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Did Dinosaurs Live In Low Gravity?

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plusk

Gone But Not Forgotten
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Don't really know which thread to put this in, so mods feel free to move.

My son has to do an extended essay involving maths for school and the teacher told him to investigate whether dinosaurs could live in the modern world like in the Jurassic Park film. Apparently there is a theory that the bones of a dinosaur would not support its weight (a bit like King Kong would be too big for real life) so the Earth's gravity must have been lower 65 million years ago. Seems absolutely barmy to me. Anybody out there heard of this theory?
 
Yeah sure I first came across this on a Usenet group well before the Web (probably Talk.Origins or Sci.Paleontology) - it's another one of those arguements from disbelief - I can't believe they could have got around being soooooo big so he gravity must have been weaker.

It coems up in number of theories about extra planets and sundry other out there Catastrophism whackiness ;)

The Talk Origins archive will have something in it but their servers appear down:

www.talkorigins.org

Here are some links to some claims:

www.bearfabrique.org/Catastrophism/saur ... anims.html
www.bearfabrique.org/Catastrophism/saur ... opods.html

I would have argued that recent megafauna put the lie to this but apprently they are in too:

www.bearfabrique.org/Catastrophism/saur ... mmoth.html

Coooo Ted Holden there is a baslt from the past (as is Ed "MAN AS OLD AS COAL" Conrad mentioned on the main page).

Of course the Blue Whale is thought to be the largest animal that ever lived...

Ahhhhhhhh I found these links on another page so when TO is up and running you can go straight there:

www.talkorigins.org/faqs/sauropods.html
www.talkorigins.org/faqs/teds-world.html
www.talkorigins.org/faqs/ted-qfa-reply.html
www.talkorigins.org/faqs/homs/holden.html

[edit: If desperate you can WayBack those - I did it with the first link and it is all stored there.]

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One question: Did the teacher say that in class? I'd complain to the school if they meant it seriously.
 
Crumbs,

Thanks ME.

I think the teacher set it as a maths problem in calculating if the leg bone would actually support the dinosaur's weight, he didn't put it forward as a serious hypothesis.
 
plusk said:
Crumbs,

Thanks ME.

I think the teacher set it as a maths problem in calculating if the leg bone would actually support the dinosaur's weight, he didn't put it forward as a serious hypothesis.
Click to expand...

OK cool - they cover all that on T.O. The site is back up now so check:

www.talkorigins.org/faqs/sauropods/saur ... metry.html

In particular they rely on:

Hokkanen, J.E.I., 1986. "The Size of the Largest Land Animal"
Journal of Theoretical Biology, v.118, p.491-499.

Abstract: The upper mass limit to terrestrial animals is studied using physical arguments and allometric laws for bone and muscle strength and animal locomotion. The limit is suggested to lie between 10^5 and 10^6 kg. A possibility for a still larger mass, in case of new adaptations, is not excluded.
Click to expand...

There is probably enough information on the page to work out what is needed for the project.
 
There was something in National Geographic around a year ago talking about why modern animals are, in general, smaller than in the past. I seem to recall them saying the air was thinner, which had more to do with circulation than bone support. I always wondered about it as a kid.
 
Or it could be that smaller animals (by smaller I mean say an elephant compared to something like a large dinosaur) put comparitively less strain on the resorces of the natural environment so can wander around in larger numbers this, if you're somethings prey gives you better protection from predators as statisticly it's less likely to be you that gets eatten. predator size is in most cases determined by the size or availibility of prey. Another advantage of large numbers is that if there are more individules in a species it's more likely that some will survive desease epidemics. So the reason why a lot of species of very large animal are no longer with us is because from an evolutionary point of veiw it's better to have animals of more manageable sizes so more of these species survive to pass on their genes.
 
If that were strictly true, it wouldn't have taken them so many millions of years to catch on. Indeed, why would they have grown so large in the first place?
 
Was it something to do with the world being a hotter place back then?
 
I know they claim insects were bigger back then, because the world was hotter and so the atmosphere contained more oxygen. Due to the respiratory system of insects, this tends to limit their size. I think some present day underwater insects are also rather large due to high oxygen levels in cold water.
 
Hi Xanatico,

I read somewhere that the oxygen levels in the air now are about optimum. Any more and anything burnable would catch fire really easily, so oxygen would be used up until it got down to today's levels.
 
I would posit that the reason there are no "big" animals around is that all the megafauna are extinct in Eurasia, the Americas and Oceania. I would still count African/Indian elephants, rhinos, buffaloes etc. as big but not huge.
The extinct megafauna were huge- sloths bigger than elephants (Eremotherium), mammoths bigger than elephants (Mammuthus columbi), armadillo relatives the size of VW beetles (Glyptodonts, the beetle is a classic scale measure for megafuna).
Its our depleted landscape that forces the false comparison. If we were surrounded by mammohs, giant sloths, woolly rhinos and glyptodons i doubt the need to explain the size of dinosaurs would have come up.
Having re-read this it sounds a bit convoluted. I hope it makes some sense.
 
