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The Pennsylvania State University

The Graduate School

Department of Geosciences

TAXIC AND PHYLOGENETIC APPROACHES TO UNDERSTANDING THE

LATE ORDOVICIAN MASS EXTINCTION AND EARLY SILURIAN

RECOVERY

A Thesis in

Geosciences

Andrew Z. Krug

Submitted in Partial Fulfillment of the Requirements for the Degree of

Doctor of Philosophy

May 2006

The thesis of Andrew Z. Krug was reviewed and approved* by the following:

Mark E. Patzkowsky Associate Professor of Geosciences Thesis Adviser Chair of Committee

Timothy J. Bralower Professor of Geosciences Head of the Department of Geosciences

Christopher H. House Assistant Professor of Geosciences

Peter Wilf Assistant Professor of Geosciences

Alan Walker Evan Pugh Professor of Anthropology and Biology

*Signatures are on file in the Graduate School

iii

ABSTRACT

The rules governing the accumulation and depletion of diversity vary at different geographic scales. Because of the spatially complex nature of the global ecosystem, understanding major macroevolutionary events requires an understanding of the processes that control diversity and turnover at a variety of geographic and temporal scales. This is of particular importance in the study of mass extinction events, which can eliminate established evolutionary lineages and ecologically dominant taxa, setting the stage for post-extinction radiation of previously obscure or minor lineages. If the macroevolutionary consequences of extinctions and recoveries are to be understood and predicted, the spatial and temporal variations in diversity and turnover must be quantified and the processes underlying these patterns dissected. Here, I analyze regional diversity and turnover patterns spanning the Late Ordovician mass extinction and Early Silurian recovery using a database of genus occurrences for inarticulate and articulate brachiopods, bivalves, anthozoans and trilobites. Chapter 2 compares sampling standardized diversity and turnover trends for the paleocontinent of Laurentia to the global pattern derived from genus first and last appearances. After accounting for variation in sampling intensity, we find that marine benthic diversity in Laurentia recovered to pre-extinction levels within 5 Myr, which is nearly 15 Myr sooner than suggested by global compilations. The rapid turnover in Laurentia suggests that processes such as immigration may be particularly important in the recovery of regional ecosystems from environmental perturbations. Chapter 3 explores variability in the dynamics of recovery at the regional scale, by expanding the database both by doubling the number of occurrences for Laurentia and including data from Baltica and Avalonia. These data show that sampling standardized diversity trends for the three regions are variable. Despite the expansion of the database, diversity continues to rebound to pre-extinction levels within 5 Myr of the extinction event in the paleocontinent of Laurentia. However, diversity in Baltica and Avalonia requires 15 Myr or longer to reach pre-extinction levels. This increased rate of recovery in Laurentia is due to both lower Late Ordovician extinction intensities and higher Early Silurian origination rates relative to the other continents. Using brachiopod data, the Rhuddanian recovery was dissected into genus origination and invasion. This analysis reveals that standing diversity in the Rhuddanian of Laurentia consists of a higher proportion of invading taxa than in either Baltica or Avalonia, indicating invading taxa were prominent in driving the rapid Laurentian rebound. However, when invading taxa are excluded from diversity counts, Laurentian diversity still rebounds to pre-extinction levels within 10 Myr of the extinction event, suggesting genus origination rates were also higher in Laurentia than in either Baltica or Avalonia. Higher rates of origination in Laurentia may be expected due to its large size, paleogeographic location, and environmental make-up. Hypotheses explaining the increased levels of invasion into Laurentia remain largely untested and require further scrutiny. In chapter 4, a phylogenetic analysis of strophomenid brachiopods was performed to explore the decoupling of ecological, evolutionary, and taxonomic severity resulting from the Late Ordovician mass extinction. After calibrating the cladogram to the fossil record of strophomenids, the stratigraphic ranges of genera were adjusted and ghost iv lineages were added where applicable. Many genera sampled only from the Silurian had their ranges extended into the Ordovician after phylogenetic correction. Using lineages instead of genera resulted in only minor changes to counts of diversity and origination rates. Lineage terminations were accurately recorded using genera, though proportional extinction patterns were altered due to the addition of Ashgillian lineages through the backwards extension of Silurian lineage ranges. No monophyla were eliminated in the Ashgill, and surviving lineages were derived from throughout the phylogenetic tree. This enabled strophomenids to diversify and fill many of the same ecological niches as they had prior to the extinction event. v

TABLE OF CONTENTS

List of Tables v List of Figures vii

Chapter 1. Introduction 1 Mass Extinction 1 Recovery 2 The Fossil Record 3 Research 5

Chapter 2. Laurentian Sampling Standardized Diversity Trends 10 Introduction 10 Data 12 Methods 15 Results 17 Discussion 20 Conclusions 25

Chapter 3. Geographic Variability in Turnover and Recovery Patterns 32 Introduction 32 Data and Methods 34 Results 41 Discussion 48 Conclusions 57

Chapter 4. The Evolutionary Impact of the Late Ordovician Mass Extinction: Insights from Phylogenetic Analyses 68 Introduction 68 Terminology 71 Data and Methods 72 Results 77 Discussion 83 Future Work 90 Conclusions 90

Chapter 5. Conclusions 100 Geographic Variability 100 Phylogenetic Insights into Diversity 103 Future Work 104

References 107 Appendix A. Community Lists 115 Appendix B. Character States 141 Appendix C. Character Assignments 143

List of Figures

Figure Page Figure Caption Number Number Number of occurrences per time interval. Note the similarity between these data and the total diversity curve for Laurentia (see Fig. 3A). 2.1 Particularly striking is the large drop in sampling intensity from the 27 Ashgill (Upper Ordovician) to the Rhuddanian

A. Global diversity calculated from Sepkoski's compendium of generic first and last appearances (16). B. Global proportional origination and 2.2 extinction metrics. L.C. Lower Caradoc. M.C. Middle Caradoc. U.C. 28 Upper Caradoc. Dashed line marks the Ordovician-Silurian boundary.

A. Laurentian total generic diversity. The Caradoc is divided into two intervals here, with all others the same as in the global plot. Diversity is calculated as the total number of genera existing in Laurentia found within or ranged through a time interval. B. Proportional origination and 2.3 extinction metrics calculated for Laurentia. Unlike global rate metrics, 29 regional rate metrics can incorporate factors such as immigration and local extinction in addition to taxonomic origination or extinctions. Dashed line marks the Ordovician-Silurian boundary.

2.4 Rarefaction curves for the seven time bins used in this project. 30

A. Standardized diversity curve generated using rarefaction with range- through (see text for explanation). B. Proportional extinction and 2.5 origination metrics based on the standardized data. Dashed line marks the 31 Ordovician-Silurian boundary.

Paleogeographic reconstruction showing the positions of Laurentia, Baltica, and Avalonia (dark gray) at the beginning of the Caradoc, 458 3.1 Ma. Redrawn from Scotese and McKerrow 1990 59 (http://scotese.com/Default.htm)

Global diversity and turnover metrics. (A) Global diversity for brachiopods, anthozoans, bivalves, and trilobites calculated from Sepkoski’s compendium of genus first and last appearances. (Sepkoski 3.2 2002) (B) origination and extinction metrics. L.C., Lower Caradoc; 60 M.C., Middle Caradoc; U.C., Upper Caradoc. Error bars are 95% confidence intervals. Vertical dashed line marks the Ordovician-Silurian boundary.

Unstandardized diversity curves for (A) Laurentia, (B) Baltica, and (C) Avalonia. Solid lines record diversity with genera ranged-through 3.3 intermediate time intervals. Dashed lines record diversity using only 61 genera sampled from within an interval. Vertical dashed line marks the Ordovician-Silurian boundary.

Unstandardized proportional origination and extinction metrics for (A) Laurentia, (B) Baltica, and (C) Avalonia. Error bars are 95% confidence 3.4 intervals calculated using the binomial probability distribution. Vertical 62 dashed line marks the Ordovician-Silurian boundary. vii

Analytical rarefaction curves for each of the seven time intervals for (A) 3.5 Laurentia, (B) Baltica, and (C) Avalonia. 63

Sampling standardized diversity curves for (A) Laurentia, (B) Baltica, and (C) Avalonia. Diversity was derived using a subsampling algorithm 3.6 that standardizes to a constant number of occurrences per interval. Error 64 bars are 95% confidence intervals. Vertical dashed line marks the Ordovician-Silurian boundary.

Sampling standardized proportional origination and extinction metrics for (A) Laurentia, (B) Baltica, and (C) Avalonia. Error bars are 95% 3.7 confidence intervals. Vertical dashed line marks the Ordovician-Silurian 65 boundary.

Sampling standardized diversity curves for brachiopods from Laurentia, 3.8 Baltica, and Avalonia. Error bars are 95% confidence intervals. Vertical 66 dashed line marks the Ordovician-Silurian boundary.

Proportional contribution of survivorship, genus origination, and invasion to standing diversity in the Rhuddanian time interval for Baltica, 3.9 Avalonia, and Laurentia. Relative contributions were determined using a 66 subsampling program that standardizes by the number of occurrences in each continent.

Sampling standardized brachiopod diversity curves for the paleocontinent of Laurentia. Sold line was calculated using all brachiopods for a given time interval. The dashed line was derived by subtracting invading 3.10 genera from diversity counts in the Silurian time intervals. Error bars are 67 95% confidence intervals. Vertical dashed line marks the Ordovician- Silurian boundary.

Schematic of two scenarios for lineages within monophyla during a mass extinction. A. Four surviving lineages are derived from 4 separate monophyla. In this scenario, the evolutionary and ecological impact of the mass extinction event is expected to be minimal, as most of the 4.1 evolutionary pathways utilized by the group survive the event. B. Four 93 surviving lineages are derived from the same monophyla, with all other monophyla terminated at the boundary. The potential for the evolution of new, unique forms is increased in this scenario, as is the potential ecological impact of the mass extinction event.

4.2 Number of occurrences of strophomenid brachiopods in Laurentia. 93

Geographic distribution of strophomenid brachiopod collections in Laurentia in the Ashgill (A) and Rhuddanian (B). Circles mark locations 4.3 in Laurentia from which collections containing strophomenid 94 brachiopods were collected. Map drawn using programs online at http://paleodb.org. viii

Majority rule consensus tree calculated from 103 most parsimonious trees resulting from a heuristic search. An initial heuristic search was run with all characters unordered and of equal weight. Characters were then 4.4 reweighted based on their consistency index, resulting in 103 equally 95 parsimonious trees of length 58 steps. Numbers indicate the percentage of trees supporting each branch of the consensus tree. Billingsella is used to define the outgroup.

A. Global diversity for strophomenid brachiopods. B. Global 4.5 proportional origination and extinction metrics for strophomenid 96 brachiopods. Dashed line marks the Ordovician-Silurian boundary.

A. Diversity of strophomenid brachiopods in Laurentia. Solid curve represents diversity for all strophomenid genera in the database. Dashed curve represents only genera used in the phylogenetic analysis. See text 4.6 for explanation. B. Proportional origination and extinction metrics for 97 all strophomenid brachiopods in Laurentia, including genera removed from the phylogenetic analysis. Vertical dashed lines marks the Ordovician-Silurian boundary.

Cladogram of Laurentian Ordovician and Silurian strophomenid brachiopods calibrated against their fossil record in Laurentia. Solid 4.7 black lines indicate the occurrence of a genus in the stratigraphic record. 98 Vertical black line indicates the Ordovician-Silurian boundary.

Comparison of diversity and turnover derived from lineages and genera for strophomenid brachiopods in Laurentia. A. Diversity; B. 4.8 Proportional origination; C. Proportional extinction. Dashed lines mark 99 the Ordovician-Silurian boundary.

List of Tables

Table Number Table Caption Page Number Environmental distribution of lists. Numbers designate the 2.1 number of lists entered for each environment in each time 13 interval.

Geographic distribution of lists. Numbers designate the 2.2 number of lists from each state or province in each time 13 interval.

Environmental distribution of lists from Laurentia, Baltica, 3.1 and Avalonia. Numbers designate the number of lists 37 entered for each environment in each time interval.

Chapter 1. Introduction

Mass Extinction

Studies of mass extinctions have traditionally focused on diversity and turnover

patterns at the global scale using synoptic databases of taxonomic first and last

appearances (Bambach et al. 2004, Raup 1976, Sepkoski 1993, 2002). It is from these

databases that mass extinctions were recognized and quantified traditionally as the

proportion of paraclades lost in a given interval of time (Bambach et al. 2004, Raup and

Sepkoski 1982, 1986). Many studies have since attempted to determine the evolutionary

and ecological impacts of both mass extinctions and their subsequent recoveries (Droser

et al. 2000, Hallam 1991, Jablonski 1989, 2004, Lidgard et al. 1993, Miller and Sepkoski

1988, Sepkoski 1984, Sepkoski et al. 2000). Though this has been difficult, many such

attempts suggest the evolutionary and ecological severity of a mass extinction may be

decoupled from its taxonomic severity (Droser et al. 2000, McGhee et al. 2004).

Such studies are critical, as mass extinctions remove large numbers of taxa from the global ecosystem in a geologically short period of time. It has been estimated that the

Late Permian mass extinction (250 Ma) removed the same number of taxa within a few million years as would have been removed in 85 Myr of normal, background extinction

(Raup 1978). Additionally, traits that favor survival during times of normal, or

background, extinction may not confer adaptive advantages during times of mass

extinction (Jablonski 1986, 2004). Because ecological dominants and other diverse clades are suddenly removed, previously minor clades can undergo evolutionary radiations during the post-extinction recoveries. Mass extinctions can therefore cause a 2

complete shift in the evolutionary paths followed by clades, resulting in dramatic changes

to the global ecosystem.

However, global diversity and turnover dynamics are only a small part of the

complex interplay between organisms and their environment. The global ecosystem is

not homogeneous but rather spatially complex, broken up into biological and

environmental subdivisions of various scales. The processes which operate to control

extinction and origination at the global scale may differ from or be driven by those

operating at the regional or local scale. Studies of regional diversity dynamics are few,

yet those undertaken point to globally heterogeneous patterns during times of large scale

radiations (Miller 1997a, Miller and Mao 1998), extinctions (Shen and Shi 2002), and

post-extinction recoveries (Jablonski 1998). If the evolutionary roles of mass extinctions are to be understood, detailed analysis of diversity and turnover dynamics must be undertaken over a wide range of spatial and temporal scales.

Recovery

Extinction is only half of the story when considering the dramatic evolutionary consequences of a mass extinction event. The recovery period following mass extinctions are equally as important, as it is here that evolutionary strategies that will dominate the global landscape emerge. Considerably less focus has been placed on post- extinction recoveries than on the extinction themselves, and the discussion has generally focused on expected models of recovery (Erwin 1998, Sole et al. 2002). Diversification may lag owing to a slow response of the global environment to the perturbation that caused the mass extinction (Hallam 1991). Diversification may be logistic with the shape 3

and duration of the rebound dependent on the magnitude and duration of the extinction

and whether or not the system was at equilibrium immediately prior to the mass

extinction (Sepkoski 1984). Diversification of some taxonomic groups may increase

dramatically in the wake of mass extinctions if other groups that inhibited diversification

during background times are dramatically reduced in species numbers (Miller and

Sepkoski 1988). Finally, diversification may be synergistic as new species facilitate the

evolution of more new species causing per-taxon origination rates to increase continually for several million years following the mass extinction (Kirchner and Weil 2000,

Sepkoski 1998).

Understanding which model or models best describe the diversification following

a mass extinction would reveal much about the ecological and evolutionary processes that

govern global biodiversity. At the regional scale, however, recovery patterns may be

more complex. Diversification may vary geographically, with each region having

different diversity trajectories and varying proportions of bloom taxa and invaders

(Jablonski 1998). Additionally, while speciation is the only process that replenishes

diversity at the global scale, immigrations can replenish diversity and fill ecological

niches at the regional level. The interplay between speciation and immigration within

different regions can drive the success or failure of lineages in the post-extinction world.

The Fossil Record

Many studies of mass extinction and post-extinction recovery are based at least in part on the assumption that the fossil record is an accurate and unbiased record of diversity. However, it has long been known that variability of sampling through time may 4 exert a strong control on perceptions of Phanerozoic diversity trends (Raup 1972). Recent studies have begun to evaluate in greater detail sampling biases on diversity using a variety of methods and databases (Alroy et al. 2001, Crampton et al. 2003, Peters 2005,

Smith et al. 2001). Some intervals of mass extinction have come under close scrutiny because they tend to have a close association with sea level changes and decreases in rock volume that bias the preserved record of diversity, extinction, and origination (Foote

2003, Holland 1995, Peters 2001, 2002, Smith 2001, Smith et al. 2001).

Many procedures have been developed with the goal of decoupling diversity patterns from sampling and preservational biases. Error bars can be placed on stratigraphic ranges using the distribution of sampled horizons through time (Marshall

1990, 1997). Range offsets in first and last appearances can be modeled in a sequence stratigraphic framework using the depth tolerances of organisms and their subsequent probability of collection (Holland and Patzkowsky 1999, 2002). Subsampling and analytical techniques can correct for variations in sample size among collections (Raup

1975, Tipper 1979), and the creation of comprehensive electronic databases of lists of occurrences allows these techniques to be performed across large time intervals (Alroy

2000, Alroy et al. 2001, Miller and Foote 1996). Finally, phylogenetic techniques can produce hypotheses on the evolutionary relationships among taxa through time, which can then be calibrated against the fossil record to imply missing portions of a taxon’s stratigraphic range as well as identify completely un-sampled lineages (Smith 1994,

Smith et al. 2001, Wagner 1995).

Thesis Research

Here I focus on patterns of diversity, origination, and extinction spanning the Late

Ordovician mass extinction and Early Silurian recovery. The Late Ordovician is recognized as the second largest of the Phanerozoic (Sepkoski 1993, 2002), and is thought to be the result of large-scale sea-level fluctuations and environmental changes related to the expansion and contraction of glaciers in an otherwise greenhouse world

(Brenchley et al. 1995). Despite its severity, however, the Late Ordovician extinction brought about only minor paleoecological changes (Bottjer et al. 2001, Droser et al. 1997,

2000), and thus is unlike other mass extinction events, many of which reset macroecological and macroevolutionary trends that had been in existence for millions of years (Erwin 2001).

Sepkoski (1998) described the Late Ordovician mass extinction as typifying patterns of diversity and turnover during mass extinctions and post-extinction recoveries when analyzed at the global scale , including a sharp decline in diversity and a lag of several geologic stages before origination rates increase. However, because of the biases inherent in quantifying diversity and turnover (Alroy 2000, Alroy et al. 2001, Foote 2000,

Miller and Foote 1996), diversity and turnover patterns are analyzed here in a sampling standardized framework using a database of genus occurrences. Classes included in this analysis are articulate and inarticulate brachiopods, trilobites, corals, and bivalves. The database spans the Caradoc (Late Ordovician) through the Wenlock (Early Silurian), a duration of roughly 35 Myr.

Chapter 2

Raw and sampling standardized diversity turnover trends from the paleocontinent of Laurentia (North America, parts of Nova Scotia) were compared to those derived from

Sepkoski’s global compilation of genus first and last occurrences. This allowed the effects of variations in sampling intensity to be determined for one of the most diverse regions of the world at the time. Comparisons with the global curve allowed assessment of the processes governing diversity depletion and recovery at the global versus regional scales.

Results from this chapter indicate that Laurentian diversity curves are heavily biased by variations in sampling intensity. When these biases are removed, diversity remains generally flat throughout the time period considered, including across the

Ordovician-Silurian boundary. Analysis of sampling standardized diversity patterns indicate that high origination rates in the first interval following the mass extinction drive a rapid recovery in Laurentia. This pattern differs considerably from the global pattern, suggesting that the processes governing the post-extinction rebound in Laurentia vary from those operating at the global scale. The dramatic change in the diversity pattern in

Laurentia after sampling standardization suggests that similar analyses may be necessary at the global scale.

This chapter was submitted for publication with my coauthor, Dr. Mark

Patzkowsky. It was published by the Proceedings of the National Academy of Sciences

(Krug and Patzkowsky 2004).

Chapter 3

The database used in chapter 2 was expanded to include the paleocontinents of

Baltica (Scandinavia, eastern Europe) and Avalonia (England, Ireland, parts of Nova

Scotia, parts of Scotland), as well as nearly doubling the number of occurrences representing Laurentia. The spatial complexity underlying global diversity and turnover patterns were analyzed thoroughly in a sampling standardized framework, including variations in diversity, extinction, origination, survivorship, and invasion among the three

continents. Hypotheses regarding the role of biotic invasions driving the post-extinction

rebound in Laurentia were tested using brachiopod data.

We find that diversity and turnover counts in Laurentia continue to be heavily

altered by variations in sampling intensity, whereas those of Baltica and Avalonia are

insignificantly affected by these biases. Sampling standardized diversity and turnover

dynamics in Laurentia vary from those of Baltica and Avalonia. Diversity in Laurentia

rebounds within 5 Myr of the Ordovician-Silurian boundary, the result of both lower

levels of extinction in the Late Ordovician and increased rates of origination in the Early

Silurian when compared with the other two continents. The high origination rates are the

result of both higher rates of genus origination and invasion into Laurentia in the Early

Silurian. These results indicate that global patterns mask an underlying spatial

heterogeneity in which the processes of extinction, genus origination, and invasion act to

produce highly variable regional responses to a global catastrophe. Thus, the Late

Ordovician joins the end-Permian and end-Cretaceous as mass extinction events with underlying geographic complexity. 8

Chapter 3 was written as a manuscript for submission to the journal Paleobiology.

It will be submitted in the near future, and will be coauthored by my adviser, Dr. Mark

Patzkowsky.

Chapter 4

Phylogenetic analyses were used to determine the evolutionary relationships of strophomenid brachiopods spanning the Late Ordovician and Early Silurian. The resulting cladogram was scaled to the fossil record of strophomenid brachiopods, and the stratigraphic ranges of genera in Laurentia were adjusted. The diversity and turnover of lineages and clades were analyzed, as well as the influence of pseudoextinction during the mass extinction event.

The analyses show that the last occurrence of a genus generally remains unaltered after phylogenetic correction, but first appearances are often extended backwards in time.

As a result, many genera thought to be part of the post-extinction recovery actually

belong to Ordovician clades. Therefore, while pseudoextinction appears to be negligible

within strophomenid brachiopods in Laurentia, the extinction intensity is reduced using

lineages because of the addition of previously undocumented lineages in the Ordovician

that survived the mass extinction. These survivors are derived from throughout the

phylogenetic tree, and no monophyla terminate as a result of the mass extinction event.

This suggests that strophomenids utilizing many evolutionary strategies pass through the

extinction boundary, potentially enabling strophomenids to re-diversify along many of

the evolutionary pathways as they did before the extinction. Such a pattern explains the

diminished ecological and evolutionary response to the mass extinction, as the reduction 9

in diversity failed to eliminate evolutionary strategies and, as a consequence, potential

ecological breadth.

Conclusions

The Late Ordovician mass extinction is therefore a geographically complex event

in which the processes of immigration, local origination, and survivorship are variable

among paleocontinents. The global pattern of delayed recovery in the Early Silurian

masks a rapid recovery in Laurentia, driven by increased immigration and elevated

origination rates. Though variations in sampling intensity dramatically alter diversity and

turnover patterns in Laurentia, the dramatic increase in proportional extinction rates are

never eliminated for any paleocontinent, either through sampling standardization or

phylogenetic correction, preserving the Late Ordovician mass extinction as one of the

most dramatic taxonomic events of the Phanerozoic. The decoupling of the taxonomic

and ecological severity of the extinction is therefore not the result of biased extinction

metrics, but rather may be the result of the distribution of extinctions within clades.

Expansion of this research to include additional geographic regions, diversity measures,

and ecological analyses would allow a more direct comparison between the Late

Ordovician and other mass extinction events of the Phanerozoic. 10

Chapter 2. Sampling Standardized Diversity Trends for the Paleocontinent of

Laurentia

Introduction

The pace of diversification following mass extinction reveals much about the

ecological and evolutionary processes that govern global biodiversity. Diversification

may lag owing to a slow response of the global environment to the perturbation that

caused the mass extinction (Hallam 1991). Diversification may be logistic with the shape and duration of the rebound dependent on the magnitude and duration of the extinction

and whether or not the system was at equilibrium immediately prior to the mass

extinction (Sepkoski 1984). Diversification of some taxonomic groups may jump

dramatically in the wake of mass extinctions if other groups that inhibited diversification

during background times are dramatically reduced in species numbers (Miller and

Sepkoski 1988). Diversification may be synergistic as new species facilitate the formation of more new species causing per-taxon origination rates to increase continually for several million years following the mass extinction (Kirchner and Weil 2000,

Sepkoski 1998). Finally, diversification may vary geographically, with each region having different diversity trajectories and varying proportions of bloom taxa and invaders

(Jablonski 1998).

The models of post-extinction diversity recovery above are all based at least in part on a direct reading of the fossil record with the assumption that the fossil record is an accurate and unbiased record of diversity. However, it has long been known that variability of sampling through time may exert a strong control on perceptions of 11

Phanerozoic diversity trends (Raup 1972). Recent studies have begun to evaluate in greater detail sampling biases on diversity using a variety of methods and databases

(Alroy et al. 2001, Crampton et al. 2003, Smith et al. 2001). Some intervals of mass

extinction have come under close scrutiny because they tend to have a close association

with sea level changes and drops in rock volume that bias the preserved record of

diversity, extinction, and origination (Foote 2003, Holland 1995, Peters 2001, 2002,

Smith 2001, Smith et al. 2001).

Here, we examine diversity and taxonomic rates through the Late Ordovician

mass extinction and Early Silurian recovery in Laurentia based on genus occurrence data

for articulate and inarticulate brachiopods, trilobites, bivalve mollusks, and corals.

Laurentia contains some of the best-documented Upper Ordovician and Lower Silurian

tropical marine benthic faunas known from this time interval. The occurrence data

permitted us to perform a sampling-standardized analysis of extinction and recovery in

this region and compare it to the global picture based on the Sepkoski compendium

(Sepkoski 2002). A much more rapid rebound of diversity in Laurentia compared to

globally suggests that the ecological processes of recovery were different between these

two geographic scales. Our results also point to the need for sampling-standardized

analyses on other paleocontinents and for the whole globe, in order to determine how

regional and global patterns relate. This analytical approach should be extended to other

Phanerozoic mass extinctions where variations in sampling intensity are of concern.

Data

There are many sources of bias inherent in measuring diversity through time, including variations in sampling intensity (Alroy et al. 2001, Foote 2000, Miller and

Foote 1996, Raup 1975), variations in sampling across environmental gradients

(Patzkowsky 1995, Sepkoski 1985, Smith et al. 2001), and variations in sampling among

geographic regions (Maurer 1999, Rosenzweig 1995). We attempted to minimize these

biases in compiling the data for this study. The database for Laurentia was constructed

using lists of genus occurrences. A total of 5762 occurrences from 746 lists were

downloaded from the Paleobiology Database (Alroy 2000) and supplemented through an

independent literature search. Most supplemental lists have since been entered into the

Paleobiology Database (see supporting information). Taxonomic lists were placed into one of seven time intervals (see below). Each of the time intervals is well sampled from offshore through the shallow subtidal environmental zones with the exception of the

Aeronian, where the deep subtidal environment is undersampled (Table 2.1). All of the time intervals also show a fairly broad geographic distribution of lists (Table 2.2).

Despite attempts to obtain even sampling intensities, however, variability exists in the number of occurrences per time interval (Fig. 2.1). Particularly important is a large drop in sampling intensity from the Ashgill (Late Ordovician) to the Rhuddanian (Early

Silurian), strengthening the need for sample standardization (see Methods below).

Environment Basin Offshore Deep Shallow Peritidal Reefs Undefined Time Interval Subtidal Subtidal Wenlock 1 50 23 10 18 10 Telychian 10 18 27 29 1 3 18 Aeronian 0 38 7 25 1 1 Rhuddanian 2 15 23 5 2 16 Ashgill 1 33 21 31 2 22 Upper Caradoc 4 54 43 48 3 7 Lower 4 62 35 17 4 2 Caradoc Table 2.1. Environmental distribution of lists. Numbers designate the number of lists entered for each environment in each time interval.

Lower Caradoc: Tennessee (59), British Columbia (27), Virginia (22), Tennessee and Virginia (6), Minnesota (2), Mississippi (2), New York (2), Wisconsin (2), Nevada (1), Ontario (1).

