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I've read some conflicting theories regarding ancient atmosphere (some say it had more oxygen, but others dispute it) being relevant to survival of large dinosaurs.

So my question is: is it realistic, from the point of view of known science to have Cretaceous Period dinosaur alive today? (Assuming it was successfully brought over somehow, maybe in a large time-truck)

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  • $\begingroup$ if the dinosaurs are hardy why not life will find a way! sometimes and this is based on my 2 minutes of experience with my pet goldfish (it wants to play with a clownfish and a Regal Tang and it was fun for a while)... no animals are harmed in making this comment $\endgroup$
    – user6760
    May 22, 2015 at 1:27
  • $\begingroup$ We did have a question not that long ago about what time was the earliest when the Earth's atmosphere would support modern humans. The answer was, almost surprisingly late. I can't find the question, though... $\endgroup$
    – user
    May 22, 2015 at 13:59
  • $\begingroup$ What about the surface to interior ratio? Could this animal really exist and be able to moderate his core temperature pushing that much body mass cooling off with that little surface.. Must have been something much different ..less gravity maybe.. $\endgroup$
    – user18769
    Mar 6, 2016 at 19:04
  • $\begingroup$ Actually 02 content was 25 -35 percent with 30 being on average according to Scientific data from extracted gasses in Amber samples from that time. Dinosaurs would have a really hard time breathing. We require 19 percent and it's at 21.. think about that. Whoever thinks o2 content was lower needs to do more research ..in fact science is starting to believe the water or ice above the earth..which would have made the air content higher and plant and animal life much bigger. I'm sure it's controversial, but not the O2 content being almost 30 percent in the Jurassic period. That's a fact backed up $\endgroup$ Nov 12, 2021 at 20:04
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    $\begingroup$ @TimothyGould Dinosaurs were anatomically similar to birds, which can tolerate much lower Oxygen partial pressures than mammals. It is therefore reasonable to assume that Dinosaurs would be able to tolerate our present levels of oxygen. $\endgroup$
    – Monty Wild
    Nov 13, 2021 at 3:35

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Dinosaurs might be able to live in today's atmosphere, but a dinosaur suddenly transported into modern times might have other issues.

Plants have evolved considerably in the last 65 million years. Grasses and flowering plants really only came into being near the end of the Cretaceous period, so dinosaurs from earlier periods would have difficulty even recognizing them as food. As well, plants have evolved various toxins and other strategies to resist being eaten, which might poison a dinosaur or make it very sick. As well, dinosaurs might develop severe allergic reactions to modern plants. Herbivorous dinosaurs would, for the most part, require gigantic amounts of plant matter that they could digest. It is thought that the sauropods ate coniferous tree needles, for example, so a herd would lay entire forests to waste, and you would need a vast area for them to roam and the trees to recover.

Carnivores might have many of the same issues. The other problem for apex predators is current megafauna would only be sufficient as an appetizer or snack, rather than a full meal. Bringing back T-rex would put you on the hook for some pretty hefty bags of dino-kibble, or a large Texas cattle ranch.

Some "do it yourself" projects are underway to see if evolution can be essentially reversed in chickens to make a pseudo dinosaur, and if these efforts are successful, then Chicken-rex will be much better adapted to modern environments.

For more information see:

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    $\begingroup$ Or you could use hamburgers to feed T-rex. It only takes about 80. $\endgroup$
    – Frostfyre
    May 22, 2015 at 1:11
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    $\begingroup$ After 80 greasy hamburgers go down a Tyrannosaur's gullet, I'd want to be very far away from where he makes his nest..... $\endgroup$
    – Thucydides
    May 22, 2015 at 1:17
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    $\begingroup$ So if I ever do bring them over, I better vaccinate them first, fortunately pine needles aren't problem where I live so I can have a few sauropods. $\endgroup$
    – Maxim
    May 22, 2015 at 20:30
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Probably, but many would die.

You all seem to be forgetting that most bacteria and diseases have evolved in 65 million years in addition to the atmosphere, plants, and other animals. I'm no biology expert, but I'd bet that without up-to-date resistances, modern dinosaurs would face something akin to what happened when Europeans first reached the Americas: a lot of indigenous people were killed by germs.

