Uppermost Hamilton Group, Middle Devonian (New York State: USA)

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Palaeogeography, Palaeoclimatology, Palaeoecology 185 (2002) 1^24 www.elsevier.com/locate/palaeo

Statistical testing of community patterns: uppermost Hamilton Group, Middle Devonian (New York State: USA)

Nicole Bonuso , Cathryn R. Newton, James C. Brower, Linda C. Ivany

Syracuse University, Department of Earth Sciences, Syracuse, NY 13244, USA

Received 3 September 2001; accepted 28 February 2002

Abstract

We present an extensive and rigorously controlled quantitative paleoecological study within an interval of inferred coordinated stasis. This Middle Devonian Hamilton Group study completes a 20-yr project by providing data within the unresolved upper Hamilton Group section. Together with other rigorously controlled studies, these data sets have the potential to address the larger question of coordinated stasis in the fossil record. We collected data from the Windom Member, Moscow Formation (uppermost Hamilton Group), to test different statistical approaches to define paleocommunities. We evaluate various techniques, including non-parametric multidimensional scaling and agglomerative hierarchical clustering to decipher community patterns. Additionally, we advocate regular use of cluster significance testing along with ANOSIM (i.e. analysis of similarities) when examining ecological data. Together these techniques test the significance of sample groups more rigorously than conventional testing (e.g. discriminant analysis or analysis of variance (ANOVA)). Our results indicate that communities within this upper Hamilton Group interval exhibit variable taxonomic membership within a relatively stable ecological structure. ß 2002 Elsevier Science B.V. All rights reserved.

Keywords: Hamilton Group; Middle Devonian; paleoecology; statistical methods

1. Introduction the Hamilton Group to the scienti¢c community through his work on regional stratigraphy. In the The Middle Devonian Hamilton Group of New early 1900s, a number of studies on stratigraphy York State has captivated geologists and paleon- and associated facies were published (e.g. Cleland, tologists for nearly 200 yr with its beautifully pre- 1903; Cooper, 1930, 1933). Cooper (1957) and served and richly diverse fossils. Vanuxem (1840), Rickard (1975) later revised this work. By the one of the ¢rst to study this rock unit, introduced 1970s, researchers began to take advantage of the Hamilton Group’s excellent stratigraphic framework by embarking upon comparative facies anal- * Corresponding author. Present address: University of yses and paleoecological studies (Grasso, 1970, Southern California, Earth Sciences Department, Los Angeles, CA90089-0740, USA.Tel.: +1-213-740-5121; Fax: +1-213- 1973; Thayer, 1974; Bowen et al., 1974; Brett, 740-8801. 1974; Selleck and Hall, 1977). E-mail address: [email protected] (N. Bonuso). During this time, the speciation model of punc-

PALAEO 2883 9-8-02 2 N. Bonuso et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 185 (2002) 1^24 tuated equilibria (Eldredge and Gould, 1972) was taxa and proposed the ecological locking model. derived in part from observations of the Hamilton This model suggests that interspeci¢c interactions Group trilobite Phacops rana. Although this introduce some degree of stability to the commun- work as pivotal, the Hamilton Group was none- ity; consequently, faunas can tolerate modest £uc- theless considered scienti¢cally underdeveloped tuations in the environment. with respect to paleoecology and paleoenviron- In their original paper, Brett and Baird (1995) mental studies especially in comparison to other compiled data on the occurrence of species from classic fossiliferous sites (Brett, 1986). With this in the Silurian through mid-Devonian of New York, mind, Brett and Baird, and others have estab- Pennsylvania, and Ontario. The Middle Devonian lished an outstanding stratigraphic and paleoenvi- data set included counts of carryover and hold- ronmental framework for the Hamilton Group over species and comparisons of common taxa (e.g. Baird and Brett, 1983; Brett and Baird, within congruent facies. Brett and Baird (1995) 1985, 1986; Brett, 1986; Landing and Brett, 1991). concluded that 80% of species occur throughout Brower et al. (1978) also helped to expand the 5^6-Ma Middle Devonian, Hamilton^Tully Hamilton Group studies by contributing one of interval and display minor or no net morpholog- the ¢rst quantitative paleoecological analyses em- ical change. Likewise, both common and rare taxa phasizing faunal dynamics of a shallowing-up- in coral-rich beds persist in similar rank abundan- ward cycle in the lower Hamilton. Brower’s con- ces throughout the Hamilton Group (Brett and tinuing research (Brower, 1987; Brower and Nye, Baird, 1995). 1991) and contributions of other workers (e.g. The proposal of coordinated stasis engendered Savarese et al., 1986; McCollum, 1991; Lieber- a wave of research on patterns of stability within man et al., 1995; Newton et al., 2001) served to the fossil record, before a quantitative test of document faunal and ecological patterns within stability patterns had fully been analyzed tempo- the lower and middle Hamilton Group, but quan- rally within the Hamilton Group (e.g. DiMichele titative data from the uppermost Hamilton inter- and Phillips, 1995; Morris, 1996; Tang and vals remain unresolved. Bottjer, 1996; Patzkowsky and Holland, 1997; Hamilton Group paleoecological studies con- Ivany, 1997; Huynh et al., 1999; for a fuller over- tinued with the landmark proposal of coordinated view, see Ivany and Schopf, 1996 and references stasis (Brett and Baird, 1992, 1995). This paleo- herein). To date, within Hamilton Group studies, ecological and evolutionary model describes a quantitative testing has been accomplished in the pattern of co-occurring taxa that display a high lower Hamilton (i.e. Newton et al. (2001)) and in degree of persistence and experience little mor- the middle Hamilton (i.e. Savarese et al., 1986; phological change for upwards of 3^7 Myr (Brett Brower and Nye, 1991; McCollum, 1991) but et al., 1996). These intervals of persistence are uppermost Hamilton faunas have remained unre- bracketed by contrasting intervals of simulta- solved. Here, we present data from the uppermost neous, abrupt, faunal turnover involving extinc- Hamilton Group to complement these earlier tion of generally 70% or more of the original works and to complete the picture of faunal taxa (Brett et al., 1996). stability and change within this important inter- Two mechanisms proposed to account for the val. faunal stability of coordinated stasis are the envi- Acrucial question, therefore, is whether com- ronmental tracking model and the ecological lock- munity patterns, as revealed by quantitative pa- ing model. The environmental tracking model leoecological data, re£ect stability throughout holds that taxa migrate with a preferred environ- the temporal range of the Hamilton Group. To ment as it shifts in space and time (Brett and approach this question one needs consistent sta- Baird, 1995; Bennington and Bambach, 1996). tistical methodologies in order to promote com- Morris (1995) believed that environmental track- parisons among studies. Quantitative analyses ing failed to account for the observed degree of throughout the Hamilton, with standardization coordinated stability and change across unrelated of methodologies, allow resolution of community

