Why are animals and fauna no longer as large as they once were? What has changed about our world that mega fauna and mega animals no longer exist?

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Why are animals and fauna no longer as large as they once were? What has changed about our world that mega fauna and mega animals no longer exist?

In: Biology

Cold. Bigger bodies are better at retaining heat in cold climate. As the climate warmed over the past 10-20,000 years smaller bodies that shed heat quickly became more advantageous.

We don’t *actually* know but some theories are that temperature of the earth was the major factor for mammals getting so big. If the ambient temperature is lower, the heat/energy of a larger mammal is much easier.

For insects (and maybe plants), there was a much higher concentrations of oxygen in the atmosphere that helped produce gigantic bugs (we think) and when birds were getting bigger and preying on them (we think) they started to die off (we think)

I will point out that the blue whale is the biggest animal to have ever existed as far as we know

Humans. Look at Australia, Europe, America. Wherever humans spread to, megafauna vanish. They’re either really good food sources or dangerous predators to exterminate, and early humans had zero interest in conservation.

The oxygen levels were about 30% as compared to the 20% we live in now …due to Oxygen rich atmosphere the plants and animals would be larger than those existing today