When you load animation that was not created on multiple layers, you can display its keyframes by selecting the BaseAnimation layer in the Animation Layer editor.
To view non-layered animation:
The BaseAnimation layer is the default layer of every take. Keyframes set on the BaseAnimation layer are always part of the result animation.
When you select the BaseAnimation layer, the keyframes set for the animated object display in the Transport Controls.
The BaseAnimation layer can be locked, but because it is the take’s default and bottom-most layer, it cannot be muted, soloed, or parented to other layers. To mute or solo the animation set on the BaseAnimation layer, duplicate the BaseAnimation layer. See Copying animation layers.