Eli5: Why do mammals have endoskeletons rather than exoskeletons when it makes them vulnerable to attack?
In: Biology
Because they did evolve from creatures that do not have exoskeletons.
Exoskeletons might have advantages in some situations but they have a lot of disadvantages. One is that it cant grow so you need to shed it (molt) and then a new large has to be formed. The creature is very vulnerable then because that can move around.
The exoskeleton is also heavy and when you scale them put the weight them will increase faster than the animal’s muscle strenght.
The joins are also a problem. Exoceleton needs to use a hinge joint that bends in only one direction so you need more, they are also quite limited in strength because of the small contact area. The ball and socket joint that we have can move in more direct and is stronger.
The result is especially for land animals you can get a lot larger and faster if you have an internal skeleton compared to an external.
The largest land animal with an exoskeleton is the coconut crab with a weight of 4.1 kg (9.0 lb). You will not get anything much larger because of the scaling problem
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