Worm Salad


Remarkable Reptile #7
December 4, 2008, 9:02 pm
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I will admit that I am a sucker for snakes. They’re fascinating, they’re venomous (at least some), they’re beautiful, they’re diverse, they’ve invaded a huge variety of habitats and occupy a surprisingly large niche space, they have a great mythological association; basically, snakes are pretty darned cool animals, and they managed this huge extent of awesome all without legs. I actually gave a presentation in my evolutionary developmental biology class yesterday on how snakes lost their legs, and while I might blog that later, this post is yet another entry in my remarkable reptiles countdown.

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 by brian.gratwicke on flickr

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 by teejaybee on flickr, CC licensed

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, teejaybee, flickr, CC

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 by myrmician on flickr, CC licensed

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

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

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