to the present day there’s been a relative blossoming of monotreme types, leaving us now with two families); family Tachyglossidae has four: the short-beaked echidna (), found in Australia and New Guinea, and the long-beaked echidnas found only in New Guinea – , and . Known from the fossil record and extant in tantalisingly recent times are the comparatively larger echidnas and (a comparison of their femur and tibia lengths to those of surviving species appears below). Absent from their fossils and bones are the feature that mark out all older ancestral monotremes: teeth. , which appears in the fossil record from 26 to 13 mya is the most recent toothed genus (right).
