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Elachistocleis ovalis, known as the oval frog and as the slate burrowing frog, is a species complex of microhylid frogs whose distribution stretches across South America on the east side of the Andes, from Panama, Columbia and across the Guiana Shield, south through most Brazil, Bolivia and Paraguay.
A pointy-headed frog, the oval frog has an oval-shaped body with smooth skin, speckled white, grey and black on the dorsal side, and white on the ventral surface. It has small eyes, a small head, and short, sturdy limbs. The back of the thighs have a thin yellow line.
Adults live in open savannah up to 500m asl, and burrow underground in the dry season. They breed in the wet season when the plains flood, calling with a sharp “eee” sound. Eggs hatch very fast (2 days) and tadpole metamorphose into full adults in about eight weeks.
Elachistocleis ovalis has a long and complicated taxonomic history, with no identified type specimens, and geographical limits and ventral coloration patterns not clearly defining the species. Lavilla et al. (2003, cited in Rodrigues et al. 2010) separated lineages of E. ovalis with no pigment on ventral surface and that inhabited the southern part of the range (Argentina, Paraguay, Uruguay) as E. bicolor though this may also represent multiple species. In 2010, Caramaschi reviewed Brazilian Elachistocleis ovalis breaking the wide distribution into six species: E. ovalis, E. surum, E. matogrosso, E. helianneae, E. carvalhoi, E. bumbameuboi, but did not address E. ovalis populations outside Brazil. Classifications in EOL have these synonymized under E. ovalis.
(Lavilla et al. 2003; De la Riva et al. 1996; Caramaschi 2010; Rodrigues et al. 2010; STRI, n.d.)