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 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" 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. A cladogram based on Luo, Cifelli & Kielan-Jaworowska, 2001, Luo, Kielan-Jaworowska & Cifelli, 2002 and, Kielan-Jaworowska, Cifelli & Luo, 2004. See also. One example of a Trechnotheria mammal is the Zhangheotheriids. This mammal forms into the sister group of the Spalacotheriddad (Bi, Zheng, X., Meng, J., Wang, X., Robinson, N., & Davis, B., 2016). The sister group is a taxon that shares a common ancestor like any other taxon. In a trechnotheria  mammal, some evolution aspects depend on the different histories in morphological diversification depending on survivors. Zhangheotheriidis mammals include partial or complete skulls and this group comes from the Early Cretaceous of China and Siberia. A Zhangheotheriids would also be described from the Yixian Formation which also represent skulls and dentaries. The rostrum and orbital musical are present and while there is a lack of preservation of the basicranium and postcranial skeleton, this specimen is the first symmetodont in which the morphology for dental series is exposed. This represents that the trechnotherian diversity includes isolated teeth and jaws which show a  different homology with symmetrodonts (Bi, Zheng, X., Meng, J., Wang, X., Robinson, N., & Davis, B., 2016). This symmetrodont mammal is also part of the diversity evolution of a trechnotherian character and discovered early in the Cretaceous of China.