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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Fossils provide a powerful tool for the study of the nearly 4-billion-year history of life, and its role in the evolution of Earth systems. They also provide important data for evolutionary studies, and contribute to our understanding of the extinction of organisms and the origins of modern biodiversity.
Fossils At A Glance is written for students taking an introductory level course in paleontology. Short chapters introduce the main topics in the modern study of fossils. The most important fossil groups are discussed, from microfossils through invertebrates to vertebrates and plants, followed by a brief narrative of life on Earth.
Diagrams are central to the book and allow the reader to see most of the important data “at a glance”. Each topic covers two pages and provides a self-contained suite of information or a starting point for future study.
This second edition has been thoroughly revised and brought up to date. It includes new line diagrams as well as photographs of selected fossils
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Contents
Acknowledgments
Chapter 1 Introduction
Introduction
Types of fossils (Fig. 1.1)
Time and fossils
Life and the evolution of continents
Fossil preservation
Biases in the fossil record
Exceptionally preserved fossils
The Cambrian lagerstätten
More examples of Konservat-Lagerstätten
Reconstructing the ecology of fossils
Glossary
Chapter 2 Fossil classification and evolution
Introduction
Taxonomy
Cladistics
Evolution by natural selection
The genetic basis for evolution
Evolution in action
Human DNA and evolution
Glossary
Chapter 3 Sponges
Introduction
Sponge morphology
Sponges as reef builders
Biogenic silica
Glossary
Chapter 4 Corals
Introduction
Coral morphology and evolution
Tabulate corals
Rugose corals
Lower Palaeozoic reefs
Scleractinian corals
Corals as climatic indicators
Glossary
Chapter 5 Bryozoans
Introduction
Bryozoan morphology
Bryozoan ecology
Bryozoan evolution
Bryozoans as environmental indicators
Glossary
Chapter 6 Brachiopods
Introduction
Internal morphology of brachiopods
External morphology of brachiopods
Brachiopod evolution
Brachiopod ecology and paleoecology
Community paleoecology
Discriminating between brachiopods and bivalves
Glossary
Chapter 7 Echinoderms
Introduction
The water vascular system and echinoderm lifestyle
Classification and evolutionary history of echinoderms
Crinoid morphology
Crinoid evolution
Asteroids
Ophiuroids
Echinoid morphology
Echinoid ecology and evolution
Glossary
Chapter 8 Trilobites
Introduction
Trilobite morphology
Trilobite mode of life
Trilobite evolution
Trilobite paleogeography
Glossary
Chapter 9 Mollusks
Introduction
Basic morphology
Molluskan origins
Molluskan classification
Molluskan shell growth
Gastropods
Bivalves
Cephalopods
Glossary
Chapter 10 Graptolites
Introduction
Graptolite morphology
Pterobranchs: the living relatives of graptolites
Graptolite mode of life
Glossary
Chapter 11 Vertebrates
Introduction
Fish
Amphibians
Tetrapod evolution and climate change
Amniotes
Anapsids
Synapsids
Diapsids
Birds
Glossary
Chapter 12 Land plants
Introduction
Land plant classification
Plant life histories
Key steps in plant evolution
The earliest land plants
Colonization of the land
Early vascular plants
Spore-bearing plants
Carboniferous coal forests
Seed-bearing plants: gymnosperms
Seed-bearing plants: angiosperms
Glossary
Chapter 13 Microfossils
Introduction
Autotropic protists
Heterotrophic protists
Microinvertebrates
Microvertebrates
Plants
Glossary
Chapter 14 Trace fossils
Introduction
Preservation
Ethological (behavioral) classification
Ichnofacies
Evolution of trace fossils
Dinosaur trackways
Glossary
Chapter 15 Precambrian life
Introduction
Evidence for early life
The origin of complexity
Multicellular animals
Classifying animals
Ediacaran life
Glossary
Chapter 16 Phanerozoic life
Introduction
The Cambrian explosion
Phanerozoic diversity
Life on land
Diversification
Mass extinctions
Glossary
Reading list
Geological timescale
Index
This edition first published 2010, © 2010 by Clare Milsom and Sue Rigby
Previous edition: 2004
Blackwell Publishing was acquired by John Wiley & Sons in February 2007. Blackwell’s publishing program has been merged with Wiley’s global Scientific, Technical and Medical business to form Wiley-Blackwell.
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Library of Congress Cataloguing-in-Publication Data
Milsom, Clare.
Fossils at a glance / Clare Milsom and Sue Rigby. – 2nd ed.
p. cm.
Includes bibliographical references and index.
ISBN 978-1-4051-9336-8 (pbk. : alk. paper) 1. Paleontology. 2. Fossils. I. Rigby, Susan. II. Title.
QE711.3.M55 2010
560–dc22
2009015238
ISBN: 978-1-4051-9336-8
A catalogue record for this book is available from the British Library.
