I later found some mentions of the species Z. tsingy, which is found in Ankarana and was described only in 2000 (thus explaining why it's not in the 1994 2nd edition of Glaw and Vences). But I could only find three photos apparently intended to be of this species. One of them is labeled "Zonosaurus petite tsingy", and is on a number of different websites, including wildmadagascar.org. However, that's clearly not the species I saw. I think the photo is probably Z. haraldmeieri or possibly Z. laticaudatus, and is incorrectly or just misleadingly labeled. (Maybe "Zonosaurus petite tsingy" was just intended to mean "Zonosaurus seen in the small tsingy", or "Small Zonosaurus seen in the tsingy".)
The other two photos I initially found were these ones from Bill Love's Blue Chameleon Ventures site. These show a bright blue lizard, with text explaining that other specimens are even brighter blue. So I came away with the impression that Zonosaurus tsingy is bright blue, whereas the lizards I had seen had iridescent sheens and pale blue tails, but were certainly not bright blue.
But I remained unconvinced that the lizards I had seen were Z. haraldmeieri, and a few weeks after my initial attempt to find photos of this species I Googled like mad, and this time I hit the jackpot: a PDF issue of Yale Environmental News that included a photograph of the individual Zonosaurus tsingy lizard that was used to describe the species, a.k.a. the holotype. And how about that, it looks precisely like the lizards I saw, pale blue tail and all. So I'm now confident that I've identified these lizards correctly, and I assume that the bright blue individuals shown and described on the Blue Chameleon Ventures site are probably males in full breeding season plumage.
Here is a list of all the reptiles and frogs I saw on this trip to Madagascar.
- Yale Environmental News issue with photograph of Zonosaurus tsingy holotype
- Glaw, F., Vences, M. 2007. A Field Guide to the Amphibians and Reptiles of Madagascar, Third Edition