#ScanAllSnakes (yes, all of them!)

The Rabosky and Davis Rabosky labs at the University of Michigan are generating high-resolution computed tomography (CT) scans for all of the world’s snakes – and will make these data publicly available for use by the research community, with no restrictions. This idea is motivated by our love of snake diversity and by similar projects for other groups of organisms, especially the #ScanAllFish project led by Adam Summers (University of Washington) and the Blackburn Lab amphibian and reptile digitization project (University of Florida). We are also a collaborating institution on a recently-funded NSF initiative to CT scan a huge fraction of vertebrate diversity and to make these data available as a digital morphology resource for everyone. Read more about our oVert project here!

For our inaugural data release, we’ve chosen the Asian mock viper – Psammodynastes pulverulentus – a small and relatively common snake from southeast Asian, including islands of the Sunda shelf and Wallaceae. The phylogenetic position of this snake was long considered uncertain, though recent analyses have placed it within the Afro-Asian clade Lamprophiidae (Pyron et al, 2013).

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Asian mock vipers, Psammodynastes pulverulentus. Images: Wikipedia

The snake is pretty cool, because it has several dental specializations that are immediately obvious from the skull and which distinguish it from most other snakes. First, like a number of so-called “rear-fanged” snakes, mock vipers have enlarged and grooved posterior fangs. These fangs appear to conduct venom that is involved in subduing prey, and both the fangs and the presumed venom channels are obvious on the imaged specimen shown below (fangs in red; click to view rotation).

 

The weirder aspect of these snakes involves their massively enlarged anterior maxillary teeth (also in red), which presumably is part of the reason these snakes are known as “mock vipers”. Enlarged maxillary teeth are ubiquitous within the two primary lineages of front-fanged venomous snakes (elapids and vipers), but relatively few other groups of snakes have this particular type of dentition. Similarly enlarged teeth show up in a number of other snake genera that specialize on skinks, a group of lizards known for having hard and slippery scales that thwart many would-be-predators. Among the more-interesting yet unresolved issues is whether the front “fangs” in mock vipers play any role in conducting venom. A previous study on mock vipers found some evidence for grooving using electron microscopy. Grooving, at least in rear-fanged snakes (and Gila monsters!), plays a role in conducting venom into the tissues of whatever unfortunate animal is on the receiving end of a bite. However, it isn’t yet known whether venom glands are actually “hooked up” to the anterior teeth (Jackson & Fritts, 1996), so it’s possible that venom only moves along the posterior fangs.

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Distribution of mock vipers (P. pulverulentus). Each point represents a vouchered museum specimen available on VertNet (credit: Pascal Title)

In any event, these snakes aren’t dangerous to humans, but their venom does appear to subdue skinks. Greene (1989) has a nice review of what is known about defensive and feeding behavior in these snakes. There is speculation that these snakes also mimic montane pitvipers in both coloration and behavior (specifically, the Himalayan pitviper, Gloydius himalayanus).

References
Greene, H. W. 1989. Defensive behavior and feeding biology of the Asian mock viper, Psammodynastes pulverulentus (Colubridae), a specialized predator on scincid lizards. Chinese Herpetological Research 2: 21-32.
Jackson, K., and T. H. Fritts. 1996. Observations of a grooved anterior fang in Psammodynastes pulverulentus: does the mock viper resemble a protoelapid? J. Herpetology 30: 128-131.
Pyron, R. A., F. T. Burbrink, and J. J. Wiens. 2013. A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes. BMC Evol. Biol. 13:93.