401-380 million years ago
Lots going on in the Devonian
Forests are spreading. The first tree, Wattieza, is kin to ferns and horsetails. It stands 10 meters tall. No leaves yet, just fronds. The first forests will absorb carbon dioxide, and cool the planet.
Life is moving onto land. Tiktaaklik roseae, the “fishapod” discovered in 2006, is as nice a link between fish and amphibians as one could hope for, with both lungs and gills. Here’s a book by Neil Shubin, the co-discoverer.
You can see a lot further in the air than underwater. This may be one of the early selective pressures for evolving a proper neck and sticking one’s head out of water. Eventually, for some, the rest of the body would follow.
And evolution seems to be generally speeded up on land. It’s not just that animals and plants develop adaptations for life on land (obviously). But there is also a more general acceleration in the pace of evolution. Major innovations come at a faster pace among terrestrial organisms.