During the Paleozoic Era (541–252 million years ago), there was enough atmospheric oxygen to support giant superbugs and insects. For example, the largest giant dragonfly had a wingspan of up to 28 inches (71 cm). The giant centipede could reach eight feet in length (8.5 meters), making it the largest known invertebrate in history.
Picture a giant centipede crawling across the jungle floor with a long body eight feet long. Now picture a huge dragonfly that can stretch its wings to an incredible half a meter across. This may have been what life was like in the oxygen-rich environments of the early Paleozoic Era (541 million years ago – 252 million years ago), featuring the largest creepy crawlies the Earth has ever known.
Along with the lack of predatory birds, an atmosphere with a potential oxygen concentration of up to 35 percent (compared to 21 percent on modern Earth) allowed these giant insects and land arthropods to grow to enormous sizes both in the air and on the ground.
Arthropleura Armata
Arthropods are a group of invertebrates that include insects, centipedes, and spiders; they collect oxygen through openings in their bodies called spiracles, which branch into a network of tubes that disperse the gas throughout their bodies. The high concentration of oxygen allowed arthropods to continue to grow because they could easily absorb the gas as they grew larger.
Researchers believe that the insect population boom began in the early Paleozoic era, from the Cambrian to the Silurian periods. But giant insects actually began to evolve in the Devonian and Carboniferous periods more than 300 million years ago, when the Earth had many more trees and oxygen-producing plants.
At the time, fossils show that the giant dragonfly Meganeura Monyi had a wingspan of over 0.5 meters and fed on smaller insects. Probably living in open areas where its wings could stretch, its growing huge eyes helped it “spot” its prey and then use its spiny legs to catch it.
The Mazothairos insect from the Paleodictyoptera group may not have been all that big – its wingspan was probably around 22 inches (0.5 meters) – but interestingly, it evolved a beak-like mouth.
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Crawling on the ground was an eight-foot-long millipede called Arthropleura Armata (8.5 meters); it is believed to be the largest invertebrate in the history of the Earth. It is likely a true forager of fruits and seeds, and its enormous size can be explained in part by both the lack of predators and the oxygen-rich environment.
Of course, it wasn’t just friendly centipedes that grew to giant sizes. An early scorpion known as Pulmonoscorpius kirktonensis could reach a size of 27 inches (69 cm).
But as the Carboniferous began to fade, so did the high oxygen levels, causing global temperatures to drop. And even when oxygen levels rose sharply again, the emergence of birds of prey made large insects a thing of the past.
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