If you need to identify a snake, try the Snake Identification Facebook group.
For professional, respectful, and non-lethal snake removal and consultation services in your town, try Wildlife Removal USA.

Wednesday, December 26, 2012

The Unusual Soft Anatomy of Snakes

This year I had the opportunity to help my friend Lori Neuman-Lee dissect a number of Wandering Gartersnakes (Thamnophis elegans) for her research on the effect of toxic chemicals on reptile physiology. During my Master's, I had the opportunity to help teach a Comparative Anatomy course, during which I learned a great deal about the internal anatomy of vertebrates. However, dissecting an animal for research requires greater accuracy and precision than dissecting for teaching, and we decided to read up on snake anatomy before we got started. Because we found few resources to aid us in our work, we video-taped one of the dissections to help future would-be snake anatomists locate and identify snake organs, several of which can be a little tricky. Check out the video below and learn to dissect a snake! Lori is doing the dissection in the video, and like many things, she makes it look easy. I would recommend some pretty intense practice first if you want to become as accomplished as she is. Salvaged, all-too-common road-killed specimens often make for ideal practice if you don't mind bits of them being smashed, and they sometimes have interesting things in their stomachs.

A few notes: Snakes are long - it's in the blog title. But the implications of being long for the internal anatomy of an animal are not usually considered. For example, in humans and most other animals, paired organs, such as kidneys, lungs, and gonads, are found next to one another, across the body's plane of symmetry. This is not so in snakes; there simply isn't room. Add to their body shape the fact that a great deal of the body cavity must sometimes be filled with eggs or prey items, and there's little room left for the vital organs: heart, lungs, liver, kidneys, spleen and pancreas. That's why snakes have A) evolved elongate organs, B) evolved staggered paired organs, and C) lost some organs or members of paired organs.

Many snake organs are similar in shape to their overall body form. The liver, stomach, gonads, kidneys, and lung are all elongate. Those that come in pairs are either staggered, such as the kidneys and gonads (right always anterior to left), or asymmetrical, such as the lungs. See the tiny left lung near the heart? In a real snake it's almost impossible to find. It is a vestigial organ, meaning it does not function in breathing any more, although in some sea snakes it does have a co-opted function: it helps regulate buoyancy much like the swim bladder of a fish. These adaptations are part of what makes snakes so amazing and unique.

Finally, because 2013 has been designated the Year of the Snake by non-profit conservation group Partners in Amphibian and Reptile Conservation, I hope to help them promote snake research and snake conservation through frequent writing and outreach. As always, thanks for your comments and your readership. Life is Short but Snakes are Long received over 22,000 hits in 2012 and I'm looking forward to an even bigger 2013!

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Life is Short, but Snakes are Long by Andrew M. Durso is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

Monday, December 10, 2012

Magnificent Meizodon

It isn't often that I'm sent a photo of a snake that I can't identify, but last week Alvaro Pemartin found the time both to finish translating all of my old blog posts into Spanish (many thanks to him!) and to obtain photographs of a snake that I had never heard of before. When he sent them to me, I was struck by how beautiful and distinctive the snake was, and it turned out to be quite difficult to identify. I shouldn't have been surprised, because it is from a herpetologically-poorly-known region of the world, western Africa. Alvaro works as a doctor in Guinea, and his nurse, Sandrine Chabassieu, photographed the snake as it crawled across their porch one day.

The mystery snake
Although Kate Jackson's new key to identifying snakes of western and central Africa is a great tool, we couldn't use it to identify this snake because we didn't have close-up pictures of the all-important scale characters that can be indispensable in identifying species of snakes. The backup method, sending the photos to as many people who might know as possible, eventually proved effective when Laurent Chirio, of the Muséum National d'Histoire Naturelle in Paris, France, wrote me that "This is without any doubt a beautiful Meizodon coronatus. I found some specimens with this kind of colour pattern in Guinea."

I wanted to learn what I could about this snake, because it was so striking and previous unknown to me. There isn't a lot out there. Meizodon coronatus, also known as the Western Crowned Snake, is one of five species in Meizodon, a genus of poorly known colubrine snakes found in sub-Saharan Africa. Western Crowned Snakes are found from Senegal to the Congo along the coast of western Africa, while the other four species are found in eastern and central Africa. The Western Crowned Snake was the first species of Meizodon described, by Hermann Schlegel in 1837, who called it Calamaria coronata in his first major published work (Essai sur la Physionomie des Serpens) as assistant curator of the Natural History Museum of Leiden in the Netherlands. The species was later moved to Coronella (subgenus "Mizodon") by Giorgio Jan of the Milan Museum in 1866, then placed in Meizodon in 1955 by Arthur Loveridge.

Plate from Jan 1866

No genes of any species of Meizodon have been sequenced, so it's difficult to say exactly how they are related to other snakes, but if their placement in Colubrinae is correct, then they are probably closely related to other west African species of colubrine, such as the egg-eating Dasypeltis and wolf-toothed Lycodon. These snakes are descended from the same common ancestor as North American kingsnakes and ratsnakes, from which they diverged about 33 million years ago.

Another of Sandrine's photos

Meizodon are primarily predators of lizards, especially skinks, although they are also known to eat geckos, small mammals, and frogs. They are not as specialized for feeding on skinks as their relatives the wolf snakes (Lycodon), on which an upcoming article will focus, but their genus name describes their teeth, which increase in robustness toward the back of the jaw. Meizodon coronatus seem to be a diurnal foragers. A few individuals were observed foraging along the base of a crumbling wall by Godfrey Akani and colleagues at Rumueme, Nigeria. These snakes probed with their heads into holes and crevices where geckos and other lizards were sleeping. Typically, Meizodon are apparently found in refugia such as under rocks, within hollow trees, and underneath loose bark during the day. Don Broadley of the Zimbabwe Natural History Museum  recalls capturing several Meizodon semiornatus that were sheltering inside tree hollows in a flooded forest in western Botswana, along with the psammophine snakes Psammophylax and Psammophis. Broadley noted that several snakes were sometimes captured per tree, including evidence of shed skins and skeletons, although these observations might be atypical given the flooded nature of the forest at the time of Broadley's visit.