Acknowledgments
We are grateful to the following people for reading parts of the manuscript and improving it significantly: Chris Settle, Chris Paul, Liz Hide, Paul Taylor, Robin Cocks, Graham Budd, Liz Harper, Ivan Sansom, Jason Hilton, Bridget Wade, Simon Braddy, Nick Butterfield, and Sarah Gabbott.
In addition, our families provided endless distractions and generous support during the writing both editions of this book. Thanks are due in this respect to Maurizio, Ivy, and Peter Bartozzi and to Michael, Peter, and Thomas Fuller.
Figure acknowledgments
Figure 1.1: from Treatise on Invertebrate Paleontology, part O, Geol. Soc. Amer. and Univ. Kansas Press (Figure 159.6, O218); Crimes, T.P., Legg, I., Marcos, A. and Arboleya, M., 1977, in Crimes, T.P. and Harper, J.C. (eds) Trace Fossils 2, Seel House Press (Figure 10, p. 134). Figure 1.2: based on Williams, S.H., 1986, in Hughes, C.P. and Rickards, R.B. (eds) Palaeoecology and Biostratigraphy of Graptolites, Geological Society Special Publication 20 (Figure 1, pp. 166–7) and Barnes, C.R. and Williams, S.H., 1990, in Briggs, D.E.G. and Crowther, P.R. (eds) Palaeobiology: A Synthesis, Blackwell Scientific Publications (Figure 1, p. 479). Figure 1.5: redrawn from Fortey, R.A. and Cocks, L.R.M., 1986, Journal of the Geological Society, 143, 151–60. Figure 1.8: redrawn and modified from Seilacher, A., Reif, W.-E. and Westphal, F., 1985, Philosophical Transactions of the Royal Society of London, B11, 5–23.
Figure 2.2: redrawn from British Mesozoic Fossils, British Musuem (Natural History) (Plate 28(2)). Figure 2.3: modified and redrawn from Campbell, N.A., 1996, Biology, 4th edn (Figure 23-15, p. 476). Figure 2.4: modified and redrawn from Skeleton, P., 1993, Evolution: A Biological and Palaeontological Approach, Addison Wesley (Figure 11.1, p. 512).
Figure 3.1a, b: redrawn from Benton, M. and Harper, D., 1997, Basic Palaeontology, Addison Wesley Longman (Figure 5.10); Figure 3.1c, d: redrawn and simplified from McKinney, F.K., 1991, Exercises in Invertebrate Paleontology, Blackwell Scientific Publications (Figures 4.1, 4.2). Figure 3.2: redrawn and simplified from Prothero, D.R., 1998, Bringing Fossils to Life, W.C.B./McGraw-Hill USA (Figure 12.7). Figure 3.3: redrawn and simplified from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 4.16a). Siphonia, Rhaphidonema: from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 4.6a, d).
Figure 4.2: simplified from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 5.20). Figure 4.3: redrawn from McKinney, F.K., 1991, Exercises in Invertebrate Paleontology, Blackwell Scientific Publications (Figure 5.2d). Figure 4.4a: redrawn from McKinney, F.K., 1991, Exercises in Invertebrate Paleontology, Blackwell Scientific Publications (Figure 5.6); Figure 4.4b: redrawn from various sources. Figure 4.5: after McKinney, F.K., 1991, Exercises in Invertebrate Paleontology, Blackwell Scientific Publications (Figures 5.4, 5.6). Figure 4.6: redrawn and simplified from Prothero, D.R., 1998, Bringing Fossils to Life, W.C.B./McGraw-Hill USA (Figure 12.13). Figure 4.7: redrawn from British Palaeozoic Fossils, British Museum (Natural History) (Plate 3(7)). Figure 4.8: simplified from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 5.7f). Figure 4.9: based on various sources. Favosites, Halysites: redrawn from British Palaeozoic Fossils, British Museum (Natural History) (Plate 15(1,3)). Palaeosmilia: redrawn from British Palaeozoic Fossils, British Museum (Natural History) (Plate 44(6)). Isastraea, Thecosmilia, Montlivaltia: redrawn from British Mesozoic Fossils, British Museum (Natural History) (Plate 3(2,4,6)). Lithostrotion, Dibunophyllum: redrawn from British Palaeozoic Fossils, British Museum (Natural History) (Plate 43(1,2)).
Figure 5.1: courtesy of Simone Duerr, Liverpool John Moores University. Figure 5.2a, c: simplified and redrawn from Benton, M. and Harper, D., 1997, Basic Palaeontology, Addison Wesley Longman (Figure 6.34); Figure 5.2b: redrawn from McKinney, F.K., 1991, Exercises in Invertebrate Paleontology, Blackwell Scientific Publications (Figure 12.3). Figure 5.3: simplified from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 6.7). Fenestella: redrawn from British Palaeozoic Fossils, British Museum (Natural History) (Plate 4(1)). Stomatopora: redrawn from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 6.11d).