Upper Caradoc: Tennessee (74), Virginia (19), British Columbia (18), Ohio (15), Kentucky (12), Ohio and Kentucky (3), Northwest Territories/Arctic Canada (3), Virginia and Kentucky (3), Indiana (2), Minnesota (2), Nevada (2), Oklahoma (2), New York (1), Ontario (1), Pennsylvania (1), Quebec (1).

Ashgill: Quebec (32), Tennessee (19), Indiana (18), Ohio (16), Kentucky (5), Illinois (4), Missouri (4), Virginia (4), Iowa (2), Oklahoma (2), British Columbia (1), Michigan (1), Minnesota (1), Northwest Territories/Arctic Canada (1).

Rhuddanian: Quebec (22), Ontario (11), British Columbia (10), Northwest Territories/Arctic Canada (10), Missouri (5), New York and Ontario (4), Iowa (3), Greenland (2), Illinois (1), New Brunswick (1), Ohio (1), Yukon (1).

Aeronian: Northwest Territories (28), Iowa (12), Ohio (7), Kentucky (5), Wisconsin (5), Michigan (2), Quebec (7), British Columbia (2), Illinois (1), Indiana (2), Ontario (1).

Telychian: Iowa (29), British Columbia (17), Quebec (17), New York (10), Northwest Territories (10), Wisconsin (10), Ontario (2), New York and Ontario (2), Michigan (3), Illinois and Michigan and Iowa (1), Indiana (1), Nevada (1), Virginia (1), Ohio (1), Pennsylvania (1).

Wenlock: New York (22), Wisconsin (32), Northwest Territories/Arctic Canada (34), Iowa (6), Indiana (4), Quebec (3), Tennessee (7), New York and Ontario (2), Illinois (1). Table 2.2. Geographic distribution of lists. Numbers designate the number of lists from each state or province in each time interval.

Taxonomic assignments were updated where applicable through examination of the recent literature. In order to assess the effects of any remaining taxonomic problems, we also eliminated from our analyses very old lists, lists from references that appeared otherwise especially problematic, and singletons (see below). Culling the data in these 14

ways did not alter the overall diversity trends significantly, suggesting that the patterns

are robust and that any remaining taxonomic problems are distributed randomly and do

not obscure the underlying diversity patterns (Adrain and Westrop 2000).

Global diversity was calculated from Sepkoski’s compendium of genus first and

last appearances (Sepkoski 2002). The compendium data can be ranged through to determine diversity, proportional origination, and proportional extinction. Because of the structure of the data (a record of first and last appearances rather than a list of all

occurrences), it cannot be standardized for sample size, as can the Laurentian data.

However, it does serve as a basis for comparison for the Laurentian diversity and

turnover metrics.

Varying durations of time intervals can affect both diversity and turnover

calculations (Foote 2000). For example, as the duration of a time interval increases,

diversity within that interval rises, while proportional extinction and origination metrics

asymptotically approach one. To reduce the effects of this bias, the Laurentian timescale

was divided into seven time intervals of roughly equal duration. The Caradoc series was

divided into upper and lower intervals at the base of the Rocklandian stage, the Ashgill

and Wenlock were left intact, and the Llandovery was divided into its three stages, the

Rhuddanian, Aeronian, and Telychian. Correlation between North American and global

series and stages are based on Webby (1998), Ross et al. (1982), Barnes et al. (1981),

Berry et al. (1970), and Norford (1997). Dates for the base of each Ordovician and

Silurian series were taken from Tucker and McKerrow (1995), and the dates for the

intervening stages were determined by linear interpolation. The average duration of each

Laurentian time interval is 5 Myr, with a standard deviation of 0.5 Myr. We note that the 15 radiometric dates used by Tucker and McKerrow (1995) contain uncertainties in the range of plus or minus two million years. However, when we exclude singletons, which are sensitive to interval duration, the resulting diversity curve is minimally affected (see

Methods below).

Time intervals used for the calculation of global diversity were taken from

Sepkoski’s (2002) compendium, and were combined where possible to match time intervals used for the Laurentian data set. For example, while Sepkoski’s two Ashgillian bins were combined to match the Laurentian, his three Caradoc subdivisions could not easily be combined into the two used for the Laurentian data.

Taxonomic groups analyzed were articulate and inarticulate brachiopods, bivalves, trilobites, and anthozoans. These taxa are generally well preserved and consistently reported and provide a good range of sampling of the three evolutionary faunas (Sepkoski 1981), accounting for 37% of Sepkoski’s global Ordovician and

Silurian data.

Methods

Total diversity in a time interval was calculated as the sum of the genera ranging into the interval, the genera that ranged through the interval, and the genera existing only in that interval (singletons). Proportional origination and extinction metrics were calculated as the number of originations or extinctions in a time interval divided by the total diversity in that interval.

Singletons are particularly sensitive to temporal variations in sampling, and can produce misleadingly high turnover rates in such cases (Foote 2000). However, because 16

our time intervals have approximately equal durations, and because we standardize

sample size in each interval (see below), much of the bias that singletons introduce was removed from our analysis. Also, singletons are expected to make up a greater proportion of diversity in the time interval containing a mass extinction, as a large proportion of the lineages originating in that stage are eliminated prematurely. Indeed, when singletons are

removed from the analysis of the Laurentian data, the most notable difference is a

reduction of Ashgillian diversity to Rhuddanian levels (figure not shown). Although the

curve is flatter overall, most other features of the diversity curve are retained, including

the slight drop in diversity from the Upper Caradoc into the Ashgill, the relative lows in

diversity in the Rhuddanian and Aeronian, and the increase in diversity in the Telychian

(see Fig. 2.3A). Foote (2000) discussed the issue of singletons in detail in the context of

their effects on long-term variations in taxonomic rates through time. No discussion,

however, is given to short time intervals such as around mass extinction events. We

believe that the approximately equal duration of our time intervals and the use of sample

standardization should remove most of the biases inherent in the use of singletons.

Removing singletons would remove a large amount of legitimate data, especially within

the interval containing the extinction event, and thus we retain singletons in our analyses

presented here.

Data for the global curve included genera that were ranged through from older

and younger intervals (i.e. older than the Caradoc and younger than the Wenlock). It was

not possible to do the same for the Laurentian data, as no data from outside the interval

were collected. Because of this, diversity near the edges of the study interval (Lower 17

Caradoc and Wenlock) is reduced. These edge effects have minimal effect on diversity

across the Ordovician-Silurian boundary.

Rarefaction of genus occurrences was performed initially to determine the effects

of variations in sampling intensity (Fig. 2.1) on diversity among time intervals. We used

Analytical Rarefaction 1.3 [http://www.uga.edu/~strata/software/, (Raup 1975, Tipper

1979)] to perform these analyses. Rarefaction uses the relationship between diversity and

sample size (here number of occurrences) to predict diversity at a smaller, standard

sample size. This allows diversity between collections of unequal sample size to be

compared directly. However, standard rarefaction only handles diversity within a single

sample (e.g. a time interval) and does not permit the calculation of range-through diversity or turnover metrics (Miller and Foote 1996, Raup 1975, Tipper 1979). In order

to perform a sample standardization of range-through data, a subsampling program was written to expand the rarefaction analysis (Alroy 2000, Alroy et al. 2001). A standard number of occurrences were drawn at random from each of the time intervals, genera were ranged-through intermediate time intervals, and diversity and turnover metrics were calculated. This process was repeated 1000 times, the results averaged, and error bars calculated.

Results

Global diversity for articulate and inarticulate brachiopods, trilobites, anthozoans and bivalves shows a slight dip through the Caradoc, a spike into the Ashgill, and then a sharp drop across the Ordovician-Silurian boundary (Fig. 2.2A) resulting in a diversity drop of 49%. Diversity was slow to rebound, achieving pre-extinction levels of diversity 18

around 15 Myr later in the Wenlock. The sharp drop in diversity across the Ordovician-

Silurian boundary and slow rebound in the Silurian for this subset of Sepkoski’s compendium is similar to that for the total Sepkoski data (Sepkoski 1995, 1998).

Proportional extinction (Fig. 2.2B) based on Figure 2A shows a significant spike in extinction in the Ashgill (69%) and then dropping in the Lower Llandovery

(Rhuddanian) before a steady rise into the Wenlock. Proportional origination (Fig. 2.2B) is low in the Lower and Upper Caradoc, higher in the Ashgill and Lower Llandovery

(Rhuddanian) spanning the Ordovician-Silurian boundary, and low again in the Middle

Llandovery (Aeronian) before rising into the Wenlock. Although origination is elevated across the Ordovician-Silurian boundary, it does not spike in the Lower Llandovery

(Rhuddanian). These patterns are generally similar to origination and extinction based on the total Sepkoski data (Sepkoski 1998) with the exception of elevated origination in the

Ashgill and Lower Llandovery (Rhuddanian) seen in the subset of the Sepkoski data (Fig.

2.2B), which is not present in the global data.

The Laurentian diversity curve (Fig. 2.3A), though similar, contains some important differences from the global curve (Fig. 2.2A). In the Laurentian curve, diversity rises from the Lower Caradoc to the Upper Caradoc, drops slightly in the

Ashgill, and then drops more sharply into the Rhuddanian as a result of the extinction.

Diversity drops by only 14% from the Ashgill to the Lower Llandovery (Rhuddanian) significantly less than in the global data. The rebound to pre-extinction levels of diversity occurs by the Telychian, about 5 Myr earlier than suggested by the global curve.

Proportional extinction (Fig. 2.3B) based on the Laurentian data (Fig. 2.3A) shows increasing extinction through the Lower and Upper Caradoc to a peak in the 19

Ashgill of 53%, before dropping sharply in the Lower Llandovery (Rhuddanian) and then

rising slowly through the Middle and Upper Llandovery (Telychian). The Laurentian

extinction data (Fig. 2.3B) are generally similar to the Sepkoski global data (Fig. 2.2B)

although the Ashgill extinction peak is lower (53% vs. 69%) in Laurentia and extinction

in the other time intervals is generally higher than the global data. Proportional

origination is high in the Upper Caradoc and Ashgill and bumps up slightly in the Lower

Llandovery before dropping to lower levels in the Middle Llandovery through Wenlock.

The Laurentian origination data (Fig. 2.3B) differ from the global data (Fig. 2.2B) in that

origination was generally high beginning in the Upper Caradoc and then bumped up

slightly in the Lower Llandovery, before attaining a lower level in the Middle Llandovery

through Wenlock.

Rarefaction curves for each time interval (Fig. 2.4) show the effect of variations

in sampling intensity on perceived diversity trends for the paleocontinent of Laurentia.

For example, with the exception of the Middle Llandovery (Aeronian) curve, all other

Silurian time intervals (Rhuddanian, Telychian, and Wenlock) lie above the Ordovician curves (Lower and Upper Caradoc, Ashgill). This result suggests that for a standard level of sampling, diversity is similar to or slightly higher in the Silurian compared to the

Ordovician. The Middle Llandovery (Aeronian) may be lower because of the poorer sampling in deep subtidal environments compared to other time intervals (Table 2.1).

Rarefaction with range-through produced a diversity trend across the Late

Ordovician mass extinction that was markedly different from both the global and

Laurentian total diversity curves (Fig. 5A). Diversity remains generally flat from the

Lower Caradoc through Middle Llandovery (Aeronian), including across the extinction 20

boundary. Lower Llandovery (Rhuddanian) diversity falls within the 95% confidence

interval for the Ashgill, suggesting that, following the mass extinction, diversity

rebounded to pre-extinction levels within 5 Myr, about 15 Myr sooner than implied by

the global curve. Diversity rises slightly in the Upper Llandovery (Telychian) before

dropping in the Wenlock, which most likely results from edge effects rather than an

actual diversity decline.

Although Ashgillian diversity equaled Lower Llandovery diversity (Fig. 5A), proportional extinction on the subsampled data still shows that 55% of Laurentian genera

go extinct in the Ashgill (Fig. 2.5B). The Rhuddanian, however, sees a significant drop in

extinction while origination peaks, bringing diversity back to pre-extinction levels. Both

origination and extinction metrics drop below Ordovician levels by the Middle

Llandovery. These data therefore suggest that diversity changes in Laurentia are being

driven by fluctuations in both extinction and origination. Importantly, these standardized

data show a significant peak in origination in the first five million years of the Silurian

(Lower Llandovery; Rhuddanian), which the unstandardized data at both the regional

scale (Laurentia) and the global scale do not show.

Discussion

Analysis of the Laurentian data indicates that the recovery from the Late

Ordovician mass extinction occurred within 5 myr in Laurentia (Fig. 2.5A) compared to

between 15 and 20 million years globally (Fig. 2.2A). Adjusting for sample size had a

significant affect on the Laurentian diversity patterns. The unstandardized diversity curve

for Laurentia (Fig. 2.3A) changed dramatically following sample-standardization with the 21

peaks and valleys of diversity smoothed out across the Ordovician-Silurian boundary

(Fig. 2.5A). Likewise, the patterns and absolute magnitudes of taxonomic rates change

following adjustments for sample size (Figs. 2.3B and 2.5B). Because global diversity is

built from many regional patterns, the current study points to the need for similar

analyses on other paleocontinents in order to gain a more complete understanding of how

global and regional patterns relate. Nonetheless, comparison of Laurentian diversity with

global diversity has implications for the nature of the post-extinction recovery.

Evidence for a rapid rebound of diversity following the Late Ordovician mass extinction also comes from studies of local community structure. Sheehan et. al. (1996) has suggested that reassembly of community structure following mass extinctions throughout the Phanerozoic and including the Early Silurian occurred within three to eight million years. In the Great Basin, Lower Silurian benthic communities are depauperate in the recovery interval, but rebound in diversity by the upper Aeronian

(Sheehan and Harris 1997, 2004). Several studies indicate that graptolites and conodonts rebounded by the middle Llandovery (Armstrong 1996, Berry 1996, Kaljo 1996, Koren and Rickards 2004). Adrain et al. (2000) looked at Ordovician and Silurian alpha diversity of trilobites across a range of depositional environments and on several paleocontinents and found little or no impact of the Late Ordovician mass extinction on the number of trilobite species that occupied local habitats, despite a nearly fifty percent drop in clade diversity globally. They argued that the processes that govern alpha diversity exert little control on global diversity, at least in this context, and that the processes that govern between-habitat (beta) or geographic (gamma) diversity may exert the overriding control on global diversity. Our results suggest that diversity in Laurentia 22

fluctuated little at the five million year time scale, suggesting a cap on gamma diversity.

Thus, higher resolution studies are needed (Sheehan and Harris 1997) from multiple paleocontinents to tease apart how diversity was partitioned among alpha, beta, and gamma diversity across the Ordovician-Silurian boundary.

The disparity in rates of recovery in Laurentia compared to the whole globe suggests the processes that govern regional ecosystem recovery were somehow different or decoupled from processes operating at the global level. Indeed, recovery of global diversity is limited by taxonomic diversification rates, whereas diversity of regional ecosystems, such as paleocontinents, can recover much more quickly because taxonomic diversification can be augmented by immigration. There is evidence to suggest that immigration played an important role in recovery of diversity in the early Silurian of

Laurentia (Sheehan 1973, 1975). Following a glacioeustatic sea-level fall that drained epicontinental seas and disrupted marine habitats, sea level rose, permitting brachiopod taxa to migrate into Laurentia from Baltica (northern Europe) and causing a rapid turnover in brachiopod faunas and a switch to more cosmopolitan taxa (Sheehan 1975).

The early Llandovery peak of origination in Laurentia reflects at least in part this influx of Baltic genera (Fig. 2.5B). Globally, origination does not peak in the early Llandovery, rather extinction rates drop below origination rates and then origination rates begin a slow rise (Fig. 2.2B; (Sepkoski 1998)). Thus, regional diversity can remain constant while global diversity drops if regional diversity is replenished by immigration from other paleocontinents, causing a shift from highly endemic to cosmopolitan distributions of taxa. Additional studies from other paleocontinents are needed to test this general hypothesis. 23

The results of our analyses also have implications for diversity studies throughout

the Phanerozoic. Based on high-resolution (epoch level) analyses of the number of

sedimentary formations (a proxy for quantity of sedimentary rock) and global diversity,

Peters and Foote (2001) found that much of the short-term variation in global diversity is dependent on the amount of sedimentary rock available for sampling. Notably, mass extinctions tend to occur at times when the quality of the record, as estimated by the amount of sedimentary rock available for sampling, changes from high in the extinction interval to low in the recovery interval. This pattern of record quality is related to major drops in sea level that are coeval with a large number of mass extinctions in the

Phanerozoic (Hallam and Wignall 1999). Indeed, the Late Ordovician mass extinction has been linked directly to a significant fall and rise in eustatic sea level associated with the waxing and waning of a large Gondwanan ice sheet (Brenchley et al. 1995) and this is directly associated with fluctuations in the quantity of sedimentary rock available for study (Peters 2001). Out results are consistent with a number of recent modeling (Holland

and Patzkowsky 1999, 2002) and empirical studies (Crampton et al. 2003, Peters 2001,

Smith 2001, Smith et al. 2001) that suggest the need for a reassessment of stratigraphic

bias on perceived trends in diversity and taxonomic rates across all mass extinction

horizons. Such studies are critical for understanding the full impact of environmental

perturbations on biodiversity and the processes of post-extinction recovery. In a study of

rates of speciation in the fossil record, Sepkoski (1998) described the recovery from the

Late Ordovician extinction as typical of a post-extinction recovery period, with a

protracted increase in origination rates beginning in the Lower Llandovery and

continuing through the Wenlock. The protracted increase in origination rates at the global 24

scale may reflect a biased record (Foote 2002). Although the study presented here is

based on only a single paleocontinent, it does point out the importance of sample

standardization in diversity studies. Thus, any model of recovery that hinges on the

timing of origination (Hallam 1991, Kirchner and Weil 2000, Miller and Sepkoski 1988,

Sepkoski 1984, 1998) must be re-evaluated in light of analyses that account for variation

in sampling intensity among paleocontinents and for the whole globe.

Though sampling bias is one of the most important issues affecting diversity

trajectories through time, there are other issues that must be resolved in order to fully

understand the nature of the post-extinction recovery. First, the degree to which pseudoextinction affects turnover metrics must be addressed. Though inconsistent taxonomic assignments do not seem to affect the total or subsampled curves for

Laurentia, the phylogenetic relationships of these taxa can add insight into the nature of the recovery. If a portion of the Early Silurian taxa had sister taxa in the Ordovician that survived the event, then the Ashgillian extinction and Rhuddanian origination rates would both be overestimates (Adrain and Westrop 2003). Such data would not only provide independent support for the effects of sampling biases on diversity curves (Smith 1994)

for this time period, but may aid in our understanding of the diminished ecological and

evolutionary effects of the Late Ordovician mass extinction (Bottjer et al. 2001, Droser et

al. 1997, Droser et al. 2000). Second, diversification events have been shown to display a

high degree of geographic heterogeneity (Jablonski 1998, Miller 1997a, b, Novack-

Gottshall and Miller 2003, Westrop and Adrain 1998), and including other paleocontinents in the current analysis is necessary to understand the influence of 25

regional processes on the recovery as well as how regional patterns relate to global

patterns.

Conclusions

1. After adjusting for variations in sampling intensity through time, Late Ordovician

(Ashgill) diversity in Laurentia equals diversity in the Early Silurian

(Rhuddanian). This indicates that diversity in Laurentia rebounded to pre-

extinction levels within the first five million years of the Silurian, approximately

fifteen millions years sooner than suggested by global compilations.

2. A peak in extinction in the Ashgill is followed immediately by a peak in

origination in the Lower Llandovery, suggesting a relatively rapid turnover of

taxa in Laurentia. The difference in the rate of recovery of Laurentian diversity

compared to global diversity suggests that processes different from those affecting

global diversity governed recovery of diversity in Laurentia. For example,

immigration of taxa from other paleocontinents, such as Baltica, may have

replenished local and regional biotas, but had no affect on global diversity,

leading to a more cosmopolitan global fauna. Data from other paleocontinents are

necessary to confirm this hypothesis, as well as to gain a better understanding of

how regional patterns relate to the global picture.

3. Because the sampling-standardized diversity and taxonomic rate curves for

Laurentia differ substantially from the curves based on the unstandardized data, it

raises the question of whether the global curves are in need of similar

adjustments. Indeed, several recent studies point to the incompleteness of the rock 26

record that distort estimates of diversity and taxonomic rates associated with mass

extinctions and post-extinction recoveries throughout the Phanerozoic (Foote

2003, Peters 2001, Smith 2001, Smith et al. 2001). Though no definite

conclusions on this issue can be drawn from the analysis of only one paleocontinent, our results suggest that future studies of Phanerozoic mass extinctions should attempt to remove the distorting effects of incompleteness and variation in sampling intensity if the macroevolutionary and ecological processes

of mass extinctions and post-extinction recoveries are to be fully understood. 27

Figure 2.1. Number of occurrences per time interval. Note the similarity between these data and the total diversity curve for Laurentia (see Fig. 3A). Particularly striking is the large drop in sampling intensity from the Ashgill (Upper Ordovician) to the Rhuddanian

Figure 2.2. A. Global diversity calculated from Sepkoski's compendium of generic first and last appearances (16). B. Global proportional origination and extinction metrics. L.C. Lower Caradoc. M.C. Middle Caradoc. U.C. Upper Caradoc. Dashed line marks the Ordovician-Silurian boundary. 29

Figure 2.3. A. Laurentian total generic diversity. The Caradoc is divided into two intervals here, with all others the same as in the global plot. Diversity is calculated as the total number of genera existing in Laurentia found within or ranged through a time interval. B. Proportional origination and extinction metrics calculated for Laurentia. Unlike global rate metrics, regional rate metrics can incorporate factors such as immigration and local extinction in addition to taxonomic origination or extinctions. Dashed line marks the Ordovician-Silurian boundary.

Figure 2.4. Rarefaction curves for the seven time bins used in this project. 31

Figure 2.5. A. Standardized diversity curve generated using rarefaction with range-through (see text for explanation). B. Proportional extinction and origination metrics based on the standardized data. Dashed line marks the Ordovician-Silurian boundary. 32

Chapter 3. Geographic Variability in Turnover and Recovery Patterns

Introduction

Studies of mass extinctions have traditionally focused on diversity and turnover patterns at the global scale using synoptic databases of taxonomic first and last appearances (Bambach et al. 2004, Sepkoski 1993, 2002). It is from these databases that mass extinctions were recognized and quantified (Raup and Sepkoski 1982), and many studies have since attempted to determine the evolutionary and ecological impacts of both mass extinctions and their subsequent recoveries (Droser et al. 2000, Hallam 1991,

Jablonski 1989, 2004, Labandeira et al. 2002, Miller and Sepkoski 1988, Rees 2002,

Sepkoski 1984, Wilf and Johnson 2004). Yet the global ecosystem is not homogeneous but rather spatially complex, broken up into biological and environmental subdivisions of various scales, and the processes that operate to control diversity may vary considerably at different scales. Studies of regional diversity dynamics are few, yet those undertaken point to globally heterogeneous patterns during times of large scale radiations (Miller

1997a, Miller and Mao 1998), extinctions (Shen and Shi 2002), and post-extinction recoveries (Jablonski 1998). If the evolutionary roles of mass extinctions are to be understood, detailed analysis of diversity and turnover dynamics must be undertaken over a wide range of spatial and temporal scales.

Here we focus on patterns of diversity, origination, and extinction trends for the paleocontinents of Laurentia, Baltica, and Avalonia (Fig 3.1) spanning the Late

Ordovician mass extinction and Early Silurian recovery. The Late Ordovician is recognized as the second largest of the Phanerozoic in terms of proportion of genera lost 33

(Sepkoski 1993, 2002), and is thought to be the result of large-scale sea-level fluctuations

and environmental changes related to the expansion and contraction of glaciers in an

otherwise greenhouse world (Brenchley et al. 1995). It therefore stands in contrast to the

end Cretaceous and Late Permian mass extinctions, which are thought to be associated

with either extraterrestrial, tectonic, or volcanic forces. Despite its severity, however, the

Late Ordovician extinction brought about only minor paleoecological changes (Bottjer et

al. 2001, Droser et al. 1997, Droser et al. 2000). Most major classes rebounded after the

extinction, megaguilds were replenished (Bambach 1985, Bottjer et al. 2001), and even

reef faunas, normally devastated during mass extinction events (Hallam and Wignall

1997, Sheehan 1985, Wood 2000), recovered in the Silurian (Copper 1994). Thus, the

Late Ordovician mass extinction is unlike other mass extinction events, many of which

remove ecological dominants and eliminate long-standing and diverse clades, resulting in

a fundamental restructuring of the global ecosystem (Erwin 2001).

Patterns of diversity and turnover during the Late Ordovician and Early Silurian

are typical of mass extinctions and post-extinction recoveries when analyzed at the global scale (Sepkoski 1998), with a sharp decline in diversity and a lag of several geologic stages before origination rates begin to rise (Fig. 2.1). However, the biases inherent in quantifying diversity and turnover are well known (Alroy 2000, Alroy et al. 2001, Foote

2000, Miller and Foote 1996), and require the use of counting methods and sampling standardization techniques that produce unbiased estimates through time. Diversity and turnover patterns are analyzed here in a sampling standardized framework using a database of genus occurrences of articulate and inarticulate brachiopods, trilobites, corals, and bivalves. The database spans the Caradoc (Upper Ordovician) through the Wenlock 34

(Lower Silurian), a duration of roughly 35 Myr. We find that diversity and turnover dynamics in Laurentia vary from those of Baltica and Avalonia. Diversity in Laurentia rebounds within 5 Myr of the Ordovician-Silurian boundary, the result of both lower levels of extinction in the Late Ordovician and increased rates of origination in the Early

Silurian when compared with the other two continents. The high origination rates are the result of both higher rates of genus origination and invasion into Laurentia in the Early

Silurian. These results indicate that global patterns mask an underlying spatial complexity in which the processes of extinction, genus origination, and invasion act to produce highly variable regional responses to a global catastrophe.

Data and Methods

This study focuses on diversity and turnover patterns for the paleocontinents of

Laurentia (North America, parts of Scotland, parts of Ireland), Baltica (Scandanavia,

Eastern Europe, Western Russia), and Avalonia (parts of Great Britain, Ireland, and Nova

Scotia) (Fig 3.1). These continents are generally arrayed along a latitudinal gradient, with Laurentia straddling the equator, Baltica slightly to the south and east (~ 30? S) and

Avalonia in high southern latitudes (~ 50? S). Paleogeographic reconstructions used to differentiate paleocontinents were primarily taken from the Paleomap research of Scotese

[http://scotese.com/Default.htm; (Scotese and McKerrow 1990)], although higher resolution maps of local areas were occasionally necessary (Bassett et al. 1992, Bevins et al. 1992, Cocks 2000, Cocks and Fortey 1998, Cocks et al. 2003, Cocks and Torsvik

2002). 35

Because this database incorporates data from several continents, the Ordovician timescale of Webby (1998) was used to correlate Ordovician series and stages from various continents. Ordovician chronostratigraphic units are heterogeneous throughout the world, and Webby’s timescale is a recent and accurate attempt at global stratigraphic correlations. British Ordovician chronostratigraphic subdivisions will be referred to in this text. Series and stage names for the Silurian system are agreed upon internationally, making correlation among sections straightforward (Cocks et al. 1992). Analyses for this study span the Upper Ordovician (Caradoc) through the Lower Silurian (Wenlock), for a total duration of around 35 Myr. The time scale was divided into 7 time intervals of roughly equal durations, with the Caradoc series divided into two intervals at the top of the Soudleyan stage and the Llandovery divided into its three stages, the Rhuddanian,

Aeronian, and Telychian. Ages for the bases of these intervals were taken from Tucker and McKerrow (1995), and the dates for intervening stages were determined through a linear interpolation. We prefer Tucker and McKerrow (1995) because it is an internally consistent dataset. Dates from Gradstein et al. (2004) vary slightly but do not change our overall results.

