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The study of dinosaurs and prehistoric animals is ongoing, and every so often, archaeologists and paleontologists make new, exciting discoveries. A question that often comes up and is still investigated is why these animals were so large.
There are several theories as to why prehistoric animals were so large. Paleontologists and archaeologists have numerous - sometimes conflicting - ideas about this subject. These theories include Cope's Rule, the availability of food, the climate, and the animals' physiological structure.
I’ll go into more detail on each of these theories below. Continue reading to learn more.
The reason why prehistoric animals were so large is still being debated. However, there are numerous theories. One of the most often cited reasons for their size is that they grew to suit their environment, which was large, open, and gave them plenty of room to grow.
Next, we’ll look at some of the most common theories for explaining the gigantic size of some prehistoric animals.
One theory that explains why prehistoric animals were so large is Cope's Rule. Cope's Rule says that animals grow larger and larger over the evolution of time before becoming extinct. This means that an animal would start off smaller and continue evolving over thousands of years until it becomes gigantic.
Then this animal will become extinct, making way for a new type of smaller animal that will grow over thousands of years to become massive and be wiped out by mass extinction.
I touched on this above, but I’ll go into more detail on it here.
The environmental landscape plays a role in how animals grow. The environment was completely different during the Triassic, Jurassic, and Cretaceous periods when dinosaurs and other giant animals lived, compared to how it is today. The main differences include the availability of space and the amount of oxygen and carbon dioxide.
Since the earth was undeveloped, leaving tons of available land space, some archeologists and paleontologists believe that the animal that inhibited it would naturally grow larger to take up the open space. Undeveloped land meant much more vegetation was available, making food easily accessible.
According to some researchers, there was a much higher oxygen content in the atmosphere when these giant creatures lived. More oxygen meant that the animals grew larger.
Another environmental difference was that there was also about four times as much carbon dioxide on earth as today. More carbon dioxide meant that the plants and trees grew rapidly and much bigger than now, providing food for herbivorous dinosaurs. Since food was abundant, these animals could eat more and, over the years, grew larger.
A contradictory belief was that the oxygen levels were actually lower during prehistoric times, which meant that dinosaurs had to develop a more efficient way to breathe so that they could survive.
The exact physiology that allowed them to breathe more efficiently will be discussed in the next point. As the levels of oxygen in the atmosphere increased, these animals had more oxygen than they required, which made them grow bigger.
More recent studies have found that dinosaurs had bones and lungs that were very similar to the bones and lungs of birds in that their bones were hollow. These hollow bones contained little air sacs that served two purposes:
Their lungs were also robust, allowing their respiration system to work more efficiently.
The bigger an animal is, the less likely it is to be attacked as prey by a predator. It is also more likely to secure food and water, so these animals evolved over time to be massive as a means of surviving.
Since herbivores were becoming larger because of the factors mentioned above, carnivores needed to evolve to be bigger too so that they could hunt effectively. A carnivore needs to be larger in size than its prey to be able to kill it.
Dinosaurs also needed to adapt to their climate. For warm-blooded animals that lived in colder climates, having a large body enabled them to retain heat. Cold-blooded animals living in warmer temperatures needed bigger bodies as a more oversized frame prevented them from overheating.
Just as there are various theories for why prehistoric animals were so large, the same is true for this question.
There are several theories to explain why there are no animals as big as dinosaurs living today. These include Cope's Rule, our current ecosystem, and the fact that there are no existing animals capable of growing the way dinosaurs did.
Cope's Rule says that mass extinction takes place around every 200 million years before another group of animals is born and grows over thousands of years to be gigantic. The Cretaceous time period was the last time dinosaurs roamed the earth and were wiped out about 66 million years ago.
According to Cope’s Rule, not enough time has passed for animals to become enormous again.
Another reason is our modern ecosystem. Since the earth has become more developed for humans, it leaves less land space and vegetation for animals. There is less food available for animals and less room for them to take up.
Lastly, if you look at the physiological structure of animals, none possess the same body type that allows animals to grow to that extent. Their bodies and bones are not developed to hold that size and weight, so scientists believe that the earth will not see any massive animals in the future.
There are a number of theories surrounding why prehistoric animals were so large. These include their evolution for survival, the environment they lived in, their physiological makeup, and Cope's Rule.
Unfortunately, the modern landscape does not allow for animals to grow to the extent that prehistoric animals did, so it is unlikely that the world will see a return of animals as magnificent as creatures from the past.
