Notices
Results 1 to 47 of 47

Thread: Oxygen Deprivation Caused Dinosaur Extinction

  1. #1 Oxygen Deprivation Caused Dinosaur Extinction 
    Forum Freshman
    Join Date
    May 2011
    Location
    Canada
    Posts
    8
    I've written an amateur scientific paper putting forth the theory that it was a decrease in atmospheric oxygen that was the cause of the extinction of the dinosaurs. Let me know what you think:

    http://amincd.tumblr.com/post/569058...aur-extinction

    Oxygen Deprivation Caused Dinosaur Extinction

    The Cretaceous–Tertiary extinction event, commonly known as the K-T extinction, was the mass-extinction of a large percentage of plant and animal species 65 million years ago, including all non-avian dinosaurs.

    It is generally believed that the Chicxulub asteroid impact triggered the K-T extinction due to some combination of the following effects of the impact: global firestorms, infrared radiation, an intense greenhouse effect due to CO2 released by fires, and a reduction in sunlight due to dust released into the atmosphere.

    I contend that the primary cause of the mass extinction of animals in the K-T extinction was oxygen deprivation caused by a reduction in atmospheric oxygen due to effects of the Chicxulub asteroid impact.

    The support for this theory can be found by looking at which species survived the event, and which did not.

    Marine Animals:

    Most species of coral close to the surface died out, while those living in oxygen-poor areas below the photic zone survived. 1 Species of Echinoderms (the phylum that includes sea urchins) that lived in shallow waters suffered the highest extinction rates while a those that lived in deeper waters had higher survival rates. 2

    Many species of cold-blooded marine vertebrates like fish and crocodyliforms, though no large members of the crocodilian clade, survived. 3 No species of mosasaurs or plesiosaurs, which were warm-blooded 4, survived.

    Terrestrial Animals:

    All non-avian dinosaurs died out, while avian dinosaurs (birds) survived. Small burrowing mammals survived. 5

    Terrestial Plants:

    A high percentage of plant species found in North America went extinct 6 while those further from the asteroid impact site, in New Zealand and Antarctica, were less affected. 7

    For the animals species, the major factors correlating with survival seem to be:

    • Small size

      Cold-bloodedness

      Burrowing adaptations

      Flight adaptations

      Deep-sea adaptations


    The biological advantage that all of the above are associated with is lower oxygen requirements. Smaller sized animals have lower environmental oxygen requirements than large one. 8 Cold-blooded animals have slower metabolisms and thus lower oxygen requirements than warm-blooded animals.

    Burrowing animals are adapted to survive in low oxygen underground environments. 9 Birds are adapted to survive in low oxygen high altitude environments. 10 Deep-sea marine life is adapted to survive in low oxygen aquatic environments. 11

    I contend that the decline in atmospheric O2 of the early Tertiary period which followed the Chicxulub asteroid impact, perhaps due to oxygen combustion in widespread fires or oxygen being used in the oxidation of the massive amounts of sulphur released by the impact 12, wiped out all species not able to survive in this new low oxygen environment.

    Marine animal life adapted to low oxygen deep-sea environments would have been able to ascend to shallow higher oxygen depths.

    Burrowing animals could have emerged from their burrows into the more oxygen rich outer environment.

    Birds could have stayed at sea level where oxygen levels are higher than high altitudes.

    Cold-blooded animals, particularly small ones, could have reduced their activity to slow their metabolism and require less oxygen.

    These options didn't exist for animals adapted to live in oxygen rich surface environments and, due to warm-blooded-ness and larger-size, had higher atmospheric oxygen requirements.

    The effect of the K-T extinction on plant species supports this theory. If high levels of infrared radiation or reduced photosynthesis due to particles reducing the amount of sunlight reaching the surface of the earth were the cause of the mass-extinction of animals, then plants would have seen a globally uniform reduction in species numbers, as animals did, since they would have been equally affected by these effects.

    Instead, plant extinctions occurred at their highest rate near the impact, where the firestorms would have been, and at their lowest rates in the southern hemisphere far from the impact.



    The ejecta blast created by the Chicxulub impact caused immediate destruction of animal and plant life near the impact site and reduced atmospheric oxygen levels, and the result was a globally uniform extinction of animal species poorly adapted to survive a low oxygen environment, and a more localized mass-extinction of plants that were killed by firestorms caused by the impact.


    Reply With Quote  
     

  2.  
     

  3. #2  
    Moderator Moderator TheBiologista's Avatar
    Join Date
    Aug 2008
    Posts
    2,564
    New hypotheses go in the new hypotheses sub forum.


    Reply With Quote  
     

  4. #3  
    Forum Freshman
    Join Date
    May 2011
    Location
    Canada
    Posts
    8
    Thank you, I see that now.
    Reply With Quote  
     

  5. #4  
    Forum Bachelors Degree PetTastic's Avatar
    Join Date
    Jul 2010
    Location
    London UK
    Posts
    421
    I think you need to consider how much of the oxygen was lost, and what happened to it.
    How much oxygen do you need to lose to make animals die 10% 80%?
    If you convert 10% of oxygen into carbon dioxide or sulphur dioxide, would the animals not die of poisoning first?

    Maybe you could go with the asteroid or comet was very hydrogen rich and the oxygen was converted to water, or that a large volume of the earths atmosphere was blasted into space and lost to the solar winds, making the atmosphere thinner.
    I believe in nothing, but trust gravity to hold me down and the electromagnetic force to stop me falling through
    Physics is the search for the best model not the truth, as only mythical beings know that.
    Reply With Quote  
     

  6. #5  
    Forum Freshman
    Join Date
    May 2011
    Location
    Canada
    Posts
    8
    The ground where the asteroid impacted is sulphur rich as my twelfth reference mentions. I didn't have the time to explain that in the paper. The reference also mentions that a possible outcome of this was a loss of atmospheric oxygen. You're right that I don't specify how much oxygen loss would be necessary to kill the dinosaurs. That would take a lot of research and analysis to find out.