Figure 6.1a: redrawn and modified from Prothero, D.R., 1998, Bringing Fossils to Life, W.C.B./McGraw-Hill USA (Figure 13.2C, p. 228); Figure 6.1b: redrawn and modified from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 7.1e, f, p. 159). Figure 6.2a: redrawn and modified from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 7.1a, b, p. 159); Figure 6.2b: redrawn and modified from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 7.5a, p. 165). Figure 6.3: redrawn from British Palaeozoic Fossils, British Museum (Natural History) (Plate 50(3)). Figure 6.4: based on Ziegler, A.M., Cocks, L.R.M. and Bambach, R.K., 1968, Lethaia, 1, 1–27. Lingula: redrawn from Black, R., 1979, The Elements of Palaeontology, Cambridge University Press (Figure 91a, p. 149). Megellania: redrawn from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 7.1d, p. 159). Gigantoproductus: redrawn from British Palaeozoic Fossils, British Museum (Natural History) (Plate 47(6)). Pentamerus: redrawn from British Palaeozoic Fossils, British Museum (Natural History) (Plate 17(10)). Spirifer: redrawn from Black, R., 1979, The Elements of Palaeontology, Cambridge University Press (Figure 93a, d, p. 152). Prorichthofenia: redrawn from Black, R., 1979, The Elements of Palaeontology, Cambridge University Press (Figure 92j, p. 151). Tetrarynchia: redrawn from Black, R., 1979, The Elements of Palaeontology, Cambridge University Press (Figure 94a, b, p. 155). Colaptomena: redrawn from McKinney, F.K., 1991, Exercises in Invertebrate Palaeontology, Blackwell Scientific Publications (Figure 11.7, p. 160).
Figure 7.1: courtesy of Simone Duerr, Liverpool John Moores University. Figure 7.2: courtesy of H. Hess; redrawn from Hess, H., Ausich, W.I., Brett, C.E. and Simms, M.J., 1999, Fossil Crinoids, Cambridge University Press (Figure 90, p. 78). Figure 7.3: redrawn and modified from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 9.34b, p. 265). Figure 7.4: redrawn and modified from Moore, J., 2001, Introduction to the Invertebrates, Cambridge University Press (Figure 17.4ei, p. 271). Figure 7.5: redrawn from McKinney, F.K., 1991, Exercises in Invertebrate Palaeontology, Blackwell Scientific Publications (Figure 13.1, p. 186). Figure 7.6: courtesy of Simone Duerr, Liverpool John Moores University. Figure 7.7: based on McKinney, F.K., 1991, Exercises in Invertebrate Palaeontology, Blackwell Scientific Publications (Figure 13.6, p. 192). Figure 7.8: redrawn and modified from Moore, J., 2001, Introduction to the Invertebrates, Cambridge University Press (Figure 17.4eii, p. 271). Figure 7.9: based on various sources. All echinoderms redrawn from British Palaeozoic Fossils, British Museum (Natural History) (Plates 59(8,9), 60(3)); British Mesozoic Fossils, British Museum (Natural History) (Plates 42(1,2), 44(1), 45(2), 69(1), 70(3)).
Figures 8.1, 8.2: courtesy of Sam Stubbs, Neal Immega. Figure 8.3: based on various sources. Figure 8.4: based on various sources. All trilobites redrawn from British Palaeozoic Fossils, British Museum (Natural History).
Figure 9.1: redrawn and modified from Moore, J., 2001, Introduction to the Invertebrates, Cambridge University Press (Figure 10.1a, p. 132). Figure 9.2: based on various sources. Figure 9.4a, b: redrawn and modified from Prothero, D.R., 1998, Bringing Fossils to Life, W.C.B./McGraw-Hill USA (Figure 15.11F, G, p. 288); Figure 9.4c: redrawn and modified from Moore, J., 2001, Introduction to the Invertebrates, Cambridge University Press (Figure 11.1d, p. 153). Table 9.3: based on various sources. Figure 9.5: based on Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 8.11, p. 211). Figures 9.6, 9.7: redrawn and modified from Stanley, S.M., 1968, Journal of Paleontology, 42, 214–29 (Figures 6 and 4, respectively). Figure 9.8: redrawn and modified from Moore, J., 2001, Introduction to the Invertebrates, Cambridge University Press (Figure 11.4a, p. 160). Figure 9.9: redrawn from Doyle, P., 1996, Understanding Fossils, Wiley and Sons (Figure 9.12, p. 172). Figure 9.10: redrawn and modified from Boss, K.J., 1982, in Parker, S.P. (ed.) Synopsis and Classification of Living Organisms, McGraw-Hill (p. 968). Figure 9.11: redrawn and modified from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 8.21a, p. 231). Figure 9.12: redrawn and modified from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 8.24c, p. 239). Figure 9.13: redrawn from Callomon, J.H., 1963, Transactions of the