Birds on the Brain

rhamphotheca:

Meganeura 

… a genus of extinct insects from the Carboniferous period approximately 300 million years ago, which resembled and are related to the present-day dragonflies. With wingspans of up to 65 cm (2.1 ft), M. monyi is one of the largest known flying insect species; the Permian Meganeuropsis permiana is another. Meganeura were predatory, and fed on other insects, and even small amphibians.

Controversy has prevailed as to how insects of the Carboniferous period were able to grow so large. The way oxygen isdiffused 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. It was originally proposed  that Meganeura was only able to fly because the atmosphere at that time contained more oxygen than the present 20%. This theory was dismissed by fellow scientists, but has found approval more recently through further study into the relationship between gigantism and oxygen availability. If this theory is correct, these insects would have been susceptible to falling oxygen levels and certainly could not survive in our modern atmosphere…

(read more: Wikipedia)       (images: T - illustration by Dodoni; B - photo by Hcrepin)