Which is to say, expect me to get back to my regular blogging schedule soon.

Now, medieval bestiaries were written by monks, who very rarely got into the fresh air, and while they might have been fairly familiar with the habits of common barnyard dogs and cats, they had to take a little license and a lot of faith when describing animals they had never seen; like crocodiles, elephants and giraffes. Understandably, they didn’t always get things right: while we might, today, associate the giraffe with the fabulous camelopard, it’s a far cry from its description today, and no one has yet found a living unicorn or (my personal favorite) bonnacon.

That being said, sometimes natural history has a way of sneaking back on you and asserting itself in the strangest of medieval legends. Take the following passage from Isidore of Seville (my very rough translation follows, and better classicists than me are invited to tell me that I have failed).

Amphisbaena dicta, eo quod duo capita habeat, unum in loco suo, alterum in cauda, currens ex utroque capite, tractu corporis circulato. Haec sola serpentium frigori se committit [...] Cuius oculi lucent veluti lucernae.

Etymologies, Book 12

It is said of the Amphisbaena that it is a serpent with two heads, one in its proper place, the other on the tail. It can run in the direction of either head, moving its body in a circular motion. This is the only snake able to live in the cold. His eyes shine like lamps.

Like I said, I’m no classicist, and the translation is a pretty rough one. (I know enough to get the gist of a text, not enough to stake my life on knowing what it says.) But, what’s interesting is that there’s a real-life beast called an amphisbaenian, named after the mythological monster.

The Amphisbaena, courtesy of bestiary.ca

And while they don’t look exactly like their medieval counterparts, they are more similar than you might think. We’re going to take a look at one particularly unique member of the group. So, by all means, read on to find out more.

Most amphisbaenians are limbless and earthworm-shaped. They burrow into the sediment using their modified skulls as a combined shovel and jackhammer, smashing through dirt in search of tasty little invertebrates. Most are tiny, and if you weren’t looking closely, you might dismiss them as tiny worms, instead of the reptiles that they truly are. Because of their incredibly weird, derived skull morphology and elongated body shape, they used to be considered a totally separate order of reptiles, only distantly related to snakes and lizards. But, like the snakes, their classification has recently undergone an update, and it is now thought that their closest relatives are the lacertillians, or true lizards (all of this work is based on DNA, and not on their bizarrely derived morphology).

So, what could these beasts, who are almost entirely confined to the tropics have in common with a two-headed serpent of medieval mythology? To illustrate that, I’d like to introduce you to a unique member of the Amphisbaenian group, the ajolote, also known as Bipes. Here’s a close-up of his cute little face … along with a unique anatomical feature that separates him out from the rest of the world’s legless lizards.

Bipes, photo by G. Nafis (californiaherps.com)

Waitaminute. I know, I know. I told you that amphisbaenians were legless, and, yet, that little lizard clearly has two pairs of well-developed, if stubby legs, complete with toes, claws and some pretty hefty musculature. It doesn’t look much like a worm-lizard to you …

That’s because Bipes is the world’s only amphisbaenian with functional legs. Those legs aren’t some evolutionary relic, like the cloacal spurs of pythons or the flaps on pygopodids (remember Lialis?) — they serve a very important function in the amphisbaenian’s day-to-day life. Because, unlike other amphisbaenians, Bipes uses these little legs, not his head, to dig through the soil of his Mexican and Californian habitat. Beyond that, it’s not even the most primitive member of the amphisbaenian group; instead its evolutionary relationships suggest that Amphisbaenians lost their legs on more than one occasion, as a convergent adaptation to their soil-swimming lifestyle. This may make them a very good candidate for examining the developmental processes that lead to limb loss, since most of the developmental work that’s been done on the subject to date involves snakes, which have undergone a remarkable genetic shift that completely eliminates their pectoral girdle and front legs. Understanding amphisbaenian limb reduction is probably a better way to understand the general rules governing limb shortening, digit reduction and limb loss, since their repeated re-evolution of the character provides a good experimental background (unfortunately, the little guys are a pain in the butt to breed in a laboratory).