The database was constructed using lists of genus occurrences. Lists of inarticulate and articulate brachiopods, trilobites, anthozoans, and bivalves were collected from a survey of the literature and supplemented using the Paleobiology Database

(http://paleodb.org), though most independently collected data is now housed online as part of the Paleobiology Database. These taxa are well studied and represented in the literature, have been the focus of considerable taxonomic scrutiny, and represent important taxa from each of Sepkoski’s three Evolutionary Faunas (Sepkoski 1981). In 36

all, 17615 occurrences representing 886 genera were collected from 2076 lists, and the

number of occurrences for the paleocontinent of Laurentia is roughly double the number

used in a previous study of the continent (Krug and Patzkowsky 2004). Despite efforts to

obtain even sampling intensities, however, all of the paleocontinents show variability in

the distribution of occurrences between intervals. This uneven sampling reinforces the

need for sampling standardization techniques (see below).

Whenever possible, lists were assigned to a paleoenvironmental category arrayed

along an onshore-offshore transect in order to insure a consistent environmental

distribution of lists through time. Environmental assignments were made using lithologic

rather than taxonomic information, providing an independent assessment of the

depositional environment from which the occurrences were sampled. Overall, 95% of

our lists could be resolved to one of the five environmental divisions. All three

continents are fairly evenly sampled among the shallow subtidal, deep subtidal, and

offshore environments in each of the time intervals (Table 3.1). The basin and peritidal

environments are consistently undersampled relative to the three mid-shelf environmental settings. This is expected, as these environments are generally underrepresented in the geologic record. Because the environmental distribution of lists remains relatively even through time, it is unlikely that changes in apparent diversity and taxonomic rates are driven by variations in sampled depositional environments.

Laurentia Wenlock 57 56 56 19 15 21 7 Telychian 10 35 27 32 2 2 Aeronian 0 35 21 25 7 2 Rhuddanian 0 23 19 16 5 12 Ashgill 1 40 76 96 4 11 48 Upper Caradoc 7 59 86 131 8 Lower Caradoc 7 72 90 39 7 Baltica Wenlock 0 22 27 30 5 4 10 Telychian 1 9 7 2 0 3 Aeronian 0 6 6 3 0 Rhuddanian 0 15 2 2 0 Ashgill 3 12 6 3 1 3 2 Upper Caradoc 2 13 4 4 2 3 Lower Caradoc 2 1 3 3 0 Avalonia Wenlock 6 9 7 1 Telychian 1 8 28 39 Aeronian 5 22 81 14 5 7 Rhuddanian 11 156 15 6 Ashgill 55 9 13 Upper Caradoc 20 20 4 Lower Caradoc 13 8 8 Basin Offshore Deep Shallow Peritidal Reefs Undefined Subtidal Subtidal Table 3.1. Environmental distribution of lists from Laurentia, Baltica, and Avalonia. Numbers designate the number of lists entered for each environment in each time interval.

We calculated total diversity within each time interval as the sum of genera

ranging into the interval, genera ranging through the interval, and genera existing only in that interval (singletons). Proportional origination and extinction metrics were calculated as the number of originations (first appearance of a genus in a paleocontinent) or extinctions (last appearance of a genus in a paleocontinent) divided by the total diversity of a paleocontinent in that interval.

The tabulation of diversity, origination, and extinction can be biased by many

factors, including variability in bin duration, counting method, and variations in sample

size (Alroy 2000, Alroy et al. 2001, Foote 2000). Variability in interval duration can bias

both diversity and turnover metrics because the more time an interval represents, the 38

more likely it is to capture a portion of the stratigraphic range of a given taxon. Diversity

is therefore likely to increase in longer intervals regardless of real changes in standing

diversity. Additionally, the probability that the entire duration of a taxon will be captured

within an interval (i.e. that a taxon will be considered a singleton) increases as the

duration of an interval increases, causing longer time intervals to have artificially high

origination and extinction intensities (Foote 2000) without a real increase in the initiation

or termination of lineages.

Because our time intervals were constructed so as to represent equal durations of

time, we expect these biases to be minimal. However, Tucker and McKerrow (1995)

report errors of plus or minus 2 Myr on their radiometric dates. Additionally, new

Phanerozoic timescales (Gradstein et al. 2004) contain ages that vary slightly from those

used here, potentially altering the equality of our interval durations. Two analyses were

undertaken in order to assess the degree to which interval duration is affecting diversity

and turnover trajectories. First, because singletons are especially sensitive to interval duration, they were removed from diversity tabulations. Dramatic changes in the shapes of the diversity curves would suggest that variability in interval duration may be biasing our diversity trends. For all three continents, the shapes of the curves were retained (data not shown), with the only notable change being the elimination of Ashgillian peaks in diversity. However, the change in Ashgillian diversity with the removal of singletons is probably not the result of variability in interval duration. Singletons are expected to make up a larger proportion of total diversity in the interval before a mass extinction boundary, as the extinction event would prematurely truncate lineages with their origins in that interval. This was the case in the Late Ordovician, as several distinct and 39

sometimes diverse brachiopod faunas evolved throughout the world in the Hirnantian

stage of the Ashgill (Rong and Harper 1988). The Hirnantia faunas evolved with the

expansion of the Gondwanan ice sheets and went extinct before the end of the Ashgill,

making them Ashgillian singletons. However, these singletons are not the result of

variations in interval duration and should therefore be counted towards diversity and

turnover. The general agreement in the shapes of the curves in the remaining time

intervals suggests that variations in interval duration are not significantly biasing

diversity trajectories, and singletons are retained in the final analysis.

Second, per-capita origination and extinction rates (Foote 2000) were calculated.

These metrics tacitly ignore singletons in their calculations, normalize for interval

duration, and are derived from branching theory, making them unbiased by variations in

interval duration, true taxonomic rates, and incomplete preservation (Foote 2000).

Again, for all three continents, the per-capita origination and extinction rates produce similar temporal patterns to those derived from proportional origination and extinction metrics. This again suggests that variations in the duration of our intervals are not

biasing turnover estimates.

Methods used to tabulate diversity and turnover can themselves bias perceived trajectories. Range-through diversity assumes that a taxon sampled in two non-adjacent

time intervals is necessarily present in any intervening time intervals. Because taxa can

only be ranged-through intervals within the timescale of study, diversity in intervals

towards the center of a timescale tend to be inflated relative to intervals near the edges of

the timescale (known as edge effects). Range-through diversity is commonly used at the global scale, but may be problematic at the regional scale, where taxa can go extinct in a 40

region, then migrate back to the region at a later time. We expect the biasing effects of

this counting method to be minimal in this study, however, as range-through data make up only a small proportion of total diversity in any given bin, and raw diversity trajectories determined using only data sampled within a bin show similar patterns to those using range-through data (Fig 3.3). The intervals immediately following a mass extinction event, however, may be times of increased migration, as climatic fluctuations and diversity depletions may allow dispersal into areas previously impossible for physical

or biological reasons. The affects of migration on diversity in the post-extinction

recovery intervals are discussed separately.

Finally, variations in sample size can bias diversity and taxonomic rate counts because larger sample sizes are expected to recover more rare taxa. Therefore, if the

sample size within an interval is larger than that of surrounding intervals, diversity,

origination, and extinction metrics will all be inflated. This is especially significant for

mass extinctions and post-extinction recoveries, as many of these events are associated

with sea-level changes and drops in rock volume (Peters 2001). Because our database is

constructed of lists of genus occurrences, we can account for these biases by

standardizing the sample sizes, here the number of occurrences, within each bin. First,

analytical rarefaction was performed on genus occurrences within an interval.

Rarefaction uses the relationship between sampling and diversity to analytically predict

the expected diversity for decreasing sample sizes (Raup 1975, Tipper 1979). This

technique, however, is only applicable to diversity within a single interval. In order to

calculate sampling standardized range -through diversity and turnover metrics, a subsampling program was written that randomly draws a standardized number of 41

occurrences from each time interval, records the genera subsampled in each interval,

ranges genera through intermediate time intervals, and calculates diversity and taxonomic

rates. This process is repeated 1000 times, the results are averaged, and error bars are

calculated. Total diversity and proportional turnover metrics were calculated using this

technique.

Global diversity was calculated directly from Sepkoski’s compendium of genus

first and last appearances (Sepkoski 2002). These data can be ranged through

intermediate time intervals to tabulate diversity and taxonomic rates. Where reasonable,

the intervals used by Sepkoski were combined to match the binning scheme used in the

regional database. Therefore, Sepkoski’s Ashgillian and Wenlockian subdivisions were

combined in our tabulations. This was not easily accomplished for the Caradoc,

however, and so the three subdivisions used by Sepkoski for this epoch are retained for

the global curves.

Results

Unstandardized Diversity and Turnover

The global diversity pattern for the subset of taxa considered here is similar to

patterns derived by Sepkoski for the entire dataset (Sepkoski 1993, 1995, 2002).

Diversity declines slightly through the Caradoc, spikes in the Ashgill, and drops

dramatically across the Ordovician-Silurian boundary (Fig 3.2A). The rebound in

diversity is slow, and pre-extinction levels of diversity are not achieved until the

Wenlock. Proportional extinction rates (Fig 3.2B) are low through the Ordovician but increase dramatically in the Ashgill to well above background levels. They then decline 42

to low levels in the Silurian. Origination rates increase from the Upper Caradoc into the

Ashgill, remain flat across the Ordovician-Silurian boundary, decline in the Aeronian, and increase through the Wenlock.

Raw diversity patterns for the three paleocontinents are shown in figure 3.3. The shape of the diversity curves for all three paleocontinents is similar, and all show features in common with the global diversity curve. Diversity in all three continents rises from the Caradoc through the Ashgill, drops to at or below Caradocian levels in the

Rhuddanian, remains low in the Aeronian, and begins to increase again in the Telychian.

The doubling of the number of occurrences in the Laurentian database has altered the raw diversity pattern for the continent seen in chapter 1 (Fig. 3.3), indicating that the raw diversity pattern is continuing to be influenced by changing the sampling intensity within each interval. None of the curves appear significantly altered by edge effects introduced by the use of range-through data, as the shape of all three curves is the same when only taxa sampled within a bin are counted towards diversity (Fig. 3.3).

Several key differences exist between the raw diversity patterns for the three paleocontinents. Raw diversity curves based on range-through genera in Laurentia suggest that diversity begins to recover earlier for this paleocontinent than in Baltica or

Avalonia (Fig. 3.3A). Diversity appears to rise slightly in the Aeronian, around 10 Myr after the mass extinction event, and pre-extinction levels of diversity are nearly recovered by the Telychian. In Baltica, diversity remains low in the Rhuddanian and Aeronian (Fig.

3.3B). In Avalonia, diversity actually decreases from the Rhuddanian to the Aeronian

(Fig. 3.3C). The rebound for both Baltica and Avalonia begins in the Telychian, roughly 43

15 Myr after the Ordovician-Silurian boundary, and Baltica replenishes diversity to pre- extinction levels by the Wenlock.

Analysis of proportional extinction rates reveals a significant peak in extinction occurred in all three regions analyzed in this study (Fig 3.4). Extinction rates rise significantly from the Upper Caradoc into the Ashgill, and then drop again in the

Rhuddanian interval. In Laurentia, extinction rates drop to well below Ordovician levels in the Rhuddanian and remain low throughout the Early Silurian. In Baltica (Fig 3.4A,

B), Rhuddanian extinction rates are again at Lower Caradoc levels, and remain low in the

Aeronian and Telychian. In Avalonia (Fig 3.4C), extinction rates also drop to Caradocian levels in the Rhuddanian, and begin to rise in subsequent intervals.

Origination rates vary between the three paleocontinents. Laurentia shows a gradual decline in origination rates from the Ashgill through the Aeronian before an increase in the Telychian (Fig 3.4A). Baltic origination rates increase dramatically from the Upper Caradoc into the Ashgill, then drop to well below Ordovician values in the

Rhuddanian, Aeronian, and Telychian intervals (Fig 3.4B). Avalonian origination rates increase from the Upper Caradoc into the Ashgill, decline slightly in the Rhuddanian, decrease dramatically in the Aeronian, and increase again in the Telychian (Fig 3.4C).

Sampling Standardized Diversity and Turnover

Rarefaction analysis performed on occurrences within a time interval shows the

affect of variations in sampling intensity on diversity within each paleocontinent (Fig

3.5). In Laurentia, the Rhuddanian and Aeronian are undersampled relative to the other

intervals. Rarefied diversity for these intervals is indistinguishable from Ordovician 44 diversity (Fig 3.5A). Indeed, all Silurian curves in Laurentia lie on or above the

Ordovician curves, indicating diversity changed very little throughout the time period of study. This suggests that, given consistent levels of sampling intensity through time, diversity in Laurentia is expected to be at similar levels after the Late Ordovician extinction as it was before the extinction.

Neither Baltica nor Avalonia show patterns similar to those of Laurentia. In

Baltica, the Rhuddanian and Aeronian rarefaction curves stand significantly lower than the rarefaction curves from all other intervals (Fig 3.5B). The same can be said of

Avalonia, where the Rhuddanian and Aeronian curves again lie well below the curve for the Ashgill, despite being the best sampled in terms of number of occurrences (Fig 3.5C).

Therefore, the diversity drop from the Ashgill to the Rhuddanian and the continued low in the Aeronian do not appear to be the result of poor sampling in either Baltica or

Avalonia.

Avalonian diversity is difficult to interpret using rarefaction, as the shapes of the

Telychian and Wenlock curves are steeper than curves for the other intervals. The rarefaction curve for the Telychian interval actually crosses the Lower and Upper

Caradoc, meaning Telychian diversity could be either higher or lower than Caradoc diversity depending on the chosen sample size. The slope of the steepest part of rarefaction curves is related to the evenness of that sample, with steeper slopes representing increased evenness (Olszewski 2004). This suggests that the evenness of the regional biota in Avalonia may have decreased in the Telychian and Wenlock. However, these inconsistencies do not affect the comparison between the Ashgill, Rhuddanian, and

Aeronian intervals, as these curves all have similar shapes and fail to cross at any point. 45

This means the rebound could have begun no earlier than the Telychian, a result

consistent with the unstandardized diversity trajectory for Avalonia (Fig. 3.3C).

Classical rarefaction with range-through produced sampling standardized

diversity curves that reveal a large amount of geographic variability in diversity trends

during this time period (Fig 3.6). Diversity patterns in Laurentia are markedly different

from the unstandardized diversity curves (Fig 3.6A). Diversity rises from the Lower

Caradoc through the Ashgill and remains flat through the Wenlock, including across the

extinction boundary. The mean diversity for all Silurian time bins falls within the 95%

confident intervals for the Ashgill, suggesting that diversity did not change significantly

at any point after the Ashgill. This indicates that diversity in Laurentia rebounded to pre- extinction levels of diversity within the first 5 Myr of the mass extinction event. Krug and Patzkowsky (2004) analyzed data for Laurentia and found very similar sampling standardized diversity patterns as described here. However, the database here has nearly

double the number of occurrences than does the previous study, and several poorly

sampled environments are filled. Despite the improved sampling, the only significant

difference between the two standardized diversity curves is a steeper rise in diversity

from the Upper Caradoc to the Ashgill. All other aspects of the curve remain unchanged,

indicating a robust pattern.

Standardized diversity patterns for the paleocontinent of Baltica are similar to

unstandardized patterns (Fig 3.6B). Diversity is flat in the Caradoc, increases in the

Ashgill, and drops to a low in the Rhuddanian. Diversity then remains low in the

Aeronian, increases slightly in the Telychian, and remains flat in the Wenlock. Two

differences exist between standardized and unstandardized diversity curves for this 46

paleocontinent. First, the magnitudes of diversity changes from one time interval to the

next are greater in the unstandardized diversity curves. Second, diversity fails to increase

from the Telychian to the Wenlock in the sampling standardized curve, preventing diversity from rebounding to Ashgillian levels.

Diversity patterns in Avalonia also change very little after sampling

standardization procedures are applied to the data (Fig 3.6C), with most features of the

unstandardized diversity curves retained. Diversity increases steadily from the Lower

Caradoc to the Ashgill, drops across the extinction boundary to lows in the Rhuddanian

and Aeronian, increases in the Telychian and remains constant into the Wenlock. This

suggests that diversity patterns in Avalonia are not greatly influenced by variations in

sampling intensity. It therefore appears that diversity patterns for both Baltica and

Avalonia are less biased by variations in sampling intensity than those for Laurentia, and

that the drop in diversity following the mass extinction in these two continents is a real

feature rather than a sampling artifact.

As stated above, the use of classical rarefaction with range-through allows

taxonomic rates to be calculated from sampling standardized datasets because each genus

subsampled in a run is recorded and its first and last appearance within a paleocontinent

determined. In Laurentia, 54% of genera go extinct in the Ashgill (Fig 3.7A), indicating

that the mass extinction is still intense in this region. Extinction levels then fall in the

Rhuddanian and remain low through the Telychian. Diversity is flat across the

Ordovician-Silurian boundary, however, because proportional origination peaks in the

Rhuddanian, replenishing the extinct genera and causing diversity to remain at pre- 47

extinction levels. Origination rates then fall in the Aeronian and increase slowly through

the Wenlock, balancing extinction rates throughout the Silurian.

In Baltica, proportional extinction metrics increase through the Ordovician to a

peak of 65% in the Ashgill (Fig 3.7B). Extinction rates then drop dramatically in the

Rhuddanian before rising again in the Aeronian and Telychian. Proportional origination

also rises to a peak in the Ashgill, with 59% of genera originating in this interval.

However, origination metrics decline in the Rhuddanian and Aeronian before rising in the

Telychian. Proportional origination rates are not able to compensate for extinction

intensities until the Telychian, causing the Early Silurian diversity lows in these time periods.

The turnover patterns in Avalonia are very similar to those of Baltica. Again, extinction rises dramatically from the Upper Caradoc to a high of 66% in the Ashgill before dropping to low values in the Silurian (Fig 3.7C). Proportional origination peaks in the Ashgill and then declines in the Rhuddanian and Aeronian, again causing the diversity lows in these time intervals in Avalonia. Origination fails to rise until the

Telychian, beginning the rebound seen in standardized diversity curves.

Several important differences exists between standardized and unstandardized

turnover rates in Laurentia and Baltica (Fig 3.4A, B), causing significant shifts in

diversity trajectories after sampling standardization. In Laurentia, the most significant

difference is a change from decreasing to increasing origination rates across the

Ordovician-Silurian boundary. Additionally, extinction rates in Laurentia increase from

the Rhuddanian through the Telychian after sampling standardization, as opposed to

remaining at low values in the unstandardized data. These changes result in a flat 48

diversity trajectory in Laurentia rather than a decrease across the extinction boundary

followed by a recovery. In Baltica, unstandardized data shows extinction rates dropping

to low values in the Rhuddanian and remaining low through the Silurian. In the

standardized data, extinction rates drop in the Rhuddanian but then increase again in the

Aeronian and Telychian, preventing diversity from rebounding by the Wenlock as seen in

the unstandardized data. Avalonian standardized and unstandardized turnover rates show

only minor differences, resulting in diversity curves that appear largely similar.

Discussion

These results suggest that biases introduced by variations in sampling intensity

vary geographically during the Late Ordovician and Early Silurian. Diversity patterns in

Laurentia change drastically when sampling standardization procedures are applied to the

data. Rather than retain the general pattern of increasing diversity through the

Ordovician, a drop in the Rhuddanian, a lag, and a recovery, the Laurentian curve

becomes flat from the Ashgill through the Wenlock, including across the extinction

boundary (Fig. 3.6A). Unlike raw diversity patterns in Laurentia, the sampling standardized diversity pattern has remained unaltered even after a significant increase in the number of occurrences for this continent. Both Baltic and Avalonian diversity patterns retain their structure after sampling standardization despite variable sample sizes among time bins in these continents. Though standardization procedures necessarily flatten diversity curves, first-order changes between time intervals are the same in raw

and standardized diversity patterns for these continents. 49

Rarefaction analyses suggest biogeographic variability in the response of regional biota during both the mass extinction and the post-extinction recovery period.

Specifically, the Laurentian pattern of unchanging diversity from the Upper Ordovician through the Middle Silurian differs markedly from Baltic and Avalonian diversity patterns, which show the more familiar drop in diversity at the extinction boundary and a

10 – 15 Myr lag before diversity increases (Fig 3.6). The differences in the patterns can be attributed to two features revealed by proportional turnover metrics. First, the extinction intensity in the Ashgill of Laurentia is significantly lower than in Baltica or

Avalonia, peaking at 54% in Laurentia rather than 65% in the other two. Additionally, proportional origination rates in Laurentia are high through the Ordovician and increase after the extinction event to a high of 54%. Combined with the lower extinction values for this continent, the Rhuddanian origination is able to compensate for lost genera and keep diversity at the same level as the Ashgill. Origination rates in Baltica and Avalonia decline after the extinction event in both the Rhuddanian and Aeronian time bins.

Coupled with the severity of the extinction in these continents, diversity drops in the

Rhuddanian and remains low until the Telychian, when origination rates increase.

Geographic variability in both origination and extinction therefore played a critical role in governing survivorship and recovery during the Late Ordovician mass extinction and post-extinction recovery. Though studies of spatial complexity are limited, the importance of geography is emerging as a consistent theme in the study of major macroevolutionary events. Variable patterns in diversity and turnover have been described for the Late Permian mass extinction (Shen and Shi 2002), the Paleocene recoveries from the end-Cretaceous mass extinction (Jablonski 1998), and the Ordovician 50

radiations (Miller 1997a, b, Novack-Gottshall and Miller 2003). With the addition of the

Late Ordovician mass extinction and Early Silurian recovery, it appears that geographic complexity in extinction and recovery underlie most global patterns.

Many causes could be responsible for the variable patterns in origination and extinction described here. The lower levels of extinction in Laurentia with respect to the other two continents may be directly related to proposed climatic causes of this extinction event. The Late Ordovician is associated with the rapid advance and retreat of a large

Gondwanan ice sheet in the uppermost Ashgill (Hirnantian) that drove the fall and rise of eustatic sea-level at this time (Brenchley et al. 1995). This pace of glaciation was the

result of a rapid climatic cooling event in an otherwise greenhouse world (Brenchley et

al. 1995, Brenchley et al. 1994), and it is reasonable to expect that the consequences of

such an environmental perturbation would be greater at higher latitudes, explaining the

increased levels of extinction in the higher latitude continents of Baltica and Avalonia.

The warm, tropical environments of Laurentia may have acted as a buffer to these

climatic variations, with the large sea-level fall and accompanying reduction in habitat

area acting as the primary cause of extinctions in this region.

Explanations for the increased Laurentian origination rates following the mass

extinction are more complex. At the regional scale, origination of new taxa can consist

of both newly evolved lineages and invading taxa from other regions. It is therefore

possible that diversity in Laurentia was replenished not only by the evolution of new

lineages but also by the invasion of taxa from other paleocontinents in the Early Silurian

(Krug and Patzkowsky 2004). Conversely, the lack of invading genera in Baltica or

Avalonia may have underscored the declining origination rates in these two continents, 51 which required the evolution of new genera alone to replenish diversity. Previous evidence for this scenario has been provided for the Late Ordovician mass extinction by

Sheehan (1975), who documented an invasion of Baltic brachiopod taxa into Laurentia following the mass extinction event, resulting in cosmopolitan faunas in the Early

Silurian.

In order to test this hypothesis, regional diversity of each continent for the

Rhuddanian time interval was dissected into genera surviving from the previous interval, genera evolving within that interval (here referred to as genus origination), and genera invading from the other two continents. However, the patterns of invasion are subject to the same sampling biases as the diversity curves themselves. For example, if all continents are well sampled in the Silurian, but Laurentia is undersampled in the

Ordovician, the invasion into Laurentia in the Silurian may appear inflated, as fewer taxa present in all three continents were recovered from the Ordovician of Laurentia. In order to remove these biases, the contributions of survivors, newly evolved lineages, and invading taxa to standing diversity for a region within any given bin must be analyzed in a sampling standardized framework similar to that used to produce diversity and turnover patterns. A subsampling program was written in which a constant number of occurrences are drawn at random for each continent in each interval. The genera recovered for a continent are recorded, and diversity and turnover are calculated. The relative contributions of invading versus newly evolved genera towards origination within a continent are calculated, the process repeated 1000 times, and the results averaged.

Because the database consists only of Laurentia, Baltica, and Avalonia, only invading taxa from within these three paleocontinents could be counted. In addition, the analyses 52

were limited to articulate and inarticulate brachiopod genera. This was done for several

reasons. First, brachiopods were very abundant in Ordovician and Silurian marine

environments, and were the dominant members of the Paleozoic Evolutionary Fauna in

terms of diversity (Sepkoski 1981, 1985). Patterns of survivorship, invasion, and

recovery in brachiopods should therefore provide a good estimate for patterns of whole

faunas during the Late Ordovician and Early Silurian. Second, it is important when using

sampling standardization that the number of occurrences be at a relatively high level for

all time intervals, and brachiopods are particularly well sampled in the database. Of

particular importance, however, is the level of sampling of brachiopods around the

Ordovician-Silurian boundary. In these intervals, brachiopods make up 65% of the total

occurrences. Brachiopods should therefore produce reliable patterns in a sampling

standardized framework.

Sampling standardized diversity patterns for articulate and inarticulate

brachiopods closely resemble patterns derived from the complete database (Fig 3.8).

Diversity in Baltica and Avalonia drops from a high in the Ashgill to a low in the

Rhuddanian. In neither continent does diversity rise to pre-extinction levels by the

Wenlock. Laurentian diversity is flat or increases throughout the time period considered,

including across the Ordovician-Silurian boundary.

Interestingly, these diversity trends suggest that latitudinal diversity patterns for brachiopods were altered by the Late Ordovician mass extinction. Brachiopod diversity

in Laurentia was lower than the higher latitude continents of Baltica and Avalonia in the

Ordovician, in contrast to the common pattern of high low latitude diversity seen in most

taxa. Following the mass extinction, however, brachiopod diversity in Laurentia 53 increases rapidly and exceeds the more northerly continents in the Lower Silurian. Only in Baltica does diversity begin to increase to Laurentian levels by the Telychian. This suggests that brachiopod diversity in tropical latitudes was actually lower than in higher latitudes before the extinction and became more diverse after the mass extinction event.

Because the three continents converge on each other throughout the time period considered here, it is difficult to determine the extent to which the mass extinction event is driving latitudinal patterns. Additional research that bins the data latitudinally rather than by paleocontinent is required to test hypotheses involving the affect of the mass extinction on latitudinal diversity trends. However, these data at least imply that a pervasive macroecological pattern for brachiopods was altered by the Late Ordovician mass extinction.

Figure 3.9 shows the relative contributions of surviving genera, invading genera, and newly evolved genera for each paleocontinent in the Rhuddanian. Data are shown as the proportion of standing diversity within each continent. In Baltica, only 7% of brachiopod genera invaded from the other two continents, with 29% of standing diversity the result of newly evolved lineages and 64% of diversity resulting from survivors of the extinction event. In Avalonia, 14% of brachiopod diversity is the result of taxa invading from either Baltica or Laurentia. The remaining diversity is divided evenly between surviving genera and newly evolved endemics. Laurentian diversity is comprised of a larger proportion of invading taxa than either of the other two continents. Twenty one percent of standing diversity in Laurentia is the result of genera that invaded from Baltica or Avalonia. Thirty-five percent of standing diversity is the result of newly evolved genera, and 44% is the result of surviving genera. 54

It therefore appears that invading taxa are more important in replenishing diversity in Laurentia than for the other two continents. Removing invading taxa from

Silurian intervals causes Laurentian diversity to drop slightly from the Ashgill to the

Rhuddanian (Fig 3.10). Invading genera are therefore necessary to cause the 5 Myr rebound in diversity seen in the standardized diversity curves in Laurentia. However, the drop in diversity is not nearly as dramatic as the diversity reductions seen in Baltica or

Avalonia with invading genera included. Additionally, even with invading taxa excluded, diversity in Laurentia rebounds to above Ashgillian levels of diversity by the

Aeronian. This suggests a complete rebound in brachiopod diversity would still have occurred within 10 Myr of the extinction if newly evolved brachiopod genera were the only component of origination rates in Laurentia. Neither Baltica nor Avalonia rebound to pre-extinction levels of diversity by the Wenlock, despite all new taxa contributing to origination in these continents.

These data therefore suggest that both invading genera and newly evolved genera were important contributors to diversity during the post-extinction recovery in Laurentia.

