- from Bones
You have fewer bones in your body now than you did when you were born. We all start off with more than 300 bones. By age 20, we have only about 206.
In those 20 years, some bones just grow together to make your skeleton stronger.
Skeletons are rare in the animal kingdom. Only 3 percent of animals have backbones. Backbones make us vertebrates. There are way more invertebrates, or animals without a backbone. But vertebrates are bigger and can move around better. We get our shape from a flexible system under our skin. It’s called an endoskeleton. Invertebrates have either a hard outer shell called an exoskeleton (think crabs), or no skeleton at all (think jellyfish).