Prehistoric monotremes

Obdurodon is a genus of extinct platypus-like Australian monotreme which lived from the Late Oligocene to the Late Miocene. Three species have been described in the genus, the type species Obdurodon insignis, plus Obdurodon dicksoni and Obdurodon tharalkooschild. Obdurodon appeared much like their modern day relative the platypus, except adults retained their molar teeth, and unlike the platypus, which forages on the lakebed, they may have foraged in the water column or surface.

Kollikodon is an extinct species of mammal, considered to be an early monotreme. It is known only from an opalised dentary fragment, with one premolar and two molars in situ, as well as a referred maxillary fragment containing the last premolar and all four molars. The fossils were found in the Griman Creek Formation at Lightning Ridge, New South Wales, Australia. Kollikodon lived in the Late Cretaceous period, during the Cenomanian age (99–96 million years ago). Several other monotremes are known from the Griman Creek Formation, including Dharragarra, Opalios, Parvopalus, Steropodon, and Stir

Steropodon is a genus of prehistoric platypus-like monotreme, or egg-laying mammal. It contains a single species, Steropodon galmani, that lived about 100.2–96.6 million years ago during the Cretaceous period, from early to middle Cenomanian. It is one of the oldest monotremes discovered, and is one of the oldest Australian mammal discoveries. Several other monotremes are known from the Griman Creek Formation, including Dharragarra, Kollikodon, Opalios, Parvopalus, and Stirtodon.

Murrayglossus is an extinct genus of echidna from the Pleistocene of Western Australia. It contains a single species, Murrayglossus hacketti, also called '''Hackett's giant echidna'. Though only from a few bones, researchers suggest that Murrayglossus was the largest monotreme to have ever lived, measuring around long and weighing around . Historically treated as a species of long-beaked echidnas, it was separated into its own genus Murrayglossus in 2022. The generic name combines the last name of paleontologist Peter Murray and glossus'', the Greek word for "tongue".

Megalibgwilia is a genus of echidna known only from Australian fossils that incorporates the oldest-known echidna species. The genus ranged from the Pliocene until the late Pleistocene, becoming extinct about 50,000 years ago. Megalibgwilia species were more widespread in warmer and moist climates. Their extinction can be attributed to increasing aridification in Southern Australia.

Teinolophos, from Ancient Greek τείνω (teínō), meaning "extend", and λόφος (lóphos), meaning "crest", is a genus of teinolophid monotreme that lived during the late Barremian age of the Early Cretaceous. It is known from four specimens, each consisting of a partial lower jawbone collected from the Wonthaggi Formation at Flat Rocks, Victoria, Australia.

Steropodontidae is an extinct family of early monotreme mammals known from the Cretaceous of Australia.

Monotrematum sudamericanum is an extinct monotreme species from the Paleocene (Peligran) Salamanca Formation in Patagonia, Argentina. It is one of only two monotremes found outside Oceania.

species of mammal (fossil)

Kryoryctes is a genus of prehistoric monotreme mammal from the Early Cretaceous (Albian) Eumeralla Formation of Victoria, Australia from the Otway Group of Dinosaur Cove. It is known only from a partial right humerus, estimated at 106 million years old, and contains one species, Kryoryctes cadburyi. The holotype, NMV P208094, was described in 2005 and is currently housed in the Museums Victoria Palaeontological Collection.

Patagorhynchus is a genus of prehistoric monotreme mammal from the Late Cretaceous (early Maastrichtian) Chorrillo Formation of Santa Cruz Province, Argentina. The genus contains a single species, Patagorhynchus pascuali. The holotype, MPM-PV-23087, consists of a lower right molar attached to a fragment of the dentary. Based on comparisons with the closely related Obdurodon, it is estimated to have weighed ~1.58 kg. It was collected near Rio Gallegos, Santa Cruz, Argentina in 2022 and is housed in the Museo Padre Molina.