Shapes are a "malleable" object. They can be converted from Linear to Bezier to B-Spline at any time. That makes "managing" the Bezier/B-Spline tangent controls nearly impossible, and definitely elements that cannot be keyframed. (Hope that makes sense...)
None of this means that a Shape cannot be keyframed from start to finish... you just need to take an extra couple of steps:
Animate the Shape from the beginning of the project to the end of the project. How you do this may depend on how you need it to appear, but for this introduction, do something simple. Here's an example:
I started with a triangle, keyframed *Control Points* in 3 places (including a Bezier tangent in the middle): frame 0, halfway through the project, and a keyframe at the end. Generally, you want as many "inter-frames" as you can get.
Next: Clone the Shape.
Next: Replicate the Shape. Set the Replicator Shape to Point, Turn OFF Play Frames and Keyframe the Source Start Point. You can pretty much do whatever you want (even go backwards) with the Source Start Frame setting. Here's how the above example was keyframed for animation:
This way, you can create any contortions you like to your shape, change points from Linear to Bezier (but not with the Shape Type Paramater - Command-click-drag out tangents - the Shape Type will automatically switch to Bezier if it is set to Linear).
You will have to set all of the animation of the Shape with its Control Points. The Transforms (Position, Rotation, Scale, etc.) will not have an effect on the Clone source for the Replicator...
You could also opt to have the Source Start Frame animated with behaviors, like Ramp (which will have Easing) or Overshoot, etc...
HTH — it should get you started.
