ADVERTISEMENT
Tetrapod Zoology

Tetrapod Zoology

Amphibians, reptiles, birds and mammals - living and extinct

Monitor musings, varanid variables, goannasaurian goings-on… it's about monitor lizards

|

There’s been a bit of a monitor lizard thing going on here for the past few months: articles have covered Australian goannas, the Komodo dragon Varanus komodoensis, Dumeril’s monitor and Timor and Peachthroat monitors, and the ‘prasinoid’ tree monitors.

Current version of the monitor montage. Image by Darren Naish.

In ‘spare’ time, I’ve been working on the montage you see here, designed to depict a reasonable amount (though not all) of extant varanid diversity. I’m going to release it as a t-shirt design and see what happens. What’s new in the world of varanids? The 2013 discovery of a new (small) Komodo dragon population at Mbeliling Forest on Flores is interesting and has been well reported in the news. It suggests that the species is more widespread across Flores than otherwise thought, and it's also neat since it means that ‘undiscovered’ populations might persist elsewhere. Note, however, the Mbeliling Forest is still in the West Manggarai region in the far west of Flores, and not all that far away from other population centres for the species.

Pilbara rock monitor (note the large, grey ocelli and banded tail). Image (c) Stephen Zozaya.

Another recently named Aussie goanna: Bush's monitor (V. bushi), named in 2006, endemic to the Pilbara region, and previously included within V. caudolineatus. Image (c) Stephen Zozaya.

What about new species? A Western Australian goanna population, previously included within the Pilbara rock monitor V. pilbarensis, has just been raised to species level by Brad Maryan and colleagues, and named V. hamersleyensis (Maryan et al. 2014). The latter is much darker than V. pilbarensis proper, and has small white ocelli and a mostly unbanded tail (as opposed to large grey ocelli and a banded tail). The distinction is also reflected in range and genetics. What is that now – 77 named extant monitor species? And more to come...

Another tree monitor montage. Canopy goanna (V. keithhornei) shown at bottom. Images by Darren Naish.

In February 2014, I wrote an article about tree monitors, and of the several species included within that group I mentioned the very poorly known V. bogerti and V. telenesetes. André Koch and colleague have just published (April 2014) a new analysis of these species that covers their morphology, systematics and historical biogeography (Koch et al. 2014). While they express doubts about the validity of V. telenesetes (it’s known only from a single specimen), they still find it to be distinct and urge the need for further work. They also report another specimen of V. bogerti (collected on Fergusson Island in 2002), the first collected in more than 70 years. Seven specimens of this taxon are now known.

In other news, monitors are diurnal predators, right? Well, tell that to the Black-palmed monitors V. glebopalma that have been discovered moving around and feeding on prey animals during the night. As documented by Rhind et al. (2013), various observations indicate crepuscular or nocturnal behaviour in this species, and in fact assorted anecdotes and observations suggest that quite a few other monitors might forage during dusk, twilight or night as well. Further study is needed to see how important this behaviour is, and whether it’s reflected in eye anatomy, physiology, energetics or ecology.

Three of (arguably) the most unusual monitors. Clockwise from top left: V. dumerilii, V. rudicollis, V. komodoensis. Image by Darren Naish.

Finally on new studies, Matsubara et al. (2014) have just published their analysis of chromosomal sex determination in monitors. Monitors are known to have specialised sex-determining chromosomes, but this was previously only known for four species. The new study expands this so that we have data on species from additional lineages. Monitors have ZZ/ZW sex chromosomes (where females are heterogametic, not males), and the new data indicates that this was likely the ancestral condition for the group. A question for people who know more about this than I do: was the ZZ/ZW system so-named merely to give different ‘code’ letters (versus XX/XY) to a system where the ovum is heterogametic? I’ve never seen this properly explained.

In a previous article I wrote briefly about Dumeril’s monitor V. dumerili, and one of the things I said about it is that “its teeth are blunt and peg-like”. This is a statement that’s been repeated several time in the literature and I’ve never had the opportunity to check it. Turns out that it’s not true. Derek Larson of the University of Toronto (I know him best for his work on theropod teeth) kindly send me the images you see below: clearly, the teeth of Dumeril’s monitor are not blunt or peg-like, though they do seem seem to be less recurved and less blade-like than the teeth of species with a more ‘conventional’ varanid dentition. Derek is working on varanid ecomorphology and the relationship between tooth form and diet in these lizards; I look forward to hearing more about his work.

Skull and mandibles of Dumeril's monitor (specimen YPM R 11038, Peabody Museum). Images by Derek Larson, used with permission.

In the next Tet Zoo article on varanids, I’ll be talking at length about a geographically widespread group that has a significant presence across the Asian tropics, and which is of major importance as goes human economy and the region’s ecology. The monitors concerned might be excellent examples of what we term ‘ecosystem service providers’.

Finally, a world conference on monitors is planned for July 2015 and will happen in Bangkok. I somehow doubt that I’ll be attending but, if you’re seriously interested in varanids, you’ll definitely want to be there. Oh, if you’re interested in keeping up with monitor news, do always keep an eye on the open-access journal Biawak. Thanks to Stephen Zozaya and Derek Larson for some of the images used here.

Oh, here's a Perentie (Varanus giganteus), included simply because Perenties are awesome. Image (c) Stephen Zozaya.

For previous Tet Zoo articles on monitors, see...

Refs - -

Koch, A., Nicole, E., Eidenmüller, B. & Kraus, F. 2014. New data on the rare Varanus bogerti Mertens, 1950 and V. telenesetes Sprackland, 1991 (Squamata: Varanidae), two endemic monitor lizard taxa from island groups off southeastern New Guinea. The Herpetological Journal 24, 111-122.

Maryan, B., Oliver, P. M., Fitch, A. J. & O’Connell, M. 2014. Molecular and morphological assessment of Varanus pilbarensis (Squamata: Varanidae), with a description of a new species from the southern Pilbara, Western Australia. Zootaxa 3768, 139-158.

Matsubara, K., Sarre, S. D., Georges, A., Matsuda, Y., Marshall Graves, J. A. & Ezaz, T. 2014. Highly differentiated ZW sex microchromosomes in the Australian Varanus species evolved through rapid amplification of repetitive sequences. PLoS ONE 9(4): e95226. doi:10.1371/journal.pone.0095226

Rhind, D., Doody. J. S., Ellis, R., Ricketts, A., Scott, G., Clulow, S. & McHenry, C. 2013. Varanus glebopalma (Black-palmed monitor). Nocturnal activity and foraging. Herpetological Review 44, 687-688.

The views expressed are those of the author and are not necessarily those of Scientific American.

Share this Article:

Comments

You must sign in or register as a ScientificAmerican.com member to submit a comment.

Celebrate Pi Approximation Day
with us!

Get 3 of our best-selling Pi topic issues
Plus a FREE Bonus Issue!

Add to your cart now for just $9.99 >

X

Email this Article

X