Solid works

I decided to go with the Lumbar vertebrae or also known as the backbone. Although when a series of them are connected together they form a fluid shape, one by itself also has it's own fluidity and a peculiar beauty to it. Also being a bone it ties in with my word "prehistoric" quite well too.

Below, I have sketched out the perimeter of the shape, replicated it to give it depth, then sketched the circular connection in front.

Below: Connecting the tops of the rudimentary prerequisite shapes using the lumbar tool.

Below: Connecting the first shapes to the circular frontal shape. To my surprise it created an unexpected shape.

Below: Adding a "dome" effect to the front to give a more aesthetically pleasing shape.

Below: Using the "dome" effect again, but in reverse this time to the back, creating a concave exterior to the backing. This is to create a more interesting effect when using modifiers in 3DS MAX later on.