I don't usually use reptile field guides, I ID what I can in the field and then confirm the rest later using the internet, only resorting to the field guide for species which there are limited reliable photos of online to compare to. In this particular case, the head shape of the lizard told me it was an Acanthosaura, so I just checked what Acanthosaura species occur in Cat Tien and compared them to the photo.
For my Thailand trip I did purchase a copy of 'A field guide to the reptiles of Thailand' ( A Field Guide to the Reptiles of Thailand ) and while this did prove very useful in identifying some of the more obscure geckos, there were numerous errors in the book, particularly with some of the distribution maps and conservation status of species, as well as the wrong photo being used next to the text for some species. My friend who was also on the trip has a very battered copy of 'A field guide to the reptiles of South-East Asia' ( A Field Guide to the Reptiles of South-East Asia ) which he absolutely swears by, however this doesn't contain distribution maps.
