Could high air-pressure explained huge dinosaurs?

March 21, 2008 11:14 AM

SCIENCE! > Has anyone in paleontology explored the possibility that some aspects of dinosaur morphology can be explained by air pressure much higher than Earth's contemporary atmosphere?

I ask because it seems like a high pressure environment could explain the ridiculous size of many sauropods & winged dinosaurs. Has anyone ever looked into this? Or am I confusing properties of a high-pressure liquid environment and a high-pressure gaseous environment with this notion?

posted by joe_from_accounting to science & nature (15 comments total)

Sorry, why would a higher air pressure result in bigger winged dinosaurs?
posted by Comrade_robot at 11:17 AM on March 21

Was there a much higher air pressure? It seems like this should be easy to establish by other means instead of trying to determine whether dinosaur mophology could have been explained by higher air pressure if it did in fact exist.
posted by iknowizbirfmark at 11:21 AM on March 21

The reasons are given in this presentation.
posted by vacapinta at 11:25 AM on March 21

Do you think that higher air pressure would help to support a more massive organism? If so , the I think you may be confusing your liquids and gases.
posted by kuujjuarapik at 11:27 AM on March 21

(should be then I think...)
posted by kuujjuarapik at 11:28 AM on March 21

What holds the pressure down? Don't we constantly lose atmosphere into space because earth's gravity isn't enough to hold it all? We didn't have more gravity then, and the contents of the atmosphere wasn't significantly more or less dense.
posted by cmiller at 11:34 AM on March 21

Higher air pressure might explain the giant insects of the Carboniferous -- easier for those lungless guys to grow bigger if higher pressure could push more oxygen into their tissues -- but I'd think it would be easy enough to measure isotopes to determine air pressure, yes? Theory being, if I have this right, that the composition of ancient air locked into ancient rocks (or ice) can be more or less accurately measured, with respects to said isotopes.

Anyway, is it strictly necessary to hypothesize greater air pressure to explain dinosaurs?
posted by Guy_Inamonkeysuit at 11:37 AM on March 21

Well ... I had a look around, and it looks like there's a review article out:

The Evolutionary Physiology of Animal Flight: Paleobiological and Present Perspectives

Robert Dudley (Annual Review of Physiology Vol. 62: 135-155 (Volume publication date March 2000)

▪ Abstract Recent 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 period, plant terrestrialization and global carbon deposition resulted in a dramatic increase in atmospheric oxygen levels, ultimately yielding concentrations potentially as high as 35% relative to the contemporary value of 21%. Such hyperoxia of the late Paleozoic atmosphere may have physiologically facilitated the initial evolution of insect flight metabolism. Widespread gigantism in late Paleozoic insects and other arthropods is also consistent with enhanced oxygen flux within diffusion-limited tracheal systems. 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. 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. As with winged insects, the multiple historical origins of vertebrate flight in the late Jurassic and Cretaceous correlate temporally with periods of elevated atmospheric oxygen. Much discussion of flight performance in Archaeopteryx assumes a contemporary atmospheric composition. Elevated oxygen levels in the mid- to late Mesozoic would, however, have facilitated aerodynamic force production and enhanced muscle power output for ancestral birds, as well as for precursors to bats and pterosaurs.
posted by Comrade_robot at 12:12 PM on March 21

Guy: does geobarometry fit what you describe?
posted by jwells at 12:15 PM on March 21

There is a oft-criticized theory in evolutionary biology called Cope's Rule that hypothesizes that organisms tend to get bigger with time. Bigger animals (for plant-eaters) mean they can fight off predators more easily; the predators tend to get bigger as a result, then the plant eaters get bigger, etc. The classic example is the size of horses through time. Dinosaurs got bigger during the Mesozoic; mammals got bigger during the Cenozoic (mammoths and sloths, anyone?).

Don't forget, some of the largest species to have ever lived are around today, like the giant sequoia and the blue whale. An experiment for your idea could involve gathering evidence on the sizes of organisms at higher elevations and sea level and statically see if size is related to the pressure difference. But you would find that morphology corresponds more to climate and nutrient availability - such as oxygen or phosphate - than something like air pressure. You see the same pattern among organisms at latitude as you do with elevation.

