ausich and Peters (2005), and Peters and Ausich (2008). This middle Ordovician radiation was also expressed in the data compendium of Sepkoski (2002) and the PaleoBiology Database bpaleobd.org/cgi-bin/bridge.pl >. 3.2. New Hirnantian to Llandoverian crinoid faunas and resampling statistical analyses As discussed above, prior to 1980 Hirnantian and Llandoverian crinoids were known from a limited number of localities. For example, Hirnantian crinoids were described from North America in the Girardeau Limestone of Missouri (Brower, 1973). Llandovery faunas known before 1980 were few and typically isolated specimens rather than part of a diverse 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 Formation, Ohio). Since 1980, new Hirnantian crinoids have been described from five stratigraphic levels on Anticosti Island, Quebec (Ausich and Copper, 2010). Two small faunas from Missouri are also recognized as Hirnantian in age (Ausich, 1987c). Knowledge of Llandovery crinoid faunas has expanded greatly since 1980 (Ausich, 2009). Important new faunas include the Brassfield Formation 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 Formation, and Wolcott Limestone of New York and Ontario (Eckert, 1984, 1990; Eckert and Brett, 2001); and several new faunas from the United Kingdom and Ireland (Donovan and Sevastopulo, 1989; Donovan, 1993; Donovan and Harper, 2003; Donovan and Lewis, 2005; Fearnhead and Donovan, 2007a–d; Donovan et al, 2009). Most recently, Ausich and Copper (2010) described Llandovery crinoids from Anticosti Island, Quebec, Canada. A total of 44 genera were described from throughout the Llandovery of Anticosti Island, which has a nearly complete stratigraphic section through this interval. Despite these new discoveries, very few latest Ordovician and Early Silurian crinoids are known from anywhere outside of North American and western Europe. The latest set of analyses described below incorporated these new data. This revised compendium provides a new perspective on the transition from the early to the middle Paleozoic CEF.

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 in many ways. Ausich and Peters (2005) examined rates of origination and extinction of genera from the basal Ordovician through the Llandovery and compared this to the compendium of Sepkoski (2002). Ausich and Peters (2005) concluded that previous interpretations of the end-Ordovician interval had overestimated the rates of extinction at the end-Ordovician and underestimated richness during the Early Silurian. This conclusion was significantly different from the same analysis using only Sepkoski (2002) data, indicating net non-random errors do occur within the Sepkoski compendium. Peters and Ausich (2008) evaluated these data further using sample-standardized subsampling. The rapid rise in crinoid biodiversity as recorded by previous authors (Sandbian, herein) was confirmed. However, these methods identified only a single, statistically significant extinction among Ordovician crinoids at the end-Katian (=end-Richmondian or end-Rawtheyan in previous stratigraphic usage) (Fig. 3). Therefore, the only statistically significant decline in crinoid genus richness occurred during the onset of glaciation and habitat loss. This was the second step of extinction interpreted by Eckert (1988) and the first step recognized by Donovan (1994). Neither a middle Ordovician decline nor an end-Hirnantian extinction was confirmed by Peters and Ausich (2008). Morphological patterns have also been closely examined throughout this interval. Foote examined crinoid disparity throughout the

3.3. End-Ordovician extinction analysis After describing new Early Silurian crinoid faunas (Eckert, 1988; Eckert and Brett, 2001), Eckert (1988) considered the crinoid transition between the Ordovician and Silurian to be a two-step decline based on crinoid richness. The first step was the Caradoc/Ashgill “biotic crisis” in which approximately 50% of generic diversity attained in the previous radiation was lost. The second step for Eckert (1988) was the end-Richmondian (end-Rawtheyan of Peters and Ausich, 2008; end-Katian herein) extinction event in which only 30% genera of contained within his database survived from the Richmondian to the Hirnantian. Donovan (1988, 1989) clarified aspects of the paleogeography from (Eckert, 1988), and he examined this transition using form taxa based on only columnals and columns (Donovan, 1994). This largely independent column taxonomy was used to examine Ordovician extinctions. Donovan (1994) also recognized a two-step

