Barely a centimeter long, but nevertheless significant: Strudiella devonica is the oldest known insect fossil. © Romain Garrouste / MNHN
Reading aloud Strudiella devonica had everything an insect needs: six legs, triangular jaws, two long antennae and a ten-part abdomen. The special feature of the eight-millimeter long animal: It lived 370 million years ago, at a time when the ancestors of mammals, but also the invertebrate arthropods began to conquer the land. As French researchers around Romain Garrouste report, Strudiella is the oldest fully preserved fossil of an insect. Insects are among the most successful animal groups on earth. Since the mid-Carbon Age, about 325 million years ago, they have been populating the Earth in great diversity. But their origins are in the dark. At some point more than 400 million years ago, the line of insects separated from that of the other arthropods, which include, for example, crabs, spiders, mites and woodlice. While their ancestors still inhabited the water, the insects, along with other animal species, such as the vertebrates, adapted to the new life in the countryside.

However, little is known about the early development of insects, as there are virtually no fossils from a 60 million year period between 385 and 325 million years ago. From the time before this gap so far only a few fragments were found that do not allow accurate conclusions. Paleontologists are therefore puzzled over whether the sudden biodiversity in the Devonian developed slowly during the time of the fossil gap, or whether the evolution of the insects in the middle of the carbon gave a sudden boost.

Strudiella now suggests that the development in the carbon had a long lead time. Garrouste and his colleagues discovered the fossil in a quarry in Belgium. The fossil was relatively poorly preserved, but the combination of various body features suggested that it must be an insect. As the researchers write, the animal was petrified at the bottom of a shallow sea swarming with Triops crabs. Strudiella, however, lived on land and either fed on plants or was omnivorous. Wings could not detect the researchers, but they suspect that it was the larva of a winged insect.

Romain Garrouste, (Muséum national d'histoire naturelle, Paris) et al: Nature, Vol. 488, p. 82, doi: 10.1038 / nature11281 © science.de - Ute Kehse advertisement

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