Noted Young-Earth Creationist Kent Hovind made a claim in a 2007 video that suggested that the idea of dinosaurs living on Earth millions of years ago was implauseable if the oxygen levels were the at the same level that exist today.

TimeStamp from video

He argued that dinosaurs needed a higher partial pressure of Oxygen to account for their large size ,claiming the partial pressure of Oxygen during the period was too low, that they would not be able to get enough Oxygen. He suggested, in a light-hearted manner, that they would need so much air intake that the very process might have created enough friction to start a fire.

He used this conjecture to demonstrate that the earth might have had a water canopy above it which would increase the partial pressure of oxygen and therefor allow dinosaurs to grow to the sizes that are evident from the fossils. This is based on the Water Canopy Theory

Is his conjecture true: Was the partial pressure of Oxygen too low for dinosaurs to exist?

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    It's not "common belief" that oxygen made up a greater proportion of the atmosphere during those eras, it's established fact. During the Jurassic and Cretaceous, and even into the Paleogene and Neogene, oxygen made up a significantly greater proportion of the atmosphere. During the Jurassic, oxygen made up about 26% of the atmosphere. During the Cretaceous, it was 30%.
    – Compro01
    Nov 21, 2013 at 14:43
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    @Compro01: A claim like that deserves a reference, even in a comment.
    – Oddthinking
    Nov 21, 2013 at 15:13
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    Welcome to Skeptics, @Gerdi. While the claims of Hovind are on-topic (e.g. 1 and 2, this question isn't clear. Which specific claim do you want us to tackle: That dinosaurs would need so much air intake they would start a fire (huh?), that the partial pressure of Oxygen was higher and/or lower (when?). That dinosaurs breathed air? That the atmosphere was made of ice? What has any of that to do with Piltdown Man?
    – Oddthinking
    Nov 21, 2013 at 15:20
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    Also, please provide a reference to the videos (the names, a timestamp, a short transcript and perhaps a URL), so we can hear them for ourselves.
    – Oddthinking
    Nov 21, 2013 at 15:21
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    @Gerdi - as OddThinking asked, could you please provide a time stamp, transcript, and other details on the video? Those of us in the US are constitutionally protected from cruel and unusual punishment, so we shouldn't have to to sit through two hours of a Kent Hovind video. As far as atmospheric oxygen concentrations go, Compro01 appears to be right - the oxygen concentration was higher, not lower, during the Cretaceous period when the dinosaurs lived (geology.com/usgs/amber).
    – Mark
    Nov 26, 2013 at 4:03

2 Answers 2


The following articles suggest that dinosaurs breathed efficiently, like birds do still: which allowed them to cope with low oxygen levels that killed off other species. Note that some birds are able to breathe and fly at 20,000 feet, where the oxygen is lower (less than half sea-level pressure).

BBC Earth - Did all dinosaurs breathe like birds?

BIRDS EVOLVED from carnivorous theropod dinosaurs.

Living birds have a very unusual system of respiration, which sets them apart from all other animals: their lungs are unidirectional.

In birds, the unidirectional nature of the lung means that air with oxygen passes through the lungs during inhalation and exhalation.

Birds can do this because they have a system of air sacs that connect to the lungs, which store air during the entire breathing cycle. During inhalation, oxygen-rich air passes through the lungs directly from the trachea, but during exhalation other oxygen-rich air that had been stored in air sacs passes across the lungs.

Their lung is remarkably efficient at getting lots of oxygen into the blood. This is important because birds fly, and flight is an activity that requires a lot of energy and an elevated metabolism, both of which require a large quantity of oxygen.

So did dinosaurs have this type of lung? Some dinosaurs definitely did. We know that because the air sacs often leave characteristic traces on the bones, which fossilise.

In many birds and dinosaurs the air sacs are actually inside the bones themselves, hollowing out the centre. We can see these internal sinuses, as well as the circular or oval-shaped openings that lead into them, in many bones of theropod and sauropod dinosaurs. This is clear evidence that they had a bird-like lung.

We are not so sure about ornithischians, such as the horned dinosaurs and duck-billed dinosaurs. Their bones do not have the hollow centres and circular or ovoid ‘foramina’ that are so often seen in the bones of theropods and sauropods. This may mean that ornithischians breathed very differently compared to other dinosaurs.

