1 Introduction 1.1 The question 1.2 The context 1.3 The available evidence 1.4 Synthesis 2 The nature of higher taxa 2.1 The Linnean hierarchy, the phylocode, and higher taxa 2.2 Disparity and morphospace: a phenotypic view of higher taxa 2.3 The adaptive landscape: an ecological view of higher taxa 2.

4 Molecular taxonomy and higher taxa 2.5 The pattern of evolution of higher taxa 2.6 Conclusion: are higher taxa real? 3 The nature of organisms 3.1 The atomistic model 3.1.1 Limitations of the atomistic model 3.2 The modularity model 3.2.

1 Evidence for the reality of the modularity model 3.2.2 The implications of the modularity model for evolution 3.2.3 The limitations of the modularity model 3.3 The correlated progression model 3.3.1 Implications of the correlated progression model for evolution 3.

3.2 Evidence for the correlated progression model 3.4 Conclusion 4 The palaeontological evidence 4.1 Fossils, phylogeny, and ancestry 4.1.1 Incompleteness 4.1.2 Phylogeny 4.

1.3 Fossils and molecules 4.2 Functional anatomy and physiology of fossils 4.3 Palaeoenvironmental and palaeoecological reconstruction 5 The developmental evidence 5.1 A brief history 5.2 Ancestral stages and the pattern of character acquisition inferred from embryos 5.2.1 Recapitulation 5.

2.2 Heterochrony 5.2.3 Heterotopy 5.2.4 Allometry, miniaturization, and gigantism 5.3 Developmental mechanisms for the maintenance of phenotypic integration 5.3.

1 Embryonic cellular and tissue interactions 5.3.2 The role of molecular genetic mechanisms 5.3.3 Phenotypic plasticity 5.4 Summary 6 The ecological perspective 6.1 The correlated progression model and adaptive landscapes 6.2 Multidimensional gradients in the adaptive landscape 6.

3 Case studies: aquatic to terrestrial habitats 6.4 Case studies: low-energy to high-energy life styles 6.5 Case studies: the origin of modern invertebrate body plans 7 The invertebrate fossil record 7.1 The phylogenetic tree of crown invertebrate phyla 7.2 The Cambrian explosion 7.3 Lophotrochozoa: Mollusca 7.3.1 Kimberella 7.

3.2 Odontogriphus 7.3.3 Halkieria , Wiwaxia , and Orthrozanclus : Halwaxiidae 7.3.4 Crown Mollusca 7.4 Ecdysozoa: Arthropoda 7.4.

1 Opabinia 7.4.2 Anomalocaridida (Radiodonta) 7.4.3 Nereocaris , Canadaspis , and other bivalved arthropods 7.4.4 Fuxianhuids: Chengjiangocaris , Fuxianhuia , and Shankouia 7.4.

5 Megacheirans 7.4.6 Conclusion: the evolution of arthropod characters 7.5 Deuterostomia 7.5.1 Vetulicolia: possible stem-group deuterostomes 7.5.2 Cambroernids: possible stem-group ambulacrians 7.

5.3 Vetulocystids: possible stem-group echinoderms 7.5.4 Carpoids: the asymmetric echinoderms 7.5.5 Crown Echinodermata 7.5.6 Yunnanozoons: possible stem-group chordates 7.

5.7 Pikaea : possible stem-group chordate 7.5.8 Conodonts: possible stem-group vertebrates 7.5.9 Myllokunmingia , Haikouichthys , and Metaspriggina : stem-group vertebrates 8 The vertebrate fossil record 8.1 Mammals 8.1.

1 The grades of fossil stem mammals 8.1.2 The origin of the mammalian body plan 8.1.3 The pattern of evolution of mammalian characters 8.2 Birds 8.2.1 The grades of fossil stem birds 8.

2.2 The origin of the avian body plan 8.2.3 The pattern of acquisition of avian characters 8.3 Tetrapods 8.3.1 The grades of fossil stem tetrapods 8.3.

2 The pattern of acquisition of tetrapod characters 8.4 Turtles 8.4.1 The grades of fossil stem chelonians 8.4.2 The pattern of acquisition of chelonian characters 8.5 Cetacea 8.5.

1 The grades of fossil stem cetaceans 8.5.2 The pattern of acquisition of cetacean characters 9 A synthesis 9.1 The nature of palaeobiological explanation 9.1.1 Combining the evidence 9.1.2 Missing and conflicting evidence 9.

1.3 Evaluating palaeobiological hypotheses 9.1.4 It may be true but is it science? 9.2 A summary of the evidence 9.2.1 Evidence from the nature of living organisms 9.2.

2 Evidence from computer simulations of the evolution of complex systems 9.2.3 Evidence from the fossil record 9.2.4 Evidence from developmental biology 9.2.5 Evidence from ecology 9.3 Conclusion: a general picture of the origin of higher taxa References Index.