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

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Early Paleozoic (1994) and later the entire Phanerozoic (1999) and found a rapid morphospace occupation during the Middle Ordovician followed by little variation in the morphologic disparity during this transition despite large fluctuations in taxonomic diversity. This stasis in disparity was hypothesized to be the result of constraints in ecology or development (Foote, 1994, 1999). Further, Deline (2009), Deline and Ausich (2011), and Deline et al. (2012) re-examined crinoid morphological disparity through this interval with a higher taxonomic and temporal resolution and found a larger degree of variation in disparity than was previously reported. These results are 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 exposed on Anticosti Island, Quebec; and, as mentioned above, crinoids from Anticosti Island are now well known through this interval (Ausich and Copper, 2010). Two further questions have been asked of crinoids from the Anticosti Basin through this interval, i.e., are crinoids well sampled and did crinoid size decrease significantly through the extinction interval? Ausich (2010) evaluated sampling and concluded that, although additional collecting would undoubtedly reveal new material, the Anticosti crinoid fauna was sampled well enough to allow meaningful analyses of evolutionary and paleoecologic patterns. Further, Borths and Ausich (2011) concluded that Anticosti Island crinoids display the Lilliput Effect, through the extinction interval. The estimated volumes of crinoid calyxes became significantly smaller at the Katian–Hirnantian boundary, coinciding with the only interval of significant extinction identified by Peters and Ausich (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 compendium used by Ausich and Peters (2005) and Peters and Ausich (2008). The updates are 1) inclusion of new data published since 2004, as discussed above, and 2) the data organized using the new Ordovician chronostratigraphy. Ordovician stages now include, from bottom to top, Tremadoc, Floian, Dapingian, Darriwilian, Sandbian, Katian, and Hirnantian (Bergström et al., 2006). The Llandovery stages remain, from bottom to top, Rhuddanian, Aeronian, and Telychian (Cramer et al., 2010) (Table 2). For this analysis, generic richness was tabulated using generic data for each stage and plotted on spindle diagrams that are organized by larger taxonomic categories. These diagrams include range-through data of genera. For a family that is a Lazarus taxon, only known genera known to occur on both before and after the gap are counted. Different evolutionary patterns between the major clades were analyzed Table 2 Chronostratigraphy with duration of series that are used in this paper (Bergström et al., 2009). Series Silurian Sheinwoodian Telychian Aeronian Rhuddanian Ordovician Hirnantian Katian Sandbian Darriwilian Dapingian Floian Tremadoc

Age at base

Duration (Ma)

428.2 436.0 439.0 443.7

7.8 3.0 4.7

445.6 455.8 460.9 468.1 471.8 478.6 488.3

1.9 10.2 5.1 7.2 3.7 6.8 9.7

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based on correlation of diversity data and first differences between temporal stages. In addition, the generic richness of the families was analyzed using correspondence analysis to examine the patterns of faunal change throughout this interval. In addition to the revision in taxonomic diversity, morphologic disparity was also updated based on the new Ordovician chronostratigraphy. Crinoid morphology is characterized loosely based on the character suite assembled by Foote (1999) presented by Deline (2009) and Deline and Ausich (2011). The dataset consists of discrete characters encompassing the entire morphology of the organisms based on an additive coding scheme of 479 species of Laurentian Ordovician through Early Silurian crinoids. The dataset was analyzed using Principal Coordinate Analysis using Gower's similarity metric (Gower, 1971). The use of Gower's similarity allows for a differentiation between non-applicable, absent, and missing data (Deline, 2009; Deline and Ausich, 2011). Principle Coordinate Analysis is preferred because of the flexibility in choosing similarity metrics as well as its ability to better handle missing data compared with Principle Component Analysis (Lofgren et al., 2003). For a detailed examination of the coding scheme please refer to Deline and Ausich (2011). Disparity was then calculated as the average squared distance between crinoids that were present in each time interval. This metric is preferred because it shows the most stable patterns with small sample sizes (Ciampaglio et al., 2001). Analyses and statistics were computed using R 2.15 (R Development 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 Early and Middle Paleozoic CEF (Baumiller, 1993; Ausich et al., 1994), despite the fact that several taxon ranges have been expanded across the boundary. For example, the recent study on Anticosti Island (Ausich and Copper, 2010) recognized Eomyelodactylus and Xenocrinus as boundary crossers. Similarly, the following families are now known to cross 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 the number of major clades represented during this time has increased recently with more work (e.g., Guensburg and Sprinkle, 2003, 2009, 2010; and others). Monobathrida, Cladida, and Disparida first appeared during the Tremadoc (Fig. 1). Further, the protocrinids (Guensburg and Sprinkle, 2003) and the aethocrinids (Ausich, 1996, 1998) also appeared during the Tremadocian, although these clades are controversial. All major crinoid clades, except the Cyathocrinida and Flexibilia evolved by the Floian (Fig. 1). Tremadoc to Floian crinoid generic biodiversity was dominated by disparid crinoids, especially members of the Eustenocrinidae, Iocrinidae; the Protocrinida; and the cladid Dendrocrinidae (Figs. 4–6). A somewhat more diverse crinoid fauna began to emerge during the Dapingian and Darriwilian, but overall biodiversity remained low. During the Dapingian and Darriwilian, a modest diversification occurred in the Rhodocrinitidae (Diplobathrida); Colpodecrinidae (Cladida); Iocrinidae, Maenillocrinidae, and Tetragonocrinidae (Disparida), Hybocrinidae and Cornucrinidae (Hybocrinida). Overall crinoid disparity was stable throughout the Ordovician with a wide array of morphologic forms present in the depauperate faunas of the Tremadoc (Fig. 7) as has been previously reported by Foote (1994, 1999). Much of this early disparity is contained within the aforementioned protocrinids, which have unique though non-uniform morphologies. In addition, diplobathrids and cladids