This is an important question about dinosaur biology that is currently the subject of much research by palaeontologists, so keep your eyes peeled!

ABC Science - Did low oxygen give dinosaurs a boost?

Low oxygen levels could have triggered two giant extinctions hundreds of millions of years ago, allowing the dinosaurs to reign supreme over the ancestors of mammals, a U.S. researcher says.

University of Washington palaeontologist, Dr Peter Ward, presents his argument to a meeting of the Geological Society of America in Seattle, Washington this week.

Dinosaurs first appeared during a long period of low oxygen and therefore developed highly efficient breathing mechanisms that allowed them to thrive while many other species became extinct. Ward arrived at his theory by tying in what is known about the physiology of dinosaurs with recent geological evidence suggesting that from 275 million to 175 million years ago, oxygen levels stayed very low - comparable to levels found now at altitudes of 4,200 metres.

Ward believes low oxygen and hot greenhouse conditions caused by intense volcanic activity may have caused widespread extinctions 250 million years ago, at the boundary between the Permian and Triassic periods, and about 200 million years ago, at the boundary between the Triassic and Jurassic periods.

Ward said he put together three pieces of the puzzle - the extremely efficient breathing systems of birds, the finding that many dinosaurs had similar physiology, and a report that came out earlier this year showing that oxygen levels were low during the two extinctions.

"Someone told me they had heard of or seen geese flying above [Mount] Everest - at 31,000 feet [10,000 metres]," said Ward, pointing out the air at this altitude was very thin. "If you put a human at 30,000 feet they'd be very, very, quite dead. And the birds are not only up there, they are doing major heavy exercise."

Birds and dinosaurs both have holes in their bones. And many of the largest dinosaurs, such as brontosaurus or apatosaurus, seem to have had lungs attached to a series of thin-walled air sacs that may have acted something like bellows to move air through the body.

"The reason the birds developed these systems is that they arose from dinosaurs halfway through the Jurassic Period. They are how the dinosaurs survived," Ward said. "The literature always said that the reason birds had sacs was so they could breathe when they fly. But I don't know of any brontosaurus that could fly."

"However, when we considered that birds fly at altitudes where oxygen is significantly lower, we finally put it all together with the fact that the oxygen level at the surface was only 10% to 11% at the time the dinosaurs evolved." Currently at sea level, atmospheric oxygen levels are 21%.

If giant dinosaurs had to breathe in a low-atmosphere environment, then such an efficient breathing system would have given them a survival advantage.

"You'd be really favoured for survival in very bad, nasty, low-oxygen world," Ward said.

  • I edited (removed text from) the above articles slightly when I quoted them, but what I quoted is more than half of each article.
    – ChrisW
    Nov 26, 2013 at 0:46
  • The claim of very low O2 from 275 to 175 million years ago seems at variance with the more recent paper mentioned in my (updated) answer, see Figure 1 (d) nature.com/ngeo/journal/v3/n9/fig_tab/ngeo923_F1.html . However, I suspect proxy reconstructions going back that far are rather likely to be uncertain.
    – user18604
    Nov 26, 2013 at 11:17
  • "In many birds and dinosaurs the air sacs are actually inside the bones themselves" .. oh that is cool!! Thanks man . cool answer
    – user13859
    Nov 26, 2013 at 11:38
  • According to Fastovsky & Weishampel, "Dinosaurs - A Concise Natural History" (2nd edition), CUP, the unidirectional breathing was an adaptation that allowed long necks. With bidirectional breathing the air in the trachea at the end of the inhalation is wasted and must be pushed out before air can be exhaled from the lungs. Presumably the return route rejoined the trachea near the head so this dead space is eliminated. The book doesn't seem to mention low oxygen, so presumably thought on this may have moved on, very interesting though!
    – user18604
    Nov 27, 2013 at 9:23

The blue whale is a larger animal than any dinosaur with similarly large nostrils (see below) and is also warm blooded. It seems to be able to breathe without any problems (including spontaneous combustion ;o), in an atmosphere with lower oxygen levels than in the Cretateous (see below), which suggests there isn't really any need for higher partial pressure of oxygen.