    I don't think poisoning from an increase in atmospheric CO2/SO2/SO3 is a likely cause of the extinction as none of the theories that discuss possible rises in these gases cite poisoning as a possible outcome of the increase in their concentration.

    I also have read that oxygen levels declined significantly in the early Paleogene period, but I haven't been able to find by exactly how much they declined following the K-T event, probably because there isn't enough information available to draw that conclusion.

    This theory is highly speculative obviously, but I think it's more likely than the mainstream hypotheses of firestorms and lack of food, respectively, killing the dinosaurs off.
    Reply With Quote  
     

  7. #6  
    Moderator Moderator TheBiologista's Avatar
    Join Date
    Aug 2008
    Posts
    2,564
    Quote Originally Posted by Amincd
    The ground where the asteroid impacted is sulphur rich as my twelfth reference mentions. I didn't have the time to explain that in the paper. The reference also mentions that a possible outcome of this was a loss of atmospheric oxygen. You're right that I don't specify how much oxygen loss would be necessary to kill the dinosaurs. That would take a lot of research and analysis to find out.

    I don't think poisoning from an increase in atmospheric CO2/SO2/SO3 is a likely cause of the extinction as none of the theories that discuss possible rises in these gases cite poisoning as a possible outcome of the increase in their concentration.

    I also have read that oxygen levels declined significantly in the early Paleogene period, but I haven't been able to find by exactly how much they declined following the K-T event, probably because there isn't enough information available to draw that conclusion.

    This theory is highly speculative obviously, but I think it's more likely than the mainstream hypotheses of firestorms and lack of food, respectively, killing the dinosaurs off.
    I thought the leading hypothesis related to the climate change which followed the impact rather than the impact itself. It more neatly accounts for the differential survival of groups such as the avian dinosaurs (birds) and mammals. How does your hypothesis account for the survival of these groups in preference over most dinosaur species? Is there evidence of differing responses to oxygen deprivation?
    Reply With Quote  
     

  8. #7  
    Forum Freshman
    Join Date
    May 2011
    Location
    Canada
    Posts
    8
    The leading hypotheses are lack of food causing the extinction, and surviving species being ones that could live off of detritus (dead and broken-down organic matter), or animals that feed on the latter, and firestorms causing it, with those species that could take shelter in the water or in burrows surviving, respectively.

    How does your hypothesis account for the survival of these groups in preference over most dinosaur species? Is there evidence of differing responses to oxygen deprivation?
    I provide sources, in references 9 and 10, that show that avian dinosaurs and burrowing mammals have adaptations to survive in low oxygen environments. The links didn't copy over to the forum post, so you would need to see the original document in the first link to able to click on the links to the sources.
    Reply With Quote  
     

  9. #8  
    Time Lord Paleoichneum's Avatar
    Join Date
    Oct 2008
    Location
    Washington State, USA
    Posts
    5,154
    Quote Originally Posted by Amincd
    The leading hypotheses are lack of food causing the extinction, and surviving species being ones that could live off of detritus (dead and broken-down organic matter), or animals that feed on the latter, and firestorms causing it, with those species that could take shelter in the water or in burrows surviving, respectively.

    How does your hypothesis account for the survival of these groups in preference over most dinosaur species? Is there evidence of differing responses to oxygen deprivation?
    I provide sources, in references 9 and 10, that show that avian dinosaurs and burrowing mammals have adaptations to survive in low oxygen environments. The links didn't copy over to the forum post, so you would need to see the original document in the first link to able to click on the links to the sources.
    Why did the pterosaurs not survive, and why did crocodylomorphs make it?

    I don't think many are going ot hunt through things to find the references elsewhere unfortunately, so bringing them here would be best.
    Reply With Quote  
     

  10. #9  
    Forum Freshman
    Join Date
    May 2011
    Location
    Canada
    Posts
    8
    Only large species of pterosaurs were left by the end of the Cretaceous. Large size requires higher atmospheric oxygen levels.

    As for crocodylomorphs, they were cold-blooded, and there were many small species, so the small ones would have been better able to survive a low oxygen atmosphere, having two traits associated with lower atmospheric oxygen requirements. Only small species of crocydylomorphs survived the K-T extinction.

    I don't think many are going ot hunt through things to find the references elsewhere unfortunately, so bringing them here would be best.
    Agreed, I'll update my post.
    Reply With Quote  
     

  11. #10  
    Forum Senior
    Join Date
    May 2011
    Location
    United Kingdom
    Posts
    386
    Oxygen gets depleted from the atmosphere in burning, surely then heat is the cause for oxygen depletion.
    Reply With Quote  
     

  12. #11  
    Forum Senior
    Join Date
    May 2011
    Location
    United Kingdom
    Posts
    386
    Quote Originally Posted by Paleoichneum
    Quote Originally Posted by Amincd
    The leading hypotheses are lack of food causing the extinction, and surviving species being ones that could live off of detritus (dead and broken-down organic matter), or animals that feed on the latter, and firestorms causing it, with those species that could take shelter in the water or in burrows surviving, respectively.

    How does your hypothesis account for the survival of these groups in preference over most dinosaur species? Is there evidence of differing responses to oxygen deprivation?
    I provide sources, in references 9 and 10, that show that avian dinosaurs and burrowing mammals have adaptations to survive in low oxygen environments. The links didn't copy over to the forum post, so you would need to see the original document in the first link to able to click on the links to the sources.
    Why did the pterosaurs not survive, and why did crocodylomorphs make it?

