Feels like there was a lot more megafauna in prehistoric earth than there are today
In: 20
There is a multitude of factors, some of these include:
1. Higher oxygen levels in certain times in earths history, i.e. the Cretaceous and Carboniferous, in particular arthropods have open circulatory systems so can get bigger because oxygen can travel to this system more effectively.
2. Warmer climates, reptiles require warm climates because they are cold blooded and rely on external heat for their internal temperature to increase. This is why we had large snakes like Titanoboa(in the Palaeocene) 60 mya for example.
3. There was also an abundance of CO2, this in turn could have assisted in plants being more abundant and the herbivores would then evolve larger bodies and in turn the carnivores would of evolved larger bodies to hunt these large herbivores.
4. For mammals a cooler climate assisted in the evolution of larger animals to remain warm and store enough food in these climates. It is known that colder climates select for larger bodies in mammals(think the polar bear). Also land area was another important factor.
5. Most of the land animals went extinct in the megafaunal extinction event, due to climate change/possible human activities. Africa is said to be the only place left with its megafaunal population.
6. In regards to Cenozoic sea animals, the predators like Megalodon went extinct due to habitat change, the disappearance of their prey and other predators hunting the new prey like the ancestors of great white sharks. Though Baleen whales are doing okay in the size department, we live with the largest of all animals today the gigantic blue whale!
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