Chapter objectives Learn basic relationships among tetrapods – particularly amniotes Understand s... more Chapter objectives Learn basic relationships among tetrapods – particularly amniotes Understand something about the course of tetrapod evolution Learn who dinosaurs are (and are not) Become familiar with the characters that diagnose Dinosauria Finding the history of life In the preceding chapter, we explored the methods that scientists use to learn the identity and origin of all organisms. Now we will apply those techniques – diagnostic characters hierarchically distributed on cladograms – to properly position dinosaurs within the biota. The history of life will unfold as we systematically encounter each bifurcation in the cladistic road, reconstructing the path of evolution until we reach Dinosauria. We will be looking at increasingly small subgroups, each characterized by a suite of diagnostic characters. The appearance of each of those suites of diagnostic characters represents new features, forged by evolutionary processes. We'll go with Glinda the Good Witch's suggestion that “it's always best to start at the beginning.” In the beginning Modern life is generally understood to be monophyletic. It's united by the possession of RNA, DNA, cell membranes with distinctive chemical structure, a variety of amino acids (proteins), the metabolic pathways (that is, chemical reaction steps) for their processing, and the ability to replicate itself (not simply grow). Notice we said “modern” life – for who knows how many forms of molecular life arose, proliferated, and died out very early in Earth's history – before the thing that we now call “life” finally prevailed?
The Paleontological Society Special Publications, 1992
Coevolutionary links between plants and herbivores, often cited as examples of adaptive response ... more Coevolutionary links between plants and herbivores, often cited as examples of adaptive response of one group of organisms to another, have been much studied from both neontological and paleontological perspectives. The most commonly cited case of coevolution from the latter viewpoint is the radiation of grassland grasses and grazing mammals during the mid-Tertiary. Other promising examples are also beginning to emerge, among them the radiation of ornithischian dinosaurs and early angiosperms during the Cretaceous.Preliminary studies (Weishampel and Norman 1989) analyzed the temporal distribution of trophic groups among Ornithischia (and other herbivorous tetrapods) across the Mesozoic. Trophic groups were based on a mixture of monophyletic and paraphyletic taxa assigned to assorted taxonomic rank. Speciation, extinction, and turn-over rates were calculated from stratigraphic data to identify co-evolutionary “hot spots” between herbivores and contemporary plants: times of evolutiona...
Chapter objectives Learn basic relationships among tetrapods – particularly amniotes Understand s... more Chapter objectives Learn basic relationships among tetrapods – particularly amniotes Understand something about the course of tetrapod evolution Learn who dinosaurs are (and are not) Become familiar with the characters that diagnose Dinosauria Finding the history of life In the preceding chapter, we explored the methods that scientists use to learn the identity and origin of all organisms. Now we will apply those techniques – diagnostic characters hierarchically distributed on cladograms – to properly position dinosaurs within the biota. The history of life will unfold as we systematically encounter each bifurcation in the cladistic road, reconstructing the path of evolution until we reach Dinosauria. We will be looking at increasingly small subgroups, each characterized by a suite of diagnostic characters. The appearance of each of those suites of diagnostic characters represents new features, forged by evolutionary processes. We'll go with Glinda the Good Witch's suggestion that “it's always best to start at the beginning.” In the beginning Modern life is generally understood to be monophyletic. It's united by the possession of RNA, DNA, cell membranes with distinctive chemical structure, a variety of amino acids (proteins), the metabolic pathways (that is, chemical reaction steps) for their processing, and the ability to replicate itself (not simply grow). Notice we said “modern” life – for who knows how many forms of molecular life arose, proliferated, and died out very early in Earth's history – before the thing that we now call “life” finally prevailed?
The Paleontological Society Special Publications, 1992
Coevolutionary links between plants and herbivores, often cited as examples of adaptive response ... more Coevolutionary links between plants and herbivores, often cited as examples of adaptive response of one group of organisms to another, have been much studied from both neontological and paleontological perspectives. The most commonly cited case of coevolution from the latter viewpoint is the radiation of grassland grasses and grazing mammals during the mid-Tertiary. Other promising examples are also beginning to emerge, among them the radiation of ornithischian dinosaurs and early angiosperms during the Cretaceous.Preliminary studies (Weishampel and Norman 1989) analyzed the temporal distribution of trophic groups among Ornithischia (and other herbivorous tetrapods) across the Mesozoic. Trophic groups were based on a mixture of monophyletic and paraphyletic taxa assigned to assorted taxonomic rank. Speciation, extinction, and turn-over rates were calculated from stratigraphic data to identify co-evolutionary “hot spots” between herbivores and contemporary plants: times of evolutiona...
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