    I don't think many are going ot hunt through things to find the references elsewhere unfortunately, so bringing them here would be best.
    The crocodiles could have found air pockets in underwater caves, or those that survived anyway.
    Reply With Quote  
     

  13. #12  
    New Member
    Join Date
    Jun 2011
    Posts
    3
    Interesting analysis. It would seem to follow the original work of Gene Shoemaker and the Alvarez team in some respects. It is estimated that between 85% and 95% of the planets vegetable matter burned at that time. There would have no doubt been a deficit of 02. Soil samples from the time you speak of are often very dark, containing large amounts of carbon. This does indicate burning, and in particular, incomplete burning. There are a a couple of ideas which I would like to see addressed further. You mention shallow water life? These plants/animals would have been subjected to a sudden increase in ambient temps, probably enough to kill them. Cold blooded creatures require less 02 than those which are warm blooded no? While it is true that their overall needs are greater, I think that the fact that they were not able to take shelter from the heat generated (by the burning) probably had more to do with their demise. The predecessors of whales? They were able to escape the intense heat. The heating of the atmosphere would have caused unusual patterns of atmospheric flow, bringing ozone from the upper atmosphere down to lower altitudes, and feeding the fires which raged. Additionally, outgassing from the oceans would have occured as atmospheric levels of 02 dropped, quite possibly creating hypoxic conditions, especially in shallower areas. The amount of dust and debris/soot/particulates thrown into the atmosphere would have soon decreased available light, leading to an almost immediate collapse of phytoplankton cultures, again leading to decreases in available 02. When I was a kid, we were taught that the dinosaurs froze to death due to an ice age. Wrong that was! I have recently maintained that they burned to death, which I still do, generally. We do agree on many aspects of this though. For instance, the sudden heating of the atmosphere would have decreased atmospheric density, denying some level of 02 to terrestrial dwellers. Seeing how many small creatures survived, being able to burrow, indicates that 02 levels were sufficient. Large creatures needed huge quantities of vegetable matter to survive. Once their food was gone, they were easy prey for carnivores. Then? They died too, starved. C02 levels would have increased significantly, leading to rapid growth of plants as the skies cleared. The air, being heated as it was, would have held much more water vapor, to fall as rain, cleansing the skies, as temps came down in the weeks/months/years later.
    Reply With Quote  
     

  14. #13  
    Comet Dust Collector Moderator
    Join Date
    Mar 2011
    Location
    New Jersey, USA
    Posts
    2,848
    Hi Bysil, welcome.

    In future posts, could you maybe use paragraphs to separate thoughts?

    The "wall of text" is very hard to read.

    Wayne
    Reply With Quote  
     

  15. #14  
    New Member
    Join Date
    Jun 2011
    Posts
    3
    Thank you Sir!

    I took a look at your input on the 02 deficit extinction theory, and found it most interesting! Your thoughts on the subject are cogent and insightful.

    That was just one long thought, with input from the several of me!
    Reply With Quote  
     

  16. #15  
    New Member
    Join Date
    Jun 2011
    Posts
    3
    There are a couple of other points I might have made and will now.

    The tsunami from this event would have been beyond comprehension. Many life forms, such as sea urchins etc., shallow water species, would have been swept inland. The debris of the retreating waters would have probably covered their habitat, making it unlikely they could conitinue, even if some survived intitially. Tsunami created by plate realigment would have to be considered also, as would tsunami created by landslides (mega tsunami).

    The vast quantity of debris/dust would have covered much of the impact/peri-impact zone, probably to a depth adquate to prevent any seeds from propogating. This would account for some of the exinctions of plant species nearer the point of impact you reference.

    Intense heat would have probably warmed the oceans surface, quite possibly slowing or stopping meridional circulation. Plankton, again, would have perished over large swaths of the world's oceans. It may be possible that at that time O2 levels at depth were actually higher than they were at the waters surface.

    I would suggest that birds would not have survived at lower altitudes as you suggest, but instead at higher altitudes, at elevation, where temps would have been lower, and the air quite possibly richer in 02 as a percentage per density. Food sources for birds would have probably been found at higher elevations too, where growth is not as dense, and fires would have been less likely to spread.

    We have not really covered sea level rise as a result of this. All existing glaciers/polar ice would have probably melted, possibly raising sea levels in the scores, if not hundreds, of feet, submerging large portions of coastal/low lying areas, where the bulk of life would have lived.

    The dust alone would have suffocated many animals, regardless of 02 concentrations, especially in areas near the impact, and far downwind of it.

    Every active volcano of the planet would have probably erupted. Is there any correlation between volcanic zones and extinction zones?

    Incidentally? We appear to be on a course to test at least part of your theory. Global phytoplankton is in serious decline, with over 40% being lost during the last fifty or so years, rate of loss? About 1%/yr. An article here references 02 depletion, and how a loss of Thermohaline Circulation will contribute to lower atmospheric concentrations of 02 in the coming years.

    http://www2.mbari.org/~coletti/dropb...or_article.pdf
    Reply With Quote  
     

  17. #16  
    Time Lord
    Join Date
    Mar 2007
    Posts
    8,035
    Also we don't have to consider the possibility of oxygen deprivation directly killing anything off. It could simply create a competitive disadvantage for some species over others. I used to do cross country running in high school. Whenever we had an interstate competition, the teams from higher altitude areas like Utah or Montana pretty much always won against teams from low altitudes like the Oregon coast.

    If Tyrannosaurus Rex is going to get winded every time he tries to sprint to chase down some prey animal he's managed to track, then his days as king of jungle are numbered.
    Some clocks are only right twice a day, but they are still right when they are right.
    Reply With Quote  
     

  18. #17  
    Forum Freshman
    Join Date
    Apr 2010
    Posts
    18
    Dinosaurs, larger ones, managed to endure for at least 700,000 years after the Chicxulub impact:

    http://www.sciencedaily.com/releases...0127141707.htm

    Their remains were found in New Mexico, USA, which is not far from the impact site. This calls into question whether the impact had the destructive effects that have been touted.