PALAEO 2883 9-8-02 N. Bonuso et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 185 (2002) 1^24 3 structural patterns throughout the Hamilton Group. Coordinated stasis raises interesting ques- tions for both ecological and evolutionary theory. If coordinated stasis occurs, it implies that community patterns are stepwise and pulsed. If coordinated stasis is not occurring, then taxa might form transient, mosaic associations that might in- teract, but they are not synchronous in their ecological and evolutionary patterns (Goodall, 1954; Gauch, 1982; Etter, 1999). The potential signi¢- cance of either outcome warrants aggressive large- scale statistical testing of communities throughout the Hamilton Group. This paper is an integral part of a rigorous test of coordinated stasis throughout the Hamilton Group, because it provides the missing piece of quantitative paleocommunity data from the uppermost Hamilton interval (i.e. the Windom Member, Moscow Formation). We propose a consistent statistical methodology appropriate for testing stasis in well-preserved fossiliferous faunas such as the Hamilton Group. This approach not only allows us to decipher community patterns but also a¡ords meaningful comparisons of quantitative paleocommunity data throughout this Hamilton interval, considered the paradig- matic example of coordinated stasis (Brett and Baird, 1995).

2. Methods for characterizing communities

2.1. Sampling strategy

Fossil collections were taken from an 11-m coarsening-upward cycle within the Windom Member of the Moscow Formation (Fig. 1). Forty-¢ve samples were collected at 20-cm vertical spacing (Fig. 2). The sampling protocol involved uncovering bedding planes and identifying all common and rare taxa until 300 specimens were counted. Shell and trilobite fragments identi¢able at the species level were included in these counts, whereas presence^absence of trace fossils, crinoid stems, bryozoans, and wood fragments was noted Fig. 1. (A) Index map. (B) Stratigraphic section of the Ham- in the ¢eld but not included in multivariate anal- ilton Group in Morrisville area, Madison County, New York. yses. Rarefaction curves for these data demon- strate that this 300 count captures an adequate

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95% probability of ¢nding a species that makes up 1% of the individuals (Davis, 1986). Conse- quently, any species comprising less than 1% of each sample were deleted due to the possibility of sporadic occurrence and unreliability. All taxa constituting over 1% of a sample were retained in order to contribute temporal and spatial variation in this analysis. The data set includes 67 taxa (Table 1). Multivariate statistics, such as ordinations and clustering, establish a visual picture of samples and species groups within a data set. Both techniques should be employed together in paleoecology because clustering and ordinations are subject to di¡erent sources of distortion (Sneath and So- kal, 1973; Gauch, 1982; Brower and Nye, 1991; Fig. 3. Rarefaction curve for three samples. Curves are listed Shi, 1993; Ivany, 1999; Newton et al., 2001). from stratigraphic bottom to top: F-78, B-19, and B-31. Clustering preserves small-scale similarities at the expense of large-scale distortion; conversely, number of species (Fig. 3). At vertical increments ordinations retain large-scale patterns at the of 1 m, replicate samples were also collected from cost of small-scale distortion. We selected the sites approximately 4 m laterally along the same unweighted pair group method (UPGM) for bedding plane. Samples that lie in the same bed- agglomerative hierarchical clustering because it ding planes were compared to establish the lateral minimizes the amount of distortion in the reproducibility of faunal composition. dendrogram relative to the original similarity or di¡erence matrix (Sneath and Sokal, 1973). Two 2.2. Statistical analysis coe⁄cients were used: the Bray^Curtis dissimilarity distances for samples and Pearson’s product- When attainable, relative abundance data are moment correlation coe⁄cient for species. known to include more information in a study Ordination methods include techniques such as in comparison to presence^absence data (Sneath polar ordination, principal component analysis, and Sokal, 1973; Gauch, 1982; Rahel, 1990). reciprocal averaging, and non-parametric multidi- Quantitative abundance data are obtainable at mensional scaling (NMDS). The general patterns this outcrop and therefore are used to describe derived from these procedures are largely the faunal composition. Absolute counts were stan- same. Since NMDS uses the rank order for ordi- dardized to percentages prior to statistical analy- nation and therefore removes the assumption of sis (see Appendix 1). Rare taxa generally exhibit normality, this technique is most appropriate for high rates of turnover in both ecological and geo- paleoecological data. The NMDS analysis pre- logical time (Boucot, 1990; Stanley, 1990; El- sented uses the Euclidean distances and rank or- dredge, 1992; Gaston, 1994; Lawton et al., ders a Bray^Curtis dissimilarity matrix. 1994; Sepkoski, 1994; Boucot, 1996; McKinney After communities and clusters were recognized et al., 1996). According to binomial sampling using clustering and ordinations, we then applied probabilities, counting 300 specimens gives a cluster signi¢cance testing (Sneath, 1977) and the

Fig. 2. Loss on ignition, community and lithology data in reference to stratigraphic position of samples. Letters within the Devo- nochonetes^Longispina^Mucrospirifer community represent assemblage variation in relation to stratigraphic position. M = Mucro- spirifer cluster, B = Bivalve cluster, D = Devonochonetes scitulus cluster, and L = Longispina cluster.

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Table 1 List of taxa and taxon codes used for the data sets Code Species Code Species 2 Actinopteria boydi 48 Tellinopsis subemarginata 4 Carydium bellistriata 49 Ambocoelia umbonata 5 Carydium varicosum 50 Athyris cora 6 Cimitaria recurva 52 Athyris spiriferoides 7 Cornellites fasciculata 53 Craniops hamiltoniae 8 Cypricardella bellastriata 56 Cyrtina hamiltonensis 9 Cypricardella tenuistriatus 57 Devonochonetes coronatus 10 Eoschizodus chemungensis 58 Devonochonetes scitulus 11 Goniophora hamiltonensis 59 Elita ¢mbriata 13 Gramatodon hamiltoniae 60 Lingula punctata 14 Grammysia bisulcata 61 Longispina mucronata 15 Grammysioidea alveata 62 Mediospirifer audaculus 17 Grammysioidea arcuata 64 Mucrospirifer consobrinus 16 Grammysioidea constricta 65 Mucrospirifer mucronatus 18 Grammysioidea globosa 66 Petrocrania hamiltoniae 22 Leiopteria ra¢nesqui 67 Protoleptostrophia perplana 23 Leiopteria sayi 69 Rhipidomella penelope 25 Modiella pygmaea 71 Spinocyrtia granulosa 28 Modiomorpha amygdaloides 72 Spinulicosta spinulicosta 26 Modiomorpha concentrica 73 Strophodonta demissa 27 Modiomorpha mytiloides 74 Tropidoleptus carinatus 33 Nuculites oblongatus 75 Dipleura dekayi 29 Nuculites triqueter 77 Greenops boothi 30 Nuculoidea corbuliformis 79 Phacops rana 31 Nuculoidea lirata 80 Glyptotomaria capillaria 36 Orthonota undulata 82 Palaeozygopleura hamiltoniae 37 Palaeoneilo constricta 84 Retispira leda 38 Palaeoneilo emarginata 85 Ruedemannia trilix 39 Palaeoneilo ¢losa 88 ‘Orthoceras’ sp. 40 Paracyclas proavia 90 Straight orthocone 41 Parallelodon sp. 91 Tornoceras uniangulare 42 Pholadella radiata 95 Hyolithes sp. 45 Pterinopecten undosus 46 Pterinopecten vertumnus 47 Pterochaenia fragilis

ANOSIM (analysis of similarities) technique Gaussian distributions is usually 10%, 5%, or 1%. (Clarke, 1993) to quantitatively test for stability For rectangular distributions, the speci¢ed per- through time among samples. Cluster signi¢cance centage is 0% overlap. The more reasonable ques- testing, though seldom applied in paleoecology, tion for paleoecology is whether the samples were proves to be a more informative test than dis- drawn from two parent populations that have criminant analysis (Sneath, 1977, 1979). Unlike overlapping or non-overlapping rectangular distri- discriminant analysis, which determines whether butions (Sneath, 1977, 1979). However, for this cluster means di¡er statistically, cluster signi¢- analysis, calculations using either Gaussian or rec- cance testing resolves whether samples from two tangular distributions result in similar signi¢cance clusters are drawn from parent populations that testing results. overlap more or less than a speci¢ed percentage. Cluster signi¢cance testing is accomplished by This test can be done for Gaussian or rectangular calculating q-scores as the orthogonal projection distributions. The speci¢ed overlap percentage for of samples onto an axis that connects the cen-

