Yucatecan Casque-headed Frog
Triprion petasatus

The Yucatecan Casque-headed Frog (Triprion petasatus) is a good example of where old sayings sometimes fall short.  The old adage goes "if it looks like a duck and sounds like a duck, its a duck".   But this is a case where an animal that looks and sounds like a duck....is actually a frog!

These strange duck-billed treefrogs is restricted to the Yucatan Peninsula where they are quite common during the rainy season.  They can be found on roads and trails at night and their calls can be heard from any wooded area.




Their bizarre head ornamentation ("casque") is actually composed of bony shelves and ridges of the skull which are fused to the cranial skin.  They not only have a duck-like beak, but there is a bony ridge coming forward from each eye towards the midline of the skull.
The function of this bony ornamentation is unknown but it has been hypothesized that these frogs use these bony plants to block their burrow entrances during periods of inactivity.





These strange duck-billed treefrogs have an equally strange breeding method.  Because they live in the porous karst limestone of the Yucatan platform, there are few areas where water naturally stands on this porous ground.  These treefrogs have adapted by laying eggs in any pool of standing water.  We found the frog below calling from above a small hollow in a tree, no more than 2 inches in diameter and a few inches deep.  He was trying to attract a female to lay eggs in that small temporary pool that had formed in that tree hollow three feet off the ground.



Triprion tadpoles are as strange-looking as their parents.  Fairly early in development they get these bony casque structures on their heads and they are visible even in the tadpoles.
The problem with nesting in pools in rocks or tree holes is that there isn't much nutrition available for the developing tadpoles.  We observed these tadpoles in a water filled depression in a limestone rock.  The depression was only a few inches deep and we observed the tadpoles feeding on each other.  You can see some tadpoles feeding on another individual in this video towards the end. This tadpole cannibalism is common in other frogs that nest in ephemeral water bodies as well.


video


Just as you would imagine from a "duck-like" frog, the call is a nasal duck-like quacking. Here's an individual from near the town of Pisté, Yucatan, Mexico.





And here's a small group, also from south of Pisté, Yucatan, Mexico.



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© Chris Harrison 2017

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