The incredible leaf-tailed geckos (gekkotans part V)

Before I start, allow me to announce that Tet Zoo merchandise is now available! So far, I've only used the Tet Zoo logo for these products, but I might produce additional designs in time.


Anyway... welcome to another article in the Tet Zoo gekkotan series. I really want to get through to the end without too many distractions (like amphiumas, wayward grey whales, manatees, white rhinos, giraffe-necked tortoises), otherwise I might never finish. Look what happened with toads and temnospondyls - so much work left to do! Anyway... by now, the generalities of gekkotan diversity, biology and behaviour will be familiar to you, and in this article I want to talk very briefly about one of the most remarkable kinds of geckos: namely, the fabulous leaf-tailed geckos (Uroplatus) of Madagascar [image above of U. fimbriatus by Piotr Naskrecki].


About 13 leaf-tailed gecko species are currently recognised, but (as we'll see) this number is definitely not a true representation of species diversity within the group. They're among the most distinctive of geckos, and indeed most distinctive of lizards; they positively bristle with unique features. They have large, wedge-shaped heads, enormous eyes with patterned irides, and relatively short, dorsoventrally flattened tails. The tail in some species (like U. pietschmanni) has semi-circular fringes along its edges. In the leaf-mimicking U. phantasticus - sometimes called the Satanic leaf-tailed gecko [shown here; from wikipedia] - the tail typically has a 'rib' along its dorsal midline and may even be tattered and perforated with small holes, just like a dead, decomposing leaf. The body is dorsoventrally compressed in some species, but laterally compressed in others. At least one species (U. ebenaui) has small supraorbital horns.

Weirdosity in skin, teeth, jaws, digits and larynx

Some leaf-tailed geckos possess flaps or fringes of skin on their heads and bodies. These structures seem to help break up their outline and improve their camouflage on tree trunks. Even large leaf-tailed geckos can become near-invisible when they press their bodies, limbs and tail flat against lichen-covered bark. Dermal fringes are especially prominent on the large species U. henkeli (specimens in one population reach 30 cm in total length), which has them on its limbs, flanks, tail and on the sides of its lower jaw and neck. However, the fringes are entirely absent on U. malahelo (except for a few on the tail), and in fact this species doesn't look all that different from some 'normal' geckos [U. sameiti shown below; photo by Yannick Perret].


Another unusual feature of these geckos is their ridiculously high tooth count: in some species (like U. fimbriatus) there are as many as 169 teeth in the upper jaws and 148 in the lower (these are total counts, including teeth from both sides). I tried to find useable photos of leaf-tailed gecko skull photos online, but couldn't find anything freely available for use [UPDATE: Mokele kindly uploaded some U. phantasticus skull photos to wikipedia, one is used below]. In fact, note that there are loads of cool Uroplatus photos online: as usual with herps, these are mostly protected by copyright and hence I haven't used them (I still don't understand what is, and what is not, available for use when it comes to images that are online).


If you're wondering why these geckos have such ridiculously high tooth counts (among the highest within Tetrapoda), the answer is.... well, nobody really knows, as virtually nothing is known of the ecology, diet or feeding behaviour of the species concerned (Bauer & Russell 1989) [teeth of U. phantasticus below; image by Mokele, from wikipedia]. Ctenochasmatid pterosaurs have higher tooth counts, but I think that's about it (the ctenochasmatid Pterodaustro had about 1000; I had a recollection of some delphinid dolphins having over 300, but c. 200 seems more like it for the toothiest species).


Other peculiar features of Uroplatus include an incipient secondary palate, extensive interdigital webbing, a weird laryngotracheal system (Rittenhouse et al. 1987), inscriptional ribs (cartilaginous rods that separate the segments of the abdominal musculature), simplified, rod-like clavicles and a tiny interclavicle, finger-like lung diverticula that (apparently) ramify between the viscera, and reduced depressor mandibulae muscles (these are the muscles that open the lower jaw).

As is so often the case, we only know that these weird features are present, not what they're 'for'. The digital webbing in Uroplatus isn't just composed of sheets of skin: there are also muscles extending between the digits and embedded within the webbing. These so-called interparaphalangeal muscles are connected to the paraphalanges (Russell & Bauer 1988). As you might recall from the article on gekkotan hands and feet, the paraphalanges are rod-like elements that typically extend from either side of each phalangeal end (I'm referring to the distal end). The paraphalanges are not really rod-like in Uroplatus, but stout and trapezoidal [in the image of a Uroplatus pes digit IV shown below (from Russell & Bauer 1988): vs = venous sinus; ppe = paraphalangeal element; sep = connective tissue septum; ippm = interparaphalangeal muscle].


The enlarged bony palate might be something to do with resisting stresses incurred during biting (perhaps the broad, flattened shape of the rostrum behaves similarly to the crocodilian rostrum when loaded (e.g., Busbey 1995): crocodilians also possess large secondary palates), and I wonder also if the fused nasals that these geckos have are something to do with stress transmission. The laryngotracheal system of Uroplatus can be regarded as weird because - among other details - it includes a dilated, depressed anterior section. This might serve as a reservoir that allows air from the lungs to be pressurised before being blasted out through the larynx, and some Uroplatus species do have particularly loud voices (Rittenhouse et al. 1987). Captured leaf-tailed geckos bite repeatedly, and also make loud distress calls.

Lots more on leaf-tailed geckos to come. Next: 300 years of literature, and the 'Salamandre aquatique'.

For previous Tet Zoo articles on gekkotans see...