PALAEO 2883 9-8-02 N. Bonuso et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 185 (2002) 1^24 7 troids of the two clusters in question. The W sta- calculated the statistics for the cluster signi¢cance tistic of disjunction is calculated from these testing. PRIMER 4.0 produced the ANOSIM cal- q-scores and the signi¢cance is determined from culations. ¢g. 2 of Sneath (1979). q-scores resemble discriminant function scores but di¡er in two major 2.3. Facies analysis respects. First, they may not maximize the separation between the two clusters, whereas discrim- An excellent stratigraphic framework for the inant function scores do. Secondly, q-scores are Hamilton Group exists in the literature (e.g. not sensitive to the number of variables involved, Cooper, 1930, 1933; Grasso, 1978; Brett, 1986; whereas discriminant function scores are. Since Landing and Brett, 1991; Mayer, 1994; Brett this data set contains 45 samples and 67 species, and Baird, 1996). Data collected for ¢eld samples cluster signi¢cance testing must be used rather in this study include grain size, sediment color, than discriminant analysis. weight percent of total organics (measured by With suitable replicate samples, the ANOSIM loss on ignition; Dean (1974)) bedding type and technique (Clarke, 1993) tests for spatial and tem- thickness, type of burrows (if any), and any other poral di¡erences in community structure by com- noteworthy features. bining permutation tests with the general ‘Monte Carlo’ randomization approach (Hope, 1968; 2.4. Ecological analysis Clarke, 1993). This non-parametric, permutation procedure is based on the rank ordering of the Two measures of species diversity, species rich- Bray^Curtis similarities (Clarke and Warwick, ness and species evenness, aid in describing the 1994). The null hypothesis (H0) states there are ecological characteristics of community data. A no di¡erences in community composition between commonly applied measure of species diversity is sample intervals. To test the null hypothesis, this the Shannon^Wiener index: procedure follows three main steps (refer to Clarke, 1993 and Clarke and Warwick, 1994 for 0 H ¼ 34ðpiÞðlog2piÞ more details). The ¢rst step computes a test statistic (Global R) that contrasts the variation between pre-de¢ned clusters with variation within where HP = index of species diversity and clusters (Clarke, 1993). Next, the samples are ran- pi = proportion of total sample belonging to the domly reshu¥ed and the R statistic recomputed ith species. Although the Shannon^Wiener index for a chosen number of permutations. This calcu- incorporates species evenness in its calculation, lation establishes a predicted distribution of R in this measure is useful on its own. Equitability the case that H0 is correct (Clarke, 1993). In the (E) is a measure that indicates how evenly taxa third step, the observed value of R and the pre- are distributed within an assemblage. The equit- dicted permutation distribution are compared; If ability index is derived from the Shannon^Wiener H0 is true, the observed R value will fall within index and is calculated as: the range of the computed permutated distribu- 0 0 tion. For more information about any of the E ¼ H =H max above techniques, see Sneath and Sokal (1973), Sneath, (1977, 1979), Pielou (1977), Gauch (1982), where HPmax is equal to the value of HP if all Greig-Smith (1983), Legendre and Legendre species are evenly distributed, and is calculated (1983), Pielou (1984), Clarke (1993) and Clarke using logeS/loge2 where S = number of species. A and Warwick (1994). value of one indicates that all taxa are equally Ordination and clustering techniques were pro- abundant in the sample. duced using a combination of PC-ORD 3 and We group taxa into eight ecological categories SYSTAT 9 statistical packages. Aprogram writ- based on trophic strategy and attachment-loco- ten by Dr. J.C. Brower of Syracuse University motion type in order to characterize the ecological

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Fig. 4. (A) Dendrogram for samples from the Windom Member, upper Moscow Formation. Original data are percentages of 67 species and 45 samples. Letters on the left of the dendrogram represent assemblages within the Devonochonetes^Longispina^ Mucrospirifer community. M = Mucrospirifer cluster, B = Bivalve cluster, D = Devonochonetes scitulus cluster, and L = Longispina cluster. Communities are also labeled. Location of samples is shown in Fig. 2. (B) Dendrogram for taxa from the Windom Mem- ber, upper Moscow Formation. Original data are percentages of 67 species and 45 samples. Species groupings are named after the most common species in that particular group. Species codes are found in Table 1. structure of the various communities and clusters. 3. Lithostratigraphy Ecological categories follow Newton et al. (2001) in order to make consistent comparisons with pre- The Windom Member lithofacies constitutes viously published data. These include deep endo- thinly bedded, light-olive gray, non-calcareous byssate suspension feeders, epibyssate or shallow shale gradually grading up into a medium^dark endobyssate suspension feeders, epifaunal benthic gray, highly indurated, silty shale (Fig. 2). This crawlers, infaunal deposit feeders, infaunal fully 11-m section has an extensive storm bed deposit buried suspension feeders, nektonic carnivores, at the 5.25-m mark. This storm bed laterally ex- pedunculate suspension feeders, and reclining sus- tends across the entire outcrop and consists pension feeders. mainly of Spinocyrtia granulosa. Due to the un-

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Fig. 4 (Continued). usual nature of this bed, (i.e. transported, size Organic content slightly decreases upsection sorted), it is not included in further analyses. from 3.1 wt% of organics to the 2.1 wt% of or- Zoophycos trace fossils range throughout the ganics. Average weight percent of organics for the succession, becoming more abundant upsec- entire outcrop is approximately 2.7. An anoma- tion. lous decrease in organics to 1.9 wt% of organics