Though newly evolved genera would have produced a rebound in Laurentia significantly more rapid than in either Baltica or Avalonia, invading genera were a significant portion of standing diversity in the Rhuddanian and accelerated the rebound to pre-extinction levels to within the first 5 Myr. The addition of new genera via increased rates of speciation are consistent with the geographic position of Laurentia in the Late

Ordovician. Equatorial latitudes in the modern contain the highest levels of diversity throughout the world (Gentry 1988a, b, Rosenzweig 1992, Roy et al. 1994, 2003, 1998), and low-latitude peaks in diversity have been described at various times in the geologic 55

past (Crame 2002). High rates of speciation in the tropics are often cited as the

explanation for these patterns, and the position of Laurentia in equatorial latitudes in the

Early Silurian suggests that higher rates of evolution in this continent may be expected.

Additionally, prior to the mass extinction event, the flooded continental interior of

Laurentia contained many distinct, high-diversity faunas endemic to the region, whereas

open ocean and continental margin faunas, prevalent in Baltica and Avalonia, tended to

be widespread during these times (Sheehan and Coorough 1990). North American

provinciality is recognized for a variety of taxa during the Upper Ordovician, including

corals (Elias 1995), bryozoans (Anstey 1986), and conodonts (Sweet and Bergstrom

1984). The high degree of endemism in the continental interior with respect to the open

ocean suggests higher rates of genus origination in these regions in the Ashgill, and these

rates may have continued to be high with the return of normal environmental conditions

following the mass extinction.

Though the high genus origination rates in Laurentia make sense based on

geography and environmental make-up, it is less clear why Laurentia should be more

susceptible to invasion following the mass extinction. Extinction intensity is generally

considered to be directly proportional to invasion potential. Yet the extinction in

Laurentia was 10% less severe than in Baltica or Avalonia, while invasion intensity was

greater. Jablonski (1998, 2004) described a similar pattern for the recovery interval

following the end-Cretaceous mass extinction. Following the extinction, invasion was more intense in the North American Gulf Coast than in other well studied regions despite

similar extinction intensities. Jablonski suggests that that the relationship between 56 extinction and invasion may break down at high extinction intensities, with the types of taxa being lost superceding in importance the number of taxa being lost.

In the Ordovician, however, we cannot rule out purely environmental reasons for high numbers of invaders in Laurentia. With the closing of the Iapetus Ocean, changes in ocean circulation may have made larval dispersal more likely from Baltica to Laurentia than in the opposite direction (Herrmann et al. 2004). Additionally, the geographic extent of Laurentia coupled with extinctions in the continental interior may have provided more ecospace into which taxa could invade, even with lower overall extinction intensities for the paleocontinent as a whole. Finally, the low invasion intensities for Baltica and

Avalonia may be an artifact of the limited geographic extent of the database. Taxa from regions of the world not analyzed here, including Siberia, Kazakstania, and Gondwana, may have invaded Baltica or Avalonia during this time period, causing many of the genera defined as newly evolved here to be redefined as invaders. Though this would probably have some effect, it seems unlikely to alter the results significantly, as Baltica and Avalonia moved away from the Gondwanan mainland and converged on Laurentia during this time period. However, depending on sea-level and atmospheric pCO2 conditions in the Ashgill and Rhuddanian, ocean currents may have favored invasion from other paleocontinents into this region of study (Herrmann et al. 2004). The true affects of biotic invasion from other regions of the world will remain unclear until the database is expanded to include these regions. At present, it is unclear why regions from greater distances would contribute more taxa to Baltica and Avalonia than Laurentia.

Nevertheless, the analysis of biotic invasions must be expanded geographically, and the underlying causes of invasion, both physical and biological, must be studied in greater 57 detail, as they are crucial in understanding the macroevolutionary and macroecological processes governing the recovery intervals from mass extinctions.

Conclusions

1. Unstandardized diversity curves for Laurentia, Baltica, and Avalonia, derived

from lists of genus occurrences, all retain the basic structure of the global curve

derived from Sepkoski’s database of genus first and last appearances. The

regional curves show a slight diversity increase in the Caradoc, a spike in the

Ashgill, a drop across the extinction boundary, and a protracted rise through the

Wenlock. These diversity patterns are driven by a spike in extinction intensities

in the Ashgill coupled with declining origination rates from highs in the Ashgill to

lows in the Aeronian.

2. Rarefaction analyses indicate that the diversity drop across the extinction

boundary and the protracted post-extinction recovery are real features for Baltica

and Avalonia, but are artifacts of variations in sampling intensity in Laurentia.

When these biasing effects are removed, Laurentian diversity remains flat across

the extinction boundary and throughout the Silurian. Analysis of taxonomic rates

derived from the classical rarefaction with range-through indicate that lower

Ashgillian extinction intensities and high Rhuddanian origination rates caused

diversity to rebound in Laurentia within the first 5 Myr of the extinction event.

Declining origination rates and higher Ashgillian extinction intensities cause

diversity to remain low through the Aeronian in both Baltica and Avalonia. The 58

Late Ordovician therefore joins the Late Permian and end-Cretaceous as global

mass extinctions with an underlying spatial complexity.

3. After applying sampling standardization to data for brachiopods, Rhuddanian

brachiopod diversity for the three paleocontinents was dissected into survivors,

newly evolved genera, and invaders. This analysis revealed that invading genera

made up a greater proportion of diversity in Laurentia than in Baltica or Avalonia.

Removing invading taxa from Silurian intervals causes diversity to drop from the

Ashgill to the Rhuddanian. However, even in the absence of invading taxa,

diversity in Laurentia rebounded to pre-extinction levels by the Aeronian, well

before either Baltica or Avalonia, suggesting that the origination of new lineages

was more rapid in Laurentia than in the other two paleocontinents.

4. Though high genus origination rates may be expected in Laurentia due to its

equatorial position, large size, and vast epicontinental seas, the reasons for higher

rates of invasion into Laurentia are unclear, as extinction levels were lower in this

continent than in Baltica or Avalonia. It is possible that environmental conditions

or oceanographic features made dispersal more likely towards Laurentia, or that

the limited geographic extent of the database is masking the number of invaders

in Baltica and Avalonia from other regions of the world. It has also been

proposed that, once extinction levels exceed a threshold value, the types of genera

to go extinct, rather than the number of genera to go extinct, dictate the

susceptibility of a continent to invasion. Regardless, more research into the

underlying causes of the coupling of invasion and speciation in the recovery

intervals following mass extinction events is needed. 59

Figure 3.1. Paleogeographic reconstruction showing the positions of Laurentia, Baltica, and Avalonia (dark gray) at the beginning of the Caradoc, 458 Ma. Redrawn from Scotese and McKerrow 1990 (http://scotese.com/Default.htm) 60

Figure 3.2. Global diversity and turnover metrics. (A) Global diversity for brachiopods, anthozoans, bivalves, and trilobites calculated from Sepkoski’s compendium of genus first and last appearances. (Sepkoski 2002) (B) origination and extinction metrics. L.C., Lower Caradoc; M.C., Middle Caradoc; U.C., Upper Caradoc. Error bars are 95% confidence intervals. Vertical dashed line marks the Ordovician-Silurian boundary.

Figure 3.3. Unstandardized diversity curves for (A) Laurentia, (B) Baltica, and (C) Avalonia. Solid lines record diversity with genera ranged-through intermediate time intervals. Dashed lines record diversity using only genera sampled from within an interval. Vertical dashed line marks the Ordovician-Silurian boundary.

Figure 3.4. Unstandardized proportional origination and extinction metrics for (A) Laurentia, (B) Baltica, and (C) Avalonia. Error bars are 95% confidence intervals calculated using the binomial probability distribution. Vertical dashed line marks the Ordovician-Silurian boundary. 63

Figure 3.5. Analytical rarefaction curves for each of the seven time intervals for (A) Laurentia, (B) Baltica, and (C) Avalonia.

Figure 3.6. Sampling standardized diversity curves for (A) Laurentia, (B) Baltica, and (C) Avalonia. Diversity was derived using a subsampling algorithm that standardizes to a constant number of occurrences per interval. Error bars are 95% confidence intervals. Vertical dashed line marks the Ordovician-Silurian boundary. 65

Figure 3.7. Sampling standardized proportional origination and extinction metrics for (A) Laurentia, (B) Baltica, and (C) Avalonia. Error bars are 95% confidence intervals. Vertical dashed line marks the Ordovician-Silurian boundary. 66

Figure 3.8. Sampling standardized diversity curves for brachiopods from Laurentia, Baltica, and Avalonia. Error bars are 95% confidence intervals. Vertical dashed line marks the Ordovician- Silurian boundary.

Figure 3.9. Proportional contribution of survivorship, genus origination, and invasion to standing diversity in the Rhuddanian time interval for Baltica, Avalonia, and Laurentia. Relative contributions were determined using a subsampling program that standardizes by the number of occurrences in each continent. 67

Figure 3.10. Sampling standardized brachiopod diversity curves for the paleocontinent of Laurentia. Sold line was calculated using all brachiopods for a given time interval. The dashed line was derived by subtracting invading genera from diversity counts in the Silurian time intervals. Error bars are 95% confidence intervals. Vertical dashed line marks the Ordovician-Silurian boundary. 68

Chapter 4. The Evolutionary Impact of the Late Ordovician Mass Extinction:

Insights from Phylogenetic Analyses

Introduction

Mass extinctions have reshaped evolutionary trends throughout the Phanerozoic.

Because large numbers of taxa are removed from the ecosystem in a geologically short

period of time, previously minor groups can undergo evolutionary radiations that allow

them to occupy niches vacated by victims of the extinction. Additionally, traits that favor

survival during times of normal, or background, extinction may not confer adaptive

advantages during times of mass extinction (Jablonski 1986, 2004). In this way, mass

extinctions can cause a complete shift in the evolutionary paths followed by clades,

resulting in unique and sometimes large-scale changes to the global biota.

Mass extinctions have traditionally been defined by the proportion of taxa lost in a given interval of time (Bambach et al. 2004, Raup and Sepkoski 1982, 1986).

Quantifying the evolutionary impact of a mass extinction event has proven more difficult,

yet recent attempts have concluded that the evolutionary and ecological severity of a

mass extinction may be decoupled from its taxonomic severity (Droser et al. 2000,

McGhee et al. 2004). For example, studies of two important bryozoan clades, the

Cyclostomata and Cheilostomata, through the end-Cretaceous mass extinction have shown a general pattern of displacement of cyclostomes by cheilostomes. These diversity patterns conform well with coupled-logistic models of clade replacement, suggesting that competition was the driving factor behind the cheilostome success

(Lidgard et al. 1993, Sepkoski et al. 2000). However, diversity patterns alone fail to 69

capture patterns of ecological replacement spanning the extinction and recovery periods

(McKinney et al. 1998). Relative proportions of skeletal mass for the two clades follow the same pattern as proportional diversity prior to the extinction, yet they are reset after the extinction event, with cyclostomes again the dominant contributor of biomass in the

Paleocene (McKinney et al. 1998). This post-extinction shift in community dominance is decoupled from taxonomic success, and is not recognized in diversity studies.

The Late Ordovician mass extinction is the second largest of the Phanerozoic in

terms of proportion of diversity (i.e. genera, families) lost, yet it brought about only

minor ecological changes (McGhee et al. 2004, Sheehan 1996). Although diversity

within guilds was reduced, none were eliminated (Bambach 1985), morphological change was minimal within some groups (Brenchley et al. 2001, Underwood et al. 1998), and most higher taxonomic groups rediversified in the wake of the mass extinction event.

The diminished evolutionary impact of the Late Ordovician mass extinction sets it apart from other mass extinctions, and the processes underlying the decoupling of taxonomic and ecological severity during the event remain poorly understood.

Here, I use phylogenetic techniques to investigate the causes of the lack of

evolutionary restructuring resulting from the Late Ordovician mass extinction.

Phylogenetic hypotheses are derived independently of the fossil record, making them less

biased by imperfections in the rock record that can alter the distribution of first and last appearances (Smith 1994, Smith et al. 2001). Evolutionary relationships among taxa are determined based on shared derived characters. These relationships are then calibrated to the fossil record using the stratigraphic distribution of fossils, resulting in less biased estimates of the stratigraphic ranges of taxa. These data are used to address a variety of 70

important issues concerning the Late Ordovician mass extinction. First, the evolutionary

relationships among taxa are used to infer the presence of intermediate lineages and

portions of a taxon’s stratigraphic range that have remained unrecorded due to

imperfections in the fossil record. Diversity is therefore adjusted through both implied

range extensions and the inference of ghost lineages in the fossil record (Norell 1992).

Second, the impact of the mass extinction on lineages and monophyla is

investigated to add insight into the resulting evolutionary pathways followed by survivors

of the event. If many genera following a mass extinction are sister taxa to genera existing

before the mass extinction, then pseudoextinction may bias proportional extinction and

origination rates. Additionally, the distribution of surviving lineages in a cladogram

should have an impact on the expected ecological and evolutionary changes brought

about by a mass extinction event (Fig. 4.1). If surviving lineages are derived from a

variety of different monophyla, then the post-extinction recovery in diversity should

include many of the evolutionary pathways in existence before the extinction event (Fig

4.1A). In this case, only minor changes would be expected, as many of the ecological

niches and evolutionary strategies previously occupied by the group would simply be

refilled. However, should the majority of monophyla terminate as a result of the mass

extinction, the post-extinction recovery would be driven by a small proportion of lineages, increasing the possibility for new, unique evolutionary pathways (Fig. 4.1B).

This research focuses on strophomenid brachiopods in the paleocontinent of

Laurentia spanning the Late Ordovician mass extinction and Early Silurian recovery

(Caradoc to Wenlock). Using an extensive database of characters including muscle field

structure, articulation type, and internal and external shell features, a cladogram was 71

produced and calibrated against the stratigraphic column in order to estimate diversity

and turnover patterns for lineages. The data show that the last occurrence of a genus

generally remains unaltered after phylogenetic correction, implying that pseudoextinction

is negligible within this group. First appearances, however, are often extended

backwards in time, and many Silurian genera are shown to have their origins in the

Ordovician. As a result, many genera thought to be part of the post-extinction recovery

are actually Ordovician survivors. Importantly, these survivors are derived from

throughout the phylogenetic tree (as in Fig. 4.1A), suggesting that strophomenids

utilizing many evolutionary strategies cross the extinction boundary. Because a high

diversity of forms are implied to survive the event, it is reasonable that strophomenids

would rediversify along many of the evolutionary pathways occupied prior to the

extinction. Therefore, in the case of strophomenid brachiopods, it is expected that many

of the ecological niches would also be reoccupied. Should this pattern typify other taxa

during the Late Ordovician mass extinction, the decoupling of taxonomic and

ecological/evolutionary severity would fit with phylogenetic expectations.

Terminology

Phylogenetic terminology is often imprecisely defined, and many terms are applied interchangeably in the literature. For this reason, it is necessary to define the terminology as it will be used throughout this section. A genus refers to the Linnaean classification designation. A lineage refers to an evolutionary line of genera, with a single point anywhere within a lineage being the equivalent of a genus. The terms clade and monophylum are essentially interchangeable, with a clade traditionally referring to 72 any monophyletic subdivision of lineages. However, though their meanings will be retained, these terms will be used to refer to slightly different lineage groups. The term monophylum refers to any unnamed monophyletic group of lineages derived for the

Strophomenida in the phylogenetic analysis presented. These can vary in terms of size and inclusiveness, and one monophylum can be contained within a larger monophylum.

The term clade refers to large monophyletic groups that are associated with a taxonomic designation (i.e. Strophomenida) in the literature. The term monophylum is therefore slightly more ambiguous than the term clade, and will be limited to divisions within the cladogram (Fig. 4.4).

Data and Methods

The stratigraphic distribution of strophomenid brachiopods in Laurentia was determined using the distribution of occurrences in the Paleobiology Database

(http://paleodb.org). This allows phylogenetically adjusted diversity trends to be compared directly to taxic diversity counts based on a comprehensive database of fossil occurrences. The database contained 75 strophomenid brachiopod genera spanning the

Caradoc through the Wenlock. Of these, eight have been reclassified within new orders, and four have been placed in synonymy with other genera since the publications as cited in the Paleobiology Database (Williams et al. 2000). This results in 63 strophomenid genera from which diversity and turnover in Laurentia were calculated. Raw diversity was counted as the number of genera sampled within an interval, ranging through that interval, or existing only in that interval. The extinction of a genus represents the last 73 occurrence of that genus in Laurentia, and the origination of a genus represents its first occurrence in Laurentia.

The deficiencies in the Early Silurian fossil record have been discussed previously

(chapters 2 and 3), along with many of the statistical techniques commonly used to remove such biases. Strophomenid brachiopods, like many other taxa, show an extreme reduction in sampling intensity coincident with Early Silurian diversity lows (Fig. 4.2).

This decrease is related to a decline in the number of sampled localities from North

America (Fig. 4.3). Because the focus of this chapter is restricted to strophomenid brachiopods, the sampled area is less than when considering the five classes used in previous chapters. Strophomenids from the Lower Silurian are nevertheless represented in several different geographic regions of Laurentia, including Anticosti Island (Dewing

2004), the Northern Appalachians (Ayrton et al. 1969), the Edgewood province (Amsden

1974), and the Great Basin (Sheehan 1980).

Whereas previous chapters have focused on statistical methods for correcting sampling intensity, phylogenetic analyses are used here to correct for these biases.

Because the evolutionary relationships illustrated in cladograms are determined independently of the rock record, scaling them to the stratigraphic column can determine the amount of diversity implied to be missing in a given interval. The range of a genus is corrected using its evolutionary relationship to other genera within the tree (see below).

Diversity within a time interval is defined as any lineage either present or implied

(through phylogenetic analysis) to exist within that interval. Similarly, originations and extinctions of lineages are tallied as the first or last appearance of a lineage within a stratigraphic interval. 74

The phylogenetic data used here were derived from characters described by Cocks

and Rong (1989), Rong and Cocks (1994), and Dewing (2004) for the Order

Strophomenida. Previous workers placed special emphasis on the form of the cardinal

process, using this character to designate superfamilies and families within the order.

Additionally, articulation type, in particular the presence of denticles on the hinge-line

and teeth, is considered of particular importance in the familial designation within the

superfamily Strophomenoidea. In all, 25 characters and 82 character states were used to

define genera present in Laurentia from the Upper Ordovician (Caradoc) through the

Lower Silurian (Wenlock). A complete list of characters and their designations for

individual genera can be found in Appendices B and C. Character states were assigned

through analysis of monographs and specimens housed at the Smithsonian Museum of

Natural History. Type species were used to define the character states of a genus. A

parsimony analysis was then run using PAUP 4.0 (Swofford 2000).

Forty-six strophomenid genera were included in the phylogenetic analysis

(appendix C). These represent the families Strophomenidae, Rafinesquinidae,

Glyptomenidae, Christianiidae, Amphistrophiidae, Leptostrophiidae,

Eopholidostrophiidae, Strophodontidae, and Strophonellidae. This includes almost all of the families present in the Caradoc through the Wenlock as determined by Rong and

Cocks (1994). The only exceptions are the Foliomenidae, which is a low diversity family

related to the Glyptomenidae, and the Douvilinidae, a family that may have branched as

early as the Wenlock but did not diversify until the Devonian. Billingsella, a Middle

Cambrian genus representing the superfamily Billingselloidea, was used as the outgroup

in the analysis because the Billingselloidea are thought the be ancestral to the 75

Strophomenoidea and Plectambonitoidea and are limited to Middle Cambrian and Lower

Ordovician.

Taxa were excluded from the analysis if they are considered junior synonyms of

other taxa and were independently identified as having identical character designations as

their synonym, or if the majority of characters could not be determined accurately

through the analysis of specimens or monograph pictures. This resulted in the exclusion

of 17 genera from the analysis. Of the other 17 removed, 16 are singletons with four or

fewer occurrences in the database, with nine of those occurring in the Wenlock. Seven

genera classified as strophomenids were removed from Ordovician intervals, and only

one genus (represented by one occurrence) was removed from the three Early Silurian

intervals. No families were removed from the dataset.

Because of the large size of the database, a heuristic search was run with all

characters unordered and of equal weight. The characters were then re-weighted based

on their consistency index (CI), and the analysis repeated. The consistency index of a

character is a measurement of its homoplasy in the most parsimonious tree. Therefore,

re-weighting characters based on the CI is an objective way to add more weight to characters showing the least amount of homoplasy. Based on the CI, the most conservative characters were the presence of denticles on the teeth and hingeline, the presence of crenulations on the teeth, the presence and form of a dorsal side septum, the shape of the ventral muscle field, the presence of a pseudodeltidium, and the form of the cardinal process. The weight of these characters as designated by the consistency index is in general agreement with their importance as described by Cocks and Rong (1989) 76 and Rong and Cocks (1994). The only exception is the cardinal process, which is less consistent in this analysis than suggested by Rong and Cocks (1994).

The heuristic search using the re-weighted characters produced 103 equally parsimonious trees of length 58 steps. A majority rule consensus tree was calculated based on these trees (Fig. 4.4). Most of the branches of this tree are supported by 100 percent of the most parsimonious trees derived from the heuristic search. Six branches are supported by less than 100%, and only one is supported by less than 50% but was included in the tree because it does not affect the structure of any of the other branches.

Using the distribution of genera in the fossil record, the consensus tree was calibrated against the stratigraphic column and the ranges of genera and lineages were adjusted. Because of imperfections in the fossil record, sister taxa, as derived from parsimony analysis, often have displaced stratigraphic ranges. When scaling a cladogram to the stratigraphic column, sister taxa can have two possible interpretations. If the two genera are both defined based on apomorphies (derived characters), then they originated as part of the same evolutionary event (bifurcating cladogenesis), and the ancestral lineage of the two sister taxa as inferred from the cladogram can be considered a real, un- sampled taxon. This inferred lineage is termed a ghost lineage or ghost taxon (Norell

1992). In this case, the stratigraphic range of the sister taxon occurring later in the stratigraphic record can be extended back to the first appearance of the earlier occurring taxon. When counting diversity based on lineages, the two taxa and the ghost lineage are counted within the interval containing the first occurrence of the two sister taxa. The termination of the ghost lineage within that interval is considered a pseudoextinction, and both sister taxa are counted as originations. 77

If only one of the two sister taxa contains a derived character, then an ancestor- descendent relationship between the two may be implied. If the ancestral taxon appears first in the stratigraphic record, then it is possible that the two taxa are part of an anagenetically evolving lineage. In this case, the stratigraphic range of the ancestral taxon will be extended forward and linked with the lineage of the descendant taxa. This lineage is considered to exist continuously through all intermediate time intervals, and no originations or extinctions are recorded. If the ancestral taxon occurs later in the stratigraphic column, then its range must be extended back to the interval containing the descendent taxon. Both taxa are counted as originating in this interval. If the descendent taxon co-exists with its ancestral taxon, then the branch point from the ancestral taxon is shown in the interval in which it occurs, and is counted as an origination in that interval.

The stratigraphic column was subdivided into seven intervals of roughly equal

duration. Ages for the bases of these intervals were taken from Tucker and McKerrow

(Tucker 1995). Global diversity was calculated directly from Sepkoski’s (2002)

compendium of genus first and last appearances. These data can be ranged through

intermediate time intervals to tabulate diversity and taxonomic rates. Where reasonable,

the intervals used by Sepkoski were combined to match the binning scheme used in the

regional database (see chapters 2 and 3 for details).

Results

Global diversity of strophomenid brachiopods (Fig 4.5A) is high in the Early

Caradoc and remains relatively flat through the Late Caradoc. Diversity then falls in the

Ashgill and the Rhuddanian, remains low in the Aeronian, increases in the Telychian and 78 again in the Wenlock. Pre-extinction levels of diversity are not achieved in this time period. Proportional extinction rates (Fig. 4.5B) increase from the Middle Caradoc to a high of 70% in the Ashgill before dropping to relatively low levels in the Silurian.

Proportional origination rates (Fig 4.5B) increase from less than 10% in the Middle

Caradoc to 40% in the Ashgill, decrease slightly across the extinction boundary, remain constant through the Telychian and increase in the Wenlock.

Raw diversity trends for strophomenid brachiopods in Laurentia differ slightly from global trends in the Ordovician but are similar in the Silurian (Fig 4.6A). The plateau in diversity in the Caradoc seen in global patterns does not occur in Laurentia.

Diversity decreases from the Lower Caradoc to the Rhuddanian. Diversity remains low in the Aeronian, rebounds in the Telychian and exceeds Ordovician levels of diversity by the Wenlock. This pattern of delayed Early Silurian recovery is similar to that seen in global taxic diversity patterns for strophomenid brachiopods. Extinction intensities rise to 44% in the Upper Caradoc and increase slightly to 50% in the Ashgill before decreasing and remaining low in all Silurian intervals (Fig. 4.6B). This is significantly lower than global extinction rates. Proportional origination peaks at 30% in the Ashgill, decreases to low values in the Rhuddanian through the Telychian, and then rises rapidly to 47% in the Wenlock (Fig. 4.6B).

Raw diversity trends for the 47 genera included in the phylogenetic portion of this analysis shows several differences from the complete Laurentian database (Fig. 4.6A).

First, the diversity decrease across the extinction boundary is less dramatic. Diversity decreases by seven genera in the complete dataset, whereas it decreases by three genera in the reduced dataset. Proportional extinction is reduced to 38% in the Ashgill and 41% 79

in the Upper Caradoc, down from 50% and 44%, respectively, in the complete dataset

(proportional rates for the reduced dataset are not shown). Reduced turnover rates are

expected when removing singletons from the analysis because they both originate and go

extinct in the same interval. However, though reduced, the pattern of elevated Upper

Caradoc and Ashgillian extinction intensities with respect to the other intervals remains

intact.

Additionally, the rebound of diversity in the Wenlock is diminished when only

genera utilized for the phylogenetic analysis are counted. Though the rebound in diversity is the same through the Rhuddanian, Aeronian, and Telychian, only a moderate increase is recorded in the Wenlock using the reduced database. However, diversity increases in that interval, and pre-extinction levels of diversity are still achieved.

Calibrating the consensus tree using the stratigraphic record shows that much of

the evolution of the strophomenid brachiopods in Laurentia occurred prior to the Lower

Caradoc (Fig. 4.7). Most of the internal nodes of the consensus tree are located before the time interval considered here, including the ancestral lineages to many of the Silurian genera. This is not unexpected, as many important clades diversified dramatically during the Ordovician radiations prior to the Caradoc (Rong and Cocks 1994). However, the

lack of new monophyla throughout the Late Ordovician and Early Silurian is striking,

particularly following the Late Ordovician mass extinction. Many recovery periods

following mass extinction events document dramatic radiations, commonly of previously

low diversity clades (Erwin 1998), yet little radiation occurs in this group within the first

20 Myr following the Late Ordovician mass extinction. The calibrated tree shows that no

genus going extinct in the Ashgill has its range extended into the Silurian as a result of 80 phylogenetic correction. Last appearances of genera correspond well to last appearances of lineages throughout the stratigraphic column. However, eight of the 13 genera with occurrences limited to the Silurian have their ranges extended back into the Ordovician, usually as far as the Caradoc. Of those eight, only three have Ordovician fossil occurrences elsewhere in the world (Aegiria, Leangella, Leptelloidea). All others have been identified in previous studies as having stratigraphic ranges limited to the Silurian and younger (Williams et al. 2000), consistent with the database of occurrences used here. Therefore, the ranges of those five genera would be extended into the Ordovician regardless of the geographic extent of this database. This suggests that many of the genera contributing to the post-extinction recovery in Laurentia may be survivors of the extinction event and are derived from evolutionary events 20 Myr before their appearance in the Laurentian stratigraphic record. Because much of the evolutionary history of the lineages analyzed here occurs prior to the Caradoc, the minimal range extension seen in

Ordovician lineages is probably a function of the limited temporal range of the database.

