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Evolution of the Tree Squirrel

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Squirrels

Currently:

  • 51 Genre
  • 285 species
  • Evolved ~33 million years ago
  • Live on 6 continents

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Squirrel Taxonomy

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Mammalia
  • Order: Rodentia
  • Family: Sciuridae
  • Genus: Sciurus
  • Species: …

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Tree Squirrels

  • Lives in trees
  • Eat mostly nuts & seeds
    • Some insects
  • Evolved 33.7 million years ago
    • Fossil evidence

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Rugosodon eurasiaticus

  • 160 million years ago
  • Liaoning province, China
  • Omnivore
  • Comparative Anatomy: specialized ankle bone
    • Allowed animal wide range of motion
    • Lived in trees

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Jurassic

  • Warm & humid – tropical
    • Forests & jungles
  • Pangea breaking up
    • Laurasia
    • Gondwanaland
  • Atlantic ocean forms & gets bigger

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Protungulatum donnae

  • 66 million years ago
  • Montana & Saskatchewan, North America
  • Omnivore
  • Had a placenta and live birth

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Paleogene

  • After Cretaceous–Paleogene extinction event
  • Continents separated
  • Warming period with jungles reaching poles

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Douglassciurus Jeffersoni

  • 36 million years ago
  • Western North America
  • Very Similar to modern squirrels

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Eocene Epoch

  • Development of world-wide ocean currents
  • Cooling climate
  • Dominance of evergreen forests
  • Continents separated

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Speciation

  • Tracked squirrel migration using “molecular clock” techniques

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30 million years ago

  • Laurasia still connected
  • Squirrels migrate to Europe

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20 million years ago

  • Africa crashes into Europe
  • Squirrels migrate to Africa

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11 million years ago

  • Sea levels drop
  • Squirrels migrate to Southeast Asian islands

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7 million years ago

  • Land bridge between Siberia & Alaska
  • Squirrels migrate to Siberia

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3 million years ago

  • Volcanos form Panama and link North & South America
  • Squirrels migrate to South America

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Future of Squirrels

  • Not much change in the near future
  • Less tree squirrels with more deforestation
  • May adapt to spending more time on the ground