The three new species -- Oreophryne cameroni, Oreophryne parkopanorum and Oreophryne gagneorum -- have total body lengths of about 20 millimeters, or 0.787 inches, the university said in a release Friday.
The subfamily to which the three new species belong is mainly found on New Guinea and its satellite islands, researchers said.
The presence of the three new species suggests other species likely await description, University of Michigan researcher Fred Kraus said.
"I have at least a dozen more new Oreophryne species remaining to be described from this region, and large portions of this terrane system remain unsurveyed."
The university said Paedophryne dekot and Paedophryne verrucosa, which Kraus described in 2001, were half of the length of the three new additions to the frog diversity of Papua New Guinea, with a body size ranging from 8 mm to 9 mm (roughly 0.3 inch).