Dinosaur Growth and Brain Size: The Truth Behind Their Evolution

[Tyger]

This is sort of an unofficial poll on two questions. How was it that Dinosaurs could grow so big, and why did they have such small brains.

I'll give my ideas of why, please add yours.

So big? Because they had gizzards like chickens have. That means they didn't have to use their teeth to chew their food, which mammals spend a lot of time doing. They could just eat and eat and let the gizzard break down the food. Also mammmals have fairly short lives becasue their teeth tend to wear out quickly, but Dinosaur teeth would last much longer. That gave them more time to grow larger. Although some plant eating Dinosaurs had formidable rows of teeth in the skulls.

Small brains? Because they were hatched from eggs. Brains use a lot of nutrients and oxygen but eggs only provide a limited supply of both.

 

[FZ+]

What I think...

Big size? Some theories propose that this was due to relatively large oxygen concentrations at the time. Not all dinos are so big, and it could be just luck of the draw that a few did, and lived in surroundings that encouraged it.

Small brains? Because they didn't need big brains. Brains are expensive when it comes to energy consumption, and it may be that having a big brain just wasn't advantageous for dinosaurs. Who needs a big brain when your size is your primary defense? However, some of the smaller dinos have very well developed brains for their small size. Hence the theory that they used them for advanced tactics like pack hunting. And remember, evolution is based on random chance. You can't gaurantee what would happen...

 

[Dissident Dan]

Originally posted by Tyger
Also mammmals have fairly short lives becasue their teeth tend to wear out quickly, but Dinosaur teeth would last much longer. That gave them more time to grow larger. Although some plant eating Dinosaurs had formidable rows of teeth in the skulls.

Some mammals live quite a while...primates, dolphins, elephants. And being large isn't that directly related to how long you live (for animals, as opposed to plants). We have growth periods and decay periods. As you may have noticed, most people stop growing by the time that they reach 20.

 

[damgo]

Actually mammals trump dinosaurs for largest species by a lot (blue whales) -- but for land animals you're right. :) I've heard the theory that dinosaurs, being egg-layers, had to commit to defending their nest from predators, which forced them into a size "arms race", despite the fact that gigantism is generally a poor evolutionary strategy. Mammals who were able carry their children with them could adopt strategies of fleeing or scattering and did not have to resort to large size.

 

[Phobos]

There is* a niche for large animals and a niche for small animals. With such a possibility available, it's likely that some creature will fill it. Size has some benefits such as safety from predators, less heat loss, etc. So as long as there is ample food supply to support such an anatomy, there is the possibility for such growth. Many time periods since the dinos have had giant-sized animals (but it seems that the dinos hold the record for largest land mammals in history).

* Or, "used to be" at least. Nowadays (geologically speaking), humans have a way of eliminating large animals through direct predation and/or habitat destruction, etc.

 

[rdjon]

Originally posted by Phobos
Many time periods since the dinos have had giant-sized animals (but it seems that the dinos hold the record for largest land mammals in history).

Except of course, dinosaurs weren't mammals! ;)

 

[Phobos]

d'oh! There goes all my credibility!
...um, Phobos, what credibility?

Of course, I meant "animals". Such typos happen now and then when you draw your posts from an infinite number of monkeys typing on an infinite number of typewriters.

 

[LURCH]

I've pretty much agree with Phobos (about that niche thing, not about his credibility been gone). Gigantism is an evolutionary strategy that works. The dinosaurs ran this planet for a very long time, time enough to develop this strategy to grade extremes. Unlike other strategies, gigantism leaves an excellent fossil record.

There were probably dinosaurs faster than anything we have today, but the only way we have of directly gauging the speed of dinosaurs is by their footprints. Since becoming fast means becoming light weight, the real speedsters probably didn't leave much evidence. I would imagine dinosaurs developed extreme proficiency in venoms, toxicity, camouflage, maybe even electrocution. None of it would show up in a fossil.