#(meanwhile pan over to the side and you can see how miranda can fully take limbs off with a good chomp)

[rxttenfish]

amused by how miranda has two tons of bite force but aaravi keeps putting various body parts in miranda’s mouth with no reaction worse than mild irritation

[royalreef]

(( ENJOY A MASSIVE POST ABOUT MERFOLK TAXONOMY, because biology has long been my BIGGEST special interest ( yes I’m including paleontology under this, I know it’s more considered an earth science and part of geology, shush ).

Merfolk as a whole are a part of an ancient group of animals that diverged from basal amniotes around the same time amniotes themselves came about, 312 mya (million years ago). I say about, because I haven’t fully decided where exactly to put them in this case, whether they’re fully counted as amniotes or no, and I still need to do a large amount of research into this.

I classify this split as happening there, as opposed to somewhere else, because merfolk are obviously tetrapods, and have some adaptations for full land living that amniotes have, though the merfolk themselves are fully adapted for a watery niche. Their eggs certainly were carried internally for a long time, so there’s probably some convergent evolution to how mammalian live birth happened, hence all the more reason to put them under amniotes, but they’re definitely not synapsids and thus definitely not mammals.

These early ancestors also retained their gills and ability to breathe water. They do have lungs too, and conceptually they filled a very fluid niche, where they had to be able to rapidly switch from aquatic life to terrestrial life, with most being oppurtunists who used this wide variability to be able to get a wider variety of food and resources that other animals couldn’t.

I will say these early ancestors mostly resembled newts/salamanders or small lizards, and somewhere along the line they independently evolved scales, both for providing armor and for retaining water when they were on land, along with all the other reasons to evolve scales. 

( Ideally, I’d say they never evolved hair, but considering that I can’t fully redesign Miranda for this blog for fear of inability to use my icons and basically making her fully an OC, she has to keep the hair on her head. Her eyebrows are a maybe, since I joke aplenty about them just being markings or her drawing them on. Landfolk get weird when they see her without any eyebrows, so she has to appear to have them! )

They also generally retained the same amount of digits as other tetrapods, so that’s how Miranda has five fingers still, though merfolk lost one of the toes on their feet, bringing that total down to four.

And yes, all of this does mean that merfolk have plenty of ancestors in deep time that probably fossilized and could be found by even human scientists, but they’re probably thought of in this world as an offshoot of tetrapods that has no extant relatives, with what fossils remain being sparse or incomplete, or even caught in nomen dubium hell. Certainly they weren’t featured in this world’s Jurassic Park, that’s for sure, and if they are represented it’d be in something like ARK.

This also does mean that there are plenty of ancestors that fell into more unique or odd niches, with stranger body plans or something much more different from the rest. 312 mya is a long time, after all! Lots of time for there to be more experimental species, though they didn’t pan out in the long run.

So, with merfolk themselves, I generally have the idea of them as coming from a branch of that tree that hung around the ocean’s edge, sticking closer to the shoreline than the mer alive today, though they were oddly social for a tiny, lizard-like species, probably already communicating through small squeaks and chirps. Lizardy kinda sounds. They spend a good amount of their time on rocky shores and cliffs, so they’re good at climbing over and up them. Likely already had something akin to their fins on the sides of their face, used for communication and display, along with pushing additional water over their gills, or maybe even the fins being used in addition to the gills to extract extra oxygen from the water is basal to merfolk, but only the abyssals really retained most of that feature.

As token as it sounds, I think the K/T extinction event was probably what pushed them to evolve into the branch that became merfolk. The death of much larger marine creatures opened up the ability to go more fully ocean-bound, and to take over a role akin to marine reptiles in the past and the marine mammals that were also evolving at that time, but with the addition of having gills to not have to surface for oxygen.

Their evolution from that point probably was a bit like primates - lots of trying out different shapes and styles, more of that basal form than true merfolk, except their roles being out competeted or otherwise led to extinction, until you get the “true” merfolk - which would occur with a focus on social behavior and language, along with tool use, as was the bonus to being a tetrapod that went back into the ocean but never lost their hands.

This is where we get to the merfolk family tree. I’d say probably the first mer was mid-size, generally had all of the traits of the merfolk you see today, very general, but very adaptive.

The abyssal (royal) merfolk were probably the first to branch off. Their tails resemble mosasaurs’ and early icthyosaurs’ a lot, having a much larger lower lobe of their tail where the bone is, and the upper lobe, being all fleshy, isn’t too pronounced. They went down into the deep sea, branching off early from the rest of the merfolk, and thus were generally super isolated from the rest, which you can see today in how the Merkingdom itself generally is conducted.

