The Ornithorhynchidae are one of the two extant families in the order Monotremata, and contain the

platypus The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or monotypi ...

and its extinct relatives. The other family is the Tachyglossidae, or

echidna Echidnas (), sometimes known as spiny anteaters, are quill-covered monotremes (egg-laying mammals) belonging to the Family (biology), family Tachyglossidae , living in Australia and New Guinea. The four Extant taxon, extant species of echidnas ...

s. Within the Ornithorhynchidae are the main

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

Ornithorhynchus The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or monotypi ...

'' and ''

Obdurodon ''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 several potential

stem Stem or STEM most commonly refers to: * Plant stem, a structural axis of a vascular plant * Stem group * Science, technology, engineering, and mathematics Stem or STEM can also refer to: Language and writing * Word stem, part of a word respon ...

-genera dating back to the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

, of which the oldest is possibly ''

Dharragarra ''Dharragarra'' (meaning "platypus" in the Gamilaraay language) is an extinct genus of monotreme mammal from the Late Cretaceous (Cenomanian) Griman Creek Formation of Australia. The genus contains a single species, ''D. aurora'', known from a ...

''. Although fossil evidence suggests the presence of ornithorhynchids in the Cretaceous, phylogenetic evidence has largely found that they and the Tachyglossidae only diverged during the Cenozoic, although this varies based on the specific constraints used.

Taxonomy

The following species are known: *Family Ornithorhynchidae **Genus ''

'' (Pliocene to present) ***''

Ornithorhynchus anatinus The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to Eastern states of Australia, eastern Australia, including Tasmania. The platypus is the sole livi ...

'' (the modern

) **Genus †''

'' (

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

) ***†'' Obdurodon dicksoni'' ***†''

Obdurodon insignis ''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'' a ...

'' ***†''

Obdurodon tharalkooschild ''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'' a ...

'' **Genus ?†''

'' (Late Cretaceous;

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

) ***?†'' Dharragarra aurora'' **Genus ?†''

Monotrematum ''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. Taxonomy A species described in 1992 and assigned t ...

'' (

Early Paleocene The Danian is the oldest age (geology), age or lowest stage (stratigraphy), stage of the Paleocene Epoch or series (stratigraphy), Series, of the Paleogene Period or system (stratigraphy), System, and of the Cenozoic Era or Erathem. The beginnin ...

) ***?†'' Monotrematum sudamericanum'' **Genus ?†''

Patagorhynchus ''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, ...

'' (Late Cretaceous;

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

) *** ?†'' Patagorhynchus pascuali'' Although extant ornithorhynchids and most fossil genera are known from Australia, at least two potential genera (''Monotrematum'' and ''Patagorhynchus'') inhabited the southern tip of South America during the Maastrichtian and Paleocene, having presumably dispersed across

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

from Australia. Another two genera, ''

Steropodon ''Steropodon'' is a genus of prehistoric platypus-like monotreme, or Oviparity, 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 m ...

'' and ''

Teinolophos ''Teinolophos'', from Ancient Greek τείνω (''teínō''), meaning "extend", and λόφος (''lóphos''), meaning "crest", is a genus of Teinolophidae, teinolophid monotreme that lived during the late Barremian Age (geology), age of the Ear ...

'', were originally thought to belong to the Ornithorhynchidae. However, they were both placed into a new family, the

Steropodontidae Steropodontidae is an extinct family of early monotreme mammals known from the Cretaceous of Australia. Taxonomy ''Steropodon'' was initially placed in the crown group monotreme family Ornithorhynchidae but was subsequently made the type ...

. This decision was made based on differences in the

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

recovered from the Griman Creek Formation, Lightning Ridge, New South Wales, Australia. This dentary is the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

for the genus ''Steropodon'', thus the lack of information led to the original misclassification. Further research on ''Teinolophos'' has indeed shown it to be an animal much different from ornithochrynchids, lacking a beak, possessing a more complete mammalian dentition, and retaining primitive ears connected to the jaw as in more basal mammals. In 2022 it was proposed to move ''Teinolophos'' into its own family,

Teinolophidae Teinolophidae is an extinct family of small mammals that are among the earliest known monotremes and were endemic to what would become Australia. Two genera have been described as belonging to this family: ''Teinolophos'' (the type genus), and '' ...

. The extinct ''Ornithorhynchus maximus'' has been included in ''Ornithorhynchus'', but later placed with the echidna family Tachyglossidae as '' Zaglossus robustus''.

Evolution

Most extinct ornithorhynchids, including the close platypus relative ''

'', appear to have had teeth in their jaws. This contrasts with the modern platypus, where adults are entirely toothless. It has been theorized that the loss of teeth in the platypus was a geologically recent event, occurring only in the

Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

(after over 95 million years of tooth presence in the ornithorhynchid lineage) after the migration of the

rakali The rakali (''Hydromys chrysogaster''), also known as the rabe, the "Australian otter" or water-rat, is an Australian native rodent first scientifically described in 1804. Adoption of the Ngarrindjeri name ''rakali'' is intended to foster a posit ...

(''Hydromys chrysogaster''), a large semiaquatic

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

, to Australia. Competition between the rakali and platypus for hard-shelled prey may have led to trophic displacement of the platypus to instead rely on softer-bodied prey, losing its teeth in the process.

References

* {{Authority control Taxa named by John Edward Gray Extant Chattian first appearances