Posted on 07/17/2012 2:44:00 PM PDT by 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.
(Excerpt) Read more at news.sciencemag.org ...
“The higher atmospheric pressure in the past created more buoyancy, offsetting gravity to an extent.”
Not to be a nitpicker, but the “mass of a Brachiosaurus lies between 50 and 200 tons” http://www.dinosaurtheory.com/big_dinosaur.html, thus, it would have displaced between 50 & 200 cubic meters of air. (most animals have about the same density as water or slightly less)
Since “The density of dry air at sea level is about 1/800th the density of water” (1.25 kg/m3), if the atmosphere was twice as dense back then, the added buoyancy for a Brachiosaurus would have amounted to about 63kg to 250kg. (add a bit for moist air)
Not much help when you weight 50 to 200 tons.
They’re all lurking somewhere alongside the road when I come home on the Harley after dark.
I don’t know where they are the rest of the time.
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?
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.
Flipping poles and gravitational fluctuation...little explored..
:’)
Like what for instance?
Aieeyaa! No no no! Common fallacy and you would think moist air is more heavy than dry air. No so. Pilots know all about this as it takes longer to to take off when the air is moist. I know it is counter-intuitive, but it is true.
Hawk sized insects Vs. Cessna sized flying reptiles...
Kent Hovind talks about the large size of the animals, insects and plants plus the longevity of human beings before the Flood.
http://www.youtube.com/watch?v=PoRSBGD7vbA
http://en.wikipedia.org/wiki/Kent_Hovind
Residence Florence, Colorado, currently incarcerated at USP Florence ADMAX in the Florence Federal Correctional Complex by the Federal Bureau of Prisons... convicted of tax-related crimes.
“Not much help when you weight 50 to 200 tons.”
Correct, the atmosphere must have been much more than twice as dense in order for the largest terrestrial dinosaurs to have been supported by buoyancy.
Rhode Island?
If you have actually been convicted of tax-related crimes nowadays you must be doing something right.
Does him being in jail for tax-related crimes disprove the evidence he presents?
“Didn’t someone figure out that those really big guys were all “hip waders”?”
That proposal had to be abandoned because their feet are adapted to walking on dry land and not muddy lake beds. Besides which, if that were correct, the big sauropods could never leave the lakes, so they should be totally aquatic and not “waders”.
Well....DUH. Where else would they go? They were all drafted by the EPA and are presently flying spy missions over private farms in Iowa.
“Not much help when you weight 50 to 200 tons.”
Or when pregnant with twins. :-P
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