The skeleton of an embryo is originally made of cartilage, not bone. This is called the cartilaginous skeleton.

Here's why:

* Flexibility: Cartilage is flexible and allows for the embryo to grow and develop. Bone, being rigid, wouldn't allow for the necessary changes in shape.

* Formation of Bones: The cartilaginous skeleton serves as a template for bone formation. As the embryo grows, the cartilage is gradually replaced by bone in a process called endochondral ossification.

So, while the skeleton of a newborn baby is made of bone, it originally began as a cartilaginous structure.