Now, fossils found in the Silurian Brandon Bridge Formation in Waukesha, Wisconsin have revealed that a long-lost ancestor of myriapods already had many unbranched legs while still living underwater. The finding, described in a new study published in Proceedings of the Royal Society B: Biological Sciences, contradicts the idea that this particular type of limb was an adaptation for land.

Waukesha fossils reveal a new aquatic arthropod

Paleontologists discovered 35 fossils of a myriapod-like arthropod in Waukesha's Silurian Brandon Bridge Formation dating from around 437 million years ago. The Silurian Brandon Bridge Formation is a geological formation known as the Waukesha Lagerstätte—an exceptional deposit of soft-bodied fossils from the Llandovery epoch. The area's finely laminated dolomitic mudstones preserve a diverse, shallow marine community, including early arthropods.

The new arthropod, called Waukartus muscularis, resembles modern myriapods with a head and long segmented body featuring many sets of legs. Many of the fossils were well-preserved, with evidence of uniramous, or single-branched, limbs, muscle tissue, and a cuticular endoskeleton. Although some specimens were incomplete, the research team says that among the fossils there is no evidence for less than 11 segments in Waukartus muscularis. They say it also features multiple "head appendages," which increase in size toward the rear of the head.