The Great Ordovician Biodiversification Event

The Great Ordovician Biodiversification Event

Barry D. Webby
Florentin Paris
Mary L. Droser
Ian G. Percival
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    The Great Ordovician Biodiversification Event
    Book Description:

    Two of the greatest evolutionary events in the history of life on Earth occurred during Early Paleozoic time. The first was the Cambrian explosion of skeletonized marine animals about 540 million years ago. The second was the "Great Ordovician Biodiversification Event," which is the focus of this book. During the 46-million-year Ordovician Period (489--443 m.y.), a bewildering array of adaptive radiations of "Paleozoic- and Modern-type" biotas appeared in marine habitats, the first animals (arthropods) walked on land, and the first non-vascular bryophyte-like plants (based on their cryptospore record) colonized terrestrial areas with damp environments.

    This book represents a compilation by a large team of Ordovician specialists from around the world, who have enthusiastically cooperated to produce this first globally orientated, internationally sponsored IGCP (International Geological Correlation Program) project on Ordovician biotas. The major part is an assembly of genus- and species-level diversity data for the many Ordovician fossil groups. The book also presents an evaluation of how each group diversified through Ordovician time, with assessments of patterns of change and rates of origination and extinction. As such, it will become the standard work and data source for biotic studies on the Ordovician Period.

    eISBN: 978-0-231-50163-7
    Subjects: Paleontology, Ecology & Evolutionary Biology

Table of Contents

  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-viii)
    (pp. ix-xii)
  4. 1 Introduction
    (pp. 1-38)
    Barry D. Webby

    This introductory chapter presents the scope, aims, and organization of the volume; outlines previous work on Ordovician biodiversity topics; and gives an overview of the chapters in the volume, from those briefly appraising the Ordovician World to those more comprehensively surveying the diversification patterns of the main Ordovician taxonomic groups. The chapter ends with some closing remarks on the Ordovician Radiation and future directions.

    Two of the greatest evolutionary events in the history of life on earth occurred during Early Paleozoic time. The first was the Cambrian explosion of skeletonized marine animals—what Wilson (1992: 188) called the “big bang...

  5. PART I Scaling of Ordovician Time and Measures for Assessing Biodiversity Change
    • 2 Stratigraphic Framework and Time Slices
      (pp. 41-47)
      Barry D. Webby, Roger A. Cooper, Stig M. Bergström and Florentin Paris

      In compiling data for this volume, it was regarded as crucial for all participants to have access to a well-integrated Ordovician timescale based on the global and regional subdivisions, the key graptolite, conodont, and chitinozoan zonations (those with the greatest utility for wide-ranging correlation, though they are provincially distinct), and a set of close-spaced global time lines. This provides the highest-resolution correlation for the Ordovician biodiversity data collected and for global analysis of the data (for example, in determining the patterns of biologic and other significant marker events). In establishing a precise stratigraphic framework, it was vitally important to utilize...

    • 3 Calibration of the Ordovician Timescale
      (pp. 48-51)
      Peter M. Sadler and Roger A. Cooper

      Ordovician deep-water shales contain the prerequisites for a high-resolution timescale: rich successions of graptolite faunas, datable ash-fall K-bentonites, and minimally interrupted accumulation. Traditionally, the first appearances of selected graptolite taxa define provincial sets of zones, into which radiometrically dated bentonites are subsequently arrayed to achieve a numerical timescale. Provincial differences and the modest numbers of zones impose the primary limits on resolution. We have taken a different approach that avoids the constraint of zones.

      To achieve a unifying timescale for this book, we applied computer-assisted optimization to combine graptolite range charts from all provinces directly, without using zones. The optimization...

    • 4 Measures of Diversity
      (pp. 52-58)
      Roger A. Cooper

      Measuring diversity change through geologic time faces difficulties from several sources. The obvious ones include variable preservation quality and collection completeness. Incomplete collecting will tend to shorten the stratigraphic ranges of taxa and reduce diversity. It will also be unlikely to detect the rare species, affecting diversity estimates as well as origination and extinction rates. A less obvious bias stems from the nature of most biostratigraphic data sets and is discussed in this chapter.

