Trechnotheria
Encyclopedia
Trechnotheria is a group of mammals that includes the theria
ns 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.
Theria
Theria is a subclass of mammals that give birth to live young without using a shelled egg, including both eutherians and metatherians . The only omitted extant mammal group is the egg-laying monotremes....
ns and some fossil mammals from the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
Era. In the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
through Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
periods, the group was endemic to what would be Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
and Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
Trechnotheria is a clade that includes symmetrodonts
Symmetrodonta
Symmetrodonta is a basal group of Mesozoic mammals characterized by the triangular aspect of the molars when viewed from above and the absence of a well-developed talonid. The traditional group of symmetrodonts ranges in age from the latest Triassic to the Late Cretaceous. One species,...
, Spalacotheriids, dryolestids
Dryolestida
Dryolestida is an extinct order of mammals known from the Jurassic to Tertiary. It has been suggested that these mammals are either the possible ancestors of therian mammals or an offshoot from the same evolutionary line. It is also believed that they developed a fully mammalian jaw and also had...
and therians
Theria
Theria is a subclass of mammals that give birth to live young without using a shelled egg, including both eutherians and metatherians . The only omitted extant mammal group is the egg-laying monotremes....
. 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
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 from a complete skeleton. It was dated to between 145-125...
and living therian mammals, and all its descendants.