Ausktribosphenidae
Encyclopedia
Ausktribosphenidae is a group name that has been given to some rather puzzling fossils—Ausktribosphenos nyktos and Bishops whitmorei—which
  • Appear to have tribosphenic molars
    Molar (tooth)
    Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....

    , a type of tooth which is otherwise known only in Theria
    Theria
    Theria is a subclass of mammals that give birth to live young without using a shelled egg, including both eutherians and metatherians . The only omitted extant mammal group is the egg-laying monotremes....

    ns.
  • Come from mid Cretaceous
    Cretaceous
    The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

     deposits in Australia - but Australia was connected only to Antarctica, and placentals originated in the northern hemisphere and were confined to it until continental drift
    Continental drift
    Continental drift is the movement of the Earth's continents relative to each other. The hypothesis that continents 'drift' was first put forward by Abraham Ortelius in 1596 and was fully developed by Alfred Wegener in 1912...

     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.
  • Are represented only by skull and jaw fragments, which are not very helpful.


Ausktribosphenidae and monotremes have been assigned to the larger group Australosphenida
Australosphenida
The Australosphenida are a clade of mammals. Today, living specimens exist only in Australia and New Guinea with only five surviving species, but fossils have been found in Madagascar and Argentina...

. But Australosphenida is a group which has been defined only in order to include the Ausktribosphenidae and monotremes - in other words, it may be just a fiction, unless someone finds a fossil which can sensibly be described as a "basal australosphenid" (member of the Australosphenida which belongs to neither Ausktribosphenidae nor monotremes).
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