Good tidings and well-wishes!
“Seems like every monitor lizard and its mother are within the Varanus genus. In fact, I can’t think of one that’s not. Have there been any large-scale comparisons between Varanids? Are they all really that similar?”
Having never considered that point, I replied that I’d enlist the services of the gang at “Ask A Biologist” to provide an answer. Unfortunately, after a few weeks, I forgot about it (sorry, Zach…). To redeem myself, I’ve posted their comments below.
First, Corwin Sullivan wrote:
“Yes, as far as I know, all living monitors are currently assigned to the genus Varanus. This is indeed an unusual situation, since a few dozen species exist and they vary widely in size and to some extent in body structure. Some taxonomists do recognise “subgenera” within Varanus, such as one called Odatria for the Australian “pygmy monitors”, and it is certainly possible that Varanus will some day be broken up into multiple genera.
The real issue here is that genera, like other ranks in the Linnean system, are entirely arbitrary. Every taxonomist who uses these ranks has some intuitive sense of how broadly a genus, class or family should be defined, but the intuitive senses of any two taxonomists might not agree. This tends to be especially true if they work on different groups of organisms, so there’s no guarantee that a genus of lizards is in any way comparable to a genus of flies or mushrooms. It may look like the genus Varanus includes an impressive range of variation, but all this really means is that the genus has been rather broadly defined. There is no central taxonomic authority to, er, monitor genus definitions and keep them meaningful and consistent.”
Shortly thereafter, Mike Taylor added:
“… and the genus Quercus (the oak tree) contains at lease FOUR HUNDRED species, some of which look so different from what we usually think of as an oak that, from my vertebrate-o-centric perspective, it beggars belief that they all belong to the same genus. It just goes to show that one man’s genus is another man’s family (or species).
That said, at least within groups, systematists really ought to try to keep the disparity encompassed at each rank similar as far as possible — e.g. one lizard genus should encompass about as much disparity (morphological difference) as another lizard genus, even if we accept at the outset that oak taxonomy is never going to follow the same standard! And on that basis you do have to wonder whether Varanus is overlumped. As it happens, I have before me right now the partially prepared (and rather smelly) skull of a mature savannah monitor lizard (Varanus exanthematicus), and it looks DRAMATICALLY different from the skull of the komodo dragon (Varanus komodoensis) shown on the Skulls Unlimited site at http://www.skullsunlimited.com/komodo-dragon-skull.html
BTW., you can look over a nice 3d scan of the V. exanthematicus skull at http://musom.marshall.edu/anatomy/holli … skull.html “
It can therefore hardly be argued that monitors, as a group, are far more diverse and taxonomically interesting than their current classification suggests.
May the fossil record (and the rest of the natural world) continue to enchant us all!