Regarding atmospheric oxygen during the Phanerozoic era, this paper looks interesting [*emphasi*s mine]

Ian J. Glasspool & Andrew C. Scott, Phanerozoic concentrations of atmospheric oxygen reconstructed from sedimentary charcoal, Nature Geoscience 3, 627 - 630 (2010)


Variations of the Earth’s atmospheric oxygen concentration (pO2) are thought to be closely tied to the evolution of life, with strong feedbacks between uni- and multicellular life and oxygen1, 2. On the geologic timescale, pO2 is regulated by the burial of organic carbon and sulphur, as well as by weathering3. Reconstructions of atmospheric O2 for the past 400 million years have therefore been based on geochemical models of carbon and sulphur cycling4, 5, 6. However, these reconstructions vary widely4, 5, 6, 7, 8, 9, 10, particularly for the Mesozoic and early Cenozoic eras. Here we show that the abundance of charcoal in mire settings is controlled by pO2, and use this proxy to reconstruct the concentration of atmospheric oxygen for the past 400 million years. We estimate that pO2 was continuously above 26% during the Carboniferous and Permian periods, and that it declined abruptly around the time of the Permian–Triassic mass extinction. During the Triassic and Jurassic periods, pO2 fluctuated cyclically, with amplitudes up to 10% and a frequency of 20–30 million years. Atmospheric oxygen concentrations have declined steadily from the middle of the Cretaceous period to present-day values of about 21%. We conclude, however, that variation in pO2 was not the main driver of the loss of faunal diversity during the Permo–Triassic and Triassic–Jurassic mass extinction events.

Dinosaurs evolved in the Triassic and persisted through the Jurassic and Cretateous, and it seems that Oxygen levels have fluctuated considerably during the time, but for the most part were higher than they are now. If lung efficiency was the issue that caused the dominance of the dinosaurs it seems odd that this continued through the Cretaceous where oxygen levels were apparently generally higher than they are now (why didn't any other groups evolve similar compensatory mechanisms given the long timescale available). However, this is only one study, and I am no expert on this topic.

Also, from what I remember large dinosaurs developed largely from the mid-Jurassic to Cretaceous.

Lastly, having seen some of the video, the claim is that Apatosaurus had nostrils the size of a horse. According to Weischampel, Dodson and Osmolska, "Dinosauria", page 273 "In general terms, the most striking features of the sauropod skull include the enlarged and retracted externel nares [DM: nostrils]". See also

Lawrence M. Witmer "Nostril position in dinosaurs and other vertebrates and its significance for nasal function", Science 3 August 2001: Vol. 293 no. 5531 pp. 850-853 DOI:10.1126/science.1062681

Many dinosaurs have enormous and complicated bony nasal apertures. Functional interpretation requires knowledge of the location of the external opening in the skin. Traditionally, the fleshy nostril of dinosaurs has been placed in the back of the bony opening, but studies of extant dinosaur relatives suggest that it is located far forward. Narial blood supply and cavernous tissue corroborate the rostral position in dinosaurs. A rostral nostril was, and remains, a virtually invariant rule of construction among Amniota, which has consequences for (i) nasal airstreaming, and hence various physiological parameters, and (ii) the collection of behaviorally relevant circumoral odorants.

Note that as soft tissue rarely gets significantly fossilised, the "enormous and complicated bony nasal apertures" are pretty much all we have to go on, so I suspect Hovind's comment about the size of their nostrils is at best a guess. Clearly if the dinosaurs needed bigger fleshy nostrils, their skulls could have accommodated them.

See also CrisW's answer for another possible explanation.

  • it does have a lung capacity of 5000 liters to help with that Nov 21, 2013 at 14:48
  • Dinosaurs had rather large rib cages as well, at the London science museum they have skeletons of both (though not in the same room) for comparison.
    – user18604
    Nov 21, 2013 at 14:50
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    Are you sure that's the Science Museum? The Natural History Museum just down the road seems more likely.
    – bdsl
    Nov 22, 2013 at 14:31
  • yes, you are of course quite right, I was there only a couple of months ago as well - doh! Well worth a visit though.
    – user18604
    Nov 22, 2013 at 17:46
  • Hey @DikranMarsupial Yeah it actually makes sense that it is so large considering that it breaths oxygen. The pressure depth at which it mainly lives makes the oxygen in its blood a very high partial pressure according to Boyle's law.
    – user13859
    Nov 25, 2013 at 10:17

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