There are plenty of other species of merfolk, however, and the abyssals (and Miranda) are not representative of the entire group. There’s a lot of different takes on the same body plan, with different niches and different adaptations and different types of behavior associated with each. They’re all super vocal and adapted to be able to hear well, so that’s also basal to the group, but that also means when they all started forming their own societies and cultures and general settlements, it’s even weirder than how humans do it.

Effectively, merfolk are a lot like the homonid family tree, and for that reason they also generally take after the concept of the “braided stream” more than just the tree of life. It’s also why I can feel more confident saying they’re seperate species and not subspecies, despite being able to reproduce and make viable offspring - and anyway species as a whole are fake and weird. There’s a lot of hybridization going on, with some populations getting some genes from others that benefit them and get genetic and physical variation. In more nomadic merfolk, there’s a lot of their genes spread around in other species and a lot of genetic variation in them, because they roam and run into different species - meanwhile, the abyssals are much more genetically restricted, since the abyss is a generally isolated place that isn’t easy to access unless you’re made for it.

I’m pretty bad at clarifying when I’m talking about abyssal mer vs all merfolk, since there’s a huge amount of difference between the two. Abyssals are probably the merfolk with the most bioluminenscence - while some species probably do have a little or even a lot, it’s not as much of a need as with the abyssals. The abyssals also might have gone through deep-sea gigantism? They’re pretty big by merfolk standards. And yes, that is taking into account how tiny Miranda herself is - since she’s kind of an exception to the rule, being that she didn’t really grow right and her bones didn’t get the chance to form correctly, leaving her as a rather unhealthy-looking runt of an abyssal. I’m generally thinking mer grow throughout their entire lives, as something that’s also basal to the group, they just slow down after a point - so if you got proper care for Miranda’s health issues she might be able to fix some of that problems, and mer medicine is waaaaay more sophisticated and generally ahead than current human medicine, so if it was treated she might be able to come up to a respectable height and avoid some of the isssues of that kind of deformity that’ll occur later in life.

I do believe as a whole, merfolk are rather large. Some are more sleek than others, but especially with abyssal mer, they put on fat and muscle really easily. They’re a lot like large crocodiles in that respect. Again, Miranda is an exception to this rule, as she’s really not healthy - but overall, merfolk are DENSE. Abyssals tend to have tough armor, dense bones, put on muscle and fat easily, and generally should be MUCH heavier than a human of the same size. Not to mention their tails, as unless a mer is in the really late stages of starvation, they keep most of the muscle on their tails. It’s how they swim and get around, so losing that muscle is basically a death sentence to merfolk.

There’s also variation in diet, dentition, and what they can digest. I will say all merfolk generally can handle meat - some of them are more adapted towards eating coral or plant matter or filter-feeding, but generally they can all digest and handle it and won’t turn it down if they do get it. The abyssals do tend towards being carnivores and most of their diet should be meat, but they can handle other biological material as well. They’re equal parts predator and scavenger - their jaw strength is a lot like a hyena’s or a T. rex’s (at least, in the theory of them being scavengers and not predators). It’s VERY useful in getting into any hard material the ocean can throw at them, cracking not only bone but shell and scale and cartilage and shell too, and to extract as much nutrition from any food they find. I can say their jaw strength is probably the strongest among the merfolk for that reason. 

This also means, while abyssal mer have their triangular, serrated teeth like a great white shark’s - that tooth shape is more unique to them and their specific niche than to merfolk as a whole, who have a LOT more variation. I imagine at least one has teeth that come together a bit like a parrotfish’s beak, and one has teeth more similar to a crabeater seal’s, useful for seiving through water. 

Abyssal mer are also the ones that really retained the ability to extract extra oxygen from the water through their facial fins. That’s why Miranda’s fins are so fluffy and large - they’re basically pseudo-gills, and that’s why they’re so sensitive. Other mer do also have some of that ability, but it’s to a lesser degree than abyssal merfolk, and most are probably less sensitive because of that. That being said, the shape of the fins is kept, as is the “fluff” closer to the cheek. That fluff actually has a purpose beyond oxygen extraction - they’re little outgrowths of flesh and skin that act a lot like an owl’s facial feathers. They’re effectively radar dishes, helping pick up on sounds in the water and assists their hearing and communication. The fins are also universally used for communication and display - they move with a merfolk’s emotions for a reason! They’re really good silent communication when hunting.

I also think mer do universally have the pads on their hands and feet. Honestly, they aren’t really anaogous to a cat’s or dog’s paws. They’re far closer to what you’d find on an Osprey’s foot, and provide a lot of the same uses - namely being used as a grip in holding onto slippery prey, but also in movement, when mer cling to sheer rocks or climb over coral or what have you. Normally they’re very rough and thick - but because Miranda is a royal, she files hers down, and so they’re much softer and thinner. They’re all pretty squishy though.

I’d add more but I think that’s MOSTLY it. Can you tell I have a special interest?