Why were dinosaurs so large?

[TheBigDog]

There are a couple of references in this thread to Dinosaurs being reptiles. I believe that current science disagrees with that idea. And I have read some theory that they were in fact warm blooded. Size was dictated by survival and reproductive advantage from size.

 

And we think about dinosaurs as big because that is what we are exposed to. MB and INow are correct on that point. Think about how many shows you have seen about the Great White Shark. Now, how many have you seen about the Leopard Shark? Why? Because leopard sharks are small and they don't kill people, while Great White Sharks are huge fearsome creatures that capture the imagination. In fact there are over 400 species of shark, but most people can only name a dozen or so. And the great white is almost always the first off the lips, but one of the more rare species in the wild. Dinosaurs were probably very much the same way.

 

There are less than 20 T-Rex finds in history, compared to literally thoudsands of samples of other species. Yet you would think from our interpretations of the Jurrasic that you couldn't take three steps without running into one. I would be willing to bet that it would have taken weeks to find a T-Rex because their size and food demands would prohibit them from being densly populated. And because there were thousands more smaller predators who were also part of the food chain, and who's needs would come into conflict with the giants.

 

There is also a proportion to the food pyramid. I remember the rule of thumb from High School Biology being that each level of the food chain could be no more than 10% of the mass of the level it depends upon. With this in mind the driving force for large dinosaurs is the vegetation that they depend upon. The long necks of large Sauropods would have given them a food supply advantage over other creatures. And access to nutrients that may have been unique in areas that they alone could reach. But at the same time they would have put an increadible strain on vegetion and if there were too many large sauropods in an area they would soon be forced to compete with smaller creatures for lower foods.

 

So, while it is romantic to think that there were large dinosaurs as far as the eye could see, it is far more likely that they were in small scattered groups that prevented to much impact on the available vegatation.

 

Now one of the things that was probably rampant with the presence of these dinosaurs would be animals that fed exclusivly on the feces of the large plant eating Dinos. I can imagine small dinos that would be like ramoras to a shark, and follow them around feeding on the waste they left behind. Even the Sauropod young may have fed this way until they reached critical mass size.

 

now I have gotten a long way from the original question of why Dinosaurs were so big, so let me sum up. Some were big, and we love them. Most were much smaller, and much less interesting. And there is a gap; a twist to our perception that leads us to think of the dinosaur era in ways that it probably wasn't. Like it was nothing but Blue Whales and Great White Sharks.

 

Bill

[alxian]

kinda makes you wonder why humans at the top (so we like to think) of our food chain.. manage to live so closely together in such high numbers...

 

if Homo Sapiens were bigger and stronger, self sufficient, would we still be communal?

[HydrogenBond]

The BigDog is probably correct about large dinos being the exception rather than the rule. The human imagination likes to think in terms of extremes maybe leading to an erronoeus assumption about size distribution. We beleive what we want to believe, since extreme is more exciting than average these fuel our imagination.

 

But that being said, the size of many of these dino critters is far bigger than their evolutionary descendants. One only has to look at the mammoth compared to the modern elephant. Maybe cooling trends and less food favored smaller animals.

 

If this was true, than maybe heating trends and plentiful food favored larger animals. This would suggest the earth being much warmer during the hayday of the dinos. The extra heating and fertilization, needed for the large dinos may have been from the earth. For example the separation of the orginal singular continent would have required a lot of mantle convection compared to modern times. This would not only kick up extra heat but also extra fertilizer and CO2. The result was a very lush earth that could support the big guys.

[haloman]

Quote:

Originally Posted by InfiniteNow

Greater size meant fewer competitors could harm them physically.

 

Quote:

Originally Posted by Boerseun

Which only helped until T-Rex came along

 

T-Rex was actually not as great as it seems becuase a triceratops (and most of the other ceritopsians) could kill one so most likey a spinosorous would be much worse.

 

The reason I think is that were so large is so they could either get to all the high trees, and for eating meat they have to get through the tough skin and a small animal cannot get through as easily as a 12 ft. tall dino. Pretty much evolutionary advantages.

[Turtle]

More on the oxygen component in regard to dinosaurs large size:

 

Ward pictures a world in which dinosaurs were able to adapt to low atmospheric oxygen content relatively easily, and when oxygen levels rose the dinosaurs developed into giant creatures that dominated the Earth.

 

http://www.terradaily.com/reports/Jumping_The_Oxygen_Gap_999.html