    I'm not sure if it has been established whether the impact was from an asteroid or comet. A comet impact would not have the equivalent thermal effects of an asteroid.

    And, if their was an extreme reducton in oxygen levels, why would those dinosaurs manage to survive for 700,000 years? Without much competition, why wouldn't they flourish well beyond that time?
    Reply With Quote  
     

  19. #18  
    Forum Freshman
    Join Date
    May 2011
    Location
    Canada
    Posts
    8
    Quote Originally Posted by kojax
    Also we don't have to consider the possibility of oxygen deprivation directly killing anything off. It could simply create a competitive disadvantage for some species over others. I used to do cross country running in high school.
    Good point.

    Quote Originally Posted by Batman
    Dinosaurs, larger ones, managed to endure for at least 700,000 years after the Chicxulub impact:

    http://www.sciencedaily.com/releases...0127141707.htm

    Their remains were found in New Mexico, USA, which is not far from the impact site. This calls into question whether the impact had the destructive effects that have been touted.
    If this is corroborated, that would change a lot. So far though, all the evidence I've seen shows an abrupt extinction of dinosaur species after the K-T impact, so I'm not convinced by a single fossil find.
    Reply With Quote  
     

  20. #19  
    Forum Freshman
    Join Date
    Apr 2010
    Posts
    18
    Some scientists don’t agree with the “sudden” extinction of dinosaurs after the impact:

    http://www.physorg.com/news160324445.html


    An earlier discovery, also in New Mexico, parallels the one I made in the prior post:

    http://esciencenews.com/sources/la.t...eat.extinction
    Reply With Quote  
     

  21. #20  
    Time Lord Paleoichneum's Avatar
    Join Date
    Oct 2008
    Location
    Washington State, USA
    Posts
    5,154
    Quote Originally Posted by Batman
    Some scientists don’t agree with the “sudden” extinction of dinosaurs after the impact:

    http://www.physorg.com/news160324445.html


    An earlier discovery, also in New Mexico, parallels the one I made in the prior post:

    http://esciencenews.com/sources/la.t...eat.extinction
    Geologically speaking a million years after the impact is still sudden. Also it opens the problems of the bones not being that young at death, but rather having been alluvialy reworked at somepoint.
    Reply With Quote  
     

  22. #21  
    Forum Freshman
    Join Date
    Apr 2010
    Posts
    18
    Yes, geologically one million years is sudden but this thread, if I’m not mistaken, theorizes that a drop in oxygen levels is what wiped out the dinosaurs. And, that sudden drop in oxygen levels was a direct result of the impact, which would have happened in days and weeks, not a million years.

    The question of reworked bones is always a possibility but from my first link:

    “Heaman and colleagues used a new direct-dating method called U-Pb (uranium-lead) dating. A laser beam unseats minute particles of the fossil, which then undergo isotopic analysis. This new technique not only allows the age of fossil bone to be determined but potentially can distinguish the type of food a dinosaur eats.”
    Reply With Quote  
     

  23. #22  
    Time Lord Paleoichneum's Avatar
    Join Date
    Oct 2008
    Location
    Washington State, USA
    Posts
    5,154
    Quote Originally Posted by Batman
    Yes, geologically one million years is sudden but this thread, if I’m not mistaken, theorizes that a drop in oxygen levels is what wiped out the dinosaurs. And, that sudden drop in oxygen levels was a direct result of the impact, which would have happened in days and weeks, not a million years.

    The question of reworked bones is always a possibility but from my first link:

    “Heaman and colleagues used a new direct-dating method called U-Pb (uranium-lead) dating. A laser beam unseats minute particles of the fossil, which then undergo isotopic analysis. This new technique not only allows the age of fossil bone to be determined but potentially can distinguish the type of food a dinosaur eats.”
    I am still concerned by the amount of oxygen that would need to be taken out of the system for a worldwide extinction to occur. I would mean a complete dead zone near the impact and and a resulting drop that would spread across the globe at a high enough level for the affected taxa to be killed off. It would also be shown in a measurable change in the composition of all the sedimentary rocks formed during the event.

    Interesting, I would be curious as to if it is measuring from time of death or from time of fossilization, but I need more information. I will note that U-Pb dating has been around for a number of years already, and thus the "new" comment is odd, new in what way? If its measuring from fossilization then it is still dependent on when the bones were finally emplaced in an environment long enough for fossilization to occur. If they are emplaced within a bog or other anoxic environment and preserved for a period of time then displaced and moved to an environment where fossilization started (eg ice age fossils eroding out of banks and into rivers) the fossilization time will be shifted. Thus the isotopic age only reflects the point at which the fossilization occurred.
    Reply With Quote  
     

  24. #23  
    Forum Freshman
    Join Date
    Apr 2010
    Posts
    18
    Paleoichneum,

    It would appear that the uranium-lead analysis technique has been improved:

    http://www.physorg.com/news/2011-02-...que-paper.html
    Reply With Quote  
     

  25. #24  
    Time Lord
    Join Date
    Mar 2007
    Posts
    8,035
    Quote Originally Posted by Paleoichneum
    Quote Originally Posted by Batman
    Yes, geologically one million years is sudden but this thread, if I’m not mistaken, theorizes that a drop in oxygen levels is what wiped out the dinosaurs. And, that sudden drop in oxygen levels was a direct result of the impact, which would have happened in days and weeks, not a million years.

