Cover of Species and Speciation in the Fossil Record
Species and Speciation in the Fossil Record
edited by Warren D. Allmon and Margaret M. Yacobucci
University of Chicago Press, 2016
Cloth: 978-0-226-37744-5 | Electronic: 978-0-226-37758-2
DOI: 10.7208/chicago/9780226377582.001.0001

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ABOUT THIS BOOKAUTHOR BIOGRAPHYREVIEWSTABLE OF CONTENTS

ABOUT THIS BOOK

Although the species is one of the fundamental units of biological classification, there is remarkably little consensus among biologists about what defines a species, even within distinct sub-disciplines. The literature of paleobiology, in particular, is littered with qualifiers and cautions about applying the term to the fossil record or equating such species with those recognized among living organisms. In Species and Speciation in the Fossil Record, experts in the field examine how they conceive of species of fossil animals and consider the implications these different approaches have for thinking about species in the context of macroevolution.

After outlining views of the Modern Synthesis of evolutionary disciplines and detailing the development within paleobiology of quantitative methods for documenting and analyzing variation within fossil assemblages, contributors explore the challenges of recognizing and defining species from fossil specimens—and offer potential solutions. Addressing both the tempo and mode of speciation over time, they show how with careful interpretation and a clear species concept, fossil species may be sufficiently robust for meaningful paleobiological analyses. Indeed, they demonstrate that the species concept, if more refined, could unearth a wealth of information about the interplay between species origins and extinctions, between local and global climate change, and greatly deepen our understanding of the evolution of life.

AUTHOR BIOGRAPHY

Warren D. Allmon is director of the Paleontological Research Institution in Ithaca, New York, and professor in the Department of Earth and Atmospheric Sciences at Cornell University. Margaret M. Yacobucci is professor of geology at Bowling Green State University.

REVIEWS

“Core to evolution are the species concept and the origin of species, with ramifications in biology, paleobiology, and philosophy. These thoughtful essays place the questions in a rich historical context and integrate modern statistical and computational approaches with molecular data to reach a consensus position, with important recommendations in several chapters of key research questions and model assumptions.”
— Michael J. Benton, University of Bristol, author of “When Life Nearly Died: The Greatest Mass Extinction of All Time”

“Darwin’s famous title, On the Origin of Species, implies that the very issue of biological evolution centers on species. But what are species? Darwin began his evolutionary explorations agreeing with early naturalists, like Giammbattista Brocchi, who thought species, just like their component individual organisms, are discrete entities, with naturally caused births, histories, and eventual deaths, strung together into ancestor-descendant lineages. But, after discovering natural selection in the late 1830s, Darwin switched his concept of species, adopting instead the other great evolutionary pioneer Jean-Baptiste Lamarck’s vision of species as arbitrarily defined segments of a smoothly evolving evolutionary continuum. These dual concepts of species as seen in the fossil record have survived in variant forms down to the present day. Allmon and Yacobucci’s book traces all the nuances of discord that have continued to plague the meaning of the term species, bringing the best minds together to produce a succinct overview of the nature of species and the role species play in the evolutionary process, especially as seen in the fossil record. Thanks to this book, much of the disparities historically seen between paleontological and neontological species melt away—and the strong role that speciation plays in the history of life comes to the fore in a unified and coherent manner.”
— Niles Eldredge, curator emeritus of paleontology, American Museum of Natural History

“Species are THE fundamental unit for evolutionary studies, but many aspects of their recognition and definition get tossed around without really being examined. Allmon and Yacobucci are trying to change that, having encouraged their chapter authors to be explicit about their own approach to defining and recognizing species, and to discuss how their approach ‘trickles down’ into their research. A significant project that will be valuable to working paleontologists and biologists, Species and Speciation in the Fossil Record will serve its purpose nicely.”
— Dana Geary, University of Wisconsin–Madison

TABLE OF CONTENTS

Introduction: Taking Fossil Species Seriously / W. D. Allmon and M. M. Yacobucci


DOI: 10.7208/chicago/9780226377582.003.0001
[Modern Synthesis;George Gaylord Simpson;species question]
In the late 1940s, the discipline of paleontology took major steps towards becoming more fully integrated into the community of evolutionary biology. Key to this process was the development of quantitative ways of documenting and analyzing morphological variation in fossils, which allowed paleontologists to integrate paleontology into the Modern Evolutionary Synthesis. Paleontologists, however, wrestled with accommodating fossil data to the populational understanding of species promoted by geneticists in the Synthesis. In so doing, these paleontologists posed a solution to the problem of incorporating “population thinking” into paleontology; introduced greater analytical and quantitative rigor into paleontology; and introduced new theoretical possibilities for interpreting the evolutionary significance of the fossil record, which greatly contributed to the further growth of evolutionary paleobiology. (pages 9 - 27)
This chapter is available at:
    University of Chicago Press
    https://academic.oup.com/chica...


