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I recently came up with a lizard that had a sort of crystal-gem like attachment on its back. The problem was finding a way for such a thing to have evolved to have a largish crystal on its back.

The lizard is around 2 metres long, has a height of around 1 metre tall, probably carnivorous, could stand on 2 legs or 4 legs if it chooses to (there was a dinosaur that did this, I can't remember what it's called).

Now the crystal sail, it should be composed of Euhedral crystals pillars that line its back to form a sort of 'sail'(I'm not sure whether a singular large piece of crystal is better/less fragile or having multiple crystal pillars is better), the crystal itself shouldn't be very clear, I mean, we don't find very clear crystals naturally so it probably won't be clear on an animal. It's like the Dimetrodon or Spinosaurus 'sails' but one made of crystal. The sail peaks at 1 metre tall. How would such a creature have evolved to have crystals growing out of its back?

To clarify a bit, my conclusion has been that the crystals would 'grow' with the lizard during its lifetime due to the inherent problems of having eggs to fit young with a metre-long sail. This means that its diet would consist of meat, more meat and probably the occasional mineral that goes to building the 'sail'? <<< maybe?

The other problem I have is that crystal is usually quite heavy and brittle. Not all crystals of course but there might be more difficulty to have a less brittle crystal like diamond growing from its back. The heaviness part could be hand waved by 'strong' muscles and bones. The brittle part is worrying, I don't think a creature that breaks its sail every time it runs is gonna need it. (It's a good source of income for humans though.)

I haven't decided on a specific crystal yet, but if you need a specific one then go with either ruby, sapphire, obsidian or diamond. Or if none of these work then it's up to the experts.

If this creature couldn't possibly exist then I probably wasted the time you have spent reading this poorly written description.

I'm not sure if answers to this question require the function of a crystal sail but I'll get around to asking that question soon.

If you have no idea what a sail is then it's that really large extension on top of the creature you see down here; replace that with either a large crystal or multiple crystal pillars and voila. Not to be confused with these sails you find on ships

Dimetrodon skeleton

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    $\begingroup$ I'd like to think a Spinachsaurus was the never-mentioned cousin of the Spinosaurus who tried to get everyone to become vegetarian. :) $\endgroup$ – Frostfyre Oct 5 '16 at 13:34
  • $\begingroup$ I blame the spinach that I killed for dinner. Thanks for the edit. $\endgroup$ – Skye Oct 5 '16 at 13:40
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    $\begingroup$ Obsidian is not a crystal, it is volcanic glass, and is really brittle. Both ruby and sapphire are the same material (Al2O3), the only difference being the inclusion of tiny amounts of impurities which give the stone its color. $\endgroup$ – WhatRoughBeast Oct 5 '16 at 13:45
  • $\begingroup$ @WhatRoughBeast Do you have any other crystals to suggest? I'll edit them in. $\endgroup$ – Skye Oct 5 '16 at 13:47
  • $\begingroup$ What properties of a crystal do you require? Being transparent? Sparkly? Being faceted like a cut diamond or lumpy like a raw diamond? $\endgroup$ – DrBob Oct 5 '16 at 15:12
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Your crystalline sail must exist for some purpose. It will be a heavy, unwieldy and cost a lot of energy to produce so it must provide some great fitness benefit to the organism. I have two potential solutions for you:

Sexual selection

Sexual selection can be invoked to explain all sorts of crazy things that seem wildly impractical at first. Especially things that look cool. The tail of a peacock is a classic example of sexual selection as are the fanciful colorations of most birds. Sexual selection is responsible for a large proportion of natural ornamentation. A large, shiny crystalline sail strikes me as something that might catch a potential mate’s eye. So the crystalline sail evolved simply due to mate preference, most likely females choosing males. Males that incorporated bright, colorful, shiny crystals into their sail were more attractive to females than their otherwise more fit competitors. This creates a positive feedback loop known as a Fisherian runaway. It’s worth noting that the large sail of the Dimetrodon is theorized by many to be the result of just such a Fisherian runaway.

Piezoelectricity

While sexual selection is almost certainly the most plausible answer maybe you want your crystalline sail to do something beyond look pretty. Piezoelectricity is an electrical charge generated by certain materials in response to mechanical stress. Crystals are especially good at creating this electrical charge. A sail composed of piezoelectric-compatible crystals arranged properly could generate electrical charge from the mechanical energy of walking or wind acting to bend the sail. Harvesting this piezoelectricity is actually possible and is an active area of research in the advancement of wearable technology. It’s perhaps implausible but not impossible to think that an organism might be able to make use of the electricity generated by the sail either to charge a capacitor for the purposes of attack or defense or directly convert that electrical energy into chemical energy such as ATP. So the sail acts as something of a passive electrical generator for any purpose you want to apply it to. As to how this actually came about evolutionarily, well, I did say sexual selection was the more plausible answer, but I think this one is more fun.

