Answers are grounded in this paper and cite their sources.
Lizards without parietal eyes tend to be restricted to low latitudes, whereas lizards with parietal eyes are successful at higher latitudes also. These zoogeographical data, along with current theories of parietal eye physiology, strongly suggest that the overall significance of the parietal eye to lizards as a group is that it facilitates survival at higher latitudes, thus making possible the exploitation of a wider variety of habitats.
No takes yet. Share an insight, caveat, or question.
Gundy et al. (1975) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: