Arriving in update 2.1.0, the Skeleton Assembly Table is a specialized type of Crafting Table that is used to assemble the mounted skeleton of ancient creatures.
It is crafted using 1 Lapis Lazuli (or Blue Dye if you have the Biomes O' Plenty mod), 2 Paper, 1 Crafting Table, 2 Wooden Slabs of any type, 2 Oak Fence posts, and 1 Fence Wire.
The crafting grid of the Skeleton Assembly table has 5x5 input slots instead of the normal 3x3 of a Crafting Table. Place the complete set of different bones from any particular creature (obtained from either the Cleaning Station, or from the carcass of a living specimen) in the input slots to make a placeable Skeleton.
Note that all the bones have to be of the same class, i.e. either all fossilized or all fresh.