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Evolution of Freshwater Fishes
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Timescale of Earth

A. Paleozoic Era
  1. Precambrian Period = 4.6 billion years ago, lasted 4 billion years = algae and bacteria in warm waters
  2. Cambrian Period = 570 million years ago, lasted 70 million years = all life in seas, invertebrates begin (no backbone)
  3. Ordovician Period = 500 million years ago, lasted 60 million years = corals, first vertebrates, all life is in seas
  4. Silurian Period = 440 million years ago, lasted 45 million years = jawed fishes, first land plants, seaweed is abundant
  5. Devonian Period = 395 million years ago, lasted 50 million years = many fish, ancestors of modern fish evolve, first amphibians
  6. Carboniferous Period = 345 million years ago, lasted 65 million years = reptiles, insects and ferns appear
  7. Permian Period = 280 million years ago, lasted 55 million years = modern insects, much sea and freshwater life

B. Mesozoic Era
  1. Triassic Period = 225 million years ago, lasted 30 million years = many deserts, first mammals, many reptiles, early dinosaurs
  2. Jurassic Era = 195 million years ago, lasted 60 million years = first birds, many reptiles, many coniferous forests
  3. Cretaceous Period = 135 million years ago, lasted 70 million years = fishes evolve, many mammals and birds, reptiles dominate, flowering plants appear

C. Cenozoic Era
  1. Tertiary Period = 65 million years ago, lasted 63 million years = Flowering plants are numerous, whales adjust to marine life, Primates and hoofed mammals appear, teleost fish are dominant
  2. Quaternary Period = 2 million years ago, lasted to today = Modern man develops, marine life becomes what it is today

Sources:
"SeaLife" A Complete Guide to the Marine Environment, edited by Geoffrey Waller, Principal Contributors - Marc Dando and Michael Burchett "World Book Encyclopedia" by World Book, Inc. 1990


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