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Tetrapod Zoology

Tetrapod Zoology

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Love for Mastigodryas, Tomodon, Sordellina and all their buddies: you know it's right

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I’m feeling on a roll with the obscure colubrid snakes, so here are some more (see the previous article if you feel like you need an introduction). Again, the photos are used with kind permission of Bangor University’s Wolfgang Wüster unless stated otherwise.

Photo courtesy W. Wüster.

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Mastigodryas bifossatus (photographed here at Sao Paulo in Brazil) is a slender-bodied, oviparous American colubrid. All 12 or so Mastigodryas species are large-eyed, diurnal predators of amphibians, lizards, snakes, birds and small mammals. They also eat eggs on occasion. They’re sometimes called racers, a name used elsewhere for species in the colubrid genera Coluber, Drymobius, Alsophis and Lampropeltis, but M. boddaerti is known as the machete cuesse across parts of its range. A new species in the group, M. moratoi Montingelli & Zaher, 2011, was named from Brazil just last year.

Mastigodryas has generally been regarded as closely related to Coluber and Masticophis. Pyron et al. (2011) recovered it as part of the tropical American colubrine clade that includes cribos (Drymarchon), coachwhips (Masticophis), tiger snakes (Spilotes), green snakes (Opheodrys) and the vine snakes (Oxybelis) we looked at in the previous article. Within this clade, Mastigodryas seems especially closely related to the Drymoluber species, also often known as racers.

Photo courtesy W. Wüster.

This is Tropidodryas striaticeps, a semi-arboreal, nocturnal colubrid from south-eastern Brazil that preys on diverse vertebrates. It’s extremely unusual among colubrids, and among snakes, in having a prehensile tail. There are two Tropidodryas species: the other one is T. serra. Adult individuals of both species are greenish grey or brownish, with dark blotches forming what seems to be a cryptic pattern. Juveniles, however, differ in having a highly conspicuous whitish or yellowish tail where flaring scales make the tail-tip appear broader than it is in adults.

Western ratsnake (Pantherophis obsoletus); photo by furryscaly, from wikipedia.

Could – some herpetologists suggested – this tail-tip be used in caudal luring, a form of behaviour (elsewhere seen in some pythons, wood snakes, vipers and Australian elapids) used by some snakes to trick frogs, lizards and mammals into coming within striking range? Sazima & Puorto (1993) observed what seemed to be caudal luring in T. striaticeps, making it the first colubrid known to engage in this behaviour. It was later reported in the dipsadine Alsophis (Leal & Thomas 1994) and in the Western ratsnake Pantherophis obsoletus, a colubrine (Tiebout 1997) [adjacent Western ratsnake image by furryscaly, from wikipedia]. The last case is the weirdest since Pantherophis doesn’t have a distinctly pigmented tail, perhaps showing that the field is open for any snake to engage in caudal luring so long as it uses its tail tip in the right way. Incidentally, some colubrids employ lingual luring: that is, they use the tongue to attract prey. This behaviour is documented for American watersnakes (Nerodia) and gartersnakes (Thamnophis) where the prey are fish, but it’s also rumoured for the African twigsnake Thelotornis kirtlandii where the prey are assumed to be birds (Mattison 1998).

Like several of the other ‘colubrids’ we’ve looked at before, Tropidodryas is a dipsadine, and in fact molecular data indicates that it’s part of the same dipsadine clade as Xenoxybelis and Philodryas (two taxa both mentioned in the previous article) (Pyron et al. 2011).

Photo courtesy W. Wüster.

Oxyrhopus contains 11 species of superficially coralsnake-like colubrids (coralsnakes [Micrurus] are elapids, not ‘colubrids’). This one is O. guibei, photographed in Brazil. Oxyrhopus species are back-fanged and diurnal; they’re generalist predators, eating amphibians, lizards, snakes and rodents. The most northerly species occur in Mexico and the most southerly ones are in Peru. Again, Oxyrhopus is a dipsadine. Within this large group, it seems to belong to the clade that also includes Arrhyton, Uromacer and Xenodon, being especially close to Phimophis, Drepanoides, Pseudoboa and Boiruna (Pyron et al. 2011). This latter, Pseudoboa-and-kin clade corresponds more or less with the ‘Tribe’ Pseudoboini, recognised on the basis of morphological (hemipenis-based) characters (Jenner & Dowling 1985, Zaher 1999).

Photo courtesy W. Wüster.

Tomodon dorsatus is a small, viviparous colubrid and yet another dipsadine. It’s a back-fanged predator (notable for particularly long rear fangs) that’s mostly terrestrial but may also climb on occasion. There’s some disagreement as to what it eats. Some sources regard it as a predator of lizards and rodents while Greene (1997) suggested that those long back fangs might assist in a diet of slugs. Greene also noted that a gaping Tomodon, bearing its enlarged fangs, might benefit from a superficial resemblance to pit vipers. T. dorsatus is one of two Tomodon species (the other one is T. ocellatus), both of which are unique to south-eastern South America.

Some authors (e.g., Bailey 1967) have classified Tomodon and a list of other dipsadines within the ‘Tribe’ Tachymenini. Other members are Tachymenis (of course), Thamnodynastes, Ptychophis, Gomesophis, Pseudotomodon and Calamodontophis. This is a diverse lot: some (Pseudotomodon) are superficially viper-like, others burrow in damp mud and eat earthworms (Gomesophis), while others (Thamnodynastes) are slender, long-tailed snakes that climb and swim in wetland habitats. However, the only character used to unite ‘tachymenins’ is viviparity. As is well known (or should be well known), viviparity has evolved on innumerable separate occasions within Squamata, so this isn’t really compelling. Zaher (1999) couldn’t find any characters supporting tachymenin monophyly (though their hemipenes do look similar) and left the alleged members of this group as incertae sedis within Dipsadinae. Molecular phylogenetic studies have generally failed to incorporate them.

Photo courtesy W. Wüster.

Finally, here’s the peculiar and little-known Dotted brown snake Sordellina punctata from south-eastern Brazil, the only species in its genus. It’s an oviparous dipsadine, named in 1923, and often said to frequent wet places. Pereira et al. (2007) concluded that Sordellina is mostly a snake of well vegetated, boggy waterside habitats. There are suggestions that it eats frogs and their tadpoles, but I don’t know if these are anything more than speculations. Procter (1923) actually found a specimen of the typhlonectid caecilian Chthonerpeton indistinctum in the stomach of the holotype.

Sordellina’s affinities are somewhat uninvestigated. One suggestion is that it’s close to the terrestrial, sometimes semi-fossorial graceful brown snakes (Rhadinaea) (Jenner 1981) and part of the dipsadine ‘Tribe’ Diaphorolepidini. Zaher (1999) said that these ideas weren’t supported by hemipenial anatomy, but beyond this it wasn’t possible to pin down the affinities of this taxon within Dipsadinae.

Participants of the CITES Asian Snake Trade Workshop, Guangzhou, China, April 11th-14th, 2011

As always, there are so many other snakes that still need some love at Tet Zoo. We can all help snakes by being more aware of habitat loss and degradation – many of the species here are tropical forest animals that are threatened by logging, mining and other forms of destruction. The mostly Asian trade in snake meat, and the global trade in snake skin and other products, desperately needs more regulation: it’s presently completely unsustainable and putting many snake populations in danger. Ivan Kwan of The Lazy Lizard’s Tales reminds me that CITES held a special Asian Snake Trade Workshop in China during April 2011: you can view and/or download numerous free documents from that meeting here.

And I was horribly inconsistent in this article as goes the use of colubrid or ‘colubrid’, sorry. You’ll know why. Right?

For previous Tet Zoo articles on colubrid snakes (using ‘colubrid’ in the maximally inclusive sense), see...

And for articles on other kinds of snakes, see...

Refs - -

Bailey, J. R. 1967. The synthetic approach to colubrid classification. Herpetologica 23, 155-161.

Greene, H. W. 1997. Snakes: the Evolution and Mystery in Nature. University of California Press, Berkeley.

Jenner, J. V. 1981. A Zoogeographic Study and the Taxonomy of the Xenodontine Colubrid Snakes. Unpublished Ph.D. dissertation, New York Univ., New York.

- . & Dowling, H. G. 1985. Taxonomy of American xenodontine snakes: the tribe Pseudoboini. Herpetologica 41, 161-172.

Leal, M. & Thomas, R. 1994. Notes on the feeding behavior and caudal luring by juvenile Alsophis portoricensis (Serpentes: Colubridae). Journal of Herpetology 28, 126-128.

Mattison, C. 1998. The Encyclopedia of Snakes. Blandford, London.

Pereira, D. N., Stender-Oliveira, F., Rodrigues, M. G. & Bérnils, R. S. 2007. Distribution and habitat use of Sordellina punctata (Serpentes, Colubridae), with a new record from State of São Paulo, Brazil. Herpetological Bulletin 100, 18-22.

Procter, J. B. 1923. On a new genus and species of Colubrinae snake from SE Brazil. Annals and Magazine of Natural History 9, 227–230.

Pyron, R., Burbrink, F., Colli, G., de Oca, A., Vitt, L., Kuczynski, C., & Wiens, J. (2011). The phylogeny of advanced snakes (Colubroidea), with discovery of a new subfamily and comparison of support methods for likelihood trees Molecular Phylogenetics and Evolution, 58 (2), 329-342 DOI: 10.1016/j.ympev.2010.11.006

Sazima, I. & Puorto, G. 1993. Feeding technique of juvenile Tropidodryas striaticeps: probable caudal luring in a colubrid snake. Copeia 1993, 222-226.

Tiebout, H. M. 1997. Caudal luring by a temperate colubrid snake, Elaphe obsoleta, and its implications for the evolution of the rattle among rattlesnakes. Journal of Herpetology 31, 290-292.

Zaher, H. 1999. Hemipenial morphology of the South American xenodontine snakes, with a proposal for a monophyletic Xenodontinae and a reappraisal of colubroid hemipenes.Bulletin of the American Museum of Natural History 240, 1-168.

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

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