Ornithorhynchidae

The Ornithorhynchidae are one of the two extant families in the order Monotremata, and contains the platypus and its extinct relatives. The other family is the Tachyglossidae, or echidnas. Within Ornithorhynchidae are two genera, Obdurodon and Ornithorhynchus:

Another two genera, Steropodon and Teinolophos, may also belong to Ornithorhynchidae. However, they are both very ancient, and scientific literature seems to indicate they are closely related to, but not a part of, the Ornithorhynchids.
 * Family Ornithorhynchidae
 * Genus †Obdurodon — an ancient branch of the platypus family
 * †Obdurodon dicksoni
 * †Obdurodon insignis
 * †Obdurodon/Monotrematum sudamericanum
 * †Obdurodon tharalkooschild
 * Genus Ornithorhynchus
 * Ornithorhynchus anatinus (the modern platypus)

The extinct Ornithorhynchus maximus was once included in Ornithorhynchus, but has now been concluded to be from the echidna family as Zaglossus robustus.