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I wonder how bones evolve where there are none. (This is the question, read the sub-questions as examples :) )

Lets take an elephant as an example. If it was adaptive for the elephant, could bones somehow evolve in their soft-tissue trunks? If so, what tissue would they develop from?

Perhaps the sheet of cartilage in their ears are more likely to somehow calcify and become a new bone?

And would then several connected bones and joints evolve from the new bone tissue?

Is it very rare for new bones to evolve from scratch? Or, do today's bones entirely trace back to the set that evolved in early tetrapods?

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closed as primarily opinion-based by kmm, Remi.b, David, Chris May 22 '18 at 11:28

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ I remember being curious about how bones were made and I eventually found out that bones develop from cartilage, so bones develop from cartilage. Is this what you were looking for? $\endgroup$ – Danielle Wilson May 19 '18 at 18:22
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New bones do form occasionally so it is not impossible, Ornithischian dinosaurs are defined by a evolution of a new bone (predentary). There are many pieces of cartilage in the body that become ossified in some animals and not others, the kneecap is a great example since a bony kneecap has evolved and been lost many times independently, it is just a matter of ossifying existing tissue. The trunk however is more difficult since it does not have any suitable cartilage.

Cartilage however is not necessary to form bone, but it is the most common way to get it. Endochondral ossification forms bone from cartilage and is responsible for the majority of the bones in the body. Intramembranous ossification forms bones in other connective tissue, the bones of the skull and dermal bones are examples of this process. Dermal bone has evolved separately many times but tends to form in the skin.

Given enough time and the right selective pressures it is certainly possible for bones to evolve in the trunk but it is not going to happen quickly.

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