Why were animals and insects so much bigger during the time before humans?

Question

Why were animals and insects so much bigger during the time before humans?

In: Biology

Answer 1

I suspect a lot of it is due to survival of the fittest with primitive animals. Survival mostly came down to physical strength and so size often wins. Certain animals evolved to larger sizes, until they developed venom, at which point they evolved to smaller sizes since they no longer needed to crush their prey. You might notice that shorter people can be kind of nasty. OK, that last sentence was a joke.

Answer 2

The surrounding environment allowed for certain animals, such as sauropods to get very large. By environment I mean there was a lot of open space and plenty of food.

Some have mentioned oxygen levels as a reason, but this is not really a factor. The oxygen levels during the Mesozoic, while varying over time, was never much different than now and in some cases was on the lower end of current amounts.

Vast space and enormous trees along with ample vegetation allowed for the animals to develop large sizes to consume the available foliage. In turn, predators grew large in response to the extra large prey animals.

Dinosaurs specifically were also able to grow large because of their bone structure. Their hollow bones were very light but very strong, thus allowing for large bodies that could support the weight. Mammals have solid bones and the larger the animal the larger the bone and so the heavier the body.

Water mammals, such as whales, have the advantage of the water for buoyancy and so, could grow to a large size without weight being a major inhibitor. However the largest land mammal, Indricotheres, grew no larger than about 18 feet high and 22 feet long. They were sort ancient giant rhinos without the horn.

The 80 feet long diplodocus was roughly the same weight as an Indricothere, but it’s long neck and tail and hollow bones relieve much of the mass.

Today, most open space is dwindling. There is no real giant open wilderness that does not end up competing with humanity. Essentially humans are the reason nothing gets big in the present.