Genus: Monotrematum Pascual R, Archer M, Juareguizar EO, Prado JL, Godthelp H, & Hand SJ, 1992
Species: Monotrematum sudamericanum Pascual et al, 1992
Place: Punta Peligro, Patagonia
Age: Lower Paleocene
Remarks: A platypus tooth from South America. Update: three teeth, two lower and one upper, (Pascual et al, 2002). This is the only known non-Australasian taxon. The two new specimens were discovered in 1992, but they've only just been described.
"The preserved enamel in the central region shows that the crown pattern is almost identical to that of Obdurodon (Fig. 2A): it is composed of two V-shaped lobes, the anterior of which is wider, separated from the posterior one by a valley that connects the lingual and buccal sides of the crown separating the anterior and posterior lobes," (Pascual et al, 2002). The main difference, apart from continent and age, is the size. The M. teeth are around twice as large.
These fossils presently live in the collections of Museo de La Plata and Museo Paleontológico Egidio Feruglio, both in Argentina.
Reference: Pascual et al (1992), First discovery of monotremes in South America. Nature 356, p.704-706.
(This information is derived from  MESOZOIC MAMMALS?; Monotremata, an internet directory. As that's my webpage, there are no issues of copyright.)