A worm-like creature from 518 million years ago evolved to lose its back legs, the earliest known example of an animal losing body parts it no longer needed
Source:
https://www.newscientist.com/article/2235594-weird-worm-is-earliest-known-animal-to-evolve-away-body-parts/?utm_campaign=RSS%7CNSNS&utm_source=NSNS&utm_medium=RSS&utm_content=home