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Reconstruction of Waukartus muscularis. The myriapod is shown turning and employing a slow gait (i.e. only the appendages in the mid part of the trunk are in the recovery stroke and not in contact with the substrate). The short anterior pairs of head appendages are not involved in walking, and their structure is unknown. The exoskeleton is not preserved, but is assumed to have been smooth. (Illustration by Leia Francis). Credit: Proceedings of the Royal Society B: Biological Sciences (2026). DOI: 10.1098/rspb.2026.0131
The myriapoda group of arthropods includes the many-legged centipedes and millipedes that most people are familiar with. Although myriapods are all terrestrial creatures, researchers are unclear about when and how they evolved their many legs.
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.
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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.
Waukartus muscularis. (A–E) Holotype, UWGM 7595a,b part and counterpart. Credit: Proceedings of the Royal Society B: Biological Sciences (2026). DOI: 10.1098/rspb.2026.0131
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.
"The head appendages of Waukartus appear to resemble those of the trunk, but details are not preserved. Their shorter length may indicate that they were not involved in walking but specialized for sensory or feeding functions, but the mode of feeding is unknown. The trunk of Waukartus was flexible as evidenced by curved specimens and variation in the nature of the overlap between successive segments," the study authors write.
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