Are the planets growing?

[Aardwolf]

Kori Bustard

Kori Bustard is a large terrestrial bird. It is not flightless, it is just about the heaviest flying bird there is. It flies only when necessary, because of its weight. Its flight is strong with slow flapping wings. It takes off with very heavy wing beats, but once in flight, it flies quickly and strongly.

How odd. Someone should try to explain to the worlds largest flying bird that 40lb is tiny compared to the 500lb prehistoric predators. Another 100 million years and evolution has forgotton how to provide easy flight for birds less than 10% of the size of its predecessors.

[StefanR]

Aardwolf,
You have made a false comparison between modern and prehistoric beasts. The modern-sized beasts were in existence alongside the gargantuan beasts.

My point is that gravity creates an upper limit for nature which is what I'm comparing. Of course smaller animals existed, because there was a niche for them to fill and no limiting factor regarding weight. Do you believe anything can be scaled up? Then why no 1,000lb eagles, 30ft tall bears os 20 ton buffalo? Seems they would dominate their environments and they have had plenty of time to evolve that size without any competition.

Gravity is no setting up an upper limit alone. There are many more factors that determine size and weight.
And no not everything can just be scaled up. But life can sometimes be very creative, and can have a structural solution like pneumatized bones and tissue, for weight reduction and structural strenght. But as with the Meganeura it is not gravity but oxygen that is the limiting factor.

Consider the size of T-rex in comparison to it's tiny cousin Compsognathus. When you work the math to determine the relative massiveness of bone and musculature you find that the ratios work out according to a single plan for cross sectional area [of supporting bones, for example], load, surface area, etc. and that the massive dinosaurs were at a size limit for the loads they were carrying. This all in recognition that most creatures today operate in the same size dimensions as they always have.

The dimensions are not in question. If nature has a working efficient model then it will continue to use it. The question is regarding the larger size in those dimensions and why none now exist even though they have had time to do so.

Weight, volume, height and such are all dimensions that can very much play a factor. A cubic meter of granite is totally different than a cubic meter of pummice. But than again a ton of lead weighs the same as a ton of feathers.

Now compare a modern great lizard, such as the alligator, to its contemporary smallest lizard, the length of a dime's diameter. WIth only the smaller creatures surviving some planetary catastrophe, a far future scientist might look back and wonder how on the earth's "present" gravity a creature such as an alligator could have survived on land, not crushed under it's own humungous weight.

Well maybe they would if nothing as large as an alligator existed in their own time. They must be very small scientists though.

No no, those small scientists will be experts, and as is known experts already have selected evolutionary for smaller brains.

The planetary catastrophe scenario brings up another difficulty with your view... what caused the diminished size of terrestrial creatures. There is no gradual diminish-ING in the record, just the sudden disappearance of large forms. If the size issue was a matter of a gradual earth expansion, where is the evidence for this correlation? On the other hand, sedimentary stratification with worldwide markers and representative fossils at various levels indicates a [at least one] global catastrophe. No gravitational inflation is needed to explain why larger bulkier animals may be less viable in such a circumstance.

Sudden? What year did they all die off then? Putting dating difficulties to one side, the largest dinosaurs (up to 80 ton) existed between 150 and 200 mya. The smaller dinosaurs (up to 15 ton) existed between 150 and 50 mya. And between 50 mya and now we have up to 6 ton. That’s about as accurate as you can get and due to its vagueness it fits both scenarios and disputes neither.

This pertinently not true. Again Meganeura was also large as insects were the only species in the air. So there was no competition with other animals. The biggest dinosaurs lived at the end of the dinosaur era, the largest of pterosaurs were some of the last of their species.

Also, please explain why nature and evolution after tens of millions of years and potentially billions of generations has never replaced the gap vacated by the larger beasts? If they are possible, why no flying lions and rat sized dragonflies? And why do all the birds that millions of years ago would have happily flown about (and actually did because they all have wings), now all choose to walk? Seems very dumb on their part to allow this vast opportunity with no competition. It’s completely against everything we know about evolution and its ability for life to thrive and adapt in every way and everywhere possible. To grow a bit larger without any detrimental effects seems an easy option for evolution and all flightless birds would certainly gain an advantage if they could fly.

