West Coast US Prehistoric Life Forms

 what kinds of prehistoric animals lived on the western coast of the United States from Washington State to California 25 million years ago?

25 million years ago, during the 
Late Oligocene, the West Coast was a transition zone between ancient and modern ecosystems. Much of what is now coastal Washington, Oregon, and California was submerged under a shallow sea or consisted of lush, temperate coastal plains.
Marine Animals
The Pacific Ocean was home to unique "transitional" species that bridge the gap between ancient ancestors and modern marine life.
  • Toothed Baleen Whales
     (
    Aetiocetus
    ):     One of the most significant finds from this period, particularly in Oregon and Washington. These 25-million-year-old whale ancestors possessed both fully developed teeth and baleen plates, allowing them to eat both fish and plankton.
  • Primitive Seals
     and 
    Sea Lions
    :     Early pinnipeds were beginning to diversify along the coast of Oregon and California.
  • Ancient Sharks
    :     While the famous 
    Megalodon
     appeared slightly later, smaller ancestral sharks and various 
    bony fish
     were abundant in the coastal waters    .
  • Invertebrates
    :     The seafloor was teeming with 
    giant bivalves
     (
    clams
     and 
    mussels
    ), 
    snails
    , and 
    crabs
    . Fossils of these are frequently found today in the     Yaquina Formation (Oregon) and Pysht Formation (Washington).
Terrestrial Animals
On land, the landscape was dominated by early versions of familiar mammals and several strange, extinct lineages.
  • Nimravids
    :     These were "false" saber-toothed cats. Footprints and fossils from the John Day Fossil Beds in Oregon suggest these bobcat-sized predators prowled the volcanic landscapes.
  • Early 
    Canids
     (Dog-like creatures):     Fossils and tracks of small, fox-like carnivorous mammals weighing about 10–12 pounds have been found in Southern California (Vasquez Rocks), representing some of the earliest relatives of modern dogs.
  • Ancient Ungulates: 
    Primitive three-toed horses
    , tiny squirrel-sized beaver ancestors (
    Microtheriomys
    ), and ancestors of 
    tapirs
     and 
    rhinoceroses
     roamed the inland forests and plains    .
  • Oreodonts
    :     These were "ruminating hogs"—sheep-sized herbivores that were once incredibly common across the western U.S. during this era.

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