Here at AA, we’re a bit obsessed with lizards with things on their noses, technically called “rostral appendages,” and sometimes, depending on shape, “horns.” A lot of this interest comes Anolis proboscis, the horned anole of Ecuador, about which we’ve written much before.
Almost as cool as horned anoles (really, that’s an unfair standard) is the Sri Lankan lizard genus Ceratophora, which contains three species with rostral (or nasal) appendages, and two other species that are appendage-less. In a recent paper in Journal of Zoology, Johnston et al. discuss the evolution of these appendages. It’s long been debated whether the appendages evolved independently in each species or once in the ancestral Ceratophora, followed by loss in the two nasally-naked species. By combining analyses of phylogeny (which produces somewhat inconclusive reconstructions of ancestral phenotype), morphology and allometry, the authors conclude that the appendages most likely evolved independently in each of the three species. Moreover, they suggest the blob-like appendage of C. tennenti (bottom photo) may have evolved for crypsis, but the more horn-like appendages of the other two species probably resulted from sexual selection.
While on the topic of nasal horns, I decided to see if there are any new photos of the other horned anole, A. phyllorhinus, on the web, and indeed there are. See below. The natural history of this species, which likely evolved its horn independently of A. proboscis, awaits further study.
from http://ipt.olhares.com/data/big/506/5069364.jpg
- from http://www.reptarium.cz/content/photo_rd_05/Anolis-phyllorhinus-03000033975_01.jpg
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Kevin de Queiroz
The dewlap of the Anolis phyllorhinus in the upper photo looks anomalous; perhaps as the result of injury or atypical development. Compare with the one in Fig. 4 of the following publication: http://www.scielo.br/scielo.php?pid=S0031-10492002001600001&script=sci_arttext
Luke Mahler
I noticed the same thing Kevin. I’m going to suggest an alternative hypothesis: that the dewlap was extended with forceps, with the latter photoshopped out afterwards. I’ve seen this technique a lot recently, sometimes done pretty convincingly, but other times not so much. Usually you can detect this by the presence of creases or folds in a fully extended dewlap that converge to a point on the anterior edge of the dewlap (these creases suggest the skin is being pulled from the outside; you wouldn’t expect them if the dewlap was being pushed from the inside by the second ceratobranchials during dewlap extension).
In this case though, it was the shape that suggested it, and suspiciously repeated patterns on the brown leaves to the right of the dewlap would seem to confirm it. These patterns are from the use of some sort of “clone stamp” tool used to cover the tracks of the offending forceps and fingers. 😉
Joe Burgess
Luke, you missed your other calling… a forensic detective.
Daniel Scantlebury
Factor in Lyriocephalus and you end up with at least 4 independent origins of nasal protuberances in Sri Lanka. I wonder if there’s something conducive about the habitat there that might help us understand why these traits have also evolved multiple times in chameleons and anoles.
Peter Mudde
It’s not just the ‘horns’ also the heterogenic scalation, with patches of enlarged scales (slow movement and curly prehensile tail) that seems to go with it in chamaeleons and sri-lankean agamids. (and a few indonesian species of Harpesaurus as well).