      The basic data for the study of diversity change through geologic time are generally in the form of stratigraphic range charts. They are compiled from either...

  6. PART II Conspectus of the Ordovician World
    • 5 Major Terranes in the Ordovician
      (pp. 61-67)
      L. Robin M. Cocks and Trond H. Torsvik

      From Jurassic times onward, magnetic stripes from spreading centers are preserved on the modern ocean floors, and unraveling these are good guides to the migration of terranes through time. However, the old ocean floors present in the Ordovician have been either lost through subduction or distorted and displaced through obduction, and thus the identification and positioning of the terranes present at that time must rely on less direct methods. Chief among these are paleomagnetism, but that can indicate only paleolatitude, not paleolongitude, and faunal studies, which can indicate terrane separation and to a general extent paleolatitude, but in a more...

    • 6 Isotopic Signatures
      (pp. 68-71)
      Graham A. Shields and Ján Veizer

      Here we review current understanding of the isotope chemistry of Ordovician seawater as determined from published analyses of the isotopic compositions (strontium, neodymium, sulfur, carbon, and oxygen) of marine authigenic precipitates. Isotopic data have implications for our understanding of global dynamics and paleoenvironmental evolution; however, many published interpretations are still controversial. In general, the past 20 years have witnessed a laudable departure from using bulk samples to carefully selected calcite components, such as micro-structurally pristine brachiopods and early marine cements, as subjects of geochemical study.

      Because of the long, 2–5 m.y., residence time of strontium in the oceans, the...

    • 7 Ordovician Oceans and Climate
      (pp. 72-76)
      Christopher R. Barnes

      The Ordovician world was very different in many respects from that of today. Although many of the specific conditions are still speculative and need additional quantification, for the purpose of this chapter it is accepted that the prevailing conditions included the following (reference citations restricted by space limitations):

      1. Significantly lower oxygen levels in the coupled ocean-atmosphere system, probably about 50 percent present atmospheric level (PAL) (Berner 2001)

      2. A greenhouse climate state with high carbon dioxide levels of 8–18 × PAL (Berner 1994), with a reduction during the latest Caradoc–latest Llandovery glacial phases that peaked in the...

    • 8 Was There an Ordovician Superplume Event?
      (pp. 77-80)
      Christopher R. Barnes

      A mantle superplume event occurs when hotter mantle material rises from near the core-mantle boundary as a continuous or discontinuous plume to intersect the base of the lithosphere (Condie 2001). At that point, it spreads out below the colder lithosphere as a mushroom-shaped head. Some penetration of material and associated gases may rise and leak through the lithosphere to produce volcanic activity. Upwelling superplumes, typically arising from the core-mantle boundary (“D” Zone) during periods of anomalous heat flux from the core, are associated with an interval of cessation of magnetic reversals. In recent years, the development of mantle tomography to...

    • 9 End Ordovician Glaciation
      (pp. 81-83)
      Patrick J. Brenchley

      The link between the extensive end Ordovician glaciation in North Africa and contemporaneous glacio-eustatic and faunal changes was first recognized by Berry and Boucot (1973). Subsequently it has been shown that in the two phases of extinction, which together constitute the mass extinction, an estimated 85 percent of species and 61 percent of genera disappeared (Jablonski 1991), drastically lowering the high levels of diversity that had been attained during the “Great Ordovician Biodiversification.” During the first phase of extinction, at the start of the Hirnantian (uppermost stage of the Ashgill), a large fall in diversity occurred in most groups. However,...

    • 10 Ordovician Sea Level Changes: A Baltoscandian Perspective
      (pp. 84-94)
      Arne Thorshøj Nielsen

      A detailed knowledge of sea level changes is likely to greatly assist the understanding of biodiversity patterns, adaptive radiations, and related topics because sea level exerts a strong first-order control on shifts in the marine environment. However, relatively little attention has been devoted to the reconstruction of Ordovician sea level changes. In order to improve this situation, an analysis of Baltoscandian successions was undertaken (full documentation, including interpretations of all age relationships and correlations is in preparation, Nielsen unpubl.). The scope of this chapter is to summarize this study and to make comparisons with the North American sea level curve...

