This chapter details the geography and ecology of the Mesozoic period. It explains that the Mesozoic period was a time of major diversification and radiation, leading to large-scale changes in flora and fauna by the end of the era. In Mesozoic oceans, neoselachians diversified, while the total diversity of tetrapods changed relatively slowly. Meanwhile, lissamphibians evolved and the two major lineages of amniotes diversified into Synapsida and Sauropsida. The chapter highlights how the era's history of extinction events opened the way for a new faunal balance in the Cenozoic period. Most Mesozoic extinction events resulted from intense episodes of volcanic activity accompanying collisions and splitting of continents as Pangaea formed and later ruptured.
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Geography and Ecology of the Mesozoic
Chapter
Species and Speciation
This chapter explores the distinction between species and speciation. It notes there are
several definitions of species, but most evolutionary biologists use the biological species
concept (BSC). Genetic and phenotypic differences enable people to recognize and distinguish
species, but they do not define species according to the BSC. While taxonomists classify
different species groups of organisms based on preserved specimens, ambiguous cases only
grew as knowledge of organisms grew. The chapter discusses the origins and evolution of
reproductive isolation, which includes its hindrance by ongoing interbreeding and
recombination and its contribution to speciation. It then details the genomics of
speciation, diversification, and hybridization.
Chapter
Why are there so many kinds of beetles?
This chapter studies beetle diversity. Beetles are the largest order of animals on earth; their diversity eclipses other insect orders, even their nearest relatives. Why are beetles, of all groups, so diverse? Is there something about their biology or ecology that has promoted diversification, do they have a longer evolutionary history than other groups, or is the great diversity of beetles simply the outcome of random diversification processes? By investigating some of the proposed explanations for the great diversity of beetles, we can get to grips with the basic logic of setting up comparative analyses to discover why diversity is so unevenly distributed among clades. Exploring beetle diversity is also a good way to become familiar with the ways that evidence from phylogenetics, biogeography, and palaeontology can be used to describe patterns and test hypotheses for variation in diversity.
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Origins of Lissamphibia and Amniota
This chapter examines the origins of lissamphibia and amniota. It provides an overview of Paleozoic tetrapods, which includes the taxa on the divergence and diversification of lissamphibians and amniotes. Evolutionary changes in skulls, vertebrae, limb girdles, limbs, and ankles have enabled the tracking of the diversification of Paleozoic tetrapods and the interpretation of aspects of their biology. Meanwhile, the evolution of the amniotic egg in the Carboniferous has allowed amniotes to escape their dependence on water for reproduction. The chapter details the characteristics of amniotes that allowed for greater independence from moist habitats and the ability to grow very large. It explains how studying fossils can result in a greater understanding of the biology, ecology, and functional morphology of amniotes and their subsequent diversification.
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Were dinosaurs evolutionary failures?
This chapter focuses on dinosaurs as a case study for examining the macroevolutionary processes of adaptive radiation and mass extinction. Considering the rise of dinosaurs allows us to examine the role of both key adaptations and chance in diversification, while considering their fall prompts us to examine our ability to resolve events and determine cause and effect in deep time. The study of fossils sheds light on physiology, locomotion, behaviour, and ecology of extinct species. The diversification of dinosaurs may have been driven by key adaptations, such as upright gait and fast metabolism, which allowed them to exploit a wide range of niches, or it may have been triggered by opportunity through the extinction of other reptile groups. Given that vertebrate fossils are rare, and biased in terms of location, taxa, and time period, there is some uncertainty over the timing and nature of dinosaur extinctions.
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Was the diversification of mammals due to luck?
This chapter assesses the diversification of mammals, which is often considered a classic example of ecological opportunity prompting evolutionary radiation. The fossil record shows a dramatic increase in the diversity of placental mammals as they evolved to occupy the niches left vacant by the extinction of the dinosaurs. But date estimates based on DNA analysis have been used to question the assumed timing of this radiation, suggesting that the major placental mammal lineages diverged from each other long before the dinosaurs' demise. Given that different molecular dating analyses give very different estimates for the timing of the mammalian radiation, the quetsion is, how reliable are these molecular dates? Can we estimate the timing of divergence events from DNA sequences when rates of molecular evolution vary between lineages? The chapter finally considers the Bayesian molecular dating methods.
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The Origin of Species
This chapter assesses how lineages that acquire new genes evolve into new species. Lineages always tend to change because they adapt to new conditions of growth or evolve different ways of mating. In time, they may become sufficiently different from their ancestor to be recognized as a distinct species. The chapter then looks at how diversification is the natural tendency of lineages; how populations that are permanently separated may diverge through drift or selection; and how divergent selection leads to more or less strongly marked varieties. It also considers how species are recognized when ecologically distinctive forms become sexually isolated; how rapid speciation gives rise to swarms of sister species; and how diversity is the dynamic equilibrium between the origin and extinction of species.
Chapter
The Geography of Diversification and Regionalization
This chapter explores the geography of diversification and regionalization. It explains the fundamental biogeographic patterns that emerge from a history of the dispersal, diversification, and extinction of lineages and biotas. Moreover, the diversity of life on Earth reflects the outcome of opposing forces promoting both convergence and divergence among biotas. The chapter explains that evolutionary conservatism, phylogenetic constraints, gene flow, and similar environments limit the rates and directions of diversification. They also maintain similarities among biotas. The directions of divergence and diversification tend to promote differences among biotas. The chapter also examines provincialism, the quantification of similarity among biotas, and biotic interchange.
