Dinosaurs

[madviking]

As I said, you might hyperventilate. But nothing about a 30% oxygen atmosphere is inherently dead inducing.

 

[Synobun]

??
What do you mean by this?
Every organism alive today has had 65,000,000 MORE years of ancestors' evolution than dinosaurs did.

Somehow overlooked this. Thanks CFC.

I should have mentioned that I was referring to the evolution of a single species and not a family. Hominidae as we know it began evolving around eight-fifteen million years ago, Homo Sapiens reached near modern stature almost 300, 000 years ago. Compare this to the 15 million years of species evolution the velociraptor had in a much more fierce environment. Our strongest foe in our evolution was disease and each other, and thus we evolved to adapt to those conditions (good immune systems, imprinted social skills). A fiercer environment calls for more efficient and faster evolution or else they're an easy meal.

Do you get what I'm hinting at or should I go on?

 

[Synobun]

As I said, you might hyperventilate. But nothing about a 30% oxygen atmosphere is inherently dead inducing.

I'm not exactly up to date on prehistoric atmosphere, but wasn't there a lot more methane and toxic chemicals in the atmosphere back then that, to our lungs, would be fatal? Based on oxygen alone we'd probably be fine, but I was thinking more of everything else that'd be in the air.

*looks at post I replied to* Oh. He was specifically asking about oxygen. My response to him is moot.

 

[Lord_Iggy]

That periodization is unpopular now in this country. We usually use the Pennsylvanian and Mississippian epochs instead.

But yes.

To clarify on this, Mississippian and Pennsylvanian are two sub-periods, though they are not epochs. Whether or not it is most appropriate to call the period 'Carboniferous' or 'Mississippian/Pennsylvanian' depends on the location you're discussing. In North America there is a delineation between the fossil records of the Mississippian and Pennsylvanian, but in Europe there is no such delineation.

At any rate, I think we all understand what madviking's talking about, so 'Carboniferous' is still perfectly appropriate in this situation.

 

[madviking]

I'm not exactly up to date on prehistoric atmosphere, but wasn't there a lot more methane and toxic chemicals in the atmosphere back then that, to our lungs, would be fatal? Based on oxygen alone we'd probably be fine, but I was thinking more of everything else that'd be in the air.

*looks at post I replied to* Oh. He was specifically asking about oxygen. My response to him is moot.

Waaaaaaaaaaaay back in the day. Like in the Cambrian. Not in the Carboniferous.

 

[Super55]

According to wiki, mammoths were usually around the size of the Asian elephant, so they weren't really as unusual in size compared to dinosaurs.

In the past, some mammals achieved almost dinosaurian proportions. The Songhua River Mammoth, for example, reached a height of 17 feet and a weight of almost 20 tons, compared to 10 feet and 6 tons for a modern day African Elephant. The Paraceratherium were even larger, being over 18 feet tall and perhaps up to 30 tons, putting it in the same range as some sauropod dinosaurs.
I believe there are two main reasons why dinosaurs were so much larger then modern day animals; one, the food they ate and the ecosystems they lived in encouraged it. The plants and vegetation of the Mesozoic era were much different; angiosperm plants and broad leafed trees didn't exist during most of this era, and the dominant plants were ferns and conifers. These are hard to digest, so herbivorous animals needed to eat more of them and have large stomachs and digestive tracks to digest all that food. This necessitated that these animals become larger. Carnivorous animals needed to become larger as well, so that they could hunt the plant eaters.
The Mesozoic was a much warmer time then our current age, which allowed a much more robust ecosystem. There was much more food to support a much higher number of large animals. Which brings us to my second point;
In the last several million years, we have been living in an ice age cycle. The polar ice caps have been growing and retreating in a continuous cycle every few hundred thousand years or so. Even during a interglacial period, in which we are currently in, the Earth's temperature is still much cooler then it was say, twenty million years ago.
The cooler temperatures only allow a fraction of the large animals that flourished in the Mesozoic ecosystem.
Also keep in mind that humans have been putting extra stress on the ecosystem pretty much the entire time we have existed. Before humans, animals the size of elephants such as Mammoths and wholly rhinos were pretty common, and lions (and similar big cats) were spread across all of Europe, Asia, Africa and the Americas.

As far as the oxygen level argument goes, I believe that oxygen level has a much larger effect on arthropods then vertebrate animals such as dinosaurs and mammals. Consider the oceans; many of our modern whale species are much larger then any dinosaurs, or even any of the animals that lived in the Mesozoic oceans. I believe that this suggests that oxygen rates aren't a decisive issue here.
If you brought a Brachiosaurus through time to the present, for example, I don't think it would suffocate due to the oxygen level. It might be somewhat more sluggish, but I think its biggest problem would be finding enough food to support itself in our colder ecosystem.

 

[IAM]

mostly the enviroment temps, food, oxygen as already stated but also dinos were reptiles. they don't stop growing even today. A 100 year old human is not twice the size of a 50 year old but a snake, gator, turtle continues to increase in size the longer it lives. The past enviroment allowed the dinos to live longer.

Yes carnivores were bigger but look at carnivores today. Lions are much more likely to attack zebras than elephants. carnivores are opportunist and elephants are only attacked if they are sick, wounded or seperated from the group and small enough. the size of elephants is self-limiting and they don't need a predator to keep them in check.

 

[Shaihulud]

Some experts believe they have a more efficient respiratory system, like the birds of today.

 

[Tecknojock]

As I said, you might hyperventilate. But nothing about a 30% oxygen atmosphere is inherently dead inducing.

At STP 100% oxygen is not toxic to humans for short periods of time. Its only once the partial pressure climbs above 1.6 bars that immediate effects can be felt. Long term vascular damage, however, sets in with extended exposre to a .5 bar partial pressure or 50% Oxygen at sea level.