The calibrated phylogenetic tree also implies that lineages surviving the extinction event are derived from throughout the phylogenetic tree. Most monophyletic subdivisions within the consensus tree have lineages that cross the Ordovician-Silurian boundary. Only one monophylum (Apatomorpha, Glyptambonites, Palaeostrophomena) has no lineages that survive to the Silurian. Similarly, only one monophylum

(Leptostrophia, Mclearnites, Mesodouvillina) is implied to originate in the Silurian. This suggests that many of the evolutionary strategies utilized by strophomenid brachiopods also crossed the boundary, enabling those paths to be followed after the mass extinction event. 81

When diversity is corrected through the addition of range extensions and implied

ghost lineages, diversity declines steadily from the Early Caradoc through the

Rhuddanian and becomes flat through the remaining time intervals (Fig 4.8A). Diversity

fails to increase in any of the Early Silurian time intervals, indicating that strophomenid

diversity failed to rebound until after the Wenlock. This diversity trend is similar to that

derived using genus counts. Counting lineages inflates diversity in all of the time

intervals except the Wenlock. This is expected, as new lineages can be implied to exist

through the evolutionary relationships among taxa but rarely will an existing lineage be

eliminated. The most striking difference between lineage and genus diversity is the lack

of an increase in diversity in the Early Silurian. This change occurs primarily through

range extensions of Silurian taxa into the Ordovician, changing many newly evolved

Silurian genera into Ordovician survivors. However, edge effects may be biasing lineage diversity patterns in the Telychian and Wenlock, as no data are included from the Late

Silurian or Devonian. Should taxa from these intervals also have their ranges extended backwards, diversity may again appear to increase in the Early Silurian.

With the exception of the Ashgill, genus and lineage origination trends are

similar, differing only in magnitude (Fig. 4.8B). Proportional origination rates were low

for strophomenid brachiopods throughout the Late Ordovician and Early Silurian. When

determined using lineages, origination rates decrease even further (Fig 4.8B).

Proportional origination is at or below 12% in every time interval, and in two, the Ashgill

and the Aeronian, no originations are recorded. This occurs because the stratigraphic

ranges of many genera are extended backwards to the Caradoc. These lineages therefore

originated during the Ordovician radiations rather than in the Late Ordovician or Early 82

Silurian. As stated above, only one new monophyletic group radiates in the Silurian

(Leptostrophia, Mclearnites, Mesodouvillina).

Though the presence or origination of a lineage may be accurately represented using either monophyletic or paraphyletic groups (Raup 1985, Wagner 1995), it has been argued that the extinction (or termination) of a lineage may only be accurately represented using monophyletic groups (Smith 1994). This is because the extinction of a paraphyletic group may not represent the termination of an entire clade, and therefore would not be considered a biological extinction in the strict sense. If true, the greatest discrepancy between lineage and taxic diversity estimates is expected to be in calculations of extinction intensity (Smith 1994). Indeed, proportional extinction patterns in Ordovician intervals derived using lineages differ from patterns derived using genus counts (Fig. 4.8C). Proportional extinction declines from a high of 35% in the Upper

Caradoc to 24% in the Ashgill before decreasing to low values in the Silurian intervals.

This stands in contrast to the rise in extinction intensities in the Upper Caradoc and

Ashgill seen in raw extinction counts. However, the decline in proportional extinction is caused by the extension of lineage ranges from Silurian into Ordovician intervals. As stated above, all genera shown to go extinct in the Ashgill in this database are also shown to go extinct as lineages. When the total number of extinctions are counted rather than proportional extinction, the largest differences occur in the Lower and Upper Caradoc, mostly through the addition of ghost lineages that bifurcate in those intervals. Though the original lineage disappears in the interval, these can be considered pseudoextinctions because the original lineage bifurcated into two new lineages. Therefore the last appearance of a strophomenid genus in Laurentia is the same as the last appearance of a 83

lineage. No monophyletic groups are eliminated as part of the Late Ordovician mass

extinction. The only monophyletic group defined in the consensus tree to go extinct in

this time interval is the Apatomorpha, Glyptambonites, Paleostrophomena group in the

Lower Caradoc.

Discussion

Genus Versus Lineage Diversity and Turnover Patterns

Pseudoextinction is a major concern in the study of mass extinction events

because mass extinctions may be correlated with sea-level drops and corresponding reductions in rock volume (Peters 2001, 2002). If environments are not consistently preserved through time, taxonomic counts may fail to record accurately the last appearance of a taxon, resulting in biased turnover estimates. Pseudoextinction has been shown to bias extinction and origination intensities for the Cenomanian-Turonian extinction event (Smith et al. 2001), and is of concern whenever there is inconsistent preservation of environments through time.

The Late Ordovician mass extinction is coincident with dramatic sea-level fluctuations at the end of the Ashgill, and therefore the degree of pseudoextinction must be addressed. Ausich and Peters (2005) demonstrated that diversity and turnover patterns produced from Sepkoski’s (2002) global database of first and last occurrences may have inaccurately recorded the stratigraphic ranges of crinoids at the substage level, exaggerating extinction intensities in the Ashgill. This exemplifies the need for methods that calibrate perceived diversity and turnover patterns independently of the fossil record.

The data here show that many strophomenid genera in the Silurian have sister taxa in the 84

Ordovician. Over half of the genera thought to contribute to the post-extinction rebound have Ordovician sister taxa, and these lineages survived the extinction event rather than evolving during the recovery interval. Phylogenetically corrected stratigraphic ranges show that pseudoextinction within strophomenid brachiopods is negligible, suggesting lineage termination is accurately reflected using traditional taxonomic practices (Fig.

4.7). However, perceived extinction intensities in the Ashgill are reduced to lower values after phylogenetic correction due to backwards range extension of Silurian lineages (Fig.

4.8C). This acts to dilute the magnitude of the extinction event by adding surviving lineages to the Ashgill. Therefore, while the last appearance of lineages were accurately recorded, the overall intensity of the extinction event was overestimated due to poor sampling of surviving taxa at the end of the Ordovician.

Traditional taxonomic counts of strophomenid diversity and origination are in general agreement with those derived from calibrating the strophomenid cladogram to the fossil record (Fig. 4.8A, B). Diversity and origination patterns change little when corrected using phylogeny. The inflation in total diversity is an expected consequence of calibrating phylogenetic patterns, as ranges can be extended using this method but not contracted. Additionally, extension of the database into the Upper Silurian and Devonian may result in an increase in the number of lineages in the Telychian and Wenlock. Edge effects may therefore bias lineage diversity patterns in the Telychian and Wenlock, and expansion of the database may recover the increase in diversity by the Wenlock. Because of backwards range extension of Silurian lineages into the Ordovician, origination rates are consistently lower using lineages than genera. However, with the exception of the 85 lack of originations in the Ashgill, the general structure of the proportional origination curve based on lineages is in agreement with that derived using genera.

These results agree with those of Wagner (1995), who demonstrated a high correlation between diversity patterns for Ordovician and Silurian gastropods derived from species, lineages, or monophyla. Wagner (1995) suggested that the intensity of the extinction event was actually higher when counting lineages, and that the elevated extinction intensities in the Late Ordovician were not an artifact of sampling or poor taxonomy. Few gastropod genera in the analysis were monophyletic, suggesting that poorly resolved taxonomic classification introduces noise into diversity curves rather than a systematic bias. A high correlation also exists between strophomenid genus and lineage diversity and turnover, and though the extinction appears less severe using phylogenetic analysis, last appearance of a lineage in Laurentia during this time period is generally well recorded. These studies suggest that relative diversity and turnover patterns can be recovered using taxonomic approaches.

Parsimony is a powerful methodological approach to establishing the evolutionary history of a group because it minimizes the number of ad hoc assumptions necessary to explain a set of observations (Kluge 1984, Smith 1994). However, the usefulness of phylogenetic methods depends upon the accuracy of inferred phylogenies. An inconsistency between a cladogram and the fossil record can arise from poor sampling of the fossil record or inaccurate phylogenetic hypotheses, resulting either from homoplasy or poor data. As cladograms become less accurate, range extensions are expected to be exaggerated, causing first appearances to be shifted backwards in time (Wagner 2000).

The range extensions of Silurian genera into the Ordovician can only be trusted to the 86 extent that the implied phylogeny is accurate. Because many of the branches within the cladogram are consistently represented in 100% of the most parsimonious trees and only one limb is represented in fewer than half of the trees, the majority rule consensus appears to be accurately representing the evolutionary history of the group. Additionally, many of the conservative characters as defined by the consistency index are the same characters argued by Rong and Cocks (1994) to be important in defining families and genera. Because of this, it is likely that the derived cladogram is accurately reflecting the evolutionary history of Laurentian strophomenid brachiopods. Though the addition of taxa from other regions and intervals will continue to revise phylogenetic hypotheses, it is doubtful that these changes will dramatically affect strophomenid diversity and turnover as represented here for the Ordovician-Silurian boundary.

Evolutionary Impact of the Late Ordovician Mass Extinction

Mass extinction events are important not only because of the number of taxa lost but because of their ability to reset macroevolutionary and macroecological patterns that had been in existence for millions of years (Erwin 2001, Jablonski 2004, Jablonski 2001).

Although the Late Ordovician mass extinction was the second largest of the Phanerozoic, it had a disproportionately small effect on macroevolutionary and macroecological patterns. Using the hierarchical levels of ecological change defined by Droser (2000), the

Late Ordovician brought about only third and fourth level ecological turnover (Bottjer et al. 2001, Droser et al. 2000), and ranks last among the five mass extinction events in terms of ecological severity (McGhee et al. 2004). 87

Analysis of the calibrated phylogenetic tree (Fig. 4.7) offers an explanation for the lack of evolutionary response brought about by the Late Ordovician mass extinction event. Lineages from throughout the tree survive the mass extinction event, and only one monophylum terminates in the Ordovician. This is of particular importance, as a monophylum consists of all of the descendants of a particular lineage, encompassing all of the evolutionary innovation derived thus far from an ancestral form. Because no monophyla are lost as a result of the Late Ordovician mass extinction, the diversity of character states within strophomenid brachiopods was well preserved following the event. In an analysis of articulate brachiopods during the Permian mass extinction,

Ciampaglio (2004) found that disparity rebounded to levels seen prior to the extinction, indicating that ecological structure rather than developmental constraint was governing patterns of disparity for this group. The preservation of a wide range of strophomenid character states in the Early Silurian suggests that disparity for strophomenids also remained consistent following the Late Ordovician mass extinction, minimizing the potential for ecological restructuring or evolutionary radiation in the Early Silurian.

Because of the limited geographic scope of the database, it is possible that the range extensions of Silurian genera into the Ordovician is recording an invasion of genera existing in the Ordovician in other regions of the world into Laurentia. Therefore, range extensions would be unnecessary if the database encompassed a larger geographic area.

Of the eight genera whose ranges are extended from the Silurian into the Ordovician, however, only Aegiria is recorded in databases of genus occurrences for Baltica

(Scandanavia, Northeast Europe, portions of Russia) or Avalonia (Great Britain, portions of Nova Scotia and New England), and two others are independently recorded from 88

Baltica or other regions (Williams et al. 2000). Baltica and Avalonia are the most likely

regions from which invading genera might originate, for several reasons. First, these

regions converge on Laurentia throughout the time period considered due to the closing

of the Iapetus Ocean, making invasion more likely than from regions located at much

greater distances away from Laurentia. Second, biological invasions of Baltic genera into

Laurentia have been described previously for articulate brachiopods (Sheehan 1975,

Sheehan and Coorough 1990). However, depending on sea-level and atmospheric pCO2

conditions, it is possible that ocean currents could have driven an invasion from other

regions of the world in the Ashgill (Herrmann et al. 2004) or Rhuddanian despite the

greater distances involved. It is important that the invasion into Laurentia of taxa from

regions of the world outside of Baltica and Avalonia be quantified, as this would improve

our understanding of the Early Silurian rebound in Laurentia from both a taxic (chapter 3)

and a phylogenetic standpoint. At present, it seems more likely that many of the range

extensions implied by phylogenetic correction are endemic to the paleocontinent of

Laurentia.

The pattern presented above stands in contrast to many other mass extinction

events, in which large-scale turnover of lineages is common. For example, the end-

Permian mass extinction eliminated many clades associated with the Paleozoic

Evolutionary Fauna (Sepkoski 1981), accelerating the expansion of the Modern

Evolutionary Fauna through the Mesozoic and Cenozoic and fundamentally restructuring global marine ecosystems as a result. Similarly dramatic turnover took place on land, with dominant flora and amphibian groups replaced as a result of the extinction (Benton et al. 2004, Erwin 1990). The end-Cretaceous mass extinction is known to have 89

fundamentally restructured terrestrial communities by allowing mammalian clades to

diversify in the wake of dinosaur extinctions (Alroy 1999).

These extinctions caused the termination of many long-standing clades in a short period of time. Total extinction and “Dead Clade Walking” (Jablonski 2001) were the preeminent patterns among clades during these events, with surviving taxa generally not adapted to the selective conditions in place prior to the mass extinction event (Erwin

1989, Jablonski 1986, Stanley and Yang 1994). The pattern illustrated by strophomenid brachiopods during this time is more consistent with “continuity with setbacks”

(Jablonski 2001), in which their evolutionary trend was inhibited by the dramatic events at the end of the Ordovician but then resumed following the event. This is surprising, as nearly 70% of strophomenid genera go extinct globally in the Ashgill. However, because surviving lineages were derived from throughout the phylogenetic tree, including from deep within the evolutionary history of the clade, many of the evolutionary strategies utilized by strophomenids were still occupied following the event, allowing the group to continue as they had before the extinction event.

Though it is premature to identify this pattern as pervasive among clades spanning the Late Ordovician extinction event, there is evidence that other groups may show similar trends. Adrain and Westrop (2003) have suggested that many Silurian trilobite genera thought to arise during the post-extinction rebound actually had sister taxa in the

Ordovician, implying that ghost lineages survived the event. If this is a pervasive pattern among clades spanning the Ordovician-Silurian boundary, the lack of major evolutionary response following the Late Ordovician mass extinction would be expected.

Future Work

Though many interesting conclusions can be drawn about the impact of the Late

Ordovician mass extinction on strophomenid brachiopod evolution, much remains to be done. The database here is limited in geographic scope, yet the evolutionary factors underlying the geographic distribution of this group before and after the extinction event could add greater insight into the underlying causes of extinction, survival, and recovery within the clade. Additionally, because much of the evolutionary history of strophomenid brachiopods occurred prior to the time period considered, extending the database to include the Ordovician radiations would help to resolve how much range extension is implied for this group of brachiopods, and when many of the internal nodes of the tree evolved. This database should also be extended forward into the Devonian to assess when the creation of new monophyla begins and which parts of the tree contribute to the rebound in diversity. Finally, environmental information should be included in the analysis of the calibrated phylogenetic tree in order to determine whether range extensions and ghost lineages be derived from groups from particular environments. This would directly relate the stratigraphic gaps implied by phylogeny to sampling or preservational variations through time.

Conclusions

1. Strophomenid brachiopod diversity declines from the Upper Caradoc through the

Rhuddanian in both global and Laurentian datasets. The drop in diversity is more

dramatic and proportional extinction rates are much more severe globally than in

Laurentia. 91

2. Diversity trends based on lineages are consistent with diversity based on genus

counts, with a few exceptions. Diversity is generally higher throughout the time

period when counting lineages, though this is expected due to range extensions

and the addition of ghost lineages. Additionally, counting lineages causes

diversity to be flat rather than increase in the Early Silurian, indicating the

recovery from the extinction occurred later than implied by genus counts.

However, only a slight recovery was originally implied using genus counts, and

edge affects may be biasing the lineage diversity trend in the Telychian and

Wenlock.

3. Proportional origination was low using genera and was reduced and more variable

using lineages. Two intervals, the Ashgill and Aeronian, record no originations

using lineages, whereas all intervals record originations using genera.

4. Proportional extinction patterns change significantly when lineages are counted

rather than genera, but much of this is the addition of surviving genera in the

Ordovician through range extensions. Lineage terminations were accurately

recorded using genera.

5. Calibrating the majority rules consensus tree against the fossil record of

strophomenid brachiopods in Laurentia reveals that few monophyla are created or

eliminated in the Late Ordovician or Early Silurian. Therefore, there is little

major evolutionary change within the group immediately following the

Ordovician radiations. Strophomenid genus diversity is in decline both globally

and in Laurentia beginning in the Upper Caradoc, yet almost all Caradoc

monophyla have lineages that cross the extinction boundary. Additionally, there 92

is little radiation in the Early Silurian intervals. Lineage originations are

generally re-filling already established monophyla, with one new monophylum

established in the Early Silurian. The dramatic recovery in the Wenlock is

therefore probably the result of un-sampled portions of lineages in the

Llandovery, Ashgill, and Caradoc.

6. Because lineages from throughout the phylogenetic tree survive the event, many

of the evolutionary paths followed by strophomenids prior to the extinction

remain occupied following the extinction. Should this pattern be pervasive

amongst clades during this time period, it could explain the lack of evolutionary

and ecological impact resulting from an event as severe as the Late Ordovician

mass extinction.

Figure 4.1. Schematic of two scenarios for lineages within monophyla during a mass extinction. A. Four surviving lineages are derived from 4 separate monophyla. In this scenario, the evolutionary and ecological impact of the mass extinction event is expected to be minimal, as most of the evolutionary pathways utilized by the group survive the event. B. Four surviving lineages are derived from the same monophylum, with all other monophyla terminated at the boundary. The potential for the evolution of new, unique forms is increased in this scenario, as is the potential ecological impact of the mass extinction event.

Figure 4.2. Number of occurrences of strophomenid brachiopods in Laurentia.

Figure 4.3. Geographic distribution of strophomenid brachiopod collections in Laurentia in the Ashgill (A) and Rhuddanian (B). Circles mark locations in Laurentia from which collections containing strophomenid brachiopods were collected. Map drawn using programs online at http://paleodb.org. 95

Figure 4.4. Majority rule consensus tree calculated from 103 most parsimonious trees resulting from a heuristic search. An initial heuristic search was run with all characters unordered and of equal weight. Characters were then reweighted based on their consistency index, resulting in 103 equally parsimonious trees of length 58 steps. Numbers indicate the percentage of trees supporting each branch of the consensus tree. Billingsella is used to define the outgroup. 96

Figure 4.5. A. Global diversity for strophomenid brachiopods. B. Global proportional origination and extinction metrics for strophomenid brachiopods. Dashed line marks the Ordovician-Silurian boundary. 97

Figure 4.6. A. Diversity of strophomenid brachiopods in Laurentia. Solid curve represents diversity for all strophomenid genera in the database. Dashed curve represents only genera used in the phylogenetic analysis. See text for explanation. B. Proportional origination and extinction metrics for all strophomenid brachiopods in Laurentia, including genera removed from the phylogenetic analysis. Vertical dashed lines marks the Ordovician-Silurian boundary. 98

Figure 4.7. Cladogram of Laurentian Ordovician and Silurian strophomenid brachiopods calibrated against their fossil record in Laurentia. Solid black lines indicate the occurrence of a genus in the stratigraphic record. Vertical black line indicates the Ordovician-Silurian boundary. 99

Figure 4.8. Comparison of diversity and turnover derived from lineages and genera for strophomenid brachiopods in Laurentia. A. Diversity; B. Proportional origination; C. Proportional extinction. Dashed lines mark the Ordovician-Silurian boundary. 100

Chapter 5. Conclusions

Geographic Variability

Unstandardized diversity patterns for the paleocontinent of Laurentia are similar

to global patterns. However, Laurentian diversity is heavily biased by variations in

sampling intensity. Removing these biases results in a flat diversity trend spanning the

Late Ordovician (Ashgill) through the Early Silurian (Rhuddanian). Analysis of sampling

standardized turnover patterns shows a peak in extinction in the Ashgill is followed

immediately by a peak in origination in the Rhuddanian, suggesting a relatively rapid

turnover of taxa in Laurentia. Though the extinction rate is lower in Laurentia than it is

globally, over half of the genera present in the paleocontinent are still eliminated.

Increased origination rates in the Rhuddanian drive diversity back to pre-extinction levels

within the first 5 Myr. This pattern is significantly different from global patterns,

indicating a rebound in diversity approximately fifteen millions years later in the

Wenlock.

Because sampling-standardized diversity and taxonomic rate curves for Laurentia

differ substantially from unstandardized curves, it raises the question as to whether the

global curves are in need of similar adjustments. Incompleteness in the rock record can

distort estimates of diversity and taxonomic rates, and mass extinctions and post- extinction recoveries are often associated with dramatic sea-level fluctuations that could alter preservation potential through time (Foote 2003, Peters 2001, Smith 2001, Smith et al. 2001). These results strongly suggest that the distorting effects variation in sampling intensity may be biasing perceived global diversity during the Late Ordovician mass 101

extinction, and a global, sampling standardized analysis of the event is necessary in order

to determine the true timing of the rebound.

As with Laurentia, unstandardized diversity curves for Baltica and Avalonia

retain the basic structure of the global curve derived from Sepkoski’s (2002) database of genus first and last appearances. The regional curves show a slight diversity increase in the Caradoc, a spike in the Ashgill, a drop across the extinction boundary, and a protracted rise through the Wenlock. These diversity patterns are driven by a spike in

extinction intensities in the Ashgill coupled with declining origination rates from highs in

the Ashgill to lows in the Aeronian.

Sampling standardization procedures indicate that the drop in diversity across the

mass extinction boundary and the protracted recovery are real features for Baltica and

Avalonia. This stands in contrast to Laurentian patterns, which were heavily biased by

variations in sampling intensity. As in chapter 1, Laurentian diversity remains flat across

the extinction boundary and throughout the Silurian. The pattern holds despite nearly

doubling the number of occurrences in the database for this continent and adding data to

poorly sampled environments within various time intervals. Raw diversity patterns in

Laurentia, however, changed when the database was expanded, again pointing to the influence of sampling on diversity from this region.

Ashgillian extinction intensities are lower in Laurentia than in other continents, while Rhuddanian origination rates were relatively high, causing diversity to rebound in

Laurentia 10 Myr earlier than in either Baltica or Avalonia. Analysis of sampling standardized taxonomic rates show that declining origination rates and higher Ashgillian 102

extinction intensities cause diversity to remain low through the Aeronian in both Baltica

and Avalonia.

Using sampling standardized brachiopod data, the relative contribution of survivors, invaders, and newly originating genera to Rhuddanian standing diversity were

determined for each continent. This analysis revealed that invading genera made up a

greater proportion of diversity in Laurentia than in either Baltica or Avalonia. With

invading genera removed, diversity dropped across the extinction boundary and

rebounded to pre-extinction levels by the Aeronian, 5 Myr later than with invading

genera included. However, this is still well before either Baltica or Avalonia, neither of

which rebounded by the Wenlock. Invading genera were therefore integral in driving

Laurentian diversity to pre-extinction levels within 5 Myr of the extinction. However,

genus origination was also more rapid in Laurentia than in the other continents, and still

would have driven a more rapid rebound in this region in the absence of invading genera.

The size, equatorial position, and environmental composition of Laurentia may

have contributed to the high rates of genus origination in this paleocontinent. The

reasons for higher rates of invasion into Laurentia are unclear, however, as extinction

levels were lower in this continent than in Baltica or Avalonia. Environmental or

oceanographic conditions were probably integral in dictating the direction of dispersal

from Baltica and Avalonia towards Laurentia. It is also possible that the limited

geographic extent of the database is masking the number of invaders in Baltica and

Avalonia from other regions of the world. Macroecological processes may also be

influencing these patterns, with the types of genera lost during the extinction causing

Laurentia to be more susceptible to invasion, regardless of relative extinction intensities. 103

The interactions between extinction, invasion, and speciation in post-extinction recovery

intervals are complicated, and additional research is needed in order to fully understand how these processes operate to replenish regional diversity.

Phylogenetic Insights

Phylogenetic relationships among strophomenid brachiopods suggest that diversity trends based on lineages are consistent with diversity trends based on genus

counts, with a few exceptions. The use of lineages raises diversity throughout the time

period considered and diminishes the Early Silurian recovery. Neither of these changes

are significant. The increase in diversity is expected because range extensions and ghost

lineages can be inferred using phylogenetic analyses but existing lineages are rarely

eliminated. The Early Silurian recovery was only slight when using genus counts, and

edge effects may reduce lineage diversity to low levels in the Telychian and Wenlock

because of the lack of Upper Silurian and Devonian data.

Many genera thought to originate in the Early Silurian had their ranges extended into the Late Ordovician as a result of phylogenetic correction. The addition of surviving

lineages to the Upper Ordovician time intervals caused proportional extinction patterns to

decrease in the Upper Caradoc and Ashgill. However, lineage terminations were

accurately recorded using genera.

Though lineages go extinct in all Ordovician intervals, no monophyla are

eliminated as a result of the mass extinction event. Strophomenid genus diversity is in

decline both globally and in Laurentia beginning in the Upper Caradoc, yet almost all

Caradoc monophyla have lineages that cross the extinction boundary. Additionally, there 104

is little radiation in the Early Silurian intervals. Only one new monophylum radiates in

the Early Silurian, and that occurs in the Wenlock. This suggests that little major

evolutionary change occurred within strophomenid brachiopods following the Ordovician

radiations, including after the extinction event. Importantly, because lineages from

throughout the phylogenetic tree survive the event, many of the evolutionary paths

followed by strophomenids prior to the extinction remain occupied following the

extinction. The presence of most Ordovician monophyla in the Early Silurian strongly

implies that strophomenids would re-diversify and obtain much of their morphological variability. This would allow strophomenids to fill similar ecological niches in the wake of the extinction. Should this pattern be pervasive amongst clades during this time period, it could explain the lack of evolutionary impact resulting from an event as severe as the Late Ordovician mass extinction.

Future Work

Many aspects of the Late Ordovician mass extinction remain in need of study.

The taxonomic database must be expanded to include additional regions of the world, in particular regions within Gondwana. This large continent stretches from the South Pole to the above the equator in the Late Ordovician, and its inclusion would allow the geographic nature of the extinction and recovery to be explored for a large, continuous land mass. It would also allow geographic patterns to be dissected beyond paleocontinents, and latitudinal influences on the post-extinction recovery could be tested. Finally, the construction of a globally comprehensive database would allow 105

global, sampling standardized diversity and turnover patterns to be produced and used to

test global models of recovery.

The exploration of spatial patterns of diversity should also be expanded beyond

taxonomic richness. Quantitative analyses of morphological, functional, and ecological

diversity patterns must be incorporated. These measures are often decoupled from patterns of taxonomic richness (Foote 1997), and would allow biological aspects of the mass extinction to be explored directly. Additionally, macroecological patterns such as trends in body size and geographic range would move beyond simple taxonomic counts and allow for a more comprehensive view of the impact of the mass extinction.

Similarly, quantitative analyses of changes in community structure from continuous sections across the Ordovician-Silurian boundary would enable the ecological impact of the Late Ordovician extinction to be determined and compared to other mass extinction events. Analysis of various diversity, ecological, and macroecological aspects of the Late

Ordovician mass extinction would reveal spatial and temporal patterns not evident in studies of taxonomic richness.

The phylogenetic analyses presented here revealed many interesting features regarding the evolutionary impact of the mass extinction event. Again, however, additional information can be incorporated into these analyses, including geographic and environmental information. Such information can reveal underlying patterns of lineage origination and extinction, including whether terminating lineages occurred in specific environments, whether range extensions occurred because environments were no longer preserved in the stratigraphic record, or whether lineages preferentially evolved in particular regions of the world and expanded geographically. Such information would be 106 invaluable in understanding the processes governing extinction and recovery during mass extinction events.

107

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Appendix A

Community Lists

The following are records of community lists used in this project for each of the time periods. References for all lists are given. Reference numbers for the lists currently entered into the Paleobiology Database are located after their respective references. These reference numbers can be used by the public to access the lists at http://www.paleodb.org. References for lists obtained through a literature search but not yet entered into the Paleobiology Database are followed by the number of community lists which came from the reference.

