Where Have the Hawk-Sized Insects Gone?

ScienceNOW ^ | June 4, 2012 | Sid Perkins

[SunkenCiv]

Around 300 million years ago, dragonflies with the wingspans of hawks flitted above coal-producing swamps. Such giants don't exist today, partly because oxygen levels in the atmosphere are much lower. But another reason is that the evolution of birds and their increasing agility in the air forced flying insects to shrink, according to a new study.

Like all multicellular animals, insects fuel their metabolism by taking in oxygen. Unlike creatures with lungs, however, insects draw in air through holes in their shell-like exoskeletons. The oxygen diffuses from those holes to the creatures' tissues through a dense network of tubes. Because diffusion becomes less efficient as the tubes get longer, the atmospheric concentration of oxygen is a powerful constraint on body size, especially for active insects that fly. The higher the concentration, the larger the insects can grow...

Several previous studies, especially those in the past 5 years, have hinted that factors other than oxygen levels influenced insect size.

For their new study, paleontologists Matthew Clapham and Jered Karr of the University of California, Santa Cruz, sorted more than 10,500 fossils of flying insects that lived in the past 320 million years into 10-million-year intervals. In each interval, they compared the largest wing length, which presumably belonged to the largest insect that lived during that particular period, to the average oxygen concentration in Earth's atmosphere during that time.

Results of the study, which the researchers report online today in the Proceedings of the National Academy of Sciences, show that for the first 170 million years or so of flying-insect evolution, wing length grew and shrank in step with variations in average oxygen concentration. Then, between 140 million and 130 million years ago, wing length dropped even though oxygen levels began to rise.

[Pharmboy]

Just let a cicada-killer wasp get into your kitchen some time. Your wife will scream as only a woman can when a large, fierce looking insect invades her space. Luckily, they are not very aggressive to humans, so it’s easy to look like a hero.

[TexasTransplant]

As to the link

That guy is

“willingly ignorant”

“purposely stupid”

His words

JMHO

TT

[TexasTransplant]

****** “I had a silly dream once. I dreamed that someone figured out a geological mechanism by which really really old fossils expanded in size over the millions of years and thus proved that nothing back then was as big as the fossils indicate.” ******

I had a dream ... well more than one ... where I could Fly and did ... (hated to wake up)

TT

[Jack Hydrazine]

Which guy?

[haroldeveryman]

Mosquitoes like B-29’s and roaches like Sherman tanks.

[JimSEA]

For an insect, the difference between 16 % and 31 % with the decreasing concentration of CO2 could have driven the increase in size initially until something (s) evolve to munch on them. Of course, horsetails and fern trees where much larger then as well.

[SunkenCiv]

;’)

[bigheadfred]

I prolly should apologize for bugging you.

[1010RD]

I know you’ll call me a liar and say I’m making it up, but that photo really happened. My friend was there, saw it and told me.

[1010RD]

They had to go with the tax angle. Our government won’t prosecute crimes against science (see: Global Warming).

[editor-surveyor]

>> “Considering the fact that the article is about evolution...” <<

.
No, the article is an attempt to manipulate facts to support evolution (and it didn’t work)

[1010RD]

You misspelled “tacks”.

[Oztrich Boy]

Didn’t someone figure out that those really big guys were all “hip waders”? Like a moose, they spent most of their time standing in water up to their ribs feeding on water plants?

Nope. Then they'd be rolly polly round like hippos for maximum bouyancy. Instead they had slim but deep bodies like rhinos and elephants to get the legs more directly under the centre of mass.

[thecodont]

I liked the bbq recipe you posted for giant ground sloth.

[a fool in paradise]

Mosquitoes like B-29’s and roaches like Sherman tanks.

We still have the latter in Texas.

[JRandomFreeper]

In the current economy, you cook what you can. ;)

johnny

[BwanaNdege]

Thank you!

It’s a wonder I managed to get airplanes and helicopters off the ground all those years! My main concern was Temp & Altitude. No easy way to measure Humidity rather than “feel”.

“To see why humid air is less dense than dry air, we need to turn to one of the laws of nature the Italian physicist Amadeo Avogadro discovered in the early 1800s. In simple terms, he found that a fixed volume of gas, say one cubic meter, at the same temperature and pressure, would always have the same number of molecules no matter what gas is in the container. Most beginning chemistry books explain how this works.

Imagine a cubic foot of perfectly dry air. It contains about 78% nitrogen molecules, which each have a molecular weight of 28 (2 atoms with atomic weight 14) . Another 21% of the air is oxygen, with each molecule having a molecular weight of 32 (2 stoms with atomic weight 16). The final one percent is a mixture of other gases, which we won’t worry about.

Molecules are free to move in and out of our cubic foot of air. What Avogadro discovered leads us to conclude that if we added water vapor molecules to our cubic foot of air, some of the nitrogen and oxygen molecules would leave — remember, the total number of molecules in our cubic foot of air stays the same.

The water molecules, which replace nitrogen or oxygen, have a molecular weight of 18. (One oxygen atom with atomic weight of 16, and two hudrogen atoms each with atomic weight of 1). This is lighter than both nitrogen and oxygen. In other words, replacing nitrogen and oxygen with water vapor decreases the weight of the air in the cubic foot; that is, it’s density decreases. “

http://www.usatoday.com/weather/wdensity.htm

[bigheadfred]

That is HILARIOUS!

[1010RD]

I thought you’d appreciate that. Best to you. ;-]

[Yollopoliuhqui]

There had to be gravity attenuation of some sort. The largest contemporary land mammal is the elephant. Nothing can grow larger and still retain mobility. Giraffes are at the upper limit of neck length. A sauropod 10 times larger with a long neck could neither pump blood to it’s head without experiencing capillary leakage due to the pressures involved in pumping a viscous liquid 20’+ high, but neck tendons could not support horizontal browsing in Earth’s present gravity.