  7. PART III Taxonomic Groups
    • 11 Radiolarians
      (pp. 97-101)
      Paula J. Noble and Taniel Danelian

      Ordovician radiolarian studies are in their infancy. Only a few dozen studies have been published worldwide, most of which focus on descriptive taxonomy. Little attention has been paid to discerning evolutionary patterns, most likely because much basic descriptive work remains to be done. This poses many challenges in estimating Ordovician radiolarian biodiversity patterns. Nonetheless, we provide a review of the existing data and make some qualitative assessments of which data are most appropriate for revealing these patterns. These data are compiled and used to estimate biodiversity throughout the Ordovician by applying some commonly used diversity measures.

      Early taxonomic studies on...

    • 12 Sponges
      (pp. 102-111)
      Marcelo G. Carrera and J. Keith Rigby

      Sponges include the most primitive multicellular organisms and have a record commencing in the Late Precambrian. All major sponge groups are represented as Cambrian fossils. Ordovician sponges are only moderately well known when compared with other groups of fossils, though they are known from most continents and 275 species have been described. This relatively limited known diversity may be due in part to the scarcity of taxonomic studies and in part to the phylum’s conservative history.

      Ordovician diversification is marked by the extensive radiation of some groups, whereas others remained limited and little diversified. Even though several sponge groups are...

    • 13 Stromatoporoids
      (pp. 112-118)
      Barry D. Webby

      Representatives of the class Stromatoporoidea Nicholson and Murie 1878 (ex order Nicholson and Murie 1878; emended Stearn 1980) are simple, large, aspiculate, Paleozoic calcified sponges that show an essential unity. The calcified basal skeletons have laminar, domical, bulbous, branching or columnar external form and internally a more or less continuous, monotonous skeletal meshwork of growth-normal and growth-parallel structural elements, as well as, in places dependent on preservation, canal-like aquiferous systems. The group as a whole comprises seven orders, 26 families, 120 genera, and approximately 1,190 described species (Stearn et al. 1999). The stromatoporoids were important frame-building contributors to Ordovician-Devonian reefs....

    • 14 Conulariids
      (pp. 119-123)
      Heyo Van Iten and Zdenka Vyhlasová

      Conulariids are an extinct group of benthic marine cnidarians the extant nearest relatives of which are the stauromedusans or the coronatid scyphozoans (Van Iten 1992a, 1992b; Jerre 1994a, 1994b; Van Iten et al. 1996; Collins et al. 2000; Hughes et al. 2000). Conulariids (e.g., Conularia Sowerby 1821) having a pyramidal theca may form a monophyletic group that excludes morphologically similar taxa such as circoconulariids. Relatively small conulariids were sessile animals, attached to firm substrates at their apex, but conulariids (e.g., many specimens of Metaconularia Foerste 1928) whose thecae exceeded about 10 cm in length may have become recumbent at some...

    • 15 Corals
      (pp. 124-146)
      Barry D. Webby, Robert J. Elias, Graham A. Young, Björn E. E. Neuman and Dimitri Kaljo

      This contribution includes an overview of relationships between the various Paleozoic coral groups, a global diversity analysis of the exclusively Ordovician tetradiid corals, and regional analyses of the Laurentian corals, Baltoscandian rugose corals, and Australasian corals.

      The history of Paleozoic corals (phylum Cnidaria, subclass Zoantharia) has been much discussed, especially in relation to the origins and early evolutionary development of the two major groups, Tabulata and Rugosa. Sokolov (1955, 1962), Flower (1961), Weyer (1973), Flower and Duncan (1975), Scrutton (1979, 1984, 1988, 1997), Hill (1981), Neuman (1984), and Oliver (1996) have been at the forefront of these studies. The Ordovician...

