''Obdurodon'' is a genus of extinct

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 mono ...

-like

Australian Australian(s) may refer to: Australia * Australia, a country * Australians, citizens of the Commonwealth of Australia ** European Australians ** Anglo-Celtic Australians, Australians descended principally from British colonists ** Aboriginal A ...

monotreme which lived from the

Late Oligocene The Chattian is, in the geologic timescale, the younger of two ages or upper of two stages of the Oligocene Epoch/ Series. It spans the time between . The Chattian is preceded by the Rupelian and is followed by the Aquitanian (the lowest stage ...

to the Late Miocene. Three species have been described in the genus, the type species ''Obdurodon insignis'', plus ''Obdurodon dicksoni'' and ''Obdurodon tharalkooschild''. The species appeared much like their modern day relative the platypus, except adults retained their

molar teeth The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone t ...

, and unlike the platypus, which forages on the lakebed, they may have foraged in the water column or surface.

Taxonomy

The ''Obdurodon insignis''

holotype specimen A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

, SAM P18087, a tooth, was uncovered in 1971 from the Etadunna Formation in the

Tirari Desert The Tirari Desert is a desert in the eastern part of the Far North region of South Australia. It stretches 212 km from north to south and 153 km from east to west. Location and description The Tirari Desert features salt lakes and ...

of South Australia. The second specimen discovered there,

AMNH The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 i ...

97228, is an upper right molar. In total, 4 specimens are reported, dating from the Oligocene to the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58 The holotype tooth was placed into the newly erected genus ''Obdurodon'' upon description in 1975 by American palaeontologists

Michael O. Woodburne Michael O. Woodburne (born 1937) is an American geologist currently Professor Emeritus at University of California, Riverside The University of California, Riverside (UCR or UC Riverside) is a public land-grant research university in Riverside, ...

and

Richard H. Tedford Richard Hall Tedford (April 25, 1929 – July 15, 2011) was Curator Emeritus in the Department of Vertebrate Paleontology of the American Museum of Natural History in New York City, having been named as curator in 1969.Staff"14 ARE APPOINTED AT MU ...

. They coined the genus named from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''obduros'', meaning "persistent", and ''don'', meaning "tooth" in reference to the permanency of the molars, a feature which is lost in the modern platypus. The species name ''insignis'' refers to the importance of the new taxon's "distinguishing mark" in the fossil record. The genus is one of several to have been placed with the family

Ornithorhynchidae The Ornithorhynchidae are one of the two extant families in the order Monotremata, and contain the platypus and its extinct relatives. The other family is the Tachyglossidae, or echidnas. Within the Ornithorhynchidae are the genera '' Monotrem ...

, whose only living member is the

. The second species named, ''Obdurodon dicksoni'', occasionally called the Riversleigh Platypus, was described by Archer ''et al'' ( 1992) who detailed a skull and several teeth found in lower-middle Miocene deposits from the Riversleigh Ringtail Site. The type specimen, an exceptionally well preserved skull, is one of the most intact fossil skulls to be excavated from Riversleigh. The type locality is referred to as the Ringtail Site. Other than the skull and teeth, no other fossilized material of ''O. dicksoni'' has been identified. The third known species, ''Obdurodon tharalkooschild'' is the second species described from the Riversleigh sites, and the largest species. The holotype tooth was discovered in 2012 at the "Two Trees Site", part of Riversleigh's Gag Plateau sequence, and dated to the Miocene though dates as young as the Pliocene have been suggested. The species was described the following year by a team from the

University of New South Wales The University of New South Wales (UNSW), also known as UNSW Sydney, is a public research university based in Sydney, New South Wales, Australia. It is one of the founding members of Group of Eight, a coalition of Australian research-intensiv ...

including Rebecca Pian, Mike Archer, and

Suzanne Hand Suzanne J. Hand (born 1955) is an associate professor at the University of New South Wales, a teacher of geology and biology, who has a special interest in vertebrate palaeontology and modern mammals. Her research has been published in over a hund ...

, who published the article in the ''

Journal of Vertebrate Paleontology The ''Journal of Vertebrate Paleontology'' is a bimonthly peer-reviewed scientific journal that was established in 1980 by Jiri Zidek (University of Oklahoma). It covers all aspects of vertebrate paleontology, including vertebrate origins, evolu ...

''. The specific 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

rakali The rakali (''Hydromys chrysogaster)'', also known as the rabe or water-rat, is an Australian native rodent first described in 1804. Adoption of the Aboriginal name Rakali is intended to foster a positive public attitude by Environment Australia ...