Leicester Literary and Philosophical Society, 57, 21–6. Figure 9.14: redrawn from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 8.30, p. 29); Treatise on Invertebrate Paleontology, part L, Geol. Soc. Amer. and Univ. Kansas Press. Figure 9.15: redrawn and modified from Benton, M. and Harper, D. 1997, Basic Palaeontology, Addison Wesley Longman (Figure 8.31a, p. 188). Figure 9.16: redrawn and modified from Prothero, D.R., 1998, Bringing Fossils to Life, W.C.B./McGraw-Hill USA (Figure 15.27, p. 304); Batt, R.J., 1989, Palaios, 4, 32–42. Figure 9.17: redrawn and modified from Brusca, R.C. and Brusca, G.J., 1990, Invertebrates, Sinauer Associates (Figure 13G, p. 712). Figure 9.18: redrawn from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 8.32a–c, p. 253). Mya: redrawn from British Caenozoic Fossils, British Museum (Natural History) (Plate 38(11)). Ensis: redrawn from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 8.11m, p. 211). Teredo: redrawn and modified from Black, R.M., 1970, The Elements of Palaeontology, Cambridge University Press (Figure 21b, p. 44). Radiolites: redrawn from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 8.13j). Turritella, Planorbis, Hygromia: redrawn from British Caenozoic Fossils, British Museum (Natural History) (Plates 39(5), 41(15), 42(2)). Buccinum: redrawn and modified from Clarkson, E.N.K., 1998, Invertebrate Palaeontology and Evolution, Chapman and Hall (Figure 8.17b, p. 222). Patella: redrawn and modified from Black, R.M., 1970, The Elements of Palaeontology, Cambridge University Press (Figure 35a, p. 64). Ammonites: redrawn from British Mesozoic Fossils, British Museum (Natural History) (Plates 30(2), 32(1,2), 37(4), 66(2)); British Palaeozoic Fossils, British Museum (Natural History) (Plate 58(6)). Neohibolites: redrawn from British Mesozoic Fossils, British Museum (Natural History) (Plate 67(4)).
Figure 10.1: based on various sources.
Figures 11.1, 11.2, 11.5, 11.8, 11.10, 11.12: original diagrams, with cartoons of skeletons redrawn from a variety of sources, most commonly from Benton, M., 1997, Vertebrate Palaeontology, Chapman and Hall. Figure 11.3: simplified from Benton, M., 1997, Vertebrate Palaeontology, Chapman and Hall (Figure 9.6d). Figure 11.4: redrawn from Benton, M. 1990, Vertebrate Palaeontology, Chapman and Hall (Figure 3.1a, b, p. 47). Figure 11.7: redrawn Hylonomous. Figures in Table 11.1: redrawn from Black, R., 1979, The Elements of Palaeontology, Cambridge University Press (Figure 188). Figure 11.11: redrawn from hominin phylogeny, Home of Nature’s Holism, http://www.ecotao.com/holism/index.htm. Figure 11.13: redrawn from Prothero, D.R., 1998, Bringing Fossils to Life, W.C.B./McGraw-Hill USA (Figure 17.46).
Figure 12.1: redrawn and modified from Benton, M. and Harper, D., 1997, Basic Palaeontology, Addison Wesley Longman (Figure 10.8, p. 232). Figure 12.3: redrawn from Andrews, H.N. Jr., 1960, Palaeobotanist, 7, 85–9. Figure 12.4: courtesy of D. Edwards; redrawn from Edwards, D., 1970, Palaeontology, 13, 150–5. Figure 12.5: redrawn from Edwards, D.S., 1980, Reviews of Paleobotany and Palynology, 29, 177–88. Figure 12.6: redrawn from Andrews, H.N. and Kasper, A.E., 1970, Maine State Geological Survey Bulletin, 23, 3–16 (Figure 6). Figure 12.7: redrawn and modified from Eggert, D.A., 1974, American Journal of Botany, 61, 405–13. Figure 12.8: based on various sources. Figure 12.9a: redrawn and modified from Bold, H.C., Alexopoulos, C.J. and Delevoryas, T., 1987, Morphology of Plants and Fungi, Harper International Edition (Figure 25-16, p. 613); Figure 12.9b: redrawn from Stewart, W.N. and Delevoryas, T., 1956, Botanical Review, 22, 45–80 (Figure 9). Figure 12.10: redrawn from Andrews, H.N., 1961, Studies in Paleobotany, Wiley and Sons (Figure 11-1). Figure 12.11: redrawn from Delevoryas, T., 1971, Proceedings of the North American Paleontological Convention, 1, 1660–74. Figure 12.12: redrawn and modified from Bold, H.C., Alexopoulos, C.J. and Delevoryas, T., 1987, Morphology of Plants and Fungi, Harper International Edition (Figure 24-2, p. 584). Figure 12.13: redrawn from Crane, P.R. and Lidgard, S., 1989, Science, 246, 675–8. Figure 12.14: courtesy of G. Sun et al.; redrawn from Sun, G., Ji, Q., Dilcher, D.L., Zheng, S., Nixon, K.C. and Wang, X., 2002, Science, 296, 899–904 (Figure 3). All fossil plants: redrawn from British Palaeozoic Fossils, British Museum (Natural History) (Plates 38(1,2,3,5), 39(2,4,5), 40(3)).