DOI: 10.7208/chicago/9780226377582.003.0002
[evolutionary species concept;phenotypes;George Gaylord Simpson;macroevolution]
There is a growing consensus around the lineage species concept, and paleontologists can provide the temporal perspective that this view of species requires. The “species problem” involves more than just debating operational species concepts. It also involves making the case that species correspond to real evolutionary entities and visualizing what those entities could be – the ontology of species. These issues are closely connected to practical approaches for identifying taxa in fossil samples. Despite all the debate, there is a general concept of species applicable to all kinds of organisms. Paleontologists have a central role in this discussion, because when the crucial element of time is added to the discussion, the nature of species-as-lineages becomes much clearer. (pages 28 - 58)
This chapter is available at:
    University of Chicago Press
    https://academic.oup.com/chica...


DOI: 10.7208/chicago/9780226377582.003.0003
[cryptic species;morphospecies;species concepts]
The theoretical literature on species and speciation is often viewed as chaotic and/or useless, and the situation in paleontology has frequently seemed, if anything, even murkier. Despite this, there is in fact something of a working consensus on several important aspects of what species are and how they arise, both in living forms and in the fossil record. This often unrecognized consensus provides an opportunity for at least some standardization of methods for recognizing and discussing species, especially as they are perceived in fossils. This chapter argues for adoption by paleontologists of a single, “unified” species concept, of the sort that is becoming widely accepted among neontologists. I recommend that paleontologists formally embrace the general lineage concept (GLC) of species as the best description of both what species are and how they can be understood in the fossil record. Second, I provide an overview of the current operational status of species in studies of fossil animals. (pages 59 - 120)
This chapter is available at:
    University of Chicago Press
    https://academic.oup.com/chica...


DOI: 10.7208/chicago/9780226377582.003.0004
[models of speciation;speciation cycle;incipient species]
Little standardization of method exists for studies of speciation using fossils, and this makes relative frequency of patterns and processes very difficult to judge. Although one or two specific causal mechanisms are often invoked as the key factor influencing speciation, rarely is it made explicit how this influence has occurred. These problems are important in paleontology, where actual events and processes cannot be directly observed. It may be helpful to divide speciation into its components so that we can try to identify exactly where and when different changes occur. Four elements appear to be common to all: (1) isolated populations must form, becoming separate from parent populations; (2) these populations must persist in isolation, neither going extinct nor merging with the parental population by interbreeding; (3) these populations must diverge (become differentiated) genetically from the parent such that they will maintain their separate evolutionary status and not merge with the parent; and (4) these new species must stabilize or expand their population to survive long enough to play a separate evolutionary role. This “stages of speciation” (SOS) framework permits greater resolution of the impact of the causal factors involved, and can serve as a standard method for studying speciation. (pages 121 - 167)
This chapter is available at:
    University of Chicago Press
    https://academic.oup.com/chica...


DOI: 10.7208/chicago/9780226377582.003.0005
[phenotypic variation;molecular clock;origin of species;morphology;distance]
Our understanding of processes that contribute to the origin of species is informed by the study of phenotypic variation (morphology) through geologic time and broader phenotypes of living organisms in modern ecological space. Molecular data (DNA) and ecological theory have greatly enhanced our understanding, but it has proven difficult to combine morphologic data from the fossil record with molecular data into integrated studies of evolutionary rates. I propose a method in which morphologic and molecular data are collected from the same suite of closely related living specimens. Morphologic and molecular data are standardized within the study and scaled in a way such that geologic time (chronostratigraphy) and time derived from a molecular clock can also be scaled, creating a data set in a single, comparable, mathematical space where changes within and among species can be plotted by morphologic distance, molecular distance and calibrated geologic time. This method allows for hypothesis testing of relationships within and among species in a morpho-molecular-temporal space, and exploration of patterns of change and fixation in the genes responsible for variation in morphologic systems. (pages 168 - 197)
This chapter is available at:
    University of Chicago Press
    https://academic.oup.com/chica...