PALAEO 2883 9-8-02 10 N. Bonuso et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 185 (2002) 1^24 in sample B-17 (Fig. 2) occurs at the base of the valve cluster to 30% in the Longispina cluster). storm bed. This anomalous drop in organics was Other taxa occur in relatively low percentages (i.e. most likely caused by winnowing during deposi- 6 1%) throughout the section. tion. In summary, both grain size and weight per- b Devonochonetes scitulus/Mucrospirifer group: cent of total organics indicate that the site gener- (S58 through S53) contains many common spe- ally has a dark and ¢ne-grained lithofacies that cies, such as D. scitulus (ranging from 13% to subtly changes into a slightly coarser lithofacies 56% in all clusters except the Tropidoleptus sam- with a lower organic content (Fig. 2). ple), Mucrospirifer mucronatus (9% to 50%), Pale- oneilo constricta (3% to 6%), Devonochonetes coronatus (3% to 4%), and Greenops boothi (1% to 4. Description of community patterns 8%). All species are present within the Mucrospiri- fer, Longispina, Bivalve and D. scitulus sample 4.1. Cluster analysis clusters except where noted. b Tropidoleptus group: (S36 through S74) con- 4.1.1. Sample clusters tains common and rare species. The most com- Fig. 4Aillustrates the dendrogram for the 45 mon taxon in the group, Tropidoleptus carinatus, samples based on 67 species. Five distinct groups ranges from 2% to 31% and is present in all clus- cluster out at a distance of 0.475: a Mucrospirifer ters. Carydium bellistriata, Cypricardella tenuis- cluster, Bivalve cluster, Longispina cluster, Devo- triatus, and Palaeoneilo emarginata are the domi- nochonetes scitulus cluster and a Tropidoleptus nant bivalves found in this group. sample (Fig. 4A). Names are assigned after the b Spinulicosta/Ambocoelia group: (S5 through most common taxon in its group. All samples S91) consists mainly of rare species. Spinulicosta with these groups are labeled in Fig. 4Aand their spinulicosta and Ambocoelia umbonata are the stratigraphic positions are shown in Fig. 2. Begin- only common species with relatively high percen- ning at the bottom, the stratigraphic sequence of tages. Notably, both taxa display low frequencies clusters originates with the Mucrospirifer cluster. (i.e. V2%) in all clusters especially the Mucro- Next, the D. scitulus cluster and Longispina cluster spirifer sample cluster ( 6 0.3%). Rhipidomella pe- alternate with one another throughout the middle nelope is another notable taxon that comprises of the section with the Longispina cluster being approximately 3% of the Tropidoleptus sample. concentrated toward the bottom and the D. scitu- b Palaeozygopleura group: (S79 through S33) lus cluster toward the top (Fig. 2). The Bivalve contains rare species that range throughout the cluster is then overlain by the Tropidoleptus outcrop, including Palaeozygopleura hamiltoniae. sample (Fig. 2). According to the dendrogram, All are present in the Mucrospirifer, Longispina, sample B-38 (i.e. the Tropidoleptus sample) clus- Bivalve, and Devonochonetes scitulus sample clusters at a similarity of 0.679 suggesting that this ters. Only small frequencies of Nuculites oblonga- sample is an outlier from the other clusters (Fig. tus and Tellinopsis subemarginata (i.e. 1%) are 4A). also encountered in the Tropidoleptus cluster.

4.1.2. Species clusters 4.2. NMDS Clusters were also generated for 67 species (Fig. 4B). The following groups of species can NMDS reveals a community pattern similar to be recognized, beginning at the top of the dendro- that in the cluster analysis (Figs. 5 and 4A). All gram (Fig. 4B); species codes are in parentheses the clusters swarm together and are distinct from after each species group name (see Table 1 for the Tropidoleptus sample. Within that cluster identi¢cations). swarm, NMDS emphasizes the relationships be- b Longispina group: (S56 through S73) consists tween clusters by partitioning each cluster and mostly of rare species with the exception of Lon- visually displaying them together. In Fig. 5, the gispina mucronata (ranging from 2% in the Bi- samples within the Devonochonetes scitulus cluster

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Fig. 5. NMDS analysis for benthic assemblages. Original data are percentages of 67 species and 45 samples. Final stress for the two-dimensional solution is 13.86%. are plotted together near the samples within the 5. Taxonomic and ecological patterns through time Longispina cluster. Together, these two clusters are more closely related to the Bivalve cluster Fig. 6 demonstrates that Devonochonetes scitu- and the Bivalve cluster is linked to the Mucrospiri- lus generally dominates this outcrop and is nota- fer cluster. All other clusters di¡er from the Tro- bly present in all samples except B-38 (i.e. the pidoleptus sample. These relationships between Tropidoleptus sample). sampling units correspond well to the dendrogram In addition, there is visible variation of domi- in Fig. 4A. An underlying ecological gradient is nant taxa within each cluster. At the bottom of not evident within this NMDS plot or within the section, Mucrospirifer mucronatus dominates other ordinations (i.e. polar ordination, principal the ¢rst cluster. As we move upsection, the Lon- component analysis, and reciprocal averaging). gispina and Devonochonetes scitulus clusters have This may be due to distortion because 45 dimen- a similar taxonomic composition but vary in cat- sions (i.e. 45 samples) are represented in two di- egory percentages. Next, although the Bivalve mensions (i.e. Axis 1 and Axis 2). cluster is dominated by D. scitulus, bivalves mark-

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Fig. 6. Taxonomic composition through time within the Soule Road outcrop.

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Fig. 7. Shannon^Wiener diversity index and equitability index plotted through time. edly increase in percentages within this cluster. F3 (Fig. 4A), contains a high percentage of Mu- The Tropidoleptus sample is clearly di¡erent in crospirifer mucronatus (approximately 50%) and a reference to taxonomic composition; D. scitulus low percentage of Devonochonetes scitulus (ap- disappears and Tropidoleptus carinatus dominates proximately 14%). Greenops boothi, another com- the sample. mon species, constitutes 8% of the three samples.

5.1. Taxonomic patterns 5.1.2. The Devonochonetes scitulus and Longispina cluster 5.1.1. The Mucrospirifer cluster The next two clusters, when superimposed on Beginning from stratigraphic bottom, the Mu- the stratigraphic section, alternate with one an- crospirifer cluster, containing samples F1 through other throughout the next interval (Fig. 2). With-

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Fig. 8. Ecological structure of the clusters.

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Table 2 Results of cluster signi¢cance testing for the Soule Road outcrop Pairs of clusters W statistic Approximate Total Observed Non-central Min. and Max. critical of critical W sample percentage Student’s t Student’s t values with disjunction statistic value size of q-score values corresponding percentage (at p = 0.05) overlap of population overlap (t value at 0.95) Devonochonetes vs. Longispina 1.7 2.1 38 7.9 10.3 Min: t = 9.9, 25% cluster overlap; Max: t = 10.9, 20% overlap Devonochonetes, Longispina cluster 1.5 2.2 41 0 9.8 Min: t = 9.7, 25% vs. Mucrospirifer cluster overlap; Max: t = 10.2, 20% overlap Devonochonetes, Longispina, 1.6 2.1 44 9.1 10.2 Min: t = 9.7, 70% Mucrospirifer cluster vs. Bivalve overlap; Max: t = 12.5, cluster 60% overlap Devonochonetes^Longispina^ 3.9 2.1 45 0 26.3 Min: t = 21.7, 0% Mucrospirifer community vs. overlap; Max: t s 21.7, Tropidoleptus community 0% overlap Replicate sample comparisons 0.4 2.9 11 27.3 1.4 Min: t 6 1.8, 100% overlap; Max: t = 1.8, 100% overlap The critical values for the W statistic are for non-overlapping rectangular distributions of the parent populations. The W statistic is taken from Sneath (1979, ¢g. 2). See Sneath (1977) for discussion of the non-central Student’s t values. in the Devonochonetes scitulus cluster, D. scitulus 5.1.3. The Bivalve cluster averages 58%, Ambocoelia umbonata 13%, Mucro- Samples B-35 through B-37 constitute the Bi- spirifer mucronatus 7%, and Longispina mucronata valve cluster (Fig. 4A). Although almost equally 6% (Fig. 6). The Longispina cluster averages high in average percentages of Devonochonetes approximately 33% L. mucronata, 24% D. scitu- scitulus and Mucrospirifer mucronatus (i.e. 32% lus, 15% M. mucronatus, and 10% A. umbonata and 26%), this cluster shows the highest percen- (Fig. 6). tages of bivalves. For example, Cypricardella bel-

Table 3 ANOSIM results for the Windom Member data Global test: Sample statistic (Global R) 0.377 Number of permutations: 5000 Number of permutated statistics greater than or equal to Global R:0 Signi¢cance level of sample statistic: 0.0% Pairwise tests: Groups useda Statistic value Possible permutations Permutations used Signi¢cant statistics Signi¢cance level 1, 2 1.000 10 10 1 10.0% 1, 3 0.851 445 445 1 0.2% 1, 4 0.870 3654 3654 1 0.0% 2, 3 0.738 455 455 1 0.2% 2. 4 0.315 3654 3654 185 5.1% 3, 4 0.160 2.707D+09 5000 119 2.4% a 1^Mucrospirifer cluster; 2 ^ Bivalve cluster; 3 ^ Longispina cluster; 4 ^ Devonochonetes scitulus cluster.

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Table 4 Species correlations for the following species D. scitulus L. mucronata M. mucronatus T. carinatus D. scitulus 1.00 L. mucronatus 30.43 1.00 M. mucronata 30.52 0.00 1.00 T. carinatus 30.20 0.25 30.22 1.00