    • 16 Bryozoans
      (pp. 147-156)
      Paul D. Taylor and Andrej Ernst

      Ordovician benthic assemblages commonly contain bryozoans, sometimes in rock-forming abundance, for example, the Cincinnatian of the U.S. Midwest. These colonial suspension feeders were often major components of Ordovician seabed communities and, like their living relatives, undoubtedly had important roles in sediment stabilization and binding, as well as providing habitats and sources of food for other benthic organisms. In the absence of unequivocal records of bryozoans in the Cambrian, the Ordovician holds considerable evolutionary significance for the phylum, not only in furnishing the oldest known bryozoans but also in recording the first of three major evolutionary radiations that can be recognized...

    • 17 Brachiopods
      (pp. 157-178)
      David A. T. Harper, L. Robin M. Cocks, Leonid E. Popov, Peter M. Sheehan, Michael G. Bassett, Paul Copper, Lars E. Holmer, Jisuo Jin and Rong Jia-yu

      The Ordovician brachiopod radiation was the most marked interval of diversification in the entire history of the phylum (Harper and Rong 2001). Apart from the initial acquisition of hard shells in the earliest Cambrian, the Ordovician was the most important period for brachiopod evolution and diversification in the whole Phanerozoic with the continued exponential increase in numbers of brachiopod genera seeded during the Cambrian (Patzkowsky 1995a). A series of stepwise radiations across most of the major orders helped set the agenda for much of life on the Paleozoic seafloor. In particular, the articulated brachiopods, now termed the subphylum Rhynchonelliformea, diversified...

    • 18 Polyplacophoran and Symmetrical Univalve Mollusks
      (pp. 179-183)
      Lesley Cherns, David M. Rohr and Jiří Frýda

      Generalized taxonomic relationships and biodiversity patterns of the Ordovician representatives of two small molluscan groups—the sclerite-bearing polyplacophorans (or chitons), and the symmetrical univalves (Tryblidiida and Bellerophontida—are discussed here.

      The polyplacophorans (or chitons) have a long fossil record (Cambrian–Recent) but are rare fossils and are mostly known from isolated intermediate sclerites. Head and tail plates, which commonly differ markedly in morphology, size, and ornament from the series of intermediate plates, are notably few in the fossil record. A similar complement of eight sclerites to Recent polyplacophorans is apparent from rare articulated specimens (e.g., Rolfe 1981) and also a...

    • 19 Gastropods
      (pp. 184-195)
      Jiří Frýda and David M. Rohr

      Gastropods are one of the most diverse groups of animals and include more than 100,000 living species. The number of fossil species must have been much higher, and estimates of gastropod diversity suggest about 13,000 extant and fossil genera (Bieler 1992). Gastropods’ rich and long-ranging fossil record (more than 500 million years [m.y.]), coupled with their occurrence in almost all marine, freshwater, and terrestrial environments, makes them a unique animal group for evolutionary, ecologic, and biogeographic investigations. Even the early evolution of the class Gastropoda seems to be well documented by rich fossil material from Ordovician strata. However, attempting a...

    • 20 Bivalve and Rostroconch Mollusks
      (pp. 196-208)
      John C. W. Cope

      Bivalves and rostroconchs are often similar in shape, and some rostroconchs were identified originally as bivalves. The apparently bivalved condition of the rostroconchs is, however, illusory, as they develop from a univalved protoconch as opposed to the bivalved protoconch of bivalves. Rostroconchs are therefore pseudobivalved; they appear to have developed from laterally compressed monoplacaphorans in the Early Cambrian and are believed in turn to have given rise to the bivalves, also in the Early Cambrian. The two groups share a laterally compressed body organization that clearly had a relatively straight gut with mouth and anus well separated at the anterior...

    • 21 Nautiloid Cephalopods
      (pp. 209-213)
      Robert C. Frey, Matilde S. Beresi, David H. Evans, Alan H. King and Ian G. Percival

      The Ordovician Period marks the time of the great radiation of nautiloids, which proliferated from a single order at the beginning of the Ordovician (489 Ma) to a maximum of at least nine orders by the early Late Ordovician (455 Ma). It is also in the Ordovician that the greatest diversity of shell form and structures occurs in these externally shelled cephalopods (Flower 1976; Holland 1987; Teichert 1988). Most of these various shell architectures were new solutions to the problem of buoyancy control in these mobile mollusks (Crick 1988). Ordovician nautiloids are represented in strata exposed from the Arctic Circle...

    • 22 Tube-Shaped Incertae Sedis
      (pp. 214-222)
      John M. Malinky, Mark A. Wilson, Lars E. Holmer and Hubert Lardeux

      The hyoliths, cornulitids, coleoloids, sphenothallids, bryoniids, and tentaculitids included in this chapter represent unrelated, exclusively Paleozoic benthic and pelagic groups of organisms, with radial to bilateral symmetry, solitary (or rarely clustered), tube-or cone-shaped shells, and calcitic (possibly in some, originally aragonitic), phosphatic, and organicwalled shell preservation. The conical-shelled, operculate hyoliths are a moderately diverse Ordovician group, and though they did not reach the peak of abundance and diversity attained previously, in the Cambrian, they did become well diversified in higher-latitude cooler waters of the Mediterranean Province. The smaller groups comprising the mainly calcitic cone-shaped solitary coleoloids, the branched (compound) sphenothallids,...

    • 23 Worms, Wormlike and Sclerite-Bearing Taxa
      (pp. 223-230)
      Olle Hints, Mats Eriksson, Anette E. S. Högström, Petr Kraft and Oliver Lehnert

      The biodiversity of four wormlike groups is outlined in this chapter. The first is a larger group, the jaw-bearing polychaetes, which are represented by scolecodonts, the organic-walled elements of their jaw apparatuses. The others are smaller, more problematic groups. The machaeridians are most commonly preserved as isolated calcitic sclerite, derived from the dorsal exoskeletal armor of an unknown, bilaterally symmetrical wormlike organism. The palaeoscolecideans and chaetognaths (arrow worms) are phosphatic, identified mainly by their microfossil remains and a few by more complete body fossils. Characteristic microfossil elements of palaeoscolecidans are platelike tubercles, and the chaetognaths exhibit spinelike grasping elements that...

    • 24 Trilobites
      (pp. 231-254)
      Jonathan M. Adrain, Gregory D. Edgecombe, Richard A. Fortey, Øyvind Hammer, John R. Laurie, Timothy McCormick, Alan W. Owen, Beatriz G. Waisfeld, Barry D. Webby, Stephen R. Westrop and Zhou Zhi-yi

      The taxonomic diversity history of Ordovician trilobites has been explored on a broad global scale by Adrain et al. (1998), who provided an estimate based on a fourfold division of Ordovician time. Adrain and Westrop (2000) subsequently published a trilobite diversity curve based on nine Ordovician and five Early Silurian sampling intervals, and the pattern of trilobite alpha (within-habitat) diversity during the Ordovician has been documented by Westrop and Adrain (1998) and Adrain et al. (2000). The nature of the Ordovician radiation of trilobites is further characterized herein, through a new global analysis at finer resolution and by documenting geographic...

    • 25 Eurypterids, Phyllocarids, and Ostracodes
      (pp. 255-265)
      Simon J. Braddy, Victor P. Tollerton Jr., Patrick R. Racheboeuf and Roger Schallreuter

      Overviews of three arthropod groups, the eurypterids, phyllocarids, and ostracodes, are included here. Ordovician eurypterids are rare. Reliable records, mostly from North America, include megalograptids and rarer carcinosomatids, stylonurids, and erieopterids. Of the 31 species described from the Ordovician of New York State, only one is a eurypterid, one is a phyllocarid, and the remainder comprise indistinguishable remains (pseudofossils). Eurypterid taxonomy and phylogeny are in a state of flux; calculations of diversity measures are thus inappropriate.

      Ordovician phyllocarid crustaceans are widely distributed in graptolitic black shale facies, but documentation of the group remains inadequate. Biodiversity studies are limited to a...