For previous Tet Zoo articles on neat squamates see...

Refs - -

Bauer, A., & Russell, A. (1989). A systematic review of the genus Uroplatus (Reptilia: Gekkonidae), with comments on its biology Journal of Natural History, 23 (1), 169-203 DOI: 10.1080/00222938900770101

Busbey, A. B. 1995. The structural consequences of skull flattening in crocodilians. In Thomason, J. J. (ed) Functional Morphology in Vertebrate Paleontology. Cambridge University Press (Cambridge), pp. 173-192.

Rittenhouse, D. R., Russell, A. P. & Bauer, A. M. 1997. Laryngotracheal morphology of the Uroplatus fimbriatus complex (Reptilia Gekkonidae): yet another autapomorphic organ system in a group of highly aberrant geckos. African Journal of Herpetology 46, 36-48.

Russell, A. P. & Bauer, A. M. 1988. Paraphalangeal elements of gekkonid lizards: a comparative survey. Journal of Morphology 197, 221-240.

More like this

It's interesting that there is another group of leaf-tailed geckos from Australia and New Guinea (Phyllurus & Saltuarius), which appear to have convergently evolved the flattened, leaf-shaped tails. Don't know how similar they are morphologically or behaviourally to Uroplatus though.

Phyllurus platurus has a reasonably similar overall skull shape to that Uroplatus Hai-Ren links to, but lots of differences in the skull roof (including highly sculptured surface and extensive temporal roofing), quadrate (generally broader, more inflated and less weird) and mandible (longer adductor fossa). The secondary palate (maxilla/vomer/palatine) doesn't seem any better developed than in the shorter & deeper-snouted Underwoodisaurus ("Nephrurus") milii. I don't have skulls of other Australasian leaf-tails but the flattening of the skull in P. platurus is probably among the most extreme, due to their use of narrow sandstone crevices; other non-leaf-tail carphodactylines have much deeper heads. I count about 65 teeth on one side of the upper jaw. I think Saltuarius are probably a better match to Uroplatus behaviourally, mainly found on trees rather than rock outcrops, larger, and with more extreme tail shapes and excrescences than Phyllurus.

Somehow I'd missed the skull pic on wikipedia, thanks for that. As for Australian geckos... yeah, Uroplatus is weird, but by no means is it the only very weird gecko.

Oh, you didn't miss them; I happened to have a Uroplatus skull, so I snapped some quick pics and put them up on WP.

Well, thanks much - really appreciated! If I may ask, how the hell did you get the skull? Is it from a deceased pet?

Pelicanimimus is supposed to have a really high teeth count. Maybe a high tooth count is an evolutionary "symptom" of being adapted for catching prey much smaller and possibly slipperier or more agile than themselves (i.e. insects, fish).

By Anonymous (not verified) on 19 May 2010 #permalink

Indirectly, it was - I got it from a colleague studying fish feeding who sells off skeletonized odds & ends now then from animals acquired through various sources, often the pet trade. I've also got a complete Boelen's python skeleton and a Crotalus durissus skull from him (the latter may well be from the pet trade too - you can buy *anything* in the US).

Actually, the three of them were my parent's ingenious solution to me being so hard to buy Xmas/b-day gifts for - I'm at full capacity for living herps, but dead ones don't need cages, lighting, or food, and assembling skeletons is like the best bio-geek jigsaw puzzle ever. Wikipedia also has photos of a Ceratophrys cornuta and Desmodus rotundus I mounted, plus all the photos on the snake dentition page. I've still got about half a dozen skeletons awaiting mounting, plus a baggie-of-herps my MS adviser gave me in order to clear our fridge space.

When you are not sure whether you can use a picture freely, you can just link to the original website from your blog.

Clertar: that sounds emminently logical, but I have been asked (admittedly, on only a handful of occasions) to remove images because I haven't paid for them. This is even after linking to the original page and including credit. As one example, a monitor lizard photo originally used here had to be removed after the site owner said "That picture of varanus rudicollis belongs to me, You'd better donate something quick. Or else". Those are his exact words (I kept his email). So, these days, I try and be careful.

virtually nothing is known of the ecology, diet or feeding behaviour of the species concerned (Bauer & Russell 1989)

Future herpetologists please take note. This statement is all too common for most reptiles. There is a huge and untapped field out there for anyone willing to simply document the life history of all these species that have been described and forgotten.

I haven't got the Rittenhouse et al. paper, but weird throat morphology plus the reduced depressor mandibulae makes me wonder if the mouth-opening system has changed in a way parallel to that in whales (Inside Nature's Giants is being shown here in Oz, and that episode was on a couple of nights ago). The larynx is clearly below the quadratomandibular articulations in the top picture, so parasagittal muscles from shoulder girdle to hyoid to symphysis could probably do the job.

By John Scanlon FCD (not verified) on 19 May 2010 #permalink

virtually nothing is known of the ecology, diet or feeding behaviour of the species concerned (Bauer & Russell 1989)...

Anyone who's ever looked for these damned things in the field understands immediately why this is so. Chamaeleons stand out glaringly in comparison. Even Brookesia.

Thanks for the article, Darren. It doesn't seem to have anything relevant to the alternative jaw-opening mechanism I conjectured, but I haven't read it all yet. It's mainly concerned with structures associated with phonation (I suppose this is a pedantic expression for what's usually called 'vocalization' but without a true 'voice').

Thanks, Luis - much appreciated :) And... a year later and I still haven't finished the series on gekkotans...