Geology and Earth ScienceBig Bugs of the Paleozoic
Bill Marrs
Fossil evidence shows that during the Paleozoic era (245-570 million years ago), insects such as dragonflies, cockroaches and millipedes were a lot bigger than today’s insect relatives. Jon Harrison, a professor of biology at Arizona State University, became interested as the reason why some insects were larger than today’s. He believes the answer lies with what researcher’s found when analyzing the composition of ancient soils. Researchers found that there may have been periods of time during the Paleozoic when the oxygen concentration in Earth’s atmosphere was considerably higher than ever before. These findings suggest a concentration of 35% oxygen in the atmosphere that occurred for approximately 100 million years, and then dropped to 15% before reaching a current concentration of 21%. The geologic record shows a rise and fall of oxygen levels that coincide with the evolution and extinction of large insects. Flight muscles of insect’s burn more oxygen than any other animal tissue. Harrison claims that if these insects existed, there must have been oxygen levels that supported these muscles. Harrison plans future research to examine what he found in the lab under more natural conditions.
The method of research Harrison used involved examining the study of the previous geologic findings of Robert Dudley from the University of Texas, at Austin, and Jeffery Graham of the Scripps Institute of Oceanography in La Jolla, California. In their own research in controlled environments, Harrison and Scoot Kirkton (a graduate student at Arizona State University) tested aerobic performance of grasshoppers and dragonflies. They tested different sized grasshoppers and dragonflies at varying oxygen levels to see how they performed. They found that large grasshoppers and dragonflies were more active at high oxygen levels while activity diminished at low oxygen levels. They also found that small grasshoppers are also more active and are not bothered by oxygen levels as low as 5%.
I believe this research is relevant to modern atmospheric and climate research because it shows us that there has been a great change in our atmospheric composition since the Paleozoic. This gives us insight into how our atmosphere was formed and how it may change in the future.
I never knew that oxygen levels changed that drastically since the Paleozoic. I thought oxygen levels gradually rose to a maximum level of 21% and that this level did not fluctuate from this value a great deal since the Paleozoic. I also did not know that there is such a tight relationship between body size and metabolic rates in animals as small as insects.
I think it is quite possible that increased oxygen levels during the Paleozoic could have paved the way for the evolution of super-sized insects during that time. However, I also believe there must have been other factors involved as well. I believe that many factors such as the amount of possible available food resources during that time and the likelihood that larger insects would have been easier prey for predators and were not discussed in the article. Although the fossil record may not be able to give us this information, I believe that a rise in oxygen levels discussed in the article is a credible reason for seeing large insects in the fossil record as Harrison’s theory predicts.
The article can be found at: http://researchmag.asu.edu/stories/bugs.html
3 Comments:
Insects are an interesting bunch to talk about. No matter when or where they existed, there is always something different and unusual about them. When you examine or watch an insect live its life, when you study it innards through dissection or a microscope, even when you study those that are long dead; you begin to realize something, these creepy crawlies are not like us. They are so significantly different than us, it's no wonder that so many people fear or are disgusted by them. There is no surprise that these Paleozoic giants might have been so significantly affected by the amount of oxygen in the air.
Even with this in mind, much can be thought of as to how these Paleozoic insects functioned, and if it really was anything like the experiments done on the grasshoppers. How well adapted were the grasshoppers to the oxygen amounts given to them. Even though the bigger grasshoppers had become more active to the oxygen increase, would that be the case if they were used to that amount of oxygen. When one is adapted to a situation, it would show "normal" activity instead of a change in what we were used to seeing.
Take, for example, a comparison of mountain dwelling life to those that live closer to sea level, both of the same species just with different locations. If you were to take a sea level dweller and place it on the mountain, it would show an adverse reaction to the drop in oxygen. That dweller would start to have labored breathes, possibly gasping if taken high enough, along with a fatigue-like weakness and possibly move sluggishly. The mountain dweller, on the other hand, has been so used to the low amounts of oxygen that it is not affected by it. Take the mountain dweller down to sea level, and the air would feel to it to be over oxygenated, practically drowning in the thickness of it. The mountain dweller would feel over energized, breathing in the air that the sea level dweller normally breathed.
The only aspect that shows that this example wouldn't apply to the grasshopper experiment would be that the smaller grasshoppers had shown little to no change in activity amidst the change in oxygen levels. Being that, in essence, both the big and small were breathing in the same air, with equal oxygen percentage; both should react similarly if not the same. This is stating that the bigger they are the more air capacity they have, sustaining the body with a similar amount to the smaller ones with a smaller air capacity.
Either way, the idea is about how the higher oxygen levels in the Paleozoic era gives reason to the bigger insects of the time. Both the example and the grasshopper testing in some way apply.
Here's a link to another article pertaining to the relation between insects and oxygen:
http://gsa.confex.com/gsa/2005ESP/finalprogram/abstract_87840.htm
I can’t imagine sitting outside on a beautiful sunny day and then have a bug the size of my hand crawling right next to me. I freak out now when bugs come near me, I think I’d have a heart attack if they were any bigger. I don’t even want to imagine what the sting or bite might feel like from a giant insect. But, I do have to wonder, if their were humans around during the Paleozoic, would these bugs appear as big as they are to us now? Would humans be taller, therefore the ratio from a bug to a human be the same?
The theory of oxygen being more abundant during the Paleozoic making bugs bigger in mass makes complete sense. The drop in oxygen with the atmospheric changes over a period time probably made it hard for the bugs to adapted, therefore becoming smaller. A good analogy for this is climbing a mountain. The higher you climb the less oxygen, the harder it is to breathe, High Altitude Sickness. As show in the experiments with the dragonflies and the grasshoppers, bigger sized dragonflies and grasshoppers performed better with higher levels of oxygen, whereas when they were put into lower levels, their activity decreased. In almost every situation where someone or something is put into a new environment, they need to adapt. It’s not healthy for a human to eat and drink only a tablespoon of food and water a day, nor is it easy for a big bug to live with lack of oxygen when their use to so much more.
I found this article very interesting. Even though these scientists aren’t exactly sure that oxygen levels contributed to larger bugs, their hypothesis is convincing to me. I hope to read more into this theory when more evidence comes about.
I‘m convinced. During late Paleozoic times, evolution brought the first oxygen producing land plants. In doing so, over the gradual growth of size and the widespread of these plants I think it may have caused the concentration peak of 35%, maybe even greater. Since the evolution from fish to land developed., forests and swamps could have covered the masses. With that high amount of plant vegetation, the amount of oxygen produced by these plants would have clearly made big bugs possible. There are probably more than a million different species of insects on the planet today. And today the size ratio with humans and insects are pretty great. So to say that they were bigger than people just frightens me, yet it gives me the curiosity of the possibility if it was indeed true. Was the planet actually inhabited by “Starship Trooper” sized bugs? I think so. But if it did happen in the past, could it happen in the future millions of years from now as well?
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