How did dinosaurs get so big?

Question

I mean, if one fell over it would be crushed by its own weight. How could a creature that heavy exist?

Look, I understand not all dinosaurs were big. Sure, the big ones ate more or there was no predators or whatever. My question is, how could they support their own weight? Look at an elephant's foot, then a Tyrannosaurus foot. It's not possible for the Tyrannosaurus to stand like it does.

Answer 1

To give the shortest possible answer: because they could. It may sound silly, but this is accurate to a point, the size of an animal is limited by the environment, and without limitations, it can and will grow unchecked. Obviously no such limitless environment exists on Earth, there are always such things to consider as food availability, gravity and oxygen. There are also certain advantages to being really big which may be causal to growing big or simply a beneficial side effect.

Before I go into the reasons dinosaur were big, I must point out that most dinosaurs were not exceedingly big. Such iconic genera as Tyrannosaurus, Triceratops, Ankylosaurus, Anatotitan and Stegosaurus were no more massive than modern African bush elephants, some were even smaller! It's only sauropods like Brachiosaurus, Apatosaurus, Diplodocus, and later the titanosaurs, that overgrew these limits. Even still, these dinosaurs never reached the calculated theoretical size limit for terrestrial animals (100 000 - 1 000 000 kg). Once you reach this limit, the animal becomes too large to move or even support its own weight. Since the megasauropod Amphicoelias has been estimated to have reached a size close to this theoretic maximum, it seems sauropods had eliminated all other limits to their growth.

So, why were sauropods so big? Of the list of limiting factors, the first one to tackle is oxygen. Atmospheric Oxygen levels were much lower than today during the Triassic, when the ancestors of dinosaurs evolved. Already back then the ancestors of sauropods were growing bigger than anything else. During the Jurassic period, oxygen levels soared to modern-like levels enabling dinosaurs with their unusually effective air-sac lungs to grow much larger much faster than all the other animals. The Jurassic atmosphere was different from the present in other ways, too. Global temperatures were high and level of CO2, which not only warms the temperature but also is required by plants to grow, was multiple times the modern amount.

While this may make the Jurassic seem like a time of plenty, which would neatly explain gigantism, it has actually been shown that the diet of the sauropods was nutrient-poor. So why would they grow so big if their diet was so poor? Actually, modern megaherbivores provide an explanation: the larger an animal is, the larger digestive system it has. The larger the digestive system, the longer it can digest its food, making use of poorer browse or graze. The sauropods had immense guts acting like fermentation chambers which extracted all the needed nutrients from plentiful but nutrient-poor plants the other dinosaurs could not exploit. By tapping into an otherwise unused food resource allowed them to thrive, even though it meant growing into a humongous size.

Obviously growing so big caused major limitations. A sauropod could not run, nor jump, nor even fall down without risking serious injury. However, being so immense meant they did not have to. Even the largest carnivores of the time would have had great difficulties killing a full-grown megasauropod. That difficulty was amplified by the fact that sauropods lived in groups and could use their long tails as effective weapons. It was much less trouble for an allosaur to go hunting smaller but still massive prey, such as Iguanodons.

It has also been suggested that sauropods took advantage of their giant size in another way: to keep their body temperature stable. When an animal becomes sufficiently large, its sheer volume is able to retain heat effectively without the animal having to produce its heat itself or worrying about losing most of its body heat in cool conditions. This is known as gigantothermy, and certain cold-blooded marine animals take advantage of this phenomenon today. Analysis of different types of dinosaurs suggests that while a lot of dinosaur groups seem to have been able to regulate their body temperature like modern mammals and birds, sauropods weren't among them. Since they were cold-blooded and immensely massive, they would have been perfect candidates for gigantothermy.

Answer 2

There is no good answer. My paleontologist pals are still scratching their heads. One theory, is that it is thought that perhaps the herbivorous dinosaurs grew big as a defensive mechanism. (Today, there are no predators that will take on a healthy adult elephant). In response to this, many of the predators grew bigger so that they could take on the large herbivores. A positive feedback loop developed. Possibly, the larger dinosaurs were able to out compete the smaller ones in their quest for survival. So, the genes that would produce yet larger animals were propagated producing larger and larger dinosaurs. That's one theory. It's also possible that there was simply so much large food around for the herbivores, and just the perfect amount of heat and atmospheric gases, that everyone just grew larger. It has also been stated that they grew large because of a difference in lifestyles. The significant difference between growth in reptiles and that in mammals is that a reptile has the potential of growing throughout its entire life, where a puny mammal such as ourselves, reaches our "terminal size" (cool scientific term) and stops growing, even though most of us continue to live for many years. That's why you see no 82 year old basketball stars. To continue with another thought, the size of the dinosaurs is possibly a simple consequence of how they fed. Vegetation is a tough diet for all animals and the sauropods were high browsers relying on the particularly tough leaves of conifers. Their teeth were simple and designed for nipping or raking foliage from trees, rather than for chewing (somewhat like a modern giraffe). They had stone laden gizzards (just like vultures) which they used to grind up the tough leaves, but breaking down the plant cells could only be achieved by using the stomach as a huge fermentation tank. Sauropods had to be big because they had to contain a huge stomach. Being big is a useful adaptation in itself. It gives some protection against predators - unless they too evolve bigger. It also gives more insulation, either to prevent overheating in the sun, or to avoid heat loss when it gets cold. In the end, the simple answer is, "because that was the perfect body-form for the time." All dinosaurs were not huge. But a few modern large animals - mammals - such as elephants and whales have grown that way just because evolution made them that way. Sort of a cop-out answer, I know, but the fact is, I have paleontologist friends, but I'm not a paleontologist - and they don't know anyway. But your question is a very popular question.

Answer 3

Why Were Dinosaurs So Big

Answer 4

This Site Might Help You.

RE:
How did dinosaurs get so big?
I mean, if one fell over it would be crushed by its own weight. How could a creature that heavy exist?

Answer 5

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Answer 6

Dinosaurs were genetically programed to be big, and they must have eaten a lot. They were probably careful not to fall over. Or maybe they did fall over, and that is how they became extinct.

Answer 7

In the eyes of the creator (call it God or Nature, if you like), nothing is too big or too small. Imagine an engineer with several draft designs for machines meant for different purposes. Some of these machines might turn out to fit the purpose for which they are meant and therefore be in use indefitely, whilst others might work for only a short time or might not work at all. Nature, the Supreme Engineer, works basically the same way (or to put it the other way round, we as human engineers basically try to mimic nature). Many of nature's creations now around may last for millions of years, as the dinosaurs actually did, provided their lifestyles are compatible with their environments, whilst others, like our own homo sapiens, may disappear after only a relatively short period, if we continue to mess up with our environment.

Answer 8

thats a cute question

its like something my niece would ask, anyway dinosaurs were a product of their environment, like Darwins theory of natural selection.

Trees were tall, and in order for them to get food if is theyre big enough to reach them. why trees were tall back then? I have no idea

Answer 9

It's all relative, think of your size compare to an Ant, couldn't the same be said about you? It is just the way the evolved... and ate all their vegetables

Answer 10

Because they lived on earth rather than jupiter