DOI: 10.7208/chicago/9780226377582.003.0006
[age-dependent extinction;speciation hazard function;macroperforate foraminifera;bryozoan;bathtub model;Weibull model]
While models of extinction are a subject of intense study, models of speciation are somewhat under-explored among paleobiologists working with paleontological datasets. On the other hand, comparative biologists working with extant lineages have largely focused on the net process of extinction and speciation, namely diversification. Such models of diversification have included those that have constant, diversity-dependent or time-varying rates over the history of a given clade. In this chapter, we specifically explore models of age-dependent speciation, where the probability of speciation for a given ancestral species might change as it ages. We discuss the properties of speciation models with continuous age-dependent hazard functions and devise an approach to fit these models to empirical data while accounting for extinctions of the ancestral species. While there are few empirical datasets that are suitable for the exploration of age-dependent speciation models, we found evidence for declining, increasing and constant speciation rates with age in different taxa. We discuss the biological implications and consequences of each of these models. (pages 198 - 216)
This chapter is available at:
    University of Chicago Press
    https://academic.oup.com/chica...


DOI: 10.7208/chicago/9780226377582.003.0007
[species problem;cryptic species;Orbicella annularis;morphospecies;Montastraea cavernosa;Favia fragum]
The “species problem” is long-standing in studies of evolutionary patterns in scleractinian reef corals, in which it is frequently difficult to recognize species, due to high ecophenotypic plasticity, simple morphologies that often overlap among species, and patchy distributions in space and time. Recently, molecular techniques, coupled with lab and field experiments on coral reproduction, have provided new independent data, which have improved understanding of the nature of species boundaries. These new methods have revealed the presence of cryptic species as well as differences in patterns of larval connectivity and population differentiation among species. We examine how recent advances involving cryptic species and population connectivity in modern reef corals contribute to understanding species in the fossil record. Our results reveal significant differences in patterns of morphologic variation among species, which may be related to patterns of population differentiation. The diagnostic morphological characters of species differ among families, and so do patterns of morphological variation within species and overlap among species. The causes of differences appear to be related to reproductive biology and larval dispersal. These results indicate that any general predictions regarding morphologic variation within and among species are complex, and would need to take a number of factors into consideration. (pages 217 - 237)
This chapter is available at:
    University of Chicago Press
    https://academic.oup.com/chica...


DOI: 10.7208/chicago/9780226377582.003.0008
[cephalopods;homeomorphy;heterochrony;sea level;sympatry]
Ammonoid cephalopods show a remarkably high rate of speciation when compared to other metazoans although the drivers of this evolutionary volatility are not clear. Ammonoid evolution is characterized by high degrees of homeomorphy, heterochrony, and other patterns that reveal a flexible developmental growth program. Ammonoid biodiversity through time appears to be linked to major environmental changes, particularly sea level change. The model of speciation presented synthesizes these observations with contemporary views on ecological speciation, emphasizing the role of developmental flexibility in permitting the rapid production of new anatomical variants that then sort into ecological niches and diverge. In this model, a newly formed habitat space plays host to the rapid endemic radiation of ammonoids from one or a few ancestral species. Anatomical variants are produced via changes in developmental timing and then sort into different niches based on microhabitats within the environment. Assortative mating and disruptive selection lead to reproductive isolation and speciation among these morphs. The same processes will occur each time sea level rises; given developmental constraints on shell form, homeomorphic species will result. More data on the phylogeny, biogeography, ecology, and developmental flexibility of ammonoids, will allow us to test this speciation model in other ammonoid clades. (pages 238 - 277)
This chapter is available at:
    University of Chicago Press
    https://academic.oup.com/chica...


DOI: 10.7208/chicago/9780226377582.003.0009
[species recognition;single specimens;sexual dimorphism;fossil preservation]
Although the definition of species in the fossil record has been well understood for half a century and is generally congruent with the definition of extant species, both based primarily on morphology, fossil species of decapod crustaceans remain victims of the vagaries of the fossil record. Partial remains of organisms comprised of hundreds or thousands of individual elements results in related species being named on very different body parts. Limited numbers of specimens of many taxa render studies of individual variation, sexual dimorphism, and ontogenetic variation challenging. Because neontologists often base species definitions on morphological features not often preserved on fossils, paleontologists must employ proxy characters on fossils to permit comparison with extant forms. These are among the major challenges for paleontologists. Nonetheless, phylogenetic analyses of fossil and extant higher taxa suggest that paleontological and neontological studies are generally congruent. (pages 278 - 300)
This chapter is available at:
    University of Chicago Press
    https://academic.oup.com/chica...


DOI: 10.7208/chicago/9780226377582.003.0010
[species question;incomplete fossil record;crinoids]
Our intuition is that species-level, fossil data are problematic for studying the tempo and mode of evolutionary history. In this chapter, the fidelity of species-level data of fossil echinoderms is considered in order to evaluate the usefulness of species for answering evolutionary and paleobiological questions. Although such species-level data are problematic for many studies, significant information is recorded by fossil species. A fossil species represents a unique morphological entity in time and space, despite varying degrees of resolution for species as a whole. (pages 301 - 311)
This chapter is available at:
    University of Chicago Press
    https://academic.oup.com/chica...