    The question of reworked bones is always a possibility but from my first link:

    “Heaman and colleagues used a new direct-dating method called U-Pb (uranium-lead) dating. A laser beam unseats minute particles of the fossil, which then undergo isotopic analysis. This new technique not only allows the age of fossil bone to be determined but potentially can distinguish the type of food a dinosaur eats.”
    I am still concerned by the amount of oxygen that would need to be taken out of the system for a worldwide extinction to occur. I would mean a complete dead zone near the impact and and a resulting drop that would spread across the globe at a high enough level for the affected taxa to be killed off. It would also be shown in a measurable change in the composition of all the sedimentary rocks formed during the event.
    It wouldn't really require a huge drop, so long as it's a permanent drop. As I was saying earlier about long distance running in High School, if you're accustomed to running at low altitude and you try to run a race at high altitude, it's a grueling experience.

    It's not a question of how much oxygen dinosaurs needed just to survive. Survival itself is only the beginning. If all it costs them is competitive advantage against the smaller mammals, that's still enough to guarantee they'll die out. My understanding of the proposed hypothesis is that the dinosaurs didn't choke to death. They just became sluggish, and lost their edge.
    Some clocks are only right twice a day, but they are still right when they are right.
    Reply With Quote  
     

  26. #25  
    Time Lord Paleoichneum's Avatar
    Join Date
    Oct 2008
    Location
    Washington State, USA
    Posts
    5,154
    Quote Originally Posted by kojax
    Quote Originally Posted by Paleoichneum
    Quote Originally Posted by Batman
    Yes, geologically one million years is sudden but this thread, if I’m not mistaken, theorizes that a drop in oxygen levels is what wiped out the dinosaurs. And, that sudden drop in oxygen levels was a direct result of the impact, which would have happened in days and weeks, not a million years.

    The question of reworked bones is always a possibility but from my first link:

    “Heaman and colleagues used a new direct-dating method called U-Pb (uranium-lead) dating. A laser beam unseats minute particles of the fossil, which then undergo isotopic analysis. This new technique not only allows the age of fossil bone to be determined but potentially can distinguish the type of food a dinosaur eats.”
    I am still concerned by the amount of oxygen that would need to be taken out of the system for a worldwide extinction to occur. I would mean a complete dead zone near the impact and and a resulting drop that would spread across the globe at a high enough level for the affected taxa to be killed off. It would also be shown in a measurable change in the composition of all the sedimentary rocks formed during the event.
    It wouldn't really require a huge drop, so long as it's a permanent drop. As I was saying earlier about long distance running in High School, if you're accustomed to running at low altitude and you try to run a race at high altitude, it's a grueling experience.

    It's not a question of how much oxygen dinosaurs needed just to survive. Survival itself is only the beginning. If all it costs them is competitive advantage against the smaller mammals, that's still enough to guarantee they'll die out. My understanding of the proposed hypothesis is that the dinosaurs didn't choke to death. They just became sluggish, and lost their edge.
    It would have been a fairly uniform drop across both the herbivores and carnivores thus its likely that the carnivore would catch the prey before it got winded still. Plus this doesn't explain the wide range of taxa in different environments that went extinct, verses the wide variety of taxa that survived.
    Reply With Quote  
     

  27. #26  
    Forum Freshman
    Join Date
    Apr 2010
    Posts
    18
    I subscribe to the "canary in a coalmine" thesis. Coal miners, at one time, carried these avian dinosaurs down into the mines as an early warning indication.
    One would have to assume that, if the impact was as devastating as most people believe, birds would have been completely annihilated.

    The fact that birds survived but all sea-going reptiles became extinct, in my opinion, points to a different cause for the mass extinction at the K-T boundary.
    Reply With Quote  
     

  28. #27  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    Quote Originally Posted by Batman
    Coal miners, at one time, carried these avian dinosaurs down into the mines as an early warning indication.
    You notice that they did not take pigeons, or sparrow, or starlings, or a host of mich more commonplace birds with them, but always canaries. Do you suppose it is remotely possible that different species of bird have different senstivities ot anoxic conditions and toxic gases? I guess you don't, or you wouldn't have made that post.
    Reply With Quote  
     

  29. #28  
    Forum Freshman
    Join Date
    Apr 2010
    Posts
    18
    You wrote:

    "You notice that they did not take pigeons, or sparrow, or starlings, or a host of mich more commonplace birds with them, but always canaries. Do you suppose it is remotely possible that different species of bird have different senstivities ot anoxic conditions and toxic gases? I guess you don't, or you wouldn't have made that post."

    It is not important whether there are relative variations in the sensitivity of various avian dinosaurs to anoxic conditions. I'm sure that if we compare them as a group to, say, mammals, they will be far more sensitive to air quality. Therefore, my original point that they would be one of the least likely survivors of the K-T impact still applies (if the impact had the touted devastation.)

    BTW, maybe those other birds you mention are not as easy to deal with in a deep mine situation.
    Reply With Quote  
     

  30. #29  
    Moderator Moderator TheBiologista's Avatar
    Join Date
    Aug 2008
    Posts
    2,564
    Quote Originally Posted by Batman
    I'm sure that if we compare them as a group to, say, mammals, they will be far more sensitive to air quality.
    Honest question. Why are you sure of that?
    Reply With Quote  
     

  31. #30  
    Universal Mind John Galt's Avatar
    Join Date
    Jul 2005
    Posts
    14,168
    Quote Originally Posted by Batman
    I'm sure that if we compare them as a group to, say, mammals, they will be far more sensitive to air quality.
    That is an opinion. If you wish it to be accorded serious attention then offer some science to back it up.
    Reply With Quote  
     

  32. #31  
    Time Lord Paleoichneum's Avatar
    Join Date
    Oct 2008
    Location
    Washington State, USA
    Posts
    5,154
    I would also not that if that proposition were true it seems very likely the most avian dinosaurs of the group, and the existing birds would have all gone extinct leaving the less avian dinosaurs, such as small sauropods, less affected.
    Reply With Quote  
     

  33. #32  
    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
    Join Date
    Mar 2008
    Location
    Montreal
    Posts
    2,256
    In general, we should expect larger animals to tolerate low oxygen levels better. It is true in absolute terms that large animals require more oxygen, but really this is irrelevant. What is relevant is efficiency of oxygen use and ability to extract oxygen from the atmosphere. In which case, large animals tend to be better users of limited oxygen than small animals. Small animals tend to require more rapid metabolism to oxygenate their blood, and they also expend more energy maintaining homeostasis, since they are more susceptible to environmental stresses.

