Obdurodon

Species: Obdurodon dicksoni Archer M, Jenkins FA, Hand SJ, Murray P, & Godthelp H, 1992
Place: Riversleigh
Country: Australia
Age: Miocene
Remarks: A skull with an almost complete set of teeth. Excepting for juveniles, the modern platypus doesn’t have teeth.

Reference: Archer et al (1992), Description of the skull and non-vestigial dentition of a Miocene platypus (Obdurodon dicksoni n. sp.) from Riversleigh, Australia, and the problem of monotreme origins. p. 15-27 in M.L. Augee (ed.) "Platypus and Echidnas", Royal Zoological Society of New South Wales.

Species: Obdurodon insignis Woodburne MO & Tedford RH, 1975 Place: Tirari Desert, South Australia
Country: Australia
Age: Mid Miocene
Remarks: Teeth and fragments of jaw and pelvis are known.

Reference: Woodburne & Tedford (1975), The first Tertiary Monotreme from Australia. American Museum, Novitates Number 2588, p.1-11.

(This information is derived from [1] (http://home.arcor.de/ktdykes/monotrem.htm) MESOZOIC MAMMALS?; Monotremata, an internet directory. As that's my webpage, there are no issues of copyright.)