The best of Sandrine's photos, in my opinion, showing the gorgeous anterior pattern.

Likely viviparous, Meizodon coronatus inhabits savannahs, forests, plantations, and urban areas. They are mentioned in a study conducted by Godfrey Akani and colleagues on anthropogenic causes of snake mortality in west African suburbs. They found that anthropogenic snake mortality in suburbs of southeastern Nigeria were about 50% intentional, 50% unintentional (e.g., roadkills, snares set to trap more edible wildlife), and that more snakes were killed in the wet season, when they are presumably more active. Even though most of the snake species in this region are harmless and beneficial to humans (in that they exert strong top-down control on populations of pesty rodents, by eating them), most people did not know how to differentiate venomous from non-venomous snakes. It's interesting to know that some ecological problems are common to places as different as North America and Africa. I was glad to hear from Alvaro and Sandrine that, now that they know their beautiful snake is a harmless Meizodon, they have encouraged their camp guards not to kill other Meizodon they might see in the future.

M. coronatus from Cameroon. Not nearly as striking as the one from Guinea.
Edit: 4-Dec-2019: In response to a claim that Meizodon are opisthoglyphous, I revisited some of the literature and found that the original description of Meizodon coronatus by Schlegel in 1837 states (p. 47):
Elle a les dents toutes d'égale longueur ("The teeth are all of equal length")
Günther (1860, p. 429) wrote of M. coronatus that:
The maxillary teeth form one continuous series; anteriorly small, they gradually become longer and stouter posteriorly; none of them are grooved.
Oberkiefer mit 18-19 Zähnen; die ersten sind sehr klein, dicht gedrängt; sie werden nach hinten etwas grösser und weitläuftiger, so dass die letzten doppelt so gross sind als die ersten; ohne Lücken, Keiner derselben ist gefurcht. Unterkiefer mit 20-22 Zähnen, von denen die ersten wenig grössen sind als die letzten, und nach hinten allmählich an Grösse abnehmen. Gaumenzähne: Palatini 12, pterygoidei 14-16, die letzten schwach nach innen gekrümmt (Upper jaw with 18-19 teeth; the first ones are very small, densely crowded; they become slightly larger and wider towards the back, so that the last ones are twice as big as the first ones; without gaps; none of them are grooved. Lower jaw with 20-22 teeth, of which the first are slightly larger than the last, and gradually decreasing in size towards the back. Palatine teeth: 12, pterygoid teeth 14-16, the last teeth slightly curved inwards)
Although the genus name Meizodon comes from the Greek words meizo ("larger" or "greater") and -don (from odonto = "tooth"), this seems to refer to a gradually increasing series rather than an enlarged rear tooth or pair of teeth. I was only able to find a single illustration of the teeth of these snakes (here and above; reprinted from Jan 1866 as part of a detailed comparison of M. regularis and M. coronatus written in 1969). Although there are opisthoglyphous colubrine colubrids (e.g. Dispholidus, Thelotornis) that can kill humans, most species, even those with enlarged rear teeth, do not possess venom dangerous to humans (although colubrid venom and its relationship to tooth anatomy is still on its way to becoming well-understood). Eventually the skull of a Meizodon will be CT scanned & posted here, but until then the single drawing from 1866 and the written descriptions are all we have to go on.


Thanks to Alvaro and Sandrine for the photos, and to Pierson Hill, Peter Uetz, and Laurent Chirio for nailing the ID.


Akani G, Eyo E, Odegbune E, Eniang E, Luiselli L (2002) Ecological patterns of anthropogenic mortality of suburban snakes in an African tropical region. Isr J Zool 48:1-11 <link>

Barbault R (1976) Population dynamics and reproductive patterns of three African skinks. Copeia 1976:483-490 <link>

Böhme W (2000) Diversity of a snake community in a Guinean rain forest (Reptilia, Serpentes). Bonn Zool Monogr 46:69-78

Broadley DG (1988) Meizodon semiornatus semiornatus: Semiornate Snake. Habitat, Diet, and Distribution. The Journal of the Herpetological Association of Africa 34:44

Günther A (1860) On a West-African genus of snakes (Meizodon). Proc Zool Soc Lond 28:427-430

Jan G (1866) Iconographie Générale des Ophidiens. Livraison. J.B. Bailière et Fils, Paris <link>

Luiselli L, Akani GC, Angelici FM (2001) Diet and foraging behaviour of three ecologically little-known African forest snakes: Meizodon coronatus, Dipsadoboa duchesnei and Hapsidophrys lineatus. Folia Zool 50:151-158

Schlegel H (1837) Essai sur la physionomie des serpens. Partie descriptive. Kips and Van Stockum, La Haye

Segniagbeto GH, Trape JF, David P, Ohler A, Dubois A, Glitho IA (2011) The snake fauna of Togo: systematics, distribution and biogeography, with remarks on selected taxonomic problems. Zoosystema 33:325-360

Roux-Estève, R. 1969. Étude comparée de Meizodon coronatus (Schlegel) et de Meizodon regularis Fischer (Colubridés - Serpentes). Bull. Mus. Natl. Hist. Nat. Paris (ser. 2) 41: 395-409

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Life is Short, but Snakes are Long by Andrew M. Durso is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.