Laurentia

Lower Caradoc:

References and collection numbers for lists currently in the Paleobiology Database:

B. A. Liberty. 1969. Palaeozoic geology of the Lake Simcoe Area, Ontario. Geological Survey of Canada Memoirs (355)1-201 (PD Collection Numbers: 26172, 26174, 26175) R. Ludvigsen. 1975. Ordovician formations and faunas, southern Mackenzie Mountains. Canadian Journal of Earth Sciences 12:663-697 (PD Collection Numbers: 25303, 25304, 25305, 25308, 25309, 25310, 25311, 25312) R. Ludvigsen. 1979. A trilobite zonation of Middle Ordovician rocks, southwestern District of Mackenzie. Geological Survey of Canada Bulletin 312:1-99 (PD Collection Numbers: 24628, 24631, 24634) M. E. Patzkowsky. 1995. Gradient analysis of Middle Ordovician brachiopod biofacies: Biostratigraphic, biogeographic, and Macroevolutionary Implications. Palaios 10(2):154-179 (PD Collection Numbers: 6276, 6345, 6346, 6386, 6387, 6388, 6389, 6432, 6438, 6668, 6671, 6674, 6680, 6682, 6683, 6684, 6685, 6686, 6687, 6688, 6689, 6690, 6691, 6692, 6693, 6694, 6695, 6696, 6697, 6702, 6703, 6704, 6705, 6707, 6708, 6709) M. E. Patzkowsky and S. M. Holland. 1999. Biofacies Replacement in a Sequence Stratigraphic Framework: Middle and Upper Ordovician of the Nashville Dome, Tennessee, USA. Palaios 14(4): 301-323 (PD Collection Numbers: 1685, 1686, 1687, 1688, 1689, 1690, 1691, 1692, 1693, 1702, 1703, 1704, 1705, 1896, 1922, 1923, 1928, 1934, 1935, 1936, 1939, 1942, 1943, 1944, 1945, 1946, 1947, 1950, 1951, 1952, 1954, 1959, 1960 J. J. Sepkoski Jr. 1998 (PD Collection Numbers: 402, 320, 327, 328, 418, 419, 420, 326, 328, 418, 416, 417, 405) H.M. Steele and G.W. Sinclair. 1971. A Middle Ordovician fauna from Braeside, Ottawa Valley, Ontario. Geological Survey of Canada Bulletin 211:1-97 (PD Collection Number: 55999) 116

C. W. Wilson. 1949. Pre-Chattanooga stratigraphy in Central Tennessee. Tennessee Division of Geology Bulletin 56:1-415 (PD Collection Number: 5331)

References for lists not part of the Paleobiology Database:

Bretsky et al. 1977. Molluscan and brachiopod-dominated biofacies in the Platterville Formation (Middle Ordovician), Upper Mississippi Valley. Bulletin - Geological Society of Denmark 26:115-132. (2 collections). Byers, C.W., Gravlin, S. 1979. Two contemporaneous equilibrium communities in the Ordovician of Wisconsin. Lethaia 12: 297-305. (1 collection). Cooper, G.A. 1956. Chazyan and related brachiopods. Smithsonian Miscellaneous Contributions 127: 1-145. (16 collections). Ludvigsen, R. 1978. Middle Ordovician trilobite biofacies, Southern Mackenzie Mountains. Western and Arctic Canadian Biostratigraphy. The Geological Association of Canada, Special Paper 18: 1-38. (27 collections)

Upper Caradoc:

References and collection numbers for lists currently in the Paleobiology Database:

L. P. Alberstadt. 1973. Articulate brachiopods of the Viola Formation (Ordovician) in the Arbuckle Mountains, Oklahoma. Oklahoma Geological Survey Bulletin 117:1-90 (PD Collection Numbers: 55504, 55505, 55506, 55507, 55508, 55510, 55511, 55512, 55513, 55514, 55515, 55516) E. R. Cressman. 1973. Lithostratigraphy and depositional environments of the Lexington Limestone (Ordovician) of central kentucky . USGS Professional Paper 768:1-61 (PD Collection Numbers: 10720, 10722, 10723, 10745, 10746, 10752, 10757, 10758) E. A. Frederickson and J. M. Pollack. 1952. Two Trilobite Genera from the Harding Formation (Ordovician) of Colorado. Journal of Paleontology 26(4):641-644 (PD Collection Number: 10391) S. M. Holland. 1988. Taphonomic effects of sea-floor exposure on an Ordovician brachiopod assemblage. Palaios 3(6):588-597 (PD Collection Numbers: 5394)J. J. Sepkoski Jr. 1998 (PD Collection Numbers: 320, 326, 327, 331, 336, 340, 341, 342, 343, 344, 345, 349, 369, 375, 376, 383, 384, 385, 386, 387, 388, 389, 390, 391, 401, 406, 407, 408, 409, 410, 411) B. A. Liberty. 1969. Palaeozoic geology of the Lake Simcoe Area, Ontario. Geological Survey of Canada Memoirs (355)1-201 (PD Collection Numbers: 6188, 26191, 26192, 26263, 26267, 26268, 26269, 26270, 26271, 26272, 26273, 26274, 26275, 26276, 26277, 26290, 26293, 26294, 26295, 26296, 26297, 26298, 26299, 26302) D. Lehman and J.K. Pope. 1990. Upper Ordovician tempestites from Swatara Gap, Pennsylvania: depositional processes affecting the sediments and paleoecology of the fossil faunas. Palaios 4:553-564 (PD Collection Number: 34895) 117

P. J. Lesperance. 1968. Ordovician and Silurian trilobite faunas of the White Head Formation, Perce Region, Quebec. Journal of Paleontology 42(3):811-826 (PD Collection Numbers: 13128, 13129) R. Ludvigsen. 1975. Ordovician formations and faunas, southern Mackenzie Mountains. Canadian Journal of Earth Sciences 12:663-697 (PD Collection Numbers: 25313, 25314, 25315, 25316, 25317, 25318, 25319, 25320, 25321, 25322, 25323, 25324, 25331, 25333, 25341, 25344, 25345) R. Ludvigsen. 1976. New cheirurinid trilobites from the lower Whittaker Formation (Ordovician), southern Mackenzie Mountains. Canadian Journal of Earth Sciences 13(7):947-959 (PD Collection Numbers: 25172, 25173, 25174, 25175, 25176, 25177) R. Ludvigsen. 1979. A trilobite zonation of Middle Ordovician rocks, southwestern District of Mackenzie. Geological Survey of Canada Bulletin 312:1-99 (PD Collection Numbers: 24635, 24636, 24637) R. Ludvigsen and B. D. E. Chatterton. 1991. The peculiar Ordovician trilobite Hypodicranotus from the Whittaker Formation, District of Mackenzie. Canadian Journal of Earth Sciences 28(4):616-622 (PD Collection Numbers: 25178, 25179) M. E. Patzkowsky. 1995. Gradient analysis of Middle Ordovician brachiopod biofacies: Biostratigraphic, biogeographic, and Macroevolutionary Implications. Palaios 10(2):154-179 (PD Collection Numbers: 6351, 6355, 6384, 6385) M. E. Patzkowsky and S. M. Holland. 1999. Biofacies Replacement in a Sequence Stratigraphic Framework: Middle and Upper Ordovician of the Nashville Dome, Tennessee, USA. Palaios 14(4): 301-323 (PD Collection Numbers: 1694, 1695, 1696, 1697, 1698, 1700, 1701, 1706, 1707, 1708, 1709, 1710, 1711, 1892, 1893, 1894, 1895, 1902, 1905, 1908, 1913, 1916, 1918, 1919, 1921, 1924, 1925, 1926, 1929, 1930, 1931, 1932, 1933, 1937, 1938, 1940, 1941, 1948, 1949, 1953, 1955, 1956, 1957, 1958, 1961, 1963, 1972, 1973, 1974, 1975, 1976, 1977, 1978, 1979) W. F. Rice. 1987. The systematics and biostratigraphy of the Brachiopoda of the Decorah Shale at St. Paul, Minnesota. Middle and Late Ordovician lithostratigraphy and biostratigraphy of the Upper Mississippi Valley: Minnesota Geological Survey Report of Investigations 35 136-166 (PD Collection Number: 23290) R. Ruedemann and G. M. Ehlers. 1924. Occurrence of the Collingwood Formation in Michigan. Michigan University Contributions from the Museum of Geology 2:13-18 (PD Collection Numbers: 26337, 26338, 26339) M. H. Secrist and W. R. Evitt. 1943. The paleontology and stratigraphy of the upper Martinsburg formation of Massanutten Mountain, Virginia. Journal of the Washington Academy of Sciences 33(12):358-368 (PD Collection Numbers: 5333, 5346, 5347, 5348, 5350, 5351, 5352, 5355, 5356, 5357, 5358, 5359, 5360, 5361, 5368, 5369, 5370, 5371, 53725395, 5396, 5397, 5398, 5399) R. E. Sloan and D.R. Kolata. 1987. The Middle and Late Ordovician strata and fossils of southeastern Minnesota. Minnesota Geological Survey, University of Minnesota Guidebook Series (15)70-96 (PD Collection Number: 10754) W. C. Sweet. 1954. Harding and Fremont Formations, Colorado. Bulletin of the American Association of Petroleum Geologists 38(2):284-305 (PD Collection Number: 10380) C. W. Wilson. 1949. Pre-Chattanooga stratigraphy in Central Tennessee. Tennessee Division of Geology Bulletin 56:1-415 (PD Collection Numbers: 5333, 5346, 5347, 118

5348, 5350, 5351, 5352, 5355, 5356, 5357, 5358, 5359, 5360, 5361, 5368, 5369, 5370, 5371, 5372)

References for lists not part of the Paleobiology Database:

L.P. Alberstadt. 1973. Articulate brachiopods of the Viola Formation (Ordovician) in the Arbuckle Mountains, Oklahoma. Bulletin - Oklahoma Geological Survey 117: 90 pp. (4 collections). G.A. Cooper 1956. Chazyan and related brachiopods. Smithsonian Miscellaneous Contributions 127: 1-145. (1 collection). S.M. Holland 1990. Distinguishing eustasy and tectonics in foreland basin sequences: the Upper Ordovician of the Cincinnati Arch and Appalacian Basin. University of Chicago, unpublished PHD dissertation. 390 pp. (22 collections). R.E. Sloan, W.F. Rice, E. Hedblom, J.M. Mazzullo. 1987. The Middle Ordovician Fossils of the Twin Cities, Minnesota. Minnesota Geological Survey, University of Minnesota, Guidebook Series no. 15: 53-69 (1 collection). R.E. Sloan, D.R. Kolata. 1987. The Middle and Late Ordovician strata and fossils of Southern Minnesota. Minnesota Geological Survey, University of Minnesota, Guidebook Series 15: 70-96 (4 collections).

Ashgill:

References and collection numbers for lists currently in the Paleobiology Database:

L. P. Alberstadt. 1973. Articulate brachiopods of the Viola Formation (Ordovician) in the ARbuckle Mountains, Oklahoma. Oklahoma Geological Survey Bulletin 117:1-90 (PD Collection Number: 10753) C. R. Barnes, A. A. Petryk, and T. E. Bolton. 1981. Anticosti Island, Québec. Field meeting, Anticosti-Gaspé, Québec, 1981: IUGS Subcommssion on Silurian Stratigraphy, Ordovician-Silurian Boundary Working Group Guidebook 1:1-24 (PD Collection Numbers: 24343, 24380, 24384, 24386, 24443, 24444, 24445, 24446, 24449, 24450, 24452) T.E. Bolton. 1970. Subsurface Ordovician fuana, Anticosti Island, Quebec. Geological Survey of Canada, Bulletin 187:1-145 (PD Collection Number: 56000) T. E. Bolton. 1988. Stromatoporoidea from the Ordovician rocks of central and eastern Canada. Contributions to Canadian paleontology, Geological Survey of Canada Bulletin 379:17-45 (PD Collection Number: 27112) A. J. Boucot and P. A. Bourque. 1981. Brachiopod biostratigraphy of the Llandoverian rocks of the Gaspé Peninsula. Field meeting, Anticosti-Gaspé, Québec, 1981: IUGS Subcommssion on Silurian Stratigraphy, Ordovician-Silurian Boundary Working Group Guidebook 2:315-321 (PD Collection Numbers: 25122, 25123, 25124, 25159) R. G. Browne. 1964. The coral horizons and stratigraphy of the upper Richmond Group in Kentucky west of the Cincinnati Arch. Journal of Paleontology 38(2):385-392 (PD Collection Number: 24034) 119

C. J. Buttler, R. J. Elias, and B. S. Norford. 1988. Upper Ordovician to lowermost Silurian solitary rugose corals from the Beaverfoot Formation, southern Rocky Mountains, British Columbia and Alberta. Contributions to Canadian paleontology, Geological Survey of Canada Bulletin 379:47-91 (PD Collection Numbers: 27246, 27247, 27248, 27250, 27251, 27252, 27253, 27254, 27255, 27256, 27257, 27258, 27259, 27260, 27280, 27281, 27282, 27283, 27284, 27285, 27286, 27287, 27288, 27289, 27290, 27291, 27299, 27301, 27302, 27303, 27304, 27305, 27306, 27307, 27308, 27309, 27310) P. Copper and D. J. Grawbarger. 1978. Paleoecological succession leading to a late Ordovician biostrome on Manitoulin Island, Ontario. Canadian Journal of Earth Sciences 15:1987-2005 (PD Collection Numbers: 22949, 22950, 22951, 22952, 22954, 22955, 22957, 22958, 22959, 22960, 22961) P. Copper. 1981. Atrypoid brachiopods and their distribution in the Ordovician-Silurian sequence of Anticosti Island. Field meeting, Anticosti-Gaspé, Québec, 1981: IUGS Subcommssion on Silurian Stratigraphy, Ordovician-Silurian Boundary Working Group, Stratigraphy and Paleontology 2:137-141 (PD Collection Numbers: 24584, 24585, 24586) E. Dalve. 1948. The fossil fauna of the Ordovician in the Cincinnati Region. University Museum, Department of Geology and Geography, University of Cincinnati, Ohio 1- 56 (PD Collection Number: 5326) H.H. Ecke. 1986. Palynologie des Zechsteins und Unteren Buntsandsteins im Germanische Becken. Dissertation Georg-Agust-Universitaet Goettingen 1-117 (PD Collection Numbers: 26307, 26308, 26309, 26311, 26312, 26313, 26314, 26315, 26316, 26317, 26331, 26333) R. J. Elias. 1983. Late Ordovician solitary rugose corals of the Stony Mountain Formation, southern Manitoba, and its equivalents. Journal of Paleontology 57(5):924-956 (PD Collection Numbers: 28156, 28163, 28166, 28167, 28187, 28188, 28190, 28481, 28482) R. J. Elias and D. Lee. 1993. Microborings and growth in Late Ordovician halysitids and other corals. Journal of Paleontology 67(6):922-934 (PD Collection Numbers: 28023, 28024, 28025, 28026, 28027, 28028, 28030, 28031, 28033, 28034, 28035, 28036, 28037) R. J. Elias, A. W. Potter, and R. Watkins. 1994. Late Ordovician Rugose Corals of the Northern Sierra Nevada, California. Journal of Paleontology 68(1):164-168 (PD Collection Numbers: 13494) T. J. Frest, C. E. Brett, and B. J. Witzke. 1999. Caradocian-Gedinnian echinoderm associations of Central and Eastern North America. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 638-783 (PD Collection Numbers: 13204, 13260, 26684) R. C. Frey. 1988. Paleoecology of Treptoceras duseri (Michelinoceratida, Proteoceratidae) from Late Ordovician of southwestern Ohio. New Mexico Bureau of Mines and Mineral Resources Memoir 44:79-101 (PD Collection Numbers: 27499, 27500) 120

L. M. Gould, A. F. Foerste, and R. C. Hussey. 1928. Contributions to the geology of Foxe Land, Baffin Island. Michigan University Contributions from the Museum of Geology 3:19-76 (PD Collection Number: 26346) S. M. Holland. 1988. Taphonomic effects of sea-floor exposure on an Ordovician brachiopod assemblage. Palaios 3(6):588-597 (PD Collection Number: 5394) H. J. Howe. 1988. Articulate brachiopods from the Richmondian of Tennessee. Journal of Paleontology 62(2):204-218 (PD Collection Numbers: 13496) J. Jin, W.G.E. Caldwell, and B.S. Norford. 1989. Rhynchonellid Brachiopods from the Upper Ordovician - Lower Silurian Beaverfoot and Nonda Formations of the Rocky Mountains, British Columbia. Geological Survey of Canada, Bulletin 396:21-42 (PD Collection Numbers: 12703) J. Jin and B. D. E. Chatterton. 1997. Latest Ordovician-Silurian articulate brachiopods and biostratigraphy of the Avalanche Lake area, southwestern District of Mackenzie, Canada. Palaeontographica Canadiana 13:1-62 (PD Collection Numbers: 26070, 26071) A. C. Lenz and M. Churkin, Jr. 1966. Upper Ordovician trilobites from Northern Yukon. Palaeontology 9(1):39-47 (PD Collection Number: 25166) P. J. Lesperance. 1968. Ordovician and Silurian trilobite faunas of the White Head Formation, Perce Region, Quebec. Journal of Paleontology 42(3):811-826 (PD Collection Numbers: 13130, 13131, 13132) P. J. Lesperance. 1974. The Hirnantian fauna of the Perce area (Quebec) and the Ordovician-Silurian boundary. American Journal of Science 274:10-30 (PD Collection Numbers: 12582, 12583) P. J. Lesperance and P.M. Sheehan. 1976. Brachiopods from the Hirnantian Stage (Ordovician-Silurian) at Perce, Quebec. Paleontology 19(4):719-731 (PD Collection Numbers: 12303) P. J. Lespérance and P. M. Sheehan. 1981. Hirnantian fauna in and around Percé, Québec. Field meeting, Anticosti-Gaspé, Québec, 1981: IUGS Subcommssion on Silurian Stratigraphy, Ordovician-Silurian Boundary Working Group Guidebook 2:231-245 (PD Collection Numbers: 24832, 24833) B. A. Liberty. 1969. Palaeozoic geology of the Lake Simcoe Area, Ontario. Geological Survey of Canada Memoirs (355)1-201 (PD Collection Numbers: 26303, 26304, 26305) A. D. McCracken and G. S. Nowlan. 1989. Conodont paleontology and biostratigraphy of Ordovician carbonates and petroliferous carbonates on Southampton, Baffin, and Akpatok islands in the eastern Canadian Arctic. Canadian Journal of Earth Sciences 26(10):1880-1903 (PD Collection Numbers: 26091, 26093, 26094, 26095, 26096, 26097) A. K. Miller, W. Youngquist, and C. Collinson. 1954. Ordovician cephalopod fauna of Baffin Island. Geological Society of America Memoir 62:1-234 (PD Collection Numbers: 24120, 24121, 24186, 24187) S. J. Nelson. 1963. Ordovician paleontology of the Northern Hudson Bay lowland. Geological Society of America Memoir 90:1-152 (PD Collection Numbers: 13654, 13655, 13656, 13657, 13658, 14120, 23011, 23013, 23014, 23016, 23018, 23023, 23024, 23026, 23031, 23035, 23037, 23039) 121

G. S. Nowlan. 1981. Late Ordovician - Early Silurian conodont biostratigraphy of the Gaspé Peninsula - a preliminary report. Field meeting, Anticosti-Gaspé, Québec, 1981: IUGS Subcommssion on Silurian Stratigraphy, Ordovician-Silurian Boundary Working Group Guidebook 2:257-291 (PD Collection Numbers: 24972, 24975) M. E. Patzkowsky and S. M. Holland. 1999. Biofacies Replacement in a Sequence Stratigraphic Framework: Middle and Upper Ordovician of the Nashville Dome, Tennessee, USA. Palaios 14(4): 301-323 (PD Collection Numbers: 1699, 1894, 1897, 1898, 1927, 1962, 1964, 1965, 1966, 1967, 1968, 1969, 1970, 1971) J. J. Sepkoski Jr. 1998 (PD Collection Numbers: 353, 354, 355, 356, 357, 358, 359, 360, 361, 367, 368, 369, 370, 371, 372, 373, 374, 375, 376, 377, 382, 392, 393, 394, 395, 396, 399, 400, 421) P. M. Sheehan and P. J. Lespérance. 1979. Late Ordovician (Ashgillian) brachiopods from the Percé region of Québec. Journal of Paleontology 53(4):950-967 (PD Collection Numbers: 28126, 28136, 28137, 28138, 28139, 28140) P. M. Sheehan and P.J. Lesperance. 1981. Brachiopods from the White Head Formation (Late Ordovician-Early Silurian) of the Perce region, Quebec, Canada. IUGS Subcommission on Silurian Stratigraphy, Ordovician-Silurian Boundary Working Group, Field meeting, Anticosti-Gaspe, Quebec, 1981 2:1-321 (PD Collection Numbers: 11554, 11555, 11556, 11557, 11568, 11689, 11690, 11702, 11703, 11706, 11707, 11723, 11724, 11725, 11735, 11736, 11737, 11822, 11845, 11927, 11928, 11930, 11934, 11936, 11937, 11938, 12058, 12059, 12060, 12061, 12062, 12063, 12070, 12145, 12146) W. B. Skidmore and P. J. Lespérance. 1981. Gaspé Peninsula, Percé area. Field meeting, Anticosti-Gaspé, Québec, 1981: IUGS Subcommssion on Silurian Stratigraphy, Ordovician-Silurian Boundary Working Group Guidebook 1:31-40 (PD Collection Numbers: 24455, 24528) C. W. Stearn. 1956. Stratigraphy and palaeontology of the Interlake Group and Stonewall Formation of Southern Manitoba. Geological Survey of Canada Memoir 281 1-162 (PD Collection Numbers: 26358, 26359, 26360, 26361, 26362, 26363, 26364) C. W. Wilson. 1949. Pre-Chattanooga stratigraphy in Central Tennessee. Tennessee Division of Geology Bulletin 56:1-415 (PD Collection Numbers: 5373, 5374, 5390, 5391, 5392, 5393)

References for lists not part of the Paleobiology Database:

T.W. Amsden. 1974. Late Ordovician and Early Silurian articulate brachiopods from Oklahoma, Southwestern Illinois, and Eastern Missouri. Bulletin - Oklahoma Geological Survey 119: 1-154. (5 collections). T.E. Bolton. 1981. Late Ordovician and Early Silurian Anthozoa of Anticosti Island, Quebec. Field Meeting, Anticosti - Gaspe, Quebec 2: 107-135. (1 collection). R.C. Frey. 1987. The occurrence of pelecypods in Early Paleozoic epiric-sea environments, Late Ordovician of the Cincinnati, Ohio area. Palaios 2: 3-23. (7 collections) 122

S.M. Holland. 1990. Distinguishing eustasy and tectonics in foreland basin sequences: the Upper Ordovician of the Cincinnati Arch and Appalacian Basin. University of Chicago, unpublished PHD dissertation. 390 pp. (14 collections).

Rhuddanian:

References and collection numbers for lists currently in the Paleobiology Database:

T. W. Amsden. 1974. Late Ordovician and Early Silurian articulate brachiopods from Oklahoma, southwestern Illinois, and eastern Missouri. Bulletin - Oklahoma Geological Survey 119:1-154 (PD Collection Numbers: 3348, 3349, 3350, 3351, 3352) W. G. Ayrton, W.B.N. Berry, A.J. Boucot, J. Lajoie, P.J. Lesperance, L. Pavlides, and W.B. Skidmore. 1969. Lower Llandovery of the Northern Appalachians and Adjacent Regions. Geological Society of America Bulletin 80:459-484 (PD Collection Numbers: 11317, 11320, 11353, 11385, 11391, 11407, 11411, 11412, 11413, 11416, 11417, 11418, 11422, 11423, 11424, 11437, 11439, 11443, 11453, 44964) T. E. Bolton. 1981. Early Silurian Anthozoa of Chaleurs Group, Port Daniel-Black Cape region, Gaspe Peninsula, Quebec. IUGS Subcommission on Silurian Stratigraphy, Ordovician - Silurian Boundary Working Group, Field Meeting, Anticosti - Gaspe, Quebec, 1981 2:299-314 (PD Collection Number: 12446) T. E. Bolton. 1981. Late Ordovician and Early Anthozoa of Anticosti Island, Quebec. IUGS Subcommission on Silurian Stratigraphy, Ordovician - Silurian Boundary Working Group, Field Meeting, Anticosti - Gaspe, Quebec, 1981 2:107-109 (PD Collection Number: 12938) T. J. Frest, C. E. Brett, and B. J. Witzke. 1999. Caradocian-Gedinnian echinoderm associations of Central and Eastern North America. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 638-783 (PD Collection Number: 26860) W. Hickerson. 1995. An early Silurian (Early-Middle Llandoverian) trilobite fauna from the Mosalem Formation of northwestern Illinois. Abstracts with Programs - Geological Society of America 27(3):58-58 (PD Collection Number: 2860) J. Jin, W.G.E. Caldwell, and B.S. Norford. 1989. Rhynchonellid Brachiopods from the Upper Ordovician - Lower Silurian Beaverfoot and Nonda Formations of the Rocky Mountains, British Columbia. Geological Survey of Canada, Bulletin 396:21-42 (PD Collection Number: 12702) P. D. Lane. 1979. Llandovery trilobites from Washington Land, North Greenland. Bulletin - Gronlands Geologiske Undersogelse 131:1-9 (PD Collection Number: 12937) B. S. Norford. 1962. The Beaverfoot - Brisco Formation in the Stanford Range, British Columbia. Journal of the Alberta Society of Petroleum Geologists 10(7):443-453 (PD Collection Numbers: 3353, 3354, 3355, 3356, 3357, 3358, 3359, 3360, 3361) J. J. Sepkoski Jr. 1998 (PD Collection Numbers: 442, 443, 444, 445, 446, 447, 448, 508, 512, 515) 123

P.M. Sheehan. 1980. The Late Ordovician and Silurian of the Eastern Great Basin, Part 3. Brachiopods of the Tony Grove Lake Member of the Laketown Dolomite. Milwaukee Public Museum Contributions in Biology and Geology 30:1-23 (PD Collection Numbers: 51492, 51493, 51494, 51495, 51496, 51497, 51498, 51499) P. M. Sheehan and P.J. Lesperance. 1981. Brachiopods from the White Head Formation (Late Ordovician-Early Silurian) of the Perce region, Quebec, Canada. IUGS Subcommission on Silurian Stratigraphy, Ordovician-Silurian Boundary Working Group, Field meeting, Anticosti-Gaspe, Quebec, 1981 2:1-321 (PD Collection Numbers: 12181, 12182, 12282)

References for lists not part of the Paleobiology Database:

M. Bjerreskov, V. Poulsen. 1973. Ordovician and Silurian faunas from Northern Peary Land, North Greenland. Bulletin - Gronlands Geologiske Undersogelse 55: 10-14. (1 collection). B. D. E Chatterton, D. G., Perry. 1983. Silicified Silurian odontopleurid trilobites from the Mackenzie Mountains. Palaeontographica Canadiana 1:1-55 (10 collections). M.E Johnson. 1977. Community succession and replacement in Early Silurian platform seas: The Llandovery series of Iowa. PhD dissertation, Department Geosciences, University of Chicago. (3 collections).

Aeronian:

References and collection numbers for lists currently in the Paleobiology Database:

Mountains, British Columbia. Geological Survey of Canada, Bulletin 396:21-42 (PD Collection Numbers: 12701, 12702) J. Jin and P. Copper. 1999. The deep-water brachiopod Dicoelosia King, 1850, from the early Silurian tropical carbonate shelf of Anticosti Island, eastern Canada. Journal of Paleontology 73(6):1042-1055 (PD Collection Numbers: 5784, 5785) J. J. Sepkoski Jr. 1998. (PD Collection Numbers: 508) P. M. Sheehan and P.J. Lesperance. 1981. Brachiopods from the White Head Formation (Late Ordovician-Early Silurian) of the Perce region, Quebec, Canada. IUGS Subcommission on Silurian Stratigraphy, Ordovician-Silurian Boundary Working Group, Field meeting, Anticosti-Gaspe, Quebec, 1981 2:1-321 (PD Collection Numbers: 12180, 12181, 12182, 12282) R. Watkins. 1994. Evolution of Silurian Pentamerid Communities in Wisconsin. Palaios 9:488-499 (PD Collection Numbers: 12986, 12987, 12988, 12989, 12990) P.M. Sheehan. 1980. The Late Ordovician and Silurian of the Eastern Great Basin, Part 3. Brachiopods of the Tony Grove Lake Member of the Laketown Dolomite. Milwaukee Public Museum Contributions in Biology and Geology 30:1-23 (PD Collection Numbers: 51519, 51523, 51524, 51533) P.M. Sheehan. 1982. Late Ordovician and Silurian of the eastern Great Basin Part 4. Late Llandovery and Wenlock brachiopods. Milwaukee Public Museum Contributions in Biology and Geology 50:1-73 (PD Collection Numbers: 51515, 51520, 51522, 51525, 51528, 51530, 51531, 51536)

References for lists not part of the Paleobiology Database:

B. D. E. Chatterton, D. G., Perry. 1983. Silicified Silurian odontopleurid trilobites from the Mackenzie Mountains. Palaeontographica Canadiana 1:1-55 (28 collections). M.E . Johnson. 1977. Community succession and replacement in Early Silurian platform seas: The Llandovery series of Iowa. PhD dissertation, Department Geosciences, University of Chicago. (11 collections). M.E. Johnson. 1980. Paleoecological structure in Early Silurian platform seas of the North American midcontinent. Palaeogeography, Palaeoclimatology, Palaeoecology 30: 191-216. (1 collection). M.E. Johnson. 1980. Recurrent carbonate environments in the Lower Silurian of Northern Michigan and their inter-regional correlation. Journal of Paleontology 54 (5): 1041-1057. (2 collections). R.S. Laub. 1979. The corals of the Brassfield Formation (mid-Llandovery, Lower Silurian) in the Cincinnati Arch Region. Bulletins of American Paleontology 75 (305): 1-457. (13 collections).

