Return to the Tomb of Zootoca

One of my recent posts took a close look at the mummified corpse of a juvenile common lizard (Zootoca vivipara). Apart from noting that the fungus on it suggested it hadn't mummified too well, I also made the point (aided by a friend who knows about those strange tetrapod thingies) that there was surprisingly little written about lizard teeth/dentition. While mammalian dentition commands many pages of diagrams showing the different types of teeth, lizards - at least in the books and websites I could find - tend to simply be described as 'homodont' i.e. having all teeth of the same form. While the variation isn't as striking as in mammals (canines, incisors, molars etc), this is an oversimplification, so I decided to stay well outside my invertebrate comfort zone and delve further. First of all, an overview of the upper and lower jaws.

Fig. 1. Dorsal view of the lower jaw.

Fig. 2. Ventral view of the upper jaw.

Fig. 3. Side view of the upper jaw.

Fig. 4. Side view of the lower jaw (the red line parallels the curve of the jaw).

Comparing Figs. 1 & 2, the outline shapes of the jaws are clear and it can be seen that they match well, widening behind the snout - unsurprising as they wouldn't work if they didn't fit together. In Fig. 1, the dark central structure is taken to be the tongue which has mummified and appears to match the shape of the upper palate in Fig. 2. Looking at Figs. 3 & 4, the upper jawline is approximately straight in side view, while there is a slight curve in the lower jawline. However, the front section of the lower jaw (where the majority of teeth can be seen) is quite straight and so still fits well with the upper jaw, and I imagine that there could be some flexing when biting, especially as this is a juvenile with small bones. This is somewhat speculative however, and I'm more than happy for anyone who knows more about such things to send me info on errors or omissions! Now, zooming in on the jaws...

Fig. 5. Lower jaw - curved tooth arrowed.

Fig. 6. Lower jaw - 'appendiculate' teeth arrowed.

Fig. 7. Lower jaw - apparently serrated tooth arrowed.

Fig. 8. Upper jaw - three apparently fused teeth indicated by the position of the scale bar.

The homodont description of lizard teeth where they are all considered to be 'conical' is clearly not the whole story when looking at Fig. 5 which shows backwards-curving teeth at the front of the lower jaw - presumably for holding on to prey when it is initially captured. While some of the cheek-teeth do have simple conical points on a cylindrical shaft, others are again more complex as in Fig. 6 (you may need to enlarge it) which shows that some are 'appendiculate' or at least asymmetrical with a protrusion on the forward side. I don't know what the function of this might be - maybe a closer fit is ensured with the upper jaw, and/or there could be some element of shearing'cutting which a simple conical point would not achieve. To me, the latter idea is possibly supported by Fig. 7 which (as well as the asymmetrical shape) shows what appears to be a serrated edge. Given that Z. vivipara feeds on prey such as invertebrates with tough exoskeletons, such dentition may be useful.

Lastly, Fig. 8 shows a small section of the upper jaw where three teeth appeared to be fused. Again, the function is not clear (to me, anyway), but I can imagine the 'inter-tooth' sections acting like blades and/or providing a close fit against teeth in the lower jaw. As you can see from the scale bar, the structures here are small and were distinctly difficult to dissect but I hope that the key features are clear. As I say, I particularly welcome comments on this topic and fully expect this to get updated as I learn more.