The oldest platypus and its bearing on divergence timing of the platypus and echidna clades

Source: Proceedings of the National Academy of Sciences, vol.105 (4) 2008
"Monotremes have left a poor fossil record, and paleontology has been virtually mute during two decades of discussion about molecular clock estimates of the timing of divergence between the platypus and echidna clades. We describe evidence from highresolution x-ray computed tomography indicating that Teinolophos, an Early Cretaceous fossil from Australia’s Flat Rocks locality (121–112.5 Ma), lies within the crown clade Monotremata, as a basal platypus."