March 12, 2015

The Atomic Worm-Lizard and Other Aprasia Flapfoots

I'm feeling the urge to blog about lizards. So, today I'd like to talk about the Aprasia species, a group of short-tailed, near-limbless gekkotans that belong to the Australian Pygopodidae family, the so-called flapfoots, flap-footed lizards or pygopods.

By Darren Naish

This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American

I’m feeling the urge to blog about lizards. So, today I’d like to talk about the Aprasia species, a group of short-tailed, near-limbless gekkotans that belong to the Australian Pygopodidae family, the so-called flapfoots, flap-footed lizards or pygopods. Historically, the term Pygopodidae has been used in more than one fashion. For the purposes of removing ambiguity, I’m specifically using it here for the limbless or near-limbless flap-footed lizards alone. About eight genera are presently recognised within this group, of which Aprasia is the most speciose after Delma. Long-time readers might recall the series of articles on these lizards that appeared at ver 2 back in 2011. This article is an extract from that series, though it’s been substantially updated and expanded.

The 13 or so Aprasia species – generally called worm-lizards* – somewhat resemble blindsnakes (Typhlopidae) in overall appearance and, like all pygopodids, have strongly reduced limbs [photo of A. parapulchella above by Matt]. The forelimb is represented only by an internal relictual humerus, and the hindlimb by a splint-like femur. Aprasia species also recall blindsnakes in having a reduced dentition (there are no teeth in the maxillae) and a tail that's only about half as long as the rest of the animal. That last feature is a real contrast to the condition present in other pygopodids, since there are other taxa where the tail can be as much as four times the length of the body.

* But beware... this term is used for all kinds of superficially worm-like squamates (most notably amphisbaenians).

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And on dentition... perhaps the most remarkable anatomical detail pertaining to these lizards is that they have sexually dimorphic teeth: males have teeth in their premaxillae while females (usually) don’t. I have no idea why this condition exists and am not aware of any work that’s been done on it. Sexual dimorphism in tooth form has been reported in a few other squamates, most notably some cobras. [Adjacent photo by Matt.]

The Aprasia species are also typhlopid-like in being binge-feeders (Webb & Shine 1994). That is, they feed infrequently but consume large numbers of prey on the occasions when they do. In snakes, there’s a debate as to what binge-feeding in blindsnakes (and other scolecophidian snakes) might tell us about the early stages of snake feeding behaviour. But back to that idea that Aprasia worm-lizards are blindsnake-like... it should be noted that blindsnakes differ from worm-lizards in being able to inhabit a much broader range of habitat and sediment types and to feed on a far broader diversity of ant species (Maryan et al. 2013). Consequently, blindsnakes have a much broader geographical range than worm-lizards (the latter being endemic to relatively narrow strips of western and southern Australia). Furthermore, for all their similarities, blindsnakes and worm-lizards can live in sympatry. This reminds me of what I said recently about sympatric nuthatches and woodpeckers: if these were imaginary creatures invented for a speculative zoology project, would we think of putting them in the same ecosystem? Probably not.

The Aprasia species are variable in head shape. They aren’t big animals (total length is usually something like 140-150 mm), so head length is usually less than 5 mm. Most have deep, short, rounded snouts, but A. haroldi at least has a more pointed snout and a sloping dorsal outline to its head. A. rostrata has a distinctly overhanging, pointed snout tip [diagram shown here from Kluge (1974). It also has an extra postnasal scale, marked here with an arrow].

A. smithi is unique among Aprasia species in having a black head. Its tail is black too, raising the possibility that this is likely one of those squamates where the tail-tip functions as a ‘head mimic’. One species (A. aurita) differs from the others in possessing a small external ear (Kluge 1974).

Extinction, taxonomic elevation and resurrection of the Atomic worm-lizard

Having mentioned A. rostrata, it’s worth saying that its type locality – Hermite Island off the north-west coast of Western Australia (one of the Montebello Islands) – was the place where the very first British atomic weapons tests were carried out in 1952. In fact, the two type specimens of this species were collected by Frank L. Hill when he was doing a biological survey specifically on behalf of the British military. This fact, combined with the lack of A. rostrata reports made during the 1960s and 70s, led to the idea that A. rostrata – sometimes termed the Atomic worm-lizard (the common name Ningaloo worm-lizard is in more widespread use, alas) – might be extinct.