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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.

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

rapid evolutionary change in morphologically plastic organisms such that the first representatives of different clades are substantially partitioned.

Fig. 6. Family spindle diagrams of generic diversity of Ordovician to Llandovery Protocrinida, Aethocrinida, and Diplobathrida.

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Fig. 7. Ordovician through early Silurian crinoid disparity. Crinoid disparity is calculated 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 crinoid species during this interval.

5.3. Sandbian radiation The Sandbian radiation was dominated by diplobathrid camerates (Fig. 6) and disparids (Fig. 4), but both dendrocrinids and cyathocrinids also diversified considerably (Fig. 5). Important aspects of the Sandbian radiation were 1) origination of the Porocrinidae (Cladida) and the Dimerocrinitidae (Diplobathrida); 2) radiation of the important disparid families Calceocrinidae, Cincinnaticrinidae, Homocrinidae, and Iocrinidae; and 3) radiation of the diplobathrid family Rhodocrinitidae. Less significant in terms of biodiversity, but still important were further radiations by the monobathrid family Glyptocrinidae, origination of the monobathrid family Patelliocrinidae (Fig. 9), and the origination of the disparid family Pisocrinidae (Fig. 4). The Cyathocrinida originated during the Sandbian, and the Flexibilia originated during the Katian. For the most part, Sandbian through Katian, generic diversity of families experienced relatively minor fluctuations (Fig. 5). Familial extinction at the close of the Sandbian was restricted to the Cyathocrinidae and the Disparida. The Cyathocrinida family that

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became extinct was the Agostocrinidae; and the following disparid families became extinct: Acolocrinidae, Dulkumnocrinidae, and Columbicrinidae. This major Ordovician diversification of crinoids resulted in only a minor expansion of the boundaries of morphospace, but was typified mostly by a filling in the space around the taxa that first appeared during the Tremadoc and Floian (Figs. 7, 8). This filling of morphospace reduced the overall disparity during this expansion as crinoids became more diverse and stereotypical within the different crinoid orders. Disparids are the exception to this pattern, the large taxonomic diversification is coupled with an increase in disparity, which is caused by the origination of several new body plans within the group (e.g. calceocrinids and acolocrinids) that differ markedly from the average morphology 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 single major extinction event (Peters and Ausich, 2008) (Fig. 3). Further, this extinction coincided with the change to a fauna composed of significantly small individual crionoids (Lilliput Effect) (Borths and Ausich, 2011). The three dominant Ordovician clades experienced at least 75% generic extinction (Diplobathrida 76.3%, Disparida 75.7%, and Hybocrinida 100%) (Figs. 4, 6). No new diplobathrid and disparid genera originated during the Hirnantian, resulting in Hirnantian diversities of 6 and 9 respectively. Thus, these clades dramatically decreased from the Katian to the Hirnantian (Table 3). The clades that would eventually dominate post-Ordovician faunas (Monobathrida, Cyathocrinida, Dendrocrinidae, and Flexibilia) also experienced less but significant extinction. Similar to the diplobathrids and disparids, more than 76% of Katian dendrocrinid genera became extinct; and 60% of monobathrids, 66.6% of cyathocrinids, and 60.0% of flexibles became extinct. Overall disparity decreased slightly during the end-Katian extinction, this is largely an effect of retaining the major clades of crinoids while reducing the disparity contained within each subgroup (Figs. 7, 8). The orders most affected morphologically are the disparids and diplobathrids indicating that

Fig. 8. Disparity and generic diversity from the Ordovician through Early Silurian for the four major orders of crinoids. Crinoid disparity is calculated 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). Disparity is represented by solid lines while diversity is presented as a dashed line.

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

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

5.5. Hirnantian and end-Hirnantian extinctions Very few new genera arose during the Hirnantian. The two clades with the least generic end-Katian extinctions experienced the most Hirnantian origination, i.e. Monobathrida (four new genera, 37.5%) (Fig. 9) (Table 2) and Flexibilia (two new genera, 50%) (Fig. 5). For the 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, respectively. Interestingly, generic diversity was most volatile for the Diplobathrida and Disparida, the two major Ordovician clades (Fig. 1). During the Hirnantian, three diplobathrid genera became extinct, but one originated. Disparids experienced no Hirnantian extinction of genera, and six genera arose (four were ghost lineages, so known generic biodiversity only increased by two) (Table 3). Three new families originated during the Hirnantian, all of which were the monobathrids. Compared to the end-Katian, relatively little change occurred at the end-Hirnantian (Peters and Ausich, 2008). Only five total genera became extinct; in contrast, 7 genera originated during the Hirnantian. Disparity remained fairly constant which is consistent with the lack of taxonomic change across this interval. A marginal increase in overall disparity is observed because of an origination of new clades within the disparids.

5.6. Llandovery crinoid radiation All major clades that survived into the Rhuddanian expanded through the entire Llandovery, except the Disparida that maintained diversity until after the Aeronian. Monobathrids, cyathocrinids, and flexibles all increased in both generic and familial diversity from the Rhuddanian through the Telychian, which is consistent with the radiation of the middle Paleozoic CEF (Baumiller, 1993; Ausich et al., 1994) (Fig. 1). Genus level biodiversity rebounded to pre-extinction levels during the Aeronian (Fig. 3), which coincided with significantly larger crinoid individuals (Borths and Ausich, 2011). During the Llandovery, monobathrid camerates increased in generic diversity from 7 to 28 (Fig. 9). Of the boundary crossers, four persisted through the Llandovery and two became extinct (Tanaocrinidae and Glyptocrinidae, which had been important Ordovician families). However, ten new monobathrid families originated during the Llandovery. Among the Dendrocrinida, one family that crossed the boundary became extinct and others persisted through the Llandovery. One dendrocrinid family originated during the Llandovery. Of the boundary crossers among the Cyathocrinida, one family became extinct and six new families originated (Fig. 5). All Flexibilia families that crossed the Hirnantian–Rhuddanian boundary continued through the Llandovery, and two new families originated (Fig. 5). Diplobathrids experienced a modest increase in generic diversity due to the Aeronian expansion of the Rhodocrinitidae (followed by a Telychian decline), Telychian radiation of the Dimerocrinitidae, and the origination of a few low-diversity, short-lived families (Fig. 6). The increased diversity of the Disparida was due largely to the radiation of the Calceocrinidae, which was the most diverse disparid clade during the Llandovery (Fig. 4). Other diversity among disparids remained basically stable with extinction of important Ordovician families (Eustenocrinidae and Iocrinidae) and minor expansion of clades that would remain important during the

Table 3 Generic diversity, generic extinction, and percent extinction for the Katian and generic diversity, generic origination, and percent origination for the Hirnantian. Crinoid clade

Katian generic diversity

Katian generic extinction

Percent Katian extinction

Hirnantian generic origination

Percent Hirnantian origination

Hirnantian generic diversity

Diplobathrida Monobathrida Dendrocrinida Cyathocrinida Flexibilia Disparida Hybocrinida