Organisms also have to account for differences in surface area/volume ratios as they grow/evolve. Smaller organisms have a much larger surface area/volume ratio and lose heat more rapidly. Growing bigger also allows you to maintain heat more efficiently, an attribute important in both hot and cool climates. Size would also depend on your "thermic-ness" - are you endothermic or ectothermic, and in what type of climate do you live?

Back to Cope, Cope's Rule is criticized because it's more of a rule of thumb than a law and not exactly based on empirical evidence. Also, you have to remember, just as dinosaurs were storming around, rat sized or smaller mammals and chicken sized dinos were scurrying away from them - or eating their eggs.
posted by barchan at 12:21 PM on March 21

comrade robot, that extract seems to be talking about the relative levels of oxygen in the atmosphere fluctuating, not an increase in barometric pressure, unless there were a slight change in pressure due to the differences in the weight of oxygen gas vs. nitrogen gas.
posted by jenkinsEar at 2:29 PM on March 21

I remember when I was six and I thought that everybody who knew anything knew that there were no such things as winged dinosaurs. And yes, I would have said that in just that tone. Then I would have looked at that Levenspiel article and wondered why the Brachiosaurus was identified as a Brontosaur/Apatosaur. Seriously, what?

In all fairness, it is true that there aren't any mobile land or air organisms as big as the sauropods and pterosaurs around today, and it's hard to explain Quetzacoatl. I'm just a little skeptical of "CONTEMPORARY EARTH PHYSICS CAN'T EXPLAIN THIS!!!" when we used to say that about bees, and when a paper stating this hypothesis has been so widely rejected (and, uh, the Brontosaur thing bothers me, I admit).
posted by bettafish at 3:40 PM on March 21

I don't have the link bookmarked... this is crazy biblical creationist talk. There was high pressure and a shell of water around the planet that let the old biblical folk live hundreds of years. Then the flood, water from the heavens and from underneath the ground, 40 days and 40 nights, and everything not on the ark dies (um, fish???). Afterwards, the golden age of living for hundreds of years is over, no high pressure, no protective water barrier in outer space and people are suddenly human. There's a Google video somewhere explaining all of this, crazy whack-job people who think the world is 4000 years old and people had dinosaurs as pets.

see here.
posted by zengargoyle at 4:32 PM on March 21

Your theory opens up many more questions than it addresses. The main one is: By what mechanism would Earth have been sustaining a higher air pressure? Was Earth's gravity increased? If so, that raises a whole slew of other problems that you'd have to address.

Unless you have compelling answers for these questions, Occam's Razor suggests that we should discard your theory.
posted by chrisamiller at 4:39 PM on March 21

I've heard from several places (but none really authoritatively) that the ancient atmosphere may have contained much more oxygen.

Oxygen in the air, to be precise. Some scientists think that the air at the time of the dinosaurs contained a lot more oxygen gas than it does today. Since the oxygen animals breathe is used in chemical reactions that power their muscles, more oxygen in the air might have made it possible for dinosaurs to get more oxygen into their muscles. That could have made them much stronger than animals today—strong enough to carry around huge bodies. It might also explain how sauropods managed to breathe through those long, skinny necks of theirs. To see why that's a problem, try putting a drinking straw in your mouth and breathing through it. Quite a challenge, isn't it? But it would be easier to breathe if the air had more oxygen in it.

The evidence for more oxygen in the air at the time of the dinosaurs comes from bubbles in 100-million-year-old amber, tree sap that hardened during the time of the dinosaurs. By crushing the amber and analyzing the gases that come out, scientists at the U. S. Geological Survey think they can tell what the air was like back then. Other scientists who have done similar experiments, however, think the oxygen content probably was not higher. Still others suspect that dinosaurs were better at capturing oxygen because they had more efficient lungs than mammals do. That's certainly possible—after all, birds, the closest living relatives of ancient dinosaurs, have better lungs than mammals. Until some lucky paleontologist digs up a dinosaur lung, though, nobody will know for sure.

More here.
posted by wfrgms at 5:00 PM on March 21