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Before we start, I'm not talking about the continuously growing teeth of rodents, or the tusks of elephants. Instead, what I'm looking for is one set of teeth that could fit in a newborn's skull, that grow in diameter and length as the animal matures.These teeth would not be replaced with larger teeth like the typical mammalian route of milk teeth to permanent teeth; the teeth you are born with are the teeth you keep.

I'm thinking their growth would be more analogous to the lengthening of bone, but I'm not sure applying the same process would yield adequate results. I've also considered them growing from periods of shedding, like the scales of reptiles, which may involve the animal needing to chew tough fibrous foods to slough the 'dead' layer off. I've thought of a mechanism similar to how trees grow in diameter, but I don't know if that would work either. Lastly, I've considered teeth like parrotfish beaks, where the tooth is just comprised of several very small teeth, but I've already seen someone do this and I don't wanna be a copycat lol.

What I need to know is if any of these solutions (or some external mechanism) could produce what I want given the following stipulations:

  • The teeth have to have a genetically inherited and consistent shape. In other words, if the tooth in one specimen is triangular with ridges along the edge, then that trait should be seen across all members of it's species.*

  • The tooth needs to have a similar rigidity and sharpness to most earth animals. They cannot break constantly or deform under regular use.

  • The tooth has to be vascularized and innervated in some way; so something similar to a root might be necessary.

  • The tooth cannot have a 'cap' like seen in the horns of earth animals.

  • The tooth should be made out of materials found readily in an earth-like ecosystem.

  • The tooth should not dehydrate easily.

  • The tooth MUST grow with the animal; keeping the skull it's newborn size is not an option.

*The tooth could be one particular shape genetically, but is widdled down to another (still effective) shape with regular wear, like the self sharpening molars of Triceratops.

(If anyone is wondering why these stipulations are in place, I'm designing an alien that nurses via maternal dermatophagy, and they cannot afford to be without teeth in any part of their lifecycle)

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  • $\begingroup$ You should consider shark teeth. This will allow for the teeth to subtly change size and shape with maturity. This will allow a change over from skin scraping to predatory dentition. en.wikipedia.org/wiki/Shark_tooth $\endgroup$ Mar 23, 2021 at 12:54
  • $\begingroup$ you do realize reptiles and dinosaurs continuously grow replacement teeth but are never without teeth, they don't grow the new sets all at once like mammals but staggered. $\endgroup$
    – John
    Mar 25, 2021 at 1:02
  • $\begingroup$ Why do you need individual teeth that grow, that is a very strange requirement and given what little you seem to know about teeth you may not need it. heck mammals only evolved it because they can't replace teeth. most vertebrates just continuously grow new teeth. $\endgroup$
    – John
    Mar 25, 2021 at 1:18

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It sounds like you are talking about the ever-growing teeth of rodents or elephants. Rodents don't have milk teeth, in fact their chisel-like incisors are actually retained baby teeth that continually grow throughout the animal's life. The incisor teeth of a capybara are the same incisors it had as an infant. Elephants do go through two sets of teeth, a deciduous pair of tushes and an adult pair of tusks, but one of the benefits of tusks is that given the rather pronounced shift in body size elephants go through from when they get their tusks to when they reach full sexual maturity, the tusks grow with them in size and stay proportional with the body. This is in fact one of the major reasons that ever-growing teeth evolves beyond offsetting wear.

I'm thinking their growth would be more analogous to the lengthening of bone, but I'm not sure applying the same process would yield adequate results.

Teeth do not grow this way. Teeth can only grow from the base of the tooth, and they can only grow so long as a root has yet to form. This is why rodent/elephant/etc. teeth grow the way they do, the tooth has no living tissue at its tip to replace the enamel so the only place the tooth can grow from is at the pulp cavity at the base. This is why for most vertebrates the only option to replace teeth when lost are either to have continual growth at the base or outright replace teeth like the milk teeth of mammals or the multiple replacement sets of sharks and reptiles.

