Depends on when in the Jurassic. Oxygen levels crashed during the Triassic (e.g., down to ~15%), so at the beginning of the Jurassic, O[sub]2[/sub] levels were low. They began climbing, and by the end of the period where slightly higher than current levels (i.e., around 22-23%). During the Cretaceous, they climbed further still, and peaked at around 27% in the late Cretaceous. Throughout the Tertiary, they fell steadily to the current levels.
It was during the late Carboniferous/early Permian that oxygen levels reached their maximum, at around 35%.
It should be noted that, in the mid-Jurassic, when sauropods had their “Golden Age” and birds first appear, oxygen levels were still lower than they are today.
Cool, thanks. I remember hearing about the ‘35% oxygen’ thing from a biogeochemist at my research station a couple years ago, for some reason it stuck in my head.
Do they think that plants and animals around the late Carboniferous had more of a problem with oxidative stress than they do today? And did they have particular mechanisms to deal with it?
That, I’m not entirely certain of. This paper discusses some of the effects of increased oxygen on insects during the Carboniferous. And chapter 5 of this book discusses the effects of increased oxygen on early tetrapods.
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You’d need to specify the number of legs. The size limit for a huge millipede would be much higher than the size limit for a huge biped.
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How about a millipedal dinosaur analog? A hexapodal dinosaur-like creature is quite easy to imagine; how about an octopodal dino? A centipod? a millipod? I bet there are much stranger things out there in the universe, even if they are rare.
At some point having a body that long serviced by a single set of lungs and a single digestive track would be a problem. Some hypothesize that the largest sauropods had to be near-continual eating machines as it was.
Metabolic rate decreases monotonically with size (roughly, with the 0.75 power of bodymass, though the exact number is disputed), so large animals have to eat less often than small ones. (or more precisely, have to eat a lower proportion of their bodymass per unit time).
Hummingbirds are a lot closer to ‘continual eating machines’ than, say, sperm whales.
The atmospheric pressure wasn’t significantly worse, and humans don’t have the same limitations related to oxygen as insects. Humans growing up in high altitude, and thus less oxygen, don’t end up shorter.
Neither was the conditions back then such that all insects grew larger due to increased oxygen levels, the higher oxygen just raised the upper limit on size, allowing some species to evolve into “monsters” by today’s standards.
Not being an expert I’m not even sure current science reports that much, but it definitely doesn’t support your musings.
But humans are evolved for today’s oxygen so if modern humans today gone in time machine to that timeline the oxygen would be much higher than what modern humans today are use to.
If vertebrates had evolved with three pairs of limbs instead of two, that would probably be workable or even better in some cases. But beyond that you would get diminishing returns. Too many legs would simply be in each others way.
P.S. In one RPG campaign the game master asked for suggestions for a tunnel monster (to be created magically against some evil dwarfs). I came up with the Dwarf Eater: a six-limbed weasel-like creature about the thickness of a black bear and fifteen feet long. The dice gods must have liked the concept because it ended up clearing out most of a dwarf mine.
Yes, and it would do nothing to their size. Oxygen level is not a determining factor for the size of an animal. You do realize there were lots of small animals around at that time as well?
Yes that is what I was saying.But I don’t think you can scale down humans or animals because organs and circulation system would also have to be scale down.And there may be limit to how small it can be before it does not work.
Even in the movie honey I shrunk the kids from what I understand you would not even see much being that small.
No. Just no. Some of them had armor. They did not have exoskeletons. There’s no way they’d develop exoskeletal limbs, or extra limbs, or extra eyes, or … well most of what makes those fantasy creatures fantastical.
