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365 million years old and no wrinkles

9/7/12

How did insects appear on Earth ? The question remains a mystery to this day. A discovery made in Strud in the province of Namur (Belgium), could provide the key to unlocking the secrets of these little animals. A team of researchers (including from the University of Liege)  have discovered the oldest complete fossil insect  ever found. Called Strudiella devonica, it lived no less than 365 million years ago. In spite of its great age, it is remarkably well preserved.

Strudiella-devonicaIt all started with another no less important fossil, which had remained dormant in the collections of the University of Liege for a very long time, since the end of the 19th century to be exact. At this time, the geologist Maximin Lohest (who, anecdotally, also discovered the bones of the “ Man of Spy ” with the help of  prehistory expert Marcel Du Puydt) had placed it there. The paleontologist was convinced: this fossil could only be the mandible of a fish (seven centimeters long), dating from the Upper Famennian. However, he did not carry his analysis any further and the discovery remained in the collections of the University of Liege among other discarded fossils.

This all changed when a young paleontologist from the Natural History Museum of Paris, Gaël Clément, spotted a drawing of this fossil in an old publication. For him, something was not quite right : the orientation of the teeth, the jaw…nothing seemed to truly resemble the mandible of a fish. He arrived in Liege, studied this piece of sandstone closer and found the laconic inscription  “ Strud ” on it.  

It took few time before this name became associated with a small quarry located in a village of the municipality of  Gesves, in the province of Namur in Belgium. The team of researchers from Belgium, armed with the new geological map of Wallonia found the exact location of the quarry where the mandible was found. This was a “ hole ” around four meters wide and fifteen meters long which was examined with a fine-tooth comb.

In 2003, Gaël Clément confirmed his earlier intuition: the fossil was not that of a fish but was in fact that of a tetrapod, Ichthyostega. This discovery caused quite a stir at the time but that’s another story.

And then there were arthropods

Since then, research in the former quarry in Strud has not stopped. Under the aegis of the Natural History Museum of Paris, the Royal Institute of Natural Science of Brussels and the University of Liege, a team comes here twice a year and continues to probe the rock over a ten-day period. The rock appears to be very rich. The river that ran through the area more than 365 million years ago (which is today completely full of sediment) left a lot of traces. Fossils - sometimes well preserved - of crustaceans, plants and vertebrates…

This was all very interesting although not earth-shattering from a scientific point of view, until a researcher, who specialized in insects, arrived on the site and started to carefully cut into the shale slabs. On one piece of material that was found the team noticed what seemed from a distance to be a tiny stain but which was shown to be a hexapod upon further analysis. It was an insect in other words. This may seem like nothing  at first glance but actually represents a major discovery. It is extremely rare to find such a complete fossil of an early insect. For although insects seem to have dominated animal biodiversity during the Carboniferous (geological period stretching roughly across a period of 350 to 300 million years), no complete fossil dating from the Devonian (the geological period before the Carboniferous) had ever been discovered. Not only had this fossil been discovered but it was in very good condition: insects are not usually well preserved due to the fact that they are fragile and lack internal skeletons.

However, this was not true of the insect found at Strud, which was soon nammed Strudiella devonica. Eight millimeters long, the arthropod had two long unforked antennae, external mandibles, a head with large round eyes, six legs, a body divided into three parts but has no wings.

Closer-view-strudiella

A missing  part in order to understand the origin of insects

This discovery was revealed to be so exceptional that it caught the interest of the American journal Nature, which has just published an article devoted to Strudiella(1). Among the signatories, there are three researchers linked to the University of Liege: Julien Denayer, doctoral student and assistant lecturer, Sébastien Olive, doctoral student, both in the Animal and Human paleontology department directed by Professor Edouard Poty, and Cyrille Prestianni, paleobotanist and scientific collaborator at the University of Liege.

“ This fossil has all the basic characteristics of the insect group, it is a very interesting discovery because we still don’t know where they came from. This arthropod is therefore a proof that during the Late Devonian, insects were already well-developed, ” explain the three researchers. Consequently, insects have a much earlier origin than was previously imagined.

The researchers have even formulated a theory: if Strudiella devonica does not have wings, it may be because it is the larva of a winged insect, given that its mandibles are typical of those that we normally find in this category. This would seem to reinforce the idea that insects were already well installed on Earth 365 million years ago and that other species, even older, still remain to be discovered.

On the Net (where the discovery spread like wildfire in just a few days and where a google search now yields thousands of results!), some people mention the resemblance of  this little animal to grasshoppers. However, to speak of Strudiella as an ancestor of one or other species is undoubtedly a bit premature. “ What we can say, is that its group must be close to something that gave rise to the insects we know today and which points to a particular evolution ”, explains Julien Denayer.    

Fossilerous-levels

The debate is open

Since this discovery, the paleontologists from Liege have tasked themselves with describing the environment in which the insect must have lived. The chances are, given the shape of its mandibles, that it was phytophageous (that is to say that it fed exclusively on plants) or omnivorous (eating a mixture of food of both plant and animal origin). It undoubtedly lived on land (seemingly, its body does not seem to possess any organ or morphological characteristic that would allow it to develop in an aquatic environment). Could it have fallen into the water one day to find itself  “imprisoned ” in the sediment of this river? The little animal has not yet revealed all its secrets.

Yet what counts for the three researchers, is that the debate is now open. “ A lot of work remains to be done. The discovery of this fossil will invite a lot of critical analysis, questions and reactions on the part of the scientific community. Indeed it has already done so to a great extent! ”, says Cyrille Prestianni.

Some ask questions about the real “ identity ” of Strudiella: is it really an insect? But in the end it doesn’t matter: “ That is the interest of scientific discoveries! The material is available to all the researchers who want it. ” The fossil, which will be preserved in the collections of the Royal Institute of Natural Sciences of Belgium, is likely to attract a throng of international specialists in the next few months.

“ We hope that this will encourage researchers to concentrate more on the Devonian, because it is a difficult period and is relatively unstudied ”. Often, science is blocked due to lack of financial means. Now that we know this type of insect exists, this may help to unlock funding ”, add the three collaborators.

In the meantime, the research will probably continue until 2015 in the small quarry of Strud. The excavations of a Belgian deposit will rarely have been so long. Yet, having revealed the presence of Ichtyostega and then Strudiella, the rocks of the quarry in Namur probably still have a lot of things to reveal…


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