DOI: 10.7208/chicago/9780226377582.003.0011
[systematics;taxonomy;International Code of Zoological Nomenclature]
Naming new species of fossil fishes serves two related but different purposes: 1) species names provide practical constructs for understanding paleodiversity by linking specimens to localities and stratigraphic information; and 2) species names provide tools for phylogenetic and biogeographic studies. If species names for fossil fishes primarily serve as practical tools for cataloging paleodiversity and secondarily as tools for phylogenetic and biogeographic analyses, then a need for the future is the development of a comprehensive, global, universally accessible digital catalog of fossil fishes. It should be designed to be comparable to and compatible with the Catalog of Fishes and build directly upon original species descriptions since 1758. The goal would be to catalog: 1) all available generic names; 2) all valid generic names; and 3) all type localities, including stratigraphic information. This effort could be extended to document all available species names, valid species names, and type localities. Such a multi-decadal project could become an important catalyst for revisionary studies of fossil and living fishes. In the meantime, we continue to differentially diagnose extant species of fishes based primarily on morphology and do not know to what extent most of these named species actually operate in nature as biological species. (pages 312 - 339)
This chapter is available at:
    University of Chicago Press
    https://academic.oup.com/chica...


DOI: 10.7208/chicago/9780226377582.003.0012
[Late Devonian mass extinction;Richmondian invasion;niche stability]
Among modern taxa, speciation by geographic isolation is more prevalent than biologically-based isolation mechanisms, and studies of speciation style among modern species indicate that vicariant speciation has occurred much more frequently than speciation by dispersal in the development of the modern biota. Fewer analyses have tested the relative frequency of speciation styles in the fossil record directly, but these also found vicariance to be more widespread than dispersal speciation among Paleozoic marine benthos. The dramatic increase in human-facilitated species invasions in recent decades has been documented to alter the evolutionary pathway of native species. Analyzing the evolutionary impacts of species invasions within the fossil record provides a framework for examining the impact of species introductions on evolutionary time scales. Both the Late Ordovician and Middle Devonian saw major invasions and suppression of speciation in benthic marine faunas. This seems to have occurred by depression of vicariance due to the ecological effects of invading species on native species. (pages 340 - 365)
This chapter is available at:
    University of Chicago Press
    https://academic.oup.com/chica...


DOI: 10.7208/chicago/9780226377582.003.0013
[mode of evolution;stasis;species delimitation;punctuated equilibrium;taxonomy;likelihood;morphological traits]
A primary claim within the theory of punctuated equilibrium is that most fossil species exhibit morphological stasis. However, an often-overlooked critique of the theory is that the morphological species concept in paleontology leads to the conflation of species delimitation with the recognition of stasis. Here, we use a likelihood method to estimate the mode of evolution of 635 morphological traits measured from temporal sequences of fossil samples across eukaryotes. We then compare these estimates with the taxonomic usefulness of each trait as inferred from the systematic literature. Our results indicate that the outcomes of studies analyzing evolutionary mode in the fossil record have been influenced by taxonomic practice, particularly where studies have focused on trait evolution within lineages linking nominate species. We consider a variety of factors—including the use of trends in single traits trends as proxies for species-level trends—that may contribute to this complex relationship. (pages 366 - 388)
This chapter is available at:
    University of Chicago Press
    https://academic.oup.com/chica...


DOI: 10.7208/chicago/9780226377582.003.0014
[mammals;species problem;punctuated equilibrium]
Conventional evolutionary biology has long emphasized the importance of fragmentation of variable populations within geographic clines in the production of new species. The same kind of thinking has been applied to chronoclines in the fossil record, and how to define new species by breaking up continuous anagenetic sequences. The assumption is that geographic clines and chronoclines are formed by similar environmental influences, such as changes in temperature and other climatic variables. However, detailed studies of most of the common fossil birds and mammals at Rancho la Brea tar pits that lived over the past 35,000 years show that they are static over the entire range of climate changes of the last glacial-interglacial cycle, and show no changes that might be responses to the peak glacial cooling and climate changes of 20,000 years ago. Yet most of these same fossil birds and mammals have close living relatives (usually in the same genus) that show very strong clinal size and morphological changes, typically following Bergmann’s Rule and/or Allen’s rule. Thus, the processes that form geographic clines are not necessarily relevant to understanding change (or lack thereof) of morphology or size in the fossil record. (pages 389 - 404)
This chapter is available at:
    University of Chicago Press
    https://academic.oup.com/chica...

List of Contributors

Index

Book published by University of Chicago Press, 2016. Page maintained by BiblioVault.