ElI5 why dinosaurs were so big and now everything on land is rather small
In: Biology
Like birds (which remember are dinosaurs themselves) they had more efficient lungs with airsacks throughout their body and bones. Their lungs allowed them to get more oxygen to their body and the airsacks combined with hollow bones made their bodies lighter. Scientists believe this is why they were able to get so big in land (although the blue whale today is bigger than any dinosaur)
Humans kill and eat all the big things now.
There used to be mammoths and other large mammals that rivaled some of the big dinosaurs, but sadly they were made of meat.
We even hunted whales to near extinction, and they’re bigger than dinosaurs ever were.
An animal size requires a trade off. The larger an animal, the more food it needs to survive and it requires a longer pregnancy period so there is an upper limit on how big an animal is before it is unable to move due to its own weight on land. Dinosaurs bypass the long pregnancy problem by laying eggs.
The atmosphere contained much more oxygen (as much as 35%, compared to about 20% today). This allowed many animals to be larger than their modern equivalents, because their size was not (as) limited by three efficiency of their lungs. For example, there were dragonflies the size of hawks!
https://askanearthspacescientist.asu.edu/oxygen-animal-evolution#:~:text=But%2C%20the%20success%20of%20animals,dragonflies%20the%20size%20of%20hawks!
I don’t think anyone has actually answered this. Either tangent facts or guesses. But the real answer? We don’t really know. There’s some theories…
“Paleontologists don’t know for certain, but perhaps a large body size protected them from most predators, helped to regulate internal body temperature, or let them reach new sources of food (some probably browsed treetops, as giraffes do today). No modern animals except whales are even close in size to the largest dinosaurs; therefore, paleontologists think that the dinosaurs’ world was much different from the world today and that climate and food supplies must have been favorable for reaching great size.” https://www.usgs.gov/faqs/why-did-some-dinosaurs-grow-so-big#:~:text=Paleontologists%20don’t%20know%20for,%2C%20as%20giraffes%20do%20today).
I think it’s almost important to understand there wasn’t just one dinosaur age. They are believed to have existed for 165-245 million years. We, for example, have existed for about 300,000 years as homo sapiens and the genus homo has existed for up to 2 million years. So the dinosaurs were around for 100x longer than our earliest ancestors existed. Not to mention there were dinosaur-like ancestors before they were “dinosaurs”. There’ve been multiple mass extinctions in Earth’s history that have wiped out almost life on earth and what does comeback is different from previous species with new adaptions for surviving the new world.
Another interesting note about prehistoric gigantism is that oxygen levels affected the size of insects. The are points in history where prehistoric insects were much larger and it’s primarily because the oxygen level was higher than modern day. This is not necessarily true for all species, but insect size is greatly affected by oxygen in the atmosphere.
Plus, the big ones with the long necks just stood around and ate plants all around themselves so they didn’t have to walk around a lot (unlike giraffes that use their neck to get leaves from tall trees)
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