Macroevolution: Processes of Vertebrate and Mammalian Evolution

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Chapter 5

• Macroevolution Processes of Vertebrate and
  Mammalian Evolution

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Chapter Outline

• The Human Place in the Organic World
• Principles of Classification
• Definition of Species
• Vertebrate Evolutionary History A Brief Summary

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Chapter Outline

• Mammalian Evolution
• The Emergence of Major Mammalian Groups
• Processes of Macroevolution

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Classification

• Classification is used to order organisms into
  categories to show evolutionary relationships.
• Example - human classification
• Kingdom Animalia
• Subkingdom Metazoan
• Phyla Chordata
• Subphyla Vertebrata
• Class Mammalia

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Classification Definitions

• Metazoa
• Multicellular animals.
• Chordata
• The phylum of the animal kingdom that includes
  vertebrates.
• Vertebrates
• Animals with segmented bony spinal columns
  includes fishes, amphibians, reptiles, birds, and
  mammals.

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Principles of Classification

• The field that specializes in establishing the
  rules of classification is called taxonomy.
• Organisms are classified first on the basis of
  physical similarities.
• Basic physical similarities must reflect
  evolutionary descent in order for them to be
  useful.

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Principles of Classification

• Homologies
• Similarities based on descent from a common
  ancestor.
• Analogies
• Similarities based on common function, with no
  assumed common evolutionary descent.
• Homoplasy
• The separate evolutionary development of similar
  characteristics in different groups of organisms.

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Homologies
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Two Approaches to Classification

• Evolutionary systematics
• A traditional approach in which presumed
  ancestors and descendants are traced in time by
  analysis of homologous characters.
• Cladistics
• Attempts to make rigorous evolutionary
  interpretations based solely on analysis of
  certain types of homologous characters.

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Ancestral and Modified Characters

• Ancestral characters
• Refers to characters inherited by a group of
  organisms from a remote ancestor and thus not
  diagnostic of groups (lineages) that diverged
  after the character first appeared.
• Derived characters
• Refers to characters that are modified from the
  ancestral condition and thus are diagnostic of
  particular evolutionary lineages.

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Approaches to Classification
Evolutionary Systematics Cladistics
Goal Construction of a phylogenetic tree Construction of a cladogram
Similarities Compare specific traits Construct classifications to show evolutionary relationships Focus on homologies Compare specific traits Construct classifications to show evolutionary relationships Focus on homologies
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Approaches to Classification
Evolutionary Systematics Cladistics
Differences Might use any homologous character Attempts to make ancestor-descendant links Attempts to place fossils in a chronological framework Use only explicitly defined derived characters No attempt is made to make conclusions regarding ancestor-descendant relationships All members of an evolutionary group are interpreted in one dimension
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Definition of Species

• Biological species concept
• Depiction of species as groups of individuals
  capable of interbreeding, but reproductively
  isolated from other such groups.
• Speciation
• Process by which a new species evolves from a
  prior species.
• Speciation is the most basic process in
  macroevolution.

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Speciation Model
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Recognition of Fossil Species

• The minimum biological category we would like to
  define in fossil primate samples is the species.
• Variations
• Intraspecific - Variation is accounted for by
  individual, age, and sex differences seen within
  every biological species
• Interspecific - Variation represents differences
  between reproductively isolated groups.

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Recognition of Fossil Species

• Defining where species boundaries begin and end
  is often difficult.
• Splitters are researchers who claim speciation
  occurred frequently during hominid evolution.
• Lumpers assume speciation was less common and
  see much variation as being intraspecific.

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Recognition of Fossil Genera

• A genus is a group of species composed of members
  more closely related to each other than to
  species from any other genus.
• Species that are members of the same genus share
  the same broad adaptive zone.
• Members of the same genus should all share
  derived characters not seen in members of other
  genera.