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    $\begingroup$ My geology profs felt the same. They mentioned that herbivorous dinosaurs could not digest deciduous vegetation. Such plant life might even have been toxic to them. Even if the carnivores could have survived, they'd be much less vigorous than they were 100 million years ago - they'd be oxygen deprived. How active and athletic are humans with 40% less oxygen than they are used to? $\endgroup$
    – Jim2B
    May 22, 2015 at 4:12
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    $\begingroup$ You need to take into account that bacteria and especially virii are pretty targeted; they don't just attack things "without resistance", they exploit specific systems. The diseases that European diseases developed from were 100% harmless to humans until they specifically adapted to humans. It's no coincidence that almost all the deadly bacteria and virii come from animals - killing your host is not a good reproduction strategy. You'd need modern diseases exploiting systems that dinosaurs and modern reptiles/birds have in common that escalated over all those millions of years. Not very likely. $\endgroup$
    – Luaan
    Jan 30, 2018 at 11:51
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Yes, numerous dinosaurs could survive, and actually many would do quite well. We know this because dinosaurs are actually more numerous than mammals. Yes, I said they are, as in currently. Technically speaking a bird is a dinosaur, and birds outnumber any other land vertebrate in terms of of species.

Many people have brought up very valid points about how many herbivorous dinosaurs may not be able to eat the plant life, and that large canivores may simply not be able to find enough food. This is all true, but I think people often times forget and underappreciate just how diverse dinosaurs used to be, and paint them with far too broad of a brush stroke. Most theropod dinosaurs were not these towering super predators that we like to think of them as, most were actually quite small, and would probably compete favourably with small canivorous mammals such as racoons. Dinosaurs such as Troodon, Velociraptor, and small Tyrannosaurs like Stokesosaurus would probably be able to cut out a comfortable niche for themselves, and probably would prove to become a very problematic invasive species. Medium sized carnivores like Ceratasaurus and Utahraptor could probably sustain themselves for a while in places where large mammalian megafauana still exists like Africa, although I'd be willing to bet they would cause an ecological meltdown in the area. Also, large predatory Terror Birds from South America would also probably be able to very quickly establish themselves as an apex predator, and still technically count as dinosaurs.

Hope this helps.

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Yes. Given the recent studies as described here and here show that oxygen levels were actually lower (10 to 15% as compared to 21% today). So breathing would be the least of dinosaurs problem.


Also take a look at this question at skeptics which has quite a bit of info on the subject

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  • $\begingroup$ Dinosaurs might then be subject to oxygen toxicity effects, which can be lethal. $\endgroup$
    – Frostfyre
    May 22, 2015 at 0:24
  • $\begingroup$ Nah..... usually animals use only 10%-20% of the oxygen they breathe.... and if pure oxygen doesn't kill us it won't kill a giant colossus lizard. $\endgroup$
    – Charon
    Aug 21, 2016 at 22:01
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I would say most dinosaurs would survive. Given the facts I have seen dinosaurs could survive many obstacles. Dinosaurs roamed the earth for more than 180 million years. Not all could go extinct. If we talk about dinosaurs not being able to adapt to plant life because it has evolved to be poisonous I don't think the same. If we talk about the largest dinosaur argentinosaurus it is unlikely poison would take down a creature that weighs about 60 tons. Carnivores coexisting with herbivores could work, however if we talk about real world standards the apex predators will be affected greatly however medium to small class dinosaurs will not be affected. Large titan dinosaurs could survive in current rainforests and untouchable by regular fauna. Flying reptiles on the other hand not affected. Animals like quetzalcoatlus could survive in africa scavenging of of lions. Marine reptiles like liopleurodon and mosasaurus could survive on whales and larger animals. However it is unlikely some dinosaurs survive. Upon arrival into the world,About 20% would go extinct due to the climate. However being feathered helps the dinosaurs survive in cold environments, so in places like canada and greenland will not affect the habitat of dinosaurs. So my final conclusion is yes however some would die.

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  • $\begingroup$ Many studies suggest the bigger the organism, the more specialized it becomes as far as diet and environment. After every mass extinction its the larger animals that take the biggest hit. Also note that the bigger the animal the lower the diversity in the ecosystem. Because That animals offspring likely takes up ecological niches that would have been taken up by animals in that creatures size range as it grows. $\endgroup$
    – Gillgamesh
    Nov 12, 2021 at 20:26
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If they were recreated using genetic engineering and/or synthetic biology they would need to live isolated in an area where very few people( to be harmless for civilization) or live in a controlled environment like in Jurassic Park.

The dinosaurs that were herbivorous would need to live in the rainforests and only a small number of all dinosaurs that existed could be brought back to life for safety issues.

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