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Unformatted text preview: PHYLOGENY AND PHYLOGENY SYSTEMATICS Chapter 25 Sedimentary rocks are the richest source of fossils of Fossils are the preserved remnants or impressions left by Fossils organisms that lived in the past. Sedimentary rocks form from layers of sand and silt that are Sedimentary carried by rivers to seas and swamps, where the minerals settle to the bottom along with the remains of organisms. The fossil record is the ordered array in which fossils appear The within sedimentary rock strata. Fossils can be used to construct phylogenies only if we can Fossils determine their ages. The fossil record is a substantial, but incomplete, chronicle of The evolutionary change. Fossils Morphological and molecular similarities may provide clues to phylogeny may Similarities due to shared ancestry are called Similarities homologies. Organisms that share similar morphologies or DNA Organisms sequences are likely to be more closely related than organisms without such similarities. Similarity due to convergent evolution is called analogy. Similarity When two organisms from different evolutionary When lineages experience similar environmental pressures, natural selection may result in convergent evolution. Homology vs. Analogy For example, both birds and bats have adaptations that For allow them to fly. However, a close examination of a bat’s wing shows a However, greater similarity to a cat’s forelimb that to a bird’s wing. Fossil evidence also documents that bat and bird wings Fossil arose independently from walking forelimbs of different ancestors. Thus a bat’s wing is homologous to other mammalian Thus forelimbs but is analogous in function to a bird’s wing. Dating Fossils Dating Relative Dating estimates the order of prehistoric and geological events were determined by using basic stratigraphic rules, and by observing where fossil organisms lay in the geological record, stratified bands of rocks present throughout the world. Absolute Dating is the process of determining a specific date for an archaeological or palaeontological site or artifact. The Geologic Time Scale Taxonomy employs a hierarchical system of classification of Under the binomial system, each species is assigned a Under two-part Latinized name, a binomial. The first part, the genus, is the closest group to which a The species belongs. The second part, the specific epithet, refers to one The species within each genus. The first letter of the genus is capitalized and both The names are italicized and Latinized. For example, Linnaeus assigned to humans the For optimistic scientific name Homo sapiens, which means “wise man.” Taxonomy contd. Taxonomy A hierarchical classification groups species into increasingly broad hierarchical taxonomic categories. Species to Genus to Family to Order to Class to Phylum to Species Kingdom to Domain. Kingdom Classification and phylogeny are linked Classification Systematists explore phylogeny by examining various Systematists characteristics in living and fossil organisms. They construct branching diagrams called phylogenetic They trees to depict their hypotheses about evolutionary relationships. The branching of the tree reflects the hierarchical The classification of groups nested within more inclusive groups. Methods for tracing phylogeny began with Darwin, who Methods realized the evolutionary implications of Linnaean hierarchy. Darwin introduced phylogenetic systematics in On the Darwin Origin of Species when he wrote: “Our classifications will come to be, as far as they can be so made, genealogies.” Molecular clocks help track evolutionary time time Molecular clocks serve as yardsticks for measuring the Molecular absolute time of evolutionary change. They are based on the observation that some regions They of the genome evolve at constant rates. For these regions, the number of nucleotide For substitutions in orthologous genes is proportional to the time that has elapsed since the two species last shared a common ancestor. In the case of paralogous genes, the number of In substitutions is proportional to the time since the genes became duplicated. ...
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This note was uploaded on 12/02/2009 for the course SCI 90210 taught by Professor Durkka during the Spring '09 term at École Normale Supérieure.

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