Well I can only say, I personally think you got an odd way of looking at life. So pinguins were stupid for stopping flight and starting swimming under water and such? perhaps they are stupid, but all along they seem quite succesful in making a living. The same with an ostridge, why would it fly if it can run. It suffices to stay alive in the mode of living the ostridge does, there is no need to fly. Same as with lions, why would they fly? Are they not able to take on their prey?

[Aardwolf]

StefanR,

What are your views regarding meganeura and their ability to fly?

Ther were some discussion earlier on this thread, pages 24-26, for reference.

Why would it not have the ability to fly? As again I see no objections to it flying. But perhaps you have found new
arguments in the mean time?

Sorry I should have been clearer.

What are your views regarding meganeura and their ability to fly in our gravity?

There are no problems for Meganeura. As size is accounted for by way of higher oxygen-levels, and there is a lot of recent findings and research about it if you just use google. So aside from that, those biggest of big insects lived at an end of a period where insects dominated the skies. No other animal was up there to compete. In later epochs, insects not only had to do with less oxygen but also had to do with other animals taking flight and predation.

Thats one theory and a controversial one at that. An increase in oxygen from 21% to a maximum of 35% allows for an insect 20 times in size? And it offers no explanation how flimsy insect wings can lift a 450 gram creature not only into the air, but provide it with the best flight of any creature. Forwards, backwards, instant turning, and also hunts and carries away its prey. Magical stuff this oxygen.

[StefanR]

StefanR,

What are your views regarding meganeura and their ability to fly?

Ther were some discussion earlier on this thread, pages 24-26, for reference.

Why would it not have the ability to fly? As again I see no objections to it flying. But perhaps you have found new
arguments in the mean time?

Sorry I should have been clearer.

What are your views regarding meganeura and their ability to fly in our gravity?

There are no problems for Meganeura. As size is accounted for by way of higher oxygen-levels, and there is a lot of recent findings and research about it if you just use google. So aside from that, those biggest of big insects lived at an end of a period where insects dominated the skies. No other animal was up there to compete. In later epochs, insects not only had to do with less oxygen but also had to do with other animals taking flight and predation.

Thats one theory and a controversial one at that. An increase in oxygen from 21% to a maximum of 35% allows for an insect 20 times in size? And it offers no explanation how flimsy insect wings can lift a 450 gram creature not only into the air, but provide it with the best flight of any creature. Forwards, backwards, instant turning, and also hunts and carries away its prey. Magical stuff this oxygen.

But do allow me to show some of this controversial theory:

ATMOSPHERIC OXYGEN AND THE EVOLUTION OF INSECT GIGANTISM
VANDENBROOKS, John M., School of Life Sciences, Arizona State University, PO Box 874601, Tempe, AZ 85287, jvandenb@asu.edu, HARRISON, Jon Fewell, School of Life Sciences, Arizona State University, Mail Code 4501, Tempe, AZ 85287-4501, and KAISER, Alex, Dept. of Basic Science, Midwestern University, 19555 N. 59th Ave, Glendale, AZ 85308

Most models estimate that over the last 500 million years atmospheric oxygen has varied from ~12% to 35%. Most strikingly, the giant insects of the late Paleozoic (i.e. dragonflies) existed when atmospheric oxygen was hyperoxic, supporting a role for oxygen in the evolution of insect body size. However, the fact that not all groups during this time period were giant (i.e. cockroaches) coupled with the paucity of the insect fossil record and the complex interactions between oxygen, organisms and communities makes it difficult to definitively accept or reject the historical oxygen-size link. Nevertheless, we have successfully reared dragonflies, cockroaches and a variety of other insect species under varying oxygen levels and the results of these studies do support a link between oxygen and the evolution of insect size: 1) dragonflies and other insect groups do develop and evolve larger body sizes in hyperoxia, while almost all insects develop smaller body sizes in hypoxia; yet cockroaches show no size difference when reared under hyperoxia, 2) insects developmentally and evolutionarily reduce their investment in the tracheal respiratory system when living in higher oxygen levels; suggesting there are significant costs associated with tracheal system structure and function and 3) larger insects invest more of their body in the tracheal system, potentially leading to greater effects of oxygen on large insects. These results provide several mechanisms by which the tracheal oxygen delivery system may be involved in the small size of modern insects and hyperoxia-enabled Paleozoic gigantism. When we begin to examine the fossil record closely, we see that certain groups have responded more strongly to oxygen variation. While taxa such as Protodonata and Paleodictyoptera have gigantic members, they are outliers to an overall pattern of oxygen-mediated body size change. On the other hand, Blattodea contain no giant representatives and demonstrate little effect on maximum body size, but do show shifts in average size correlated with changes in atmospheric oxygen levels. Here we examine the role of atmospheric oxygen in the evolution of insect body size and discuss the possibility of imaging fossil tracheae as a proxy for paleo-oxygen levels. This research was supported by NSF EAR 0746352 and DOD 3000654843 to JH and JVB.