    If oxygen levels dropped rapidly, we would expect small animals to die out before large ones, since their metabolic needs of oxygen are higher. It is true, perhaps, in absolute terms that a mouse requires less oxygen than a human being. However, this isn't relevant, because the mouse relies on the same concentration of atmospheric oxygen to make its lungs work as we do. It isn't really the absolute amount that matters, but how efficiently they can get that oxygen out of the air when it is present in lower concentrations.

    This is why high oxygen levels allow large arthropods to exist, because their book lungs are highly inefficient at getting oxygen out of the air. Birds, reptiles, and mammals all have similarly structured lungs. It doesn't follow that a drop in atmospheric oxygen would favour small animals over large ones, a lower availability of food would favour small animals over large ones. Thus, the OP makes a small error when they conclude that small size is favored by low oxygen, this is really only true of organism that rely on diffusion for oxygen delivery.

    Edit: Birds do have highly efficient lungs, the most efficient of extant species. However, we would not expect the small birds to be favoured over larger birds simply because of oxygen levels.
    "I almost went to bed
    without remembering
    the four white violets
    I put in the button-hole
    of your green sweater

    and how i kissed you then
    and you kissed me
    shy as though I'd
    never been your lover "
    - Leonard Cohen
    Reply With Quote  
     

  34. #33  
    Forum Freshman
    Join Date
    Apr 2010
    Posts
    18
    Ophiolite & TheBiologista,

    If you are questioning whether birds, in general, are more susceptible to air quality issues than mammals, you have to think about why when a large group of birds suddenly die in a locale, air quality is immediately the prime suspect:

    http://www.usatoday.com/news/nation/...in-birds_x.htm

    If you are looking for a scientific study to confirm my opinion, you will have to search for one.

    We are getting away from the primary issue of this thread, which is whether a major decline in oxygen levels at the K-T boundary caused the extinction of the last non-avian dinosaurs. I’m sure geologists would have found clear indications of this in their studies of sediments, lava flow analysis, etc. This is the data that needs to be put forth to confirm the hypothesis proposed.
    Reply With Quote  
     

  35. #34  
    Moderator Moderator TheBiologista's Avatar
    Join Date
    Aug 2008
    Posts
    2,564
    Quote Originally Posted by Batman
    Ophiolite & TheBiologista,

    If you are questioning whether birds, in general, are more susceptible to air quality issues than mammals, you have to think about why when a large group of birds suddenly die in a locale, air quality is immediately the prime suspect:

    http://www.usatoday.com/news/nation/...in-birds_x.htm

    If you are looking for a scientific study to confirm my opinion, you will have to search for one.
    No we won't. You made the claim, not us.

    Air quality problems are bound to be an issue for a species that spends a fair chunk of it's time up in the air, where airborne pollutants tend to go...
    Reply With Quote  
     

  36. #35  
    Forum Freshman
    Join Date
    Apr 2010
    Posts
    18
    TheBologista,

    In an earlier post, you wrote, in response to the hypothesis proferred:

    “I thought the leading hypothesis related to the climate change which followed the impact rather than the impact itself. It more neatly accounts for the differential survival of groups such as the avian dinosaurs (birds) and mammals.”

    Could you provide some references that support your belief that climate change neatly accounts for the differential survival of groups such as birds and mammals ?
    Reply With Quote  
     

  37. #36  
    Moderator Moderator TheBiologista's Avatar
    Join Date
    Aug 2008
    Posts
    2,564
    Quote Originally Posted by Batman
    TheBologista,

    In an earlier post, you wrote, in response to the hypothesis proferred:

    “I thought the leading hypothesis related to the climate change which followed the impact rather than the impact itself. It more neatly accounts for the differential survival of groups such as the avian dinosaurs (birds) and mammals.”

    Could you provide some references that support your belief that climate change neatly accounts for the differential survival of groups such as birds and mammals ?
    It's not my hypothesis, I have only a vague notion of what caused the extinction of the bulk of dinosaur species. The reason I said it accounts better for our observations is because a massive impact event tends to kill rather suddenly and non-specifically, whereas we'd expect climate change over an extended time to present a less severe selective pressure. It might be total crap for all I know.

    It seems to me that you've made several claims, and you've been asked some questions about those. Rather than answer them, you're trying to put me on the defensive. I'm not making any claims here, I'm asking you to convince me.

    So, back to that comment on birds and susceptibility to air quality- do you have some evidence to support that assertion or were you speculating?
    Reply With Quote  
     

  38. #37  
    Forum Freshman
    Join Date
    Apr 2010
    Posts
    18
    TheBiologista,

    If you reread my post from yesterday, I wrote:

    "If you are looking for a scientific study to confirm my OPINION , you will have to search for one."
    Reply With Quote  
     

  39. #38  
    Moderator Moderator TheBiologista's Avatar
    Join Date
    Aug 2008
    Posts
    2,564
    Quote Originally Posted by Batman
    TheBiologista,

    If you reread my post from yesterday, I wrote:

    "If you are looking for a scientific study to confirm my OPINION , you will have to search for one."
    And I said that I'm not obliged to look. Everyone's got opinions, should I research them all or should I prioritize the ones backed up with some threshold level of evidence?