lastriata and Carydium bellistriatum constitute D. scitulus clusters di¡er from the Mucrospirifer 12% and 9% of this cluster. cluster by their increase in pedunculate suspension feeders; essentially these two clusters have identi- 5.1.4. The Tropidoleptus sample cal ecological structure aside from slight di¡eren- Sample B-38 clusters at a distance of 0.679 ces in ecological category percentages. Upsection, (Fig. 4A). Tropidoleptus carinatus comprises 36% the Bivalve cluster begins to increase in infaunal of this sample (Fig. 6). Among the common cho- deposit and suspension feeders and decrease in netids, Devonochonetes scitulus is conspicuously pedunculate suspension feeders. absent from this sample, but Longispina mucrona- The Tropidoleptus sample consists mostly of re- ta contributes 14%. Mucrospirifer mucronatus and clining suspension feeders (Fig. 8). However, the Ambocoelia umbonata display a frequency of 11%, dominant recliner is Tropidoleptus carinatus rather and 9% in this sample. Sample B-38 di¡ers par- than Devonochonetes scitulus, which is prevalent ticularly from the other clusters with respect to throughout the rest of the section (Fig. 6). In the less common taxa. For example, Carydium fact, D. scitulus is absent entirely from sample varicosum and Elita ¢mbriata represent 8% of B-38. Pedunculate suspension feeders (e.g. Ambo- this sample, whereas within the other clusters, coelia umbonata and Rhipidomella penelope) and C. varicosum and E. ¢mbriata constitute on aver- infaunal deposit feeders (e.g. Carydium bellistria- age 1^2%. tum and Paleoneilo emarginata) constitute 13^12% of the community. Other ecological categories dis- 5.2. Ecological patterns play minor frequencies within this cluster, or are absent altogether (Fig. 8). The Shannon^Wiener diversity index £uctuates greatly from sample to sample (Fig. 7). Speci¢c equability calculations for each sample indicate 6. Testing stability that samples are relatively consistent at an average of 0.67 (Fig. 7). 6.1. Cluster signi¢cance testing Fig. 8 indicates that the dominant ecological structure of all clusters is relatively similar, with Two main communities are recognized in this faunas dominated by reclining suspension feeders study according to the clustering signi¢cance test- (i.e. Devonochonetes scitulus, Mucrospirifer mucro- ing results, namely the Devonochonetes^Longi- natus, Longispina mucronata, Tropidoleptus cari- spina^Mucrospirifer community and Tropidoleptus natus, and Spinulicosta spinulicosta). Ecological community. These communities are named for structures of remaining cluster proportions are their most common taxa. more variable. Beginning with the stratigraphic Cluster signi¢cance testing was applied to the bottom, the Mucrospirifer cluster has a substantial samples in the clusters and then to the commun- amount of deep endobyssate suspension feeders, ities (Table 2). First, the Devonochonetes scitulus as well as infaunal deposit feeders and epifaunal cluster and the Longispina cluster comparison re- benthic crawlers (Fig. 8). The Longispina and vealed that the parent populations of the two

PALAEO 2883 9-8-02 N. Bonuso et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 185 (2002) 1^24 17 clusters have rectangular distributions that over- this procedure, the various clusters were not lap. Next, the combination of the D. scitulus clus- drawn from the same population; hence, there ter and the Longispina cluster was compared with is signi¢cant change in taxonomic composition the Mucrospirifer cluster; according to the W sta- within this upper Hamilton Group community tistic, these underlying populations overlap. Next, (Table 3). D. scitulus, Longispina, and Mucrospirifer clusters were tested against the Bivalve cluster. This comparison also indicates that the rectangular distributions of the parent populations overlap. There- 7. Discussion fore, we place these four clusters into the Devonochonetes^Longispina^Mucrospirifer com- 7.1. Taxonomic and guild-level patterns munity. The Devonochonetes^Longispina^Mucro- spirifer community was then compared to sample According to the cluster signi¢cance testing, B-38. The W statistic of disjunction demonstrated this particular site generally consists of one large that the two clusters were drawn from popula- community, the Devonochonetes^Longispina^Mu- tions with rectangular distributions that do not crospirifer community. When examined rigor- overlap at the 0.05 probability level (Table 2). ously, this long-ranging community exhibits taxo- Consequently, these results con¢rmed the statisti- nomic variation within a relatively consistent cal separation of the Devonochonetes^Longispina^ ecological structure. Our ANOSIM results suggest Mucrospirifer community from the Tropidoleptus the taxonomic variation seen between clusters community. di¡ers from the taxonomic variation within clus- Cluster signi¢cance testing also con¢rms the ters (Table 3). An example of this taxonomic var- lateral reproducibility of taxonomic composition. iation begins with the most abundant species Replicate samples were taken every meter, ap- Devonochonetes scitulus. D. scitulus occurs wide- proximately 4 m down bedding plane, and com- ly within the Devonochonetes^Longispina^Mucro- pared with samples along the same stratigraphic spirifer community, but £uctuates in percentage interval. The W statistic of disjunction illustrates from sample to sample. When there is a high per- that the replicate samples are drawn from the centage of Longispina mucronata, there is a low same distribution because their rectangular distri- percentage of D. scitulus. Likewise, when there butions overlap signi¢cantly (Table 2). is a percentage increase in Mucrospirifer mucronatus there is a decrease in D. scitulus. D. scitulus is 6.2. ANOSIM negatively correlated with L. mucronata and M. mucronatus. However, M. mucronatus and In order to test community stability within a L. mucronata are independent of each other as relatively consistent environment, sample B-38 seen in their low correlation of 0.0 (Table 4). was removed from the ANOSIM analysis data These patterns suggest that D. scitulus replaces set. The deletion is justi¢ed, since sample B-38 L. mucronata and M. mucronatus perhaps as a occurs within a di¡erent lithofacies and belongs consequence of larval recruitment. to a di¡erent community (see Figs. 2, 4Aand 5, This negative correlation between dominant and Table 2). The new matrix includes data taxa is consistent with the cluster groups in Fig. from the Mucrospirifer, Bivalve, Longispina, and 6. Through time taxonomic composition changes Devonochonetes scitulus clusters, which make from Mucrospirifer mucronatus to the alternating up the Devonochonetes^Longispina^Mucrospirifer relationship of Longispina mucronatus and Devo- community. This test resulted in an observed nochonetes scitulus followed by an increase in bi- test statistic (Global R) of 0.377 with a signi¢- valves. According to Fig. 6, there are notable var- cance level of 0.0%. This suggests there was a 0 iations within the less common taxa as well. For in 5000 chance that Global R comes from the example, Ambocoelia umbonata is abundant stochastic distribution (Table 3). According to throughout the Longispina cluster, the D. scitulus

