Temporal range: Mid Jurassic-Recent, 165–0 Ma
A cat (Felis catus) with her kittens
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Subclass: Theria
Parker & Haswell, 1897 [1]

Theria (play /ˈθɪəriə/; Greek: θηρίον, wild beast) is a subclass of mammals[2] that give birth to live young without using a shelled egg, including both eutherians (placental mammals) and metatherians (marsupials and their ancestors). The only omitted extant mammal group is the egg-laying monotremes.

Kangaroo, a marsupial, with her joey


The rank of 'Theria' may vary depending on the classification system used. The textbook classification system by Vaughan et al. (2000)[3] gives the following:

Class Mammalia

  • Subclass Theria: live-bearing mammals

In the above system Theria is a subclass. Alternatively, in the system proposed by McKenna and Bell (1997)[4] it is ranked as a supercohort under the subclass Theriiformes:

Class Mammalia

  • Subclass Theriiformes: live-bearing mammals and their prehistoric relatives
    • Infraclass Holotheria: modern live-bearing mammals and their prehistoric relatives
      • Legion Cladotheria
        • Sublegion Zatheria
          • Infralegion Tribosphenida
            • Supercohort Theria: therian mammals
              • Cohort Marsupialia: marsupials
              • Cohort Placentalia: placentals

Another classification proposed by Luo et al. (2002)[5] does not assign any rank to the taxonomic levels, but uses a purely cladistic system instead.


  1. ^ ITIS Standard Report Page: Theria
  2. ^ Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. "Subclass Theria". Animal Diversity Web. 
  3. ^ Vaughan, Terry A., James M. Ryan, and Nicholas J. Czaplewski. 2000. Mammalogy: Fourth Edition. Saunders College Publishing, 565 pp. ISBN 0-03-025034-X
  4. ^ McKenna, Malcolm C., and Bell, Susan K. 1997. Classification of Mammals Above the Species Level. Columbia University Press, New York, 631 pp. ISBN 0-231-11013-8
  5. ^ Luo, Z.-X., Z. Kielan-Jaworowska, and R. L. Cifelli. 2002. In quest for a phylogeny of Mesozoic mammals. Acta Palaeontologica Polonica, 47:1-78.

See also

  • marsupials
  • monotremes
  • placental mammals