Obdurodon

Obdurodon is an extinct monotreme genus containing four species. It is sometimes referred as the Riversleigh Platypus, after the location of its discovery at Riversleigh. The Obdurodon differed from modern platypuses in that adult individuals retained their molar teeth (in the modern platypus, individuals lose all of their teeth upon reaching adulthood).

Obdurodon dicksoni

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


 * Obdurodon dicksoni grew profoundly larger than the modern 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 and angulary processes of O. dicksoni have quite disappeared in the platypus, leaving the platypus's skull flat on the sides. This indicates the mastication technique of O. dicksoni was different from that of the platypus, using the muscles anchored to these processes.
 * O. dicksoni's beak has an oval hole surrounded by bones in the center, whereas the platypus' beak has a V-shape and no longer surrounded by bones.
 * O. dicksoni' retained molar teeth into adulthood, whereas in the modern platypus, the adults only have keratinized pads (juveniles lose their molar teeth upon adulthood).
 * The shape of its beak suggests that O. dicksoni sought prey by digging in the sides of rivers, whereas the modern platypus digs in the bottom of the river.
 * O. dicksoni had (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 were not well-anchored.

Obdurodon insignis

 * 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 proportionally smaller than the one of Obdurodon dicksoni.

Obdurodon tharalkooschild

 * Discovered in 2012 by a team from University of New South Wales including Mike Archer, Suzanne Hand, and Rebecca Pian
 * Habitat : Queensland
 * Epoch : Middle and upper Miocene (5–15 mya)
 * Evidence for Obdurodon tharalkooschild was based on a single molar tooth discovered at the Two Tree Site of the Riversleigh fossil beds in northwest Queensland. The species is believed to have been carnivorous and twice the size of the modern platypus at a metre long. The name was chosen in honour of an indigenous Australian creation story for the platypus, where a duck named Tharalkoo gives birth to a chimeric creature after being ravished by a water-rat.

Monotrematum sudamericanum

 * 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."