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Chapter 25- Phylogenies and the History of Life

25.1 Tools for Studying Life’s History: Phylogenetic Trees

  • The branching evolutionary history of species or other groups of organisms is called a phylogeny.

  • A phylogenetic tree is a simplified diagram of this history.

  • Systematics is the discipline of biology that characterizes and classifies the relationships among all organisms on Earth.

  • The tree of life is the most universal of all phylogenetic trees.

  • Sister groups are two descendants that split from the same node and therefore are each other’ s closest relatives.

  • A useful character, or trait, is any heritable genetic, morphological, physiological, developmental, or behavioral characteristic that varies among the taxa to be studied.

  • Outgroup is a taxon that is not part of the taxonomic group being studied but is closely related.

  • An ancestral trait is a character that existed in an ancestor.

  • A derived trait is one that is a modified form of the ancestral trait, found in a descendant.

  • A synapomorphy is a trait found in two or more taxa that is present in their most recent common ancestor but is missing in more distant ancestors.

  • Synapomorphies are important because they allow biologists to recognize monophyletic groups-also called clades or lineages.

  • A monophyletic group is an evolutionary unit that includes an ancestral species and all of its descendants, but no others.

  • Convergent evolution is the independent evolution of similar traits in distantly related organisms due to adaptation to similar environments and lifestyles.

25.2 Tools for Studying Life’s History: The Fossil Record

  • Paleontologists are scientists who study fossils, pieces of physical evidence from an organism that lived in the past.

  • The fossil record is the total collection of fossils that paleontologists and amateur collectors have found throughout the world and archived in thousands of private and public collections.

  • The Paleozoic (“ancient life”) era begins with the appearance of most major animal lineages and ends with the obliteration of almost all multicellular life-forms at the end of the Permian period.

  • The Mesozoic (“middle life”) era begins with the end-Permian extinction events and ends with the extinction of the dinosaurs ( except birds) and other groups at the boundary between the Cretaceous period and Paleogene period.

  • The Cenozoic (“recent life”) era is divided into the Paleogene, Neogene, and Quaternary periods.

25.3 Large-Scale Pattern in Life’s History: Adaptive Radiation

  • When a single lineage rapidly produces mαny descendant species with a wide range of adaptive forms, biologists say that an adaptive radiation has occurred.

25.4 Large-Scale Pattern in Life’s History: Mass Extinction

  • A mass extinction refers to the rapid extinction of a large number of diverse species around the world.

  • Background extinction refers to the lower, average rate of extinction observed when a mass extinction is not occurring

  • Some researchers estimate that the current extinction rate is 100 or even 1000 times higher than the background extinction rate

Chapter 25- Phylogenies and the History of Life

25.1 Tools for Studying Life’s History: Phylogenetic Trees

  • The branching evolutionary history of species or other groups of organisms is called a phylogeny.

  • A phylogenetic tree is a simplified diagram of this history.

  • Systematics is the discipline of biology that characterizes and classifies the relationships among all organisms on Earth.

  • The tree of life is the most universal of all phylogenetic trees.

  • Sister groups are two descendants that split from the same node and therefore are each other’ s closest relatives.

  • A useful character, or trait, is any heritable genetic, morphological, physiological, developmental, or behavioral characteristic that varies among the taxa to be studied.

  • Outgroup is a taxon that is not part of the taxonomic group being studied but is closely related.

  • An ancestral trait is a character that existed in an ancestor.

  • A derived trait is one that is a modified form of the ancestral trait, found in a descendant.

  • A synapomorphy is a trait found in two or more taxa that is present in their most recent common ancestor but is missing in more distant ancestors.

  • Synapomorphies are important because they allow biologists to recognize monophyletic groups-also called clades or lineages.

  • A monophyletic group is an evolutionary unit that includes an ancestral species and all of its descendants, but no others.

  • Convergent evolution is the independent evolution of similar traits in distantly related organisms due to adaptation to similar environments and lifestyles.

25.2 Tools for Studying Life’s History: The Fossil Record

  • Paleontologists are scientists who study fossils, pieces of physical evidence from an organism that lived in the past.

  • The fossil record is the total collection of fossils that paleontologists and amateur collectors have found throughout the world and archived in thousands of private and public collections.

  • The Paleozoic (“ancient life”) era begins with the appearance of most major animal lineages and ends with the obliteration of almost all multicellular life-forms at the end of the Permian period.

  • The Mesozoic (“middle life”) era begins with the end-Permian extinction events and ends with the extinction of the dinosaurs ( except birds) and other groups at the boundary between the Cretaceous period and Paleogene period.

  • The Cenozoic (“recent life”) era is divided into the Paleogene, Neogene, and Quaternary periods.

25.3 Large-Scale Pattern in Life’s History: Adaptive Radiation

  • When a single lineage rapidly produces mαny descendant species with a wide range of adaptive forms, biologists say that an adaptive radiation has occurred.

25.4 Large-Scale Pattern in Life’s History: Mass Extinction

  • A mass extinction refers to the rapid extinction of a large number of diverse species around the world.

  • Background extinction refers to the lower, average rate of extinction observed when a mass extinction is not occurring

  • Some researchers estimate that the current extinction rate is 100 or even 1000 times higher than the background extinction rate