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The unassuming 425-million-year-old fossilized millipede appears to be the oldest recorded "bug" specimen, a loosely defined category of arthropods which includes land-dwelling insects, arachnids, and centipedes, and also marine crustaceans like crabs, lobsters, and shrimp.
Detailed in a new study published by scientists at the University of Texas at Austin in the journal Historical Biology, this short-bodied, sectional prehistoric millipede named Kampecaris obanensisonce resided during the Silurian period and measures out at just 2-3 cm in length. The Silurian is the shortest period in the entire Paleozoic Era and spanned just 24.6 million years.
The Scottish millipede-like fossil was discovered on the island of Kerrera in the Scottish Inner Hebrides and made its home beside a lake in a semi-arid forested ecosystem subsiding on decomposing plants in the area.
Paleontologists' conclusions were tested employing an aging method called molecular clock dating, a different type of scientific technique pinpointing evolutionary events using statistical analysis of rates of change of DNA or amino acid sequences.
According to the research paper, a rapid radiative evolution from simple intermontane lake communities into more advanced lowland communities took only about 40 million years to reach complex forest grade communities by the Middle Devonian Givetian circa 385 million years ago, revealing that the complexities of cohabitation between bugs and plants happened far faster than previously believed.
“Although it’s certainly possible there are older fossils of both bugs and plants, the fact they haven’t been found — even in deposits known for preserving delicate fossils from this era — could indicate that the ancient millipede and plant fossils that have already been discovered are the oldest specimens,” said Dr. Michael Brookfield, a researcher in the Department of Geological Sciences at the Jackson School of Geosciences at the University of Texas at Austin and the University of Massachusetts Boston.
“It’s a big jump from these tiny guys to very complex forest communities, and in the scheme of things, it didn’t take that long. It seems to be a rapid radiation of evolution from these mountain valleys, down to the lowlands, and then worldwide after that.”
During the Silurian, Earth was going through major growing pains, which had vital consequences for the environment and life forms that inhabited the period. With warmer, more stable temperatures came the melting of massive glacial formations, contributing to a measurable rise in the levels of major oceans.
It was here that the first coral reefs made their appearance, allowing for the rapid evolution of numerous species of fishes, including not only a proliferation of jawless fish, but also the beginning of the first known freshwater fish and the first fish equipped with jaws.
Many essential marine specimens have been unearthed within the Silurian fossil record, not limited to trilobites, graptolites, conodonts, corals, stromatoporoids, and mollusks. The Silurian is also associated with the emergence of life on land, with rare preserved records of ancient relatives of spiders and centipedes, and also the earliest fossils of vascular plants.