Coragyps

There's another graph of this in Jennifer Clack's Gaining Ground, which shows the highest oxygen levels in the earliest Permian, before the big dinosaurs. Carbon dioxide levels were comparable to today's then, and quite a bit higher in the Triassic and Jurassic.
It's odd that amber would preserve oxygen-rich air that well - I would have expected the oxygen to react with the hydrocarbons in the tree sap over that long a period. I'm sure that it would if it were modern pine-tree sap - but maybe that's why amber is preserved: it's not as reactive as turpentine.

BTW, the Clack book is pretty hard going - it reads like a text instead of a "popular treatment" - but it gives a fantastic overview of just how complicated and difficult a paleontologist's work must really be. It traces the fossil record of the transition of "fish" to land animal in wonderful detail: you'll learn all about ectopterygoid bones and how they changed over time.

ps418

Oddly, I could find very little information about gas inclusions in amber. However, Berner et al's (2000) paleo O2 curve does show a major Permian-Carboniferous peak in PO2, and a smaller and more diffuse late Mesozoic peak. Gale et al (2001) cites estimates of 28kPa O2 for the end-Cretaceous, which is higher than the present atmospheric level of 21 kPa O2, but much lower than the up to ~40kPa O2 indicated for the Permian-Carboniferous by Berner et al's paper. 28 kPa O2 for the end Cretaceous is consistent with Berner's data, but is at the upper limit of the estimated error range.



Berner et al, Isotope Fractionation and Atmospheric Oxygen: Implications for Phanerozoic O2 Evolution

Gale et al, The high oxygen atmosphere toward the end-Cretaceous; a possible contributing factor to the K/T boundary extinctions and to the emergence of C4 species

Berner, Atmospheric oxygen over Phanerozoic time.

Patrick

The Lone Ranger

As far as I know, the biggest land mammal was Indricotherium, a hornless rhinoceros that lived during the early Miocene. A large adult would have weighed about 20 tons, which puts it in the range of the "smaller" sauropods. (Of course, the really big sauropods like Brachiosaurus would have weighed 80 tons or more, and dwarfed even something like Indricotherium.)

Angelos Economos has argued that "metabolic cost" limits the size to which land mammals can grow, and that Indricotherium was at or near the size limit for a land mammal. [Economos, A. C. 1981. "The Largest Land Mammal." Journal of Theoretical Biology, 89: 211-215.] I don't know how well his arguments have stood up over the past 20 years or so, however.

Cheers,

Michael

Camaban

Wow.....

I don't know what's sadder.....

my question or your answer....

scigirl

I formatted all the old html (I think??) code out - then realized that might be a mistake -

Can someone tell me whether html code will always be disabled here?

scigirl

Vorkosigan

This problem was discussed on the dino list a while back. Basically the oxy problem is two-fold; first, the biggest land dwellers were gigantic, nigh on 100 tons, and second, they had really long necks. Take this mamenchisaurus. Note that there's no way it could breathe with a pipe that long and lungs located in the chest, it would drown in its own CO2. So it is a bit of a mystery -- air sacs in the neck? -- how it managed to inhale down a windpipe that long, and then exhale, and get fresh air. I don't know what the latest is; perhaps it is a solved problem.

Vorkosigan

butswana

Last night on TLC, there was a 10,000 y.o. Mastadon skeleton. When it was alive it came in at 16 feet high and 10 tons. Not close to the sauropods, but still pretty damn big.

Mageth

would it be technically possible for them to live together?

I've heard Sauropods make terrible roommates.

From the discussion above, it sounds like it might not be possible for large dinosaurs to live with humans at today's oxygen levels. But of course, if you go outside for a bit you're likely to see a few small ones flying around or possibly singing you a nice song.

And while it might not be possible for large dinosaurs to co-exist with us today due to the lower oxygen levels, if the question is merely one of "technical possibility", I think it would have been "technically possible" for humans to survive 65+ million years ago at the higher oxygen levels (a point which seems to have been overlooked in the above responses).

MrDarwin

Fossils of giant insects are known from the Carboniferous (i.e., long before the time of dinosaurs). I don't believe they are found post-Permian. And the really bigt insects were dragonfly relatives, which were mostly wing anyway and long narrow bodies. I doubt the surface-to-volume ratio was much smaller than that of some present-day large insects, like some beetles and cockroaches.

MrDarwin

The problem with breathing through a tube is that the tube retains the air you just exhaled, and you just breathe it in again. This is one of the inefficiencies of our own lungs, but isn't a problem because the volume of the lungs is considerably greater than the volume of the trachea. For the same reason, breathing through a 1-foot tube is not a problem, but breathing through a 50-foot hose would be. It's possible that the dinosaurs were able to tolerate the same inefficiency (has anybody calculated the ratio of their lung to trachea volume?).

I can think of a couple of different ways to improve the design. One would be to have some kind of peristaltic contractions in the trachea, so air is forced in and out completely (i.e., no deoxygenated air is retained in the trachea). Another is to have a partitioned trachea, so the air only goes one way in each section, one breathing in, the other breathing out. Another way would be to have a separate exit from the lungs to expel air more or less directly, without having to go out the trachea.