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Australosphenida

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Title: Australosphenida  
Author: World Heritage Encyclopedia
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Subject: Yinotheria, Ambondro mahabo, Monotreme, Mammal, Prototheria
Collection: Australosphenida, Mammal Taxonomy
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Australosphenida

Australosphenidans
Temporal range: Middle Jurassic - Holocene, 167–0 Ma
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Short-beaked echidna
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Subclass: Yinotheria
Infraclass: Australosphenida
Luo, Cifelli, & Kielan-Jaworowska, 2001
Taxa

The Australosphenida are an infraclass of mammals. Today, there are only five surviving species, which live in Australia and New Guinea, but fossils have been found in Madagascar and Argentina. The surviving species consist of the platypus and four species of echidna.

Contents

  • Taxonomy 1
  • Australosphenid teeth 2
  • Notes 3
  • References 4

Taxonomy

This grouping includes the following taxa:

The clade Australosphenida was proposed by Luo et al. (2001, 2002) and was initially left unranked, as the authors do not apply the Linnaean hierarchy. In Benton (2005), it is ranked as a 'superdivision', i.e. one or two levels below the infraclass.

Australosphenid teeth

The grouping embodies a hypothesis about the evolution of docodonts, triconodonts and multituberculates, all of which were united with the monotremes into the 'subclass Prototheria'. Defined in this way, the 'Prototheria' is no longer recognised as a valid clade, since the linear cusp pattern is a primitive condition within Mammalia and cannot supply the shared derived character, which is required to establish a subgroup. Instead, the available evidence suggests that the monotremes descend from a Mesozoic radiation of tribosphenic mammals in the southern continents (hence the name Australosphenida, meaning 'southern wedges'), but this interpretation is highly controversial.

According to Luo et al., tribosphenic molars were evolved by the Australosphenida independently of the true Tribosphenida, or Boreosphenida (that is, the therians and their relatives) in the northern continents. Others contend that the Ausktribosphenida in fact belong to the placentals and were therefore true tribosphenids, but unrelated to the ancestry of the monotremes.[1] If this were confirmed, it would entail abandoning the clade Australosphenida.

Notes

  1. ^ Benton 2005: 300, 306-308.

References

  •  
  • Luo, Zhe-Xi; Cifelli, Richard L.; Kielan-Jaworowska, Zofia (2001). "Dual origin of tribosphenic mammals". Nature 409: 53–57.  
  • Luo, Zhe-Xi; Kielan-Jaworowska, Zofia; Cifelli, Richard L. (2002). "In quest for a phylogeny of Mesozoic mammals" (PDF). Acta Palaeontologia Polonica 47 (1): 1–78. 
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