Bipes: the leggy earthworm (G. Nafis, californiaherps.com)

This unique mode of locomotion, as the only leggy member of an almost entirely legless clade would earn it a place on our remarkable reptiles list, but it has more interesting stories to tell. But, the other reason it’s earned a place on my list is that the medieval legends are true … sort-of. Amphisbaenians don’t have two heads, although their tail and head do look remarkably similar, but they can crawl backwards in their tunnels just as easily as they go forwards. Sometimes, mythology gets things surprisingly right.

The sensory systems of amphisbaenians are also unique. While they can make sounds (a youtube video can be found here) , they have no external ears, but have a remarkably complex internal ear that has much better auditory sensitivity than that found in snakes. While the ear is primarily attuned to low-frequency sounds, it has a pretty good range into higher frequencies. Unfortunately, though, they don’t have luminously shining eyes. In fact, most amphisbaenians are practically blind: their skin-covered eyes can sense dark and light, but probably can’t form images. Nevertheless, when they are exposed to dark or light only for prolonged periods of time, their retinas degenerate even further, and they can be left totally blind (so if you decide to keep one as a pet, make sure it has a regular day/night cycle).

And to tie things back to mythology … apparently in Baja California, there is a legend that you have to be careful where you sit; otherwise an adventurous amphisbaenian might just mistake your unsavory bits for its own tunnel …

Tomorrow we’ll tackle another burrower. But unlike the amphisbaenian, tomorrow’s really does live up to its frightful legend.

Relevant Papers:

Photoreceptor degeneration in the eyes of an amphisbaenian in response to constant light or constant darkness
G.C. Gundy, Journal of Experimental Zoology, August 1977

The Ear and Hearing in Bipes biporus
Ernest Wever and Carl Gans, Proceedings of the National Academy of Sciences, September 1972

Phylogenetic relationships among amphisbaenian reptiles based on complete mitochondrial genomic sequence
J.R. Macey et al., Molecular Phylogenetics and Evolution, October 2004

Appendicular Skeleton in Amphisbaenians (Reptilia: Squamata)
Maureen Kearney, Copeia, August 2002

Well, I wish it were. With all the news of piracy that’s been cropping up lately in the news; I can’t help but be worried. And now, a recent CNN article has stated that the company for which she will be working, Hapag-Lloyd, has started to fly cruise ship passengers across the Gulf of Aden because of the risk from piracy. Nothing could be scarier to me. After all, as part of the working crew on a  container ship, she won’t have the option to just fly her way out of Somali waters. My worry is probably needless, and if she ever reads this post, she’ll roll my eyes at my needless concern, but, still, it’s scary to think that events a world away could so thoroughly rip into my own life.

Okay, enough moping. I’ll blog reptiles later, but right now, it’s off to class.

Fear not, I won’t let you down today.

Well, not unless my paper on Christine de Pizan gets totally out of hand.

Crocodiles really are my favorite animals. People will tell you that they’re living fossils and that they have remained unchanged since the Jurassic, and while that’s sort-of true in that there’s a generalized ‘croc-shape’ that crocodiles tend to fall back on (and there certainly aren’t as many around as there used to be), it ignores the incredible fossil diversity of crocodiles through time. There are crocodiles that became terrestrial herbivores and crocodiles that took to an exclusively marine life and crocodiles that evolved mammal-life teeth and crocodiles that grew to forty feet. The ancestors of crocodiles were lithe, upright little predators with long legs who lived only on land, while the more typical crocodilian niche was occupied by their close-relatives: phytosaurs … which looked pretty much like a modern croc, except that they had their nostrils between their eyes.

See, look, I knew I would digress. The point is that crocodilian diversity is amazing, and even if they aren’t as diverse as they once were, their current diversity is amazing: from the five-foot long dwarf caiman of South America to Nile Crocodiles who live in marginal environments on the edge of the Sahara and their fossil diversity is beyond incredible. Their closest living relatives are birds, and, depending on who you ask, they might be very closely related to turtles. They differ from birds, though, in the morphology of their ankle — while bird ankle joints allow for a very limited front-back flexion, crocodile ankles, like yours, can rotate. This has some pretty interesting implications for their gait: basically it allows them to adopt a variety of different walking stances — they can walk upright like a mammal, sprawl like a lizard and can even gallop. The crocodilian biology database has a really fantastic page with videos of all the exciting forms of croc locomotion.