    • 26 Crinozoan, Blastozoan, Echinozoan, Asterozoan, and Homalozoan Echinoderms
      (pp. 266-280)
      James Sprinkle and Thomas E. Guensburg

      Echinoderms rapidly evolved and underwent a major diversification during the Ordovician Period. After they radiated into eight or nine classes in the Early and Mid Cambrian to produce the members of the Cambrian Evolutionary Fauna (CEF), echinoderm diversity declined during the Late Cambrian to only four to five classes (Sumrall et al. 1997). However, a much larger echinoderm radiation began in the Early Ordovician, when many new echinoderm groups appeared and older groups expanded as part of the Paleozoic Evolutionary Fauna (PEF). The number of echinoderm classes approximately doubled, and by the early Late Ordovician, all 21 echinoderm classes had...

    • 27 Graptolites: Patterns of Diversity Across Paleolatitudes
      (pp. 281-293)
      Roger A. Cooper, Jörg Maletz, Lindsey Taylor and Jan A. Zalasiewicz

      Graptolites (Graptoloidea or planktic Graptolithina) provide an ideal group for the study of biodiversity through the Ordovician because they were widely distributed around the globe and are well represented in numerous, relatively continuous black shale sequences. They originated at the base of the Ordovician and became nearly extinct at the top, thus providing a closed system and removing the problem of “edge effects” (Foote 2000a). In addition, because they are widely used for dating and correlation, the stratigraphic ranges of species are generally well known. The level of taxonomic and biostratigraphic investigation internationally ranges widely in quality. We use the...

    • 28 Chitinozoans
      (pp. 294-311)
      Florentin Paris, Aïcha Achab, Esther Asselin, Chen Xiao-hong, Yngve Grahn, Jaak Nõlvak, Olga Obut, Joakim Samuelsson, Nikolai Sennikov, Marco Vecoli, Jacques Verniers, Wang Xiao-feng and Theresa Winchester-Seeto

      Chitinozoans are an extinct group of organic-walled microfossils. The earliest known species appeared in the Early Ordovician (Tremadocian), and the group became extinct at the end of the Devonian. Chitinozoans have been reported from most types of Ordovician marine sediments. Major constraints affecting their occurrence and preservation are high-energy hydrodynamic regimes, weathering, and medium- to high-grade metamorphism. Because of their minimal dependence on lithology, chitinozoans are usually continuously present in most Ordovician marine successions, and the first-appearance datum (FAD) and last-appearance datum (LAD) of species can be precisely controlled.

      Paris and Nõlvak (1999) postulated that chitinozoans are the eggs of...

    • 29 Conodonts: Lower to Middle Ordovician Record
      (pp. 312-326)
      Guillermo L. Albanesi and Stig M. Bergström

      Conodonts, eel-shaped animals that were common inhabitants of Paleozoic and Triassic seas, are now interpreted to be chordates (Aldridge et al. 1993). Recent phylogenetic analyses based on morphological, biochemical, and physiological characters suggest conodonts to be the most plesiomorphic member of the group Gnathostomata (Donoghue et al. 2000). Their apatitic feeding microelements are usually well preserved, and conodonts have a fossil record whose completeness competes with that of any other animal group (Foote and Sepkoski 1999). The excellent fossil record of conodonts and their rapid evolution make them key tools for establishing high-resolution biostratigraphy from the Middle Cambrian through the...

    • 30 Vertebrates (Agnathans and Gnathostomes)
      (pp. 327-335)
      Susan Turner, Alain Blieck and Godfrey S. Nowlan

      Although Cambrian-Ordovician vertebrate occurrences have been repeatedly claimed, confirmed taxa bearing mineralized tissues with such a histomorphology are still relatively rare. Cambrian records are few and controversial. Shu et al. (1999a), for example, identified possible Lower Cambrian vertebrates from South China, and Young et al. (1996) have described Late Cambrian remains from Australia that might represent the oldest definite vertebrate with hard tissues. The term “vertebrate,” as used here, designates one of a group of animals, the Vertebrata, characterized by the occurrence of a longitudinal, dorsal skeletal rachis transformed into vertebrae, sometimes cartilaginous, bearing certain phosphatic hard tissues, and having...

