Frogs of the United States and Canada, 2-vol. set

Family Rhinophrynidae

Family Rhinophrynidae Rhinophrynus dorsalis Duméril and Bibron, 1841 Mexican Burrowing Toad ETYMOLOGY dorsalis: from the Latin dorsalis, possibly referring to the dorsal pattern. NOMENCLATURE Synonyms: Rhinophryne rostratus, Rhinophrynus rostratus IDENTIFICATION Adults. Rhinophrynus dorsalis is a rotund frog with very short but powerful limbs, a pustulose and loose skin, a short little head, tiny eyes with vertical pupils, and no tympanum. The ground color is dark brown to black and appears somewhat translucent. There is a distinctive light yellow to red-orange mid-dorsal line down the back with similarly colored small spots on both sides. Venters are lighter than the dorsum but still dark in coloration. The hind legs are partially enclosed in loose body skin. Large spade-like tubercles are present on the rear feet. The snout is protuberant. They reach about 50–90 mm SUL at maturity, with females larger than males (in Fouquette, 2005). Larvae. The head is broad and depressed, with small eyes. The mouth is unique in that it is a wide slit bordered by 11 short barbels, giving it the appearance of whiskers. There are no keratinized structures associated with the jaws, and the oral disk and labial teeth are absent. The spiracles are paired and laterally positioned unlike in other native North American frogs. The tail fins and musculature are well-developed and taper to a narrow pointed tip. Larvae reach to 39.5 mm TL. Orton (1943) describes the tadpole and illustrates the unique oral barbels surrounding the mouth. Eggs. The eggs have not been described. DISTRIBUTION The Mexican Burrowing Toad occurs from south Texas to northwestern Costa Rica. In the United States, R. dorsalis is known only from Starr and Zapata counties, Texas. Important distributional references include James (1966) and Dixon (2000). FOSSIL RECORD Pleistocene fossils of R. dorsalis are known from a cave in Tamaulipas, Mexico (Holman, 2003). SYSTEMATICS AND GEOGRAPHIC VARIATION Rhinophrynus is a monotypic genus allied within a highly derived, primitive group of frogs, the aglossal pipids of the suborder Pipoidea. The diploid chromosome number is 22 (Bogart and Nelson, 1976). Distribution of Rhinophrynus dorsalis RHINOPHRYNUS DORSALIS 459 underground. Surface activity is opportunistic and occurs only in response to rainfall. They dig backward into the soil with digging spades on the rear feet. They also twist their body extensively back and forth and inflate their bodies to facilitate penetration into the soil. Body inflation also allows them to maintain a cavity space as the soil settles around them. They also can effect some forward motion using their widely spaced, powerful spatulate forelimbs and tuberculate hands (Trueb and Gans, 1983). Nothing is known concerning migration or movement patterns. CALLING ACTIVITY AND MATE SELECTION The call of R. dorsalis is a loud but low-pitched guttural moan (James, 1966; Garrett and Barker, 1987). Calling occurs from within burrows, with males emerging after heavy rains to form large breeding choruses. Males then call from the ADULT HABITAT Garrett and Barker (1987) noted that Mexican Burrowing Toads prefer areas with loose soil for digging. In Texas it is found in agricultural areas and gardens in the Matamoran District of the Tamaulipan Biotic Province. The area in Texas consists of rolling hills of sand and gravel over thin soils. These hills are interspersed by deep arroyos fed from shallow ravines and washes. Vegetation is arid to semiarid trees and shrubs. James (1966) recorded breeding in arroyos surrounded by very thick tangles of thorny vegetation consisting of cacti, acacias, and retama (Parkinsonia aculeata). TERRESTRIAL ECOLOGY As its common name implies, Rhinophrynus dorsalis is almost entirely fossorial and rarely comes to the surface. They can remain for long periods Tadpole of Rhinophrynus dorsalis. Photo: Seth Patterson Adult Rhinophrynus dorsalis, southern Texas. Photo: Seth Patterson 460 RHINOPHRYNIDAE lining folds, an ability to “double-close” the lips, and a specialized tongue apparatus for handling small prey in subterranean burrows (Trueb and Gans, 1983). The spade-like tubercles on the hind feet are used to dig into termite mounds. Larvae feed on phytoplankton. PREDATION AND DEFENSE When threatened, the Mexican Burrowing Frog inflates its body thus obscuring the head and limbs. There is no information available on predators . POPULATION BIOLOGY No information is available. DISEASES, PARASITES, AND MALFORMATIONS Parasitic opalinid protozoans have been reported from this species in Mexico. SUSCEPTIBILITY TO POTENTIAL STRESSORS No information is available. STATUS AND CONSERVATION Dixon (2000) stated that there were no records of this species since...