However, a pygopodid named A. fusca in 1979 (from the Exmouth Gulf region on the Western Australian mainland) was regarded by Cogger (2000) as conspecific with A. rostrata. If this view is followed, A. rostrata is not an island endemic, and is alive and well and living on the mainland. This view hasn’t been universally adopted. Storr et al. (1990) elevated A. fusca back to species status, and Wells (2007) even argued that it was distinct enough for its own ‘genus’, Abilenea. Some of you will know that Richard Wells, the author concerned there, is one of those notorious characters in herpetology who has published a substantial number of new names that have controversial standing within the literature. I previously discussed Wells and his writings in my 2013 article on Raymond Hoser and taxonomic vandalism. And see Kaiser et al. (2013). Anyway, Maryan et al. (2013) have since argued that neither morphological nor molecular data supports distinction of A. fusca from A. rostrata.

Anyway, what about that island population of A. rostrata? Tales of its extinction proved to be somewhat exaggerated, since it was rediscovered on Hermite Island in 2006 (Maryan & Bush 2007). Furthermore, additional populations have since been discovered on nearby Trimouille Island (another of the Montebello Islands) and on Barrow Island to the south. The latter occurrence in particular is surprising since Barrow Island is considered reasonably well sampled in biological terms and yet this species went unrecorded there until the 21st century. But, then, these lizards are cryptic and extremely hard to catch, meaning that “their basic biology is virtually unstudied, therefore any inferences on population size, declines or seasonal trends related to breeding and feeding are purely speculative” (Maryan et al. 2013, p. 161).

In keeping with our relatively scant knowledge of Aprasia worm-lizards, it follows that many species have only been discovered quite recently. Look at this list: A. aurita Kluge, 1974, A. inaurita Kluge, 1974, A. parapulchella Kluge, 1974, A. pseudopulchella Kluge, 1974, A. haroldi Storr, 1978, A. picturata Smith & Henry, 1999, A. clairae Maryan et al., 2013 and A. litorea Maryan et al., 2013. And this isn’t it, since Maryan et al. (2013) noted that additional species have been discovered and are awaiting description.

And much as I’d like to continue, time is up. More obscure lizards to be covered soon. As always, getting pictures of these animals is often really difficult, if not impossible.

Tet Zoo now features some fairly reasonable coverage of squamate diversity, but there is still so much to do.

Dibamids and amphisbaenians

Cambodia: now with dibamids!
Amphisbaenians and the origins of mammals (April 1st article!)
Portraits of amphisbaenians

Gekkotans

Iguanians

Lacertids

The Great Goswell Copse Zootoca
The New Forest Reptile Centre (on Zootoca and Lacerta)
It’s high time you were told about Psammodromus
Tale of the Takydromus
Racerunner lizards of the world unite

Skinks and cordylids

Anguimorphs

Snakes

Refs - -

Cogger, H. G. 2000. Reptiles & Amphibians of Australia (Sixth Edition). New Holland Publishers, Sydney.

Kaiser, H., Crother, B. I., Kelly, C. M. R., Luiselli, L., O’Shea, M., Ota, H., Passos, P. Schleip, W. & Wüster, W. 2013. Best practices: in the 21st Century, taxonomic decisions in herpetology are acceptable only when supported by a body of evidence and published via peer-review. Herpetological Review44, 8-23.

Kluge, A. G. 1974. A taxonomic revision of the lizard family Pygopodidae. Miscellaneous Publications, Museum of Zoology, University of Michigan 147, 1-221

Maryan, B. & Bush, B. 2007. Rediscovery of Aprasia rostrata on the Montebello Islands, Western Australia. Western Australian Naturalist 25, 247-251.

- ., Bush, B. G. & Adams, M. 2013. Morphological and molecular assessment of Aprasia fusca and A. rostrata (Squamata: Pygopodidae), with a description of a new species from the Lake MacLeod region, Western Australia. Records of the Western Australian Museum 28, 144-163.

Storr, G. M., Smith, L. A. & Johnstone, R. E. 1990. Lizards of Western Australia III. Geckos and Pygopods. Western Australian Museum, Perth.

Webb, J. K. & Shine, R. 1994. Feeding habit and reproductive biology of Australian pygopodid lizards of the genus Aprasia. Copeia 1994, 390-398.

Wells, R.W. 2007. Some taxonomic and nomenclatural considerations on the class Reptilia. A review of species in the genus Aprasia GRAY 1839 (Aprasiaidae) including the description of a new genus. Australian Biodiversity Record 6, 1-17.

Whitfield, P. 1983. Reptiles and Amphibians: an Authoritative and Illustrated Guide. Longman, Harlow (UK).