Rhizophascolonus crowcrofti is the only known species of this genus.
It was described in 1967 based on a single tooth. Many more specimens (mainly isolated teeth) of this species have now been found.
It is the only described fossil wombat with tooth roots. All other wombats have teeth that grow continuously throughout their life and do not form tooth roots.
This species is the oldest known fossil wombat. However, it is likely that wombats evolved around 40 million years ago (around 15 million years before the oldest known wombat fossils). Wombats are closely related to koalas.