I understand that in Carboniferous era insects were big because of oxygen but what about other creatures?
Why were some dinos as big as whales? Why were a lot of them many times bigger than elephants? How does it work? If mammals reigned in those eras instead of dinos and insects, would they also be this gigantic compared to modern ones? (Like gigantic sloth but 5 times the size of it?)
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Dinosaurs had some skeletal adaptations that allowed them to grow much bigger than the theoretical largest (land) mammal. Sauropods in particular were so titanic because of how their spines evolved.
We don’t know exactly why dinosaurs got so big, but it seems it’s because the environment supported gigantic animals.
Oxygen levels were a lot higher, and temperature was a lot warmer during this era. Without such high oxygen levels larger animals aren’t possible in our current era.
Having larger bodies may have helped them regulate their body temperatures better, was good defense against predators, and allowed them to access more food sources. By extension the predators got bigger because they needed to be bigger to chase down such large prey.
Blue Whales though are the largest creatures to have ever lived. Their massive weight is supported by the ocean which helps, but new theories seem to show that whales got so large because of the ice age. During periods of ocean glaciation only the largest whale species survived, possibly because of their fat content and their ability to go long distances without air and food.
I don’t think there is enough evidence in fossil record to give you a great one line answer. However animals are all pushed by the wind of evolution. So there must be a selection pressure favouring bigness, and while higher oxygen might explain the how, it is possible it doesn’t explain why for any species…. not a dinosaurologist but I think the prevailing thought is that bigger herbivores make harder targets. So the bigger you were the harder you were to take down. At the same time you would be a bigger meal when you did die. So there is probably some hunter/scavenger balance right there.
Thr point is that the hammer of evolution on the anvil of time had been working on the predators/prey of dinosaurs for a long time. And giantisim seems to be a solution until John Hammond gives us one we won’t ever know exactly what the selection pressure was that pushed them so big. But it worked that’s all we really know
Dinosaurs had the advantage o.f bone structures similar to birds that helped reduce their weight and better support the load. its also though that the environment at the time would have been warmer and more oxygen rich to support larger animals and their metabolisms.
Its also worth noting that you may be overestimating how big and heavy some of these dinosaurs were. Most were actually not that gigantic compared to many of the fauna alive today and alive shortly before humans spread out and began hunting them to extinction. A modern day african bull elephant would be of a similar size and weight class to a Tyrannosaurus and would likely be able to go head to head with one.
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