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Tetrapod Zoology

Tetrapod Zoology

Amphibians, reptiles, birds and mammals - living and extinct

Australia, land of dragons (part II)

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Highly simplified cladogram of the amphibolurine clade that includes Pogona, Ctenophorus and kin, based mostly on the tree in Pyron et al. (2013). Images by Adam Yates (Gowidon), Tony Gamble (Pogona), and Stephen Zozaya (the remainder), used with permission.

Time for more Australian agamids, or amphibolurines, or dragons, whichever you prefer. Last time round, we looked at the water dragons, Moloch and a few other taxa, meaning that ‘all’ that’s left to get through is… the remainder. And there are quite a few of them: bearded dragons, earless dragons, bicycle dragons (yes, really) and so on.

We start with the numerous Ctenophorus species, sometimes termed comb-bearing dragons (for their vaguely comb-like dorsal frills*) or military dragons. This group of mostly terrestrial lizards includes almost 30 small-scaled, long-tailed species that generally have a row of enlarged scales running from below the eye to above the ear and sometimes have the tympanum covered by small scales. There are rock-dwelling and sand-dwelling specialists within the group; some of the latter sprint across (relatively) long distances when threatened and are among the most gracile and fastest-running of Australian lizards. Some species sprint bipedally (Clemente et al. 2008), the crazy-looking rotations of their hindlimbs earning them the popular moniker ‘bicycle-dragon’. And there are those that hide in burrows, those that hide under rocks, and those that hide in vegetation. Phylogenetic studies indicate that each of these lifestyle differences have evolved, independently, at least twice.

* Thanks to Christian Kammerer for confirming that point.

Ring-tailed dragon (Ctenophorus caudicinctus), a swift-running saxicolous dragon, conventionally split into more than five subspecies. Image (c) Stephen Zozaya, used with permission.

As with several amphibolurine genera, the number of recognised species within Ctenophorus has increased notably in the last few decades. At the time of writing, the newest is the Barrier Range dragon C. mirrityana from New South Wales, named late in 2013. Another recently named one, C. nguyarna Doughty et al., 2007 from Lake Disappointment in Western Australia, is a specialist denizen of salt lake habitat, as is the Lake Eyre dragon C. maculosus of South Australia.

Montage showing some of the diversity within Ctenophorus. From top: the tiny dune specialist C. femoralis, the splendidly marked Military dragon (C. isolepis), and a gravid Central netted dragon (C. nuchalis). Images (c) Stephen Zozaya, used with permission.

Like some other amphibolurines (those included within the problematic taxon Lophognathus), an erectile dorsal crest is present in some species. Prominent lateral and/or ventral markings and brightly coloured throats are present in many species (most usually in the males alone): some are boldly patterned and really attractive. There has been substantial interest in sexual selection and sociosexual behaviour in these lizards: in some, the males are territorial and are highly aggressive in their treatment of females. This is best known in the Lake Eyre dragon, a species in which females will even flip onto their backs in order to avoid forced copulation.

Members of the group are also unusual in lacking a phalanx from the fifth toe (a feature also seen in Moloch and some Tympanocryptis species). Some of the smaller species only produce two eggs per clutch – a massive contrast to the relatively huge clutches produced by some other amphibolurines (up to 35 in Pogona) and a reminder of how variable clutch size can be within a clade. Also remarkable is how short-lived some of them are: they are apparently ‘annuals’ that are sexually mature by 10 months of age, and rarely survive into their second year. This is true for small species as well as for the relatively large Central netted dragon C. nuchalis.

The beautiful Central netted dragon (Ctenophorus nuchalis), a short-snouted, widespread dragon with a fine, dark brown reticulated pattern. Image (c) Stephen Zozaya, used with permission.

Some studies find the Ctenophorus dragons to form a clade, and to be the sister-taxon to the amphibolurine clade that includes Lophognathus, Chlamydosaurus, Diporiphora and so on (Pyron et al. 2013). Some molecular work indicates that Rankinia – the heath dragons – is nested within Ctenophorus (Melville et al. 2001, Clemente et al. 2008), a discovery that has led to the idea that the name should be dropped from use. However, Melville et al. (2011) found Rankinia to be well away from Ctenophorus, and close to Diporiphora.

Those graceful diporiphorans

The relationships between the remaining amphibolurines vary quite a bit from one study to the next. Tympanocryptis (earless dragons), Pogona (bearded dragons) and Diporiphora all seem to be close relatives (Macey et al. 2000, Hugall et al. 2008, Melville et al. 2011, Pyron et al. 2013) but the exact nature of their relationship is controversial as is the monophyly of several of these genera. Caimanops amphibolurodes – the Mulga dragon, the only member of its genus – was recently returned to synonymy with Diporiphora by Doughty et al. (2012) since it’s surrounded by Diporiphora species in phylogenetic trees. Doughty et al. (2012) also re-synonymised the Wells and Wellington names Mantichosaurus and Houstoniasaurus with Diporiphora.

Two-lined dragon (Diporiphora bilineata), a climbing species of northern Australia (and perhaps New Guinea); image (c) Stephen Zozaya, used with permission.

Three more diporiphoran dragons. From top: Diporiphora nobbi, D. phaeospinosa, and D. vescus. Images (c) Stephen Zozaya, used with permission.

A recent molecular study of the Diporiphora dragons indicated that most divergences within this group occurred during the Late Miocene (Edwards & Melville 2011). This discovery suggests that their diversification was linked to the climatic changes that occurred at this time – their adaptation to dry woodlands and similar habitats in particular being driven by these events. Given how insanely gracile and long-tailed some Diporiphora dragons are, it’s kinda pleasing to imagine them as stretched out, highly modified versions of the more terrestrial, stout-bodied ‘core’ amphibolurines like Pogona. Diporiphora dragons frequently climb in tussocks, shrubs and slender-branched trees.