Figure 13.1a, b: redrawn from Lipps, J.H., 1993, Fossil Prokaryotes and Protists, Blackwell Scientific Publications (Figure 6.2G, I, p. 79); Figure 13.1c: redrawn from Wall, D., 1962, Geological Magazine, 99, 353–62. Figure 13.2: courtesy of Nick Butterfield, University of Cambridge. Figure 13.3: redrawn and modified from Brasier, M.D., 1980, Microfossils, Chapman and Hall (Figure 4.2d, p. 23); Wall, D. and Dale, B., 1968, Micropalaeontology, 14, 265–304. Figure 13.4a: redrawn from Lipps, J.H., 1993, Fossil Prokaryotes and Protists, Blackwell Scientific Publications (Figure 11.3B, p. 171). Figure 13.6: based on various sources. Figure 13.7: modified and redrawn from various sources. Figure 13.8: courtesy of Taniel Danelian, Université Lille. Figure 13.9: based on various sources. Figure 13.10: redrawn from Brasier, M.D., 1980, Microfossils, Chapman and Hall (Figure 14.1a). Figure 13.11: courtesy of Dave Sieveter, University of Leicester. Figure 13.12: based on various sources. Figure 13.13: redrawn from Brasier, M.D., 1980, Microfossils, Chapman and Hall (Figure 14.10b, p. 134). Figure 13.14a–c: based on Brasier, M.D., 1980, Microfossils, Chapman and Hall (Figure 16.5–16.7, pp. 157–8); Figure 13.14d: redrawn from McKinney, F.K., 1991, Exercises in Invertebrate Palaeontology, Blackwell Scientific Publications (Figure 16.2a, p. 242). Figure 13.15: redrawn and modified from Briggs, D.E.G., Clarkson, E.N.K. and Smith, M.P., 1983, Lethaia, 16, 1–14 (Figure 2). Figure 13.16: redrawn from Goudie, A., 1982, Environmental Change, Oxford University Press (Figure 2.7A, p. 51). Hystrichosphaeridium: redrawn from Brasier, M.D., 1980, Microfossils, Chapman and Hall (Figure 4.3g, p. 26); Tschudy, R.H. and Scott, R.A. (eds), 1969, Aspects of Palynology, Wiley-Interscience, New York. Coscinodiscus: redrawn from Lipps, J.H., 1993, Fossil Prokaryotes and Protists, Blackwell Scientific Publications (Figure 10.5B, p. 159). Bathropyramis: redrawn from Brasier, M.D., 1980, Microfossils, Chapman and Hall (Figure 12.7c, p. 87). Globigerina, Bolivina: redrawn from Prothero, D.R., 1998, Bringing Fossils to Life, W.C.B./McGraw-Hill USA (Figure 11.7, p. 194). Elphidium: redrawn from Lipps, J.H., 1993, Fossil Prokaryotes and Protists, Blackwell Scientific Publications (Figure 12.16, p. 219). Beyrichia: redrawn from Brasier, M.D., 1980, Microfossils, Chapman and Hall (Figure 14.10c, p. 134). Cypridina: redrawn from McKinney, F.K., 1991, Exercises in Invertebrate Palaeontology, Blackwell Scientific Publications (Figure 6.7, p. 87). Emiliana: redrawn from Lipps, J.H., 1993, Fossil Prokaryotes and Protists, Blackwell Scientific Publications (Figure 11.15, p. 181). Cypris: redrawn from Brasier, M.D., 1980, Microfossils, Chapman and Hall (Figure 14.7, p. 129). Bythocertina: redrawn from Brasier, M.D., 1980, Microfossils, Chapman and Hall (Figure 14.18c, p. 141). Quercus: redrawn from Oakley, K., 1969, Frameworks for Dating Fossil Man, 3rd edn, Weidenfeld and Nicolson (Figure 16b, p. 72).
Figure 14.1: based on Frey, R.W., Pemberton, S.G. and Saunders, T.D.A., 1984, Bulletin of Canadian Petroleum Geology, 33, 72–115 (Figure 7). Figure 14.2: based on Frey, R.W., Pemberton, S.G. and Saunders, T.D.A., 1990, Journal of Paleontology, 64(1), 155–8 (Figure 1); Brenchley, P.R. and Harper, D.A.T., 1998, Palaeoecology: Ecosystems, Environments and Evolution, Chapman and Hall (Figure 5.6, p. 155). Figure 14.3: redrawn from University of Sheffield, Sorby Geology Group, http://www.sorbygeology.group.shef.ac.uk/DINOC01/dinocal1.html.
Figure 15.1b: redrawn and simplified from Benton, M. and Harper, D., 1997, Basic Palaeontology, Addison Wesley Longman (Figure 4.4). Figure 15.4: courtesy of Nick Butterfield, University of Cambridge. Figure 15.5: redrawn and modified from Benton, M. and Harper, D., 1997, Basic Palaeontology, Addison Wesley Longman (Figure 4.7). Figure 15.6: based on various sources.
