A blind and legless lizard that has just been found in Cambodia.
Cambodia: now with dibamids!
Posted on: May 29, 2011
Science Blog
by Darren Naish
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.]
Posted on: May 29, 2011
Science Blog
by Darren Naish
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.]
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