Paleontologists discovered 35 exceptionally preserved fossils of Waukartus muscularis, an aquatic arthropod from 437 million years ago in Wisconsin's Silurian Brandon Bridge Formation. This stem-myriapod had a long segmented body, at least 11 leg sets, and unbranched uniramous limbs,traits typical of land arthropods like centipedes and millipedes. The find challenges prior views, showing these legs evolved underwater via exaptation, with exopods lost before terrestrialization, preserved in Waukesha Lagerstätte mudstones.