I am at the base of many an artwork Children use me for their homework To proberly use me you shave my head only to use my spine instead

Horses, giraffes, and bison have me, but dogs, elephants, and rabbits don't. What am I?

I dance a furious, whirling jig, Though born of stillness, I grow big, What am I, touching sky to rig?

In the memosphere, I am step two of what you do to the rest of the owl.

My first something that keeps memories clear, My second the object that holds them dear. With a sturdy border, it stands still, Capturing time and moments in its will.