Trechnotheria

Trechnotherians
Temporal range: Late Triassic - Holocene, 216.5–0Ma
Kangaroo with her joey
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Clade: Holotheria
Superlegion: Trechnotheria
Subgroups
Synonyms

Theriiformes Rowe, 1988

Trechnotheria is a group of mammals that includes the therians and some fossil mammals from the Mesozoic Era. In the Jurassic through Cretaceous periods, the group was endemic to what would be Asia and Africa[1]

Trechnotheria has been assigned various ranks, but was originally called a "superlegion" by the original author.[2] One reference has defined the Trechnotheria as the clade comprising the last common ancestor of Zhangheotherium and living therian mammals, and all its descendants.[3]

Characteristics

Like most Mesozoic mammal groups, early trechnotherians are known mainly from their teeth. Hence, one of 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.[4]

Phylogeny

Below is a cladogram from Rowe (1988) and McKenna and Bell (1997) showing one hypothesis of mammal relationships:[5][6]

Mammaliaformes 

†Morganucodontidae


Mammalia 

Prototheria→Monotremata


Theriiformes

†Allotheria→†Multituberculata


Holotheria

†Kuehneotheria


Trechnotheria

†Zhangheotherium †("Symmetrodonta")


 Cladotheria 

†Dryolestoidea


 Zatheria 

†Peramura


Tribosphenida

†Aegialodontia


 Theria 

Metatheria→Marsupialia

Eutheria→Placentalia











Sources

  1. ↑ PaleoBiology Database: Trechnotheria, basic info "Trechnotheria - Mammalia". Paleobiology Database. Retrieved 2009-10-21.
  2. ↑ McKenna, Malcolm C., & Bell, Susan K. (2000). Classification of Mammals above the Species Level. University of Chicago Press. p. 43.
  3. ↑ Kielan-Jaworowska, Zofia; Cifelli, Richard; & Luo Zhe-Xi. Mammals from the age of dinosaurs: origins, evolution, and structure. Columbia University Press. p. 366. ISBN 978-0-231-11918-4.
  4. ↑ Luo, Z.−X., Kielan−Jaworowska, Z., and Cifelli, R.L. (2002). "In quest for a phylogeny of Mesozoic mammals" (PDF). Acta Palaeontologica Polonica 47 (1): 1–78.
  5. ↑ Rowe, Timothy (1988). "Definition, diagnosis, and origin of Mammalia". Journal of Vertebrate Paleontology 8 (3): 241–264. doi:10.1080/02724634.1988.10011708. ISSN 0272-4634.
  6. ↑ McKenna, Malcolm C.; Bell, Susan K. (1997). Classification of Mammals Above the Species Level. Columbia University Press. pp. 9–10. ISBN 978-0-231-11012-9. Retrieved 16 March 2015.

See also