Rhinophrynus dorsalis is the only living member of the family Rhinophrynidae. It is one of the strangest of frogs. This animal is highly fossorial (adapted for burrowing) and apparently only comes to the surface to breed, and then only during very heavy rains. The head is small and cone-shaped, and not surprisingly, the skull resembles that of a mole (Spalax). The skin is quite thick, and an early naturalist described the frog (in French) as a bag of bones. It ranges through the southern Rio Grande Valley of Texas to Costa Rica. This frog is 5-7 cm long. There is usually a broad red or orange stripe down the middle of the back. There is a spade, used for digging, on the inner edge of the foot; the first toe is also modified to extend the functional edge of the spade.

Rhinophrynus dorsalis is specialized for eating termites, and the tongue seems to be particularly modified for this activity. Instead of being flipped out over itself, as in most frogs, the tongue is projected straight out of the mouth (Trueb, 1983).

Many small eggs are laid in water, and the tadpoles aggregate and form large schools. They are specialized for filter-feeding on small particles suspended in the water, rather than grazing on algae or eating detritus from the bottom of the pond. Correlated with this behavior, the larvae lack beaks and denticles; they also have paired spiracles like most pipid tadpoles. This type of tadpole (Orton Type 1) is evidence of a close phylogenetic relationship between Rhinophrynidae and Pipidae.

These moderately large burrowing frogs have a very unique morphology. Their body is flaccid and covered with loose skin. Their snout is shortened both laterally and ventrally and both the snout and vent are covered with sensory tubercles. The head is very tiny and pointed and the eyes are also very small. They have no neck and no visible tympanum. They have short, robust limbs, and their front digits have only a trace of webbing, while the four back digits are short and extensively webbed. They also have two enlarged spades on the inner surface of the metatarsus (ankle). Coloration patterns show scattered loose spots and blotches ranging in color from yellow to reddish orange in varying degrees of shading, the dorsal color is dark brown or nearly black. The males have paired internal vocal sacs. The females tend to be substantially larger than the males in this species (description from Lee 1996).

The tadpoles of Rhynophrynus dorsalis show distinct characteristics. The dorsum of the tadpoles is generally dark gray to black while the venter is iridescent silver. At night, the head and body are often translucent, and Lee,(1996) suggests that the pigmentation may exhibit a diel cycle. The head is flat and broad with small laterally placed eyes and a slit for a mouth, which is surrounded by delicate barbles. The tail is usually about 1.5 times the length of the body and the dorsal fin extends onto the posterior third of the body. Both the dorsal and ventral fins are of about the same depth (description from Lee 1996).
 
Rhynophrynus dorsalis has a very unique call, in fact as Lee (1996) brings to our attention, the Mayan name for the species, uo, is an onomatopeic rendering of the call. The call has been described as "a loud, protracted, ascending whoop, or uooooooooo, it is also described as being well modulated with a distinct harmonic structure" (Lee 1996).. The sound is loud and travels great distances. Etymology: Rhinophrynus is from the Greek rhinos, meaning nose and phrynus, meaning toad. dorsalis, comes from Latin, meaning "pertaining to the back" (Lee 1996). Although commonly referred to as 'toads', Rhynophrynus is not related to the family Bufonidae; this species is the only extant representative of the family Rhynophrynidae (e.g. Ford and Cannatella 1992)

A Spanish-language species account can be found at the website of Instituto Nacional de Biodiversidad (INBio).

This species is found in coastal lowlands from southern Texas, USA to northwestern Honduras in Atlantic drainage, Río Balsas (Mexico) to Costa Rica in Pacific drainage. It is found at elevations of sea level to above 500m asl.

In the lowlands from Texas to Yucatan and Honduras, west coast from the Rio Balsas, Mexico, to Costa Rica. Barely enters the United States.

Biogeographic Regions: nearctic (Native ); neotropical (Native )

occurs (regularly, as a native taxon) in multiple nations

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (200,000-2,500,000 square km (about 80,000-1,000,000 square miles)) Coastal lowlands from southern Texas, United States to northwestern Honduras in Atlantic drainage, Rio Balsas (Mexico) to Costa Rica in Pacific drainage. Sea level to above 500m asl. Rare and local in Texas, common widespread in Mexico and northern Central America (Bartlett and Bartlett 1999, Lee 2000).

This species occurs at low elevations on the Atlantic slope, from southern Texas to Guatemala, and on the Pacific slope, from Guerrero to Costa Rico. They are generally found on savannas and seasonally dry forest (Lee 1996).

Identification: 2 to 2 3/4 inches (record, 3 1/2 in.). The rotund body and broad reddish/orange middorsal stripe are sufficient for identifying this toad. Horny, shovel-like appendages on feet

Length: 9 cm

Habitat and Ecology

Systems

• Terrestrial
• Freshwater

Terrestrial and nocturnal. Remain in fairly small areas.

Terrestrial Biomes: forest ; scrub forest

Comments: Lowlands inhabitant of Tropical dry and moist forest. Generally associated with seasonal flooded areas where it remains under the ground in the dry season. Forest, thornscrub, savanna, and cultivated areas with friable soils. Fossorial except after heavy rains. Eggs and larvae develop in temporary pools formed by heavy rains.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Migrates unknown distance between breeding pools and nonbreeding terrestrial habitat.

Eats insects, especially termites (which it licks up with its tongue), and other invertebrates.

Comments: Metamorphosed toads eat termites.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

Comments: Likely hundreds of occurrences.

10,000 - 1,000,000 individuals

Comments: Total adult population size is unknown but surely exceeds 10,000 and likely exceeds 100,000.

Comments: Active at night in warm wet weather.

Eggs are laid in water. Has its own mating call. Mate more than once and during any month. Breed in water, but may migrate one mile to a more suitable breeding pond. Eggs are laid in two jelly tubes. Tadpoles hatch in a few days and transform into adults in one to three months.

Lays eggs after heavy rains. Egg cluster separates and eggs float singly at surface of water. Aquatic larvae probably metamorphose within a few weeks.

It looks somewhat like a narrow-mouthed toad of giant size. This species is the only living representative of its family, the Rhinophrynidae.

IUCN Red List of Threatened Species: least concern

United States

Rounded National Status Rank: N2 - Imperiled

Rounded Global Status Rank: G5 - Secure

Intrinsic Vulnerability: Moderately vulnerable

Environmental Specificity: Narrow to moderate.

Population

Population Trend

These terrestrial frogs construct subterranean burrows to make it through the dry seasons without suffering from desiccation. They burrow backwards into the soil, using the enlarged spades on the back of their heels. Their above ground activity is limited to the rainy season when they feed on termites, ants and other insects. The beginning of the rainy season marks the mating season, and males are usually found in large choruses in temporary bodies of water. The female, after inguinal amplexus will release several thousand eggs, either individually or in small groups, into the water. The eggs will sink to the bottom and hatch within a few days (descriptions from Lee 1996).

Major Threats

Comments: None

Conservation Actions

Comments: A highly derived, monotypic genus, the only extant representative of the family.