Here’s a first approach at the Kentrosaurus head. I’ll be trying to loosen myself up with some alternative sketches after this round, but always respecting the underlying skull. A made a 3D mesh around a skull geometry and thenbeefed it up with more volume akin to the varanus studies.  then I painted over it… following my take on the cheekless, beak-like mouth. The open mouth version comes as a complete surprise even to me, as its following the concrete volumes and rotation points given by the skeleton, then you swing it open and… nice. Half dragon, half bird.