http://gsa.confex.com/gsa/2010AM/finalp ... 181665.htm

Atmospheric oxygen and the evolution of insect gigantism
Dudley, R.
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #6986

Geophysical analyses suggest the presence of a late Paleozoic oxygen pulse beginning in the late Devonian and continuing through to the late Carboniferous. During this time, atmospheric oxygen levels increased to values potentially as high as 35% relative to the contemporary value of 21%. Widespread gigantism in late Paleozoic insects and other arthropods is consistent with enhanced oxygen flux within diffusion-limited tracheal systems, and thus with relaxation of constraints on maximum insect body size. Because total atmospheric pressure increases with increased oxygen partial pressure, concurrently hyperdense conditions would have augmented aerodynamic force production in early forms of flying insects. Hyperoxia of the late Paleozoic atmosphere may also have physiologically facilitated the initial evolution of insect flight metabolism. By the late Permian, evolution of decompositional microbial and fungal communities together with disequilibrium in rates of carbon deposition gradually reduced oxygen concentrations to values possibly as low as 15%. The disappearance of giant insects by the end of the Permian is consistent with extinction of these taxa for reasons of asphyxiation on a geological time scale. In modern selection experiments with Drosophila flies, substantial plasticity in body size can be evoked under conditions of variable oxygen. In particular, moderate hyperbaria (and thus hyperoxia) evokes a 20% increase in adult body size over merely five generations, suggesting ready capacity for evolutionary responses by insects to fluctuating atmospheric oxygen.

http://adsabs.harvard.edu/abs/2003EAEJA.....6986D

Atmospheric oxygen level and the evolution of insect body size

1. Jon F. Harrison1,*,
2. Alexander Kaiser2 and
3. John M. VandenBrooks1

1.
1School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA
2.
2Department of Biochemistry, Midwestern University, Glendale, AZ 85308, USA

1. * Author for correspondence (j.harrison{at}asu.edu).


Next Section
Abstract

Insects are small relative to vertebrates, possibly owing to limitations or costs associated with their blind-ended tracheal respiratory system. The giant insects of the late Palaeozoic occurred when atmospheric PO2 (aPO2) was hyperoxic, supporting a role for oxygen in the evolution of insect body size. The paucity of the insect fossil record and the complex interactions between atmospheric oxygen level, organisms and their communities makes it impossible to definitively accept or reject the historical oxygen-size link, and multiple alternative hypotheses exist. However, a variety of recent empirical findings support a link between oxygen and insect size, including: (i) most insects develop smaller body sizes in hypoxia, and some develop and evolve larger sizes in hyperoxia; (ii) insects developmentally and evolutionarily reduce their proportional investment in the tracheal system when living in higher aPO2, suggesting that there are significant costs associated with tracheal system structure and function; and (iii) larger insects invest more of their body in the tracheal system, potentially leading to greater effects of aPO2 on larger insects. Together, these provide a wealth of plausible mechanisms by which tracheal oxygen delivery may be centrally involved in setting the relatively small size of insects and for hyperoxia-enabled Palaeozoic gigantism.

http://rspb.royalsocietypublishing.org/ ... .0001.full

The tendency of some animals to be larger at higher latitudes ('polar gigantism') has not been explained, although it has often been attributed to low temperature and metabolism. Investigation of gigantism requires widely distributed taxa with extensive species representation at many well-studied sites. We have analysed length data for 1,853 species of benthic amphipod crustaceans from 12 sites worldwide, from polar to tropical and marine (continental shelf) to freshwater environments. We find that maximum potential size (MPS) is limited by oxygen availability.

http://biolaw.blogspot.com/2008/05/rhap ... sects.html


To me it seems like a well researched subject, and although there are still lots of uncertainties, it might be wise to not totally discard the hypothesis too quickly.

