Posted by: Rob Viens | July 4, 2013

Serpents of the South

On June 29th Darwin left his lodgings in Maldonado to return to his cabin on the Beagle.  It apparently took him a little while to get his “sea legs” back:

“Arrived safely on board with all my Menagerie; am become such a complete landsman. — that I knock my head against the decks & feel the motion although in harbor.” (June 29)

Speaking of legs (or lack thereof anyway), one of the animals that was part of Darwin’s “Menagerie” were snakes.  Although he does not say much about them in his diary, he does take the time to describe them in his Zoological Notebook.  Here are a few of the “legless reptiles” that he collected:

(1) Jointed Worm Lizard  (Ophiodes vertebralis Bocourt)

Found in Uruguay and southern Brazil, here is what Darwin says about the jointed worm lizard:

“Beneath white gradually shading into a light brown above, with four dark brown lines.— the 2 central ones being the broardest was caught near the water of a lake.— motions inactive.” (Zoological Notebook)

Ophiodes vertebralis (from by Juan José Yngelmo on ecoregistros.com.ar)

Jointed worm lizard

Worm lizards not actually snakes (suborder Serpentes ) or lizards (suborder Lacertilia), they are actually their own suborder called the Amphisbaenia (all three make up the order of scaled reptiles – the Squamata). Although they look like snakes, their internal anatomy is different (more like lizards, actually) and the connection of the head to the body is indistinguishable, like a worm (snakes, on the other hand, have a discernible neck). They move differently than snake, too. Sources say the motion is “like an accordion”- essentially moving by expanding and contracting (I sort of picture one of those Slinky dogs). Nature is just so cool!

(2) Mussurana (Clelia occipitolutes Duméril)

This particular species name, reported by Darwin, does not seem to be in use today, but probably refers to what is now identified as a type of Mussurana – Clelia clelia. A Mussurana is consistent with the blue color reported by Darwin:

“Above of a uniform blackish lead colour, with an opaline bluish gloss; beneath pale, at the junction of the two sorts of scales the gloss is least seen; differs from the following one in shape of scales, & proportional length of tail &c” (Zoological Notebook)

Clelia clelia (by W Wuster from reptile-database.reptarium.cz)

mussurama

Interestingly, this is a particularly unique species of snake for a couple of reasons.  One reason is that it is venomous (mildly at least) and also a constrictor.  Most snakes are one or the other.  Another thing that make it unique is that it is a snake hunter, and because of this, it has some interesting adaptations. First, it’s teeth are in the back of its mouth, which help it hold on to another snake’s head and then “pull” it into its gullet. Secondly, it is immune to most snake venom.  In other words, it is the Rikki Tikki Tavi of the snake world. In fact, like the famous mongoose from Kipling, farmers like to have mussurana around to help keep potentially harmful snakes in check.

(3) Patagonian green racer (Philodryas patagoniensis Girard)

Named racers for their bursts of speed, Darwin describes this sample (and its interesting teeth) as such:

“The commonest species in this country; is it not same as taken at Bahia Blanca, reaches 3 or 4 feet long.— The first maxillary tooth is very large: by aid of microscope I saw a narrow deep groove running down on convex surface.— Is it for conveying poison?— Specimen of tooth is in pill-box”  (Zoological Notebook)

Philodryas patagoniensis (by R Sage from reptile-database.reptarium.cz)

Though not particularly harmful to humans, Darwin was absolutely correct – those teeth were made for conducting venom.

(4) South American hognose snake (Lystrophis dorbignyi Duméril)

The hognose gets its name from its upturned snout – like that of a pig. Darwin did not really make note of that feature, but here is what he did have to say:

“Beneath cream-coloured with irregular rows of blackish dots as if of interrupted chains; above all the scales, “yellowish” ½ “wood brown”, with lateral darker band on each side; chiefly on anterior part of body, the interstices between scales are coloured in symetrical small spaces of white, “tile red” & black, (the latter most strongly marked), this gives a singular mottled appearance to the animal.— Inhabits not uncommonly the sand dunes”

Lystrophis dorbignyi – note the tiled red and black Darwin describes above (from Jim’s Western Hognose.com via the Snakes and More Snakes blog)

South American hognose snake

There are several species of hognose in the world (including three distinct genera). What is really interesting, however, is that while most hognose species are found in the New World, there are three species (all from the same genus) found in Madagascar.  Assuming this is not just parallel evolution – how’d that happen?

I’m not sure what sort of snake handler Darwin was – I imagine, given his first-hand experience with the natural world, that he knew enough to be cautious.  Luckily, in this case, none of the snakes (or worm lizards) that he collected presented any particular risk of a serious venomous bite.

By the way… the end of June marked the year-and-a-half mark for Darwin on his voyage (and by association, for me on the Beagle Project). Just about a third of the way through… 🙂 (RJV)

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