From fins to legs
375 million years ago
With plants well-established on land, the next step was for animals to move out of the water. Insects were among the first, around 400 million years ago. But they were followed soon after by big, backboned animals such as Tiktaalik, a fish that looked a bit like a salamander. Fish like Tiktaalik would eventually evolve four limbs, and give rise to amphibians, reptiles and mammals. It may be a good thing it left the water when it did, as soon afterwards the Late Devonian Extinction wiped out many marine animals, including some terrifying-looking armoured fish.
See other: History of Life
Knowledge Guild 
And millions of more years later, some would decide that life on the land wasn’t all it was cracked up to be and returned to the sea, such as the dolphin —