Truemors
When I was 8 years old, my parents took me to the Royal Tyrrell Museum - 4 hours in a car, 2 kids, 4 juice boxes, a side-of-the-highway bathroom break and we arrived. I remember pleading with my parents to buy me a shirt from the young children's section. Ironed on the front of a fluorescent yellow Tee was a menacing Tyrannosaurus rex, its tiny little forearms curled under its gaping wide, tooth-filled mouth ready to gobble up a passing herbivore.
I remember thinking to myself, why were these dinosaurs so big, and how did they get that way? My parents received the brunt of these questions, unwaveringly answering either "because God made them that way," or, "I don't know, go ask that employee." More often than not, they answered the latter.
Furthermore, I remember the giant dragonflies in the exhibit, hiding among the tall plastic replica club mosses. They seemed like a footnote of deep time, a 100 million year old superscripted arabic numeral, a minor detail among giant strokes no one will take time to look up. Its paper-mache wings and elongated torso were important enough to be included in the exhibit, yet it appeared to be constructed with little care or interest. Why? Because strung up before me was a five meter tall animal capable of eating everyone standing dumbfounded around it.
These giant insects would make the supertroopers drop a super load in their space pants. Yet, the inquisitive eight year old in me is asking 'Why' and 'How'.
Researchers have devised an interesting way of answering 'How' - for why is much more difficult to address.
In the late Paleozoic Era, with atmospheric oxygen levels reaching record highs, some insects evolved into giants. When oxygen levels returned to lower levels, the insect giants went extinct.
The basis of this gigantism is thought to lie in the insect respiratory system. In contrast to vertebrates, where blood transports oxygen from the lung to the cell, insects deliver oxygen directly through a network of blind-ending tracheal tubes. As insects get bigger, this type of oxygen transport becomes far less effective. But if the atmospheric oxygen levels increase, as they did in the late Paleozoic, then longer tracheal tubes can work. This would allow larger-sized insects—even giants—to evolve...
...Overall, they found that larger beetle species devote a disproportionately greater fraction of their body to tracheal tubes than do smaller species...
...They then examined the tracheal measurements of the four species to see if they could predict the largest size of currently living beetles...the leg data predicted a beetle that nicely matches the size of the largest living beetle, Titanus giganteus .
“This study is a first step toward understanding what controls body size in insects. It's the legs that count in the beetles studied here, but what matters for the other hundreds of thousands of beetle species and millions of insect species overall is still an open question,” said Jake Socha, Argonne biologist.
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