    • 31 Receptaculitids and Algae
      (pp. 336-347)
      Matthew H. Nitecki, Barry D. Webby, Nils Spjeldnaes and Zhen Yong-Yi

      The meaning of the term algae is still debatable among neoalgologists; they disagree on a number of higher-level algal taxa; they continuously revise their classification based on the ultrastructural, reproductive, and biochemical analyses; and they place many algal phyla (divisions) among protists, among plant metaphytes, or, with bacteria, among Monera. While the concept of the word algae is thus changing (or even losing its meaning), paleoalgologists accept blue-greens, greens, reds, and occasionally browns as the major groups of Paleozoic calcareous algae and readily admit that the systematics of most Paleozoic algal groups is in a very uncertain state (Riding 1977;...

    • 32 Acritarchs
      (pp. 348-360)
      Thomas Servais, Jun Li, Ludovic Stricanne, Marco Vecoli and Reed Wicander

      The organisms that produced the acritarchs are thought to have been the major component of the organic-walled microphytoplankton in Proterozoic and Paleozoic oceans. As the primary producers, these organisms represent the base of the food chain in the Proterozoic and Paleozoic marine ecosystem. In order to understand the functioning and evolution of the Paleozoic marine ecosystem, it is essential to understand the marine phytoplankton. An interesting question discussed by such authors as Strother et al. (1996b) is whether Phanerozoic phytoplankton diversity and invertebrate diversity are linked or decoupled from each other.

      Is biodiversification of the major Ordovician fossil groups related...

    • 33 Miospores and the Emergence of Land Plants
      (pp. 361-366)
      Philippe Steemans and Charles H. Wellman

      During the past 30 years it has become increasingly clear that for much of the Ordovician a terrestrial vegetation existed. Evidence is in the form of dispersed microfossils (miospores and phytodebris) that are interpreted as deriving from land plants (embryophytes). As yet no megafossils have been recovered, probably owing to the low preservation potential of the plants. In the first part of this chapter the dispersed miospore fossil record is summarized, along with evidence it provides for the biodiversity and paleophytogeography of the parent plants. In the second part the affinities and nature of the vegetation are assessed based on...

  8. PART IV Aspects of the Ordovician Radiation
    • 34 The Ichnologic Record of the Ordovician Radiation
      (pp. 369-379)
      M. Gabriela Mángano and Mary L. Droser

      The picture of the Ordovician Radiation comes primarily from the record of body fossils, in particular, patterns of diversity increase (Sepkoski 1981a, 1995; Sheehan 2001a; and elsewhere in this volume). Biodiversity in earth history has been accommodated via the colonization of new or previously underused ecospace (Bambach 1983; Orr 2001). The ichnologic record contributes significantly to our understanding of paleoecologic breakthroughs associated with the Ordovician Radiation, including an increase in complexity of shallow marine endobenthic communities, invasion of continental environments, and establishment of a modern aspect deep marine ecosystem (e.g., Droser et al. 1994; Buatois et al. 1998; Orr 2001;...

    • 35 The Ordovician Radiation: Toward a New Global Synthesis
      (pp. 380-388)
      Arnold I. Miller

      By any measure, the Ordovician Period was a remarkable interval in the evolution of marine biodiversity. As described in a series of papers by the late J. John Sepkoski Jr. (e.g., Sepkoski 1979, 1981a, 1984, 1995), the period was marked by the most broadly based global radiation, at taxonomic levels ranging from species to order, in the history of life. In some ways, the preceding Cambrian explosion may have been more profound, given that it marked the first major proliferation of basic body plans expressed at the phylum and class levels (e.g., Erwin et al. 1987). However, it was during...

  9. List of Figures and Tables
    (pp. 389-394)
    (pp. 395-466)
  11. List of Contributors
    (pp. 467-472)
  12. INDEX
    (pp. 473-484)