Lacerta viridis (Fig. 1) is a common extant lizard that has more skull bones than is typical for most tetrapods. It also loses the upper temporal fenestra found in other lizards, by posterior expansion of the postfrontal.
Figure 1. Lacerta viridis skull from Digimorph.org and used with permission. Here the enlargement of the postfrontal basically erases the former upper temporal fenestra. Several novel ossifications appear around the orbit and cheek.
This Digimorph.org image
was colorized in an attempt at understanding the skull bones present here. The extant Lacerta nests with the larger extinct Eolacerta in the large reptile tree (918 taxa).
40 species are known of this genus.
Fossils are known from the Miocene (Čerňanský 2010). The tail can be shed to evade predators. This lizard is an omnivore. The curled quadrate frames an external tympanic membrane (eardrum). With the premaxillae fused, Lacerta has nine premaxillary teeth, with one in the center.
Not sure why this lizard developed extra skull bones.
It is found in bushy vegetation at woodland and field edges, and is not described as a burrower or a head basher.
Other diapsid-grade reptiles that nearly or completely lose the upper temporal fenestra include:
References
Čerňanský A 2010. Earliest world record of green lizards (Lacertilia, Lacertidae) from the Lower Miocene of Central Europe. Biologia 65(4): 737-741.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
This species has not developed more skull bones, at least not in the endochondral sense that you seem to be suggesting. Lacerta, Podarcis, Gallotia and members of that family are known for having osteoderms that fuse onto their skull bones (and a close association of those osteoderms to the overlying scutes). I’m pretty certain that is what you are colouring in here. See Arnold (1989), as well as Barahona and Barbadillo 1998 for more.
Refs:
Arnold, E.N. 1989. Towards a Phylogeny and Biogeography of the Lacertidae: Relationships within an Old-World Family of Lizards Derived from Morphology. Bull. Br. Mus. Nat. Hist. 55:525–555.
Barahona, F., Barbadillo, L.J. 1998. Inter- and Intraspecific Variation in the Post-Natal Skull of Some Lacertid Lizards. J. Zool. Lond. 245:363–405.
I understand your concerns and have found one of your refs online. Is the postfrontal your only real concern? As you are probably aware, some sister and cousin taxa have similar skull bones. Check out Podarcis, Pedioplanis, Acanthodactylus. Please send labeled images to support your concern. So far, I can find nothing to support the issue you raise.