Ancient Giant Dragonflies Ruled Skies With Two Foot Wingspans

When Giants Ruled the Skies

Imagine looking up 285 million years ago to see a predator with a wingspan nearly as wide as you are tall soaring overhead. The largest insect known to science was a predator called Meganeuropsis permiana, with a wingspan of about 71 centimetres, a little over two feet. Its body length is estimated to have been 17 to 43 cm (7–17 inches), making it comparable in size to a crow.

It flew in the Early Permian, roughly 285 million years ago, and despite the way it is usually described, it was not a true dragonfly. It was a griffinfly, a stem relative of modern dragonflies and damselflies. The skies it hunted in had no birds, no bats and no pterosaurs. Nothing with a backbone had yet learned to fly. These ancient aerial predators dominated an alien world where insects grew to sizes that would be impossible today.

For comparison, the largest living odonate, a Central American damselfly, has a wingspan of about 19 centimetres, roughly a third of the griffinfly's reach. The difference is staggering – these prehistoric giants were nearly four times larger than anything flying today.

The Oxygen Connection

The air also held considerably more oxygen than ours, and that fact has carried most of the explanation for why insects then grew to sizes no insect reaches now. In the Permian (290-283 million years ago), atmospheric oxygen was 23-30%, higher than today's 21%. This oxygen-rich atmosphere was crucial because insects do not breathe with lungs. Air enters through openings along the body called spiracles and travels to the tissues through a branching network of tubes, the tracheae, largely by diffusion.

The way oxygen is diffused through the insect's body via its tracheal breathing system puts an upper limit on body size, which prehistoric insects seem to have well exceeded. Falling oxygen levels made it harder for large insects to survive, as their breathing systems couldn't support such big bodies. However, the oxygen explanation isn't complete – very large Meganeuridae with a wingspan of 45 cm also occurred in the Late Permian of Lodève in France, when the oxygen content of the atmosphere was already much lower than in the Carboniferous and Early Permian.

A World Without Competition

Another key factor in these giants' success was the absence of aerial competition. The scarcity of aerial vertebrate predators in the Permian enabled winged insects like Meganeuropsis to reach maximum sizes. Another explanation to the large size of the insects living during the Carboniferous, and also Permian period, is the lack of aerial vertebrate predators.

Like modern dragonflies, Meganeuropsis was a predatory insect, using its large compound eyes and powerful mandibles to catch prey in flight. It likely fed on other insects and small arthropods, but there is no direct evidence that it hunted vertebrates like amphibians or mammals. These apex predators of the ancient skies had free reign in a world where they faced no competition from flying vertebrates.

The End of an Era

By the end of the Permian period, around 252 million years ago, giant insects like Meganeuropsis vanished. Falling oxygen levels made it harder for large insects to survive, as their breathing systems couldn't support such big bodies. Climate changes and the rise of new predators, like early reptiles, also played a role.

Its giant size shows how oxygen levels can influence evolution, while its extinction highlights the impact of environmental change. These prehistoric giants remind us that Earth's atmosphere has undergone dramatic changes throughout history, creating conditions that allowed life forms impossible in our current world. Their fossils serve as windows into an alien past where insects ruled the skies as apex predators in ways that seem almost fantastical today.