Meganeura libellula gigante

In prehistory there was a 75 cm large dragonfly: because there are no more large insects

An artistic representation of meganeura in its natural environment.

Monyi meganeura was aancestor of the current dragonflies lived during the late carboniferous, approximately 300 million years agoand paleontologists estimate that he could reach a wing opening of about 65-75 cm, with 32 cm per single wing. Dimensions that make it one of the larger insects ever existed of the history of the earth, record that shares with other extinct insects of a comparable size, always similar to dragonflies, such members Meganeuropsis And he lived a few million years later, in the Permian. He lived in Europe and North America and occupied an ecological niche similar to that of today’s dragonflies, was the terror of other animals such as amphibians and small mammals that hunted quickly and trapped them thanks to his legs full of spiny growths.

Until the discovery of his fossils, which took place in 1880 in some coal mines in France, his extraordinary dimensions captured the attention of paleontologists, leading some of them to assume that such a insect It would not have been able to fly into today’s atmosphereless dense than oxygen than in the past.

Because Meganeura Monyi was extinct: the hypothesis on the flight and the density of the air

The first to suggest that the Meganeura It would not have been able to survive the current atmosphere of the planet was the French engineer and paleontologist Eduard Harlé in 1911. According to Harlé, extinct volatiles such as meganeura, but also flying reptiles such as Pterodactiles, managed to take flight despite their great size thanks to the fact that the fact that the fact that the factatmosphere of our planet was thicker In the past. During the era of meganeura, in fact, the percentage of oxygen in the air era del About 30-35%compared to about 21% Today. A more dense atmosphere makes flight easier: with more molecules present in the same air space to push, the lift (i.e. the sustenance force) of a wing is greater. This allows you to fly with more energy efficiency Also for heavier means (or animals). Today, with the percentages of oxygen in the air current, too large or heavy animals would not be able to flight, or the energy expenditure necessary for a demanding operation such as the flight would be unsustainable.

The evolution would thus lead toextinction of large birds and selected those with small sizebetter suitable for a less dense air. The wingspan of the screaming albatro (Diomedea Exulansoggi), the largest flying bird nowadays, exceeds 3.5 metersbut it is very little compared to that of Quetzalcoatlus northropiextinct pterosauro that also threw the 12 meters. Among the greatest insects that exist today, such as the Scarabeo Golia (Goliathus Goliathus), you can also exceed 10 cm in length, but despite having these animals rarely fly and with great effort.

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A fossil of meganeura. Credit: Muséum de Toulouse, CC By -Ssa 4.0, via Wikimedia Commons

The hypothesis on breathing for the extinction of the giant dragonfly

Another possible correlation between the availability of oxygen and dimensions of meganeura is given by the peculiar modalities of breathing of insects. In fact, these animals do not have lungs, but absorb air through tiny cracks along their body, called stigmas, which convey it inside through a thick system of trachee And tracheole. These small ducts put the air directly in contact with the emolinfa of insects, the liquid that performs the function equivalent to our blood. The gaseous exchange therefore takes place constantly, for simple spread. It was thought that in insects there was no form of active breathing, but recent studies suggest that muscle contractions contribute to the movement of the gas within the trachee in the larger species.

In any case, the respiratory system of insects is a limiting factor For their growth: if their dimensions were too large, oxygen would struggle to reach the inside of their body through the trachee, and a body too often the would prevent you from breathing. But with a percentage of major oxygen in the air, as at the time of meganeura, a sufficient amount would be able to reach the interior of a body more often, allowing larger insects to be able to evolve.

Harlé’s hypothesis on the density of the air as an explanation of the size of meganeura was very popular, but not accepted by all experts, and gradually it was considered less credible. But recent analyzes on the relationship between Percentage of oxygen and gigantism In insects they led to re -evaluate this hypothesis: it is possible that meganeura, and other giant arthropods of the Carbonifera era (such as Arthopleuragiant millepiedi up to 2 meters long) could exist thanks to a greater amount of oxygen available, and their disappearance coincided with the decrease in density oxygen up to current levels.