PALAEO 2883 9-8-02 18 N. Bonuso et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 185 (2002) 1^24 clusters but is absent from the Mucrospirifer and in this study is to ¢nd the appropriate statistical Bivalve clusters. methodologies for testing coordinated stasis. Dif- The dominant reclining suspension feeders are ferent statistical methodologies are compared us- relatively consistent throughout this interval ing an uppermost Hamilton Group data set. Our (Fig. 8). Although the ecological category persists results con¢rm that the combination of NMDS through time, species composition within the re- and agglomerative hierarchical clustering (using clining suspension feeders varies. For example, the UPGM) re£ects community structure most within the category of recliners, Devonochonetes accurately. Furthermore, although not tradition- scitulus is the most common in the Devonocho- ally used, we advocate the use of cluster signi¢- netes cluster, Mucrospirifer mucronatus is domi- cance testing when examining ecological data. nant within the Mucrospirifer cluster, and Longi- This technique examines a highly pertinent statis- spina mucronata is common within the Longispina tical question, that is, whether or not two clusters cluster. Aside from the reclining suspension feed- of samples were drawn from overlapping or dis- ing category, other ecological categories also seem junct parent populations, based on rectangular or to change through time. The Mucrospirifer cluster Gaussian distributions. This technique for that and Longispina cluster lack infaunal suspension reason is more rigorous than conventional signi¢- feeders; however, infaunal suspension feeders cance tests such as the Student’s t-test, canonical comprise 12% of the Bivalve cluster (Fig. 8). variates, discriminant analysis, and analysis of Comparing the ¢ve clusters one can see that the variance (ANOVA), which only compare the Longispina and D. scitulus clusters are the only taxonomic means of two or more samples. clusters nearly identical in percentages of ecolog- We also suggest the regular use of the ANO- ical categories (Fig. 8). SIM technique. This non-parametric permutation procedure applied to the rank-ordered similarity 7.2. Results in context to coordinated stasis matrix provides a more valid testing framework compared to ANOVA or MANOVA because it Although this study does not compare temporal removes the assumption of normality (Clarke community patterns throughout the Hamilton and Warwick, 1994). This technique also enables Group, it does characterize community patterns researchers to evaluate the taxonomic variation within one Windom Member site; therefore, within clusters compared to between clusters in some initial conclusions concerning patterns of a simple and easily interpreted way. coordinated stasis can be drawn. Our second goal is to determine community According to coordinated stasis, taxonomic patterns within this Windom Member inter- membership and ecological structure persist val (Moscow Formation, uppermost Hamilton through time and are relatively stable within a Group) in context to coordinated stasis. Ac- similar Hamilton Group environment (Brett and cording to our results, the general community Baird, 1995). Within this relatively stable environ- pattern consists of two statistically distinct com- ment, ecological structure continues to persist munities. The Devonochonetes^Longispina^Mucro- while taxonomic membership is signi¢cantly vari- spirifer community comprises four assemblages able through time. These results are therefore not each di¡ering in taxonomic composition and consistent with the present de¢nition of coordi- named after the most common taxon (i.e. Mucro- nated stasis. spirifer cluster, Longispina and Devonochonetes scitulus clusters and the Bivalve cluster). Although consisting of one sample, the Tropidoleptus community constitutes di¡erent taxa than the 8. Conclusion Devonochonetes^Longispina^Mucrospirifer community and is determined to be statistically di¡er- Resolution of stability patterns demands consis- ent. For these reasons, the Tropidoleptus com- tent statistical approaches. One of our main goals munity is deleted and the Devonochonetes^

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Longispina^Mucrospirifer community is tested for Acknowledgements stability. Our results clearly indicate that between cluster Research was conducted as part of N.B.’s Mas- variation and within cluster variation of the ter thesis at Syracuse University and was sup- Devonochonetes^Longispina^Mucrospirifer com- ported by grants from the Paleontological Society munity is drawn from di¡erent parent dis- and the John J. Prucha Field Research Fund at tributions. Hence, this implies that the com- Syracuse University. Acknowledgements are also munity changes throughout time. Graphic rep- made to the donors of the Petroleum Research resentations of taxonomic and ecological Fund of the American Society for support of structure show that taxonomic membership varies this collaborative research program. within a relatively stable ecological structure. Since coordinated stasis requires both taxonomic and ecological consistency within a similar envi- Appendix1 ronment; our results do not meet the criteria of coordinated stasis. Data matrix in proportions

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