Why were so many ancient animals bigger than todays animals?

[Ossric]

Why were so many ancient animals bigger than todays animals? A stupid question that my mother asked but one i could not answer. If you look at the dinosaurs or the mammals from the ice-age, a lot of them are big/huge. Their size is one of the reasons why they are now extinct but why were they so big to begin with, compared the todays mammals? Why are todays mammels relatively smaller?

 

[Perfection]

First of it's not a stupid question, it's a very good one!

I'd suspect that in the dinosaurs case, as the extinctions occured the dinosaurs were hit badly because they required much more energy then a smaller creature, when the big crisis occured probobly from a meteor, the dinos didn't survive as well. After a dirastically reduced population, the mammals rose up and ate all their food, as the large preditors that would have normally kept the population in check were hardest hit.

The size changes in more modern times seems to have actually gotten bigger, huge apes came from small monkeys, large herbivores developed from smaller, on the whole I'd supsect that after the dinosaur times, the trend has been larger and larger.

 

[Tassadar]

I read something about that gravity was lower, according to those theory, it was imposible at the current gravity value, that a heart can pump blood over 30 feet high. It was kinda weird and not at all scientificaly recognise. Several link are found on a google search.

Do: dinosaur+gravity on google.


Here is one of them:http://frederic.malmartel.free.fr/Fin_des_dinosaures/eepbnonresolus.htm

 

[jpowers]

The extinction of the giant mammals and birds corresponded exactly with the development of the human brain. Until the intelligent hunter, there was an ecological niche for the 'giant' animal. Since the risk/reward ratio was so good for humans to hunt them (with very high success rate due to weaponry and social hunting), they were the first to go. Smaller animals that were less nutritious ended up being able to continue reproducing.

 

[Tassadar]

Here is a better one, it worth a look.


Link:http://microlnx.com/dinosaurs/OriginOfDinosaursAndMammals.html

 

[Aphex_Twin]

They were teetering on extinction after the last ice-age. It was then that man came and invented steak

 

[Tassadar]

Is it possible that a smaller size planet hit earth, broke pangea continent, increase gravity by over 20 % with its additional mass, and lead to smaller species ? i am serious.

Edit: it could even have lead to a new orbital ellipse with climate changes.

 

[Aphex_Twin]

That would have been a huge impact, tearing wide open the Earth's lithosphere. All life forms would disapear. I think you're talking about the impact that created the Moon (a planetoid the size of Mars).

 

[Tassadar]

Originally posted by Aphex_Twin
That would have been a huge impact, tearing wide open the Earth's lithosphere.

All life forms would disapear.

I think you're talking about the impact that created the Moon (a planetoid the size of Mars).

1.- indeed a huge impact, effect unkonow to me.

2.- How do you know ?

3.- Moon formation latest theory indeed involve the impact you are talking about, but not in the same time as the dinosaur live IIRC.

Its kinda funny, because i asked that question before to a scientist and never got ansewred. I am only a chemist, with a strong interest in astronomy and other science field like paleontology.

Sometime problem involve multidiscilinary study.

 

[jatutt]

Because before the flood there was a covering of water in the sky that protected creation from harmfull sun rays. This allowed creatures to live longer therefore growing bigger.

My simple explination. I have heard/read scientists explain this in detail but can't recall it all.

 

[Tassadar]

If the impact theory is right, then.

1.- Was their life on that small planet, with lower size's genetic code.

2.- Did the gene mixed with already existing gene on earth and lead to evolution step, with a new equilibrium within the increased gravity ?

3.- Am i talking about radio-active monkeys ? oh , wait, maybe the planetoid had a different proportion of radio-active element, and mess up our dating system ?

 

[andrewgprv]

I heard something about plants holding more proteins in them in the past. Something about the amount of Carbon Dioxide in the air affecting the amount of proteins or nutrients in plants. In the past plants had more protein thus enabling plant eaters to grow larger and in turn their prediters.

I could be wrong though, just one of those things I heard, and it was a while ago so I could have remebered it wrong.

 

[IceBlaZe]

Not only animals were bigger...
Many bugs and plants were bigger aswell (or atleast bigger plants were more widespread).

 

[Pontiuth Pilate]

Climate.

Pre-asteroid, in a muggy climate, the limiting factor on growth was circulation. The heart can only pump blood so far.

Post-asteroid, when there were often ice-ages, the limiting factor on growth was sustainability. When food is scarce, small efficient animals [birds, bugs, and mammals] rule supreme.

 

[Oruc]

cos ancient animals ate there greens

 

[carlosMM]

main size limit: weight! not blood pumping, you cna pump blood as far as you want, you jsut have to develop rpoper valves. But weight increases by the cube, you quickly get to the point where your legs have to be so fat that they touch
that's what is the general upper limit.

next: why are mammals smaller than dinos? mainly because of the different styles of endothermy: mammals of large size need a LOT mroe energy than brids or dinosaurs of the same size. You gotta eat a lot, and constantly, from a certain size on.

all the rest above is plain wrong. sorry to be so harsh, but I didn#t study that stuff for nothing.


lower gravity

 

[Double Barrel]

How do we know FOR CERTAIN that dinosaurs were cold blooded? Speculation?

 

[Pontiuth Pilate]

I really doubt they could have been cold blooded. Surface area increases at a slower rate than volume...

 

[carlosMM]

Originally posted by Double Barrel
How do we know FOR CERTAIN that dinosaurs were cold blooded? Speculation?

no, they most probably were avian-style endotherms, whcih is something very similar to mammals in the range up to an ostrich, but biger animals need less energy for the same level of activity.


I should mention that many researchers doubt this, but mostly the 'old guard' - they have been teaching other stuff, like mass homoiothermy, and are reluctant to change. But the evidence is there....... I know I am right here give me a few years and you will read about it in Nature.

 

[Perfection]

Originally posted by Pontiuth Pilate
I really doubt they could have been cold blooded. Surface area increases at a slower rate than volume...

Well, if the climate was genrally mild then it isn't much of an issue.

As for the planetary mass, we're talking something te size of Mars hitting us, not possible, however a mars sized body did hit us about 4.6 billion years ago.

"I heard something about plants holding more proteins in them in the past. Something about the amount of Carbon Dioxide in the air affecting the amount of proteins or nutrients in plants. In the past plants had more protein thus enabling plant eaters to grow larger and in turn their prediters.

I could be wrong though, just one of those things I heard, and it was a while ago so I could have remebered it wrong."

That may have some merit, a high CO2 amount would allow plants to grow quicker and larger and would also explain the higher temperatures.