 Out of the intense competition for reproductive sites in the South American rainforest had evolved over 90 species of these frogs, in which the female incubates her embryos inside her body bringing parallelism to mammalian reproduction.Marsupial frog embryos develop under saline conditions typically found in the body in contrast with the aquatic mode of development found in "Xenopus" and many other frogs.Traditional frogs and marsupial frogs also differ in how their embryos excrete waste.