Ausktribosphenidae
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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 br ...
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 Tribosphenid ...
. It includes two species, '' Ausktribosphenos nyktos'' 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, its occurrence has ramifications for knowledge of early monotreme paleobiogeography because Australia 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 pl ...
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'' recovers '' Fruitafossor'' 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 of Argentina, suggesting faunal interchange.


References

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