Mexican burrowing Toad
(Rhinophrynus dorsalis)
The only species, within the only genus of the family Rhinophrynidae, and with over 190 million years of independent evolution, the Mexican burrowing toad is the most evolutionarily distinct amphibian species on Earth today; a fruit bat, polar bear, killer whale, kangaroo and human are all more similar to one another than this species is to any other amphibian. Although relatively common, the Mexican burrowing toad is rarely seen as this species spends the majority of the year living solely underground, only emerging after the first heavy rains to congregate for breeding in temporary pools.
Urgent Conservation Actions
No conservation actions are required.
Central America, from southern Texas to Costa Rica.
The Mexican burrowing toad is a frog of Mayan mythology; this species, named uo, was the companion of the rain gods, the Chacs. The call of the uo was believed to announce the rains and cause the Chacs to empty their water filled rain gourd.

The breeding chorus of the male Mexican burrowing toads can be heard up to 4 km away.

Sapo borracho means ‘drunk toad’ a name originating from the call of males during the breeding season. The sound of the male chorus at this time has been described as resembling 'shiploads of sick sailors'.

In captivity one Mexican burrowing toad stayed buried and inactive for a period of 2 years without feeding.
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Evolutionary Distinctiveness
Order: Anura
Family: Rhinophrynidae
The Mexican burrowing toad is in the monotypic family, Rhinophrynidae, meaning that this is the only species in the family. With over 190 million years of independent evolution, beginning in the early Jurassic Period, this species is the most evolutionarily distinct amphibian alive today; a fruit bat, polar bear, killer whale, kangaroo and human are all more similar to one another than this species is to any other creature.

Two genera in the family Rhinophrynidae are known from the fossil record – Eorhinophrynus from the Paleocene to middle Eocene of Wyoming, USA, and fossils of an extinct Rhinophrynus species are known from the early Oligocene of Saskatchewan, Canada.
The Mexican burrowing toad, which grows to a maximum length of 89 mm, has a stocky body and a small head with a cone-shaped snout and very small eyes. Its limbs are short and fat, and often appear to be enclosed in the skin which, when the toad is not inflated, seems too large for its body. The front legs have no webbing, however the frog’s back legs are heavily webbed to aid swimming and have two elongated tubercules for digging. This species’ dorsum is dark purple-grey with scattered orange spots on the face and flanks, with a conspicuous orange stripe down the centre of the back, and its underside is pale grey.

Tadpoles of this species have no teeth and lack the bony beak that most tadpoles of other species have to scrape food from hard surfaces such as rocks. Mexican burrowing toad tadpoles have eleven barbells surrounding their mouths, presumably with the function of directing food particles into the mouth.

The Mexican burrowing toad is morphologically distinct from all other amphibian species as its tongue is attached posterioraly and can change shape; when relaxed the tongue is flat and triangular, but with increasing hydrostatic pressure it can be made rod shaped and projected straight forward through a small groove at the front of the lower jaw. The species is also unique as it uses both eyelids to close its eyes, unlike other amphibians.
The Mexican burrowing toad is a strictly fossorial species which feeds on ants, termites and their larvae, by pushing its snout through the wall of termite nests and protruding its unique tongue to capture the insects inside. This frog burrows with its back legs, moving backwards in a corkscrew motion, and forms an underground chamber; chambers have been found at 7 – 15 cm in the wet season, but the species probably burrows deeper at drier times of the year. The Mexican burrowing toad does not make a cocoon like many other fossorial species, and when frogs are removed from their burrows they are active, not dormant like in aestivating species.

This species only emerges from its underground burrows from reproduction after the first heavy rains, when the species congregates in seasonal pools, flooded fields, and roadside ditches. At this time the males can be heard calling with a drawn out whoooooaa sound as they make their way to the breeding pools, some even begin calling while still underground. By the evening most individuals are in amplexus. Up to 8000 eggs are laid one at a time and sink to the bottom of the pool. Here the slightly sticky eggs form clumps.