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    $\begingroup$ Piezoelectricity can be used as a defense ala electric eels. Or why not solar powered light amplification? Lizards shooting lasers! $\endgroup$ – Mark Ripley Oct 6 '16 at 10:05
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    $\begingroup$ I could steal some great ideas here $\endgroup$ – XenoDwarf Oct 7 '16 at 1:10
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I can see such a thing existing theoretically, but only because sugar is a type of crystal, such a creature would be very small, no larger than a mouse and would use its sail to store excess sugars, energy. These crystals would likely grow around long quills and theoretically speaking, a few quills could point up on their back.

enter image description here

But let's say you want something... Bigger. Well if you're willing to bend on what the sail looks like, then we can reverse the scale.

Pangolins, turtles and ankylosaurus' all have heavy objects on their back and these are for defense. But what if your defense structure served a second purpose? Let's say we have a turtle, but this turtle starts growing excess sugar formations on its shell, over millions of years these could form the sail structure you desire.

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    $\begingroup$ Things will get very sticky when it rains. $\endgroup$ – Mike Nichols Oct 5 '16 at 18:22
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    $\begingroup$ Make it an insectivore, so when bugs get attracted to the sugar, it can just lick them up when they land. $\endgroup$ – Harry David Oct 6 '16 at 1:03
  • $\begingroup$ this just gave me the best idea for a creature design $\endgroup$ – XenoDwarf Oct 7 '16 at 1:04
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There is literally so much content to talk about regarding the purpose, structure, feasibility and effectiveness of this idea that isn't related solely to the evolution of such!! But I'll just focus on the crystal and development side; alright, here 'goes.

What crystal could be used to create this sail?

As it turns out, the gemstones you've listed take on more the appearance of rock than crystal in their natural state, rather dull and usually suffocated by other minerals; they only get their inherent beauty from being cut and polished in specific ways, if they weren't, well, jewellery wouldn't be nearly as popular. They also will be unusable, these gem stones - sapphire and ruby and diamond - are all formed in extreme environments from being exposed to lots of heat and pressure, such amounts your creature wouldn't safely be able to create through natural biological processes.

So we look to alternate crystalline sources for inspiration, of which there are many; Fluorite, Calcite, Celestine, Barite, Adamite, Halite, Colemanite, Beryl structures, Aragonite, Armalcolite, all these minerals form crystals that (provided the correct conditions) can grow very large indeed; they also have the advantage of being relatively easy to form under "normal" environmental conditions - such as on the back of your creature.

"I'm not sure whether a singular large piece of crystal is better/less fragile or having multiple crystal pillars is better"

This is where some problems arise. Having a singular giant crystal on the back of your creature will not work, as it takes a great deal of time to build, per se, and will (if formed fast enough) be too thin and fragile to serve any purpose. This logically suggests that multitude of smaller pillars may work... not really. They would still take an eon to grow to the size needed, from scratch.


But this got me thinking: as a child, who hasn't tried growing crystal in cups of water, using lots of string to give it more space to develop? This is effectively the system your creature will need to develop it's sail: some kind of large framework to grow the crystals on top of, giving it a larger surface area to bind to hence allowing it to grow faster from more locations. And what better material to use than a skeleton (calcium carbonate foam).

Coral is an ideal example of what I mean, able to expand outwards into the environment by building bone-like structures to grow upon; this gives them a very large surface area too, meaning lots of room for additional coral organisms to fix to, allowing it to grow to huge sizes.

Your creature will need to have a similar, coral-like structure protruding from its back (cartilage will do just fine) that forms the basic shape of your sail where crystals can grow. This leads us to the evolutionary part of your question:

How would it have evolved to grow crystals in this way?

The animal your new creature has evolved from would have also had a sail, or fin-like protrusion from its back, that by all means could have acted in the same way a Dimetrodon or stegosauruses is suspected to have (for thermo-regulation purposes/ attracting a mate).

It would have had to have lived in/near an environment that was rich in the elements required to produce these crystals (they being iron, copper, silicon, fluorine - all abundantly available), for instance the land surrounding VOLCANIC PLAINS! They are the ideal environments, readily life-sustaining and rich in mineral-saturate lakes/pools that's sediment and water contain these required trace elements.

