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Replying to Eloi in post #1]
Have you ever looked at a dolphin and whales arms? They look like flippers, right? Look at the skeleton. They have all the same bones as us landwalkers have, scapula, collarbone, humorous, ulna, phalanges, etc.
Dolphin skeleton
two whales two sharks.
Can you tell which ones are the whales? You should be able to if you know what a scapular and phalanges (finger bones) look like. They are mammals of the sea like seals and otters.
Seals have flippers, but you can see the fingers a bit -
Now look at the seal skeleton -
Seals retain their hip bone, tibia, fibula, etc.
Is it that far-fetched to think that the reason dolphins and whales have ALL the same bones land walking mammals have is because they used to be a land walker?
So sharks are fish. Is this a fish or a mammal?
And its skeleton
It doesn't seem far out to me that land walking mammals evolved into sea-dwelling mammals.