Strudiella, The Oldest Fossil of Complete Insect in the World

Strudiella is the oldest complete fossil insect ever found.  © Romain Garrouste

The complete fossil of Strudiella, a small insect close to grasshoppers, has been uncovered in Belgium. For the journal Nature, in which the discovery was published, it represents the Holy Grail following that all specialists were running.

Animal biodiversity of the Earth is dominated by insects from the late Carboniferous (320 million years ago). But the implementation of this major group of arthropods remains mysterious because complete fossils of insects before this period are missing.

An international team, led by Roman Garrouste, Patricia Nel, Andre Nel, of the laboratory Origin of structure evolution of biodiversity (Oseb, National Museum of Natural History / CNRS), and Gaël Clément of the Centre for Research on paleobiodiversity and paleoenvironments (CR2P, National Museum of natural History / CNRS / UPMC), has just discovered a small complete insect in the Belgian deposit of Strud dating to the Frasnian stages (Late Devonian period) (365 million years (Myr) ago).

Named Strudiella, this unique fossil partly confirms the results from phylogenetic reconstructions dating the first appearance of insects before the Late Devonian, probably in the Silurian (425 Myr). The results of this study are published today in Nature.

Strudiella reappeared from the depths of the Devonian

To answer this question and in the absence of fossil traces, only the results from phylogenetic reconstructions have allowed scientists to date the first appearance of insects well before the Late Devonian, probably in the Silurian period. The insect fossils are almost absent from the fossil record of Silurian to Late Devonian, the discovery of small insect fossil, called Strudiella, has finally partially fill this gap.

The conservation status of this fossil supports the conclusion that this is probably close to a small insect of the first representatives of grasshoppers with long antennae, a relatively large head and strong mandible. Because of the absence of wings on this specimen, it was not possible to determine the developmental stage of it (larva or adult). Although found fossilized in the bottom of a temporary pond accompanied by freshwater organisms such as crustaceans triopsides, this animal has the specifics of a terrestrial insect and shows no morphological character or body allowing adaptation to life water.

A complete fossil insects to better understand

The insects were therefore present at that time of the Late Devonian (365 Myr). This discovery opens up prospects for research and raises new questions. The rarity of these fossils correspond to a bias of preservation or a paleoecological reality? What were the environmental factors that caused the growth of insects (this is called adaptive radiation)? The processes of terrestrialization of vertebrates and arthropods can be correlated with major environmental changes? These issues are fundamental to understanding the role of biodiversity in ecosystems today but also to estimate the future, as in the context of global climate change.

Rediscovered in 2005, this deposit, located in Strud in the province of Namur (Wallonia, Belgium), is already known as one of the few sites in the world to the first tetrapods (terrestrial vertebrates). The excavation missions are regularly organized under the responsibility of Gaël Clément (National Museum of Natural History), in collaboration with the Royal Institute of Natural Sciences in Brussels and Liege University. Recently focused on the discovery of Devonian arthropods, they allowed the discovery of this fragile insect fossil.

The paleoentomologistes of the Museum of Natural History and CNRS looking for several years traces the origin of insects, through numerous expeditions around the world, most recently in Spitsbergen (Norwegian island), to solve one of the mysteries of life on our planet.

Tagged Complete Insect, Earth sciences, Evolution, fossils, insect, Palaeontology, Strudiella