Why were the creatures of the Carboniferous Period so large compared to their modern day relatives?

    If we look at previous eras we know that prehistoric creatures were very large yet the Carboniferous was a period full of amphibians, fish, insects and arthropods that grew to sizes that are larger than today’s creatures from these families. We could mention lots about the fact that evolution may have made them this large but there was also another factor which I will explain giving an analysis of Meganuera (a Carboniferous Dragonfly) compared to our modern day Dragonfly.

Carboniferous Jungle - over 300 million years ago

    I will first explain what the Carboniferous Period was. The Carboniferous period lasted from 359 million years ago to 299 million years ago. It is called the Carboniferous Period because there were many coal beds containing coal balls hence the reason why Carboniferous means “coal-bearing.” The world was changing and so were the creatures that lived on it. New breeds of fish, amphibians, insects and arthropods started to evolve that looked magnificent. The landscape was lush, full of trees and swamps that were habitats to these creatures. However this new world still had its severe climate changes, rising sea levels and glaciers caused severe problems for the wildlife. Mountains were being created constantly throughout the Carboniferous Period, unfortunately despite all this change the Carboniferous ended as the climate cooled and dried leading to the ‘Carboniferous Rainforest Collapse’. Rainforests were fragmented and eventually devastated by the climate change resulting in the end of the Carboniferous Period.

    Now the reason for why the creatures of the Carboniferous Period grew so large was due to the amount of oxygen available in the Earth’s atmosphere. The atmosphere in the Carboniferous contained 136% times more oxygen in than today’s atmosphere. With this amount of oxygen creatures were able to grow to extraordinary sizes to that of what is expected in the family group. One such creature that grew to a huge size was Meganeura, a prehistoric Dragonfly that flew the skies and was widely diverse across the Carboniferous terrain.

Meganuera - The Giant Dragonfly

    Meganeura lived roughly 300 million years ago and is an extinct class of insect from the Dragonfly genus. The wingspan of this insect could reach up to 75cm (2 ½ 30cm rulers or 2.5ft) and was one of the top predators of the Carboniferous period, it fed on other insects and even small amphibians. As said due to the mass amounts of oxygen available, Meganuera grew so large because of how the oxygen was diffused in the body. It was said that Meganuera was only able to fly due to the huge oxygen levels yet this was dismissed, however new research shows that the theory gained more approval due to the relationship between oxygen levels and the gigantism theory. Therefore if this was true Meganuera would have been unable to fly in the modern day due to the reduced amounts of oxygen in the atmosphere.



Our modern day Dragonfly - much smaller than Meganeura



    The modern day Dragonfly is small in comparison with Meganuera. Its wingspan is a small 19cm on average, that’s roughly 3.9 times smaller than that of Meganuera, also our modern Dragonfly can only reach up to a maximum of about 4cm in length where as Meganeura was 1 metre long. However as our atmosphere contains way less oxygen the size of a modern day Dragonfly has to be small. Despite their smallness they are valuable to the earth as they eat mosquitoes and other ‘pests.’ Dragonflies were once one of the dominant creatures of prehistory yet now they are little insects that help get rid of ‘pests.’ Just think whenever you see a Dragonfly now you will now know that they were once gigantic insects that ruled the Carboniferous terrains.

    To conclude the answer to ‘Why creatures of the Carboniferous grew so large?” is that the amount of oxygen that was available in the atmosphere was diffused more in the bodies of the creatures enabling them to reach these enormous sizes. Just think how big other creatures such as dinosaurs and even humans may have been if that amount of oxygen was available in the atmosphere, however what prehistory has told us is that the amount of oxygen in the atmosphere is gradually decreasing. Well I hope you have thoroughly enjoyed this short report and that you have gained some valuable information about what Earth was like 300 million years ago.