Nile Crocodile, Crocodylus niloticus

Look, I’m digressing again. At this rate, we’ll never get to my remarkable crocodilian. Why don’t you just read on to find out what he is, before I get completely distracted.The most remarkable crocodilian in the world, hands-down, no-holds barred, is, of course, the Indian Gharial, Gavialis gangeticus. At a first glace, that might be hard to see. After all, one crocodilian is pretty much like another, and even the most remarkable feature of the gharial, its extraordinarily long snout, has been duplicated (although to not quite the enormous degree seen in Gavialis) in other members of the crocodilian group, like in these beautiful African Sharp-Snouted crocodiles (Mecistops cataphractus)

Mecistops cataphractus

But gharials actually rearrange the bones in their skull to allow for their thin-snouted morphology, and their nasal bones never touch their external nostrils. This is just one of hundreds of unique features found in their skull and braincase; and all of these features have traditionally been held up as solid evidence that gharials are the most primitive of all of the living crocodiles: closer to fossil forms than to anything living today.

Who're you callin' primitive?

Of course, the real story turns out to be much more complex than that. Because looking at anatomy isn’t the only way that we can trace an animal’s ancestry: we can also look at it’s DNA, to determine how closely it matches the DNA of other species. The more similar your DNA is to another species, the more closely you’re related to it …

That’s the theory, at least. There are all sorts of practical problems with applying the theory, of course, because DNA mutates, and random mutations can start to build up awfully similar patterns, without any degree of relationship at all. There are problems in groups that diverged long ago, especially if you’re also including groups with relatively recent divergence dates in the mix. No analysis is perfect, and, it’s here that the story of Gavialis gets complicated. Because, looking at the bones of the animal, no self-respecting morphologist would tell you that the gharial is closely related to another long-snouted crocodilian: the false gharial, Tomistoma schlegelii, from Southeast Asia. Tomistoma has a pretty standard crocodile’s skull, and is most closely related to all of the other true crocodiles: things like nile crocs, and sharp-snouted crocs and dwarf crocodiles. This isn’t surprising, since the group occurs around the world, and has often evolved a long-snouted form. Its bones certainly look nothing like those of the primitive-appearing gharial.

Tomistoma, the false gharial

So what do the molecules say? Well, against the wildest expectations of … anyone on the planet, really, Gavialis turns out to be most closely related to the false gahrial. The closest cousin of the true gharial, is, in fact, the false. Or, at least, that’s what the molecules say. As time has progressed, the case for the DNA signal being better than the morphological signal has definitely strengthened, and the chances of simple convergence between the genes of these two species of crocodiles are next to zero. But the debate is far from over, and the question of why gavials are so primitive in appearance is still  completely unresolved.

My current work is attempting to look at the growth and development of gharials, compared to other crocodiles, to determine whether or not they have a unique developmental path that might explain some of their weirdness. Since it’s unpublished, I probably can’t let you in on my secrets, but let’s just say that I’m finding some incredibly interesting results…

Of course, you wouldn’t expect that gharials would evolve such a remarkable anatomy if they were just doing the same thing as their crocodilian counterparts. And, of course, they aren’t. They are extremely specialized fish-eaters, and even though they are the second-largest crocodilian in the world (Saltwater crocodiles, unsurprisingly, take a terrifying first place), they pose almost no danger to humans (the exception, of course, as in all crocodiles, involves females guarding their nests or young). Unlike all other crocodiles, gharials cannot raise their body to high walk — they must slide on their belly when they are on land, but, in the water, they are extremely graceful swimmers. Even the snapping jaw motion that they use to catch fish is unique in the crocodilian world. The males are sexually dimorphic from females, and breeding males will form a large, bulbous structure on the ends of their souts in order to show dominance and court the ladies. It might be that this unique structure is the reason that these reptiles are associated with Indian fertility gods…

The ghara of a breeding male

Unfortunately, though, as with all crocodilians, the gharials have a sad story to tell. Both the true and false gharials are highly endangered, threatened by habitat loss, especially, but with lesser threats from poaching and water pollution. There are only about two hundred breeding pairs of gharial left in the wild: that’s a pretty scary number; the ICUN lists gharials as critically endangered. Crocodiles have survived for millions of years on earth, and have always come out as survivors — even at their current levels of diversity, they show remarkable adaptations to a huge variety of habitats and ways of life, from the sea-faring salt-water crocodile to the unique gem that is Gavialis. Crocodilian conservation, unsurprisingly, is one of my big passions.

Please visit the Tomistoma Task Force and Gharial Conservation Alliance to find out more. If conservation  isn’t enough to motivate you, I will point out that the GCA has the world’s most adorable gallery of little kids’ pictures of crocodiles.

And I know that after a two-day hiatus, you must be itching for some butt-kicking reptilian action. That’s good, because I have not one but two surprises planned for you … tomorrow’s post, and a new blog page, which might be up as early as tonight!

Relevant Papers:

The rapid accumulation of consistent molecular support for intergeneric crocodylian relationships
John Gatesey and George Amato, Molecular Phylogenetics and Evolution, February 2008

(Want more? Just ask … I just figured I’d put up a recent review and leave it at that, since I have every paper ever published on gharials … or so it seems.)

And so, today’s post starts with a reminder that snakes aren’t the only lizards that have lost their legs. In fact, leg loss seems to be a common thing in lizards, from the very primitive to the derived. From amphisbaenians to blind lizards to skinks, legless lizards come in all shapes, sizes and phylogenetic contexts. Really, it’s pretty amazing that this trait has evolved so many times over so many groups. It’s a trait that, in legless lizards, at least, seems to have evolved in conjunction with a burrowing lifestyle, although there’s still some pretty heated scientific controversy over whether the earliest snakes lost their limbs in order to become better swimmers or better burrowers (although the developmental and genetic context for that loss is actually pretty well understood; ask me about that sometime).

Ophisaurus apodus, the scheltopusik

The lizard above is one of my favorite legless lizards, and it’s a pretty good representative of what a standard-issue legless lizard looks like. He has eyelids and ear openings, unlike a snake, and is a substrate-burrowing insect-eater. (I have to admit, though, his scientific name does tickle my fancy: it literally translates to ‘snake-lizard without legs.’) So, if this boy is ordinary what kind of a legless monster would earn his place on my countdown? Read on to find out about a different kind of legless lizard…

At a first glance, Pygopodids might seem just like any other legless lizard. A typical member of the clade, Pygopus, looks like this.

Pygopus lepidopodus

In this photo, you can see his pretty little ears right next to his head; pygopodids also have cute little hind-leg flaps which are functionally pretty useless, but lead to their common name of flap-legged lizards. They do have some pretty cute behaviors though, which hint at their evolutionary relationships.

Pygopus licking its eyes

Instead of blinking, pygopodids lick their eyes. This feature is incredibly common in the geckos, and, in fact, pygopodids are just incredibly derived gecko lizards — their closest relatives seem to be cryptic, tree-dwelling leaf-tailed geckos and chameleon geckos, from which they differ pretty remarkably in general morphology and habitat. Still, the vast majority of pygopodids aren’t all that remarkable for legless lizards, they’re insect-eaters with a fairly conserved skull and live in pretty limited habitats. But there is one legless lizard that breaks all the rules, and shows some pretty remarkable morphology. Meet Lialis.

Lialis burtoni

Lialis eats only lizards, even in captivity they can usually only be coaxed to feed on whole lizards, instead of mice, and unlike other legless lizards, Lialis does not take invertebrate prey. It captures and swallows its prey whole, and in its dietary ecology it is much, much closer to that of a small snake than it is to a legless lizard. And this switch in diet from small invertebrate to large vertebrate prey has produced a shift in the very structure of its skull: like snakes, Lialis has a highly kinetic skull, which means that the bones of the skull allow for an enormous degree of flexibility and movement. Lialis can open its mouth to a wider degree than any other lizard, except snakes, and while it doesn’t eat exactly like a snake (unlike snakes, the tongue plays a huge role in prey capture and swallowing; in snakes, it’s the teeth and skeletal elements that do all the work), it’s still a pretty remarkable case of convergent evolution and might shed some light on how primitive burrowing snakes evolved into the deadly diversity that we see today.

