Advantages and disadvantages of enamel bones

Question

I am writing a speculative evolution project that includes terrestrial sharks. However, a shark’s skeleton is made from cartilage, which while flexible is not suited to bearing large weight on land.

So, I am considering reinforcing the skeletons of these land-sharks with enamel or dentine; the same material that teeth are made from.

What are the advantages and disadvantages of this material as an alternative to calcium phosphorous in bones?

Answer 1

As a hard substance, the hardest one in the human body, enamel makes sense for teeth, not for bones.

The large amount of mineral in enamel accounts not only for its strength but also for its brittleness.

While teeth need a hard coating because they are supposed to work by crunching and smashing whatever their bearer is eating, bones do not only crush: they need to be able to flex and bear other loads, for which a more flexible material is better suited. Just think of the type of load that goes on a human leg when the human is landing on their feet: the whole weight of the torso makes the femur bend like a trampoline. The last thing you want is a brittle material in that situation.

It might make sense to have dentin in bones which are supposed to withstand impacts and need hardness, like it can be for the skull or for bone plates used in a defensive fashion.

Answer 2

Look to composites:

You can certainly use a hard material for bones. But by itself, it is fragile like glass. You need microstructure to give the material some give.

My favorite example of this is nacre. Nacre is one of the strongest biological substances around, and has been suggested as a bone-like material. But it's made of aragonite, an extremely brittle mineral. So what gives?

Nacre is composed of tiny bricks of aragonite joined by a mortar of more flexible biological materials. This structure provides it some give, and prevents cracking that can critically damage other fragile materials. This allows a biological organism to get the advantages of a hard material, while still maximizing the resilience to give a strong composite.

Answer 3

Advantages:

1. Hardness: Enamel is the hardest biological substance in the body and dentine is also relatively hard. This could potentially help the land-sharks support their weight on land.
2. Durability: Teeth are designed to withstand a lot of wear and tear, so enamel and dentine could be a durable material for the skeletons of land-sharks.
3. Renewable: Unlike bones, teeth can continuously grow and regenerate, so using enamel or dentine as a skeleton material could be more sustainable.
4. Light weight: Enamel and dentine are lighter than bone, which could help the land-sharks be more agile and move more easily on land.
5. Improved toughness: Teeth are designed to resist cracking, breaking and wear, so incorporating enamel and dentine into the skeletons of land-sharks could lead to improved toughness compared to bones.
6. Aesthetics: Teeth often have a unique and visually appealing structure, so incorporating enamel and dentine into the skeletons of land-sharks could give them a unique and aesthetically pleasing appearance.

Disadvantages:

1. Inflexibility: While enamel and dentine are strong, they are not as flexible as bones. This could potentially lead to a higher risk of injury for the land-sharks when they move on land.
2. Complexity: The process of reinforcing a shark's skeleton with enamel or dentine could be complex and difficult to achieve in the evolutionary timeline you have set for your project.
3. Lack of minerals: Unlike bones, enamel and dentine do not contain minerals such as calcium and phosphorus. These minerals are important for bone health and strength, so reinforcing the skeletons of land-sharks with enamel or dentine could potentially lead to a lack of these important minerals.
4. Limited supply: Teeth are not as readily available as bone, which could limit the amount of enamel and dentine that is available to reinforce the skeletons of land-sharks.
5. Cost: The process of incorporating enamel and dentine into the skeletons of land-sharks could be more expensive than using bone, due to the difficulty of obtaining and processing the material.
6. Compatibility: Enamel and dentine have different properties than bones and may not be compatible with the rest of the body's tissues and systems. This could lead to issues with integration and healing if the land-sharks sustain injuries or experience other health problems.

Answer 4

This is pure memory recall ( << is the disclaimer)

Enamel is a very hard yet very brittle material. While it may be good at holding its shape when grinding against softer material, it may not be very good at load bearing, and since its a dynamic load (living being weight) it can't really stay in compression like how concrete holds up bridges and whatnot. For example if you compress a column of enamel vertically, it may be ok but if you suddenly hit the side and it snaps because of a lateral force and its brittleness, it won't do.

I'd suggest some things like normal terrestrial bone (like bird or mammal bone) but that'd be boring.

Even though titanium is often used in bone replacement, its biostable so it can't be naturally made into bone by an animal. Shame, it is light and durable, a great bone material. (aka the body can't use or move titanium and so can't do anything about it naturally)

Avatar did mention carbon-fiber bone and I suppose that is plausible considering that bodies do manipulate carbon in some form, with some furious hand-waving.

This is probably going to be a no go but keratin and chitin seem promising as a bone material: it is light, durable, and flexible (maybe keratin is a little too flexible but chitin is used in crustaceans and insects. Insects especially used to be huge in the prehistoric times, iirc.