Description

''Obdurodon'' differ from the modern platypus, it that they had more permanent dentition in the spoon-shaped bill, retaining molars and incisors. The species may have foraged in the water column or surface.Masakazu Asahara; Masahiro Koizumi; Thomas E. Macrini; Suzanne J. Hand; Michael Archer (2016). "Comparative cranial morphology in living and extinct platypuses: Feeding behavior, electroreception, and loss of teeth". Science Advances. 2 (10): e1601329. doi:10.1126/sciadv.1601329.

''Obdurodon insignis''

''O. insignis'' is thought to have had a similar build to the modern

. The holotype is the front molar of the upper right jaw, corresponding to the M² molar, with the unusual character of six

roots A root is the part of a plant, generally underground, that anchors the plant body, and absorbs and stores water and nutrients. Root or roots may also refer to: Art, entertainment, and media * ''The Root'' (magazine), an online magazine focusing ...

. Fragments of jawbone have also been assigned to the species, along with a single piece of post-cranial material, a pelvis. ''O. insignis'' had one more canine tooth (NC1) than its ancestor ''

Steropodon galmani ''Steropodon'' is a genus of prehistoric monotreme, or egg-laying mammal. It contains a single species, ''Steropodon galmani'', that lived about 105 to 93.3 million years ago (mya) in the Early to Late Cretaceous period. It is one of the oldest m ...

''.

''Obdurodon dicksoni''

''Obdurodon dicksoni'' was part of the

Riversleigh fauna Riversleigh fauna is the collective term for any species of animal identified in fossil sites located in the Riversleigh World Heritage Area. Faunal zones The presence of the Riversleigh in the Oligo-Miocene has been exceptionally well preserved ...

that inhabited pools and streams of freshwater of the Riversleigh rainforest environment. Unlike the modern species, ''O. dicksoni'' was a large animal that retained its molars into adulthood and had a spoon-shaped bill. The skull's profile is comparatively flatter than similar species, and as with crocodilians, this may indicate more foraging or feeding at the surface of the water. The diet is likely to have been crustaceans, the water-borne larvae of insects, or perhaps small vertebrates like fish and frogs. The only known area of its distribution, the Riversleigh site, was closed forest at the freshwater bodies it inhabited, surrounded by more open woodlands over the region's limestone karst terrain. 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. The beak of ''O. dicksoni'' has an oval

hole A hole is an opening in or through a particular medium, usually a solid body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of en ...

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 tharalkooschild''

''Obdurodon tharalkooschild'' is assumed to be very similar in form to a modern platypus, but larger, exceeding '' Monotrematum'' in size and length. and lived in the middle to late

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 ...

(). The wear patterns on the tooth are suggestive of crushing, perhaps by consuming hard-shelled animals such as turtles, rather than using a shearing action. ''O. tharalkooschild'' is thought to have inhabited fresh water and hunted for a variety of animal prey in the forests that dominated the Riversleigh site at the time of deposition. The species diet is assumed to have included crustacea like those consumed by the modern platypus, although larger species were available due to its greater size. The potential prey of the Riversleigh fauna also included frog, turtle, fish and the

lungfish Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...

, species that are present in the deposition at the Two Tree Site of the Riversleigh formations. The ornithorhynchid species were unknown in the later fossil record at the time of discovery, and it defied the assumptions of a single lineage of a platypus-like animal that progressively lost its teeth and became smaller in size.

Cultural references

The name given to ''O. tharalkooschild'' was first discussed in a 1990 paper by Mike Archer, an Australian mammalogist, detailing a creation story with an

Ugly Duckling "The Ugly Duckling" ( da, Den grimme ælling) is a Danish literary fairy tale by Danish poet and author Hans Christian Andersen (1805–1875). It was first published on 11 November 1843 in '' New Fairy Tales. First Volume. First Collection'' ...

motif in the context of palaeontology. A philosophical examination of historical sciences such as palaeontology, published in 2018, uses the tooth of this platypus as an example of the results obtainable by multiple methods of research into traces of evidence; the author refers to the species by the vernacular "platyzilla". An illustration of ''O. dicksoni'' by Jeanette Muirhead, depicted on a rock in a stream within a rainforest, was published by the magazine '' Natural History'' (

) in 1994.

References

{{Taxonbar, from1=Q133044, from2=Q656718, from3=Q3087702, from4=Q15138191 Prehistoric monotremes Prehistoric mammal genera Oligocene first appearances Miocene genus extinctions Oligocene mammals of Australia Miocene mammals of Australia Fossils of Australia Riversleigh fauna Fossil taxa described in 1975 Taxa named by Michael Woodburne Taxa named by Richard H. Tedford