    You can tell me to go look it up, I can politely decline and that'll be the end of the discussion. I assume you want to convince people that you're right, but your current tactic doesn't seem to work with that goal.
    Reply With Quote  
     

  40. #39  
    Forum Professor Wild Cobra's Avatar
    Join Date
    Sep 2009
    Posts
    1,140
    Years ago, some friends and myself bounced around some ideas. I ended up believing that dinosaurs indeed died because of a reduction in atmospheric oxygen. Also, that it was the millions of years of the solar winds that reduced past oxygen levels. You see, the solar winds are primarily hydrogen, which would consume some of the oxygen and make more water.
    Reply With Quote  
     

  41. #40  
    Time Lord
    Join Date
    Mar 2007
    Posts
    8,035
    Quote Originally Posted by i_feel_tiredsleepy
    In general, we should expect larger animals to tolerate low oxygen levels better. It is true in absolute terms that large animals require more oxygen, but really this is irrelevant. What is relevant is efficiency of oxygen use and ability to extract oxygen from the atmosphere. In which case, large animals tend to be better users of limited oxygen than small animals. Small animals tend to require more rapid metabolism to oxygenate their blood, and they also expend more energy maintaining homeostasis, since they are more susceptible to environmental stresses.

    .
    So, if anything, an increase in oxygen levels would have been more likely to shift the balance against them. Would an increase in oxygen also negatively impact the vegetation?
    Some clocks are only right twice a day, but they are still right when they are right.
    Reply With Quote  
     

  42. #41  
    Forum Freshman
    Join Date
    May 2011
    Location
    Canada
    Posts
    8
    Quote Originally Posted by i_feel_tired_sleepy
    In general, we should expect larger animals to tolerate low oxygen levels better. It is true in absolute terms that large animals require more oxygen, but really this is irrelevant. What is relevant is efficiency of oxygen use and ability to extract oxygen from the atmosphere. In which case, large animals tend to be better users of limited oxygen than small animals. Small animals tend to require more rapid metabolism to oxygenate their blood, and they also expend more energy maintaining homeostasis, since they are more susceptible to environmental stresses.
    Large animals require more atmospheric oxygen because they have less surface area in their lungs relative to their body mass. This is why marine animals in the arctic can get much larger than those in warmer climates: because arctic waters are richer in oxygen.
    Reply With Quote  
     

  43. #42  
    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
    Join Date
    Mar 2008
    Location
    Montreal
    Posts
    2,256
    Quote Originally Posted by Amincd

    Large animals require more atmospheric oxygen because they have less surface area in their lungs relative to their body mass. This is why marine animals in the arctic can get much larger than those in warmer climates: because arctic waters are richer in oxygen.
    No, that's because organisms which rely entirely on diffusion, like several marine animals, are more limited by oxygen availability. This is because as you get larger it becomes harder for oxygen to reach internal tissues. Water also provides a different respiratory problem than air, because water can rapidly become locally deprived of oxygen, unlike air, because oxygen is found in much lower concentration. This is why motion is an important part of respiration for several marine animals. You'll find that the largest fish actually generally live in temperate and tropical waters (Whale sharks are the largest and live in the Gulf of Mexico), because the availability of food is a larger limiter of their size than oxygen delivery. An active circulatory system makes all the difference. That is why we don't have giant dragonflies around anymore, because insects do not have an efficient circulatory system (they have a pseudo heart that circulates hemolymph inefficiently in between their organs.


    http://www.ncbi.nlm.nih.gov/pubmed/18397180

    This article looks at how determinants like adapted haemoglobins are far more important than size for determining how fish tolerate hypoxia.

    The claim that large animals have less lung surface area compared to their mass is simply wrong. Some larger animals have more lung surface area compared to their mass, some have less than small animals. That would depend on the evolutionary history of the organisms. A dog has a ratio of 4 m2/kg and a mouse has a ratio of 3 m2/kg, a human on the other hand has a ratio of 1 m2/kg. I imagine if we looked at something fairly stationary like a small tortoise, they might have a ratio closer to humans. Animals that have very active lifestyles tend to have larger surface area to mass ratios, but you don't see a trend based on size. What you do see a trend in is energy efficiency, larger animals need far less active metabolism. As an example you need only look at the heart rate of small animals compared to large ones. Or even to go back to lungs. A mouse breathes 32.4 times it's lung volume per minute, a human breathes 0.84. That's a pretty big different in ratio, that means a mouse is breathing very quickly to keep itself supplied with oxygen compared to a human. In which case, a dog may have a relatively large lung capacity for its size, but it also uses that capacity far more efficiently than a small animal does.

    The peer reviewed scientist in the article above agree with me that animals with methods of active oxygen delivery (fish, amphibians, reptiles, birds, and mammals) will see very little difference in ability to take up oxygen relative to their size. Secondly, they agree with me that larger animals will handle oxygen deprivation better than smaller ones when they are forced out of their comfort range. (As an example look at how well humans adapt to living at high altitudes)

    Size has little effect, because small mammals would not be more adapted to surviving oxygen deprivation than large dinosaurs (or even small dinosaurs for that matter), they actually would have handled it worse. There may be something to fish adapted to low oxygen surviving, but then you're left with the problem of why mammals didn't seem to suffer.
    "I almost went to bed
    without remembering
    the four white violets
    I put in the button-hole
    of your green sweater

    and how i kissed you then
    and you kissed me
    shy as though I'd
    never been your lover "
    - Leonard Cohen
    Reply With Quote  
     