The teeth have to have a genetically inherited and consistent shape. In other words, if the tooth in one specimen is triangular with ridges along the edge, then that trait should be seen across all members of it's species.

Rodent's do this. Their shape and the fact that they engage in thegosis is designed to make sure that they retain a consistent functional shape across the animal's lifespan.

The tooth has to be vascularized and innervated in some way; so something similar to a root might be necessary.

You aren't going to get a tooth that grows if this is the case. If a tooth is rooted, its growth has stopped and the tooth is just going to wear down. Teeth are not bones. They are not living tissue that grows and remodels on their own without external stimulus. In fact, what they really represent is a set of enamel-covered scales that are implanted into the skeleton, and grow like scales in fishes and reptiles do.

The tooth cannot have a 'cap' like seen in the horns of earth animals.

Teeth of Earth vertebrates have caps. An enamel cap, to be precise.

The tooth MUST grow with the animal; keeping the skull it's newborn size is not an option.

Again, this is what happens in most animals with ever-growing teeth like rodents.

(If anyone is wondering why these stipulations are in place, I'm designing an alien that nurses via maternal dermatophagy, and they cannot afford to be without teeth in any part of their lifecycle)

I'm assuming you've looked into how dermatophagy works in Earth animals? Animals that practice maternal dermatophagy do have teeth throughout their lifespan, but they have a set of embryonic teeth that they shed to replace with adult teeth. These embryonic teeth are specially designed with a "fork-like" shape to be able to scrape the skin off the mother without piercing her skin and harming her (see Fig. 1e in linked paper). These teeth aren't much use in catching or processing prey. I'm not sure which is the constraint here, is it that these species cannot survive without functional teeth because they need to be able to practice dermatophagy, and that's why they never lose them, or is it that they never lose their teeth but still need to be able to practice dermatophagy?

An alternative might be to have a species that has fork-like teeth as a baby but the fork-like nubs are worn down with use to a more conical shape in adulthood, many animals have secondary denticles on their teeth that are obliterated with wear.

Another, another option might be to do what frogs do. As tadpoles frogs rasp away at vegetation and sometimes eat small invertebrates and other tadpoles using keratinous ridges at the edge of their mouth, but when they become adults they lose the ridges and develop proper teeth.

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  • $\begingroup$ This is an EXTREMELY helpful answer, I really appreciate the in-depth explanations and counters to the majority of my bullet points, as well as the alternatives you provided at the conclusion. Well done. As an aside, I wasn't aware that rodents were born with their teeth; do they erupt after nursing or are they properly BORN with them? And regarding maternal dermatophagy, I have found incredibly limited information regarding it that isn't a pop sci article about caecilians, so the info you provided I'm doubly grateful for. $\endgroup$
    – Tardigreat
    Mar 23, 2021 at 22:20
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    $\begingroup$ @Tardigreat I'm not entirely sure, but a very brief search of the literature suggests they erupt after birth but before weaning. I do know that in shrews, which also have only one set of teeth in their lifetimes, the teeth fully erupt in the womb before the animal is born. But shrews don't have ever-growing teeth, the teeth eventually wear to stumps and the animal will die of starvation. $\endgroup$ Mar 23, 2021 at 23:29
  • $\begingroup$ many animals with ever growing teeth do have enamel on them the enamel along one surface or in the middle the enamel and dentine are produced non-stop. $\endgroup$
    – John
    Mar 25, 2021 at 1:01
  • $\begingroup$ @John New enamel and dentine can only be produced from the base of the tooth. This is why, for example, many rodents and ungulates lose enamel in the middle of the tooth as they age even if they have ever-growing teeth. Teeth, even mammalian molars, are fancy cones that can only grow from their base. $\endgroup$ Mar 25, 2021 at 3:43
  • $\begingroup$ @user2352714 yes more complex teeth will run out of enamel but simple ones like beaver and a few other rodents can keep producing indefinitely since they only have it on one surface of the tooth. $\endgroup$
    – John
    Mar 25, 2021 at 4:27
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I don't believe that all your requirements can be met simultaneously.