Figures 16.2, 16.4: redrawn and modified from various sources. Figure 16.6: redrawn from evolution.berkeley.edu/evosite/evo101/VIIB1dM. Figure 16.7: redrawn from Barton, N.H., Briggs, D.E.G., Eisen, J.A., Goldstein, D.B. and Patel, N.H., 2007, Evolution, Cold Spring Harbor Laboratory Press (Figure 10.67).
1 Introduction
Introduction
The Earth is the only planet we know to support life. Its long history shows that life and the planet it inhabits have a complicated relationship. Free oxygen in the atmosphere, the ozone shield, the movement of carbon into long-term reservoirs in the deep oceans, and the rapid weathering of rocks on the land surface are obvious examples of this relationship.
The evolutionary history of life on Earth points to the development of a series of faunas that occupied the changing surfaces of the land and sea. Through the extraordinary medium of lagerstätten, or sites of exceptional preservation, it is possible to visualize these vanished communities and to restore some of their behaviors and interactions.
In addition, the process of evolution, via Darwinian natural selection, is recorded in the fossil record. Though incomplete and tantalizing in places, fossils are the only direct information source about the nature of our ancestors, and the ancestors of any life on modern Earth.
The study of fossils offers a view of the past at all scales of space and time. From a single moment, for example the single act of making a footprint, to the study of the evolution of tetrapods, or from the study of a single locality to an analysis of the effect of the break-up of Pangea on the evolution of dinosaurs, the fossil record is the primary source of data. Paleontologists build detailed interpretations and analysis from the study of individual fossils; most are invertebrate animals, preserved in great abundance in the shallow marine record.
In this book, we provide an introduction to the methods by which fossils are studied. We discuss the biases that follow from the process of fossilization, and explain how this can be analyzed for a particular fossil locality. We provide an introduction to evolutionary theory, which is the basis for explaining the consistent changes of shape seen in fossils over time.
We describe the major groups of invertebrate fossils that form the bedrock of the discipline, and also of most introductory courses in the subject. We discuss microfossils, plants, and vertebrates, which, while less commonly encountered, are of such importance to understanding life on Earth. Finally, we briefly narrate the evolution of life on Earth as it is currently understood, including episodes of huge diversification and mass extinction. Throughout the text, we discuss the many ways in which fossils contribute to an improved understanding of the Earth’s system, for example through allowing accurate relative dating of rocks, or as proxies for particular environmental settings.
By the end of this book, you should be able to identify the most common fossils, discuss their ecology and life habits based on an analysis of their detailed shape, understand how each group contributes to the wider studies of paleontology and earth systems science, and appreciate their importance at particular points in Earth’s history. You should have a broad understanding of how life has both evolved on Earth and must be factored into any analysis of the evolution of the planet. You can read the book in sequence, or dip into it at will. You will find that some sections follow on from a previous chapter, but in most cases information is presented in self-contained pieces that fall on a couple of facing pages. We have used diagrams and tables wherever possible to summarize information and we have used as few technical terms as possible, to try to lay bare the ways in which fossils matter.
Types of fossils (Fig. 1.1)
Trace fossils
Trace fossils are the preserved impressions of biological activity. They provide indirect evidence for the existence of past life. They are direct indicators of fossil behavior. As trace fossils are usually preserved where they were made, they are very good indicators of past sedimentary environments. Trace fossils made by trilobites have provided an insight into trilobite life habits, in particular walking, feeding, burrowing, and mating behavior.
Coprolites
Coprolites are fossilized animal feces. They may be considered as a form of trace fossil recording the activity of an organism. In some coprolites recognizable parts of plants and animals are preserved, providing information about feeding habits and the interaction of coexisting organisms.
Chemical fossils
When some organisms decompose they leave a characteristic chemical signature. Such chemical traces provide indirect evidence for the existence of past life. For example, when plants decompose their chlorophyll breaks down into distinctive, stable, organic molecules. Such molecules are known from rocks more than 2 billion years old and indicate the presence of very early plants.
Body fossils
Body fossils are the remains of living organisms and are direct evidence of past life. Usually only hard tissues are preserved, for example shells, bones, or carapaces. In particular environmental conditions the soft tissues may fossilize but this is generally a rare occurrence. Most body fossils are the remains of animals that have died, but death is not a prerequisite, since some body fossils represent parts of an animal that were shed during its lifetime. For example, trilobites shed their exoskeleton as they grew and these molts may be preserved in the fossil record.
Fig. 1.1 Types of fossils.
Time and fossils
Geological time can be determined absolutely or relatively. The ages of rocks are estimated numerically using the radioactive elements that are present in minute amounts in particular rocks and minerals. Relative ages of different units of rocks are established using the sequence of rocks and zone fossils. Sediments are deposited in layers according to the principle of superposition, which simply states that in an undisturbed sequence, older rocks are overlain by younger rocks.
