This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Today: LIZARDS. Even better: obscure Australian agamids, or dragon lizards, or dragons, if you prefer. I’ve written about agamids a few times on Tet Zoo but have never gotten to say much (if anything) about the Australian radiation, grouped together into the clade Amphibolurinae.
In this article, I won’t – I’m very sorry to say – be providing a grand tour of this remarkable and fascinating radiation but, instead, will merely talk about but one of the many species: the endangered and poorly known Grassland earless dragon Tympanocryptis pinguicolla, long misinterpreted as a subspecies of a supposedly well-known, widely distributed species but now rightfully recognised as a taxonomically distinct grassland specialist associated with arthropod burrows. Or... is that – a complex of species of distinct grassland specialists associated with arthropod burrows?
T. pinguicolla was originally named as a subspecies of the White-streaked earless dragon T. lineata back in 1948 (Mitchell 1948). This is the widespread, longitudinally striped dragon that’s supposed to occur throughout the Australian interior. However, a study of morphological and allozyme variation across earless dragons found pinguicolla to be consistently distinct from the rest of T. lineata as well as from other earless dragon taxa: it is not part of T. lineata but warrants distinction as a separate species (Smith et al. 1999).
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Temperate-grassland, arthropod-burrow-dwelling specialist
All of the eight or so Tympanocryptis dragons are predominantly terrestrial. As you might guess from the generic name, their tympanic region is obscured by scaly skin. Does this mean that they’re completely deaf? I don’t know. Other obvious anatomical features include raised, spiny dorsal scales and a shortened fifth toe formed from three phalanges as opposed to four (Cogger 2000).
Grassland earless dragons inhabit fragile temperate grasslands in south-eastern Australia. They are highly cryptic, taking refuge in grass tussocks but also in burrows made by wolf spiders and crickets (these lizards are small: less than 15 cm in total, and just 7-9 cm SVL). In fact, individuals have sometimes been found sharing active burrows with Lycosa spiders – I don’t know if the nature of this relationship has been studied, but it would be fascinating to know more about it. Do the spiders simply tolerate the lizards, is there a mutualistic relationship of some sort, or is aggression and mortal danger involved? Very little is known about reproductive behaviour in this lizard – apparently only two egg clutches have ever been found. One was deposited under stones and soil in a shallow scrape; the second one was disturbed before the nest form was observed; the eggs were later incubated in a laboratory (DoE 2014).
Grassland loss, degradation and fragmentation seem to be the main threats to this lizard: something like 95% of its habitat has been lost in recent decades and there are concerns that loss of key vegetation to rabbits and the destruction of arthropod burrows due to soil disturbance are major continuing threats to the integrity of its populations (DoE 2014). It seems to be one of Australia’s most endangered lizards.
Are we really dealing with one species here? Err…
Three distinct modern populations are known: the two Canberra and Cooma populations in eastern New South Wales and the Darling Downs population of south-eastern Queenland, discovered in 2001. Grassland earless dragons certainly occurred in Victoria as well until recently – five sightings were reported there between 1988 and 1990 – but they haven’t been seen since and are now thought locally extinct.
And here where things are made more complicated, since phylogenetic studies done on these populations don’t find them to group together. The Canberra and Cooma populations are highly divergent in genetic terms, their 5% genetic divergence apparently being ancient and pre-dating habitat fragmentation caused since European settlement (Scott & Keogh 2000). These differences are significant enough that some authors imply that they should eventually warrant recognition as distinct species. A museum specimen of one of the Victorian lizards indicates that this (probably) extinct population was close to, but outside, the clade that includes the Canberra and Cooma populations (Melville et al. 2007)… so, should this be recognised as a species as well?
As for the Darling Downs population, it doesn’t group together with any of the others, instead being genetically closest to another earless dragon species: the Long-tailed earless dragon T. tetraporophora (Melville et al. 2007) [adjacent photo by Joachim Frische]. When it comes to morphology, Darling Downs animals have larger spiny scales than other Grassland earless dragons, proportionally longer hindlimbs, spines along the sides of the body that are lacking in the other populations, and they also differ in head shape and in labial scale counts. In short, a strong case can be made for the idea that the Darling Downs dragons are not conspecific with the other Grassland earless dragon populations: Melville et al. (2007) suggested that the Darling Downs animals have been distinct from the others for at least 5.5 million years, and – pending further work – they suggested that this population be referred to as T. cf. tetraporophora for now, the possibility existing that it’s part of the Long-tailed earless dragon, not a new species. If the Darling Downs dragons are a new species, then an urgent reassessment of their conservation status is needed. If they’re actually conspecific with the Long-tailed earless dragon, things aren’t so urgent, since this species is not regarded as being of conservation concern.
So – what was thought to be a single species (and, pre-1999, a single subspecies of a far more widespread species) now seems to be a complex of perhaps three distinct earless dragon taxa that have been separate since – or before – the Pliocene. I need not remind you that major climatic and palaeoenvironment changes occurred across south-eastern Australia during the Pliocene in particular – it being precisely the time when grassland-dwelling species could get broken up, isolated, and forced to speciate.
If we are looking at a species complex that involves a patchwork of long-distinct, locally distributed, specialised populations – some of which are extinct – a new picture emerges. It used to be thought that Australia’s small mammals – its marsupials and rodents – had not fared too badly in the face of human-caused changed. Alas, this proved woefully naïve: in recent decades it’s been shown that numerous species have been severely affected by human hunting and habitat change, with over 20 extinctions now on record. The story for now is that reptiles have not experienced any extinctions since European settlement but.. are we sure about that? Well, whatever, the persisting Grassland earless dragon populations definitely need our help if they are survive into the future.
Finally, this whole article was made possible by Tony Gamble of the University of Minnesota, who kindly shared the photos you see here. Thanks indeed, Tony. More agamids to come – it all depends on getting the images. For previous Tet Zoo articles on agamids and other iguanian lizards, see…
Harduns and toad-heads; a tale of arenicoly and over-looked convergence
The Squamozoic actually happened (kind of): giant herbivorous lizards in the Paleogene
Refs - -
Cogger, H. G. 2000. Reptiles and Amphibians of Australia. Reed New Holland, Sydney.
Department of the Environment. 2014. Tympanocryptis pinguicolla in Species Profile and Threats Database, Department of the Environment, Canberra. Available from: http://www.environment.gov.au/sprat. Accessed Sat, 4 Jan 2014 06:56:47 +1100.
Melville, J., Goebel, S., Starr, C., Keogh, J. S. & Austin, J. J. 2007. Conservation genetics and species status of an endangered Australian dragon, Tympanocryptis pinguicolla (Reptilia: Agamidae). Conservation Genetics 8, 185-195.
Mitchell, F. J. 1948. A revision of the lacertilian genus Tympanocryptis. Records of the SouthAustralianMuseum 9, 57-86.
Scott, I. A. W. & Keogh, J. S. 2000. Conservation genetics of the endangered grassland earless dragon Tympanocryptis pinguicolla (Reptilia: Agamidae) in Southeastern Australia. Conservation Genetics 1, 357-363.
Smith, W. J. S., Osborne, W. S., Donnellan, S. C. & Cooper, P. D. 1999. The systematic status of earless dragon lizards Tympanocryptis (Reptilia: Agamidae) in south-eastern Australia. Australian Journal of Zoology 47, 551-564.