Dragonflies the size of seagull used to roam our planet 300 million years ago. One theory suggests that abundant of oxygen at that time led to the rise of giant insects and one of them were dragonflies.
This period is known as carboniferous period which lasted from 359 to 299 million years ago.
Meganeura was first discovered in France in 1880. It was one of the largest species of insects to ever exists. It was a carnivore, it would tear apart and eat other insects right away.
In current time the oxygen percentage in our atmosphere is 21% of all gases but in carboniferous period it was more than 35% which led to rise of giant insects like Maganeura.
It had a wing span of 70 centimeters or 2.5 feet. They used their long spine covered legs to catch their pray. They mainly ate small insects, small amphibians and vertebrates.
One theory suggests why these insects grew so large is that at that time there were no predatory Ariel vertebrates who could eat meganeura.
Meganeura means large veins. The drop in the level of oxygen in our atmosphere many have contributed their extinction.