Zone fossils are fossils with a known relative age. In order for the zone to be applicable globally, the fossils must be abundant on a worldwide scale. Most organisms with this distribution are pelagic – that is they live in the open sea. The preservation potential of the organism must also be high – that is they should have some hard tissues, which are readily preserved.
Stratigraphy
The study of sequences of rocks is called stratigraphy. There are three main aspects to this study: chronostratigraphy, lithostratigraphy, and biostratigraphy (Fig. 1.2).
Chronostratigraphy establishes the age of rock sequences and their time relations. Type sections are often established. These are the most complete and representative sequences of rocks corresponding with a particular time interval. For example, outcrops along Wenlock Edge in Shropshire, UK, form the type section for the Wenlock Series of the Silurian.
A point in a sequence is chosen for a boundary between one geological time interval and the next. It represents an instant in geological time and also corresponds with the first appearance of distinctive zone fossils. Relative timescales can then be established with reference to this precise point. These points are called “golden spikes”.
The differentiation of rocks into units, usually called formations, with similar physical characteristics is termed lithostratigraphy. Units are described with reference to a type section in a type area that can be mapped, irrespective of thickness, across a wide geographic area.
In biostratigraphy, intervals of geological time represented by layers of rock are characterized by distinct fossil taxa and fossil communities. For example, the dominant fossils in Palaeozoic rocks are brachiopods, trilobites, and graptolites.
Fig. 1.2 Stratigraphic description of the sequence of rocks that crosses the Ordovician–Silurian boundary at Dobb’s Linn, Southern Uplands, Scotland. Geological time is split into different zones depending on the method of analysis. Chronostratigraphy divides the section into two periods. Lithostratigraphic analysis divides the sequence into two shales. Biostratigraphy, as determined by the zone fossils, gives a more detailed division of relative age within the sequence.
Life and the evolution of continents
Life exists on a physically changing world, and these changes have both controlled the evolution of organisms and been recorded by their fossil record. Evolution operates rapidly on small populations, and so when a group of organisms becomes isolated through changes in the landscape around them, they quickly evolve to become different to their parent population. Organisms migrate across land bridges or along new seaways, as areas that were once isolated become accessible to one another. The migration of marsupial mammals such as possums into North America over the last 2 million years is a good example of this process. The analysis of the past distributions of organisms is known as paleobiogeography.
Plate tectonics drive changes to the map of the world
The continents and oceans change shape all the time, as crust is generated and modified by the forces of plate tectonics. New oceanic crust is formed at mid-ocean ridges where the mantle decompresses and melts, and as a consequence the oceans grow wider. Crust is consumed at destructive plate boundaries, where dense rock crust sinks back into the mantle. By this process oceans can become smaller or disappear altogether. Continental crust is increased in volume by the addition of island arc remnants and the sediments of the ocean floor. Continental collision joins these fragments together to form large masses, until the formation of new oceans pulls them apart.
The narrative of this evolving world map is well known for the last 200 million years, because it is recorded by the oceanic rocks of the modern sea floor. These rocks form like a conveyor belt, with the youngest rocks closest to the ridges and the oldest ones furthest away. Rock of decreasing age can be “stripped back” to reveal prior positions of the continents (Fig. 1.3). It is more difficult to reconstruct the position of oceans and continents older than 200 million years (which is only around the Triassic–Jurassic boundary), because too little oceanic crust of this age survives to produce an accurate map.
For older world maps, reconstruction is done by a variety of methods, but predominantly by tracing the latitude at which rocks cooled through the Curie point and “froze” into their minerals the direction of magnetic north. This technique, however, gives no measure of longitude, which has to be guessed from more qualitative types of data. One of the most useful of these is the distribution of the fossil remains of organisms.
Fig. 1.3 Paleogeography: maps of the world for the last 200 million years.
Fossil evidence for ancient continental distributions
During the Lower Palaeozoic, we know from paleomagnetic data that the continents were relatively small and widely dispersed. The landmass that now forms North America and parts of Scotland was close to the equator, while the area now forming Europe, Africa, and England was far away, at around 60° south. These island continents were surrounded by deep oceans which are now long vanished, but their position is recorded by an open marine animal, a type of colonial graptolite (Chapter 10), called Isograptus. This species lived only in the open ocean, and colonies were fossilized in the shales of the deep sea bed. These were sometimes preserved when the oceanic crust sank back into the mantle, scraped onto the over-riding continents as deformed strips of rock. A map of the modern distribution of Isograptus reveals their presence in these thin collisional bands, and an ancient map can be built by “tearing up” the modern continents along these bands (Fig. 1.4).
As the Lower Palaeozoic continued, these isolated continental fragments began to collide. One of the best studied collisions is that between Scotland and England, which happened during the late Silurian period (420 Ma). The line of collision runs east–west along the present Solway Firth, and the effects of the collision can be seen in the deep marine rocks preserved in the Southern Uplands, and in the seismic structure of the mantle beneath Scotland. Organisms that lived on either side of this ocean record its progressive closure as, first, deep marine, and then progressively more shallow-dwelling organisms became common to both sides of the seaway. The mixing of freshwater fish faunas of the latest Silurian age is the final sign that the ocean had gone.
