As far as i know, there arent bigger animals around today due to the square-cube law, and yet their were dinosaurs the size of whales on land?
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The square cube law doesn’t mean you can’t have bigger things, it just means you can’t scale up an existing thing indefinitely and expect it to work.
The bigger animals, like the dinosaurs you’re thinking of, simply had differently structured bodies that allowed them to be bigger (more bone to body ratio, hollow bones…).
It’s not like an elephant is the upper limit for mammal size. If you took a mouse and made it as big as an elephant, it would also collapse. If you took a small dinosaur, and made it bigger it would also (probably) not work.
The square-cube law isn’t specific to biology, it’s just an observation about how volume grows faster (cubically) than surface (squarly), which also (usually) means that mass will grow faster than the support structure for that mass. An elephants weight is supported by its bones, muscles etc. If you scaled it up the bones would get bigger too, but the mass of the bones would get bigger faster, and at some point, it would get too much. If you wanted a bigger elephant, you’d need to change how much bone it has compared to It’s body size (not just how much bone it has compared to a smaller elephant). The reason real elephants can’t get any bigger is that when a new one is born, evolution doesn’t go on a character select screen and pick what kind of bone-to-mass ratio it would want. It’s stuck with what it has, at least for now.
Edit: Just to address this, because people keep posting bits and pieces of it in the replies: yes, the square-cube law has many more biological implications than just collapsing under your own weight because your bones and what not were not prepared to handle it. That’s just the most common thing you hear when people talk about it in popularization, because it’s kinda fun, in a morbid way.
One other thing that becomes a problem, and you can see this very well with elephants specifically, is that as you grow, you become to have cooling problems, since you gradually have less and less skin to disipate the heat, proportional to how much you’re producing. That’s why elephants have such huge ears. But there’s many other implications, such as not being able to absorb enough oxygen, because your lungs are too small, not being able process nutrients fast enough, because you don’t have enough gut surface… Really anything that has anything to do with the surface or cross section of an organ will become problematic if you scale an animal up or down.
You also have to take diet into account.
Afaik the ferns that the herbivore dinosaurs fed upon were easier to digest and more nutritious than leaves and grasses of today.
Elephants eat constantly; I fathom a dinosaur eating a modern diet of leaves and grasses wouldn’t be able to feed itself at all
I can be totally wrong about this, but if my memory serves me right, the oxygen-content of the air was much higher in the times when the dinosaurs lived. Which meant that they had an easier time getting out enough oxygen to the muscles in their huge bodies, which allowed them to grow larger. In addition to the already mentioned fact that they had hollow bones etc. and were not as heavy as one might think.
Dinosaurs were built like birds (birds *are* dinosaurs in fact) – they had strong but light skeletons, weight saving air sacs throughout their upper body, and more efficient lungs than mammals that helped get oxygen for their huge bodies.
When the asteroid hit 65 million years ago every animal bigger than around 25kg went extinct, dinosaurs and mammals.
While small flighted dinosaurs did survive and are known as birds today, as both the small mammals and dinosaurs started to re-evolve large animals the mammals were able to do so better (probably because live birthed babies can be bigger than egg hatched babies) and that prevented birds from evolving back to T-Rex sized animals (just like mammals couldn’t evolve big while large dinosaurs were around).
Although one thing to remember is that blue whales are larger than any dinosaurs and are the largest animal to have ever lived.
I also read somewhere that the atmosphere had WAY more oxygen in it back then which contributed to the large sizes somehow
Nobody has seemed to mention this yet, but giving birth to live offspring and a long gestation period is more difficult for large mammals, than just laying eggs.
Pbs eons did an episode about it
https://www.pbs.org/video/the-rise-and-fall-of-the-tallest-mammal-to-walk-the-earth-cb8lyj/
I am not going so much into the square cube law, as this is explained by others.
As for why dinosaurs grew so big but land mammals don’t grow to enormous sizes, this is likely due to dinosaurs having a lot of traits that allowed it.
1) They likely had an air-sack based respiratory system like their offspring (modern birds). This is significantly more efficient them mammal lungs and the efficiency decays way less with neck size. (The air-sack system is also why modern birds can perform labour intensive flights in high altitudes)
2) For the most part, they did not posses specialized teeth, but instead relied heavily on their stomach. There is a theory that scaling up helped here.
3) Their bones where likely lighter and already carried the adaption for bipedal walking.
not just weight but oxygen intake and heat dispersal are major limiting factors on animal size
The Sauropods evolved hollow bones before birds existed.
I’ll edit this comment with more info when I can get back to the book I read about it in : ‘The Rise and Fall of The Dinosaurs’
People here explaining with math but biologically speaking wasn’t it due to the rich oxygen environment back then? Someone much better than I once explained this
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