Teeth that grow proportionately to your size

Question

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)

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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.

An extracted dental battery

A thin section cross section.

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.