Hi Barndad,

The problem for me is that the biggest dinosaurs were GINORMOUS,
the animals which followed them were smaller but ENORMOUS,
The megafauna you mention were smaller but HUGE
Current biggst animals are ljust large.
The biggest land dinosaur was 4 X as high and 20 time as heavy as an elephant.

Why this continuing reduction in size?
 
So for the 200 million years dinosaurs ruled it was more efficient and now it isn't?
 
The theory, and I believe there's a lot of evidence, is that the air was thinner, so hearts had to work less, among other things. Or maybe it was low gravity. Wish I could remember where that National Geographic article is.
 
I don't know about the low gravity thing surly the gravity depends on the mass of objects interacting with each other. I don't think that any of the celestial bodies in the solar system have changed in size by any significant amount to warrent a higher or lower gravity.
I think that the enormous size of the dinosaurs was down to the higher oxygen, higher temperatures and the type of vegetation they feed off. Considering that grasses had not evolved at the height of the largest Sauropods (Braichisours, Apatosaurs and Diplodicous - Jurassic Era) they had to digest much tougher vegitation such as ferns. OF the bigger you were the easier it was to have stomachs large enough to do the digesting. I suppose as a result of the size of the herbivores, the carnivores also grew larger to tackle this prey. It must also be remembered though that despite a lot of dinosaurs growing to huge sizes they majority of the dinosaurs were no bigger than anything that lives today.
 
195.jpg


Pangea was assembled piece-wise. The continental collisions that lead to the formation of the supercontinent began in the Devonian and continued through the Late Triassic.

In a similar fashion, the supercontinent of Pangea did not rift apart all at once, but rather was subdivided into smaller continental blocks in three main episodes. The first episode of rifting began in the middle Jurassic, about 180 million years ago. After an episode of igneous activity along the east coast of North America and the northwest coast of Africa, the Central Atlantic Ocean opened as North America moved to the northwest (See Jurassic). This movement also gave rise to the Gulf of Mexico as North America moved away from South America. At the same time, on the other side of Africa, extensive volcanic eruptions along the adjacent margins of east Africa, Antarctica, and Madagascar heralded the formation of the western Indian Ocean.

During the Mesozoic North America and Eurasia were one landmass, sometimes called Laurasia. As the Central Atlantic Ocean opened, Laurasia rotated clockwise, sending North America northward, and Eurasia southward. Coals, which were abundant in eastern Asia during the early Jurassic, were replaced by deserts and salt deposits during the Late Jurassic as Asia moved from the wet temperate belt to the dry subtropics. This clockwise, see-saw motion of Laurasia also lead to the closure of the wide V-shaped ocean, Tethys, that separated Laurasia from the fragmenting southern supercontinent, Gondwana.
Click to expand...

http://www.scotese.com/moreinfo10.htm

Must admit that i hadn't realised myself that they were still that close together that late on...
 
Just a thought, but wouldn't millions of years worth of small meteors and stuff hitting the earth, as we all know happens all the time, add to the earths mass making its gravity greater?
 
Hi Quazi,

The answer's no. Just done the maths with my son for his project. Most authorities say around 100,000 tons of stuff falls onto the Earth each year. But even if we up it to 1/2 million tons per annum to allow for the occassional big'un, the Earth would, since 200 million years ago have accumulated less than one part in a thousand extra mass.
 
I think I remember reading somewhere that the coming together of the landmasses caused desert conditions over most of the planet and encouraged the evolution of reptiles (cold blooded) over mammals (warm blooded). The article is talking about this and saying that the coldblooded animals need less food to support their metabolism than the warm blooded ones because they don't have to expend energy on keeping themselves warm.

The dinosaurs are supposed to have grown very big because they are trying to maintain a stable body temperature. In deserts it is very hot in the day and very cold at night so being very large makes them slower to loose heat and night and slower to get hot in the day.

In terms of the land mass thing the inverse can happen when a population is cut off on a smaller land mass like and island, you can get pygmy versions of the animals on the larger mainland
 
However, you also have the widely accepted theory that dinosaurs were warm-blooded to contend with.
 
Its supposed to just have been the small dinosaurs which were warm blooded, i.e. the ones which eventually evolved into birds & their near relatives
(but who knows)
 
Cold blooded as applied to large dinosaurs might not be the same as how we think of it in the contemporary sense. The surface area to volume ratio is so low that the minimal heat loss resulting from that might have allowed the heat from normal metabolic processes to raise the body temperature quite a bit.

Come to think of it, what's the theory on how large dinosaurs cooled down? I'd never thought about it before...
 
Possibly the same way other large animals such as polar bears do, they drink cold coca-colas :)
 
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