Nah, nah, tetrapod as a <i>clade</i>.

Subject: Nah, nah, tetrapod as a clade.
Author: Huinesoron
Posted on: 2021-12-15 09:00:21 UTC

Sorry, too many paleontology blogs... 'tetrapod' is the term for everything closer to humans than to fish, basically. So amphibians, reptiles, birds, mammals. 'Hexapod', meanwhile, was just used as a descriptor. ^_^ Vertebrates don't like to add limbs, was my point.

But arthropods, sure, and I actually feel like I've... read something, maybe, with arthropod 'centaurs'? As you say, a praying mantis pretty much is a centaur already. And the myths about feral creatures which will devour you if you enter their woods certainly line up... not sure Dafydd and Constance would appreciate the change, though.

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Two questions. by Tawaki on 2021-12-13 13:31:11 UTC Writing Reply

Éowine is growing proud over time, with a sense of intellectual superiority and at-least-I-have-some-common-sense. This is to set up what happens on a later mission into Arda. How do I show this gradually growing conceit without making him unsympathetic?

Another thing: How does foaling compare to human childbirth, and to which would centaur childbirth be closer?

Re. centaurs by Neshomeh on 2021-12-13 15:20:54 UTC Reply

Agreeing with hS; I reckon a centaur baby would have to be born more or less like a foal, ideally in "diving position" with hooves and head first. In the centaur's case, though, you've got a whole torso coming between the front legs, and may or may not need the arms to also be in "diving position" depending on how developed the humanoid shoulders are. That might be one of those things you don't want to let your audience think about too hard, or they might remember how impossible centaurs are. {= )

Horses can also deliver foals in breach position (hind end first), but as in humans, this is more dangerous and may not be successful without assistance. Twins are extremely dangerous in horses, partly because one twin is often breach, partly because they may both try to be born at once and get stuck, partly because labor takes longer and one or both may suffocate in the womb if the placenta detaches too soon or the umbilicus is compressed or torn.

If you want to check out some foalings for reference, the channel Friesian Horses has several videos showing the entire process. It's not for the faint of stomach, but absolutely fascinating and, IMO, beautiful.

~Neshomeh

So THAT'S why Mr. Cake was so nervous at the beginning of "Baby Cakes"! (nm) by Tawaki on 2021-12-16 12:22:43 UTC Reply

And/or the Nervous Father trope being a thing. by Neshomeh on 2021-12-16 16:08:31 UTC Reply

For the record, twins are risky in humans, too, for more or less the same reasons. Consider that the chance of every possible complication is doubled and then some new ones are introduced. Horses/foals are just even less suited for it than we are.

~Neshomeh

Do centaurs bend? by Huinesoron on 2021-12-13 15:57:43 UTC Reply

Like... the humanoid torso forms a right angle with the equine one. How the heck would you need to hinge that... pelvoulder to flatten the humanoid portion in line with the equine, either forward or backward?

Perhaps they need to be born around a right-angle too; point the horse legs backwards, and pivot the birth when you hit the shouldewaist.

Or maybe they just hatch from eggs (it works in Minecraft!), or... could centaurs be marsupials? Has there ever been a marsupial horse?

hS

(No, there hasn't, but Google is convinced that Palorchestes counts. I guess the skull is a bit horsey... and crikey, apparently it's the same size. Strewth.)

Bending forward seems possible. by Neshomeh on 2021-12-13 21:01:18 UTC Reply

I can imagine it without significant cognitive stress, anyway. {= ) I mean, horses can extend their necks all the way down to let them graze while standing, so it's not that much of a stretch that the analogous muscles attaching the centaur's humanoid torso to the equine back would work similarly. ~~At least, not if the centaur is in good shape.~~

The problem is more likely to come from the rib cage, not the spine. Maybe centaurs don't have humanoid ribs? Or, if they do, the ribs must be significantly more flexible, not quite so firmly attached to each other and the breastbone. There must be a breastbone, collarbone, and shoulder blades, otherwise the arms won't work. The pectoral muscles do attach to the ribs, too, but I think you could do away with ribs and instead have a differently shaped breastbone, like a flattened T with wings, to compensate. A centaur might not have quite as much arm strength as a human or the ability to rotate the torso in the same way, but ~~that's what the stalk eyes are for~~ it doesn't need to; the head still turns well enough.

Basically what I'm saying is, the torso isn't a torso, it's a neck with arms on. {; P

~Neshomeh

Arms? Or trunks? by Huinesoron on 2021-12-14 11:10:34 UTC Reply

I'm perfectly happy with the 'torso as neck' concept - it just means they're convergant on the likes of giraffes and azhdarchids, which do freaky things with their cervical vertebrae. Brontosaurus shows that you can also make them freakishly wide, so I can easily ('easily') believe that something could have evolved a tall, flat neck that's similar to a human torso.

But arms? Nah; you're not going to evolve a hexapedal tetrapod on this planet. I only know of one mobile manipulator that can appear that far up the neck; they must be trunks.

