28 March 2013

A short tale about a very short tail

As I’ve mentioned before, scientists are so conservative that when you see an adjective like “extraordinary” in the title, you should at least open up the paper if you can and have a peek.

I came across a paper titled, “An extraordinary tail – integrative review of the agamid genus Xenagama” in Google Reader *. I was a bit curious (and miffed) because I had no idea from the title what kind of organism this paper would be about. All kinds of animals have tails.

I love me spikes and spines and armor on critters, so I flipped out a bit when I learned this belonged to the Xenagama:

That is indeed an cool looking lizard (Xenagama taylori) with a cool looking tail. The genus Xenagama originally contained two species that was defined by this short, club-like, spiky tail. But there’s a problem when you use a single extraordinary feature to classify animals: you might overlook all the other features that tie it to other relatives.

A new paper Wagner and colleagues uses a lot of different tricks to tease apart the evolutionary relationships of the lizards in this genus: morphology, genetics, climate, and so on.

By looking at all the morphology, and not just the tails, they found that a long-tailed lizard previously put in another genus (Acanthocercus zonurus; below) sorts out with Xenagama and not Acanthocercus. Genetic analysis on this species also put it in with the rest of the Xenagama group, although it’s an early offshoot from the tree of these related lizards.

The authors also discovered a new species in the genus, that, like Acanthocercus zonurus, has a reasonably long tail; sort of intermediate between the short known species and the misidentified one. This new species is dubbed Xenagama wilmsi.

It turns out that the short tail of most of the lizards in this genus was something that was obscuring some of the relationships. There were similar problems with data on breeding colours. Some of the males in this group show different colours, which was used in creating their classifications, but the males don’t show those breeding colours all year round.

All of which doesn’t answer the obvious question: why do some of these lizards have these short tails? The tails do seem to have an adaptive function. The two species with long tails seem to be tree dwellers, while the two short-tailed species are rock-dwelling burrowers. Xenagama taylori will use its short spiked tail to close its burrow, which you can see in action below:

Xenagama taylori

How this tail has been molded through development and genetic to get so short would be a great doctorate for someone. While native to northern Africa, some of these lizards seem to be fairly available in the pet trade. Don’t know how easily these lizards would be to breed in captivity, though.

Update, 29 March 2013: When readers think of better titles than me: Malcolm Campbell dubbed this article, “Get shorty.” Brilliant!

* You know, that allegedly useless service that absolutely nobody needs because all of the people on Twitter and social media are so good at finding stuff that I want to read, yet who somehow let me down on discovering this.


Wagner P, Mazuch T, Bauer AM. 2013. An extraordinary tail - integrative review of the agamid genus Xenagama. Journal of Zoological Systematics and Evolutionary Research: in press. DOI:

Top photo from here; Acanthocercus zonurus from here.

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