I was watching a show about sharks and the scientist was saying that sharks were “cartiladgenous” (sp?); that they had no bones. But right behind him, nailed to the wall, were numerous shark jaws.
So I was thinking: Are sharks only MOSTLY boneless? What are their jaws and teeth made out of then?
Thanks!!
Cartilage is a tough material - basically gristle - it’s just not as hard and rigid as bone. When it dries out it looks whitish. The shark jaws you saw were made out of cartilage. If you looked at them closely, you would see the difference from bone.
Sharks have skeletons - skull, jaws, backbone, fin girdles, etc, - it’s just made out of cartilage, not bone. Their teeth are the same as those of other vertebrates, and made out of dentine and enamel.
In older sharks, cartilage can calcify, and then it resembles bone quite closely. However, the structure of the tissue still differs.
PS. Cartilage is what supports your ears and nose, and lines the joints between most bones. And a human infant’s skeleton is still partly cartilaginous when it is born.
As an interesting side note, sharks are secondarily cartilaginous; their ancestors had boney skeletons.