If sharks don't have any bone, than what are their teeth made of?

Answer 1

So far, the best answer you received was djddan's, and it would only be fair to give him ten points. But let me throw in some additional details, just to make it more fun.

All jawed vertebrates except for amphibian larvae have teeth with dentine as the principal component. Dentine is a mineralized tissue composed of inorganic and organic materials and forms the bulk of a tooth. It surrounds the the interior pulp cavity within the crown on the tooth and is capped by a hypermineralized layer of enamel (enameloid). Likewise composed of organic and anorganic material, the enamel is what gives the tooth its hardness and white appearance. The main component of enamel is indeed hydroxylapatite, a crystalline calcium phosphate. Here comes the part you may find interesting - and confusing: elasmobranch (sharks, skates, and rays) teeth are embedded into the lamina propria (the connective tissue covering the cartilage of the jaw) with a structure composed of acellular bone. Consequently, your question, which some thought so senseless or blatantly stupid is - as is so often the case with question - an excellent one!

So, if sharks have bone in their teeth, why are they sticking to cartilage for their skeleton? First off, it is important to look at this "bone of attachment" a little closer. The important thing here is that it is Acellular, and not Cellular. Normally, cellular bone, as you and I have it in our skeleton, originates developmentally from cartilage. In a process called ossification, the cartilage is invaded by blood vessels that bring clacium to the carilage cells. Calcium is then deposited in the ossifying tissues until we have true bone. In fact, shark cartilage is pretty hard and not at all as flexible as your ordinary cartilage (like in your ears or nose - check it out!), which likewise stems from calcium and other minerals being deposited in the cartilage. But, the skeleton never goes all the way, and so elasmobranchs maintain their cartilaginous skeleton. One could therefore assume that the bone with which the shark tooth is embedded in the jaw integument may be the exception to the rule where ossification simply happens to go all the way. But that does not seem to be the case, primarily since the microscopic picture shows that it is an acellular bone. Research suggests that the bony part of the tooth originates most likely from the enameloid of the tooth. (We call it enameloid istead of enamel since elasmobranch enameloid is slightly different in microscopic structure and probably also in developmental origin.) Your shark bone is therefore not really a shark bone.

Now, I don't want to evade your question. A fter all, you want to know why? Here we are in a tricky aspect of evolutionary biology, since we would like to see some adaptive value for all the structures we see, even if that is not necessarily true. It's a tendency you have to forgive; finding a certain adaptive advantage simply makes for such a beautifully clear story, that even level-headed scientists at times overshoot the target with their interpretations a little. Nevertheless, let's try it anyway...

For one, it is believed that ancestral species perhaps stored minerals in their cartilage. In other words, for desperate times when food or resources of needed minerals were scarce, animals charged their cartilaginous "batteries" with minerals during times when food was readily available. What supports this hypothesis is the fact that both in the shark cartilaginous vertebrae as well as in their teeth we find annual rings, not unlike those of trees. Animals indeed increase the amount of calcium deposite during times of greater food availability. The rings thus serve us well in aging sharks. The other advantage a cartilaginous skeleton might offer is that it is lighter, making it more energetically efficient. You be the judge...

Before I end this already way too long answer, let me give you just a few absolutely useless tid-bits of shark dentition information you may find interesting. First, sharks are what we call polyphydont, meaning that they produce teeth throughout their entire life and simply break off old and used ones to replace them with fresh new ones. Only the erect outer rows of teeth are functional. Such functional teeth you can actually - believe it or not - find in embryonic sharks as well. the embryos of lamnoid sharks feed on eggs the mother ovulates throughout large parts of her pregnancy. The embryos in the uterus need the teeth to be able to get the eeg capsules. When Stewart Springer probed the uterus of a female sandtiger shark with his finger, he was actually bitten by one of her embryos!

Another perhaps strange information is the seasonal morphological change of shark teeth. As I told you above, seasonally differential mienral deposite rates are a well known phenomenon in elasmobranchs. But TimTricas and one of his students found out that in fact the males have strogner teeth during mating season, which makes absolute sense, since the boys bite the girls and hold on to them by their teeth during copulation. Consequently, it makes sense to have a stronger enameloid during this period of the year.

Alright, I sign off here. If you ahve more questions, write me a note. Hope this helps.

Answer 2

Instead of bones, sharks have cartilage, which is more flexible. As for their teeth, well I'd guess they're made of cartilage too or maybe they're the only bones in their body.

Answer 3

Sharks teeth are simply very large modified placoid scales. The outer covering consists of enamel that protects the layer of dentine which encloses pulp rich in blood vessels.

Answer 4

To be precise the teeth of sharks are the modification of placoid scales which are present in them

Answer 5

Yes, Shark dont have bones..... becoz they are cartilagenous fish.......... the exoskeleton is made of cartilage.........

they are not comes under bony fish.

their teeth are made of calcium carbonate.......... CaCO3,
Male Shark have claspers as their copulatory organ..........and Female shark doesnt have claspers.......

Answer 6

Why do you think sharks don't have bones?

Answer 7

Please baby just stay the way you are!!