Scientists agree that today’s insects evolved from creatures, arthropods, that they slowly suggested in an ocean teeming with life in the Cambrian period, about 542 million years ago. Some 150 million years later, during the Paleozoic Era, large insects were already dominating the Earth.
But a recent find of a 425-million-year-old millipede fossil suggests that insects evolved much faster than previously believed. It is the oldest known fossil of an insect or arachnid, about 75 million years older than the age that other scientists had estimated for the oldest millipede . This discovery, made by researchers at the University of Texas at Austin on the Scottish island of Kerrera, provides evidence that the ancestors of insects transitioned from communities surrounding lakes to complex forest ecosystems in just 40 million years.
This is a great leap that, in the scheme of the evolution of life on Earth, did not take too long, according to Michael Brookfield, a research associate at the Jackson School of Geosciences at UT Austin and an adjunct professor at the University of Massachusetts Boston. : “It seems to be a rapid evolution from these mountainous valleys, to the lowlands, and then around the world”, as can be read in a statement issued by the University itself. The research was recently published in the journal Historical Biology.
Plants and insects could be older than we thought
To date the age of the fossil, the researchers used a technique known as molecular clock dating, which is based on the rate of DNA mutation. Other research using fossil dating found that the oldest fossil of a stem plant inhabiting the earth (also from Scotland) is 425 million years old, also 75 million years younger than previous estimates.
Brookfield believes there may be even older fossils of insects and plants. If this is the case, it also means that both insects and plants evolved much faster than the timeline indicated by the molecular clock. Abundant insect deposits have been dated to only 20 million years later than fossils. And 40 million years later, there is evidence of thriving forest communities filled with spiders, insects, and tall trees.
This study is the first to address the age of ancient millipedes. And why have we waited so long? Stephanie Suárez, a PhD student at the University of Houston, believes it is due to the difficulty of extracting zircons, a microscopic mineral needed to accurately date fossils, from the ash rock sediment in which the fossil is preserved. Zircons are easily removed when trying to loosen their grip on the sediment. And once they are successfully released from the surrounding rock, recovering the zircons involves “an accuracy comparable to working with a pin stuck to the tip of a pencil,” they explain from the University of Texas.
Referencias:
‘Myriapod divergence times differ between molecular clock and fossil evidence: U/Pb zircon ages of the earliest fossil millipede-bearing sediments and their significance’. M. E. Brookfield ,E. J. Catlos &S. E. Suarez (13 May 2020) https://doi.org/10.1080/08912963.2020.1761351