As for how the wings could held have the Meganeura aloft, is in my view not so strange. For one, just have a look at the reason for the naming the Meganeura Meganeura. Point two is these examples by analogy (so that means there remain some differences) and demonstration, some others could perhaps be found of this example but it is the principle :
http://www.youtube.com/watch?v=NwHOGkyMWWo
http://vimeo.com/798202

[seasmith]

Stephano
queven mihermano

('ad thought you gone enpilgramage with JL, thereforawhile)

Hyperoxia of the late Paleozoic atmosphere may also have physiologically facilitated the initial evolution of insect flight metabolism. By the late Permian, evolution of decompositional microbial and fungal communities together with disequilibrium in rates of carbon deposition gradually reduced oxygen concentrations to values possibly as low as 15%. The disappearance of giant insects by the end of the Permian is consistent with extinction of these taxa for reasons of asphyxiation on a geological time scale.

So, might this hyper-hypoxia thing be a cyclic affair?
What precipitated the earlier 'hypeoxiar' episode?
Will those bigbastard Insects return ??

s

[Aardwolf]

StefanR,

What are your views regarding meganeura and their ability to fly?

Ther were some discussion earlier on this thread, pages 24-26, for reference.

Why would it not have the ability to fly? As again I see no objections to it flying. But perhaps you have found new
arguments in the mean time?

Sorry I should have been clearer.

What are your views regarding meganeura and their ability to fly in our gravity?

There are no problems for Meganeura. As size is accounted for by way of higher oxygen-levels, and there is a lot of recent findings and research about it if you just use google. So aside from that, those biggest of big insects lived at an end of a period where insects dominated the skies. No other animal was up there to compete. In later epochs, insects not only had to do with less oxygen but also had to do with other animals taking flight and predation.

Thats one theory and a controversial one at that. An increase in oxygen from 21% to a maximum of 35% allows for an insect 20 times in size? And it offers no explanation how flimsy insect wings can lift a 450 gram creature not only into the air, but provide it with the best flight of any creature. Forwards, backwards, instant turning, and also hunts and carries away its prey. Magical stuff this oxygen.

But do allow me to show some of this controversial theory:

ATMOSPHERIC OXYGEN AND THE EVOLUTION OF INSECT GIGANTISM
VANDENBROOKS, John M., School of Life Sciences, Arizona State University, PO Box 874601, Tempe, AZ 85287, jvandenb@asu.edu, HARRISON, Jon Fewell, School of Life Sciences, Arizona State University, Mail Code 4501, Tempe, AZ 85287-4501, and KAISER, Alex, Dept. of Basic Science, Midwestern University, 19555 N. 59th Ave, Glendale, AZ 85308

Most models estimate that over the last 500 million years atmospheric oxygen has varied from ~12% to 35%. Most strikingly, the giant insects of the late Paleozoic (i.e. dragonflies) existed when atmospheric oxygen was hyperoxic, supporting a role for oxygen in the evolution of insect body size. However, the fact that not all groups during this time period were giant (i.e. cockroaches) coupled with the paucity of the insect fossil record and the complex interactions between oxygen, organisms and communities makes it difficult to definitively accept or reject the historical oxygen-size link. Nevertheless, we have successfully reared dragonflies, cockroaches and a variety of other insect species under varying oxygen levels and the results of these studies do support a link between oxygen and the evolution of insect size: 1) dragonflies and other insect groups do develop and evolve larger body sizes in hyperoxia, while almost all insects develop smaller body sizes in hypoxia; yet cockroaches show no size difference when reared under hyperoxia, 2) insects developmentally and evolutionarily reduce their investment in the tracheal respiratory system when living in higher oxygen levels; suggesting there are significant costs associated with tracheal system structure and function and 3) larger insects invest more of their body in the tracheal system, potentially leading to greater effects of oxygen on large insects. These results provide several mechanisms by which the tracheal oxygen delivery system may be involved in the small size of modern insects and hyperoxia-enabled Paleozoic gigantism. When we begin to examine the fossil record closely, we see that certain groups have responded more strongly to oxygen variation. While taxa such as Protodonata and Paleodictyoptera have gigantic members, they are outliers to an overall pattern of oxygen-mediated body size change. On the other hand, Blattodea contain no giant representatives and demonstrate little effect on maximum body size, but do show shifts in average size correlated with changes in atmospheric oxygen levels. Here we examine the role of atmospheric oxygen in the evolution of insect body size and discuss the possibility of imaging fossil tracheae as a proxy for paleo-oxygen levels. This research was supported by NSF EAR 0746352 and DOD 3000654843 to JH and JVB.