Bone growth requires living tissue around the bones. You've already ruled out continuously growing teeth and deciduous teeth, and you don't like the structure of eg. mammalian horns. Your idea of tree-like growth is going to be problematic with tooth-like materials, and the prospect of keeping rough, fissured teeth clean is not one that should appeal to anyone, and preventing rot, decay and inevitably infection is likely to be impractical.

Seems to me like you've ruled out anything actually resembling teeth entirely.

An alternative solution might just be something a little like a crop or gizzard, where the job of forming suitably hard things to crush and masticate food is outsourced to your local geological processes.

The parent(s) of the newborn would provide their little bundle of joy with some grit, which it would consume and retain reflexively, enabling it to sufficiently mangle its meals. The technique can be used throughout its life, with bigger stones being consumed and retained as the organism grows.

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  • $\begingroup$ These animals do have a crop actually, I just wanted to avoid making them so obviously bird analogs by giving them a proper beak. Unfortunately I don't see how a toothless (or beakless, for that matter) animal could rip off skin to nurse via dermatophagy. $\endgroup$
    – Tardigreat
    Mar 23, 2021 at 14:08
  • $\begingroup$ Regarding the living tissue issue (ha) involving bone growth, could something resembling gums suffice? It wouldn't surround the tip of the tooth, but the tip of the tooth could stay it's infantile size without hindering the animal, giving the tooth a bit of a point and conical shape. Not sure if that works though, I have a limited understanding of the mechanism. $\endgroup$
    – Tardigreat
    Mar 23, 2021 at 14:11
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    $\begingroup$ @Tardigreat species that practise dermatophagy have a means of shedding skin, at least partially, right? Little bits peel off, and the rest of the outer layer can be torn off without too much force. As regards gums, you're basically coming back towards how horns grow. Horns, hair and nails/claws are how extrusion of non-living tissue is done... seems like you may as well mimic that as anything else. $\endgroup$ Mar 23, 2021 at 14:25
  • $\begingroup$ @Tardigreat it sounds like you are trying to design a rocket when a kite will do, look at sauropods and algae-eating fish if you want lots of little teeth. they just keep growing new ones. $\endgroup$
    – John
    Mar 25, 2021 at 1:05
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Anal teeth

Sea cucumbers are a class of echinoderms. Many species are practically sessile. Other animals love to hide inside their anuses. In some cases, they have coevolved into commensalism with said other animals; The sea cucumber is generally chill with having other animals making a nest inside its anus.

Sometimes these guests are inconvenient, such as when they try to eat the sea cucumbers's anus from inside. As a deterrant, the sea cucumbers of the Actinopyga genus have anal teeth which will obliterate unwanted visitors. These teeth are made of the same material as the creature's endoskeleton: calcified microscopic ossicles connected by collagen fibers in such a way that the sea cucumber can harden or soften them at will. At its softest the sea cucumber can squeeze through small openings, at its hardest it's like a bone.

And most importantly, to fit into your requirements, these anal teeth have the same shape across species and their size is proportional to the animal throughout its life. Some species can grow to be 35cm/14" long.

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    $\begingroup$ Go home, mother nature. You're drunk. $\endgroup$ Mar 23, 2021 at 13:32
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Dental Battery

You mention triceratops teeth. well the "teeth" you refer to are not a single tooth but a dental battery, which is hundreds of tiny interlocking teeth. they continuously grow new teeth that get pushed out but due to their shape and being cemented together by tooth formation they stay interlocked with their neighboring teeth creating a large solid chewing/cutting surface. It acts like one huge tooth but is made of many tiny teeth locked together.

As the animal gets bigger the battery gets bigger as the individual tiny teeth get bigger and/or new rows are added, but the process of growth is so gradual compared to how fast individual tiny teeth are replaced the change in size does not disrupt the battery.

