Why were so many ancient denizens of Earth huge compared to the size of animal species living today?

Question

What geologic, climatic, etc. factors favored large-sized animals?

Answer 1

In the case of dinosaurs it's important to note that nost dinosaurs were actually the size of medium-sized animals today. Even so, some obiously grew very large. Being large enabled them to maintain their body temperature more efficiently, and was a good protection against predators. As far as geological and climatic conditions though, the fact that the all the continents were still linked would have enabled the largest dinosaurs to roam over a wider area, eg. some sauropods are thought to have annually migrated from South America to North America. Thus they had greater access to resources. You could also argue that, as the climate in the Mesozoic was (at least much of the time) warmer and more tropical than today, vegetation grew faster and provided more to eat. The only problem with this is vegetation in the Mesozoic was mostly conifers - pine trees - which are pretty hard to digest (flowering plants - most modern day plants - did'n't take off until very late in the Mesozoic). It's also possible that the very large size of some plant eating dinosaurs enabled them to digest conifer material more slowly and better.

Back before the age of the dinosaurs, in the late Paleozoic, it's thought that oxygen levels were much higher than today. This may have been a factor in insects growing so large (they also had fewer predators). But oxygen was probably not a factor for the dinosaurs as by then oxygen levels were about the same, or at times lower, than today.

As for the recent megafauna (mammals), it's probably no coincidence that most of them around the world went extinct around the time humans first arrived there. Being large and fearless of small animals like humans, they were probably easy prey. Large animals in Africa, and to a less extent South-east Asia, were used to dangerous hominids. Everywhere else, we probably killed them off.

Answer 2

Natural selection. During that age certain animals existed and the rules that control natural selection were supreme.

The Dinsosaur wasn't large in the beginning. Early Dinosaurs were the size of modern day small lizards. But as time went on they evolved, getting bigger and stronger, until they reached a size determined by their environment.

Nothing happens overnight. These changes happened over millions of years.

Answer 3

Are you for genuine? highway doggies have a more suitable mortality cost than doggies born to breeders. ailment, a foul moms, more suitable risk of being killed through yet another individual canines, lack of nutrition and so on. Immature bitches not often make good moms. in good structure? suitable, yeah mange, fleas and different parasites truly make for in good structure animals. No they live to inform the tale on garbage or maybe with they could capture and scavenge. won't be able to even research them to WILD canines because maximum wild animals do not breed till they're a million or older. earlier that they are nevertheless likely with their beginning %., it quite is all appropriate members. Oh and so some distance as Rabies is going - seem to china and the middle east with regard to feral canines. The very last time those 2 parts were in the files it develop into because they were going out to skinny down the feral canines inhabitants no longer only for the overall risk the proposed to human beings and different animals, yet as well because of Rabies situations. Being wild does no longer take care of ANY animal from catching rabies.

Answer 4

They weren't in fact all huge. Mostly the reptiles, which gradually got huge. The earth was very different then, mostly tropical and mostly the land was one big piece. Dinosaurs became so large because that was a survival adaptation naturally selected for - once there was one big dinosaur, it became advantageous for others to become huge, either to cope with the big predators or to compete more effectively with them. Some dinosaurs got very, very fast instead of very large, and so on...

Answer 5

I would say that the alleged hugeness is an artifact of human being's interest in giant animals. The largest animals that have ever lived, blue whales, are alive now

Answer 6

the triassic & jurassic age was the one when the creatures increased in size, the earth one supercontinent(pangea) & the atmospheric as well as climatic conditions supported it. temp were also relatively higher.

Answer 7

O2 levels played a large part.