 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: *family ornithorhynchidae **genus â obdurodon â an ancient branch of the platypus family ***â obdurodon dicksoni ***â obdurodon insignis ***â obdurodon/monotrematum sudamericanum ***â obdurodon tharalkooschild **genus ornithorhynchus ***ornithorhynchus anatinus (the modern platypus) another two genera, steropodon and teinolophos, were originally thought to belong to ornithorhynchidae, however they were both placed into a new family, steropodontidae. this decision was made based on differences in the dentary recovered from the griman creek formation, lightning ridge, new south wales, australia. this dentary is the holotype for the steropodon genus, and thus the lack of information is what led to the original misclassification. the extinct ornithorhynchus maximus was once included in ornithorhynchus, but has now been concluded to be from the echidna family as zaglossus robustus. ==references ==   *  
Monotremes