All it would have needed to do is move through these mineralised waters on a regular basis; when the water evaporates off it's skin (the majority being on it's sail) the crystal forming elements are left behind; they react with the oxygen in the air and form the foundations for further crystal growth.

As time progressed and a thicker layer of oxidised copper/iron/fluorine/ gathered, the sail became encased in a thin crystal-armour; this was good for protecting the sail, but inevitably led to it's overall destruction (deteriorating the skin, causing it to die and leaving only the bare bones behind, which quickly became coated in the same crystal).

As generations went on, young were born without their sail-skin, yet retained bones in the more flexible form of cartilage; as the creature grew these main cartilage spines split and branched inwards on one another like coral, creating a sort of mesh framework that resembled it's previous sail. As the creature moved through the lakes and exposed its sail to the crystal elements, they would oxidise on the framework and begin to grow, slowly but surely creating ever larger crystals that interwove with those in other area to cover the entire sails area in the minerals, hence effectively turning it into one giant crystal!

The colour it is will depend on the minerals used to form it but it's strength should be around 3-6 on Mohs Hardness Scale, making it pretty durable as well.

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  • $\begingroup$ Long! I know, but you can't just talk about the evolution factors without branching off somewhere else really. It was the shortest version I could do... I need another hobby. $\endgroup$ – Harry David Oct 6 '16 at 5:32
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You could go for a silicon based lifeform and quartz. Either your lizard is silicon-based itself, or is living in a symbiotic/parasitic relationship with such a lifeform.

A silicon-based creature wouldn't be very complex, because of its unstable molecular structure, which would make a simpler additional symbiotic/parasitic creature or plant more likely.

When silicon reacts with oxygen it creates quartz (silicon dioxide), a very clear and strong crytsal that comes in a lot of different colours depending on additional minerals. So maybe silicon-based, algal lifeforms are growing large quartz crystals on the back on your lizard - as a byproduct of their metabolism. This silicon algae could eat silicon in form of sand/dust found on the skin of the lizard and would grow large and clear quartz formations while "exhaling" per se.

The lizard would profit from these hard and sharp crystals, they acting as protection and/or a weapon, and since this is good for survival it would be much likely a trait favored by evolution.

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  • $\begingroup$ Very plausible; quartz gets a 7 on the moh's hardness scale, making a very resistant mineral; it can scratch things as strong as steel and come away just fine. $\endgroup$ – Harry David Oct 6 '16 at 0:57
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If such a feature were to exist it would be based on a defence mechanism to avoid being scooped up by something from above or camouflage or be developed through sexual selection or a mixture of those. It's probably an evolutionary leftover from a top fin.

The crystal in question would probably be a silicone type considering the types of available crystals, the distribution of materials, and the way the crystals can be formed.

The size of these creatures would have to be rather small, because such a structure would make the creature top heavy and thus out of balance. This could be compensated for by a wider footprint, but only to a degree, because too wide and your sail becomes useless for defence.

The climate these creatures live in would have to be very consistent and moderate; the sail increases surface area / body mass ratio, so they would cool and warm more quickly. In deserts they would die of heat during the day, of cold during the night. In the north they die to cold regardless. They are probably cold-blooded. I'm thinking southern forests or jungles.

Their diet would consist of something that can be found on the ground by relatively small, not so very agile creatures. Think either vegetation or insects.

They would hide amongst ferns for camouflage during the night, and the colour of the crystal would match the colour of the ferns. During the day they would graze/hunt when it's warmer out and restock on body heat.

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Maybe the home planet's environment of these creatures has conditions that benefit such sails. I can think of a planet that has a very thin atmosphere (so wind isn't strong enough to blow this creature away), but is close to its sun and therefore is quite hot. The crystals could be porous and have chlorophyll inside them so the lizards can run photosynthesis.

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    $\begingroup$ the dimetrodon was a cold-blooded reptile and used its sail probably for absorging heat from the sun. $\endgroup$ – Dave Oct 6 '16 at 0:53
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    $\begingroup$ @Dave This recent study says that the sail likely wasn't used for thermoregulation. $\endgroup$ – Mike Nichols Oct 6 '16 at 2:29
  • $\begingroup$ my knowledge comes from books i read when i was a dino-fan in kindergarten and elementary school, so pretty outdated. :D $\endgroup$ – Dave Oct 6 '16 at 2:36

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