Long before vertebrates walked on land, millipedes had the place to themselves.
Hundreds of millions of years before dinosaurs arrived, these early decomposers were helping establish Earth's terrestrial ecosystems. But despite their ancient history, scientists still hadn't fully unraveled their evolutionary story.
Now, a Virginia Tech-led team of international scientists has solved one of the last major mysteries in millipede evolution, revealing new clues about a group of animals that helped pave the way for life on land.
The findings , published in Current Biology, complete the first evolutionary history of all living millipede orders. By combining genomic data from living species with morphological evidence from fossils, researchers traced the group's origins to nearly 460 million years ago — suggesting millipedes may have been present long before the oldest known millipede fossils.
"Millipedes beat vertebrates onto land by more than 80 million years," said Paul Marek , the study's lead investigator and associate professor in the College of Agriculture and Life Sciences' Department of Entomology . "They really set the stage for later life on land, including humans and vertebrates."
Reconstructing the missing pieces
For more than a century, scientists knew that two rare groups of millipedes — Siphoniulida and Siphonocryptida — existed, but without fresh specimens for DNA analysis, they couldn't confirm where they belonged in the millipede family tree.
One of the groups includes millipedes barely a centimeter long that spend their entire lives underground. The other survives in just a few known locations.
"These last two were kind of like our white whales," Marek said.
Researchers traveled to Los Tuxtlas, Mexico, and Spain's Canary Islands to collect Siphoniulus neotropicus and Hirudicryptus canariensis, two millipedes whose DNA had never been included in an evolutionary analysis.
"It took 10 people over a week just to find this one tiny 10-millimeter adult," said Luisa "Fernanda" Vasquez-Valverde M.S. '21, Ph.D. '24, the paper's first author and an assistant in Marek's lab. "Finding them in the field was hard because we were just seeing this little white nematode. We didn't know for sure it was a millipede until we looked under the microscope."
By sequencing DNA from the two groups, comparing hundreds of genes across 82 millipede species, and combining those results with evidence from 29 fossils, researchers were able to determine where the groups fit in millipede history and when their lineages emerged. The effort generated terabytes of genetic data and relied on Virginia Tech's Advanced Research Computing resources to reconstruct relationships stretching back hundreds of millions of years.
One group, Siphonocryptida, turned out not to be a distinct order after all, but part of an existing lineage. The other, Siphoniulida, was finally placed among its closest relatives on the millipede evolution timeline.
Colonizing an alien Earth
The analysis revealed that millipedes may have originated nearly 460 million years ago — roughly 35 million years before the oldest known millipede fossils and much earlier than previously believed.
"The biggest surprise was just how ancient some of these lineages turned out to be," Marek said.
Back then, life on Earth looked dramatically different. Marek said millipedes helped pioneer life on land by breaking down organic material and recycling nutrients in some of the planet's first ecosystems.
"There were no vertebrates, no trees, no leaves, no flowering plants, no plants with seeds," Marek said. "Millipedes were feeding on decaying mosses, decomposed slime, and primordial gunk on the surface of the Earth."
The completed family tree also helped reveal when one of millipedes' most important adaptations first emerged.
"They made the first chemical weapons," Marek said. "They're little chemical factories."
The study traces those chemical defenses to about 260 million years ago, providing the clearest picture yet of when millipedes first developed them.
Unheralded heroes of the ecosystem
Today, millipedes remain among nature's most important detritivores, breaking down decaying plant material and returning nutrients to ecosystems.
"It's really kind of puzzling that they have such an important function in the ecosystem, and yet they're so poorly known," Marek said.
For all that scientists have learned, millipedes still hold many new discoveries. Scientists have described more than 14,000 millipede species worldwide, but experts estimate there could be tens of thousands still undiscovered. Marek and his students have helped identify new millipedes in locations ranging from Virginia Tech's Blacksburg campus to the city of Los Angeles .
For a new generation of millipede researchers like Vasquez-Valverde, that's part of what makes the animals so compelling.
"There is all this potential for discovery," she said. "It keeps me wondering what else we're going to find."
The research, funded by the National Science Foundation, also included scientists from the Field Museum of Natural History, Hampden-Sydney College, Universidad de La Laguna, Virginia Tech's School of Plant and Environmental Sciences , the Australian National Insect Collection, West Virginia University, and Universidad Autonoma del Estado de Hidalgo.
