The rig was made for an Unreal Engine-powered creature animation.
Senior Creature Technical Director at Wētā FX Stacy Yoi has recently shared a closer look at a realistic rat asset made for a UE-powered action shot. Made in collaboration with Chay Johansson, Alisha Steinberger, and Nick Gaul, this digital critter boasts an anatomically correct skeleton and muscles, as well as realistic-looking skin. According to Yoi, who was in charge of the skeleton rig, muscles, and simulation, the creature was rigged using Maya and set up in Ziva Dynamics.
And here's the animation this rig was made for: