477 utenti della rete avevano questa curiosità: [Spiegami] Why have there never been animals as big as the dinosaurs since their extinction?
Apart from a blue whale there have not been any significantly large animals since the dinosaurs roamed the planet. Why haven’t we seen another large species since that time?
Ed ecco le risposte:
As a general rule of thumb: animals gradually evolve to larger and larger sizes as the environment permits, until the a change in the environment occurs (drought, food source goes extinct, etc) and then that large animal goes extinct because it has evolved to a size that required all of the existing food and is adapted to a very specific climate and any change in either of those things will lead to extinction.
Prehistoric animals had tens of millions of years of gradually reach enormous sizes (the Cretaceous Period lasted about 79 million years) whereas the last ice age ended only about 11,000 years ago. Anytime there is a dramatic environmental change, the massive animals tend to go extinct and the smaller and more environmentally adaptive species tend to survive and be the dominant lifeforms for the next age.
When you have a climate that is rich with biomass and it doesn’t change dramatically for tens of millions of years, there is sufficient time and material for massive animals to evolve.
Comment borrowed from a previous answer 8 years ago:
Another example was the surplus of oxygen in the atmosphere:
Although they didn’t exceed the size of the dinosaurs, the megafauna of the Eocene-Oligocene grew much larger than modern mammals. The largest known being relatives of the modern rhinoceros known as Paraceratheriidae; the largest of which may have weighed up to 20 tonnes.
In addition to all that has been already said above, a land animal’s size has an upper limit because at a certain point, the animal’s skeletal structure can no longer support the mass.
Dinosaurs were able to get away with larger sizes because, like today’s birds, they had hollow areas in their bones that decrease the overall weight of the skeleton.
These hollow areas also allowed for extra air sacks in their respiratory system, which extended through the bones. These extra air sacks resulted in increased oxygenation of the body as well as faster shedding of body heat, which are both key elements in animal growth.
Isn’t blue whale bigger than dinosaurs? And it’s a mammal.
Basically
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It takes time for animals to get big and the age of mammals only just begun; reminder dinosaurs weren’t very big when they first appeared in Triassic.
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How big animals can get depends on if there are enough resources to support it. Currently humans kind of enforced a hard limiter on that.