19 10 13 6 5 33 4

14 6 10 4 3 25 4

73.6% 60.0% 76.9% 66.6% 60.0% 75.7% 100.0%

1 3 0 0 2 1 0

16.6% 37.5% 0.0% 0.0% 50.0% 11.1% 0.0%

6 8 3 2 4 9 0

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

Hirnantian generic diversity

Hirnantian generic extinction

Percent Hirnantian extinction

Rhuddanian generic origination

Percent Rhuddanian origination

Rhuddanian generic diversity

Diplobathrida Monobathrida Dendrocrinida Cyathocrinida Flexibilia Disparida

6 8 3 2 4 9

3 1 1 0 0 0

50.0% 12.5% 33.3% 0.0% 0.0% 0.0%

4 2 0 0 0 5

57.1% 28.6% 0.0% 0.0% 0.0% 35.7%

7 7 2 2 4 14

Silurian (Myelodactylidae and Pisocrinidae). The Calceocrinidae, Myelodactylidae, and Pisocrinids (the latter two relatively minor) diversified during the Llandovery. All three of these families persisted for some time (Myelodactylidae into the Devonian, Pisocrinidae into the Devonian, and Calceocrinidae into the Permian). A significant change in disparity occurred during the modest Llandovery recovery with an increase in disparity in all four orders of crinoids in concert with the increases in taxonomic diversity (Figs. 7, 8). Diplobathrids and cladids had similar patterns with an increase in disparity during the Aeronian, but no further increase during the Telychian as the rate of recovery slows. Monobathrids had a large increase in diversity through this interval that was not present within its disparity. This could be caused by two factors; first, the diversification could be occurring within the previously established Ordovician morphospace and the unique morphologies of later monobathrids were yet to appear, which is consistent with the disparity during the Aeronian. However, distinctive monobathrid crinoids originated during the Telychian (e.g. Eucalyptocrinites and Marsupiocrinus), but occurred largely in the Hopkinton Formation preserved as molds, thus many of their morphologically distinctive features are not well preserved (Witzke and Strimple, 1981). Disparids have very little turnover during the recovery, but the dominant crinoids within the group (Calceocrinidae, Myelodactylidae, and Pisocrinids) are all morphologically distinctive, such that an extinction of many of the more ‘average’ body plans creates a large distance between taxa and a spike in disparity without a large turnover or diversification.

