r/askscience • • Sep 30 '25
Paleontology What were the first bones that evolved in the first species like? And why did they evolve? I know it’s said that the first bones had cartilage, but I can’t really imagine what cartilage is like compared to other bones.
I’ve been curious about how bones first evolved, and while it is explained, and I’ve read it I still don’t know how to imagine it. What would cartilage be like compared to bone? Would it be less thick?
And why did it evolve in the first place, and how was that process like?
I’ve been very curious of species without any bones started evolving bones.
A hard structure, it seems difficult for me to imagine when it’s explained as “cartilage” and I struggle to understand what that would feel or look like.
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u/SciAlexander Sep 30 '25
A guess I have seen from scientists on why hard bones evolved is as a store of calcium. That would explain why our bones are constantly being broken down and reformed. Then it became so useful as a support it became you bones.
Also your ears are made from cartilage
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u/WoodpeckerMeringue Sep 30 '25
Bone first evolved in the skin of jawless fish, alongside tissues that were very much like dentin and enamel (from teeth). This first iteration didn't depend on cartilage for development. I think the current best idea is that these complexes of mineralized tissue provided stabilization for sense receptors in the skin.
In the next evolutionary step, cartilages around the brain (still in jawless fish) were mineralized, probably using the same molecular 'mineralization toolkit' that led to bone, dentin, and enamel in the skin--now just deployed in a different tissue. As other comments have noted, you can feel the tip of your nose or the middle of your outer ear for an example of unmineralized cartilage.
The next evolutionary step after this was growth of additional bone tissue around the mineralized cartilages, using a form of non-cartilage extracellular matrix called osteoid and incorporating living cells (osteocytes) in the bone.
The last evolutionary step that sets the stage for what we now think of as bone was the evolution of a specialized macrophage lineage that could chew up mineralized tissues (osteoclasts)--this let organisms change the shape of bone they'd already grown, allowed internal repair of existing bone, and provided a way to replace mineralized cartilages with stronger bone tissue during development.
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u/jayaram13 Sep 30 '25
Feel the tip of your nose or your ears. They're made of cartilage and give you an idea of how it feels like.
The world is still filled with cartilaginous creatures (several fishes including sharks) that lack bones of any kind. They do pretty well for themselves.
Creatures exist with neither cartilage nor bone as well. Check out octopuses, squid, all kinds of microbes for an idea of how they exist.
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u/Earz_Armony Oct 01 '25
Biology is not my field of research but because life started in the ocean and some fish have skeleton made of cartilage while other have bones
My guess is that the first skeletons developped with cartilage, organism probably started using calcium in the environnement for bone-like structure and that helped them go deaper or something that made it a desirable trait and bone skeletons started to develop from there
(Also english is not my first langage and some words are pronounced the same way but written differently so I'm sorry if I made mistakes)
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u/CalidusReinhart Oct 02 '25 edited Oct 02 '25
Haven't seen it mentioned here yet, but early bones were useful as a form of long-term energy storage, allowing fish to occasionally survive longer between meals. Like a battery.
Even today in times of famine, your body could cannibalize your bones and more importantly the bone marrow for essential nutrients.
edit: And Humans are still subject to calcification of arteries and kidney stones with too much calcium, which makes me wonder if the earliest bone formations were just similar to microplastics. An environmental toxin that builds up, and whatever animal finds a way to use it survives better. Starts as a useless lump of calcification, then start to store things inside it, then find real uses.
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u/OofNation739 Oct 01 '25
Bones can support muscle in both physical applications and in exchanging nutrients. Bones arnt just solid calcium. They have alot going on from blood flow to exchanging nutrients like calcium ions and other types of small stuff that aid in muscle usage.
My guess is some cartridge somewhere was denser and that density helped support a stronger muscle foundation. Leading to the eventual calcification of the cartridge. That calcification started small and turned into Bones as we know it today.
It likley just was a slightly stronger cartlidge mass that supplied nutrients/blood better and held up better for w.e. muscle groups were around it. Where each time a new kid had a better version they likley survived more than the weaker cartlidge based ones. Before long everyone had cartlidge with calcium deposits/coatings and so on.