For many people the Eastern Water Dragon has long been identified as Physignathus lesueurii a name combination that goes back to John Edward Gray’s work of 1845 (Amey et al., 2012). While in the genus Physignathus it shared that position with the type species of the genus the Chinese Water Dragon (Physignathus concincinus). Andrew Amey, Patrick Couper and Glenn Shea (2012) detail the long nomenclatural history of this species and other relevant species and genera and their paper can be downloaded here. So I will not revisit the entire history. Suffice it to say that with the genus Physignathus being shown to be paraphyletic, and the type species being P. concincinus there is no alternative but to put the Eastern Water Dragon elsewhere.
This particular post is a further demonstration of the type concept, but this time for genera. I am using this example because it would seem to be fairly well resolved now. In my previous post I was largely referring to types for species, in genera there is a type species, again wherever the type goes the name goes. So with P. concincinus being the type species of Physignathus it is the only species that has to go with that name, any species included in the genus alongside it must be related to it and the group must be monophyletic.
This is why various other names listed by Amey et al. (2012) are not available for the Eastern Water Dragon. Genera such as Istiurus originally described by Georges Cuvier in 1829 but for only a single species, I. amboinensis, and that species is hence the type species for Istiurus, by what is known as monotypy. If a genus is described with only one species, that species is its type species. This cannot be changed and since the genus Hydrosaurus was resurrected for the Sailfin Lizard this makes the genus Istiurus a junior synonym of Hydrosaurus, as explained by Amey et al. (2012). So this is another genus that cannot be used for the Eastern Water Dragon.
In the end it comes to the name Intellagama described by Richard Wells and Ross Wellington in 1985 as the oldest available name for the genus containing the Eastern Water Dragon (as Intellagama lesueurii). The difficulty with this name is not that it was not declared or published. Although there have been many criticisms of Wells and Wellington (1985) including a challenge to its validity to the ICZN it is a valid publication. This is because the ICZN deemed the issues with the publication to be taxonomic, not nomenclatural. As I have already pointed out earlier the ICZN only deals with nomenclature. So the publication is to be accepted but not necessarily all the names within it. Amey et al. (2012) point out that this genus has mostly been seen as a junior synonym of Physignathus mainly because it was not diagnosed from the Chinese Water Dragon.
Here is a point on the major difficulty in nomenclature. The types of information presented in a description matters. It is important to name a type species for generic descriptions. It is true that if the named genus is monotypic then the only species in it is inferred as the type species, but otherwise it must be named. It is also important to diagnose it appropriately with a significant amount of evidence from its related genera. Just as you would with a species. This can be as a revision of previously published work or done in the description.
The difficulty in the case here was that the genus Intellagama was not diagnosed from the genus containing the Chinese Water Dragon (Physignathus), this did not make the name unavailable but made it unclear how to use it, so it was put in synonymy. It was not until a paper by Townsend et al. (2011) that the usage and justification for the genus was published. It is important to note here that although the name was originally coined by Wells and Wellington (1985) that the evidence that it was actually a genus, and how the name was to be used was not defined until 2011.
It is for this reason that as has been pointed out by many recent authors when discussing a variety of issues in taxonomy and nomenclature that the preferred best practice for the erection of new names is through the peer reviewed journals in this way it can be hoped that mistakes and unclear names can be avoided.