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

Aeronian generic origination

Percent Aeronian origination

Aeronian generic diversity

Aeronian generic extinction

Percent Aeronian extinction

Diplobathrida Monobathrida Dendrocrinida Cyathocrinida Flexibilia Disparida

8 14 2 4 3 7

66.7% 77.8% 66.7% 66.7% 42.9% 38.9%

12 18 3 6 7 18

7 11 2 4 2 6

58.3% 61.1% 66.7% 66.7% 28.6% 33.3%

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

Diplobathrida Monobathrida Dendrocrinida Cyathocrinida Flexibilia Disparida

Telychian generic origination

Percent Telychian origination

Telychian generic diversity

Telychian generic extinction

Percent Telychian extinction

10 21 1 6 6 4

66.7% 75.0% 25.0% 75.0% 54.5% 25.0%

15 28 4 8 11 16

7 10 2 2 2 3

46.7% 35.7% 50.0% 25.0% 18.2% 18.8%

6. Discussion The macroevolutionary discontinuity between early and middle Paleozoic CEFs was mediated by extinction coincident with the global climate change at the close of the Ordovician. A single significant genus-level extinction interval at the close of the Katian was recognized (Peters and Ausich, 2008). However, the subclass and order transitions between CEFs were not a simple change. A statistical comparison of the diversity trends in and correlations among the different clades of crinoids is given in Tables 3–7. The lack of negative correlation values between clades in Table 7 (with the exception of a marginally negative coefficient between diplobathrids and flexibles) is initially surprising. The lack of negative correlation is caused by the origination of all of the clades in this interval, such that they all start with a low number of genera followed by diversifications and fluctuations in diversity. There are no groups that originated with a high diversity then diminished, which would be required to have a negative correlation in with the raw data or first differences. The overall pattern in faunal change as indicated by correspondence analysis (Fig. 10) indicates that the change in familial diversity through this interval is relatively constant and not concentrated at the end of the Katian. This pattern indicates that even though a mass extinction occurred during this interval, the faunal transition was not a result of the extinction, but rather longer-term ecological and environmental pressures. Unique Ordovician clades, such as the Hybocrinids, aethocrinids (sensu Ausich, 1996), and protocrinids (sensu Guensburg and Sprinkle, 2003) all became extinct well before the end of the Ordovician. The other two dominant early Paleozoic clades were the Diplobathrida and Disparida. At the end-Katian extinction three diplobathrid families became extinct, and the remaining two families suffered generic extinctions. The Rhodocrinitidae were the dominant family of Ordovician diplobathrids. They declined at the end-Katian, diversified again during the Aeronian (primarily because of their expansion in reef/encrinites facies of the Brassfield Formation, see Ausich, 1986c), and declined again during the Telychian. The most

Table 7 Statistical comparison of diversity patterns among major clades of crinoids during the Early Paleozoic. Different diversity patterns were tested based on linear correlation of raw data and first differences and correlation coefficients are presented (statistically significant values are shaded in gray). Correlation of First Differences Monobathrida Dendrocrinida Cyathocrinida Diplobathrida Monobathrida Dendrocrinida Cyathocrinida Flexibilia

0.504

Correlation Monobathrida Diplobathrida Monobathrida Dendrocrinida Cyathocrinida Flexibilia

0.588

0.657 0.388

0.95 0.704 0.622

Flexibilia Disparida -0.037 0.598 0.411 0.188

0.833 0.27 0.908 0.744 0.089

Dendrocrinida Cyathocrinida

Flexibilia Disparida

0.73 0.076

0.498 0.951 0.065 0.737

0.929 0.83 0.528

0.921 0.367 0.875 0.763 0.35

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

Fig. 10. A comparison of faunal composition and generic diversity through the Early Paleozoic. Faunal composition is quantified as the primary axis of a correspondence analysis of the percent transformed generic diversity within the 78 Early Palaeozoic crinoid families compiled for this study. Error bars for generic diversity are calculated as the square root of diversity following Sepkoski and Raup (1986).

important Silurian diplobathrid family was the Dimerocrinitidae that was diverse during the Katian, maintained diversity through the Aeronian, and diversified further during the Telychian. Similarly, among disparids one family with Ordovician origins diversified significantly through the Llandovery. Here, the calceocrinid radiation began during the Katian and continued on into the Wenlock. Also, the Myelodactylidae and Pisocrinidae experienced relatively minor diversification during the Llandovery. Dominant Ordovician disparids, such as the Cincinnaticrinidae, Homocrinidae, and Iocrinidae, survived through the end-Ordovician extinction but were never again significant clades. As presently known, all disparid families that survived the end-Katian extinction survived into the Llandovery. The monobathrid camerates, cladids, and flexibles dominated the middle Paleozoic CEF, although the assembly of this evolutionary fauna was protracted. With the exception of the monobathrid camerates described from the Tremadoc and Arenig (Guensburg and Sprinkle, 2003), all eight Ordovician monobathrid families that had evolved 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. Both monobathrid families and genera diversified during the Llandovery. The subclass Flexibilia history was somewhat similar to the monobathrids. All five Ordovician flexible families that survived into the Silurian diversified during the Llandovery (note the Homalocrinidae re-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 after the Telychian. At least six families of dendrocrinids existed during the Ordovician. Three families existed after the end-Katian extinction and two of these survived into the Silurian. Only one new dendrocrinid

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

Laurentia

Baltica

Gondwana

Avalonia

China

Wenlock Telychian Aeronian Rhuddanian

82.5% 88.6% 79.4% 80.6%

12.5% 11.4% 14.7% 12.9%

0.0% 0.0% 0.0% 0.0%

5.0% 4.5% 8.8% 6.9%

2.5% 2.3% 2.9% 0.0%

family, the Botryocrinidae, arose during the Llandovery, and only the Dendrocrinidae and Botryocrinidae were present during the Aeronian and Telychian, both of which had limited diversity. The primary cyathocrinid Ordovician family, the Porocrinidae, went extinct by the end of the Katian. Two families crossed the Ordovician–Silurian boundary, and five families arose during the Llandovery. Although their overall diversity was low, all cyathocrinid families that persisted into or arose during the Llandovery continued into the Wenlock. Therefore, unlike monobathrids and flexibles, the radiation of cladids was delayed largely until later. Through this interval, the cyathocrine diversification was largely among families, and little diversification occurred at any level among dendrocrines. Later during the Silurian, cladid assemblages were dominated by cyathocrinid and primitive dendrocrinid clades. The advanced, pinnulate cladids evolved during the Lower Devonian, and became a dominant component of the late Paleozoic CEF beginning during the Mississippian, and gave rise to the post-Paleozoic Crinoidea. In general, Ordovician faunas are more endemic than those from the Silurian faunas. The biogeographic origination of other Silurian clades and subclades is quite variable (e.g., Sheehan, 1988; Sheehan and Coorough, 1990; Berry et al., 1995; Harper and Rong, 1995; Sheehan et al., 1996; Sheehan, 2001). Unfortunately, the data for crinoids are largely limited to North America and Europe. However, given the face-value data, the biogeographic origins of the Silurian fauna were overwhelmingly from Laurentian Ordovician faunas. More than 80% of the families that survived into the Rhuddanian had Laurentian originations, more than 79% of the families that survived into the Aeronian had Laurentian originations, more than 88% of the families that survived into the Telychian had Laurentian originations, and more than 82% of the families that survived into the Wenlock had Laurentian originations (Table 8). Acknowledgments This work was partially supported by the National Geographic Society 6789‐00 and the National Science Foundation EAR-0205968 and DEB 1036416 to WIA along with an NSF ROA supplement DEB 1036416 (WIA-PI) to BD. We would like to thank M. Foote for sharing unpublished data and T. Guensburg and F. Gahn for making undescribed specimens available for morphologic analyses. References Ausich, W.I., 1984a. Calceocrinids from the Early Silurian (Llandoverian) Brassfield Formation of southwestern Ohio. Journal of Paleontology 58, 1167–1185. Ausich, W.I., 1984b. The genus Clidochirus from the Early Silurian of Ohio (Crinoidea: Llandoverian). Journal of Paleontology 58, 1341–1346. Ausich, W.I., 1985. New crinoids and revision of the superfamily Glyptocrinacea (Early Silurian, Ohio). Journal of Paleontology 59, 793–808. Ausich, W.I., 1986a. New camerate crinoids of the suborder Glyptocrinina from the Lower Silurian Brassfield Formation (southwestern Ohio). Journal of Paleontology 60, 887–897. Ausich, W.I., 1986b. Early Silurian inadunate crinoids (Brassfield Formation, Ohio). Journal of Paleontology 60, 719–735. Ausich, W.I., 1986c. Early Silurian rhodocrinitacean crinoids (Brassfield Formation, Ohio). Journal of Paleontology 60, 84–106. Ausich, W.I., 1987a. Revisions of Rowley's Ordovician (?) and Silurian crinoids from Missouri. Journal of Paleontology 61, 563–578. Ausich, W.I., 1987b. Brassfield Compsocrinina (Early Silurian crinoids) from Ohio. Journal of Paleontology 61, 552–562. Ausich, W.I., 1987c. Revision of Rowley's Ordovician(?) and Silurian crinoids from Missouri. Journal of Paleontology 61, 563–578. Ausich, W.I., 1996. Crinoid plate circlet homologies. Journal of Paleontology 70, 955–964. Ausich, W.I., 1998. Early phylogeny and subclass division of the Crinoidea (phylum Echinodermata). Journal of Paleontology 72, 499–510. Ausich, W.I., 2009. These are not the crinoids your granddaddy knew! MAPS Digest 32, 4–19. Ausich, W.I., 2010. Post-hoc sampling analysis of crinoid collections from Anticosti Island, Quebec, Canada. Memoirs of the Association of Australasion Palaeontologists 39, 19–25. Ausich, W.I., Copper, P., 2010. The Crinoidea of Anticosti Island, Quebec (Late Ordovician to Early Silurian). Palaeontographica Canadiana 29, 1–163.

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