Meganeura - The Giant Dragonfly
When: Carboniferous (~305-299 million years ago)
What: Meganeura is the largest dragonfly, with a wingspan of 2.5 feet (~75 cm) in some specimens. The largest living dragonfly is a comparatively weensy 7.5 inches (~19 cm) across at the wings. A scientific debate had centred upon why Meganeura was able to become so large. It has been suggested that it was only able to reach such a great size due to the relatively higher levels of oxygen in the Carboniferous air. This is based partly upon the way most modern insects respire, they do not truly breathe, but instead simply diffusion oxygen throughout their small bodies. However, more recent studies show that larger insects do breathe via compression and expansion of their trachea. Additionally insects much larger than those today have been found in later rocks which do not show evidence of elevated oxygen levels. More research needs to be done to determine the impact of oxygen levels upon the maximum size of insects.
Only a few fossils have been found of Meganeura, but despite this, almost every scene ever of a Carboniferous forest has one of these animals perched upon a giant club moss tree. I do not blame them, I could not resist either. Other animals in these dense forests with Meganeura were a gaggle of other gigantic insects and arthropods, a great variety of amphibians, and the first reptiles. This was the start of the true colonization of land by vertebrates; it has also been suggested it was the arrival of these predators which limited the size of insects such as Meganeura in later time periods.