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Temporal range: Middle JurassicRecent
Fossil of Zhangheotherium, a symmetrodont
Red fox, a modern-day trechnotherian
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Clade: Theriiformes
Clade: Trechnotheria
McKenna, 1975

Trechnotheria is a group of mammals that includes the therians and some fossil mammals from the Mesozoic Era. It includes both the extinct symmetrodonts and the living Cladotheria.

Trechnotheria has been assigned various ranks, but was originally described as a "superlegion" by the naming authority.[2] A later node-based definition for Trechnotheria was the clade comprising the last common ancestor of Zhangheotherium and living therian mammals, and all its descendants.[3]


Like most Mesozoic mammal groups, early trechnotherians are known mainly from their teeth. Hence, one of the most prominent features of this group is the "hypertrophied postvallum/prevallid shearing mechanism", along with other dental characters. Features of the shoulder blade, tibia, humerus, and ankle joint also diagnose this clade.[1]


A cladogram based on Luo, Cifelli & Kielan-Jaworowska, 2001, Luo, Kielan-Jaworowska & Cifelli, 2002 and, Kielan-Jaworowska, Cifelli & Luo, 2004.[4]


  1. ^ a b Luo, Z.−X.; Kielan−Jaworowska, Z.; Cifelli, R.L (2002). "In quest for a phylogeny of Mesozoic mammals" (PDF). Acta Palaeontologica Polonica. 47 (1): 1–78.
  2. ^ McKenna, Malcolm C.; Bell, Susan K. (1997). Classification of Mammals: Above the Species Level. Columbia University Press. p. 43. ISBN 978-0-231-52853-5.
  3. ^ Kielan-Jaworowska, Zofia; Cifelli, Richard; Luo Zhe-Xi (5 February 2005). Mammals from the age of dinosaurs: origins, evolution, and structure. Columbia University Press. p. 366. ISBN 978-0-231-11918-4.
  4. ^ Haaramo, Mikko. "Holotheria – holotheres". Mikko's Phylogeny Archive.

See also[edit]