Greymantle Packrat

A rodent unique to the Greymantle swamps is the giant packrat. Unlike its smaller cousins, the giant packrat is supremely adapted to a marsh lifestyle, with webbed toes, laterally flattened tail, and dense waterproof fur. In many ways, they resemble giant rats and giant beavers in appearance and behavior, but there are a few key differences.
Giant packrats will settle for any cavity space that is large enough for them to live in, but they prefer the partially flooded caves that are found in many regions of Greymantle. Like beavers, they alter the landscape around their dens, including building rudimentary dens, but instead of building lodges in the water, they build dens and midden

Giant marsh rodent especially inhabiting karst landscapes and/or caves. Huge middens, build dams and alter local area much like beavers, but can be highly carnivorous, gnawed bones make up parts of middens. "cement" sign of activity aside from obvious midden. (bog materials, urine, other?)
Extremely powerful, deadly teeth
https://en.wikipedia.org/wiki/Pack_rat
https://www.nps.gov/articles/000/studying-the-past-and-predicting-the-future-using-rat-nests.htm