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...

• The Tet Zoo guide to Gekkota, part I
• Gekkota part II: loud voices, hard eggshells and giant calcium-filled neck pouches
• Squirting sticky fluid, having a sensitive knob, etc. (gekkotans part III)
• Lamellae, scansor pads, setae and adhesion... and the secondary loss of all of these things (gekkotans part IV)

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

• Mosasaurs might have used the same microscopic streamlining tricks as sharks and dolphins
• Tongues, venom glands, and the changing face of Goronyosaurus
• Dinosaurs come out to play (so do turtles, and crocodilians, and Komodo dragons)
• Tell me something new about basilisks, puh-lease
• 'Cryptic intermediates' and the evolution of chameleons
• The Great Goswell Copse Zootoca
• Of giant plated lizards and rough-necked monitors
• Ermentrude the liolaemine
• Evolutionary intermediates among the girdled lizards
• Hell yes: Komodo dragons!!!
• Amazing social life of the Green iguana
• Arboreal alligator lizards - yes, really
• Pompey and Steepo, the world-record-holding champion slow-worms

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.