If you must have NURBS, you will most likely need to remodel your mesh object “by hand”, as animals/people etc. are difficult to find in NURBS format. Creature modeling is not an easy task with NURBS.
The question is, do you really need NURBS? What are you going to do with the model? For rendering, 3D printing or machining, a mesh will work fine. If you just need to offset it, you can try OffsetMesh. Otherwise, you may need to use some specific mesh-modeling software, as this is not Rhino’s strong suit.