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Geological Time Scale
ERA PERIOD Began m.y.a. EPOCH Began m.y.a.
CENOZOIC Tertiary 1.8 Holocene Pleistocene 0.01 1.8
CENOZOIC Quaternary 65 Pliocene Miocene Oligocene Eocene Paleocene 5 23 34 55 65
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Geological Time Scale
ERA PERIOD (Began m.y.a.)
MESOZOIC Cretaceous 136
MESOZOIC Jurassic 190
MESOZOIC Triassic 225
PALEOZOIC Permian Carboniferous Devonian Silurian Ordovician Cambrian 280 345 395 430 500 570
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Geological Eras

• Paleozoic
• The first vertebrates appeared 500 m.m.y.a.
• Mesozoic
• Reptiles were dominant land vertebrates.
• Placental mammals appeared 70 m.Y.A.
• Cenozoic
• Divided into two periods Tertiary and Quaternary
  and 7 epochs Paleocene, Eocene, Oligocene,
  Miocene, Pliocene, Pleistocene and Holocene.

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Continental Drift

• The movement of continents on sliding plates of
  the earths surface.
• As a result, the positions of large landmasses
  have shifted drastically during the earths
  history.

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Continental drift

• The positions of the continents during the
  Mesozoic (c. 125 m.y.a.).
• Pangea is breaking up into a northern landmass
  (Laurasia) and a southern landmass (Gondwanaland).

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Continental drift

• The positions of the continents at the beginning
  of the Cenozoic (c. 65 m.y.a.).

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Ecological Niches

• The positions of species within their physical
  and biological environments, together making up
  the ecosystem.
• A species ecological niche is defined by such
  components as diet, terrain, vegetation, type of
  predators, relationships with other species, and
  activity patterns, and each niche is unique to a
  given species.

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Epochs

• Categories of the geological time scale.
• In the Cenozoic, epochs include
• Paleocene
• Eocene
• Oligocene
• Miocene
• Pliocene
• Pleistocene
• Holocene

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Mammalian Evolution

• The Cenozoic era is known as the Age of Mammals.
• After dinosaurs became extinct, mammals underwent
  adaptive radiation, resulting in rapid expansion
  and diversification.
• The neocortex, which controls higher brain
  functions, comprised the majority of brain
  volume, resulting in greater ability to learn.

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Lateral View of the Brain
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Reptilian and Mammalian teeth

• Mammals are heterodont, they have different kinds
  of teeth incisors, canines, premolars, and
  molars.

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Adaptive Radiation

• A process that takes place when a life form
  rapidly takes advantage of the many newly
  available ecological niches.
• A species, or group of species, will diverge into
  as many variations as two factors allow
• Its adaptive potential.
• The adaptive opportunities of the available
  niches.

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Major Mammalian Groups

• Monotremes
• Primitive, egg laying mammals
• Marsupials
• Infants complete development in an eternal pouch
• Placental
• Longer gestation allows the central nervous
  system to develop more completely

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Quick Quiz
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• 1. The scientific discipline that delineates the
  rules of classification is
• paleontology.
• stratigraphy.
• homology.
• taxonomy.

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Answer d

• The scientific discipline that delineates the
  rules of classification is taxonomy.

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• 2. An advantage of heterodont dentition is that
  it
• allows the animal to defend itself more
  efficiently.
• allows for processing a wide variety of foods.
• opens up new ways of interacting with potential
  mates.
• allows the animal to grab prey that it could not
  catch otherwise.

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Answer b

• An advantage of heterodont dentition is that it
  allows for processing a wide variety of foods.

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• 3. The group of mammals that reproduce by laying
  eggs and who generally have more primitive traits
  than the other mammals are the
• monotremes.
• metatherians.
• marsupials.
• placentals.

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Answer a

• The group of mammals that reproduce by laying
  eggs and who generally have more primitive traits
  than the other mammals are the monotremes.

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• 4. The divergence of reptiles into many different
  forms describes
• analogies.
• sexual selection.
• adaptive radiation.
• homologies.

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Answer c

• The divergence of reptiles into many different
  forms describes adaptive radiation.