What you say about the relative who is true about its forms who and whom. However, the possessive form whose can be used to refer to inanimate things too. Your could reword your sentence: Technically, sharks are a suborder of fish the skeletons of which are made out of cartilage rather than bone.
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Julianto MakmurTechnically, sharks are a suborder of fish whose skeletons are made out of cartilage rather than bone;
My question is why the relative pronoun used in the above sentence is whose instead of of which ? Isn't whose used only for relating people to what they have, why here animal can use whose?