Why the mesh is twisting when base bone is rotated? I am trying to rig long year of dog.


It needs to bend along chain of bones
And its base bone should be able to rotate the whole ear without twist.



  I understand why there is deformation but i need to understand why there is twist in whole ear when only base bone is rotated






Please check this EAR Rig File and help me with twist.
That deformation occurs because you didn't add weights in weight paint mode.

Select the armature and change to pose mode
In pose mode with the armature selected click the mesh
Change to weight paint mode
Select bone by bone and add vertex weight


Related:
Vertex Weight Issues