http://gsa.confex.com/gsa/2010AM/finalp ... 181665.htm

Atmospheric oxygen and the evolution of insect gigantism
Dudley, R.
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #6986

Geophysical analyses suggest the presence of a late Paleozoic oxygen pulse beginning in the late Devonian and continuing through to the late Carboniferous. During this time, atmospheric oxygen levels increased to values potentially as high as 35% relative to the contemporary value of 21%. Widespread gigantism in late Paleozoic insects and other arthropods is consistent with enhanced oxygen flux within diffusion-limited tracheal systems, and thus with relaxation of constraints on maximum insect body size. Because total atmospheric pressure increases with increased oxygen partial pressure, concurrently hyperdense conditions would have augmented aerodynamic force production in early forms of flying insects. Hyperoxia of the late Paleozoic atmosphere may also have physiologically facilitated the initial evolution of insect flight metabolism. By the late Permian, evolution of decompositional microbial and fungal communities together with disequilibrium in rates of carbon deposition gradually reduced oxygen concentrations to values possibly as low as 15%. The disappearance of giant insects by the end of the Permian is consistent with extinction of these taxa for reasons of asphyxiation on a geological time scale. In modern selection experiments with Drosophila flies, substantial plasticity in body size can be evoked under conditions of variable oxygen. In particular, moderate hyperbaria (and thus hyperoxia) evokes a 20% increase in adult body size over merely five generations, suggesting ready capacity for evolutionary responses by insects to fluctuating atmospheric oxygen.

http://adsabs.harvard.edu/abs/2003EAEJA.....6986D

Atmospheric oxygen level and the evolution of insect body size

1. Jon F. Harrison1,*,
2. Alexander Kaiser2 and
3. John M. VandenBrooks1

1.
1School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA
2.
2Department of Biochemistry, Midwestern University, Glendale, AZ 85308, USA

1. * Author for correspondence (j.harrison{at}asu.edu).


Next Section
Abstract

Insects are small relative to vertebrates, possibly owing to limitations or costs associated with their blind-ended tracheal respiratory system. The giant insects of the late Palaeozoic occurred when atmospheric PO2 (aPO2) was hyperoxic, supporting a role for oxygen in the evolution of insect body size. The paucity of the insect fossil record and the complex interactions between atmospheric oxygen level, organisms and their communities makes it impossible to definitively accept or reject the historical oxygen-size link, and multiple alternative hypotheses exist. However, a variety of recent empirical findings support a link between oxygen and insect size, including: (i) most insects develop smaller body sizes in hypoxia, and some develop and evolve larger sizes in hyperoxia; (ii) insects developmentally and evolutionarily reduce their proportional investment in the tracheal system when living in higher aPO2, suggesting that there are significant costs associated with tracheal system structure and function; and (iii) larger insects invest more of their body in the tracheal system, potentially leading to greater effects of aPO2 on larger insects. Together, these provide a wealth of plausible mechanisms by which tracheal oxygen delivery may be centrally involved in setting the relatively small size of insects and for hyperoxia-enabled Palaeozoic gigantism.

http://rspb.royalsocietypublishing.org/ ... .0001.full

The tendency of some animals to be larger at higher latitudes ('polar gigantism') has not been explained, although it has often been attributed to low temperature and metabolism. Investigation of gigantism requires widely distributed taxa with extensive species representation at many well-studied sites. We have analysed length data for 1,853 species of benthic amphipod crustaceans from 12 sites worldwide, from polar to tropical and marine (continental shelf) to freshwater environments. We find that maximum potential size (MPS) is limited by oxygen availability.

http://biolaw.blogspot.com/2008/05/rhap ... sects.html


To me it seems like a well researched subject, and although there are still lots of uncertainties, it might be wise to not totally discard the hypothesis too quickly.

As for how the wings could held have the Meganeura aloft, is in my view not so strange. For one, just have a look at the reason for the naming the Meganeura Meganeura. Point two is these examples by analogy (so that means there remain some differences) and demonstration, some others could perhaps be found of this example but it is the principle :
http://www.youtube.com/watch?v=NwHOGkyMWWo
http://vimeo.com/798202

These papers are far from conclusive. They explicitly say so themselves. Scientists writing papers that leave themselves an out, do so for good carreer defining reasons. However, if meganeura cannot fly through lack of oxygen, why can dragonflies fly? They are just scaled down almost identical versions. How do they cope with only 21% oxygen? Why are they capable of flight?

As for the videos. These models weigh around 30 grams so slightly heavier than the largest dragonflies/moths/humming birds, and a little lighter than a goliath beetle. When they get one to sustain flight weighing 450 grams we can discuss. Nature did it 300 million years ago without our technical abilities so it shouldn't be a problem for them. Unless of course they've reached the same limiting factor for that style of flight that nature now has to deal with...

[Aardwolf]

Regarding the oxygen controversy, for balance here is a paper supporting a different view.

Tracheal Respiration in Insects Visualized with Synchrotron X-ray Imaging

Insects are known to exchange respiratory gases in their system of tracheal tubes by using either diffusion or changes in internal pressure that are produced through body motion or hemolymph circulation. However, the inability to see inside living insects has limited our understanding of their respiration mechanisms. We used a synchrotron beam to obtain x-ray videos of living, breathing insects. Beetles, crickets, and ants exhibited rapid cycles of tracheal compression and expansion in the head and thorax. Body movements and hemolymph circulation cannot account for these cycles; therefore, our observations demonstrate a previously unknown mechanism of respiration in insects analogous to the inflation and deflation of vertebrate lungs.

Hence, there is no limitation regarding external oxygen balance, they breathe is a similar way to vertebrates.

[Aardwolf]

Concentrating on the Meganeura is a mistake also. What about the Meganeuropsis permiana. According to the paper you linked above "By the late Permian, evolution of decompositional microbial and fungal communities together with disequilibrium in rates of carbon deposition gradually reduced oxygen concentrations to values possibly as low as 15%." Yet the Meganeuropsis permiana lived during the late Permian. How is this possible with such little oxygen around?

[StefanR]

Stephano
queven mihermano

('ad thought you gone enpilgramage with JL, thereforawhile)

Hyperoxia of the late Paleozoic atmosphere may also have physiologically facilitated the initial evolution of insect flight metabolism. By the late Permian, evolution of decompositional microbial and fungal communities together with disequilibrium in rates of carbon deposition gradually reduced oxygen concentrations to values possibly as low as 15%. The disappearance of giant insects by the end of the Permian is consistent with extinction of these taxa for reasons of asphyxiation on a geological time scale.

So, might this hyper-hypoxia thing be a cyclic affair?
What precipitated the earlier 'hypeoxiar' episode?
Will those bigbastard Insects return ??

s

Jambo! Habari mzee Smith?

No enpilgrimage for me, just a restacking of the voltaic cells and retrieve some charge.

From what I get from it there is no definite cycle to the hyperoxia-hypoxia (and all what is in between). There were specific causes for some big events. Not all is quite sure about the specific causes, and not every event had the same drivers.
Which earlier hyperoxic episode do you mean?

As for them bigbastard insects...., they're among us at this moment, don't you see? Look at all those verocious grasshoppers and cockroaches in government. Do you really want them bigger?

[StefanR]

These papers are far from conclusive. They explicitly say so themselves. Scientists writing papers that leave themselves an out, do so for good carreer defining reasons. However, if meganeura cannot fly through lack of oxygen, why can dragonflies fly? They are just scaled down almost identical versions. How do they cope with only 21% oxygen? Why are they capable of flight?

As for the videos. These models weigh around 30 grams so slightly heavier than the largest dragonflies/moths/humming birds, and a little lighter than a goliath beetle. When they get one to sustain flight weighing 450 grams we can discuss. Nature did it 300 million years ago without our technical abilities so it shouldn't be a problem for them. Unless of course they've reached the same limiting factor for that style of flight that nature now has to deal with...

