Trechnotheria

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

Trechnotheria is a clade that includes symmetrodonts, Spalacotheriids, dryolestids and therians. This clade excludes monotremata. Trechnotheria has been assigned various ranks, but was originally called a "superlegion" by the original author. One reference has defined the Trechnotheria as the clade comprising the last common ancestor of Zhangheotherium 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 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.