The tadpoles emerge from the eggs just a few days after they are laid and congregate in mid-water in large schools of several hundred individuals. Unlike other species with schooling tadpoles, tadpoles of the Mexican burrowing toad include individuals at different stages of development. In shoals all of the tadpoles face the same way so that their movements create currents which stir up detritus from the pool bottom and brings food particles to the filter-feeding tadpoles. Experiments have shown that tadpoles living in shoals grow at a faster rate than those left to grow alone. In crowded conditions when food is scarce the tadpoles of the Mexican burrowing toad may become cannibalistic, a behaviour which can been seen in a number of other amphibian species.

Metamorphasis is practically simultaneous from a single pool and the froglets depart en masse. When they leave the water the froglets have not yet reabsorbed their tails, but still burrow with their tail folded over their back. In some years, when the rains are most heavy, there may be two distinct breeding periods up to a few weeks apart.

When threatened the Mexican burrowing toad inflates its lungs making itself more rigid as a defensive response, probably helping to revent the species from being dislodged from its underground chamber. The skin can also secrete a sticky noxious fluid, although it is thought that this is to protect the frog from ant and termite bites when feeding.
The Mexican burrowing toad is found in tropical lowland dry forest and coastal plains, up to 500 m elevation. This species appears to survive well in a variety of habitats, including forest, shrubland and grassland, and also in areas altered by humans such as pasture land and cultivated fields. The Mexican burrowing toad can be found during the breeding season in seasonally flooded pools and roadside ditches.
Population Estimate
The Mexican burrowing toad is common, but is rarely seen apart from during the breeding season due to its burrowing lifestyle. No numerical population estimate is known.
Population Trend
Listed as Least Concern on the 2007 IUCN Red List of Threatened species, because this species has a wide distribution, can live in a broad range of habitats, and there is no evidence of large declines in populations of this frog.
There are no known major threats to the Mexican burrowing toad.
Conservation Underway
There are a number of protected areas within the range of the Mexican burrowing toad, which is also protected under Mexican Law as it is placed in the ‘Special Protection’ category (Pr).
Conservation Proposed
No conservation measures are required for this species, although monitoring of populations will allow for any future declines to be detected as early as possible.
AmphibiaWeb: Information on amphibian biology and conservation [web application]. 2006. Berkeley, California: AmphibiaWeb. Available: amphibiaweb. Accessed: 08 December 2006.

Campbell, J. A. 1998. Americe Natural History Series Volume 4: Amphibians and Reptiles of Northern Guatemala, the Yucatán, and Belize. University of Oklahoma Press, USA.

Duellmand, W. E. and Trueb, L. 1986. Biology of Amphibians. McGraw-Hill, Inc, USA.

Frost, Darrel R. 2006. Amphibian Species of the World: an Online Reference. Version 4 (17 August 2006). Electronic Database accessible at: . American Museum of Natural History, New York, USA.

Halliday, T. and Adler, C. (eds.). 2002. The new encyclopedia of reptiles and amphibians. Oxford University Press, Oxford.

IUCN, Conservation International and NatureServe. 2006. Global Amphibian Assessment. Global Amphibian Assessment. Accessed on 08 December 2006.

Köher, G., Vesely, M. and Greenbaum, E. 2006. The Amphibians and Reptiles of El Salvador. Krieger Publishing Company, Malabar, Florida.

Mattison, C. 2005. Encyclopedia of reptiles and amphibians: An essential guide to reptiles and amphibians of the world. Grange Books Plc. Kent.

Obst, F.J., Richter, K. and Jacob, U. 1984. The Completely Illustrated Atlas of Reptiles and Amphibians for the Terrarium. T.F.H. Publication Inc., N.J., U.S.A.

Savage, J. M. 2002. The Amphibians and Reptiles of Costa Rica: A herpetofauna between two continents, between two seas. University of Chicago Press, Chicago and London.

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Forum comments
  1. Anonymous

    This was very useful Info for my science project thanks a lot

    Posted 8 years ago #

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