Ausktribosphenidae is an extinct family of australosphenidan mammals from the Early Cretaceous of Australia and mid Cretaceous of South America.

Classification and taxonomy

Ausktribosphenidae is closely related to

monotremes Monotremes () are prototherian mammals of the order Monotremata. They are one of the three groups of living mammals, along with placentals (Eutheria), and marsupials (Metatheria). Monotremes are typified by structural differences in their brains, ...

and hence the two form the yinotherian clade

Australosphenida The Australosphenida are a clade of mammals, containing mammals with tribosphenic molars, known from the Jurassic to Mid-Cretaceous of Gondwana. They are thought to have acquired their tribosphenic molars independently from those of Tribosphenida ...

. It includes two species, ''

Ausktribosphenos nyktos ''Ausktribosphenos'' is an extinct genus of mammals from Early Cretaceous of Australia. The only recorded species, ''Ausktribosphenos nyktos'', was found on Flat Rocks, Victoria Victoria most commonly refers to: * Victoria (Australia), a st ...

'' and ''

Bishops whitmorei ''Bishops'' is an extinct genus of mammals from Early Cretaceous of Australia. The only recorded species, ''Bishops whitmorei'', was found on Flat Rocks, Wonthaggi Formation, Victoria. The genus was named in honour of Dr Barry Bishop, the fo ...

'', both of which are known only from skull and jaw fragments.

Morphology

Like other Australosphenida, ausktribosphenids have tribosphenic

molars 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 to ...

Distribution

Given that Ausktribosphenidae has been found in Early Cretaceous deposits in

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

, its occurrence has ramifications for knowledge of early monotreme paleobiogeography because

was connected only to Antarctica, and placentals originated in the northern hemisphere and were confined to it until

continental drift Continental drift is the hypothesis that the Earth's continents have moved over geologic time relative to each other, thus appearing to have "drifted" across the ocean bed. The idea of continental drift has been subsumed into the science of pla ...

formed land connections from North America to South America, from Asia to Africa and from Asia to India. The late Cretaceous map shows how the southern continents are separated. However, the cladistic analysis of ''

Cifelliodon ''Cifelliodon'' is an extinct genus of mammaliaforms from the Lower Cretaceous of North America. In the describing paper, it was considered one of the latest surviving haramiyids yet known, belonging to the family Hahnodontidae. Its discovery led ...

'' recovers ''

Fruitafossor ''Fruitafossor'' was a termite-eating mammal endemic to North America during the Late Jurassic epoch (around 150 mya). The description is based on a complete skeleton of a chipmunk-sized animal. It was discovered on March 31, 2005, in Fruita, ...

'' as a monotreme relative, suggesting that yinotherians may have originated in the Northern Hemisphere. Remains similar to ''Bishops'' are known from the mid Cretaceous

Mata Amarilla Formation The Mata Amarilla Formation is a fossiliferous formation of the Austral Basin in southern Patagonia, Argentina. The formation consists of sediments deposited during the Middle Cenomanian, dated to 96.94 to 95.52 Ma. The middle section of the fo ...

of Argentina, suggesting faunal interchange.

References

Cretaceous mammals of Australia Australosphenida Prehistoric mammal families {{cretaceous-mammal-stub