First, about the sauropod’s neck. Yes, the reference is in a Discover magazine from about a year ago but I can’t find it because I’m stranded in a foreign country. It shouldn’t be hard to find, there’s a big sauropod’s (four-legged, long-necked dinosaur’s) skeleton on the cover.
What the article said was that their neck had little vertical mobility: they couldn’t raise their neck much higher than their shoulders and not much lower than the plane of their legs. This was just enough so that they could get a drink of water, I guess.
They had much more horizontal mobility, but many couldn’t even touch their own body with their snout by curling their neck sideways. The incorrect assumption was that since sauropods had long necks they were like giraffes, the basic modern-day equivalent. Not so, it seems.
So why the long neck? One interesting theory is that the long neck counter-balanced the long tail, not the other way around. Sauropods were huge, a natural defence in itself, but they couldn’t run; they could only walk fast. A large tyrannosaurus could have walked to this big stomach on legs and have lunch without too much trouble, except if he got smacked on the head by a tail as long as he was.
The tail was a huge limb. It had good horizontal mobility and a small nudge from the big muscles at the base of the tail would have made the tail into a (possibly sound-barrier breaking) whip. So the tail was probably used for defence.
The one exception is the brachiosaurids, whose fore-limbs were longer than their hind-limbs and whose neck structure seems to have supported a near vertical stance. Now, how could the blood have been pumped up to that height? No one knows, but there are theories, such as multiple heart-like muscles distributed through the length of the neck and pumping the blood up there. That seems strange, but with dinosaurs, you never know.
As for the size issue, I would like to point out that there are no inherent problems with large-sized mammals (or any warm-blooded animals). Elephants are not the limit of mammalian gigantism. Following the extinction of the dinosaurs mammals overtook all the niches that had previously been dinosaur territory and in so doing grew to astounding sizes very quickly. One stunning example is the baluchitherium, a rhinoceros-related animal that grew to be 5m (16 feet) tall and weighted roughly 16 metric tons.
Okay, so dinosaurs still win the gold on land for sheer mass, but mammals are the biggest animals in the sea. No animal at the time of dinosaurs approached the size of the blue whale.
Size can be quite an advantage for animals in general. Naturally, larger plant-eaters deter predators, and larger predators can take on a whole new range of prey. Secondly, being bigger makes you less vulnerable to sudden temperature changes.
Here is a little math: volume increases in a given shape by the cube of its length (or any other linear dimension). If you want to visualise this, imagine a cube that has a one-unit long side. Its surface area is therefore six square units. Its volume is one square unit. If you make a cube that has twice the side length, its surface area becomes 24 square units and its volume, 8 cube units.
That means that while its length doubles, its surface becomes four times bigger and its volume, eight times bigger! That’s very significant and means that bigger animals have less surface area per volume through which they lose and gain their heat. Therefore they have a stabler body temperature.
One would figure that in the case of a very warm environment, smaller animals are better off. After all, when it gets really hot they can hide in shadows or burrow under the cool earth while big animals are just stuck out there while the heat keeps coming on. For example, just imagine a herd of elephants jostling to get under a tree in the African savanna.
Not so. Using elephants as an example again, big animals receive less heat per volume than smaller ones. As well, the excess heat is safely stored away inside their body, away from organs that wouldn’t function as well with so much heat. An elephant can do this long enough to get through the day. A small animal doesn’t have enough body volume to do this, and therefore run the risk of overheating and dying. As well, when night comes little mammals must keep moving or hide in a well-insulated place to keep their body temperature at a reasonable level. The African savanna can get rather cool at night. Elephants, on the other hand, don’t lose their heat so quickly in the first place and can just release the excess heat they had stored during the day to keep warm and cozy throughout the night.
This only works for mammals and warm-blooded animals, though. Small cold-blooded animals can let their body temperature drop without feeling ill effects, except that naturally they can’t be bothered to move then, or only very slowly. This can be a disadvantage when something hairy and warm comes to chew on them in the middle of the night. However, the argument that bigger size makes for stabler body temperature holds true for cold-blooded animals too.
Only humans do inhuman things.