Perhaps they are inconclusive to you, but at least I can give examples in research which are supportive for my view. Do you have other links that specifically build your case? The fact that the scientist state that the subject is complex and that every research has to take into account that it is looking at parts of the whole picture seems pretty fair and scientific to me. If they would be claiming that there was a concensus and finality to the conclusions I think would not be good, and I personally think you would not appreciate that as well. Modesty also in science is a virtue.
Why can dragonflies fly? Because they have wings, my friend, why else?
And no they are not exact scaled down versions. The species of Meganeura is more a proto-dragonfly as it lacks certain characteristics that modernday dragonflies do have. It is why sometimes the word Griffinflies is used. How do modern day dragonflies with 21% Oxygen? Pretty well, I gather, I can see them here in the Netherlands in summer and they seem to do fine.

Again the weight of 450 grams is a rough estimate as it con only be inferred. A goliath beetle is about 120 grams so that is about a quarter of that estimate. The fact that the toy is 25 - 30 grams is because the batteries have to last and be cheap to make sales attractive. Such a simple little toy can not compare with the flight of animals in efficiency.
And just as with the Pterosaurs it is not weight that is the limiting factor for flight but wingload. Other thing is that insects have their own specifics of flight themselves added to that. The wingbeats of insectwings has special characteristics making use of vortex turbulence in a very nifty way.

[StefanR]

Regarding the oxygen controversy, for balance here is a paper supporting a different view.

Tracheal Respiration in Insects Visualized with Synchrotron X-ray Imaging

Insects are known to exchange respiratory gases in their system of tracheal tubes by using either diffusion or changes in internal pressure that are produced through body motion or hemolymph circulation. However, the inability to see inside living insects has limited our understanding of their respiration mechanisms. We used a synchrotron beam to obtain x-ray videos of living, breathing insects. Beetles, crickets, and ants exhibited rapid cycles of tracheal compression and expansion in the head and thorax. Body movements and hemolymph circulation cannot account for these cycles; therefore, our observations demonstrate a previously unknown mechanism of respiration in insects analogous to the inflation and deflation of vertebrate lungs.

Hence, there is no limitation regarding external oxygen balance, they breathe is a similar way to vertebrates.

This only fortifies the idea that it will be possible to have these insects grow larger, at least some species. It only makes it more likely and facilitating. Oxygen will still be a limiting factor, as research has shown.

[StefanR]

Concentrating on the Meganeura is a mistake also. What about the Meganeuropsis permiana. According to the paper you linked above "By the late Permian, evolution of decompositional microbial and fungal communities together with disequilibrium in rates of carbon deposition gradually reduced oxygen concentrations to values possibly as low as 15%." Yet the Meganeuropsis permiana lived during the late Permian. How is this possible with such little oxygen around?

If I'm not totally incorrect, you were the one bringing up Meganeura. Meganeura is the name for a genus of large flying insects, your Meganeuropsis permiana is a closely related species, hence the naming. It lived during the late Permian, at the end of the Permian oxygen was declining and after the P-T extinction event they were not seen anymore.
When there is talk about these large periods of time, stating the end of a period can still comprise millions of years. Finding specimen of large size of insects from such eras can still be living before large transitions have taken place and still have to take place.

Here a link to a nice three-part docu about flight in animals. It is quite nice, and shows some very good things about flight in the different animals that took flight. Insects, pterosaurs, birds and bats. All having invented flight on their own and with their own characteristics, but also obeying similar principles dictated by nature.
http://www.youtube.com/watch?v=s-30UmnbJoc
Have fun!

[Aardwolf]

These papers are far from conclusive. They explicitly say so themselves. Scientists writing papers that leave themselves an out, do so for good carreer defining reasons. However, if meganeura cannot fly through lack of oxygen, why can dragonflies fly? They are just scaled down almost identical versions. How do they cope with only 21% oxygen? Why are they capable of flight?

As for the videos. These models weigh around 30 grams so slightly heavier than the largest dragonflies/moths/humming birds, and a little lighter than a goliath beetle. When they get one to sustain flight weighing 450 grams we can discuss. Nature did it 300 million years ago without our technical abilities so it shouldn't be a problem for them. Unless of course they've reached the same limiting factor for that style of flight that nature now has to deal with...

Perhaps they are inconclusive to you, but at least I can give examples in research which are supportive for my view. Do you have other links that specifically build your case? The fact that the scientist state that the subject is complex and that every research has to take into account that it is looking at parts of the whole picture seems pretty fair and scientific to me. If they would be claiming that there was a concensus and finality to the conclusions I think would not be good, and I personally think you would not appreciate that as well. Modesty also in science is a virtue.