Telychian:

References and collection numbers for lists currently in the Paleobiology Database:

125

W. G. Ayrton, W.B.N. Berry, A.J. Boucot, J. Lajoie, P.J. Lesperance, L. Pavlides, and W.B. Skidmore. 1969. Lower Llandovery of the Northern Appalachians and Adjacent Regions. Geological Society of America Bulletin 80:459-484 (PD Collection Numbers: 11322, 11545, 11546, 11549) T. E. Bolton. 1981. Early Silurian Anthozoa of Chaleurs Group, Port Daniel-Black Cape region, Gaspe Peninsula, Quebec. IUGS Subcommission on Silurian Stratigraphy, Ordovician - Silurian Boundary Working Group, Field Meeting, Anticosti - Gaspe, Quebec, 1981 2:299-314 (PD Collection Numbers: 12555, 12556) T. E. Bolton. 1981. Late Ordovician and Early Anthozoa of Anticosti Island, Quebec. IUGS Subcommission on Silurian Stratigraphy, Ordovician - Silurian Boundary Working Group, Field Meeting, Anticosti - Gaspe, Quebec, 1981 2:107-109 (PD Collection Number: 12941) A. J. Boucot and P. A. Bourque. 1981. Brachiopod biostratigraphy of the Llandoverian rocks of the Gaspé Peninsula. Field meeting, Anticosti-Gaspé, Québec, 1981: IUGS Subcommssion on Silurian Stratigraphy, Ordovician-Silurian Boundary Working Group Guidebook 2:315-321 (PD Collection Number: 25155) C. E. Brett. 1999. Wenlokian fossil communities in New York State and adjacent areas: Paleontology and Paleocology. 592-637 (PD Collection Numbers: 12929, 13045)B. J. Witzke and M. E. Johnson. 1999. Silurian brachiopod and related benthic communities from carbonate platform and mound environments of Iowa and surrounding areas. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 806-840 (PD Collection Number: 24968) F. R. Brunton and P. Copper. 1994. Paleoecologic, temporal, and spatial analysis of Early Silurian reefs of the Chicotte Formation, Anticosti Island, Quebec, Canada. Facies 31:57-80 (PD Collection Numbers: 25250, 25251) T. J. Frest, C. E. Brett, and B. J. Witzke. 1999. Caradocian-Gedinnian echinoderm associations of Central and Eastern North America. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 638-783 (PD Collection Number: 13291, 26693, 26699, 26711, 26763, 26768) J. Jin, W.G.E. Caldwell, and B.S. Norford. 1989. Rhynchonellid Brachiopods from the Upper Ordovician - Lower Silurian Beaverfoot and Nonda Formations of the Rocky Mountains, British Columbia. Geological Survey of Canada, Bulletin 396:21-42 (PD Collection Number: 12702) B. S. Norford. 1962. The Silurian fauna of the Sandpile Group of northern British Columbia. Geological Survey of Canada Bulletin 78:1-51 (PD Collection Numbers: 5143, 5144, 5145, 5146, 5147, 5148, 5149, 5150, 5151, 5152, 5153, 5154, 5155, 5156, 5157, 5158) J. J. Sepkoski Jr. 1998. (PD Collection Numbers: 448, 449, 450, 451, 452, 455, 456, 457, 458, 459, 461, 462, 463, 467, 527) P. M. Sheehan and P.J. Lesperance. 1981. Brachiopods from the White Head Formation (Late Ordovician-Early Silurian) of the Perce region, Quebec, Canada. IUGS Subcommission on Silurian Stratigraphy, Ordovician-Silurian Boundary Working Group, Field meeting, Anticosti-Gaspe, Quebec, 1981 2:1-321 (PD Collection Numbers: 12181, 12182, 12282, 12295, 12296, 12297, 12298) 126

R. Watkins. 1994. Evolution of Silurian Pentamerid Communities in Wisconsin. Palaios 9:488-499 (PD Collection Numbers: 12991, 12992, 12993, 12994, 12995, 12996, 12997, 12998, 12999)

References for lists not part of the Paleobiology Database:

B.D.E. Chatterton, D.G. Perry. 1983. Silicified Silurian odontopleurid trilobites from the Mackenzie Mountains. Palaeontographica Canadiana 1:1-55 (10 collections). Eckert, B., Brett, C.E. 1989. Bathymetry and paleoecology of Silurian benthic assemblages, Late Llandoverian, New York State. Palaeogeography, Palaeoclimatology, Palaeoecology 74: 297-326 (5 collections). M.E . Johnson. 1977. Community succession and replacement in Early Silurian platform seas: The Llandovery series of Iowa. PhD dissertation, Department Geosciences, University of Chicago. (20 collections). M.E. Johnson. 1980. Paleoecological structure in Early Silurian platform seas of the North American midcontinent. Palaeogeography, Palaeoclimatology, Palaeoecology 30: 191-216. (3 collection). M.E. Johnson. 1980. Recurrent carbonate environments in the Lower Silurian of Northern Michigan and their inter-regional correlation. Journal of Paleontology 54 (5): 1041-1057. (3 collections).

Wenlock:

References and collection numbers for lists currently in the Paleobiology Database:

J. M. Adrain and L. Ramskold. 1996. The lichid trilobite Radiolichas in the Silurian of Arctic Canada and Gotland, Sweden. Geological Magazine 133:147-158 (PD Collection Numbers: 25996, 25997, 26000) J.M. Adrain and E. W. MacDonald. 1996. Phacopid trilobites from the Silurian of Arctic Canada. Journal of Paleontology 70:1091-1094 (PD Collection Numbers: 26002) J. M. Adrain and G. D. Edgecombe. 1997. Silurian encrinurine trilobites from the central Canadian Arctic. Palaeontographica Canadiana 14:1-38 (PD Collection Numbers: 25974, 25975, 25976, 25977, 25978, 25979, 25980, 25981, 25986, 25987, 25988, 25989, 25990, 25991, 25992, 25993, 25994, 25995) J. M. Adrain and G. D. Edgecombe. 1997. Silurian (Wenlock) Calymenid trilobites from the Cape Phillips Formation, central Canadian Arctic. Journal of Paleontology 71(4):657-682 (PD Collection Numbers: 678, 679, 680, 681, 682, 683, 684, 685, 686, 687) J. M. Adrain and L. Ramskold. 1997. Silurian Odontopleurinae (Trilobita) from the Cape Phillips Formation, Arctic Canada. Journal of Paleontology 71(2):237-261 (PD Collection Numbers: 689, 690, 691, 694, 695, 696, 697) A.W. Archer, D.J. Bottjer, A.S. Horrowitz, S.M. Kelly, D.L. Krisher and R.H. Shaver. 1980. Stratigraphy, structure, and zonation of large Silurian reef at Delphi, Indiana. AAPG Bulletin 64(1):115-131 (PD Collection Numbers: 22818) 127

T. W. Amsden. 1968. Articulate brachiopods of the St. Clair Limestone (Silurian), Arkansas and the Clarita Formation (Silurian), Oklahoma. Paleontological Society Memoir 1:1-117 (PD Collection Numbers: 26022, 26023, 26024, 26025) T. E. Bolton. 1981. Early Silurian Anthozoa of Chaleurs Group, Port Daniel-Black Cape region, Gaspe Peninsula, Quebec. IUGS Subcommission on Silurian Stratigraphy, Ordovician - Silurian Boundary Working Group, Field Meeting, Anticosti - Gaspe, Quebec, 1981 2:299-314 (PD Collection Numbers: 12424, 12444, 12557) T. E. Bolton. 1981. Early Silurian Anthozoa of Chaleurs Group, Port Daniel-Black Cape region, Gaspe Peninsula, Quebec. IUGS Subcommission on Silurian Stratigraphy, Ordovician - Silurian Boundary Working Group, Field Meeting, Anticosti - Gaspe, Quebec, 1981 2:299-314 (PD Collection Numbers: 12443, 12445) A. J. Boucot. 1999. Some Wenlockian-Geddinian, chiefly brachiopod dominated communities of North America. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 549-591 (PD Collection Numbers: 24787, 24809, 24853, 24868, 24885, 24889) C. E. Brett. 1999. Wenlokian fossil communities in New York State and adjacent areas: Paleontology and Paleocology. 592-637 (PD Collection Numbers: 12929, 12931, 12932, 12933, 12934, 12935, 12936, 13045, 13047, 13050, 13051, 13052, 13053, 13054, 13072) C. E. Brett. 1999. Wenlokian fossil communities in New York State and adjacent areas: Paleontology and Paleocology. 592-637 (PD Collection Numbers: 26862, 26863, 26864, 26866, 26867) B. D. E. Chatterton and D. G. Perry. 1983. Silicified Silurian odontopleurid trilobites from the Mackenzie Mountains. Palaeontographica Canadiana 1:1-55 (PD Collection Numbers: 26034, 26035, 26041, 26042, 26047, 26048, 26049, 26050, 26051) R. J. Cuffey. 1989. Lock Haven coral-bryozoan reef, Middle Silurian, Pennsylvania. in (Geldsetzer, H.H.J., James, N.P. & Tebbutt, G.E., eds.): Reefs, Canada and adjacent areas. Canadian Soc. Petrol. Geologists, Memoir 13:285-287 (PD Collection Numbers: 45291) G. D. Edgecombe and B. D. E. Chatterton. 1993. Silurian (Wenlock-Ludlow) encrinurine trilobites from the Mackenzie Mountains, Canada, and related species. Palaeontographica Abteilung A 229(4-6):75-112 (PD Collection Numbers: 26066) T. J. Frest, C. E. Brett, and B. J. Witzke. 1999. Caradocian-Gedinnian echinoderm associations of Central and Eastern North America. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 638-783 (PD Collection Numbers: 13353, 13355, 26687, 26700, 26701, 26702, 26703, 26704, 26705, 26707, 26716, 26770, 26771, 26778, 26787, 26788, 26789, 26792, 26802, 26808, 26811, 26812, 26815, 26816, 26817, 26854, 26855, 26856, 26858) M.C. Hewitt and R.J. Cuffey. 1985. Lichenaliid-Fistuliporoid crust-mounds (Silurian, New York-Ontario), typical early Paleozoic bryozoan reefs. Proceedings of the Fifth International Coral Reef Congress, Tahiti 6 (PD Collection Numbers: 22817) 128

D. J. Holloway. 1980. Middle Silurian trilobites from Arkansas and Oklahoma, U.S.A. Palaeontographica Abteilung A 170(1-3):1-85 (PD Collection Numbers: 26020, 26021) J. Jin and B. D. E. Chatterton. 1997. Latest Ordovician-Silurian articulate brachiopods and biostratigraphy of the Avalanche Lake area, southwestern District of Mackenzie, Canada. Palaeontographica Canadiana 13:1-62 (PD Collection Numbers: 26073, 26074, 26075, 26076) A. C. Lenz. 1999. Wenlockian to Pragian brachiopod communities of the northern Canadian Cordillera. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 784-792 (PD Collection Numbers: 24918, 24919, 24920, 24921, 24930) D. G. Mikulic. 1999. Silurian trilobite associations in North America. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 793-798 (PD Collection Numbers: 24935, 24936, 24937, 24938, 24939, 24940, 24941, 24942, 24943, 24944) D. G. Perry and B. D. E. Chatterton. 1977. Silurian (Wenlockian) trilobites from Baillie- Hamilton Island, Canadian Arctic Archipelago. Canadian Journal of Earth Sciences 14:285-317 (PD Collection Numbers: 26003, 26004, 26005, 26006, 26008) D. G. Perry and B. D. E. Chatterton. 1979. Wenlock trilobites and brachiopods from the Mackenzie Mountains, north-western Canada. Palaeontology 22(3):569-607 (PD Collection Numbers: 26061, 26062, 26063, 26064, 26065) R. E. Plotnick. 1999. Habitat of Llandoverian-Lochkovian eurypterids . in A. J. Boucot and J. D. Lawson, eds., Paleocommunities - a case study from the Silurian and Lower Devonian 106-136 (PD Collection Numbers: 14194, 14195) J. J. Sepkoski Jr. 1998. (PD Collection Numbers: 469, 470, 471, 472, 473, 474, 497, 530, 536, 541) D. J. Siveter and B. D. E. Chatterton. 1996. Silicified calymenid trilobites from the Mackenzie Mountains, northwest Canada. Palaeontographica Abteilung A 239(1- 3):43-60 (PD Collection Numbers: 26058, 26059, 26077) P. M. Sheehan. 1980. Paleogeography and marine communities of the Silurian carbonate shelf in Utah and Nevada. in T. D. Fouch and E. R. Magathan, eds. Paleozoic paleogeography of west-central United States. Rocky Mountain Section, SEPM 19-37 (PD Collection Numbers: 24886, 24912) P.M. Sheehan. 1982. Late Ordovician and Silurian of the eastern Great Basin Part 4. Late Llandovery and Wenlock brachiopods. Milwaukee Public Museum Contributions in Biology and Geology 50:1-73 (PD Collection Numbers: 51556, 51557, 51559, 51560) R. Watkins. 1991. Guild structure and tiering in a high-diversity Silurian community, Milwaukee County, Wisconsin. Palaios 6:465-478 (PD Collection Numbers: 13017, 13021, 13023, 13024, 13026, 13027, 13028, 13040, 13041, 13042) R. Watkins. 1993. The Silurian (Wenlockian) reef fauna of Southeastern Wisconsin. Palaios 8:325-338 (PD Collection Numbers: 13069, 13075, 13104, 13107) R. Watkins. 1994. Evolution of Silurian Pentamerid Communities in Wisconsin. Palaios 9:488-499 (PD Collection Numbers: 12992, 12993, 12994, 12995, 13001, 13002, 13012, 13013, 13014) 129

R. Watkins and P. J. Coorough. 1997. Silurian sponge spicules from the Racine Formation, Wisconsin. Journal of Paleontology 71(2):208-214 (PD Collection Numbers: 688) B. J. Witzke and M. E. Johnson. 1999. Silurian brachiopod and related benthic communities from carbonate platform and mound environments of Iowa and surrounding areas. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 806-840 (PD Collection Numbers: 24960, 25017, 25018, 25019, 25020, 25031, 25032, 25034, 25036, 25044) N. Zhang. 1989. Wenlockian (Silurian) brachiopods of the Cape Phillips Formation, Baillie Hamilton Island, Arctic Canada: part I. Palaeontographica Abteilung A 206(1- 3):49-97 (PD Collection Numbers: 26010, 26011, 26014)

130

Baltica:

Lower Caradoc:

References and collection numbers for lists currently in the Paleobiology Database:

A. I. Miller. 1993. Unpublished notes on Norwegian Ordovician fossil occurrences compiled from various resources, although unknown. (PD Collection Numbers: 2945, 2947, 2948) J. J. Sepkoski Jr. 1998. (PD Collection Numbers: 380) P. M. Sheehan. 1977. Swedish Late Ordovician marine benthic assemblages and their bearing on brachiopod biogeography. In J. Grey and A. J. Boucot, eds. Historical biogeography, plate tectonics, and the changing environment. Oregon State University Press, Corvallis. 61-73 (PD Collection Numbers: 2765, 2766, 2767, 2769) L. Stormer. 1953. The Middle Ordovician of the Oslo Region, Norway I. Introduction to stratigraphy. Norsk Geologisk Tidsskrift 31: 37-141 (PD Collection Numbers: 3255)

Upper Caradoc:

References and collection numbers for lists currently in the Paleobiology Database:

A. I. Antoshkina. 1998. Organic buildups and reefs on the Paleozoic carbonate platform margin, Pechora Urals, Russia. Sedimentary Geology 118:187-211 (PD Collection Numbers: 24016) L.R.M. Cocks and T.L. Modzalevskaya. 1997. Late Ordovician brachiopods from Taimyr, Arctic Russia, and their palaeogeographical significance. Palaeontology 40:1061-1093 (PD Collection Numbers: 37636, 37637) T. L. Harland. 1980. The Middle Ordovician of the Oslo region, Norway, 28. Lithostratigraphy of the Steinvika Limestone Formation, Landesund-Skien district. Norsk Geologiske Tidsskrift 60:269-278 (PD Collection Numbers: 3252, 3253, 3254) T. L. Harland. 1981. Middle Ordovician reefs of Norway. Lethaia 14:169-188 (PD Collection Numbers: 3251) D. A. T. Harper and A. W. Owen. 1984. The Caradoc brachiopod and trilobite fauna of the Upper Kirkland Group, Hadelad, Norway. Geologica et Paleontologica 18:21-51 (PD Collection Numbers: 2761) D. A. T. Harper, A. W. Owen, and S. H. Williams. 1984. The Middle Ordovician of the Oslo Region, Norway, 34. The Type Nakholmen Formation (Upper Caradoc), Oslo, and its faunal significance. Norsk Geologisk Tidsskrift (Oslo) 64(4):293-312 (PD Collection Numbers: 2763, 2764) L. Hints. 1998. Oandu stage (Caradoc) in central North Estonia. Proceedings of the Estonian Academy of Science 47(3):158-172 (PD Collection Numbers: 37773, 37777, 37805, 37810, 38037, 38038) V. Jaanusson. 1965. The Viruan (Middle Ordovician) of Kinnekulle and northern Billingen, Vastergotland. Bulletin of Geological Institutions of the University of Uppsala 43(1):1-73 (PD Collection Numbers: 2941) 131

A. I. Miller. 1993. Unpublished notes on Norwegian Ordovician fossil occurrences compiled from various resources, although unknown. (PD Collection Numbers: 2945, 2947, 2948) R.B. Neuman, D.L. Bruton, and J.P. Projeta, Jr. 1997. Fossils from the Ordovician 'Upper Hovin Group' (Caradoc - Ashgill), Trondheim Region, Norway. Norges geologiske undersokelse Bulletin 432:25-58 (PD Collection Numbers: 55720) A. W. Owen and D. A. T. Harper. 1982. The Middle Ordovician of the Oslo Region, Norway, 31. The upper Caradoc trilobites and brachiopods from Vestbraten, Ringerike. Norsk Geologisk Tidsskrift 62:95-120 (PD Collection Numbers: 2762) J. J. Sepkoski Jr. 1998. (PD Collection Numbers: 380) P. M. Sheehan. 1977. Swedish Late Ordovician marine benthic assemblages and their bearing on brachiopod biogeography. In J. Grey and A. J. Boucot, eds. Historical biogeography, plate tectonics, and the changing environment. Oregon State University Press, Corvallis. 61-73 (PD Collection Numbers: 2771, 2772, 2770, 2771, 2772)

Ashgill:

References and collection numbers for lists currently in the Paleobiology Database:

A. I. Antoshkina. 1996. Ordovician reefs of the Ural Mountains, Russia: A review. Facies 35:1-8 (PD Collection Numbers: 24294, 24298, 24299) B. G. Baarli, H. B. Keilen, and M. E. Johnson. 1999. Silurian communities of the Oslo Region, Norway. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press. 327-349 (PD Collection Numbers: 14292) L.R.M. Cocks and T.L. Modzalevskaya. 1997. Late Ordovician brachiopods from Taimyr, Arctic Russia, and their palaeogeographical significance. Palaeontology 40:1061-1093 (PD Collection Numbers: 37638, 37639, 37640, 37641) M. Isakar. 1991. Harjuan (Late Ordovician) new bivalves and a new gastropod from north Estonia. (PD Collection Numbers: 23294, 23296) A. V. Kanygin et al. 1977. Problems in the stratigraphy of the Ordovician and Silurian of Siberia. Trudy Instituta Geologii i Geofiziki Vypusk Akademiya Nauk SSSR (in Russian) 372:1-135 (PD Collection Numbers: 9312, 9313) A. I. Miller. 1993. Unpublished notes on Norwegian Ordovician fossil occurrences compiled from various resources, although unknown. (PD Collection Numbers: 2949) R.B. Neuman, D.L. Bruton, and J.P. Projeta, Jr. 1997. Fossils from the Ordovician 'Upper Hovin Group' (Caradoc - Ashgill), Trondheim Region, Norway. Norges geologiske undersokelse Bulletin 432:25-58 (PD Collection Numbers: 55718, 55724, 55732) J. J. Sepkoski Jr. 1998. (PD Collection Numbers: 362, 363, 364, 365, 366, 378, 379, 437, 438, 439, 441) P. M. Sheehan. 1977. Swedish Late Ordovician marine benthic assemblages and their bearing on brachiopod biogeography. In J. Grey and A. J. Boucot, eds. Historical biogeography, plate tectonics, and the changing environment. Oregon State University Press, Corvallis. 61-73 (PD Collection Numbers: 2768, 2773) 132

J. T. Temple. 1965. Upper Ordovician-Brachiopods from Poland and Britain. Acta Paleontologica Polonica 10:379-450 (PD Collection Numbers: 2760)

Rhuddanian:

References and collection numbers for lists currently in the Paleobiology Database:

B. G. Baarli. 1987. Benthic faunal associations in the Lower Silurian Solvik Formation of the Oslo-Asker Districts, Norway. Lethaia 20(1):75-90 (PD Collection Numbers: 13843, 13844, 13850) B. G. Baarli, H. B. Keilen, and M. E. Johnson. 1999. Silurian communities of the Oslo Region, Norway. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press. 327-349 (PD Collection Numbers: 14301, 14318, 14322, 26104) O. K. Bogolepova and J. Kriz. 1995. Ancestral forms of Bohemian type Bivalvia from the lower Silurian of Siberia (Tungusskaja Syneclise, Russia). GEOBIOS 28(6):691- 699 (PD Collection Numbers: 3341, 3342, 3343, 3344, 3346) A. J. Boucot and J. G. Johnson. 1964. Brachiopods of the Ede Quartzite (Lower Llandovery) of Norderon, Jamtland. Bulletin of the Geological Institution of the University of Upsala 42(9):1-11 (PD Collection Numbers: 3347) J. J. Sepkoski Jr. 1998. (PD Collection Numbers: 502, 503, 504, 505, 506, 507)

Aeronian:

References and collection numbers for lists currently in the Paleobiology Database:

B. G. Baarli. 1987. Benthic faunal associations in the Lower Silurian Solvik Formation of the Oslo-Asker Districts, Norway. Lethaia 20(1):75-90 (PD Collection Numbers: 13845, 13846, 13847, 13849) B. G. Baarli, H. B. Keilen, and M. E. Johnson. 1999. Silurian communities of the Oslo Region, Norway. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press. 327-349 (PD Collection Numbers: 14267, 14279, 14292, 14303, 14309, 14311, 14315) R. Mannil and M. Rubel. 1999. Selected brachiopod and trilobite communities of the East Baltic Silurian. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge. 253-270 (PD Collection Numbers: 13722) P. Musteikis and J. J. Paskevicius. 1999. Brachiopod communities of the Lithuanian Silurian. in A. J. Boucot and J. D. Lawson, eds., Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge. 305-326 (PD Collection Numbers: 13742)

Telychian:

References and collection numbers for lists currently in the Paleobiology Database: 133

B. G. Baarli, H. B. Keilen, and M. E. Johnson. 1999. Silurian communities of the Oslo Region, Norway. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press. 327-349 (PD Collection Numbers: 14264, 14265, 14310, 14319) M. G. Bassett and L. R. M. Cocks. 1974. A review of Silurian brachiopods from Gotland. Fossils and Strata (3)1-56 (PD Collection Numbers: 13523) V. P. Gritsenko, A. A. Istchenko, L. I. Konstantinenko and P. D. Tsegelnjuk. 1999. Animal and plant communities of Podolia. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 462-487 (PD Collection Numbers: 23343, 23346, 23363) L. Liljedahl. 1994. Silurian nuculoid and modiomorphid bivalves from Sweden. Fossils and Strata (33)1-89 (PD Collection Numbers: 13638, 13639) G. Lindström. 1884. The Silurian Gastropoda and Pteropoda of Gotland. Kongliga Svenska Vetenskaps-Akademiens Handlingasr 19:1-250 (PD Collection Numbers: 3972) R. Mannil and M. Rubel. 1999. Selected brachiopod and trilobite communities of the East Baltic Silurian. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge. 253-270 (PD Collection Numbers: 13723) A. A. Manten. 1971. Silurian Reefs of Gotland (PD Collection Numbers: 13591, 13674, P. Musteikis and J. J. Paskevicius. 1999. Brachiopod communities of the Lithuanian Silurian. in A. J. Boucot and J. D. Lawson, eds., Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge. 305-326 (PD Collection Numbers: 13742, 26287, 26288) V. I. Pushkin and T. L. Modzalevskaya. 1999. Silurian and Lower Devonian brachiopod and bryozoan communities of southwestern Byelorussia. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 496-509 (PD Collection Numbers: 23675) V. P. Sapelnikov, O. V. Bogoyavlenskaya, L. I. Mizens and V. P. Shuysky. 1999. Silurian and Early Devonian benthic communities of the Ural-Tien Shan region. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 510-544 (PD Collection Numbers: 23748, 23755, 24773) J. J. Sepkoski Jr. 1998. (PD Collection Numbers: 466)

Wenlock:

References and collection numbers for lists currently in the Paleobiology Database:

A. I. Antoshkina. 1999. Origin and evolution of lower Paleozoic reefs in the Pechora Urals, Russia. Bulletin of Canadian Petroleum Geology 47(2):85-103 (PD Collection Numbers: 24014) B. G. Baarli, H. B. Keilen, and M. E. Johnson. 1999. Silurian communities of the Oslo Region, Norway. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case 134

study from the Silurian and Lower Devonian. Cambridge University Press. 327-349 (PD Collection Numbers: 14266, 14272, 14273, 14275, 14289, 14300, 14306, 14307, 14312, 14313, 14314, 14316, 14317, 14320, 14321) M. G. Bassett and L. R. M. Cocks. 1974. A review of Silurian brachiopods from Gotland. Fossils and Strata (3)1-56 (PD Collection Numbers: 13523, 13524, 13525, 13526, 13527, 13528, 13529, 13530) V. P. Gritsenko, A. A. Istchenko, L. I. Konstantinenko and P. D. Tsegelnjuk. 1999. Animal and plant communities of Podolia. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 462-487 (PD Collection Numbers: 23346, 23349, 23350, 23353, 23363, 23364, 23365, 23451, 23453, 23455, 23458) L. Liljedahl. 1985. Ecological aspects of a silicified bivalve fauna from the Silurian of Gotland. Lethaia 18(1):53-66 (PD Collection Numbers: 13851) L. Liljedahl. 1994. Silurian nuculoid and modiomorphid bivalves from Sweden. Fossils and Strata (33)1-89 (PD Collection Numbers: 13638, 13639, 13640, 13641, 13642, 13643, 13644, 13645) R. Mannil and M. Rubel. 1999. Selected brachiopod and trilobite communities of the East Baltic Silurian. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge. 253-270 (PD Collection Numbers: 13724, 13725, 13726, 13734, 13737) A. A. Manten. 1971. Silurian Reefs of Gotland (PD Collection Numbers: 13591, 13592, 13594, 13597, 13598, 13599, 13600, 13601, 13602, 13669, 13670, 13671, 13672, 13673, 13674, 13675) P. Musteikis and J. J. Paskevicius. 1999. Brachiopod communities of the Lithuanian Silurian. in A. J. Boucot and J. D. Lawson, eds., Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge. 305-326 (PD Collection Numbers: 13742, 13744, 13745, 13746, 13748, 13752, 13756, 26280, 26281, 26282, 26284, 26285, 26286, 26289) L. V. Nekhorosheva and D. K. Patrunov. 1999. The chief Wenlockian-Lochkovian benthic communities of the Vaigach to southern Novaya Zemlya region. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 488-495 (PD Collection Numbers: 23495, 23498, 23499, 23500) R. E. Plotnick. 1999. Habitat of Llandoverian-Lochkovian eurypterids . in A. J. Boucot and J. D. Lawson, eds., Paleocommunities - a case study from the Silurian and Lower Devonian 106-136 (PD Collection Numbers: 26919) V. P. Sapelnikov, O. V. Bogoyavlenskaya, L. I. Mizens and V. P. Shuysky. 1999. Silurian and Early Devonian benthic communities of the Ural-Tien Shan region. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 510-544 (PD Collection Numbers: 23748, 23755, 23759, 23772, 24690, 24744, 24749, 24758, 24760, 24776) J. J. Sepkoski Jr. 1998. (PD Collection Numbers: 476) E. V. Vladimirskaya and N. P. Kulkov. 1999. Silurian brachiopod communities of Tuva. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the 135

