Why aren't there bigger animals?

[combatant]

As we know from the fossil record, there have been some very large dinosaurs (sauropods) that have lived. Why is it, in the billions of years that evolution has been working, have we not had or known of any other land-creature outside of some dinosaurs that have gotten to be so massively large? The same processes of evolution which worked back then have been working the same way for billions of years, so there should be (or should have been) some other creatures that have gotten to be that massive. So what's the explanation?

Thank you for your understanding and response.

 

[Nooj]

1) Physiological issues.

a) It's believed that with increases in size, dinosaurs increased in temperature. The free paper is here.
b) Some organisms like insects can't get that big because of their way of breathing through the skin. With large sizes come increased demand for oxygen and the insects can't cope.

2) Selective pressures weren't there.

3) There were some mammals that got to saurapod size. For example, indricotheres.

 

[angelocrator]

Why is it, in the billions of years that evolution has been working, have we not had or known of any other land-creature outside of some dinosaurs that have gotten to be so massively large?

We have had mammals that were almost as big as large sauropods. Try here: http://en.wikipedia.org/wiki/Megafauna

 

[h2whoa]

A lot of it boils down to the simple relationship between volume and surface area.

Volume, obviously, works in a cubic fashion. However, surface area works only in a squared fashion.

So for every cubic increase in volume the surface area only increases by a square.

This is very important in things such as gas exchange. As has already been mentioned, insects breathe directly through holes in their "skin". Previously, when the levels of oxygen in the atmosphere were much higher a much larger of volume of insect was allowed because although the surfce area:volume ratio was smaller, the amount of oxygen for gas exchange was correspondingly higher. With current atmospheric levels an insect of prehistoric size would become anoxic and suffocate.

The same is true for animals with lungs. Lungs rely on surface area for gas exchange. That is why the lung is full of alveoli: they essentially artifically increase the surface area for gas exchange. If an animal's overall volume exceeds the critical ratio for surface area:volume it will not be able to supply the oxygen required.

But also, size is not necessarily in itself a bonus for an animal. In terms of numbers and biomass, bacteria are by far the most successful things on the planet. The giant sloth, however, doesn't do so well.

 

[Abongil]

so whales arent big enough?

 

[MaynardGKrebbs]

God got lazy...........

 

[JohnR7]

have we not had or known of any other land-creature outside of some dinosaurs that have gotten to be so massively large?

All reptiles get big if they live long enough. Turtles & crocodile get huge if they live long enough. So one thing the large size indicated was that the animals use to live a lot longer before the flood then what they are able to live now, after the flood. Before the flood even people could live to be almost 1000 years old.

Also there could be something blocking their size. If you look at a liger they are very big. Almost twice the size of a tiger or a lion.

 

[theFijian]

I thought the Blue Whale was the largest animal that has ever lived, except maybe Galactus.

 

[Chalnoth]

Well, I personally think that there's a very simple reason why the largest animals of the past no longer exist: larger animals have slower reproductive cycles, and thus have slower evolutionary rates. Thus whenever you have fast changes in the environment, these animals will die out (as happened to the dinosaurs).

Humans have produced on of the fastest global environmental changes of all time. So it should be no surprise that most of the largest animals died out as humans spread across the globe.

 

[BVZ]

Yea.... blue whales are the largest animals that has ever lived.

They are larger than any of the dinosaurs.

So.... does that answer your question?

 

[llDayo]

I thought the Blue Whale was the largest animal that has ever lived, except maybe Galactus.

Galactus only seemed that big because of trick photography. He always just stood really close to the camera.

 

[GoSeminoles!]

As we know from the fossil record, there have been some very large dinosaurs (sauropods) that have lived. Why is it, in the billions of years that evolution has been working, have we not had or known of any other land-creature outside of some dinosaurs that have gotten to be so massively large? The same processes of evolution which worked back then have been working the same way for billions of years, so there should be (or should have been) some other creatures that have gotten to be that massive. So what's the explanation?

Thank you for your understanding and response.

Certain whales are larger than the giant dinosaurs.

 

[Late_Cretaceous]

What is the YEC explanation for "why aren't there bigger animals?".

 

[h2whoa]

What is the YEC explanation for "why aren't there bigger animals?".

Goddidn'tdoit.

 

[Herman Hedning]

Goddidn'tdoit.

 

[shernren]

Let's not forget that early humans found it a whole lot easier to hunt massive animals than small ones. Hence a wave of megafauna extinction at about the same time as man started hunting.

At least, that's what I've heard.

 

[Hydra009]

A lot of it boils down to the simple relationship between volume and surface area.

Volume, obviously, works in a cubic fashion. However, surface area works only in a squared fashion.

So for every cubic increase in volume the surface area only increases by a square.

This is very important in things such as gas exchange. As has already been mentioned, insects breathe directly through holes in their "skin". Previously, when the levels of oxygen in the atmosphere were much higher a much larger of volume of insect was allowed because although the surfce area:volume ratio was smaller, the amount of oxygen for gas exchange was correspondingly higher. With current atmospheric levels an insect of prehistoric size would become anoxic and suffocate.

Yeah, I saw a good explaination of why giant arthropods aren't feasible here and here.

 

[mnbvcxz87]

A liger is a mutant animal, a crossbreed, not naturally ocurring. I'm sure you could breed a grashopper with an elephant and create a gigantic elehopper.

 

[RealityCheck]

A liger IS naturally occuring. It happens when a lion and tiger mate. Their genetics are compatible enough to have offspring (though usually they are sterile). You can't breed a grasshopper with an elephant.

 

[mnbvcxz87]

Oh yeh they do mate every now and then...who'd have thought.

You can't breed a grasshopper with an elephant.

But it'll be a lot of fun trying.