Skull of Lialis, image from Digimorph

Now you’ve got to admit that that’s pretty cool. But tomorrow’s reptile is even better, well, in my opinion, but I may be biased, since it’s one that is very near and dear to my heart. I’ll bet that you can even guess what it is…

Relevant papers:

Phylogenetic relationships among gekkotan lizards inferred from Cmos nuclear DNA sequences and a new classification of the Gekkota
Demin Han et al., Biological Journal of the Linnaean Society, November 2004

Feeding mechanisms in pygopodid lizards: how can Lialis swallow such large prey?
Frederick Patchell and Richard Shine, Journal of Herpetology, March 1986

So, what do you get if you cross a cobra with a colugo?

The answer, of course, is today’s featured reptile. Read on to find out …

The flying lizard, Draco is one of the most remarkable lizards in the world. It’s an agamid from the jungles of southeast Asia, and if you saw this lizard scampering in the branches and on tree trunks or flashing its dewlap in a territorial display, you might not think anything of it. That is, until you went to catch it, when a remarkable wing-like structure would unfold from the side of the lizard’s body, and the lizard would jump and then glide for perhaps hundreds of feet, coming to land a very safe distance away from your predatory intentions.

Draco volans with wings folded out

Okay, okay, I know what you’re thinking. Gliding isn’t really all that uncommon, not even among reptiles. There is a flying snake, a flying frog, flying geckos, flying squirrels, even a flying lemur out there. The ability to glide as a means of getting from one place to another has arisen multiple times in the animal kingdom, and while it’s certainly an interesting ability, it’s probably not enough to land an animal in the top ten category of remarkable diversity.

Well, that’s why I crossed my colugo with a cobra, you see. (To be fair, though, if I ever did a top ten in mammal diversity, I would definitely throw a colugo in.)

Because it isn’t just the fact that Draco flies that makes it amazing. It’s how Draco forms the membrane that keeps it aloft (known more formally as the patagium): and that mechanism is one of the most remarkable in the animal kingdom. Most gliding animals form their gliding structures with flaps of skin that either hang loose and unfurl under high air pressure, or are supported between struts of bone – for example, the patagium of a flying squirrel is formed by extending a flap of skin from the arm to the leg: when a flying squirrel spreads its arms, it creates a parachute that turns a free-fall into a glide. Flying frogs use their unusually large webbed toes to descend, and flying geckos use flaps on their toes, tails and side to create an effective parachute.

So, what does Draco use to create a gliding membrane?

The answer is, to me at least, completely astounding: ribs. That’s right, ribs. The same bones which, in you, create a nice, safe little nest for your heart and lungs, in Draco, have decided to forgo their normal function as body wall supports, and instead grow into that patagium, where specialized muscles can extend and retract them to create an airfoil. Now, this isn’t quite as absurd as the things some other reptiles do with their ribs – a similar system of flexible, modified ribs occurs in the hood of a cobra, where they are extended to create the hood’s iconic, flattened surface, and you’ll have to wait a few days to find out about what I think is probably the weirdest rib modification in the entire animal kingdom, but it’s nevertheless an extraordinary testament to the wonderful diversity of reptiles and the absolute weirdness of evolution that the structure was co-opted for such a unique purpose.

The following picture shows the undersides of Draco pretty well, where you can see the thin struts of the ribs, which push out to form the gliding surface.

Draco volans, preserved specimens

Now, I could talk about how the tradeoff between pregnancy and flight has changed the morphology of females, or how gliding impacts agamid social behavior, but it’s late, and I need to get up early tomorrow. So, I’ll compromise by sending you over to a fabulous Animal Planet clip of Draco which fabulously illustrates this adaptation and the lizard’s real-life gliding behavior.

I’ve just blogged an animal that flies with its ribcage. If you aren’t starting to agree with me that reptilian diversity is marvelous and fascinating, there’s probably no hope for you. But maybe tomorrow’s critter will change your mind. And, whoops, this officially thirty-five minutes late. Sorry about that. You may now flog me.

Relevant Papers:

Patagial morphology of Draco volans (Reptilia: Agamidae) and the origin of glissant locomotion in flying dragons
Anthony P. Russel and Luke D. Dijkstra, Journal of Zoology, April 2001