Significance The mechanisms by which genomes become smaller in lineages with large genomes, such as many frogs, are poorly understood. Here, we present the sequence of a very small genome from a frog—that of the ornate burrowing frog, Platyplectrum ornatum , whose genome is smaller than that of many birds, a group well known for small genomes. Our data show that this frog evolved molecular mechanisms to keep in check a major process characterizing large genomes: namely, proliferation of transposable elements. We also present basic data on gene expression and sex determination in this emerging model for genome miniaturization.