Millipedes, those unassuming creatures with their countless legs, have been quietly shaping Earth's ecosystems for hundreds of millions of years. While vertebrates were just a twinkle in the cosmos, millipedes were already thriving on the planet's surface, playing a crucial role in the earliest terrestrial ecosystems. Despite their remarkable history, many questions about their evolution remained unanswered until now.
An international team of researchers, led by Virginia Tech scientists, has finally filled in one of the last gaps in the millipede family tree. By combining DNA data from modern species with physical evidence preserved in fossils, they traced the origins of millipedes back nearly 460 million years, suggesting they existed long before the oldest millipede fossils discovered so far. This groundbreaking study, published in Current Biology, reveals that millipedes beat vertebrates onto land by more than 80 million years, setting the stage for later life on land, including humans and vertebrates.
The research team, led by Paul Marek, an associate professor in the College of Agriculture and Life Sciences' Department of Entomology, embarked on a quest to find two rare millipede groups, Siphoniulida and Siphonocryptida. These groups had been recognized for over 100 years but were missing from the evolutionary tree due to the unavailability of fresh specimens for DNA analysis. The researchers traveled to remote locations, including Los Tuxtlas in Mexico and the Canary Islands of Spain, to collect these elusive species, with one species, Hirudicryptus canariensis, being found in just a handful of known locations. The collection of these species was a challenging task, with one researcher, Luisa "Fernanda" Vasquez-Valverde, describing the process as finding a "little white nematode" under a microscope.
The team's efforts paid off, as they were able to sequence DNA from the two groups and compare hundreds of genes across 82 millipede species. They also incorporated evidence from 29 fossils, resulting in terabytes of genetic data. Using Virginia Tech's Advanced Research Computing resources, they reconstructed evolutionary relationships stretching back hundreds of millions of years. The results revealed that Siphonocryptida is not a separate millipede order but belongs within an existing lineage, while Siphoniulida was finally placed alongside its closest evolutionary relatives.
The analysis indicated that millipedes may have originated nearly 460 million years ago, about 35 million years earlier than the oldest known millipede fossils and significantly earlier than previous estimates. This finding is particularly fascinating because, at that time, Earth looked very different from today. Millipedes were among the early pioneers of life on land, helping recycle nutrients by feeding on decaying organic material in some of the first terrestrial ecosystems. There were no vertebrates, no trees, no leaves, no flowering plants, or plants with seeds. Millipedes were feeding on decaying mosses, decomposed slime, and primordial gunk on the surface of the Earth.
The study also shed light on the origins of millipede chemical defenses, which appeared about 260 million years ago, offering the clearest evidence yet for when millipedes first evolved this capability. These chemical defenses make millipedes little chemical factories, showcasing their remarkable adaptations.
Today, millipedes remain essential detritivores, breaking down dead plant material and recycling nutrients, supporting healthy ecosystems. However, despite their importance, millipedes are poorly known, with only 14,000 described species worldwide. Researchers believe tens of thousands of millipede species may still be undiscovered, and the sense of exploration and discovery is what drives scientists like Vasquez-Valverde to continue their work.
This groundbreaking research, funded by the National Science Foundation, involved scientists from various institutions, including 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. It highlights the importance of continued exploration and research in understanding the evolution and ecological significance of these ancient creatures, which have been quietly shaping Earth's ecosystems for hundreds of millions of years.
