Trechnotheria is a group of mammals that includes the

theria Theria (; Greek: , wild beast) is a subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the placental mammals) and the metatherians (including the marsupials) but excludes the egg-laying monotremes. ...

ns and some fossil mammals from the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

Era. In the

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

through

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

periods, the group was endemic to what would be

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

and

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

. Trechnotheria has been assigned various ranks, but was originally described as a "superlegion" by the naming authority. A later node-based definition for Trechnotheria was the clade comprising the last common ancestor of ''

Zhangheotherium ''Zhangheotherium'' is a genus of symmetrodont, an extinct order of mammals. Previously known from only the tall pointed crowned teeth, ''Zhangheotherium'', described from Liaoning Province, China, fossils in 1997, is the first symmetrodont known ...

'' and living therian mammals, and all its descendants.

Characteristics

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.

Phylogeny

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

based on Luo, Cifelli & Kielan-Jaworowska, 2001, Luo, Kielan-Jaworowska & Cifelli, 2002 and, Kielan-Jaworowska, Cifelli & Luo, 2004. * Unassigned Trechnotheria: **†'' Austrotriconodon mckennai'' Bonaparte 1986 **†'' Chaoyangodens lii'' Hou & Meng 2014 * Paraphyletic Symmetrodonta Simpson 1925 **†'' Atlasodon monbaroni'' Sigogneau-Russell 1991 ryolestida, or Zatheria indet., milk tooth (Averianov, 2002)**†'' Kennetheredium leesi'' Sigogneau-Russell 2003a **†'' Kotatherium haldanei'' Datta 1981 **†'' Trishulotherium kotaensis'' Yadagiri 1985 * Unassigned Cladotheria: **†'' Afriquiamus nesovi'' Sigogneau-Russell 1999 **†'' Butlerigale'' Kühne 1968 **†'' Chunnelodon alopekodes'' Ensom & Sigogneau-Russell 1998 **†'' Guimarota freyi'' Kuhne 1968 * Unassigned Zatheria: **†'' Arguimus khoshajari'' Dashzeveg 1979 Arguitherium_cromptoni''_Dashzeveg_1994.html" ;"title="Arguitherium.html" ;"title="'Arguitherium">Arguitherium cromptoni'' Dashzeveg 1994">Arguitherium.html" ;"title="'Arguitherium">Arguitherium cromptoni'' Dashzeveg 1994 **†''Minimus richardfoxi'' Sigogneau-Russell 1999 **†''Magnimus, Magnimus ensomi'' Sigogneau-Russell 1999 **†''Mozomus, Mozomus shikamai'' Li et al. 2005 **†''Nanolestes'' Martin 2002 ***†'' Nanolestes drescherae, N. drescherae'' Martin 2002 ***†'' N. krusati'' Martin 2002 ***†'' N. mackennai'' Martin, Averianov & Pfretzschner 2010 * Unassigned Boreosphenida: **†'' Argaliatherium robustum '' Cifelli & Davis 2015 **†'' Carinalestes murensis'' Cifelli & Davis 2015 **†'' Hypomylos'' Sigogneau-Russell 1992 ***†'' H. phelizoni'' Sigogneau-Russell 1992 ***†'' H. micros'' Sigogneau-Russell 1994 **† Picopsidae Fox 1980 ***†'' Picopsis pattersoni'' Fox 1980 ***†'' Tirotherium aptum'' Montellano-Ballesteros & Fox 2015

Characteristics

Phylogeny

Sources

See also