(This is all thanks to Luka Rejec pointing out this handy list of taxonomic affixes (don't forget the medical ones too!) to go along with the magical prehistory bandwagon)
Coelcyon ("hollow dog")
Its bones are needles and the rest is skin and fur hanging over empty space. They make a high-pitched whistling near-indistinguishable from tinnitus.
Rhodosuchus ("red crocodile")
It is very much what the name entails, though its snout is long and thin, more like a gharial. They mate during monsoon season, building house-sized nests of mangrove roots and dead fish, designed to topple over just so in the storms.
Chloracanth ("green spine")
The bony ridge that runs down the slow and daftsome creature's back is hollow and honeycombed. Symbiotic mosses grow there, which may be harvested for medicinal purposes. Otherwise unremarkable, though the meat is good.
Brontodromeus ("thunder runner")
Their slate-blue hides coruscate with bright white chromatophore signals. Thick tails provide balance when running, while folding arms and bullet-shaped heads cut down on wind resistance.They run with the rains, and slip away just as easily.
Plesiofelis ("almost cat")
Looks like a sleeping cat at first or second glance, but reveals itself under touch and closer inspection as a gelatinous non-Newtonian fluid covered in fine calico cilia. The tail, curled underneath the central mass, is far longer than it should, and trails off out of sight. The nature of the angler is unknown.
Scoliospondylus ("twisted vertebrae")
Eight-limbed hominids whose spine might only be the result of a cruel and hateful god. Each limb ends in a six-fingered hand with two opposable digits, and their catastrophic backs show clear signs of divine malice. Their black skin is hairless, and decorated with splashes of brilliant orange and blue; this does not do anything to lessen the pain and sadness in their six eyes.
Xanthopepsian ("yellow digesting")
A sort of sponge, about the size of a large melon. It may live upon land, and in desperate circumstances move under its own power. It consumes the color yellow, a diet that leads to it being a most brilliant shade of that color; anything else in its feeding radius will be bleached white
Cacopithicus ("bad ape")
Ratty red-brown fur smeared in shit. Fingernails curved like snail shells. Teeth set in gums like maggots in a side of beef. Crusty black eyes, dribbling snot and spit. Its behavior is self-evident, and all are thankful that they cannot work in unison for more than a few hours before the backstabbing begins.
Platypharyngovenator ("flat throat hunter")
Its wedge-shaped head is attached to a flexible neck nearly ten feet long and an inch thick. It is an ambush predator, burying its cumbersome soft-shelled body in loam or mud and lying in wait.
Squamotherium ("scaly beast")
Its body is like a pillar or a trunk atop ten squat legs surrounding a mouth. The scales decrease from the size of a hand to hardly more than a pinprick as one ascends towards the upper ring of eyes. They are usually a green-brown in coloration, to best imitate trees and avoid predators. It was not called dendromimus due to a certain unnatural philosopher having a love affair with the word "squamous".
Diploteratomaia ("double monster mother")
Unique among the echidnamorphs for possessing two wombs and regular simultaneous pregnancies, this creature's distinct black and white coloration is very much on point. The eyes diverge from this, being blue and ringed in black. Offspring will be of one color or the other, or bear similar separation of color. The back-quills of this variant are shorter than those of more common species.
Gnathomimus ("jaw mimic")
Descendants of agnathic fish-turned-amphibians, the species' impressive underbite is in fact an outgrowth of the head's armor plating. While useless as a manidle, they are used as weapons during territorial disputes and mating displays.
Polycetus ("many whales")
A horrifying leviathan created when a pod of whales melds into an island-sized fleshbeast of blubber and barnacles and oil and curtains of baleen and banks of paddles, singing apocalyptic songs of the abyss. Mass beachings are in truth mass suicides: the whales know that the melding is near, and their good nature drives them to sacrifice themselves for the sake of the rest of the world.
Cephalospadias ("head fissure")
A gangly, chalky-white hominid. The head contains no eyes, nose, or ears, and is disproportionately large compared to the body. Each specimen has one or more deep clefts in their heads, the insides of which are the color of a blood orange and peppercorn seeds. Each individual has a unique pattern of fissure.