Dibamids are a weird and very neat group of fossorial, near-limbless squamates that I've long planned to cover at Tet Zoo. Little is known about them and how they might relate to other squamates has long been the subject of debate (they might be close to amphisbaenians, but links with gekkotans, skinks and snakes have all been suggested in the past). I'm going to avoid saying much about them here: I just want to point to the fact that a newly named species - Dibamus dalaiensis Neang et al., 2011 [shown here; image Thy Neang/Flora & Fauna International] - extends their distribution to Cambodia. The previously recognised species of Dibamus are known from south-east Asia, India, southern China, New Guinea and the Philippines, but another dibamid - Anelytropsis papillosus (first described by Cope in 1885) - is endemic to Mexico.
This distribution is pretty weird and indicative of either fairly recent over-water dispersal (certainly not implausible in small burrowing reptiles: they could conceivably travel out to sea in sediment associated with big floating root masses etc.), of ancient use of former landbridges, or of vicariance resulting from an ancient, transcontinental distribution. Townsend et al. (2011) recently looked at this issue. In their phylogeny, they found Dibamus to be paraphyletic, with one cluster of Dibamus species being closer to Anelytropsis than to the remainder of Dibamus. They propose that dibamids crossed the Beringian landbridge during the Paleocene or Eocene, but also consider the possibility of trans-Pacific rafting. There are no fossil dibamids, by the way. [Adjacent picture shows head of D. dalaiensis; image Thy Neang/Flora & Fauna International].
Of the 22-odd species currently recognised, about half have been named since 1985. Some of these (like D. tiomanensis Diaz et al., 2004 [shown here, from Diaz et al. (2004)]) have helped bridge 'gaps' in the distribution of the group, like the one that previously existed between Thailand and Borneo. Brand-new D. dalaiensis is the first member of the group for Cambodia. Given the presence of dibamids in adjacent Thailand and Vietnam, this is far from a surprise, but it's nice to have it confirmed.
While I'm here, a few more interesting facts about dibamids. They lack external ear openings and their eyes are vestigial. They're sexually dimorphic as goes the presence of limbs. Females lack limbs entirely, but males have small, flap-like hindlimbs that they use to grip females while mating. A particularly interesting fact is that their eggs are hard and calcified like those of gekkonid gekkotans. When startled, some species elevate their body scales so that they project almost perpendicularly from the body. This gives them a rugose appearance: one suggestion is that this allows them to mimic the bristle-covered (and presumably toxic) earthworms that inhabit the same environment (Diaz et al., 2004). Bright blue rings encircling the body of D. greeri from Vietnam might also mimic similar rings seen on unpalatable earthworms (Darevsky 1992). The holotype of D. greeri, incidentally, was discovered in sediment originally located three metres up in a tree. That might sound weird, but fossorial animals are not infrequently discovered fairly high up and away from the ground in tropical, mossy habitats. [The diagram below - from Darevsky (1992) - shows, left to right, the heads of two D. greeri specimens and D. smithi in (top to bottom) dorsal, lateral and ventral views.]
Much more on dibamids some other time.
For previous Tet Zoo articles on squamates, please see...
- Pompey and Steepo, the world-record-holding champion slow-worms
- Arboreal alligator lizards - yes, really
- Amazing social life of the Green iguana
- Hell yes: Komodo dragons!!!
- Ermentrude the liolaemine
- Evolutionary intermediates among the girdled lizards
- The Great Goswell Copse Zootoca
- Of giant plated lizards and rough-necked monitors
- 'Cryptic intermediates' and the evolution of chameleons
- Tell me something new about basilisks, puh-lease
- Tongues, venom glands, and the changing face of Goronyosaurus
- Mosasaurs might have used the same microscopic streamlining tricks as sharks and dolphins
- Dinosaurs come out to play (so do turtles, and crocodilians, and Komodo dragons)
- Isopachys: worm-like skinks from Thailand and Myanmar
- Mystery emo skinks of Tonga!
And don't forget the (still unfinished) series on gekkotans...
- 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)
- The incredible leaf-tailed geckos (gekkotans part V)
- 300 years of gecko literature, and the 'Salamandre aquatique' (gekkotans part VI)
- Whence Uroplatus and... there are how many leaf-tailed gecko species now?? (gekkotans part VII)
- Ptychozoon: the geckos that glide with flaps and fringes (gekkotans part VIII)
Refs - -
Darevsky, I. S. 1992. Two new species of the worm-like lizard Dibamus(Sauria: Dibamidae) with remarks on the distribution and ecology of Dibamus in Vietnam. Asiatic Herpetological Research 4, 1-12.
Diaz, R. E., Leong, M. T., Grismer, L. L. & Yaakob, N. S. 2004. A new species of Dibamus (Squamata: Dibamidae) from West Malaysia. Asiatic Herpetological Research 10, 1-7.
Neang, T., Holden, J., Eastoe, T., Seng, R., Ith, S. & Grismer, L. L. 2011. A new species of Dibamus (Squamata: Dibamidae) from Phnom Samkos Wildlife Sanctuary, southwestern Cardamom Mountains, Cambodia. Zootaxa 2828, 58-68.
Townsend TM, Leavitt DH, & Reeder TW (2011). Intercontinental dispersal by a microendemic burrowing reptile (Dibamidae). Proceedings. Biological sciences / The Royal Society PMID: 21270029
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Neat little article. Darren, back in march, you said you were doing something for cadborosaurus (should really be cadborotherium). Any idea on how soon. Sorry, I do know that you're very busy.
Is it possible that the erection of the scales could be done to prevent the animal from being dislodged from its soil habitat if it were to be found by, say, a bird or other possible predator?
Cadborosaur thing refers to an in-press paper - more when it's published. Scale erection: I'm not sure I even knew that squamates of any kind could erect their scales like this. I have no idea how widespread it is. Can anyone provide more info?
Isn't this derived within Gekkota?
In molecular phylogenies, Squamata is a trichotomy of dibamids, gekkotans, and everything else.
Darren, what's your guess on the probability of it's existence. I guess it's possible a large undiscovered mammal exists in the waters around Canada, but there is the possibility they're sightings of swimming moose.
I remember reading about a Mymecophiliac blindsnake which was able to pinecone its scales in this manner supposedly for defence against ants until it had acquired the scent of the colony. I am fairly sure I read this in Janzen's Costa Rican Natural History which I do not have with me now so I cannot check.
I'll second what Andreas said; that's really quite amazing! Are dibamids unique among tetrapods in this regard?
How do dibamids get up in the trees in the first place? Can they climb, or are they (or their eggs) transported there by something else?
[from Darren: sorry, delayed by spam filter]
farandfew, thankyou for verbing 'pinecone'.
I've never seen any imbricate-scaled squamate do such a thing, but can believe it. E.g. in snakes there's major variation in the extent of skin between the cornified scales, from little or no free edge (barely overlapping, in a continuum with the juxtaposed bead-like or spiny scales of typical varanids, geckos, agamids etc.) to deep folds or pockets. There are various plausible functions to do with stretchability, invertebrate symbionts (what goes on with squamates and mites, anyway?!), gas exchange...
Dartian: several groups of snakes are sexually dimorphic in the presence or relative size of external hindlimbs. And small burrowers can climb in hollow trunks, under bark, or under moss, without feeling exposed for a moment.
John, thanks for that information!
There is something delightfully bizarre about the fact that some fossorial vertebrates may actually also be arboreal...