  44. #43  
    Moderator Moderator TheBiologista's Avatar
    Join Date
    Aug 2008
    Posts
    2,564
    Quote Originally Posted by Wild Cobra
    Years ago, some friends and myself bounced around some ideas. I ended up believing that dinosaurs indeed died because of a reduction in atmospheric oxygen. Also, that it was the millions of years of the solar winds that reduced past oxygen levels. You see, the solar winds are primarily hydrogen, which would consume some of the oxygen and make more water.
    At what rate? Faster than the capacity of evolution to cope? Faster than compensatory processes putting oxygen back into the atmosphere? Sounds pretty flakey to me.
    Reply With Quote  
     

  45. #44  
    Forum Professor Wild Cobra's Avatar
    Join Date
    Sep 2009
    Posts
    1,140
    Quote Originally Posted by TheBiologista
    Quote Originally Posted by Wild Cobra
    Years ago, some friends and myself bounced around some ideas. I ended up believing that dinosaurs indeed died because of a reduction in atmospheric oxygen. Also, that it was the millions of years of the solar winds that reduced past oxygen levels. You see, the solar winds are primarily hydrogen, which would consume some of the oxygen and make more water.
    At what rate? Faster than the capacity of evolution to cope? Faster than compensatory processes putting oxygen back into the atmosphere? Sounds pretty flakey to me.
    It was a just an idea. The rate would be generally slow unless there was a massive solar event causing far more than hydrogen that the earth might pass through. It could be a whole string of things, or maybe life became too difficult for large land creatures and a single event then wiped them all out.

    As foe sea creatures, they are buoyant and don't have the same 2D strength vs 3D mass to contend with.
    Reply With Quote  
     

  46. #45  
    Time Lord Paleoichneum's Avatar
    Join Date
    Oct 2008
    Location
    Washington State, USA
    Posts
    5,154
    Quote Originally Posted by Wild Cobra
    Quote Originally Posted by TheBiologista
    Quote Originally Posted by Wild Cobra
    Years ago, some friends and myself bounced around some ideas. I ended up believing that dinosaurs indeed died because of a reduction in atmospheric oxygen. Also, that it was the millions of years of the solar winds that reduced past oxygen levels. You see, the solar winds are primarily hydrogen, which would consume some of the oxygen and make more water.
    At what rate? Faster than the capacity of evolution to cope? Faster than compensatory processes putting oxygen back into the atmosphere? Sounds pretty flakey to me.
    It was a just an idea. The rate would be generally slow unless there was a massive solar event causing far more than hydrogen that the earth might pass through. It could be a whole string of things, or maybe life became too difficult for large land creatures and a single event then wiped them all out.

    As foe sea creatures, they are buoyant and don't have the same 2D strength vs 3D mass to contend with.
    The event wiped out many sessile corals, echinoderms, and brachiopods, along with all non-avian dinosaurs, no matter the size. I will note that at the end of the Cretaceous it was theropods, hadrosaurs, ceratopsians, and smaller Sauropods. Not the massive Sauropods of the Jurassic, so size was already smaller then the largest sizes that were reached.
    Reply With Quote  
     

  47. #46  
    Forum Freshman
    Join Date
    May 2011
    Location
    Canada
    Posts
    8
    Quote Originally Posted by I feel tired/sleepy
    No, that's because organisms which rely entirely on diffusion, like several marine animals, are more limited by oxygen availability. This is because as you get larger it becomes harder for oxygen to reach internal tissues.
    You're correct that size is highly correlated with greater requirements for oxygen availability in animals that rely on diffusion, as opposed to specialized respiratory surfaces, but the reason given in the citation I provided is that larger animals have a smaller surface area/volume ratio:

    http://www.arctic.uoguelph.ca/cpl/ar...th/goliath.htm

    It also makes this claim, which is consistent with my theory:

    Being a gigantic species does have a down side; should the environment change, and oxygen levels fall, the largest species will be the first to go.
    That is why we don't have giant dragonflies around anymore, because insects do not have an efficient circulatory system (they have a pseudo heart that circulates hemolymph inefficiently in between their organs.
    A decrease in atmospheric oxygen levels are thought to be primary reason why insects became smaller:

    http://www.livescience.com/1083-oxygen-giant-bugs.html

    Roughly 300 million years ago, giant insects scuttled around and fluttered over the planet, with dragonflies bearing wingspans comparable to hawks at two-and-a-half feet. Back then, oxygen made up 35 percent of the air, compared to the 21 percent we breathe now.
    http://www.ncbi.nlm.nih.gov/pubmed/18397180

    This article looks at how determinants like adapted haemoglobins are far more important than size for determining how fish tolerate hypoxia.
    I will try to look at this later when I have more time.

    The claim that large animals have less lung surface area compared to their mass is simply wrong. Some larger animals have more lung surface area compared to their mass, some have less than small animals. That would depend on the evolutionary history of the organisms.
    I would have thought the correlation between body volume and lung surface area would follow the correlation seen between body volume and body surface area, which larger animals having a smaller lung-surface-area-to-volume ratio simply because volume increases geometrically while surface area increases arithmetically.
    Reply With Quote  
     

  48. #47  
    Moderator Moderator TheBiologista's Avatar
    Join Date
    Aug 2008
    Posts
    2,564
    Quote Originally Posted by Amincd
    I would have thought the correlation between body volume and lung surface area would follow the correlation seen between body volume and body surface area, which larger animals having a smaller lung-surface-area-to-volume ratio simply because volume increases geometrically while surface area increases arithmetically.
    That's a hypothesis. When we look at reality, what do the numbers say? Is there a correlation, and if so, how strong is it?
    Reply With Quote  
     

Bookmarks
Bookmarks
Posting Permissions
  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •