Tetrapod Zoology

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That cute little Mexican snake was, obviously, a ‘colubrid’. That means, essentially, that it’s a colubroid snake that isn’t a viperid, elapid, or a member of any of the other obviously distinct colubroid clades (more on this matter below). Its small size, short-snouted, wide head and proportionally enormous eyes at least suggest that it’s a juvenile. The fact that it was photographed in Mexico, and in a region of scrubland and desert, helps narrow down the possible identities. I initially thought it was a lyre snake (Trimorphodon): they tend to have a light grey ground colour, dark grey/brownish dorsal blotches (one of which – the lyre-shaped one – extends across the back of the head, just reaching level with the eyes), and very large eyes with vertical pupils. The head is dorsoventrally flattened in lyre snakes, perhaps so that they can better reach into crevices when searching for lizards and other prey. But some things weren’t right: in particular, the dark marking that runs along the side of the Mexican snake’s face, ‘through’ the eye. That’s not seen in lyre snakes [photo by Dave Hone].

In fact, the combination of (1) dark blotches that reach around the back of the head and then travel forwards towards the nostrils, (2) the dark, finger-like marking on the back of the head, (3) the large eyes with vertical pupils, and (4) the brownish/greyish ground colour show that this is almost certainly a Night snake Hypsiglena torquata: a small colubrid that occurs in woodlands, deserts, chaparrals and other habitats across the western and south-western United States and then south to Costa Rica. Night snakes are typically 36-41 cm long as adults, with 50 cm being the world record. They’re nocturnal (as you might guess) and feed on frogs and lizards, using enlarged grooved teeth at the back of the jaws. Several subspecies have been named; they vary in the amount of spotting, in scale counts, and in the pattern of blotches on the back of the head and neck. This is in fact such a widespread snake across the USA in particular that I imagine it to be pretty familiar: how come all you Americans didn’t recognise it straight away? Congrats at least to Sven, chris (with small ‘c’), and everyone else who went with this identification.

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Hypsiglena has conventionally been classified within Xenodontinae, a large group of American ‘colubrids’ that appear pretty heterogenous and diverse but, like so many snake groups, have been united on the basis of hemipenis characters (see Zaher 1999). The mussuranas (Clelia), ringnecked snakes (Diadophis), hognose snakes (Heterodon), snail-eating and slug-eating snakes (Sibon) and many others (many mightily obscure) are all in here. So, if you identified the snake as a cat-eyed snake (Leptodeira) or a slug-eater, you were at least in the right ball park [adjacent Heterodon from wikipedia].

Some authors think that the xenodontines, while monophyletic, should be split into two groups, with Xenodontinae proper being used for the South American clade and Dipsadinae for the Central American clade (e.g., Cadle 1984). This has been generally supported by recent studies. Lawson et al. (2005) found night snakes to form a clade with the graceful brown snakes (Rhadinaea) and also suggested that at least some of the North American xenodontines (including Farancia (Rainbow snake F. erytrogramma and Mud snake F. abacura), night snakes and hognose snakes) might form a clade [a Northern cat-eyed snake Leptodeira septentrionalis shown below, from wikipedia].

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Like so many traditionally recognised ‘families’ (I’m sure we’ve covered this sort of thing before), Colubridae has, some might argue, been maintained by ‘social inertia’: defining characters have never been identified, and the numerous constituent groups have been allied through convenience, and by absence of characters rather than possession of them. I will avoid discussing this issue further, as it involves so many snake groups and so many contributions to the literature that I’ll be here all night, but for the purposes of the discussion here all you need to know is that Zaher et al. (2009) raised the xenodontine clade to ‘family’ status as Dipsadidae (Dipsadidae Bonaparte, 1838 has priority over Xenodontinae Bonaparte, 1845). It includes Dipsadinae, Carphophiinae and Xenodontinae, as well as a huge raft of genera that have yet to be classified satisfactorily. Zaher et al. (2009), in fact, decided to explode ‘Colubridae’ of tradition and to raise many of its constituent clades to ‘family’ level. They also coined the new names Colubroides (for xenodermatids and colubriforms) and Endoglyptodonta for the colubriform clade that includes viperids, homalopsids, elapoids and colubroids. Oh, and there’s a mild controversy over exactly what ‘Colubroidea’ means, as molecular scientists have developed their own ‘special’ meaning of the term that’s contrary to herpetological tradition. Yikes – - what did John Scanlon say about avoiding this mess?

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Finally… while we’re on the subject of herpetology… here’s me with something that arrived in the post this morning. Yes, if you read this article you’ll know exactly what it is, and what a big deal is it for me to hold my own cherished, much loved copy. To the person involved, thank you once again.

Finally finally… tonight saw the screening (on the UK’s Channel 4) of the last episode of Inside Nature’s Giants, a four-part TV series that, via dissection, discussions of phylogeny, functional morphology, ecology and behaviour, presented a huge amount of anatomical information on elephants, rorquals, crocodiles and giraffes to an enthralled public. A bold and fantastic series. I aim to discuss it at length some time. Stay tuned [Will took the adjacent photo. Not bad for a 7-year-old].

Refs – -

Cadle, J. E. 1984. Molecular systematics of neotropical xenodontine snakes: III. Overview of xenodontine phylogeny and the history of New World snakes. Copeia 1984, 641-652.

Lawson, R., Slowinski, J. B., Crother, B. I. & Burbrink, F. T. 2005. Phylogeny of the Colubroidea (Serpentes): new evidence from mitochondrial and nuclear genes. Molecular Phylogenetics and Evolution 37, 581-601.

Zaher, H. 1999. Hemipenial morphology of the South American Xenodontinae 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.

- ., Grazziotin, F. G., Cadle, J. E., Murphy, R. W., Cesar de Moura-Leite, J. & Bonatto, S. L. 2009. Molecular phylogeny of advanced snakes (Serpentes, Caenophidia) with an emphasis on South American xenodontines: a revised classification and descriptions of new taxa. Papéis Avulsos de Zoologia, Museu de Zoologia da Universidade de São Paulo 49, 115-153.

Comments

  1. #1 Nathan Myers
    July 20, 2009

    Is the name Dipsadidae as pleasing to the knowledgeable as it is to the ignorant?

  2. #2 Jared
    July 20, 2009

    I think a former professor of mine described Colubridae (family) best:
    “The dumping ground for everything ‘not viperid or elapid’ which has yet to be analyzed with modern genetic techniques”

  3. #3 Zach Miller
    July 20, 2009

    To paraphrase:

    These snakes are united based on characters related to their dicks.

    Hilarious!

  4. #4 Michael Ogden Erickson
    July 20, 2009

    Yeah! I did it, I did it, oh yeah yeah yeah…

    Just kidding.

    “This is in fact such a widespread snake across the USA in particular that I imagine it to be pretty familiar: how come all you Americans didn’t recognise it straight away?”

    Well, at first I thought it was a slug-eater. Thankfully I looked at it more closely and realized what it really was. I think that I didn’t identify it straight off because, although I’ve often rode down back roads looking for snakes, it was always at dusk or dawn, not at night when these snakes would have been out. In fact, I very rarely saw anything other than various species of ribbon snakes and a few Crotalus atrox. (Yes, I rescued them from being run over and no, I didn’t get close to them. We drove up beside them, stuck a butterfly net out the window, scooped them up, and tossed them into the tall grass on the side of the road. Unorthodox style, but it works – and you’re garenteed not to get bit.)

  5. #5 kad
    July 20, 2009

    “This is in fact such a widespread snake across the USA in particular that I imagine it to be pretty familiar: how come all you Americans didn’t recognise it straight away?”

    We did. We were just messin’ with ya. :)

    Actually, as widespread as this little beastie might be, I’m quite certain we don’t have them here in Vermont so I get a pass. The Green Mountains are pretty snake poor anyway, especially compared with the southwestern part of the country. We only have about 10 species of snake, and 4 of those are endangered or threatened.

  6. #6 Michael Ogden Erickson
    July 20, 2009

    “Finally finally… tonight saw the screening (on the UK’s Channel 4) of the last episode of Inside Nature’s Giants, a four-part TV series that, via dissection, discussions of phylogeny, functional morphology, ecology and behaviour, presented a huge amount of anatomical information on elephants, rorquals, crocodiles and giraffes to an enthralled public. A bold and fantastic series.”

    DANG DANG DANG! Why do you Brits get to see elephant and crocodilian dissections on TV, while us Americans are stuck with Jurassic Fight Club and SpongeBob SquarePants? What a cruel world we live in.

  7. #7 Rosel
    July 21, 2009

    Thats a pretty good pic for a seven year old!

    For any UK people who have missed ‘inside Nature’s Giants’ Channel four have the whole series online here
    http://www.channel4.com/programmes/inside-natures-giants/4od
    It’s been on a dinner time and I’m not sure my Boyfriend would appreciate dissection as dinner TV :P

  8. #8 Darren Naish
    July 21, 2009

    Inside Nature’s Giants was a monumental series – with last night’s giraffe episode being incredible. They covered just about everything you could hope to. I have loads more to say, will save it for later though. Doing some TV work myself tomorrow…

  9. #9 Joel
    July 21, 2009

    And, of course, the Looney Tunes fans were right too, I was thinking of the The Abominable Snow Rabbit – but now I’ve learnt something about its origins as well!

  10. #10 Mary Blanchard
    July 21, 2009

    Glad you finally have your own copy. One day I will attempt to ID the amphibians and reptiles I have photos of, but there are so many species. I also have to decide whether it is worth taking the hulking great book out to Madagascar with me!

  11. #11 Andreas Johansson
    July 21, 2009

    Is “Colubroides” a typo for “Colubroidea”, or is it a distinct if confusingly similarly named grouping?

  12. #12 Hai~Ren
    July 21, 2009

    ‘Colubridae’ is one confusing mess indeed. Here in Southeast Asia the snakes listed as ‘colubrids’ in older guides have been split into 5 families: Colubridae, Natricidae, Homalopsidae, Xenodermatidae and Pareatidae.

    I’m interested in finding out which of these snakes, many of which are traditionally thought to be non-venomous, actually possess venoms. I’m also wondering if more basal snakes such as boas and pythons, file snakes, sunbeam snakes, pipe snakes and scolecophidians do also possess venom, or whether they might be secondarily non-venomous.

    By the way, how accurate is this phylogeny?
    http://is.gd/1GlyN

  13. #13 Alex
    July 21, 2009

    “This is in fact such a widespread snake across the USA in particular that I imagine it to be pretty familiar: how come all you Americans didn’t recognise it straight away?”

    Pft. You’d be amazed (or maybe you wouldn’t…) how many Americans are ignorant of things like common, large and unique-to-America *mammals*. (My east-coast classmates might be able to think of 3 or 4 species of African antelope, but none of them had heard of pronghorn. /facepalm)

  14. #14 DD
    July 22, 2009

    Talking of burrowing reptiles, burrowers have major impact on geological topography (gophers, beavers, earthworms, ants, agriculture)

  15. #15 Darren Naish
    July 23, 2009

    Hi all. Some belated responses…

    Andreas (comment 11): no, Colubroides is not synonymous with Colubroidea in the scheme proposed by Zaher et al. (2009). Colubroides essentially includes all caenophidians except file snakes (they don’t say whether it’s meant to be node-based or branch-based, however), whereas Colubroidea corresponds more closely with ‘Colubridae’ of tradition.

    Hai-Ren (comment 12): which colubroids are venomous? Good question. I’m not entirely sure of the answer, but I know that some snake workers (including the late Garth Underwood) have argued that venomosity was primitive for what Zaher et al. call Colubroides, and that non-venomosity in colubroids (sensu Zaher et al.) is derived.

    As for the phylogeny you link to, this is essentially the one proposed by Vidal & Hedges (most recently used in Vidal & Hedges 2009). It’s broadly concordant with the phylogenies published by (e.g.) Kelly et al. (2003), Lawson et al. (2005) and Zaher et al. (2009). However, some studies find viperids to be more basal than pareatids. The placement of homalopsids as sister to an elapoid + colubroid (s.s.) clade does seem generally agreed upon.

    Ref – -

    Kelly, C. M. R., Barker, N, P. & Villet, M. H. 2003. Phylogenetics of advanced snakes (Caenophidia) based on four mitochondrial genes. Systematic Biology 52, 439-459.

    Vidal, N. & Hedges, S. B. 2009. The molecular evolutionary tree of lizards, snakes, and amphisbaenians. C. R. Biologies 332, 129-139.

  16. #16 Paul White
    September 17, 2010

    followed the link form another snake story, sorry if this is too old to comment on…but def. a night snake! They’re really cool, probably fairly common over much of thier range but not often seen (I’ve only found one up here, and one in south texas). I think they’re cute, and they are certainly neat little fellows, rarely attaining a length greater than 1.5 feet or so.

  17. #17 Paul White
    September 17, 2010

    hit enter too soon: I was going to say that the nocturnal tendencies may have been greatly exaggerated; both mine were found during the evening, prior to dusk. Same with most of the field guys I know that do more hiking than road cruising; they find more of this in the early-mid evening, before sunset, than they do after sunset.

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