Dental batteries are common in ornithischian dinosaurs. And quite frankly is a batter system in many ways than what mammals got stuck with.

enter image description here An extracted dental battery

enter image description here A thin section cross section.

enter image description here

https://www.nature.com/articles/s41598-017-16056-3

I want to address a few things you seem to misunderstand.

The teeth have to have a genetically inherited and consistent shape. In other words, if the tooth in one specimen is triangular with ridges along the edge, then that trait should be seen across all members of it's species.*

That is the norm for teeth, there are almost no exceptions to it. Mammals can often be identified by teeth alone.

The tooth needs to have a similar rigidity and sharpness to most earth animals. They cannot break constantly or deform under regular use.

so normal teeth

The tooth has to be vascularized and innervated in some way; so something similar to a root might be necessary.

Normal for amniotes at least. teeth in use are usually vascularized, in tetrapod's the root of a tooth is only absorbed right before it is shed.

The tooth cannot have a 'cap' like seen in the horns of earth animals.

there are no teeth like this, so again normal teeth.

The tooth should be made out of materials found readily in an earth-like ecosystem.

so again normal teeth

The tooth should not dehydrate easily.

this is only an issue in animals that have teeth exposed outside the body, which is only crocodiles, saber tooth cats, naked mole rats, and few other things.

The tooth MUST grow with the animal; keeping the skull it's newborn size is not an option.

This is the hard part. There is only one a way a tooth in use can grow and that is the way rodents and horses do it, by having ever growing teeth. But given your comments elsewhere I wonder if you actually need this, you seem to be confused about how teeth work in most animals. It would help if you clarified why you need this. Normal archosaur teeth may work for what you need, they just grow new teeth in staggered pattern so there is always fresh and worn teeth side by side. before a tooth even gets loose there is already a replacement underneath it and a functional tooth on either side of it. They are never without teeth.

enter image description here

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    $\begingroup$ It should be noted that the whole dehydration thing has never been conclusively proven. It was proposed by one researcher at a conference who extrapolated his limited conclusions based on reptiles to all of Chordata and never published his results. In particular, he didn't really consider the vast array of mammalian teeth that are exposed to the air, like suids, musk deer, and chevrotains, he only focused on reptiles. In fact I was at the conference in question and he ran out the timer so no one could criticize his conclusions, so there isn't even a good critique "on the record", so to speak. $\endgroup$ Mar 25, 2021 at 3:47
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    $\begingroup$ @user2352714 true, dry teeth has been known to cause problems in humans (mostly faster erosion) but there could easily be adaptations to combat it in species the evolve exposed teeth. $\endgroup$
    – John
    Mar 25, 2021 at 4:17
  • $\begingroup$ @John The reason I stipulated that the teeth must grow with the animal is because the creature I'm designing retrofitted their front tooth to function and appear like a bird's beak. I'm doing as such (rather than just replicating beaks as they are on Earth entirely) as a thought project to see if something like this could feasibly evolve and function. The "beak" is quite large in proportion to the animal's skull, so they couldn't be born with it as it's adult size, but they also couldn't afford to lose such an important part of their dentition (even briefly) if they shed it and regrew it. $\endgroup$
    – Tardigreat
    Mar 25, 2021 at 19:15
  • $\begingroup$ @John Given your response (as well as the other responses here) I've concluded the only two routes to proceed with where the animal wouldn't be hindered by it's growth would be to either: Approach it like triceratops and parrot fish teeth, where the "tooth" is actually comprised of several very small teeth, OR make the tooth rodent like in that it has a perpetual growth. These are possibilities I initially rejected in my question, but I don't think I have another choice. $\endgroup$
    – Tardigreat
    Mar 25, 2021 at 19:23
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    $\begingroup$ @Tardigreat If you want the shape of a beak the parrot fish route may be better, growing a single tooth would require some very deep roots in the skull. you are right that there really is no other choice but those two options. worth noting beaks have evolved independently at least half a dozen times. $\endgroup$
    – John
    Mar 25, 2021 at 21:18

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