Anatomical Overview

If you'll forgive the AI-generated horror show, this is the closest I've managed to depicting how the yinrih look in my head, with a few discrepancies explained below.

Here are a few of my own artistic attempts at depicting them.

Humans often refer to yinrih as monkey foxes because they appear to have the head of a fox and the body of a new world monkey. They are quadrupeds with prehensile, six-toed paws and a prehensile tail. The body is covered in fur, but the palms, soles, and last joint of the digits are hairless, revealing grayish black skin underneath.

Yinrih are plantigrade, with the palms of the paws bearing their weight. Each paw consists of an inner thumb, four fingers, and an outer thumb. The tips of the digits have sharp, iron-enriched claws used for climbing and defense. There are doglike paw pads on the palms and on the underside of each digit.

They have sharp, carnivorous teeth, a whiskery muzzle with a wet nose, and erect fox-like ears.

The eyes work very differently than those of Terran animals. If human eyes are cameras, yinrih eyes are radio receivers. Each "eye" is an array of millions of nanoscopic antennas sitting on a shared ground plane that couple with ambient electromagnetic radiation like a radio. The surface of the eye is very good at absorbing visible light, making it look like the eyes are coated in Vantablack. Between these nantenna patches and their primary eyelids, there are four pairs of bandpass membranes that filter incoming light. Between these bandpass membranes and signal processing in the brain, yinrih 'tune' to different light spectra. They have a much, much wider visual spectrum than humans, able to see microwaves at the low end and non-ionizing UV radiation at the high end, but they can't perceive the entire spectrum all at once.

Their senses of smell, hearing, and touch are much more acute than a human's. They rely more on pheromones then on body language to communicate emotion. You don't say "I feel happy" you say "I smell happy". A yinrih's natural musk identifies things like gender, age, and whether or not they have had children. Yinrih have expanded this olfactory communication to include complex perfumes that serve the communicative and social functions that clothes do for humans.

Having fur means they don't require clothes for sun or cold protection, and they rely heavily on the tactile information gained through their paws, so yinrih are perennially naked and unshod.

They are arboreal, and move through the trees by brachiating (swinging hand over hand). This arboreal lifestyle dovetails nicely with living in microgravity, and there are orbital colonies of spacers who live permenantly in zero G so they can overcome the limitations of their quadrupedal stance, now having four hands instead of four feet.

One of the secrets to the yinrih's meteoric rise up the tech tree, achieving spaceflight a mere five thousand Earth years after gaining sapience, is the writing claw. In each forepaw there is an ink sac located near the knuckle of their index finger. A duct leads from the sac to the tip of the claw, which has evolved to look and act like the nib of a fountain pen. Their ink is blue-black and smells strongly of petrichor, and carries the same pheromones as their ambient musk.

AS nonsapient animals the yinrih used this writing claw to mark territory. A written language emerged out of this scent marking behavior in parallel with a spoken language. They have historical records reaching back to the dawn of sapience, with the earliest written records being from "kindled" (sapient) yinrih who were born into otherwise nonsapient litters to nonsapient parents, only discovering their differences after leaving their litters and finding other sapient yinrih.