Fun fact, prior to the Cambrian explosion animals did not have hard parts. There is a theory in a book called "in the blink of an eye " that some animal evolved eyes followed quickly by the evolution hard parts and the Cambrian explosion. They're were three phyla of animals before the Cambrian explosion and whatever the current number is now I think it's like 28 after the Cambrian explosion which took place in a very short period of time. link to book edited comment to have better search