Millipedes were already thriving on the Earth’s surface billions of years before dinosaurs appeared and long before vertebrates invaded land.
These humble decomposers played an important role in some of Earth’s earliest terrestrial ecosystems. But despite its remarkable history, big questions about its evolution remained unanswered.
Now, an international team led by researchers at Virginia Tech has filled in one of the last gaps in the millipede family tree, shedding new light on the ancient creatures that helped prepare Earth for life on land.
This research current biologypresents the first complete evolutionary history of all extant Millipedes. By combining DNA data from modern species with physical evidence preserved in fossils, researchers traced the origin of millipedes back to around 460 million years ago, suggesting that millipedes existed long before the oldest millipede fossils ever discovered.
“Millipedes kept vertebrates on land for more than 80 million years,” said Paul Marek, principal investigator of the study and associate professor in the Department of Entomology in the College of Agriculture and Life Sciences. “They really set the stage for later terrestrial life, including humans and vertebrates.”
Solving the long-standing millipede mystery
For more than 100 years, scientists have recognized the existence of two groups of rare millipedes: Siphoniulida and Siphonocryptida. However, because fresh specimens were not available for DNA analysis, researchers were unable to determine exactly where these groups belonged on the millipede family tree.
One group consists of millipedes, which are less than a centimeter long and spend their entire lives underground. The other survives only in a few known locations.
“These last two were like our Moby Dick,” Malek said.
To find them, researchers traveled to Mexico’s Los Tuxtlas and Spain’s Canary Islands. So they gathered Sifoniurus neotropicus and Hildicryptus canariensisthe DNA of these two species had never been included in evolutionary studies before.
“It took over a week and 10 people just to find this one tiny 10-millimeter adult,” said Dr. Luisa “Fernanda” Vazquez Valverde MS’21. ’24, first author of the paper and assistant in Marek’s lab. “It was hard to find them in the field because we just saw this little white nematode. We didn’t know if it was a millipede until we looked at it under the microscope.”
The researchers sequenced the DNA of the two groups and compared hundreds of genes across 82 species of millipedes. They also incorporated evidence from 29 fossils. Together, these data allowed the researchers to determine where the mysterious group fits into millipede evolution and when the lineage first appeared.
The project generated terabytes of genetic data and leveraged Virginia Tech’s advanced research computing resources to reconstruct evolutionary relationships spanning hundreds of millions of years.
The results show that Siphonocryptida belongs to an existing lineage, rather than a separate millipede as previously thought. Siphoniurida, on the other hand, ended up being aligned with its closest evolutionary relatives.
ancient earth millipede
The analysis shows that millipedes may have originated around 460 million years ago, which is about 35 million years older than the oldest known millipede fossils and significantly earlier than previously suggested estimates.
“The biggest surprise was how ancient some of these lineages turned out to be,” Marek said.
The Earth then looked very different than it does now. Marek said millipedes were early pioneers of terrestrial life, feeding on rotting organic matter and helping to recycle nutrients in some of the first terrestrial ecosystems.
“There were no vertebrates, no trees, no leaves, no flowering plants, no plants with seeds,” Marek said. “Millipedes fed on rotting moss, rotting slime and primitive dirt on the ground.”
Origin of millipede chemical defenses
The newly completed evolutionary genealogy also helped researchers pinpoint when one of the group’s most notable adaptations emerged.
“They produced the first chemical weapons,” Malek said. “They are small chemical factories.”
The study suggests that these chemical defenses began about 260 million years ago, providing the clearest evidence to date of when millipedes first evolved this ability.
unknown ecosystem engineer
Today, millipedes remain one of the most important detritivores in the world. By breaking down dead plant matter, it recycles nutrients and supports a healthy ecosystem.
“It’s really puzzling that it plays such an important role in the ecosystem and yet so little is known about it,” Malek said.
Although more than 14,000 species of millipedes have been described worldwide, researchers believe that tens of thousands of millipede species may still be undiscovered. Malek and his students discovered new species in locations ranging from Virginia Tech’s Blacksburg campus to Los Angeles.
For scientists like Vázquez Valverde, that inquisitiveness is part of the appeal.
“There is every possibility of discovery,” she said. “I keep wondering what else I’ll find.”
The research was funded by the National Science Foundation and included scientists from the Field Museum of Natural History, Hampden-Sydney College, University of La Laguna, Virginia Tech’s Department of Plant and Environmental Sciences, Australian National Insect Collection, West Virginia University, and Autonomous University of Hidalgo.