There must have been some evolutionary driver for moving the nasal openings down the neck. Eventually the nose separated itself from the dual trunks, leaving them as muscular tubes half-merged with the skin of the neck. Then... hmm, reptiles have cervical ribs. The advantage of manipulator 'arms' should be obvious, so could the trunks have absorbed the ribs for structure and then separated themselves from the neck?

It'd be a long and complex process, but a look at whale fins shows that it's entirely possible for bone structures to make massive shifts like this. We'd want to start with an Eocene proboscidean, probably something like Moeritherium. Perhaps they went through an aquatic stage - true "sea-horses"!

(I admit I can't make 'and then they looked exactly like humans' make a lot of sense, unless... ooh, if we use the aquatic ape hypothesis we could say they predated on early hominids by swimming out and waving their trunks to look like a drowning human!)

hS

Now you're just being silly. by Neshomeh on 2021-12-15 06:52:58 UTC Reply

You certainly can have a hexapedal tetrapod on this planet. Consider the mantises, for example. The two forelegs have specialized as manipulator arms with an extended thorax to leverage them, leaving four hind legs as legs, just like a centaur. Of course, mantises are arthropods, so maybe we've been in the wrong phylum the whole time and your earlier thought about eggs was spot-on. {= D

~Neshomeh

Nah, nah, tetrapod as a clade. by Huinesoron on 2021-12-15 09:00:21 UTC Reply

Sorry, too many paleontology blogs... 'tetrapod' is the term for everything closer to humans than to fish, basically. So amphibians, reptiles, birds, mammals. 'Hexapod', meanwhile, was just used as a descriptor. ^_^ Vertebrates don't like to add limbs, was my point.

But arthropods, sure, and I actually feel like I've... read something, maybe, with arthropod 'centaurs'? As you say, a praying mantis pretty much is a centaur already. And the myths about feral creatures which will devour you if you enter their woods certainly line up... not sure Dafydd and Constance would appreciate the change, though.

hS

If the centaurs are arthropods, would that mean they are covered in some sort of exoskeleton? (nm) by ClaireBook1 on 2021-12-15 17:29:57 UTC Reply

Oh, definitely. by Neshomeh on 2021-12-16 15:49:01 UTC Reply

Probably a combination of soft and hard exoskeleton as needed, with a soft, hairy integument (like a flannel moth caterpillar) covering most of the body and harder plates on the legs and torso and such. I think they can even be layered, so presumably you could have some hard plates on the inside and softer stuff on the outside. The outer appearance is clearly some sort of adaptation to evolutionary pressures, though whether it's for hunting, defense, mating, or some combination is not clear to me.

(Y'know, I seem to recall reading something about arthropod centaurs, too. Alien ones? No idea where, though. And, just for the record, this whole thread is officially Too Silly; I couldn't resist the urge to call out hS for it in response to the "trunks" and then propose something equally if not more absurd. {; P Didn't know that about the word "tetrapod," though, so TIL!)

~Neshomeh

Oh, I know what I was thinking of. by Huinesoron on 2021-12-16 23:22:22 UTC Reply

It's not a centaur - it's the Winter Court unicorn somewhere in the Dresden Files. I don't know if it's insectoid, but it's definitely armour-plated and creepy looking.

Of course, arthropod-based centaurs /are/ a thing - they're usually scorpion bodies with a human torso sticking up from the front. I believe Rock "The Dwayne" Johnson played one back in the early aughts. Not the same thing, though.

hS

That reminds me... I think there were some armor-plated aliens in an episode of Star Trek TNG. (nm) by ClaireBook1 on 2021-12-17 01:24:48 UTC Reply

Now I'm imagining centaurs that look something like large praying mantises or something. (nm) by ClaireBook1 on 2021-12-16 23:04:09 UTC Reply

Fragments of answers. by Huinesoron on 2021-12-13 13:49:30 UTC Reply

1: Good flippin' question. I had to do the reverse of this with Agent hS, and managed it (I hope!) by pushing him more towards listening to others rather than suggesting his own ideas. For Éowine, you could have him show a tendency to believe his own plan is always the best one - but also make him right. That puts him on the border between 'not listening to anyone' and 'actually better at this', which leaves the reader room to wonder. Obviously that doesn't mean he should always get his own way - but sometimes, when he doesn't, things go a bit wrong. Obviously he's too superior to actually comment on this... ^_~

2: Don't know about the differences, but I assume centaur childbirth would be closer to horse than human. Humans are born useless because their heads are the biggest part of them, and have to meet the constraints of the pelvis; a horse body can have a wider pelvis (walking upright has not been good for our reproductive biology), but also I think the body is larger relative to the head, so a centaur can be born precocious (ie, able to walk from birth).

A quick check shows that a key difference is that a foal's feet come out first, and appear some 20 minutes before full delivery. Humans are usually (and most safely) born head-first, and come out very quickly: once the head is out, the baby follows at once. It looks like horses don't have the hours of contractions beforehand, though, so that's a point for their side - and yeah, I reckon a centaur would be horse-like in this respect.

hS