To make the skull I'm going to employ the same 3-step process I used for the Mosasaurus and the Styracosaurus, it's a bit of an odd approach but I like it.
- freeform a 'scaffold sculpt' to form the basic shape
- construct a low poly mesh over the scaffold
- subdivide the low poly mesh and add details
The original orthographic drawing had a 0.5 meter scalebar but I've changed it to 0.8 meter so it encloses the length of the skull. This makes it easy to set up the template images in Blender which lets you set the width of the image numerically.
Starting the scaffold by approximating the form with subdivision surfaces, this eliminates a lot of messing about push/pulling a cube or sphere into shape.