We always hear about how big ancient sharks, alligators, birds were. What was the advantage of being such a massive size and what caused them to become smaller? To my understanding its best to be smaller because of the square-cube law, then why are there exceptions like whales?
In: 3
There were plenty of smaller versions, too, but you don’t hear about them nearly as much because “this prehistoric bird was about as big as a modern bird” is not particularly interesting.
The advantage of size in animals is pretty self-evident: if you’re a predator you can more easily overwhelm smaller creatures, if you’re prey most predators won’t screw with something that has an advantage in bulk. Of course, as you point out, this has limits due to increased energy requirements and inefficiency in the relationship between surface area and volume, etc, so size doesn’t continue increasing forever.
“What caused them to become smaller” is a broad question depending on when you’re asking about and we can only really speculate. Ancient arthropods being huge is probably related to higher oxygen concentration and temperature in the atmosphere during periods like the Carboniferous. Relatively recent megafauna like mammoths and giant sloths probably went extinct through a combination of climate changes and overhunting as early homo sapiens spread across the world, but to what degree each mattered is heavily debated.
Oxygen levels were much higher then, so more energy can be gained to evolve bigger. As animals got bigger, the animals that ate those animals got bigger, and so on as evolution favoured being bigger to survive.
But after the mass extinction event 65 Million years ago, the environment now favoured being smaller; less energy required to survive. And here we are.
There were smaller animals around but people are interested in the big animals. Large animals like whales are so large it becomes difficult for a prey animal to tackle an adult. The availability of food and the presence of man led to the quaternary extinction event or the extinction of the megafauna https://youtu.be/Y3J9CzLW_p0
Some were smaller, some were bigger, some were the same. The ones that were bigger are “cooler” and are better preserved in fossils so you hear of them more.
Yes it’s been mentioned here, but I’d always heard that the key thing that allowed for larger animals was a higher concentration of oxygen in the atmosphere–allowed for much larger creatures without needing way better circulation to go along with the size, etc. Bigger plants too.
It’s just that larger animals became fossilized. Smaller ones just rotted away or were consumed.
The smallest reptile today is less than an inch. There is no reason not to believe there weren’t thousands of species of reptile from 1/2 inch to 100ft. We just don’t know.
You already know about squares and cubes, good.
In short, there was a higher concentration of oxygen.
Imagine you have a toy that you can build and change. Well, animals are kind of like that too, but they change over a really, really long time, like a super-duper long game of pretend.
A long, long time ago, when the Earth was different, animals had to be big to do certain things. For example, huge dinosaurs needed to eat a lot of plants or other animals to stay full and strong. Their big bodies helped them survive in their world.
As time went on, the Earth started to change. It became colder or hotter, the plants changed, and even the other animals they played with changed. Some of these changes made being big not as helpful as it used to be. Smaller animals could find enough food and hide better.
So, the animals that were better at being smaller and finding new ways to get food started to do well. They had babies that were good at the same things, and these little animals continued to grow and change over a super long time.
That’s why animals we see now are often smaller than the really, really big ones from long ago. The world around them changed, and they changed too, like playing a new game with new rules.
Latest Answers