Silurian and Lower Devonian. Cambridge University Press, Cambridge 545-548 (PD Collection Numbers: 24777, 24778, 24780) 136

Avalonia:

Lower Caradoc:

References and collection numbers for lists currently in the Paleobiology Database:

M. G. Lockley. 1980. The Caradoc faunal associations of the area between Bala and Dines, North Wales. Bulletin of the British Museum of Natural History (Geology) 33(3):165-235 (PD Collection Numbers: 3362, 3371) A.W. Owen and M.A. Parkes. 2000. Trilobite faunas of the Duncannon Group: Caradoc stratigraphy, environments and palaeobiogeography of hte Leinster Terrane, Ireland. Palaeontology 43(2):219-269 (PD Collection Numbers: 55711, 55712) M.A. Parkes. 1994. The brachiopods of the Duncannon Group (Middle-Upper Ordovician) of southeast Ireland. Bulletin of the Natural History Museum (Geology) 50(2):105-174 (PD Collection Numbers: 55671, 55684, 55704, 55705, 55707) A. Williams. 1974. Ordovician Brachiopoda from the Shelve District, Shropshire. Bulletin of the British Museum of Natural History (Geology), Supplement 11 1-158 (PD Collection Numbers: 45273, 45274, 45275, 45276, 45277, 45278, 45279, 46884, 46885, 46886, 46887, 46891, 46892, 46893) A. Williams. 1963. The Caradocian brachiopod faunas of the Bala District, Merionethshire. Bulletin of the British Museum of Natural History (Geology) 8(7):327-471 (PD Collection Numbers: 43634, 43635, 43636, 43637, 43638, 43639)

Upper Caradoc:

References and collection numbers for lists currently in the Paleobiology Database:

D.A.T. Harper, W.I. Mitchell, A.W. Owen and M. Romano. 1985. Upper Ordovician brachiopods and trilobites from the Clashford House Formation, near Herbertstown, Co. Meath, Ireland. Bulletin of the British Museum (Natural History), Geology Series 38(5):287-308 (PD Collection Numbers: 50346) W. T. Dean. 1959. The stratigraphy of the Caradoc series in the Cross Fell Inlier. Proceedings of the Yorkshire Geological Society 32(2):185-228 (PD Collection Numbers: 43723, 43726, 43727, 43728, 43729, 43731, 43732, 43733) J. M. Hurst. 1979. Evolution, succession & replacement in the type Caradoc (Ordovician) benthic faunas of England. Palaeogeography, Palaeoclimatology, Palaeoecology 27:189-246 (PD Collection Numbers: 3648, 3649, 3650, 3651, 3652, 3653, 3654, 3655, 3656, 3657, 3658, 3659, 3661, 3662) M. G. Lockley. 1980. The Caradoc faunal associations of the area between Bala and Dines, North Wales. Bulletin of the British Museum of Natural History (Geology) 33(3):165-235 (PD Collection Numbers: 3368, 3369, 3370, 3372, 3373) A.W. Owen and M.A. Parkes. 2000. Trilobite faunas of the Duncannon Group: Caradoc stratigraphy, environments and palaeobiogeography of hte Leinster Terrane, Ireland. Palaeontology 43(2):219-269 (PD Collection Numbers: 55714, 55715, 55716) 137

R. K. Pickerill and P. J. Brenchley. 1979. Caradoc marine benthic communities of the South Berwyn Hills, North Wales. Palaeontology 22:229-264 (PD Collection Numbers: 3301, 3302, 3303, 3304, 3305) R. K. Pickerill. 1973. Lingulasma tenuigranulata-palaeoecology of a large Ordovician linguloid that lived within a Strophomenid trilobite community. Palaeogeography, Palaeoclimatology, Palaeoecology 13(2):143-156 (PD Collection Numbers: 3363) M.A. Parkes. 1994. The brachiopods of the Duncannon Group (Middle-Upper Ordovician) of southeast Ireland. Bulletin of the Natural History Museum (Geology) 50(2):105-174 (PD Collection Numbers: 55677, 55702, 55703, 55706, 55710) J. J. Sepkoski Jr. 1998. (PD Collection Numbers: 348) A. Williams. 1963. The Caradocian brachiopod faunas of the Bala District, Merionethshire. Bulletin of the British Museum of Natural History (Geology) 8(7):327-471 (PD Collection Numbers: 43640)

Ashgill:

References and collection numbers for lists currently in the Paleobiology Database:

D. Price. 1981. Ashigill trilobite faunas from the Llyn Peninsula, North Wales, U.K. Geological Magazine 16(3):201-216 (PD Collection Numbers: 3666, 3671) P. J. Brenchley, B. Cullen, and G. Newall. 1982. The environmental distribution of associations belonging to the Hirnantia fauna - evidence from North Wales & Norway. In D. L. Bruton, ed. Aspects of the Ordovician System. Palaeontological contributions from the University of Oslo, Universitets forlaget 295:113-125 (PD Collection Numbers: 3667, 3668, 3669, 3670, 3677, 3678, 3679, 3680) D. A. Bassett, H. B. Whittington, and A. Williams. 1966. The Stratigraphy of the Bala District, Merionethshire, (with discussion). Quarterly Journal of the Geological Society of London 122(3) (PD Collection Numbers: 3675) D. Price and P. M. Magor. 1984. The ecological significance of variation in the genesis composition of Rawtheyan (Late Ordovician) trilobite faunas from North Wales, U.K. U. K. Geological Journal 19:187-200 (PD Collection Numbers: 3676, 3681) N. Hiller. 1981. The Ashgill rocks of the Glyn Ceirog district, North Wales. Geological Journal 16:181-200 (PD Collection Numbers: 8290, 8291, 8292, 8293, 8294) A. Williams and A. D. Wright. 1981. The Ordovician-Silurian boundary in the Garth area of southwest Powys, Wales. Geological Journal 16:1-39 (PD Collection Numbers: 8326, 8327, 8328, 8329, 8330, 8366, 8367, 8368, 8369, 8370, 8371, 8373, 8383, 8384, 8385, 8386, 8387, 8388, 8389, 8392, 8403, 8404, 8405) W. T. Dean. 1959. The stratigraphy of the Caradoc series in the Cross Fell Inlier. Proceedings of the Yorkshire Geological Society 32(2):185-228 (PD Collection Numbers: 42638, 43641, 43738, 43739, 43740, 43741, 43742, 43743, 43744, 43745, 43746, 43747, 43748, 43749, 43750, 43751, 43752, 43768, 43769, 43770, 43771, 43772, 43773, 43774, 43775, 43776, 43777, 43778, 43779, 43780, 43781, 43782, 43783, 43784, 43785, 43786)

138

Rhuddanian:

References and collection numbers for lists currently in the Paleobiology Database:

J. T. Temple. 1970. The Lower Llandovery brachiopods and trilobites from Ffridd Mathrafal, near Meifod, Montgomeryshire. Palaeontological Society Monographs 124(527):1-76 (PD Collection Numbers: 3207) J. T. Temple. 1975. Early Llandovery trilobites from Wales with notes on British Llandovery Calymenids. Palaeontology 18(1):137-159 (PD Collection Numbers: 3495, 3496, 3497, 3498, 3499, 3500) J. T. Temple. 1987. Early Llandovery brachiopods of Wales. Palaeontological Society Monographs 139(572):1-137 (PD Collection Numbers: 3450, 3453, 3459, 3461, 3462, 3463, 3464, 3465, 3466, 3467, 3468, 3469, 3470, 3471, 3472, 3473, 4951, 4952, 4953, 4956, 4957, 4958, 4959, 4960, 4961, 4963, 4964, 4965, 4966, 4967, 4968, 4969, 4970, 4975, 4976, 4979, 4980, 4981, 4982, 4983, 4984, 4985, 4986, 4987, 4989, 4991, 4992, 4999, 5000, 5001, 5002, 5003, 5004, 5005, 5006, 5007, 5008, 5010, 5011, 5015, 5018, 5021, 5022, 5023, 5024, 5025, 5026, 5027, 5028, 5029, 5030, 5031, 5032, 5033, 5034, 5035, 5036, 5037, 5038, 5039, 5040, 5041, 5042, 5043, 5044, 5045, 5046, 5047, 5048, 5049, 5050, 5051, 5052, 5053, 5054, 5055, 5056, 5057, 5058, 5059, 5060, 5061, 5062, 5063, 5064, 5065, 5066, 5067, 5068, 5069, 5070, 5071, 5072, 5073, 5074, 5075, 5076, 5077, 5078, 5079, 5080, 5081, 5082, 5083, 5084, 5085, 5086, 5087, 5088, 5089, 5090, 5091, 5092, 5093, 5094, 5095, 5096, 5097, 5098, 5099, 5100, 5101, 5102, 5103, 5104, 5105, 5106, 5107, 5108, 5109, 5110, 5111, 5112) A. Williams and A. D. Wright. 1981. The Ordovician-Silurian boundary in the Garth area of southwest Powys, Wales. Geological Journal 16:1-39 (PD Collection Numbers: 8406, 8407, 8408, 8409) D. A. T. Harper and S. H. Williams. 2002. A relict Ordovician brachiopod fauna from the Parakidograptus acuminatus Biozone (Lower Silurian) of the English Lake District. Lethaia 35(1):71-78 (PD Collection Numbers: 13806, 13807, 13808) R. K. Pickerill and J. M. Hurst. 1983. Sedimentary facies, depositional environments, and faunal associations of the lower Llandovery (Silurian) Beechill Cove Formation, Arisaig, Nova Scotia. Canadian Journal of Earth Sciences 20:1761-1779 (PD Collection Numbers: 3219, 3221, 3222, 3224, 3225, 3227, 3228, 3230, 3231, 3233, 3234, 3236, 3238, 3239, 3240)

Aeronian:

References and collection numbers for lists currently in the Paleobiology Database:

J. T. Temple. 1975. Early Llandovery trilobites from Wales with notes on British Llandovery Calymenids. Palaeontology 18(1):137-159 (PD Collection Numbers: 3501, 3502) J. T. Temple. 1987. Early Llandovery brachiopods of Wales. Palaeontological Society Monographs 139(572):1-137 (PD Collection Numbers: 4927, 4928, 4929, 4930, 4931, 4932, 4933, 4934, 4935, 4937, 4938, 4939, 4940, 4941, 4942, 4943, 4944, 139

4945, 4946, 4947, 4948, 4949, 4950, 4951, 4952, 4953, 4954, 4955, 4956, 4957, 4958, 4959, 4960, 4961, 4962, 4972, 4973, 4974, 4975, 4976, 4977, 4978, 4979, 4983, 4984, 4986, 4988, 4989, 4990, 4991, 4992, 4993, 4994, 4995, 4996, 4997, 4998, 4999, 5000, 5001, 5002, 5003, 5004, 5005, 5006, 5007, 5009, 5010, 5011, 5012, 5013, 5014, 5015, 5016, 5017, 5018, 5019, 5021, 5023, 5024, 5025, 5026, 5027, 5028, 5029, 5030, 5031, 5032, 5033, 5034, 5035, 5036, 5037, 5038, 5039, 5040, 5041, 5042, 5043, 5044, 5045) J. J. Sepkoski Jr. 1998. (PD Collection Numbers: 524) J. M. Hurst and R. K. Pickerill. 1986. The relationship between sedimentary facies and faunal associations in the Llandovery siliclastic Ross Brook Formation, Arisaig, Nova Scotia. Canadian Journal of Earth Science 23:705-726 (PD Collection Numbers: 3034, 3035, 3036, 3037, 3038, 3039, 3040, 3041, 3042, 3043, 3044) N.J. Curtis and P.D. Lane. 1997. The Llandovery trilobites of England and Wales. Monograph of the Palaeontographical Society 151:1-101 (PD Collection Numbers: 49600, 49601, 49602, 49603, 49604, 50277, 50278, 50282, 50285, 50286, 50287, 50288, 50289)

Telychian:

References and collection numbers for lists currently in the Paleobiology Database:

J. J. Sepkoski Jr. 1998. (PD Collection Numbers: 464, 465, 520, 521) J. M. Hurst and R. K. Pickerill. 1986. The relationship between sedimentary facies and faunal associations in the Llandovery siliclastic Ross Brook Formation, Arisaig, Nova Scotia. Canadian Journal of Earth Science 23:705-726 (PD Collection Numbers: 3045, 3046, 3047, 3048, 3050, 3051, 3052, 3053, 3054, 3055, 3056, 3057, 3058, 3059, 3060, 3061, 3062, 3063, 3064, 3065, 3066, 3067, 3068, 3069, 3134, 3136, 3137, 3147, 3149, 3151, 3159, 3160, 3162, 3163, 3164, 3165, 3167, 3168, 3170, 3171, 3172, 3173, 3174, 3176, 3178, 3185, 3186, 3187, 3188, 3189, 3190, 3191, 3192, 3193, 3200, 3201, 3202, 3203, 3204, 3205, 3206) N.J. Curtis and P.D. Lane. 1997. The Llandovery trilobites of England and Wales. Monograph of the Palaeontographical Society 151:1-101 (PD Collection Numbers: 49579, 49580, 49581, 49583, 49584, 50280, 50283, 50290) M.L.K. Curtis. 1972. The Silurian rocks of the Tortworth Inlier, Gloucestershire. Proceedings of the Geologists' Association 83(1):1-35 (PD Collection Numbers: 49635, 49638, 49639)

Wenlock:

References and collection numbers for lists currently in the Paleobiology Database:

J. J. Sepkoski Jr. 1998. (PD Collection Numbers: 477, 522) A. T. Thomas and P. D. Lane. 1999. Trilobite assemblages of the North Atlantic Region. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambrdige 444-457. (PD Collection Numbers: 23057, 23061, 23091, 23094, 23097) 140

K. T. Ratcliffe. 1999. Brachiopod assemblages from the Much Wenlock Limestone Formation of England and Wales. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 399-407 (PD Collection Numbers: 23216, 23218, 23284, 23285, 23286, 23287, 23288, 23289, 23291, 23292, 23293) A. J. Boucot. 1999. Some Wenlockian-Geddinian, chiefly brachiopod dominated communities of North America. in A. J. Boucot and J. D. Lawson, eds. Paleocommunities--a case study from the Silurian and Lower Devonian. Cambridge University Press, Cambridge 549-591 (PD Collection Numbers: 24810, 24880) M.L.K. Curtis. 1972. The Silurian rocks of the Tortworth Inlier, Gloucestershire. Proceedings of the Geologists' Association 83(1):1-35 (PD Collection Numbers: 49640, 49641, 49642) 141

Appendix B

Character States

The following are a list of characters and possible character states used to define genera in a phylogenetic analysis of strophomenid brachiopods from the paleocontinent of Laurentia (chapter 4). The characters are separated by the general region of a brachiopod they describe. Definitions of these characters can be found in Cocks and Rong (1989) and Rong and Cocks (1994). Numbers represent how a character is coded for use in Paup 4.0. The character assignments for the genera used in the analysis can be found in Appendix C.

Dorsal Valve Interior Characters: 1. Cardinal Process: absent (0); unifid (1); bifid (2); trifid (3); trifid and undercut (4). 2. Cardinal Process Lobes: absent (0); circular (1); elongate/plate-like (2); rectangular (3); triangular (4). 3. Bema: absent (0); present (1). 4. Platform: absent (0); present (1). 5. Side Septum: absent (0); present and separated structure (1); united with transmuscle ridges (2); united with lateral muscle bounding ridges (3); united with median ridges (4). 6. Subperipheral Rim: absent (0); present (1). 7. Muscle Field: absent (0); gently impressed (1); strongly impressed (2). 8. Muscle Bounding Ridge: absent (0); weak (1); strong (2). 9. Bounding Pustules: absent (0); present (1). 10. Transmuscle ridge: absent (0); weak (1); strong (2). 11. Socket Ridge: absent (0); straight (1), curved (2). 12. Median Ridge: absent (0); present (1).

Ventral Valve Interior Characters: 13. Muscle Field Shape: absent (0); flabellate (1); elongate (2); subquadrate (3); subcircular (4). 14. Muscle Field Divergence: absent (0); unified (1); divergent (2); 15. Muscle Bounding Ridges: absent (0); present (1); present and contiguous with dental plates (2). 16. Subperipheral Rim: absent (0); present (1).

Articulation: 17. Denticles on hinge line: absent (0); irregular (1); regular (2). 18. Denticles on teeth: absent (0); irregular (1); regular (2). 19. Crenulations on teeth: absent (0); irregular (1); regular (2). 20. Dental Plates: absent (0); present (1). 21. Pseudodeltidium: absent (0); small (1); large (2); 22. Chilidium: absent (0); small (1); large (2);

142

External Shell Features: 23. Valve Profile: biconvex (1); concavo-convex (2); convexo-concave (3); resupinate (4); convexo-plane (5); plano-convex (6); geniculate dorsally (7); geniculate ventrally (8). 24. Radial Ornamentation: absent (0); costae (1); costellate (2); parvicostellate (3). 25. Concentric Ornamentation: absent (0); weak – rugae occur variably throughout shell (1); strong – rugae across entire shell (2).

143

Appendix C

Character Assignments

Character assignments for strophomenid brachiopod genera included in the cladogram in figure 4.3 Characters were assigned through the analysis of monograph pictures and specimens housed at the Smithsonian Museum of Natural History. Numbers within the table represent the numbers for the character assignments as defined in Appendix B. The presence of “?” indicates the character assignment could not be determined for that genus. Billingsella is used to define the outgroup to the order Strophomenida.

Genera Characters (1-25) Aegiria 4, 2, 1, 0, 0, ?, ?, ?, 0, ?, ?, 1, ?, 2, ?, ?, 0, 0, 0, 1, 2, 2, 2, 3, 0 Amphistrophia 2, 3, 0, 0, ?, ?, 1, 0, 0, 0, 2, 1, 4, 1, 1, ?, 2, ?, ?, 0, ?, ?, 4, 2, 0 Anisopleurella 4, 4, 1, 0, 1, ?, 1, 0, 0, 2, 1, 1, 4, 2, 1, 0, 0, 0, 0, 1, 1, 1, 2, 3, 0 Apatomorpha 3, 1, 0, 0, 0, ?, 1, 1, 0, 0, 1, 1, 3, 1, 1, ?, 0, 0, 0, 1, 1, ?, 2, 3, 0 Bellimurina 2, 1, 0, 0, 0, 1, 2, 2, 0, 1, 2, 1, ?, 1, 2, ?, 0, 0, 0, 1, 2, 1, 2, 2, 1 Bilobia 3, 4, 1, 1, 0, 1, ?, 1, 0, ?, 1, 1, 4, 2, 0, 0, 0, 0, 0, 1, 1, 1, 2, 3, 0 Bimuria 1, 4, 1, ?, 1, 0, 0, 0, 0, 0, 1, 1, ?, 1, 0, 0, 2, 0, 0, 0, 1, 0, 2, 0, 0 Brachyprion 2, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 1, 1, ?, 2, 2, 0, 0, ?, ?, 2, 3, 0 Chonetoidea 4, 2, 1, 0, 0, ?, ?, ?, 0, ?, ?, 1, ?, 2, ?, ?, 0, 0, 0, 1, 1, 0, 2, 3, 0 Christiana 2, 2, 0, 0, 2, ?, 2, 1, 0, ?, 0, 0, 1, 2, 1, ?, 0, 0, 0, 1, 1, 1, 2, 0, 1 Dactylogonia 2, 1, 0, 0, 1, 1, 2, 2, 0, 2, 2, 1, 3, 1, 2, ?, 0, 0, 0, 1, 2, 1, 2, 2, 0 Eoplectodonta 4, 4, 1, 0, 1, ?, 2, 1, 1, 2, 1, 1, 4, 2, 1, 0, 2, 0, 0, 1, 1, 0, 2, 3, 1 Eostropheodonta 2, 2, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, ?, 1, 0, ?, 0, 1, 0, 1, ?, ?, 6, 3, 1 Glyptambonites 3, 1, 0, 0, 0, 0, 1, 2, 0, 1, 1, 1, ?, 2, 2, 0, 0, 0, 0, 1, 1, 2, 2, 3, 1 Glyptomena 2, 3, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 4, 1, 0, 0, 0, 0, 0, 1, 1, 0, 2, 2, 0 Holtedahlina 2, 1, 0, 0, 0, ?, 1, 0, 0, 1, 2, 1, 4, 1, 1, ?, 0, 2, 2, 1, 2, 1, 1, 2, 1 Isophragma 1, 1, 0, 1, 4, 0, 2, 0, 0, 2, 2, 1, 3, 1, 1, 1, 0, 0, 0, 1, 2, 0, 4, 2, 1 Katastrophomena 2, 1, 0, 0, 1, 0, 1, 2, 0, 0, 1, 1, 1, 2, 2, ?, 0, 1, 1, 1, 2, 2, 4, 2, 0 Leangella 3, 4, 1, 1, 0, 1, 2, 1, 0, 0, 2, 1, ?, 2, 1, 1, 0, 0, 0, 1, ?, ?, 2, 3, 0 Leptaena 2, 2, 0, 0, 0, ?, 2, 2, 1, 0, 1, 1, 4, 1, 1, ?, 0, 0, 0, 1, 1, 2, 7, 2, 2 Leptellina 3, 4, 0, 1, 0, 1, 2, 2, 0, 1, 2, 1, ?, 2, 1, 1, 0, 0, 0, 1, 1, 0, 2, 3, 0 Leptelloidea 3, 4, 0, 1, 0, 0, 1, 1, 0, 0, 2, 1, ?, 2, 1, 0, 0, 0, 0, 1, ?, ?, 2, 3, 0 Leptostrophia 2, 2, 0, 0, 0, 1, 2, 2, 0, 0, 1, 1, 1, 1, 1, 0, 2, 0, 0, ?, ?, ?, 0, 2, 0 Limbimurina 2, 2, 0, 0, ?, ?, ?, ?, 0, 2, 1, ?, 4, 1, 1, ?, 0, 0, 0, ?, ?, ?, 7, 2, 2 Macrocoelia 2, 4, 0, 0, 0, 0, 2, 2, 0, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 1, 0, 1, 6, 2, 0 Mclearnites, 2, 3, 0, 0, ?, ?, ?, 1, 0, ?, ?, ?, 1, 1, 1, ?, 1, ?, ?, ?, ?, ?, 2, 2, 0 Megamyonia 2, 1, 0, 0, 0, 0, ?, 0, 0, 1, 1, 0, 1, 1, 0, ?, 0, 0, 2, 1, 1, 2, 2, 2, 0 Mesodouvillina 2, 2, 0, 0, 0, 1, ?, 1, 0, 0, ?, 1, 1, 1, 1, ?, 1, ?, ?, ?, 1, 1, 2, 3, 0 Mesodpholidostrophia 2, 3, ?, ?, 0, ?, 1, 0, 0, ?, 2, ?, 1, 1, 0, ?, 2, ?, 0, ?, ?, ?, 2, 0, 0 Murinella 2, 1, 0, 0, 1, 1, 2, 2, 0, 2, 2, 1, 4, 1, 1, ?, 0, 0, 0, 0, 1, 1, 6, 2, 0 Oepikina 2, 1, 0, 0, 1, 1, 2, 2, 0, 2, 2, 1, 0, 0, 0, 0, 0, 0, 2, 1, 1, 0, 2, 3, 0 Palaeostrophomena 3, 1, 0, 0, 0, ?, 1, 0, 0, 0, 2, 1, 1, 1, 2, ?, 0, 0, 0, 1, 1, 2, 4, 3, 1 Pentlandia 2, 1, 0, 0, 1, 0, 2, 2, 0, 0, 2, 1, 4, 1, 2, 0, 0, 0, 0, 1, 1, 0, 1, 3, 2 Pionomena 2, 1, 0, 0, 0, ?, ?, ?, ?, ?, ?, 0, ?, ?, ?, ?, ?, ?, ?, 0, 1, 2, 1, 3, 0 Plectambonites 1, 1, 0, 1, 1, ?, 2, 2, 0, 0, 1, 0, 1, 2, 1, 1, 2, 0, 0, 1, 1, 1, 2, 3, 2 Plectodonta 4, 4, 0, 0, 1, ?, 2, 1, ?, 2, 1, 1, 4, 2, 1, 0, 2, 0, 0, 1, 2, 0, 2, 3, 1 Protomegastrophia 2, 2, ?, ?, 0, 0, 2, 1, 0, ?, 1, ?, 1, 1, 1, 0, 2, 2, 0, ?, ?, ?, 2, 3, 0 Rafinesquina 2, 4, 0, 0, 0, 0, 2, 0, 0, 2, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 2, 2, 3, 0 Rhipidomena 2, 1, 0, 0, 1, ?, ?, 0, ?, 2, 1, 1, 1, 1, 0, ?, 0, 0, 0, 1, 2, 1, 3, 3, 0 Sowerbyella 4, 4, 1, 0, 1, ?, 2, 1, 0, 0, 1, 1, 4, 2, 1, 0, 0, 0, 0, 1, 1, 0, 2, 3, 1 Sowerbyites 3, 4, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 3, 1, 1, 0, 0, 0, 0, 0, 1, 1, 2, 3, 0 Strophodonta 2, 3, ?, 1, 1, 1, ?, 2, 0, ?, ?, 1, 4, 2, 0, 1, 2, 0, 0, ?, ?, ?, 2, 2, 1 Strophomena 2, 1, 0, 0, 0, ?, 1, 0, 0, 1, 1, 1, 4, 1, 1, ?, 2, 2, 2, 1, 2, 1, 4, 2, 1 Strophonella 2, 2, ?, ?, 0, 0, 1, 0, 0, 0, ?, ?, 3, 2, 1, ?, 2, 0, 0, 0, ?, ?, 4, 3, 0 Tetraphalerella 2, 1, 0, 0, 0, ?, 1, 0, 0, 0, ?, 1, 4, 1, 1, ?, 0, 0, 0, 1, 2, 1, ?, 2, 1 Trigrammaria 2, 1, 0, 0, 1, 0, 2, 2, 0, 2, 1, 1, 4, 1, ?, ?, 0, 0, 0, ?, 1, 1, 4, 3, 0 Billingsella 1, 3, 0, 1, 1, ?, 1, 2, 0, 0, 1, 1, 2, 1, 0, 0, 0, 0, 0, 1, 2, 1, 2, 2, 2 Vita Andrew Zachary Krug

Education

(Spring 2006) Ph.D., Department of Geosciences, The Pennsylvania State University. (Spring 2002) M.S. degree, Department of Geosciences, The Pennsylvania State University. (Spring 1999) B.S. degree, Marine Science/Geology, The University of Miami. Graduated with honors, 3.3 GPA.

Research Interests

Mass extinction and recovery, spatial complexity in diversity trends, sampling and preservational biases in the fossil record, paleoecology, brachiopod phylogenetics.

Refereed Publications

Krug, A.Z. and Patzkowsky, M.E. 2004. Rapid recovery from the Late Ordovician mass extinction. Proceedings of the National Academy of Sciences 101 (51): 17605-17610

Teaching Experience

(Fall 1999 – Spring 2002; Spring 2004; Fall 2005 – Spring 2006) Teaching Assistant, Department of Geosciences, Penn State University. Courses include Physical Geology, Historical Geology, Earth and Life, The Sea Around Us, and Field Stratigraphy.

Short Courses and Workshops

(Summer 2005) Intensive Analytical Paleobiology Summer Course, National Center for Ecological Analysis and Synthesis, Santa Barbara, CA.

Awards

(Spring 2005) Earth and Mineral Sciences Centennial Research Award, College of Earth and Mineral Sciences, Penn State University. (Spring 2005) Stephen J Gould Paleontological Society Grant. (Spring 2001) Texaco Scholarship within the Department of Geosciences. (Spring 1999) Stanford Scholarship, University of Miami, for excellence in academics.

Professional Memberships

1. Geological Society of America 2. The Paleontological Society