Modern continents and mammals
The evolution of mammals coincided with, and was directly affected by, the break-up of a single giant continent, known as Pangea. The two most common groups of modern mammals – placental mammals (which gestate their young internally) and marsupial mammals (which bear tiny live young and nurture them in pouches) – are found across Pangea, and as the continent broke up they were able to migrate to all of the modern continents via land bridges. In South America, mammals have evolved independently for the last 60 million years, with little contact with the rest of the world apart from the intermittent migration of animals from North America, such as monkeys and rodents. The dominant mammals in South America were marsupials, with unusual species such as giant ground sloths and armadillos evolving. Many of these groups became extinct due to the migration of competitor placentals when the Isthmus of Panama formed, and this process of extinction was speeded up when hominids arrived a few thousand years ago.
Fig. 1.4 The distribution of Isograptus plotted on a modern map of the world, and a reconstruction of the ancient oceans in which they lived based on this distribution.
Australia, New Zealand, and Antarctica split from the rest of Pangea during the Cretaceous period, and in turn split from one another during the early Cenozoic. The isolated faunas of Australia and New Zealand evolved independently, with both landmasses being dominated by marsupials.
Africa also became isolated from the rest of the continents late in the Cretaceous period and became a center of evolution for placental mammals, including groups that became predominantly marine, such as whales and sea cows. Elephants and other large grazers evolved here. Faunal exchanges with Asia began in the early Miocene, with cats arriving to become the dominant African predator, and apes and elephants migrating out of Africa to the north and east. The distinctive mammalian faunas of different modern continents are a product of Cenozoic continental break-ups and the consequent isolation of groups of animals.
Fossil preservation
The fossil record is incomplete. Most organisms do not fossilize and most fossils are only the partial remains of once-living organisms. Those organisms that do fossilize are usually changed in some way. Most plants and animals are not preserved in their life position and their composition is usually altered.
The study of the history of an organism from its death to its discovery within a rock or sediment is known as taphonomy (Fig. 1.5). After the death of an organism, physical and biological processes interact with the organic remains. This determines the extent to which the organism is fossilized and the nature of the fossil.
The general taphonomic history of a fossil is as follows. After death, the soft tissues of the organism decay. The remaining hard tissues are then transported resulting in disarticulation and possible fragmentation. The broken hard tissues are then buried and are physically or chemically altered. Postburial modifications are termed diagenesis. This sequence of events results in a major loss of information about the organism and its life habit.
Fig. 1.5 The process of fossilization (taphonomy).
Biases in the fossil record
The fossil record is extremely selective. The term “preservation potential” is used to describe the likelihood of a living organism being fossilized. Organisms with a high preservation potential are common fossils. The nature of their morphology and the environment in which the organisms lived are important factors in determining whether they will be preserved. These inherent biases skew our view of past life. In general, the fossil record is biased towards the following:
organisms with tissues resistant to decay;
marine organisms;
organisms living in low energy environments;
more recent organisms;
organisms that were more common.
Organisms with tissues resistant to decay
Organisms with body parts that do not decay easily are more likely to be preserved in the fossil record than soft-bodied animals. In vertebrate animals, the teeth and bones are the most commonly fossilized components. Invertebrates often have shells and carapaces that are not prone to decay. The shells of most common invertebrates are formed from calcium carbonate in the form of calcite or aragonite. Aragonite may be converted to calcite during fossil diagenesis. This can be identified by a change in the shell crystal structure from layers of needle-like crystals to large, blocky crystals. Some invertebrates have skeletons composed of silica, for example sponges, that are preserved in the fossil record. The skeleton (or rhabdosome) of graptolites was composed of collagen, a protein which is extremely durable and resistant to decay. Animals with exoskeletons molt as they grow, increasing the number of potential fossils. Plant material is particularly prone to decay, although the woody tissues that form the stem and leaves, together with spores and pollen that have a resistant waxy coating, may be preserved in the fossil record.
The skeletal structure of an organism determines the completeness of the preservation. Hard tissues that are in the form of a single component, for example gastropods, are more likely to be preserved whole in the fossil record than skeletons that are made up of many pieces, for example sea urchins.
Marine organisms
Marine organisms are more likely to be preserved than those living on land. On land there is more erosion and less deposition of sediment and consequently less opportunity for burial. Terrestrial plants and animals living close to depositional areas, for example by the side of a lake, have a greater preservation potential than those living in areas of net erosion such as uplands.
The nature of the substrate that the organism inhabits does not seem to have an effect on the preservation potential of a marine animal. However, its ecology does affect the likelihood of a marine animal being fossilized. Sedentary animals, filter feeders, and herbivores are more commonly preserved in the fossil record than carnivorous animals. Sedentary animals, like corals, tend to be heavy and robust whilst active predators have more lightly constructed skeletons. In addition, mobile animals can escape from burial by sediment.
