For my discussions on nomenclature in reptiles I thought it would be best that I start off with a group I know well, the turtles of the family Chelidae. I am not going to discuss an overly controversial issue here but it is one that caused significant confusion for a while. Thankfully it is settling well now.
Within the turtle genus Chelodina there are three subgenera, Chelodina, Macrochelodina and Macrodiremys. Up until 2010 the subgenera were variably considered genera, and may be again at some point, or were ignored altogether. However this discussion is about several of the species in this genus and on this occasion I will be mostly ignoring the subgenera, suffice it to say the two species under discussion are the South Western Snake-necked Turtle, Chelodina (Macrodiremys) colliei, and the Northern Snake-necked Turtle, Chelodina (Macrochelodina) oblonga. This is the currently correct names for both of these species and I would refer readers to the IUCN Checklist for any nomenclatural clarification.
While examining all the holotypes for the Australasian Chelid Turtles (Chelodininae) I examined the types for the species Chelodina oblonga as it was known in 2000, that is the South Western Snake-necked Turtle. To my surprise at the time I found that the holotype was in fact a Northern Snake-necked Turtle. In nomenclature a misidentified holotype is a major problem. The name goes with the type, and the type is linked to a population. This is how nomenclature works. So following a strict reading of the code it was probable that the name Chelodina oblonga would need to be the valid name for the Northern Snake-necked Turtle, and the name Chelodina colliei would have to be resurrected for the South-western Snake-necked Turtle. With nearly 30 years of publications having it wrong confusion was inevitable.
I published my results so they would be available to all in the literature and at the time asked for everyone to utilize the ICZN code, Article 82.1, and maintain prevailing usage (Thomson, 2000). Unfortunately many did not follow this recommendation and hence the name Chelodina colliei was resurrected by some, while Chelodina rugosa was continued to be used at the same time. It also became apparent that this caused a potential issue for the name Macrochelodina (Wells and Wellington, 1985) who had intended to name what was often referred to as the Chelodina “B” group of species, such as Chelodina expansa, Chelodina parkeri, etc. However they had set the type species of Macrochelodina as Chelodina oblonga, this presented a conflict of intent so we as reviewers in a paper in 2001 fixed this issue by assigning Chelodina rugosa as the type species (Iverson et al., 2001).
A little history now is needed to get a greater understanding of how this happened in the first place. Both species were described by John Edward Gray of the British Museum over a century ago, he clearly diagnosed the two species, and clearly knew what he was doing. An area of confusion is that Gray listed Chelodina oblonga as coming from Western Australia, but this was in 1841; Western Australia back then was more or less everything from the modern Queensland border and westwards. Queensland was of course at the time part of New South Wales.
Following Gray’s descriptions was a series of poorly thought out synonymies. George Albert Boulenger thought that Chelodina colliei and Chelodina oblonga were the same species and so the younger name became a junior synonym. In 1890 James Douglas Ogilby named the species Chelodina rugosa and it too was synonymized with Chelodina oblonga. Then in 1901 Franz Werner named the species Chelodina siebenrocki, which was again synonymized with Chelodina oblonga by Frederic Siebenrock. So basically a great number of species were under the banner of Chelodina oblonga and it now had a range from Perth in Western Australia, up through the Kimberley across northern Australia and into Southern New Guinea. For over 60 years this was how this turtle was viewed.
Andrew Burbidge in his 1967 thesis felt that the south western turtle was not the same species and he restricted the name Chelodina oblonga to it, in error, as did John Goode. They also resurrected the name Chelodina siebenrocki but this was quickly seen to be an error and the name Chelodina rugosa became the name for the Northern Snake-neck Turtle. From 1974 until 2006 this situation remained constant. At that time I petitioned the ICZN to conserve the name Chelodina rugosa over the name Chelodina oblonga (Thomson, 2006). In the end this petition failed, due to several reasons. First is the uncertainty of the taxonomy of what had at the time become known as Chelodina rugosa, another was uncertainty due to an attempt in a hobbyist magazine, Reptilia, to fix the issue in a way that cannot be done under the ICZN Code (this same attempt also by accident erected a new species called Chelodina oblonga that is a junior synonym of Chelodina colliei). When there is an existing holotype only the ICZN can set a neotype. There were also misunderstandings over the meaning of Western Australia.
The final ruling came down in 2013 from the ICZN and it now became necessary to fix the whole situation. The ruling was to follow the Principal of Priority. I will be honest this was my own preferred position from the outset and I was grateful that the ICZN made this decision. Many people had tried to influence what I did about this situation and my proposal in the end was an act of conciliation. In the months following the decision we used as many online tools as we could to establish the name reversal, to prevent the confusion. Hence the IUCN Checklist, Wikipedia and the Reptile Database were all utilized. Our objective was to make this easy for all.
Hence at the present time the correct names for the two species in full are as follows:
Northern Snake-necked Turtle : Chelodina (Macrochelodina) oblonga Gray, 1841
South-western Snake-necked Turtle : Chelodina (Macrodiremys) colliei Gray, 1856
The species Chelodina (Macrochelodina) oblonga is a composite, it may or may not contain more than one species in it. There is evidence there are differences but this has not as yet been fully researched. The species is very complicated. However within it at present are Chelodina oblonga from the Northern Territory, Australia; Chelodina rugosa from Cape York, Australia; and Chelodina siebenrocki from New Guinea. The latter two of these are currently invalid species, so there is no such species as Chelodina (Macrochelodina) siebenrocki at this time.