Weasel-rats are neither weasels nor rats, nor closely related to either.  In fact, they aren’t even mammals, technically.  They are last surviving tritylodonts, basal karyotypes of mammalian ancestors.  Tritylodonts existed on Earth from the late Triassic to the early Cretaceous, though some researchers claim that they survived long after that.  The largely falsified claims are that both tritylondonts and the later multituberculates each filled the same roles as rodents in their times (which overlap), and that only the rise of true rodents drove them to extinction.  This seems to be the case for multituberculates, but not for tritylodonts, at least not on Earth.  This was the case on Varanganska, however, because Varanganska is much larger, and so isolated populations of tritylodonts survived in areas where they didn’t have to compete with rodents or be preyed upon by carnivorous mammals, such as triconodonts, metatherians, or carnivorans.  Weasel-rats, in fact, are the dominant scavengers in areas where there are neither rats nor weasels.  Humanoid races rarely see them, because agriculture invites rodents and their predators.

This would look better as a pencil drawing, and I may replace it later.

Tritylodonts have certain traits in common with rodents, such as elongated incisors and no canine teeth.  Unlike rodents, however, they have extremely tough molars, with up to six roots each, and very wide zygomatic arches on either side of a very narrow braincase housing massive jaw muscles.  This trait first appeared on early cynodonts such as Procynosuchus.  Therefore, tritylodonts have far greater bite force than rodents of the same size, but far smaller brains.  In addition, and this is a much more profound difference, is that they lay eggs, like monotremes, but unlike monotremes, do not produce milk (hence their classification as non-mammalian cynodonts).  True mammals are typically born toothless, whether they suckle (like zatherian mammals) or lap up milk that is sweat through pores (like monotremes).  Weasel-rats in particular are precocial, like many eutherian (placental) mammals, meaning that the juveniles are fully-formed, fully-functioning, miniature versions of the adults.  Adult females incubate their eggs, but provide almost no parental care once the eggs hatch.  Adults are roughly the size of house-cats, but the hatchlings are only the size of mice, and thus extremely vulnerable to predation from small carnivores that would never mess with an adult.

In the wild, weasel-rats live for 2,4 years, or 16 cycles, they can get up to a metre long, including the rat-like tail, and weigh as much as 9 kilograms, but most don’t get above 70 centimetres and 6 kilograms.  Their elongated, slender bodies allow them to crawl through narrow cracks in rock formations, sometimes to find food, and other times to reach nesting sites.  Since they will eat anything, they can thrive in desolate areas that more modern animals don’t bother with, scraping lichens off rocks and eating the cones of crag-bushes.  To do the latter, they will wrap their bodies around the branches and slowly pull themselves out beyond the cliff, desperately trying to not get blown off by the stiff winds.

By the time of The Nine Empires, weasel-rats are found only in unsettled areas of mainland Sondor, and generally make their nests inside caves hidden behind waterfalls.  Some larger caves, which were attractive hideouts for members of the Sondorian Mainland Independence Movement (SMIM), were found to be infested with these creatures.  At first, it was only the nests that were known about, but the destruction of wooden crates and their contents eventually led to the discovery of adult weasel-rats hiding in such caves.  Weasel-rats are, like goats, infamously omnivorous, and thanks to their teeth, they can eat through a lot more than goats can.  They will readily chew through wooden crates and devour anything inside that they can find, including explosives.  These critters treat gun-cotton as if it were cotton candy.  The little pests probably hindered the operations of the SMIM more than the police or the Black Marsh Rats (a crime syndicate that was offered immunity by the crown for the capture of SMIM members).  However, cool heads rose above the nuisance, and some SMIM partisan groups actually used weasel-rats as weapons, releasing large numbers of them into warehouses that they had no hope of emptying on their own.  The idea was that, if they couldn’t steal enemy supplies, then they ought to destroy those supplies, and fires were a bit too conspicuous.


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