Several of the Diporiphora species, including the semi-arboreal, green D. superba of the Kimberley region (named as recently as 1974) and the reddish-brown D. valens (named in 1979), have tails that are 300-400% SVL*. Incidentally, having noticed how recently named those two species are, it’s worth saying that most Diporiphora dragons are recently named. Check this out: D. convergens Storr, 1974, D. lalliae Storr, 1974, D. linga Houston, 1977, D. magna Storr, 1974, D. pindan Storr, 1979 and D. reginae Glauert, 1959, D. phaeospinosa Edwards & Melville, 2011, D. vescus Doughty et al., 2012, D. adductus Doughty et al., 2012 and D. paraconvergens Doughty et al., 2012. Diporiphora dragons – I’ve taken to calling them diporiphorans, since there doesn’t seem to be a handy, vernacular term in widespread use – are widely distributed across Australia (except the south-east) and one species inhabits New Guinea.

* snout to vent length.

The bearded dragons

Dwarf bearded dragon (Pogona minor), a semi-arboreal Pogona that lacks many of the spines present in other Pogona species. Image (c) Stephen Zozaya, used with permission.

Bearded dragons (Pogona) are terrestrial and semi-arboreal amphibolurines that have a somewhat compressed body and a proportionally short tail with laterally projecting spines on either side of the base. Bearded dragons owe their name to an expandable throat pouch, or ‘beard’, covered on all sides with erectile spines. This structure is erected as the long, curved first and second ceratohyal bones are pulled downwards and outwards by the attached anterior mandibular muscles. Within the group, P. barbata has an especially specialised hyoid mechanism, the second ceratohyal having a modified, simplified form relative to that of other Pogona species (Throckmorton et al. 1985). Like most amphibolurines, bearded dragons are predominantly insectivorous but some species (like P. barbata) eat flowers, soft leaves and fruit on occasion.

How ceratohyal depression and spreading causes expansion of Pogona's 'beard'. Series of illustrations from Throckmorton et al. (1985).

About eight species are recognised, the most familiar of which is of course the Central bearded dragon P. vitticeps, well known thanks to the pet trade. The majority of pet Central bearded dragons are of the standard ‘wild type’, but it’s becoming increasingly well known that people have created several remarkable forms through selective breeding: there are now giant bearded dragons, forms with reduced or smooth scalation termed leatherbacks and silkbacks, ‘translucent’ form with reduced pigmentation, ‘Witblits’ forms that essentially lack all patterning, the also patternless ‘silverbacks’ , and numerous colour morphs. We have created domesticated lizards that do not exist in nature.

The 7th edition is here... the 6th edition is 14 years old now, so much has changed.

Ok: in this and the previous article I’ve discussed most of Australian dragon diversity… but not all of it. There are still lineages that I didn’t cover (Amphibolurus in particular), and numerous species I didn’t even mention. So, there’s loads more to do. Oh well, maybe next time. And – while I’m here…. who else is excited about the impending publication of the Seventh Edition of Cogger’s Reptiles and Amphibians of Australia?

Thanks again to Adam Yates (who blogs at A Fragment of Gondwana), Tony Gamble and especially Stephen Zozaya (who blogs at Saurian Obsessions) for their help in providing images.

For previous Tet Zoo articles on agamids and other iguanian lizards, see…

Refs - -

Clemente, C. J., Withers, P. C., Thompson, G. & Lloyd, D. 2008. Why go bipedal? Locomotion and morphology in Australian agamid lizards. The Journal of Experimental Biology 211, 2058-2065.

Doughty, P., Kealley, L. & Melville, J. 2012. Taxonomic assessment of Diporiphora (Reptilia: Agamidae) dragon lizards from the western arid zone of Australia. Zootaxa 3518, 1-24.

Edwards, D. L. & Melville, J. 2011. Extensive phylogeographic and morphological diversity in Diporiphora nobbi (Agamidae) leads to a taxonomic review and a new species description. Journal of Herpetology 45, 530-546.

Hugall, A. F., Foster, R., Hutchinson, M. & Lee, M. S. Y. 2008. Phylogeny of Australasian agamid lizards based on nuclear and mitochondrial genes: implications for morphological evolution and biogeography. Biological Journal of the Linnean Society 93, 343-358.

Macey, J. R., Schulte, J. A., Larson, A., Ananjeva, N. B., Wang, Y., Pethiyagoda, R., Rastegar-Pouyani, N. & Papenfuss, T. J. 2000. Evaluating trans-Tethyan migration: an example using acrodont lizard phylogenetics. Systematic Biology 49, 233-256.

Melville, J., Schulte, I. & Larson, A. 2001. A molecular phylogenetic study of ecological diversification in the Australian lizard genus Ctenophorus. Journal of Experimental Zoology 291, 339-353.

Pyron, R. A., Burbrink, F. T. & Wiens, J. J. 2013. A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes. BMC Evolutionary Biology 2013, 13:93 doi:10.1186/1471-2148-13-93

Throckmorton, G. S., Bavay, J. D., Chaffey, W., Merrotsy, B., Noske, S. & Noske, R. 1985. The mechanism of frill erection in the bearded dragon Amphibolurus barbatus with comments on the jacky lizard Amphibolurus muricatus (Agamidae). Journal of Morphology 183, 285-292.

The views expressed are those of the author and are not necessarily those of Scientific American.

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