When humans first arrived to the Nether, they could not survive. They exported some mushrooms, followed by farm animals & slimes. One of animals they exported where the chickens, they were exported for food & arrows.
By the extreme temperature & radiation of the Nether the chickens evolved into a more big & fat, featherless poultry, the Bronce-Legged Poultry, that would later evolve in wath we know as a Strider.
Its name comes from the fact that its legs are pretty strong.
Some chickens did not evolve & where used by piglins that are now zombified.

This isn't as prehistoric as other submissions but in my mind the Nether wasn't habitable before the humans terraformed.

This might become a series of the ancestors of the inhabitants of the Nether.

Hope you liked it! :D

Give credit if used.