you think this is on of my shitposts, but when bone material first evolved in organisms about 1.5 billion years ago, it was in the form of exoskeletons/shells. they served as protective shields. you know, like with turtles, or sea urchin spines. 

exoskeletons helped protect the softer anatomy, but also restricted movement and surface sensory organs. eventually bones evolved to be inside the body instead of outside. this had a lot of benefits, and led to the evolution of vertebrates. 

@arsanatomica does a great job of illustrating it here!

a neat fact is all this started when violent tectonic plate movements deposited huge amounts of minerals (including calcium) into the ocean (where life was based). this allowed organisms to develop hard body parts, such as shells or spines. 

earthquakes caused bones and i think that’s nifty!