So at least we agree they can be wrong.

Why can dragonflies fly? Because they have wings, my friend, why else?
And no they are not exact scaled down versions. The species of Meganeura is more a proto-dragonfly as it lacks certain characteristics that modernday dragonflies do have. It is why sometimes the word Griffinflies is used. How do modern day dragonflies with 21% Oxygen? Pretty well, I gather, I can see them here in the Netherlands in summer and they seem to do fine.

Well I doubt they could be exact replicas after 300 million years but they are close enough for comparison. However, you avoid the question. Why are they able to fly if an almost identical ancestor would now be unable to fly due to lack of oxygen? Same principles should apply if nothing else has changed.

Again the weight of 450 grams is a rough estimate as it con only be inferred. A goliath beetle is about 120 grams so that is about a quarter of that estimate.

Well the weight estimate isn't questioned anywhere by either side so we can assume its a fair estimate. As for the weight of a Goliath Beetle, yet again I am confronted by inaccurate data to support a preconceived view. Yes Goliath Beetles can be 120 grams but I think you will find that is in the larval stage. Do you have a video of one flying in this form?

The fact that the toy is 25 - 30 grams is because the batteries have to last and be cheap to make sales attractive. Such a simple little toy can not compare with the flight of animals in efficiency.

Well you brought it up. Maybe you were unaware of the weight limitations. Do you at least find it interesting that they have a similiar ceiling to nature regarding weight (and oxygen has nothing to do with it)?

And just as with the Pterosaurs it is not weight that is the limiting factor for flight but wingload. Other thing is that insects have their own specifics of flight themselves added to that. The wingbeats of insectwings has special characteristics making use of vortex turbulence in a very nifty way.

Wingload doesnt have anything to do with flight in nature. Its a calculation for determinig flight characteristics for fixed wing structure while in flight. Theoretically you could devise a hundred ton duck with wings large enough to maintain flight. The reason we dont have any is because it would need legs strong enough to accelerate to 200mph to gain any lift. Flapping would be out of the question. It's nonsense to even discuss it. Getting in the air is the problem for nature, not maintaining flight once there.

[Aardwolf]

Regarding the oxygen controversy, for balance here is a paper supporting a different view.

Tracheal Respiration in Insects Visualized with Synchrotron X-ray Imaging

Insects are known to exchange respiratory gases in their system of tracheal tubes by using either diffusion or changes in internal pressure that are produced through body motion or hemolymph circulation. However, the inability to see inside living insects has limited our understanding of their respiration mechanisms. We used a synchrotron beam to obtain x-ray videos of living, breathing insects. Beetles, crickets, and ants exhibited rapid cycles of tracheal compression and expansion in the head and thorax. Body movements and hemolymph circulation cannot account for these cycles; therefore, our observations demonstrate a previously unknown mechanism of respiration in insects analogous to the inflation and deflation of vertebrate lungs.

Hence, there is no limitation regarding external oxygen balance, they breathe is a similar way to vertebrates.

This only fortifies the idea that it will be possible to have these insects grow larger, at least some species. It only makes it more likely and facilitating. Oxygen will still be a limiting factor, as research has shown.

This paper supports the idea that oxygen content in the air is unimortant. If, as mammals do, you need more oxygen you just breathe faster. Now its been shown insects are capable of breathing this way a drop from 35% to 21% is insignificant. Oxygen is not a signifincant limiting factor, as this research has shown.

[Aardwolf]

Concentrating on the Meganeura is a mistake also. What about the Meganeuropsis permiana. According to the paper you linked above "By the late Permian, evolution of decompositional microbial and fungal communities together with disequilibrium in rates of carbon deposition gradually reduced oxygen concentrations to values possibly as low as 15%." Yet the Meganeuropsis permiana lived during the late Permian. How is this possible with such little oxygen around?

If I'm not totally incorrect, you were the one bringing up Meganeura. Meganeura is the name for a genus of large flying insects, your Meganeuropsis permiana is a closely related species, hence the naming. It lived during the late Permian, at the end of the Permian oxygen was declining and after the P-T extinction event they were not seen anymore.
When there is talk about these large periods of time, stating the end of a period can still comprise millions of years. Finding specimen of large size of insects from such eras can still be living before large transitions have taken place and still have to take place.

Oxygen has been shown to not be a limiting factor.