I wanted so badly to answer your question earlier but I didn't have a sound explanation. However, I have it now!
"Skinks are the largest family of lizards, with more than 1000 species worldwide. Skinks are caracterised by the development of compound plates of bone (osteoderms) within the scales, giving the large overlapping scales a strength and rigidity not present in other lizards."
OK, for us bluetongue fans...
"Within this family, bluetongues belong to the subfamily Lygosominae, characterised by the development of a secondary bony palate in the roof of the mouth, a fusion of the frontal bones, and the development of ventral projections from the frontal to the palatine bones."
If you need to cite this, it is from:
Blue-Tongued Skinks
edited by Robert Hitz, Glenn Shea, Andree Hauschild, et al.
2004 Matthias Schmidt Publications
(Yes, I'm a dork and I was reading my Bluey Bible over breakfast!

)
PM me if you need anything else! Sorry it took me so long to answer! kathy