Answer:
Only two backbones and thousands of ribs.
My teeth are sharp, my back is straight, to cut things up it is my fate.
A nut cracker up in a tree.
Never alive but practically extinct. How we miss the letters pressing the ribbon of ink. What is it?
It cannot be seen, it weighs nothing, but when put into a barrel, it makes it lighter.
All about, but cannot be seen, Can be captured, cannot be held, No throat, but can be heard. Who am I?