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Obdurodon is an extinct monotreme genus containing three species. Obdurodon differed from modern Platypuses in that it still had teeth (except for juveniles, the modern platypus does not have teeth).

• Discovered in 1984 by Michael Archer, F. A. Jenkins, S. J. Hand, P. Murray, and H. Godthelp, at Riversleigh in New South Wales.
• Habitat : New South Wales
• Epoch : Lower and middle Miocene
• This species is characterized by a skull and several scattered teeth. Physically, it looked much like modern Platypus although there are a few significant differences.
• The holotype is kept at the Queensland Museum in Brisbane.

• Obdurodon dicksoni is bigger than a Platypus.
• The septomaxilla (a part of the upper jawbone) of O. dicksoni is bigger than for the Platypus, which supposes a hypertrophied beak.
• The coronoid process and angulary process of O. dicksoni have quite disappeared in the Platypus, leaving the Platypus's skull flat on the sides. This indicates that the mastication technique of O. dicksoni was different from that of the Platypus, using the muscles anchored to these processes.
• Odurodon dicksoni's beak has an oval hole surrounded by bones in the center whereas the Platypus' beak has a V-shape and isn't stopped on top.
• O. dicksoni' has molars, whereas the Platypus uses keratinized pads (only young Platypuses have teeth).
• It seems, due to the shape of the beak, that O. dicksoni nourished itself digging in the sides of rivers whereas the Platypus digs in the bottom of the river.

O. dicksoni' has (like the Platypus) shearing crests instead of incisor and canine teeth. It bore two premolars and three molars on each side of the lower jaw. The M1 had six roots, the M2 had five, and the M3 only one. The upper jaw bore two premolars and two molars on each side. The M1 had six roots, the M2 four. The premolars had only one root and a very different shape from the molars. They were separated from the shearing crests by an area without dentition. The roots of the molars were barely a third as high as the crown. Molars had only been found apart from skulls, implying that they weren't well-anchored.

• Discovered in 1975 by Mike O. Woodburne and Dick H. Tedford at Etudunna Formation in the desert of Tirari.
• Habitat : South Australia
• Epoch : Upper Oligocene
• The holotype is an inferior left molar and is kept in the South Australia's Museum, Adelaide. The tooth has six roots. There also have been found M2 with four roots and fragments of jawbone and pelvis. Obdurodon insignis had one more canine tooth (NC1) than its ancestor Steropodon galmani. Its beak must have been relatively smaller than the one of Obdurodon dicksoni.

• Discovered in 1992 by Rosendo Pascual, Michael Archer, E. O. Juareguizar, J. L. Prado, H. Godthelp, and S. J. Hand, at Punta Peligro, Argentina.
• Habitat : Patagonia
• Epoch : Lower Paleocene (61 million years)
• Monotrematum sudamericanum is now more often held as part of the same genus as Obdurodon. It is known only from two lower and one upper platypus teeth. It is the only known non-Australasian ornithorhynchid. The main difference, apart from continent and age, is its size: the teeth of Monotrematum are around twice as large as other similar species. These fossils presently reside in the collections of Museo de La Plata and Museo Paleontológico Egidio Feruglio, both in Argentina.
• According to Pascual, "The preserved enamel in the central region shows that the crown pattern is almost identical to that of Obdurodon: 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."

• Left, a skull of Obdurodon dicksoni, right, a Platypus's skull
• Fossil record of the Monotremata, with a photo of an Obdurodon tooth.

Wikispecies has information related to:

Obdurodon

• Archer, et al. "Description of the skull and non-vestigial dentition of a Miocene platypus (Obdurodon dicksoni) from Riversleigh, Australia, and the problem of monotreme origins".
• Augee, M.L. "Platypus and Echidnas". Royal Zoological Society of New South Wales. 1992. Pages 15-27. (O. dicksoni).
• Pascual, et al. "First discovery of monotremes in South America". Nature 356 (1992), Pages 704-706 (Monotrematum).
• Woodburne and Tedford. "The first Tertiary Monotreme from Australia." American Museum. Novitates Number 2588. 1975. Pages 1-11. (O. insignis).