When a long string of misidentifications ended over a century ago, a fossil housed in Harvard’s Museum of Comparative Zoology—long overlooked by experts—was revealed by a PhD candidate to be a missing piece in the evolutionary puzzle.
The discovery, detailed in a new paper published in Communications Biology, reveals that a fossilized creature, Palaeocampa anthrax, was first catalogued as a caterpillar in 1865, then reclassified several times over the following decades—first as a worm, then a millipede, and finally as a marine polychaete.
Now, in work led by Richard Knecht, a recent PhD graduate currently at the University of Michigan but a candidate at Harvard at the time of the research, Palaeocampa anthrax is revealed as the first known example of a non-marine lobopodian, indicating how the evolutionary tree that produced insects moved on from deep water environments.
Lobopodians
The group to which the creature belongs—lobopodians—is now extinct, but once served as an evolutionary bridge between modern arthropods, such as insects and crustaceans, and their primitive, worm-like ancestors. While other lobopodians have been discovered, such as Hallucigenia and Aysheaia pedunculata from the Cambrian Burgess Shale in Canada, all previously known examples have been marine species.
Notably, Palaeocampa anthrax was discovered almost 50 years before the Burgess Shale lobopodians, but is geologically much younger.
“Lobopodians were likely a common sight on Paleozoic sea beds,” said Knecht, “but apart from microscopic tardigrades and terrestrial velvet worms, we thought they were confined to the ocean.”
Knecht uncovered the Palaeocampa’s significance as he examined the millipede fossils in the Museum of Comparative Zoology collection. Pouring over the strange fossil, he recognized that legs protruded from every trunk, a feature that excluded identification as a caterpillar or worm. At that time, Knecht realized the specimen was a lobopodian.
Investigating the Fossil
To confirm the identification, Knecht assembled a team to analyze 43 fossil specimens from two Carboniferous Lagerstätten—Mazon Creek in the United States and Montceau-les-Mines in France. Specimens were sourced from institutions including the Yale Peabody Museum, the Smithsonian National Museum of Natural History, France’s Muséum d’Histoire Naturelle d’Autun, the Chicago Field Museum, and the University of Illinois at Urbana-Champaign.
The researchers employed advanced imaging techniques, including backscatter scanning electron microscopy (SEM) and energy-dispersive spectroscopy, to examine fine anatomical features with precision.
A key discovery during this analysis was the presence of nearly 1,000 bristly spines covering the fossil’s body. Further research by co-author Nanfang Yu, associate professor of physics at Columbia University, revealed that the spines were capable of secreting toxins to deter predators.
“What amazed me is that fragments of biomacromolecules could be exceptionally preserved or altered to geomacromolecules in fossils,” Yu said. “ I’m thrilled this technique possessed the sensitivity and specificity to differentiate fossilized remains from the rocky substrate.”
Evolutionary Connections
The closest relative identified by Knecht’s team was the Cambrian lobopodian Hadranax. Although Hadranax predates Palaeocampa by 200 million years, the two share many similarities—including blindness, a lack of claws, and ten pairs of legs. However, Palaeocampa exhibits signs of adaptation to freshwater and possibly amphibious environments, characterized by a dense array of protective spines above its legs, in contrast to the unarmored, deep-sea-dwelling Hadranax, which utilizes long frontal appendages to navigate its habitat.
The team’s work also redefines the Montceau-les-Mines fossil site, which was previously believed to represent a marine environment. Their findings suggest that it was, in fact, a rare ancient freshwater ecosystem.
“Mazon Creek is a mix of terrestrial, freshwater, and marine animals,” Knecht explained. “But, Montceau-les-Mines, where half of the specimens come from, was hundreds of kilometers inland, with no ocean present.”
This discovery reopens the question of what evolutionary secrets may be awaiting discovery, long forgotten in museum collections.
“The conditions required to fossilize soft-bodied creatures like lobopodians are rare,” Knecht noted. “Most of our insights come from Cambrian Lagerstätten, but the Carboniferous period—when Palaeocampa lived—offers far fewer such windows, making every new find incredibly valuable.”
“It was literally hiding in plain sight,” Knecht concluded. “Sometimes, the biggest discoveries are the ones waiting to be looked at again.”
The paper ”Palaeocampa Anthrax, an Armored Freshwater Lobopodian with Chemical Defenses from the Carboniferous” appeared on July 23, 2025, in Communications Biology.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.